Re-designing a mechanism for higher speed: A case history from textile machinery

NASA Astrophysics Data System (ADS)

Douglas, S. S.; Rooney, G. T.

The generation of general mechanism design software which is the formulation of suitable objective functions is discussed. There is a consistent drive towards higher speeds in the development of industrial sewing machines. This led to experimental analyses of dynamic performance and to a search for improved design methods. The experimental work highlighted the need for smoothness of motion at high speed, component inertias, and frame structural stiffness. Smoothness is associated with transmission properties and harmonic analysis. These are added to other design requirements of synchronization, mechanism size, and function. Some of the mechanism trains in overedte sewing machines are shown. All these trains are designed by digital optimization. The design software combines analysis of the sewing machine mechanisms, formulation of objectives innumerical terms, and suitable mathematical optimization ttechniques.

Polyimidazoles Via Aromatic Nucleophilic Displacement

NASA Technical Reports Server (NTRS)

Connell, John W.; Hergenrother, Paul M.

1990-01-01

Experiments show variety of polyimidazoles prepared by aromatic nucleophilic displacement, from reactions of bisphenol imidazoles with activated difluoro compounds. Polyimidazoles have good mechanical properties making them suitable for use as films, moldings, and adhesives.

2D materials: Graphene and others

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bansal, Suneev Anil, E-mail: suneev@gmail.com; Singh, Amrinder Pal; Kumar, Suresh

Present report reviews the recent advancements in new atomically thick 2D materials. Materials covered in this review are Graphene, Silicene, Germanene, Boron Nitride (BN) and Transition metal chalcogenides (TMC). These materials show extraordinary mechanical, electronic and optical properties which make them suitable candidates for future applications. Apart from unique properties, tune-ability of highly desirable properties of these materials is also an important area to be emphasized on.

Performance degradation mechanisms and modes in terrestrial photovoltaic arrays and technology for their diagnosis

NASA Technical Reports Server (NTRS)

Noel, G. T.; Sliemers, F. A.; Derringer, G. C.; Wood, V. E.; Wilkes, K. E.; Gaines, G. B.; Carmichael, D. C.

1978-01-01

Accelerated life-prediction test methodologies have been developed for the validation of a 20-year service life for low-cost photovoltaic arrays. Array failure modes, relevant materials property changes, and primary degradation mechanisms are discussed as a prerequisite to identifying suitable measurement techniques and instruments. Measurements must provide sufficient confidence to permit selection among alternative designs and materials and to stimulate widespread deployment of such arrays. Furthermore, the diversity of candidate materials and designs, and the variety of potential environmental stress combinations, degradation mechanisms and failure modes require that combinations of measurement techniques be identified which are suitable for the characterization of various encapsulation system-cell structure-environment combinations.

Mucoadhesive in situ gel formulation for vaginal delivery of clotrimazole: formulation, preparation, and in vitro/in vivo evaluation.

PubMed

Rençber, Seda; Karavana, Sinem Yaprak; Şenyiğit, Zeynep Ay; Eraç, Bayri; Limoncu, Mine Hoşgör; Baloğlu, Esra

2017-06-01

The purpose of this study was to develop a suitable mucoadhesive in situ gel formulation of clotrimazole (CLO) for the treatment of vaginal candidiasis. For this aim, the mixture of poloxamer (PLX) 407 and 188 were used to prepare in situ gels. Hydroxypropyl methylcellulose (HPMC) K100M or E50 was added to in situ gels in 0.5% ratio to improve the mucoadhesive and mechanical properties of formulations and to prolong the residence time in vaginal cavity. After the preparation of mucoadhesive in situ gels; gelation temperature/time, viscosity, mechanical, mucoadhesive, syringeability, spreadibility and rheological properties, in vitro release behavior, and anticandidal activities were determined. Moreover vaginal retention of mucoadhesive in situ gels was investigated with in vivo distribution studies in rats. Based on the obtained results, it was found that gels prepared with 20% PLX 407, 10% PLX 188 and 0.5% HPMC K100M/E50 might be suitable for vaginal administration of CLO. In addition, the results of in vivo distribution studies showed that gel formulations remained on the vaginal mucosa even 24 h after application. In conclusion, the mucoadhesive in situ gels of CLO would be alternative candidate for treatment of vaginal candidiasis since it has suitable gel properties with good vaginal retention.

Composition suitable for use as inert electrode having good electrical conductivity and mechanical properties

DOEpatents

Ray, S.P.; Rapp, R.A.

1984-06-12

An improved inert electrode composition is suitable for use as an inert electrode in the production of metals such as aluminum by the electrolytic reduction of metal oxide or metal salt dissolved in a molten salt bath. The composition comprises one or more metals or metal alloys and metal compounds which may include oxides of the metals comprising the alloy. The alloy and metal compounds are interwoven in a network which provides improved electrical conductivity and mechanical strength while preserving the level of chemical inertness necessary for such an electrode to function satisfactorily. 8 figs.

Composition suitable for use as inert electrode having good electrical conductivity and mechanical properties

DOEpatents

Ray, Siba P.; Rapp, Robert A.

1984-01-01

An improved inert electrode composition is suitable for use as an inert electrode in the production of metals such as aluminum by the electrolytic reduction of metal oxide or metal salt dissolved in a molten salt bath. The composition comprises one or more metals or metal alloys and metal compounds which may include oxides of the metals comprising the alloy. The alloy and metal compounds are interwoven in a network which provides improved electrical conductivity and mechanical strength while preserving the level of chemical inertness necessary for such an electrode to function satisfactorily.

Method of making composition suitable for use as inert electrode having good electrical conductivity and mechanical properties

DOEpatents

Ray, Siba P.; Rapp, Robert A.

1986-01-01

An improved inert electrode composition is suitable for use as an inert electrode in the production of metals such as aluminum by the electrolytic reduction of metal oxide or metal salt dissolved in a molten salt bath. The composition comprises one or more metals or metal alloys and metal compounds which may include oxides of the metals comprising the alloy. The alloy and metal compounds are interwoven in a network which provides improved electrical conductivity and mechanical strength while preserving the level of chemical inertness necessary for such an electrode to function satisfactorily.

Mechanical and biological properties of the micro-/nano-grain functionally graded hydroxyapatite bioceramics for bone tissue engineering.

PubMed

Zhou, Changchun; Deng, Congying; Chen, Xuening; Zhao, Xiufen; Chen, Ying; Fan, Yujiang; Zhang, Xingdong

2015-08-01

Functionally graded materials (FGM) open the promising approach for bone tissue repair. In this study, a novel functionally graded hydroxyapatite (HA) bioceramic with micrograin and nanograin structure was fabricated. Its mechanical properties were tailored by composition of micrograin and nanograin. The dynamic mechanical analysis (DMA) indicated that the graded HA ceramics had similar mechanical property compared to natural bones. Their cytocompatibility was evaluated via fluorescent microscopy and MTT colorimetric assay. The viability and proliferation of rabbit bone marrow mesenchymal stem cells (BMSCs) on ceramics indicated that this functionally graded HA ceramic had better cytocompatibility than conventional HA ceramic. This study demonstrated that functionally graded HA ceramics create suitable structures to satisfy both the mechanical and biological requirements of bone tissues. Copyright © 2015 Elsevier Ltd. All rights reserved.

Structural and mechanical properties of welded joints of reduced activation martensitic steels

NASA Astrophysics Data System (ADS)

Filacchioni, G.; Montanari, R.; Tata, M. E.; Pilloni, L.

2002-12-01

Gas tungsten arc welding and electron beam welding methods were used to realise welding pools on plates of reduced activation martensitic steels. Structural and mechanical features of these simulated joints have been investigated in as-welded and post-welding heat-treated conditions. The research allowed to assess how each welding technique affects the original mechanical properties of materials and to find suitable post-welding heat treatments. This paper reports results from experimental activities on BATMAN II and F82H mod. steels carried out in the frame of the European Blanket Project - Structural Materials Program.

Comparisons of Auricular Cartilage Tissues from Different Species.

PubMed

Chiu, Loraine L Y; Giardini-Rosa, Renata; Weber, Joanna F; Cushing, Sharon L; Waldman, Stephen D

2017-12-01

Tissue engineering of auricular cartilage has great potential in providing readily available materials for reconstructive surgeries. As the field of tissue engineering moves forward to developing human tissues, there needs to be an interspecies comparison of the native auricular cartilage in order to determine a suitable animal model to assess the performance of engineered auricular cartilage in vivo. Here, we performed interspecies comparisons of auricular cartilage by comparing tissue microstructure, protein localization, biochemical composition, and mechanical properties of auricular cartilage tissues from rat, rabbit, pig, cow, and human. Human, pig, and cow auricular cartilage have smaller lacunae compared to rat and rabbit cartilage ( P < .05). Despite differences in tissue microstructure, human auricular cartilage has similar biochemical composition to both rat and rabbit. Auricular cartilage from pig and cow, alternatively, display significantly higher glycosaminoglycan and collagen contents compared to human, rat, and rabbit ( P < .05). The mechanical properties of human auricular cartilage were comparable to that of all 4 animal species. This is the first study that compares the microstructural, biochemical, and mechanical properties of auricular cartilage from different species. This study showed that different experimental animal models of human auricular cartilage may be suitable in different cases.

Properties of cryogenically worked metals. [stainless steels

NASA Technical Reports Server (NTRS)

Schwartzberg, F. R.; Kiefer, T. F.

1975-01-01

A program was conducted to determine whether the mechanical properties of cryogenically worked 17-7PH stainless steel are suitable for service from ambient to cryogenic temperatures. It was determined that the stress corrosion resistance of the cryo-worked material is quite adequate for structural service. The tensile properties and fracture toughness at room temperature were comparable to titanium alloy 6Al-4V. However, at cryogenic temperatures, the properties were not sufficient to recommend consideration for structural service.

Fast-responding bio-based shape memory thermoplastic polyurethanes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrovic, Zoran S.; Milic, Jelena; Zhang, Fan

Fast response shape-memory polyurethanes were prepared from bio-based polyols, diphenyl methane diisocyanate and butane diol. The bio-based polyester polyols were synthesized from 9-hydroxynonanoic acid, a product obtained by ozonolysis of fatty acids extracted from soy oil and castor oil. The morphology of polyurethanes was investigated by synchrotron ultra-small angle X-ray scattering, which revealed the inter-domain spacing between the hard and soft phases, the degree of phase separation, and the level of intermixing between the hard and soft phases. We also conducted thorough investigations of the thermal, mechanical, and dielectric properties of the polyurethanes, and found that high crystallization rate ofmore » the soft segment gives these polyurethanes unique properties suitable for shapememory applications, such as adjustable transition temperatures, high degree of elastic elongations, and good mechanical strength. In conclusion, these materials are also potentially biodegradable and biocompatible, therefore suitable for biomedical and environmental applications.« less

Fast-responding bio-based shape memory thermoplastic polyurethanes

DOE PAGES

Petrovic, Zoran S.; Milic, Jelena; Zhang, Fan; ...

2017-05-31

Fast response shape-memory polyurethanes were prepared from bio-based polyols, diphenyl methane diisocyanate and butane diol. The bio-based polyester polyols were synthesized from 9-hydroxynonanoic acid, a product obtained by ozonolysis of fatty acids extracted from soy oil and castor oil. The morphology of polyurethanes was investigated by synchrotron ultra-small angle X-ray scattering, which revealed the inter-domain spacing between the hard and soft phases, the degree of phase separation, and the level of intermixing between the hard and soft phases. We also conducted thorough investigations of the thermal, mechanical, and dielectric properties of the polyurethanes, and found that high crystallization rate ofmore » the soft segment gives these polyurethanes unique properties suitable for shapememory applications, such as adjustable transition temperatures, high degree of elastic elongations, and good mechanical strength. In conclusion, these materials are also potentially biodegradable and biocompatible, therefore suitable for biomedical and environmental applications.« less

Assessment of the viscoelastic mechanical properties of polycarbonate urethane for medical devices.

PubMed

Beckmann, Agnes; Heider, Yousef; Stoffel, Marcus; Markert, Bernd

2018-06-01

The underlying research work introduces a study of the mechanical properties of polycarbonate urethane (PCU), used in the construction of various medical devices. This comprises the discussion of a suitable material model, the application of elemental experiments to identify the related parameters and the numerical simulation of the applied experiments in order to calibrate and validate the mathematical model. In particular, the model of choice for the simulation of PCU response is the non-linear viscoelastic Bergström-Boyce material model, applied in the finite-element (FE) package Abaqus®. For the parameter identification, uniaxial tension and unconfined compression tests under in-laboratory physiological conditions were carried out. The geometry of the samples together with the applied loadings were simulated in Abaqus®, to insure the suitability of the modelling approach. The obtained parameters show a very good agreement between the numerical and the experimental results. Copyright © 2018 Elsevier Ltd. All rights reserved.

Fast-Responding Bio-Based Shape Memory Thermoplastic Polyurethanes.

PubMed

Petrović, Zoran S; Milić, Jelena; Zhang, Fan; Ilavsky, Jan

2017-07-14

Novel fast response shape-memory polyurethanes were prepared from bio-based polyols, diphenyl methane diisocyanate and butane diol for the first time. The bio-based polyester polyols were synthesized from 9-hydroxynonanoic acid, a product obtained by ozonolysis of fatty acids extracted from soy oil and castor oil. The morphology of polyurethanes was investigated by synchrotron ultra-small angle X-ray scattering, which revealed the inter-domain spacing between the hard and soft phases, the degree of phase separation, and the level of intermixing between the hard and soft phases. We also conducted thorough investigations of the thermal, mechanical, and dielectric properties of the polyurethanes, and found that high crystallization rate of the soft segment gives these polyurethanes unique properties suitable for shape-memory applications, such as adjustable transition temperatures, high degree of elastic elongations, and good mechanical strength. These materials are also potentially biodegradable and biocompatible, therefore suitable for biomedical and environmental applications.

Combined Intercritical Annealing and Q&P Processing of Medium Mn Steel

NASA Astrophysics Data System (ADS)

De Cooman, Bruno C.; Lee, Seon Jong; Shin, Sunmi; Seo, Eun Jung; Speer, John G.

2017-01-01

The microstructure and mechanical properties of intercritically annealed medium Mn steel are dependent on the selection of the intercritical annealing (IA) temperature. While the yield strength (YS) decreases with increasing IA temperature, the ultimate tensile strength increases with increasing IA temperature. Strain aging phenomena, both static and dynamic, are also often observed. The present contribution shows that, by combining IA with the quench and partitioning processing of the intercritical austenite, it is possible to obtain non-aging mechanical properties which combine a high YS with an ultra-high tensile strength. These properties are particularly suitable for automotive parts related to passenger safety.

Application of P.O and R-SAC mortar for 3D printing in construction

NASA Astrophysics Data System (ADS)

Lin, J. C.; Wu, X.; Yang, W.; Zhao, R. X.; Qiao, L. G.

2018-01-01

Compared with traditional properties of building materials, 3D printing materials should have controllable setting time, appropriate workability and superior mechanical properties. Adaptability of two types of cementitious system on the 3D printing were investigated in this paper. Results showed that both of them can match of 3D printing process with the working window time required (10-90min) by using the compound adjustable solidification agents, which have the high mechanical properties (3d⩾30MPa, 28d> 63MPa), and appropriate suitable parameter range of fluidity (R-SAC:210-240mm,P.O:200-220mm).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kolopus, James A.; Boatner, Lynn A.

Nanoindenters are commonly used for measuring the mechanical properties of a wide variety of materials with both industrial and scientific applications. Typically, these instruments employ an indenter made of a material of suitable hardness bonded to an appropriate shaft or holder to create an indentation on the material being tested. While a variety of materials may be employed for the indenter, diamond and boron carbide are by far the most common materials used due to their hardness and other desirable properties. However, as the increasing complexity of new materials demands a broader range of testing capabilities, conventional indenter materials exhibitmore » significant performance limitations. Among these are the inability of diamond indenters to perform in-situ measurements at temperatures above 600oC in air due to oxidation of the diamond material and subsequent degradation of the indenters mechanical properties. Similarly, boron carbide also fails at high temperature due to fracture. [1] Transition metal carbides possess a combination of hardness and mechanical properties at high temperatures that offer an attractive alternative to conventional indenter materials. Here we describe the technical aspects for the growth of single-crystal tungsten carbide (WC) for use as a high-temperature indenter material, and we examine a possible approach to brazing these crystals to a suitable mount for grinding and attachment to the indenter instrument. The use of a by-product of the recovery process is also suggested as possibly having commercial value.« less

Method of making composition suitable for use as inert electrode having good electrical conductivity and mechanical properties

DOEpatents

Ray, S.P.; Rapp, R.A.

1986-04-22

An improved inert electrode composition is suitable for use as an inert electrode in the production of metals such as aluminum by the electrolytic reduction of metal oxide or metal salt dissolved in a molten salt bath. The composition comprises one or more metals or metal alloys and metal compounds which may include oxides of the metals comprising the alloy. The alloy and metal compounds are interwoven in a network which provides improved electrical conductivity and mechanical strength while preserving the level of chemical inertness necessary for such an electrode to function satisfactorily. 8 figs.

The inverse problem of the calculus of variations for discrete systems

NASA Astrophysics Data System (ADS)

Barbero-Liñán, María; Farré Puiggalí, Marta; Ferraro, Sebastián; Martín de Diego, David

2018-05-01

We develop a geometric version of the inverse problem of the calculus of variations for discrete mechanics and constrained discrete mechanics. The geometric approach consists of using suitable Lagrangian and isotropic submanifolds. We also provide a transition between the discrete and the continuous problems and propose variationality as an interesting geometric property to take into account in the design and computer simulation of numerical integrators for constrained systems. For instance, nonholonomic mechanics is generally non variational but some special cases admit an alternative variational description. We apply some standard nonholonomic integrators to such an example to study which ones conserve this property.

Loss of mechanical properties in vivo and bone-implant interface strength of AZ31B magnesium alloy screws with Si-containing coating.

PubMed

Tan, Lili; Wang, Qiang; Lin, Xiao; Wan, Peng; Zhang, Guangdao; Zhang, Qiang; Yang, Ke

2014-05-01

In this study the loss of mechanical properties and the interface strength of coated AZ31B magnesium alloy (a magnesium-aluminum alloy) screws with surrounding host tissues were investigated and compared with non-coated AZ31B, degradable polymer and biostable titanium alloy screws in a rabbit animal model after 1, 4, 12 and 21weeks of implantation. The interface strength was evaluated in terms of the extraction torque required to back out the screws. The loss of mechanical properties over time was indicated by one-point bending load loss of the screws after these were extracted at different times. AZ31B samples with a silicon-containing coating had a decreased degradation rate and improved biological properties. The extraction torque of Ti6Al4V, poly-l-lactide (PLLA) and coated AZ31B increased significantly from 1week to 4weeks post-implantation, indicating a rapid osteosynthesis process over 3weeks. The extraction torque of coated AZ31B increased with implantation time, and was higher than that of PLLA after 4weeks of implantation, equalling that of Ti6Al4V at 12weeks and was higher at 21weeks. The bending loads of non-coated AZ31B and PLLA screws degraded sharply after implantation, and that of coated AZ31B degraded more slowly. The biodegradation mechanism, the coating to control the degradation rate and the bioactivity of magnesium alloys influencing the mechanical properties loss over time and bone-implant interface strength are discussed in this study and it is concluded that a suitable degradation rate will result in an improvement in the mechanical performance of magnesium alloys, making them more suitable for clinical application. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Identification of Novel "Inks" for 3D Printing Using High-Throughput Screening: Bioresorbable Photocurable Polymers for Controlled Drug Delivery.

PubMed

Louzao, Iria; Koch, Britta; Taresco, Vincenzo; Ruiz-Cantu, Laura; Irvine, Derek J; Roberts, Clive J; Tuck, Christopher; Alexander, Cameron; Hague, Richard; Wildman, Ricky; Alexander, Morgan R

2018-02-28

A robust methodology is presented to identify novel biomaterials suitable for three-dimensional (3D) printing. Currently, the application of additive manufacturing is limited by the availability of functional inks, especially in the area of biomaterials; this is the first time when this method is used to tackle this problem, allowing hundreds of formulations to be readily assessed. Several functional properties, including the release of an antidepressive drug (paroxetine), cytotoxicity, and printability, are screened for 253 new ink formulations in a high-throughput format as well as mechanical properties. The selected candidates with the desirable properties are successfully scaled up using 3D printing into a range of object architectures. A full drug release study and degradability and tensile modulus experiments are presented on a simple architecture to validating the suitability of this methodology to identify printable inks for 3D printing devices with bespoke properties.

Additively Manufactured Scaffolds for Bone Tissue Engineering and the Prediction of their Mechanical Behavior: A Review

PubMed Central

Zhang, Xiang-Yu; Fang, Gang; Zhou, Jie

2017-01-01

Additive manufacturing (AM), nowadays commonly known as 3D printing, is a revolutionary materials processing technology, particularly suitable for the production of low-volume parts with high shape complexities and often with multiple functions. As such, it holds great promise for the fabrication of patient-specific implants. In recent years, remarkable progress has been made in implementing AM in the bio-fabrication field. This paper presents an overview on the state-of-the-art AM technology for bone tissue engineering (BTE) scaffolds, with a particular focus on the AM scaffolds made of metallic biomaterials. It starts with a brief description of architecture design strategies to meet the biological and mechanical property requirements of scaffolds. Then, it summarizes the working principles, advantages and limitations of each of AM methods suitable for creating porous structures and manufacturing scaffolds from powdered materials. It elaborates on the finite-element (FE) analysis applied to predict the mechanical behavior of AM scaffolds, as well as the effect of the architectural design of porous structure on its mechanical properties. The review ends up with the authors’ view on the current challenges and further research directions. PMID:28772411

Additively Manufactured Scaffolds for Bone Tissue Engineering and the Prediction of their Mechanical Behavior: A Review.

PubMed

Zhang, Xiang-Yu; Fang, Gang; Zhou, Jie

2017-01-10

Additive manufacturing (AM), nowadays commonly known as 3D printing, is a revolutionary materials processing technology, particularly suitable for the production of low-volume parts with high shape complexities and often with multiple functions. As such, it holds great promise for the fabrication of patient-specific implants. In recent years, remarkable progress has been made in implementing AM in the bio-fabrication field. This paper presents an overview on the state-of-the-art AM technology for bone tissue engineering (BTE) scaffolds, with a particular focus on the AM scaffolds made of metallic biomaterials. It starts with a brief description of architecture design strategies to meet the biological and mechanical property requirements of scaffolds. Then, it summarizes the working principles, advantages and limitations of each of AM methods suitable for creating porous structures and manufacturing scaffolds from powdered materials. It elaborates on the finite-element (FE) analysis applied to predict the mechanical behavior of AM scaffolds, as well as the effect of the architectural design of porous structure on its mechanical properties. The review ends up with the authors' view on the current challenges and further research directions.

Effect of casting geometry on mechanical properties of two nickel-base superalloys

NASA Technical Reports Server (NTRS)

Johnston, J. R.; Dreshfield, R. L.; Collins, H. E.

1976-01-01

An investigation was performed to determine mechanical properties of two rhenium-free modifications of alloy TRW, and to evaluate the suitability of the alloy for use in a small integrally cast turbine rotor. The two alloys were initially developed using stress rupture properties of specimens machined from solid gas turbine blades. Properties in this investigation were determined from cast to size bars and bars cut from 3.8 by 7.6 by 17.8 cm blocks. Specimens machined from blocks had inferior tensile strength and always had markedly poorer rupture lives than cast to size bars. At 1,000 C the cast to size bars had shorter rupture lives than those machined from blades. Alloy R generally had better properties than alloy S in the conditions evaluated. The results show the importance of casting geometry on mechanical properties of nickel base superalloys and suggest that the geometry of a component can be simulated when developing alloys for that component.

Carbon nanotubes reinforced chitosan films: mechanical properties and cell response of a novel biomaterial for cardiovascular tissue engineering.

PubMed

Kroustalli, A; Zisimopoulou, A E; Koch, S; Rongen, L; Deligianni, D; Diamantouros, S; Athanassiou, G; Kokozidou, M; Mavrilas, D; Jockenhoevel, S

2013-12-01

Carbon nanotubes have been proposed as fillers to reinforce polymeric biomaterials for the strengthening of their structural integrity to achieve better biomechanical properties. In this study, a new polymeric composite material was introduced by incorporating various low concentrations of multiwalled carbon nanotubes (MWCNTs) into chitosan (CS), aiming at achieving a novel composite biomaterial with superior mechanical and biological properties compared to neat CS, in order to be used in cardiovascular tissue engineering applications. Both mechanical and biological characteristics in contact with the two relevant cell types (endothelial cells and vascular myofibroblasts) were studied. Regarding the mechanical behavior of MWCNT reinforced CS (MWCNT/CS), 5 and 10 % concentrations of MWCNTs enhanced the mechanical behavior of CS, with that of 5 % exhibiting a superior mechanical strength compared to 10 % concentration and neat CS. Regarding biological properties, MWCNT/CS best supported proliferation of endothelial and myofibroblast cells, MWCNTs and MWCNT/CS caused no apoptosis and were not toxic of the examined cell types. Conclusively, the new material could be suitable for tissue engineering (TE) and particularly for cardiovascular TE applications.

Development of fly ash boards with thermal, acoustic and fire insulation properties.

PubMed

Leiva, C; Arenas, C; Vilches, L F; Alonso-Fariñas, B; Rodriguez-Galán, M

2015-12-01

This paper presents an experimental analysis on a new board composed of gypsum and fly ashes from coal combustion, which are mutually compatible. Physical and mechanical properties, sound absorption coefficient, thermal properties and leaching test have been obtained. The mechanical properties showed similar values to other commercial products. As far as the acoustic insulation characteristics are concerned, sound absorption coefficients of 0.3 and 0.8 were found. The board presents a low thermal conductivity and a fire resistance higher than 50 min (for 4 cm of thickness). The leaching of trace elements was below the leaching limit values. These boards can be considered as suitable to be used in building applications as partitions. Copyright © 2015 Elsevier Ltd. All rights reserved.

Molecular Sensing by Nanoporous Crystalline Polymers

PubMed Central

Pilla, Pierluigi; Cusano, Andrea; Cutolo, Antonello; Giordano, Michele; Mensitieri, Giuseppe; Rizzo, Paola; Sanguigno, Luigi; Venditto, Vincenzo; Guerra, Gaetano

2009-01-01

Chemical sensors are generally based on the integration of suitable sensitive layers and transducing mechanisms. Although inorganic porous materials can be effective, there is significant interest in the use of polymeric materials because of their easy fabrication process, lower costs and mechanical flexibility. However, porous polymeric absorbents are generally amorphous and hence present poor molecular selectivity and undesired changes of mechanical properties as a consequence of large analyte uptake. In this contribution the structure, properties and some possible applications of sensing polymeric films based on nanoporous crystalline phases, which exhibit all identical nanopores, will be reviewed. The main advantages of crystalline nanoporous polymeric materials with respect to their amorphous counterparts are, besides a higher selectivity, the ability to maintain their physical state as well as geometry, even after large guest uptake (up to 10–15 wt%), and the possibility to control guest diffusivity by controlling the orientation of the host polymeric crystalline phase. The final section of the review also describes the ability of suitable polymeric films to act as chirality sensors, i.e., to sense and memorize the presence of non-racemic volatile organic compounds. PMID:22303150

Effect of fiber orientation of collagen-based electrospun meshes on human fibroblasts for ligament tissue engineering applications.

PubMed

Full, Sean Michael; Delman, Connor; Gluck, Jessica M; Abdmaulen, Raushan; Shemin, Richard J; Heydarkhan-Hagvall, Sepideh

2015-01-01

Within the past two decades polylactic-co-glycolic acid (PLGA) has gained considerable attention as a biocompatible and biodegradable polymer that is suitable for tissue engineering and regenerative medicine. In this present study, we have investigated the potential of PLGA, collagen I (ColI), and polyurethane (PU) scaffolds for ligament tissue regeneration. Two different ratios of PLGA (50:50 and 85:15) were used to determine the effects on mechanical tensile properties and cell adhesion. The Young's modulus, tensile stress at yield, and ultimate tensile strain of PLGA(50:50)-ColI-PU scaffolds demonstrated similar tensile properties to that of ligaments found in the knee. Whereas, scaffolds composed of PLGA(85:15)-ColI-PU had lower tensile properties than that of ligaments. Furthermore, we investigated the effect of fiber orientation on mechanical properties and our results indicate that aligned fiber scaffolds demonstrate higher tensile properties than scaffolds with random fiber orientation. Also, human fibroblasts attached and proliferated with no need for additional surface modifications to the presented electrospun scaffolds in both categories. Collectively, our investigation demonstrates the effectiveness of electrospun PLGA scaffolds as a suitable candidate for regenerative medicine, capable of being manipulated and combined with other polymers to create three-dimensional microenvironments with adjustable tensile properties to mimic native tissues. © 2014 Wiley Periodicals, Inc.

Polyhydroxyalkanoate/carbon nanotube nanocomposites: flexible electrically conducting elastomers for neural applications.

PubMed

Vallejo-Giraldo, Catalina; Pugliese, Eugenia; Larrañaga, Aitor; Fernandez-Yague, Marc A; Britton, James J; Trotier, Alexandre; Tadayyon, Ghazal; Kelly, Adriona; Rago, Ilaria; Sarasua, Jose-Ramon; Dowd, Eilís; Quinlan, Leo R; Pandit, Abhay; Biggs, Manus Jp

2016-10-01

Medium chain length-polyhydroxyalkanoate/multi-walled carbon nanotube (MWCNTs) nanocomposites with a range of mechanical and electrochemical properties were fabricated via assisted dispersion and solvent casting, and their suitability as neural interface biomaterials was investigated. Mechanical and electrical properties of medium chain length-polyhydroxyalkanoate/MWCNTs nanocomposite films were evaluated by tensile test and electrical impedance spectroscopy, respectively. Primary rat mesencephalic cells were seeded on the composites and quantitative immunostaining of relevant neural biomarkers, and electrical stimulation studies were performed. Incorporation of MWCNTs to the polymeric matrix modulated the mechanical and electrical properties of resulting composites, and promoted differential cell viability, morphology and function as a function of MWCNT concentration. This study demonstrates the feasibility of a green thermoplastic MWCNTs nanocomposite for potential use in neural interfacing applications.

Non-destructive thermo-mechanical behavior assessment of glass-ceramics for dental applications

NASA Astrophysics Data System (ADS)

Kordatos, E. Z.; Abdulkadhim, Z.; Feteira, A. M.

2017-05-01

Every year millions of people seek dental treatment to either repair damaged, unaesthetic and dysfunctional teeth or replace missing natural teeth. Several dental materials have been developed to meet the stringent requirements in terms of mechanical properties, aesthetics and chemical durability in the oral environment. Glass-ceramics exhibit a suitable combination of these properties for dental restorations. This research is focused on the assessment of the thermomechanical behavior of bio-ceramics and particularly lithium aluminosilicate glass-ceramics (LAS glass-ceramics). Specifically, methodologies based on Infrared Thermography (IRT) have been applied in order the structure - property relationship to be evaluated. Non-crystallized, partially crystallized and fully crystallized glass-ceramic samples have been non-destructively assessed in order their thermo-mechanical behavior to be associated with their micro-structural features.

Fabrication and surface characterization of composite refractory compounds suitable for thermionic converters

NASA Technical Reports Server (NTRS)

Davis, P. R.; Swanson, L. W.

1979-01-01

The techniques of fabricating and characterizing the surface properties of electrode materials were investigated. The basic surface properties of these materials were studied with respect to their utilization as thermionic energy converter electrodes. Emphasis was placed on those factors (e.g, cesium disorption kinetic and mechanisms of low work function production) which are of primary concern to thermionic converter performance.

Porous Nanogold/Polyurethane Scaffolds with Improved Antibiofilm, Mechanical, and Thermal Properties and with Reduced Effects on Cell Viability: A Suitable Material for Soft Tissue Applications.

PubMed

Tamayo, L; Acuña, D; Riveros, A L; Kogan, M J; Azócar, M I; Páez, M; Leal, M; Urzúa, M; Cerda, E

2018-04-25

The use of implants carries on a series of problems, among them infections, poor biocompatibility, high levels of cytotoxicity, and significant mechanical differences between implants and host organs that promote stress shielding effects. These problems indicate that the materials used to make implants must meet essential requirements and high standards for implantations to be successful. In this work, we present the synthesis, characterization and evaluation of the antibiofilm, mechanical, and thermal properties, and cytotoxic effect of a nanocomposite-based scaffold on polyurethane (PU) and gold nanoparticles (AuNPs) for soft tissue applications. The effect of the quantity of AuNPs on the antibacterial activity of nanocomposite scaffolds was evaluated against Staphylococcus epidermidis and Klebsiella spp., with a resulting 99.99% inhibition of both bacteria using a small quantity of nanoparticles. Cytotoxicity was evaluated with the T10 1/2 test against fibroblast cells. The results demonstrated that porous nanogold/PU scaffolds have no toxic effects on fibroblast cells to the 5 day exposition. With respect to mechanical properties, stress-strain curves showed that the compressive modulus and yield strength of PU scaffolds were significantly enhanced by AuNPs (by at least 10 times). This is due to changes in the arrangement of hard segments of PU, which increase the stiffness of the polymer. Thermogravimetric analysis showed that the degradation onset temperature rises with an increase in the quantity of AuNPs. These properties and characteristics demonstrate that porous nanogold/PU scaffolds are suitable material for use in soft tissue implants.

Development of biodegradable materials; balancing degradability and performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mayer, J.M.; Allen, A.L.; Dell, P.A.

1993-12-31

The development of biodegradable materials suitable for packaging must take into consideration various performance criteria such as mechanical and barrier properties, as well as rate of biodegradability in given environments. Individual or blended biopolymer films were obtained commercially or blown into film in the laboratory and tested for tensile strength, ultimate elongation and oxygen barrier. These films were then subjected to accelerated marine biodegradation tests as well as simulated marine respirometry. Starch/ethylene vinyl alcohol films exhibited good mechanical and excellent oxygen barrier properties, but were very slow to biodegrade in the simulated and excellent oxygen barrier properties, but were verymore » slow to biodegrade in the simulated marine environment. Polyhydroxyalkanoates had good mechanical properties, average oxygen barrier and good biodegradability. Data indicate that performance and biodegradability of packaging can be tailored to needs by combining individual biopolymers in different proportions in blends and laminates.« less

3D fiber-deposited scaffolds for tissue engineering: influence of pores geometry and architecture on dynamic mechanical properties.

PubMed

Moroni, L; de Wijn, J R; van Blitterswijk, C A

2006-03-01

One of the main issues in tissue engineering is the fabrication of scaffolds that closely mimic the biomechanical properties of the tissues to be regenerated. Conventional fabrication techniques are not sufficiently suitable to control scaffold structure to modulate mechanical properties. Within novel scaffold fabrication processes 3D fiber deposition (3DF) showed great potential for tissue engineering applications because of the precision in making reproducible 3D scaffolds, characterized by 100% interconnected pores with different shapes and sizes. Evidently, these features also affect mechanical properties. Therefore, in this study we considered the influence of different structures on dynamic mechanical properties of 3DF scaffolds. Pores were varied in size and shape, by changing fibre diameter, spacing and orientation, and layer thickness. With increasing porosity, dynamic mechanical analysis (DMA) revealed a decrease in elastic properties such as dynamic stiffness and equilibrium modulus, and an increase of the viscous parameters like damping factor and creep unrecovered strain. Furthermore, the Poisson's ratio was measured, and the shear modulus computed from it. Scaffolds showed an adaptable degree of compressibility between sponges and incompressible materials. As comparison, bovine cartilage was tested and its properties fell in the fabricated scaffolds range. This investigation showed that viscoelastic properties of 3DF scaffolds could be modulated to accomplish mechanical requirements for tailored tissue engineered applications.

Mechanical Properties and Microstructure of Dissimilar Friction Stir Welds of 11Cr-Ferritic/Martensitic Steel to 316 Stainless Steel

NASA Astrophysics Data System (ADS)

Sato, Yutaka S.; Kokawa, Hiroyuki; Fujii, Hiromichi T.; Yano, Yasuhide; Sekio, Yoshihiro

2015-12-01

Dissimilar joints between ferritic and austenitic steels are of interest for selected applications in next generation fast reactors. In this study, dissimilar friction-stir welding of an 11 pct Cr ferritic/martensitic steel to a 316 austenitic stainless steel was attempted and the mechanical properties and microstructure of the resulting welds were examined. Friction-stir welding produces a stir zone without macroscopic weld-defects, but the two dissimilar steels are not intermixed. The two dissimilar steels are interleaved along a sharp zigzagging interface in the stir zone. During small-sized tensile testing of the stir zone, this sharp interface did not act as a fracture site. Furthermore, the microstructure of the stir zone was refined in both the ferritic/martensitic steel and the 316 stainless steel resulting in improved mechanical properties over the adjacent base material regions. This study demonstrates that friction-stir welding can produce welds between dissimilar steels that contain no macroscopic weld-defects and display suitable mechanical properties.

Evaluating the trade-off between mechanical and electrochemical performance of separators for lithium-ion batteries: Methodology and application

NASA Astrophysics Data System (ADS)

Plaimer, Martin; Breitfuß, Christoph; Sinz, Wolfgang; Heindl, Simon F.; Ellersdorfer, Christian; Steffan, Hermann; Wilkening, Martin; Hennige, Volker; Tatschl, Reinhard; Geier, Alexander; Schramm, Christian; Freunberger, Stefan A.

2016-02-01

Lithium-ion batteries are in widespread use in electric vehicles and hybrid vehicles. Besides features like energy density, cost, lifetime, and recyclability the safety of a battery system is of prime importance. The separator material impacts all these properties and requires therefore an informed selection. The interplay between the mechanical and electrochemical properties as key selection criteria is investigated. Mechanical properties were investigated using tensile and puncture penetration tests at abuse relevant conditions. To investigate the electrochemical performance in terms of effective conductivity a method based on impedance spectroscopy was introduced. This methodology is applied to evaluate ten commercial separators which allows for a trade-off analysis of mechanical versus electrochemical performance. Based on the results, and in combination with other factors, this offers an effective approach to select suitable separators for automotive applications.

Brillouin microspectroscopy of nanostructured biomaterials: photonics assisted tailoring mechanical properties

NASA Astrophysics Data System (ADS)

Meng, Zhaokai; Jaiswal, Manish K.; Chitrakar, Chandani; Thakur, Teena; Gaharwar, Akhilesh K.; Yakovlev, Vladislav V.

2016-03-01

Developing new biomaterials is essential for the next-generation of materials for bioenergy, bioelectronics, basic biology, medical diagnostics, cancer research, and regenerative medicine. Specifically, recent progress in nanotechnology has stimulated the development of multifunctional biomaterials for tissue engineering applications. The physical properties of nanocomposite biomaterials, including elasticity and viscosity, play key roles in controlling cell fate, which underlines therapeutic success. Conventional mechanical tests, including uniaxial compression and tension, dynamic mechanical analysis and shear rheology, require mechanical forces to be directly exerted onto the sample and therefore may not be suitable for in situ measurements or continuous monitoring of mechanical stiffness. In this study, we employ spontaneous Brillouin spectroscopy as a viscoelasticity-specific probing technique. We utilized a Brillouin spectrometer to characterize biomaterial's microscopic elasticity and correlated those with conventional mechanical tests (e.g., rheology).

Undergraduate computational physics projects on quantum computing

NASA Astrophysics Data System (ADS)

Candela, D.

2015-08-01

Computational projects on quantum computing suitable for students in a junior-level quantum mechanics course are described. In these projects students write their own programs to simulate quantum computers. Knowledge is assumed of introductory quantum mechanics through the properties of spin 1/2. Initial, more easily programmed projects treat the basics of quantum computation, quantum gates, and Grover's quantum search algorithm. These are followed by more advanced projects to increase the number of qubits and implement Shor's quantum factoring algorithm. The projects can be run on a typical laptop or desktop computer, using most programming languages. Supplementing resources available elsewhere, the projects are presented here in a self-contained format especially suitable for a short computational module for physics students.

Microstructure and mechanical properties investigation of in situ TiB2 and ZrB2 reinforced Al-4Cu composites

NASA Astrophysics Data System (ADS)

Lutfi Anis, Ahmad; Ramli, Rosmamuhammadani; Darham, Widyani; Zakaria, Azlan; Talari, Mahesh Kumar

2016-02-01

Conventional Al-Cu alloys exhibit coarse grain structure leading to inferior mechanical properties in as-cast condition. Expensive thermo-mechanical treatments are needed to improve microstructure and corresponding mechanical properties. In situ Al-based composites were developed to improve mechanical properties by dispersion strengthening and grain refinement obtained by the presence of particulates in the melt during solidification. In this work Al-4Cu - 3TiB2 and Al-4Cu-3ZrB2 in situ composites were prepared by liquid casting method. XRD, electron microscopy and mechanical tests were performed on suitably sectioned and metallographically prepared surfaces to investigate the phase distribution, hardness and tensile properties. It was found that the reinforcement particles were segregated along the grain boundaries of Al dendrites. Tensile fracture morphology for both Al-4Cu - 3TiB2 and Al-4Cu-3ZrB2 were analyzed and compared to determine the fracture propagation mechanism in the composites. Al-4Cu-3ZrB2 in situ composites displayed higher strength and hardness compared to Al-4Cu-3TiB2 which could be ascribed to the stronger interfacial bonding between the Al dendrites and ZrB2 particulates as evidenced from fractographs.

Long-term characterization of neural electrodes based on parylene-caulked polydimethylsiloxane substrate.

PubMed

Jeong, Jinmo; Chou, Namsun; Kim, Sohee

2016-06-01

This study investigates the mechanical and long-term electrical properties of parylene-caulked polydimethylsiloxane (PDMS) as a substrate for implantable electrodes. The parylene-caulked PDMS is a structure where particles of parylene fill the porous surface of PDMS. This material is expected to have low water absorption and desirable mechanical properties such as flexibility and elasticity that are beneficial in many biomedical applications. To evaluate the mechanical property and electrical stability of parylene-caulked PDMS for potential in-vivo uses, tensile tests were conducted firstly, which results showed that the mechanical strength of parylene-caulked PDMS was comparable to that of native PDMS. Next, surface electrodes based on parylene-caulked PDMS were fabricated and their impedance was measured in phosphate-buffered saline (PBS) solution at 36.5 °C over seven months. The electrodes based on parylene-caulked PDMS exhibited the improved stability in impedance over time than native PDMS. Thus, with improved electrical stability in wet environment and preserved mechanical properties of PDMS, the electrodes based on parylene-caulked PDMS are expected to be suitable for long-term in-vivo applications.

The suitability of common compressibility equations for characterizing plasticity of diverse powders.

PubMed

Paul, Shubhajit; Sun, Changquan Calvin

2017-10-30

The analysis of powder compressibility data yields useful information for characterizing compaction behavior and mechanical properties of powders, especially plasticity. Among the many compressibility equations proposed in powder compaction research, the Heckel equation and the Kawakita equation are the most commonly used, despite their known limitations. Systematic evaluation of the performance in analyzing compressibility data suggested the Kuentz-Leuenberger equation is superior to both the Heckel equation and the Kawakita equation for characterizing plasticity of powders exhibiting a wide range of mechanical properties. Copyright © 2017 Elsevier B.V. All rights reserved.

Mechanical and Tribological Characteristics of the AMC, Prepared by P/M Route along with Thermo-Mechanical Treatment

NASA Astrophysics Data System (ADS)

Mohapatra, Sambit Kumar; Maity, Kalipada; Bhuyan, Subrat Kumar; Prasad Satpathy, Mantra

2018-03-01

Thermo mechanical treatments have the ameliorated impacts on the mechanical and tribological properties of powder metallurgy components. In this investigation an aluminium matrix composite (AMC) {Al (92) + Mg (5) + Gr (1) + Ti (2)} has been prepared by following powder metallurgy technique, with double axial compaction and ulterior sintering. Secondary thermo-mechanical treatment i.e. hot extrusion through mathematical contoured cosine profiled die was considered. The die causes minimum velocity relative differences across the extrusion exit cross-section, which provides smooth material flow. Comparative result analysis for the mechanical and tribological characteristics of the specimen before and after extrusion was concentrated. Extrusion engenders significant amount of improvements of the properties those are attributed to excellent bond strength and uniform density distribution due to high compressive stress. Oxidative and delaminated wear mechanisms were found predominating type. To furnish the suitable explanation scanning electron microscopies have been performed for the wear surfaces.

Comparison of mechanical properties for several electrical spring contact alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nordstrom, Terry V.

Work was conducted to determine whether beryllium-nickel alloy 440 had mechanical properties which made it suitable as a substitute for the presently used precious metal contact alloys Paliney 7 and Neyoro G, in certain electrical contact applications. Possible areas of applicability for the alloy were where extremely low contact resistance was not necessary or in components encountering elevated temperatures above those presently seen in weapons applications. Evaluation of the alloy involved three major experimental areas: 1) measurement of the room temperature microplastic (epsilon approximately 10/sup -6/) and macroplastic (epsilon approximately 10/sup -3/) behavior of alloy 440 in various age hardeningmore » conditions, 2) determination of applied stress effects on stress relaxation or contact force loss and 3) measurement of elevated temperature mechanical properties and stress relaxation behavior. Similar measurements were also made on Neyoro G and Paliney 7 for comparison. The primary results of the study show that beryllium-nickel alloy 440 is from a mechanical properties standpoint, equal or superior to the presently used Paliney 7 and Neyoro G for normal Sandia requirements. For elevated temperature applications, alloy 440 has clearly superior mechanical properties.« less

Mechanical properties of a bioabsorbable nerve guide tube for long nerve defects.

PubMed

Ichihara, S; Facca, S; Liverneaux, P; Inada, Y; Takigawa, T; Kaneko, K; Nakamura, T

2015-09-01

The mechanical properties of nerve guide tubes must be taken into consideration when they are being developed. We previously reported the feasibility of using 50:50 tubes in a canine 40mm peroneal nerve defect model, where 50:50 represents the proportion of poly(L-lactic) acid (PLLA) and polyglycolic acid (PGA). The aim of the current study was to show that 50:50 tubes have suitable mechanical properties for repairing long nerve defects. Four types of nerve guide tubes made with PLLA to PGA fiber ratios of 100:0 (i.e. 100% PLLA) (100:0 tube), 50:50 (50:50 tube), 10:90 (10:90 tube), and 0:100 (0:100 tube) were designed and created using a tubular braiding machine. Their mechanical properties were examined in vitro (up to 16 weeks). In compression testing, 50:50 tubes had the highest normalized force value, followed in order by the 100:0, 10:90, and 0:100 tubes up to 8 weeks after immersion. From the point of view of biomechanics and bioresorbability, out of the 4 tube types tested, 50:50 tubes appeared to have the optimal mechanical properties for longer nerve defects. Copyright © 2015 Elsevier Masson SAS. All rights reserved.

Zinc alloy enhances strength and creep resistance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Machler, M.

1996-10-01

A family of high-performance ternary zinc-copper-aluminum alloys has been developed that provides higher strength, hardness, and creep resistance than the traditional zinc-aluminum alloys Zamak 3, Zamak 5, and ZA-8. Designated ACuZinc, mechanical properties comparable to those of more expensive materials make it suitable for high-load applications and those at elevated temperatures. This article describes the alloy`s composition, properties, and historical development.

A novel high-strength and highly corrosive biodegradable Fe-Pd alloy: Structural, mechanical and in vitro corrosion and cytotoxicity study.

PubMed

Čapek, Jaroslav; Msallamová, Šárka; Jablonská, Eva; Lipov, Jan; Vojtěch, Dalibor

2017-10-01

Recently, iron-based materials have been considered as candidates for the fabrication of biodegradable load-bearing implants. Alloying with palladium has been found to be a suitable approach to enhance the insufficient corrosion rate of iron-based alloys. In this work, we have extensively compared the microstructure, the mechanical and corrosion properties, and the cytotoxicity of an FePd2 (wt%) alloy prepared by three different routes - casting, mechanical alloying and spark plasma sintering (SPS), and mechanical alloying and the space holder technique (SHT). The properties of the FePd2 (wt%) were compared with pure Fe prepared in the same processes. The preparation route significantly influenced the material properties. Materials prepared by SPS possessed the highest values of mechanical properties (CYS~750-850MPa) and higher corrosion rates than the casted materials. Materials prepared by SHT contained approximately 60% porosity; therefore, their mechanical properties reached the lowest values, and they had the highest corrosion rates, approximately 0.7-1.2mm/a. Highly porous FePd2 was tested in vitro according to the ISO 10993-5 standard using L929 cells, and two-fold diluted extracts showed acceptable cytocompatibility. In general, alloying with Pd enhanced both mechanical properties and corrosion rates and did not decrease the cytocompatibility of the studied materials. Copyright © 2017 Elsevier B.V. All rights reserved.

24 CFR 200.934 - User fee system for the technical suitability of products program.

Code of Federal Regulations, 2010 CFR

2010-04-01

... COMMISSIONER, DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT GENERAL INTRODUCTION TO FHA PROGRAMS Minimum Property... section establishes fee requirements for the issuance of Structural Engineering Bulletins (SEBs), Mechanical Engineering Bulletins (MEBs), Truss Connector Bulletins (TCBs), Area Letters of Acceptance (ALAs...

Effect of molecular weight of hyaluronic acid (HA) on viscoelasticity and particle texturing feel of HA dermal biphasic fillers.

PubMed

Chun, Cheolbyong; Lee, Deuk Yong; Kim, Jin-Tae; Kwon, Mi-Kyung; Kim, Young-Zu; Kim, Seok-Soon

2016-01-01

Hyaluronic acid (HA) dermal biphasic fillers are synthesized for their efficacy in correcting aesthetic defects such as wrinkles, scars and facial contouring defects. The fillers consist of crosslinked HA microspheres suspended in a noncrosslinked HA. To extend the duration of HAs within the dermis and obtain the particle texturing feel, HAs are crosslinked to obtain the suitable mechanical properties. Hyaluronic acid (HA) dermal biphasic fillers are prepared by mixing the crosslinked HA microspheres and the noncrosslinked HAs. The elastic modulus of the fillers increased with raising the volume fraction of the microspheres. The mechanical properties and the particle texturing feel of the fillers made from crosslinked HA (1058 kDa) microspheres suspended in noncrosslinked HA (1368 kDa) are successfully achieved, which are adequate for the fillers. Dermal biphasic HA fillers made from 1058 kDa exhibit suitable elastic moduli (211 to 420 Pa) and particle texturing feel (scale 7 ~ 9).

Microstructural and mechanical characteristics of porous iron prepared by powder metallurgy.

PubMed

Capek, Jaroslav; Vojtěch, Dalibor

2014-10-01

The demand for porous biodegradable load-bearing implants has been increasing recently. Based on investigations of biodegradable stents, porous iron may be a suitable material for such applications. In this study, we prepared porous iron samples with porosities of 34-51 vol.% by powder metallurgy using ammonium bicarbonate as a space-holder material. We studied sample microstructure (SEM-EDX and XRD), flexural and compressive behaviors (universal loading machine) and hardness HV5 (hardness tester) of the prepared samples. Sample porosity increased with the amount of spacer in the initial mixtures. Only the pore surfaces had insignificant oxidation and no other contamination was observed. Increasing porosity decreased the mechanical properties of the samples; although, the properties were still comparable with human bone and higher than those of porous non-metallic biomaterials and porous magnesium prepared in a similar way. Based on these results, powder metallurgy appears to be a suitable method for the preparation of porous iron for orthopedic applications. Copyright © 2014 Elsevier B.V. All rights reserved.

Characterization of Cold Sprayed CuCrAl Coated GRCop-84 Substrates for Reusable Launch Vehicles

NASA Technical Reports Server (NTRS)

Raj, S . V.; Barrett, C. A.; Lerch, B. A.; Karthikeyan, J.; Ghosn, L. J.; Haynes, J.

2005-01-01

An advanced Cu-8(at.%)Cr-4%Nb alloy developed at NASA's Glenn Research Center, and designated as GRCop-84, is currently being considered for use as combustor liners and nozzles in NASA's future generations of reusable launch vehicles (RLVs). Despite the fact that this alloy has superior mechanical and oxidation properties compared to many commercially available copper alloys, it is felt that its high temperature and environmental resistance capabilities can be further enhanced with the development and use of suitable coatings. Several coatings and processes are currently being evaluated for their suitability and future down selection. A newly developed CuCrAl has shown excellent oxidation resistance compared to current generation Cu-Cr coating alloys. Cold spray technology for depositing the CuCrAl coating on a GRCop-84 substrate is currently being developed under NASA's Next Generation Launch Technology (NGLT) Propulsion Research and Technology (PR&T) project. The microstructures, mechanical and thermophysical properties of overlay coated GRCop-84 substrates are discussed.

Development of porous ceramsite from construction and demolition waste.

PubMed

Wang, Chuan; Wu, Jian-Zhi; Zhang, Fu-Shen

2013-01-01

The disposal of construction and demolition (C&D) waste has become a serious problem in China due to the rapid increase of Chinese construction industry in recent years. In the present study, typical C&D waste was employed for ceramsite fabrication so as to find a new way for its effective recycling. A novel process was developed for manufacturing high-quality porous ceramsite according to the special chemical composition and properties of C&D waste. Most importantly, a unique bloating agent was developed for the porous structure formation since it was difficult to obtain a suitable porous structure using traditional bloating agents. The effects of processing parameters such as sintering temperature, heating rate and soaking time were investigated, and the bloating mechanism for ceramsite was discussed. The C&D waste ceramsite (CDWC), with high-intensity, low density and homogeneous mechanical properties, was much more suitable for application in the construction field. This study provides a practical process for efficient recycling of the rapidly increasing quantities of C&D waste.

Graded porous polyurethane foam: a potential scaffold for oro-maxillary bone regeneration.

PubMed

Giannitelli, S M; Basoli, F; Mozetic, P; Piva, P; Bartuli, F N; Luciani, F; Arcuri, C; Trombetta, M; Rainer, A; Licoccia, S

2015-06-01

Bone tissue engineering applications demand for biomaterials offering a substrate for cell adhesion, migration, and proliferation, while inferring suitable mechanical properties to the construct. In the present study, polyurethane (PU) foams were synthesized to develop a graded porous material-characterized by a dense shell and a porous core-for the treatment of oro-maxillary bone defects. Foam was synthesized via a one-pot reaction starting from a polyisocyanate and a biocompatible polyester diol, using water as a foaming agent. Different foaming conditions were examined, with the aim of creating a dense/porous functional graded material that would perform at the same time as an osteoconductive scaffold for bone defect regeneration and as a membrane-barrier to gingival tissue ingrowth. The obtained PU was characterized in terms of morphological and mechanical properties. Biocompatibility assessment was performed in combination with bone-marrow-derived human mesenchymal stromal cells (hBMSCs). Our findings confirm that the material is potentially suitable for guided bone regeneration applications. Copyright © 2015 Elsevier B.V. All rights reserved.

Mechanical reinforcement of gellan gum polyelectrolyte hydrogels by cationic polyurethane soft nanoparticles.

PubMed

Sahraro, Maryam; Barikani, Mehdi; Daemi, Hamed

2018-05-01

Novel mechanically reinforced nanocomposite hydrogels (NCHs) were developed based on methacrylated gellan gum (MGG) and cationic polyurethane nanoparticles (CPUNs) through a green chemical approach. A series of NCHs were synthesized by the incorporation of CPUNs with weight ratios of 0, 10, 30 and 50 w/w% into the MGG solution, with two different methacrylation degrees (1.2, 5.6%). The chemical structure, morphology, mechanical properties, stimuli-responsivity and cytotoxicity of synthesized NCHs were investigated. Analysis of the hydrogels mechanical testing demonstrated that the addition of CPUNs affords the significant increase in compressive properties. Meanwhile, the formulation of NCH containing the MGG with lower methacrylation degree and 30 w/w% CPUNs showed the highest mechanical properties. Furthermore, equilibrium swelling ratio of the hydrogels decreased by CPUNs addition. Finally, it is worth mentioning that NCHs showed no significant toxicity to human dermal fibroblast cells (HDFs) which idealize them as the suitable hydrogels for biomedical applications. Copyright © 2018 Elsevier Ltd. All rights reserved.

Identification of a Suitable 3D Printing Material for Mimicking Brittle and Hard Rocks and Its Brittleness Enhancements

NASA Astrophysics Data System (ADS)

Zhou, T.; Zhu, J. B.

2018-03-01

Three-dimensional printing (3DP) is a computer-controlled additive manufacturing technique which is able to repeatedly and accurately fabricate objects with complicated geometry and internal structures. After 30 years of fast development, 3DP has become a mainstream manufacturing process in various fields. This study focuses on identifying the most suitable 3DP material from five targeted available 3DP materials, i.e. ceramics, gypsum, PMMA (poly(methyl methacrylate)), SR20 (acrylic copolymer) and resin (Accura® 60), to simulate brittle and hard rocks. Firstly, uniaxial compression tests were performed to determine the mechanical properties and failure patterns of the 3DP samples fabricated by those five materials. Experimental results indicate that among current 3DP techniques, the resin produced via stereolithography (SLA) is the most suitable 3DP material for mimicking brittle and hard rocks, although its brittleness needs to be improved. Subsequently, three methods including freezing, incorporation of internal macro-crack and addition of micro-defects were adopted to enhance the brittleness of the 3DP resin, followed by uniaxial compression tests on the treated samples. Experimental results reveal that 3DP resin samples with the suggested treatments exhibited brittle properties and behaved similarly to natural rocks. Finally, some prospective improvements which can be used to facilitate the application of 3DP techniques to rock mechanics were also discussed. The findings of this paper could contribute to promoting the application of 3DP technique in rock mechanics.

Manufacture and mechanical characterisation of high voltage insulation for superconducting busbars - (Part 1) Materials selection and development

NASA Astrophysics Data System (ADS)

Clayton, N.; Crouchen, M.; Devred, A.; Evans, D.; Gung, C.-Y.; Lathwell, I.

2017-04-01

It is planned that the high voltage electrical insulation on the ITER feeder busbars will consist of interleaved layers of epoxy resin pre-impregnated glass tapes ('pre-preg') and polyimide. In addition to its electrical insulation function, the busbar insulation must have adequate mechanical properties to sustain the loads imposed on it during ITER magnet operation. This paper reports an investigation into suitable materials to manufacture the high voltage insulation for the ITER superconducting busbars and pipework. An R&D programme was undertaken in order to identify suitable pre-preg and polyimide materials from a range of suppliers. Pre-preg materials were obtained from 3 suppliers and used with Kapton HN, to make mouldings using the desired insulation architecture. Two main processing routes for pre-pregs have been investigated, namely vacuum bag processing (out of autoclave processing) and processing using a material with a high coefficient of thermal expansion (silicone rubber), to apply the compaction pressure on the insulation. Insulation should have adequate mechanical properties to cope with the stresses induced by the operating environment and a low void content necessary in a high voltage application. The quality of the mouldings was assessed by mechanical testing at 77 K and by the measurement of the void content.

Mechanical characteristics of beta sheet-forming peptide hydrogels are dependent on peptide sequence, concentration and buffer composition

PubMed Central

Müller, Michael; König, Finja; Meyer, Nina; Gattlen, Jasmin; Pieles, Uwe; Peters, Kirsten; Kreikemeyer, Bernd; Mathes, Stephanie; Saxer, Sina

2018-01-01

Self-assembling peptide hydrogels can be modified regarding their biodegradability, their chemical and mechanical properties and their nanofibrillar structure. Thus, self-assembling peptide hydrogels might be suitable scaffolds for regenerative therapies and tissue engineering. Owing to the use of various peptide concentrations and buffer compositions, the self-assembling peptide hydrogels might be influenced regarding their mechanical characteristics. Therefore, the mechanical properties and stability of a set of self-assembling peptide hydrogels, consisting of 11 amino acids, made from four beta sheet self-assembling peptides in various peptide concentrations and buffer compositions were studied. The formed self-assembling peptide hydrogels exhibited stiffnesses ranging from 0.6 to 205 kPa. The hydrogel stiffness was mostly affected by peptide sequence followed by peptide concentration and buffer composition. All self-assembling peptide hydrogels examined provided a nanofibrillar network formation. A maximum self-assembling peptide hydrogel dissolution of 20% was observed for different buffer solutions after 7 days. The stability regarding enzymatic and bacterial digestion showed less degradation in comparison to the self-assembling peptide hydrogel dissolution rate in buffer. The tested set of self-assembling peptide hydrogels were able to form stable scaffolds and provided a broad spectrum of tissue-specific stiffnesses that are suitable for a regenerative therapy. PMID:29657766

Effects of Pore Size on the Osteoconductivity and Mechanical Properties of Calcium Phosphate Cement in a Rabbit Model.

PubMed

Zhao, Yi-Nan; Fan, Jun-Jun; Li, Zhi-Quan; Liu, Yan-Wu; Wu, Yao-Ping; Liu, Jian

2017-02-01

Calcium phosphate cement (CPC) porous scaffold is widely used as a suitable bone substitute to repair bone defect, but the optimal pore size is unclear yet. The current study aimed to evaluate the effect of different pore sizes on the processing of bone formation in repairing segmental bone defect of rabbits using CPC porous scaffolds. Three kinds of CPC porous scaffolds with 5 mm diameters and 12 mm length were prepared with the same porosity but different pore sizes (Group A: 200-300 µm, Group B: 300-450 µm, Group C: 450-600 µm, respectively). Twelve millimeter segmental bone defects were created in the middle of the radius bone and filled with different kinds of CPC cylindrical scaffolds. After 4, 12, and 24 weeks, alkaline phosphatase (ALP), histological assessment, and mechanical properties evaluation were performed in all three groups. After 4 weeks, ALP activity increased in all groups but was highest in Group A with smallest pore size. The new bone formation within the scaffolds was not obvious in all groups. After 12 weeks, the new bone formation within the scaffolds was obvious in each group and highest in Group A. At 24 weeks, no significant difference in new bone formation was observed among different groups. Besides the osteoconductive effect, Group A with smallest pore size also had the best mechanical properties in vivo at 12 weeks. We demonstrate that pore size has a significant effect on the osteoconductivity and mechanical properties of calcium phosphate cement porous scaffold in vivo. Small pore size favors the bone formation in the early stage and may be more suitable for repairing segmental bone defect in vivo. © 2016 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Synthesis of sea urchin-like carbon nanotubes on nano-diamond powder.

PubMed

Hwang, E J; Lee, S K; Jeong, M G; Lee, Y B; Lim, D S

2012-07-01

Carbon nanotubes (CNTs) have unique atomic structure and properties, such as a high aspect ratio and high mechanical, electrical and thermal properties. On the other hand, the agglomeration and entanglement of CNTs restrict their applications. Sea urchin-like multiwalled carbon nanotubes, which have a small aspect ratio, can minimize the problem of dispersion. The high hardness, thermal conductivity and chemical inertness of the nano-diamond powder make it suitable for a wide range of applications in the mechanical and electronic fields. CNTs were synthesized on nano-diamond powder by thermal CVD to fabricate a filler with suitable mechanical properties and chemical stability. This paper reports the growth of CNTs with a sea urchin-like structure on the surface of the nano-diamond powder. Nano-diamond powders were dispersed in an attritional milling system using zirconia beads in ethanol. After the milling process, 3-aminopropyltrimethoxysilane (APS) was added as a linker. Silanization was performed between the nano-diamond particles and the metal catalyst. Iron chloride was used as a catalyst for the fabrication of the CNTs. After drying, catalyst-attached nano-diamond powders could be achieved. The growth of the carbon nanotubes was carried out by CVD. The CNT morphology was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mean diameter and length of the CNTs were 201 nm and 3.25 microm, respectively.

Mechanical, Corrosion and Biological Properties of Room-Temperature Sputtered Aluminum Nitride Films with Dissimilar Nanostructure

PubMed Central

Besleaga, Cristina; Dumitru, Viorel; Trinca, Liliana Marinela; Popa, Adrian-Claudiu; Negrila, Constantin-Catalin; Ionescu, Gabriela-Cristina; Ripeanu, Razvan-George; Stan, George E.

2017-01-01

Aluminum Nitride (AlN) has been long time being regarded as highly interesting material for developing sensing applications (including biosensors and implantable sensors). AlN, due to its appealing electronic properties, is envisaged lately to serve as a multi-functional biosensing platform. Although generally exploited for its intrinsic piezoelectricity, its surface morphology and mechanical performance (elastic modulus, hardness, wear, scratch and tensile resistance to delamination, adherence to the substrate), corrosion resistance and cytocompatibility are also essential features for high performance sustainable biosensor devices. However, information about AlN suitability for such applications is rather scarce or at best scattered and incomplete. Here, we aim to deliver a comprehensive evaluation of the morpho-structural, compositional, mechanical, electrochemical and biological properties of reactive radio-frequency magnetron sputtered AlN nanostructured thin films with various degrees of c-axis texturing, deposited at a low temperature (~50 °C) on Si (100) substrates. The inter-conditionality elicited between the base pressure level attained in the reactor chamber and crystalline quality of AlN films is highlighted. The potential suitability of nanostructured AlN (in form of thin films) for the realization of various type of sensors (with emphasis on bio-sensors) is thoroughly probed, thus unveiling its advantages and limitations, as well as suggesting paths to safely exploit the remarkable prospects of this type of materials. PMID:29149061

Mechanical, Corrosion and Biological Properties of Room-Temperature Sputtered Aluminum Nitride Films with Dissimilar Nanostructure.

PubMed

Besleaga, Cristina; Dumitru, Viorel; Trinca, Liliana Marinela; Popa, Adrian-Claudiu; Negrila, Constantin-Catalin; Kołodziejczyk, Łukasz; Luculescu, Catalin-Romeo; Ionescu, Gabriela-Cristina; Ripeanu, Razvan-George; Vladescu, Alina; Stan, George E

2017-11-17

Aluminum Nitride (AlN) has been long time being regarded as highly interesting material for developing sensing applications (including biosensors and implantable sensors). AlN, due to its appealing electronic properties, is envisaged lately to serve as a multi-functional biosensing platform. Although generally exploited for its intrinsic piezoelectricity, its surface morphology and mechanical performance (elastic modulus, hardness, wear, scratch and tensile resistance to delamination, adherence to the substrate), corrosion resistance and cytocompatibility are also essential features for high performance sustainable biosensor devices. However, information about AlN suitability for such applications is rather scarce or at best scattered and incomplete. Here, we aim to deliver a comprehensive evaluation of the morpho-structural, compositional, mechanical, electrochemical and biological properties of reactive radio-frequency magnetron sputtered AlN nanostructured thin films with various degrees of c -axis texturing, deposited at a low temperature (~50 °C) on Si (100) substrates. The inter-conditionality elicited between the base pressure level attained in the reactor chamber and crystalline quality of AlN films is highlighted. The potential suitability of nanostructured AlN (in form of thin films) for the realization of various type of sensors (with emphasis on bio-sensors) is thoroughly probed, thus unveiling its advantages and limitations, as well as suggesting paths to safely exploit the remarkable prospects of this type of materials.

Effect of curing mode on the micro-mechanical properties of dual-cured self-adhesive resin cements.

PubMed

Ilie, Nicoleta; Simon, Alexander

2012-04-01

Light supplying to luting resin cements is impeded in several clinical situations, causing us to question whether materials can properly be cured to achieve adequately (or adequate) mechanical properties. The aim of this study was therefore to analyse the effect of light on the micro-mechanical properties of eight popular dual-cured self-adhesive resin cements by comparing them with two conventional, also dual-cured, resin cements. Four different curing procedures were applied: auto-polymerisation (dark curing) and light curing (LED unit, Freelight 2, 20 s) by applying the unit directly on the samples' surface, at a distance of 5 and 10 mm. Twenty minutes after curing, the samples were stored for 1 week at 37°C in a water-saturated atmosphere. The micro-mechanical properties-Vickers hardness, modulus of elasticity, creep and elastic/plastic deformation-were measured. Data were analysed with multivariate ANOVA followed by Tukey's test and partial eta-squared statistics (p < 0.05). A very strong influence of the material as well as filler volume and weight on the micro-mechanical properties was measured, whereas the influence of the curing procedure and type of cement-conventional or self-adhesive-was generally low. The influence of light on the polymerisation process was material dependent, with four different behaviour patterns to be distinguished. As a material category, significantly higher micro-mechanical properties were measured for the conventional compared to the self-adhesive resin cements, although this difference was low. Within the self-adhesive resin cements group, the variation in micro-mechanical properties was high. The selection of suitable resin cements should be done by considering, besides its adhesive properties, its micro-mechanical properties and curing behaviour also.

Magnetic properties of cobalt ferrite synthesized by mechanical alloying

NASA Astrophysics Data System (ADS)

Dedi, Idayanti, Novrita; Kristiantoro, Tony; Alam, Ginanjar Fajar Nur; Sudrajat, Nanang

2018-05-01

Cobalt ferrite (CoFe2O4) is a well-known hard magnetic material with high coercivity and moderate magnetization. These properties, along with their great physical and chemical stability, make CoFe2O4 suitable for many applications such as generator, audio, video-tape etc. In this study, the magnetic properties of cobalt ferrite synthesized via the mechanical alloying using α-Fe2O3 of Hot Strip Mill (HSM) waste and cobalt carbonate as the precursors have been investigated. Structural and magnetic properties were systematically investigated. The X-ray diffraction (XRD) pattern exhibited the single phase of cobalt ferrite when the sintering temperature was 1000 °C. Permagraph measurements of the sintered sample revealed a saturation magnetization (Ms) of 77-83 emu/g and coercivity (Hc) of 575 Oe which closely to the magnetic properties of references; Ms = 47.2-56.7 emu/g and Hc =233-2002 Oe.

Effect of IN718 Recycled Powder Reuse on Properties of Parts Manufactured by Means of Selective Laser Melting

NASA Astrophysics Data System (ADS)

Ardila, L. C.; Garciandia, F.; González-Díaz, J. B.; Álvarez, P.; Echeverria, A.; Petite, M. M.; Deffley, R.; Ochoa, J.

Powder quality control is essential to obtain parts with suitable mechanical properties in Selective Laser Melting manufacturing technique. One of the most important advantages of suchtechnique is that it allows an efficient use of the material, due to the possibility to recycle and reuse un-melted powder. Nevertheless, powder material properties may change due to repeated recycling, affecting this way the mechanicalbehavior of parts. In this paper the effect of powder reuse on its quality and on the mechanical properties of the resulting melted parts is studied via self-developed recycling methodology. The material considered for investigation was IN718, a nickel superalloy widely used in industry. After recycling powder up to 14 times, no significant changes were observed in powder and test parts properties. The results obtained in this work will help to validate powder recycling methodology for its use in current industrial Selective Laser Melting manufacturing.

The effects of elevated temperatures on the structural properties of fiber composite materials suitable for use in space shuttle and other space vehicles

NASA Technical Reports Server (NTRS)

Wright, M. A.

1972-01-01

The effects of high temperatures on the structural properties of fiber composite materials for use in spacecraft structures are investigated. Various mechanical properties of boron reinforced aluminum alloys were measured. It was observed that cycling these materials through temperatures that varied from room temperature to 425 C could seriously degrade the properties. The extent of the observed effects depended on alloy type and the maximum cyclic temperature used. Results are discussed in terms of upper and lower strength bonds calculated from the strengths of individual fibers.

Determination of mechanical properties of some glass fiber reinforced plastics suitable to Wind Turbine Blade construction

NASA Astrophysics Data System (ADS)

Steigmann, R.; Savin, A.; Goanta, V.; Barsanescu, P. D.; Leitoiu, B.; Iftimie, N.; Stanciu, M. D.; Curtu, I.

2016-08-01

The control of wind turbine's components is very rigorous, while the tower and gearbox have more possibility for revision and repairing, the rotor blades, once they are deteriorated, the defects can rapidly propagate, producing failure, and the damages can affect large regions around the wind turbine. This paper presents the test results, performed on glass fiber reinforced plastics (GFRP) suitable to construction of wind turbine blades (WTB). The Young modulus, shear modulus, Poisson's ratio, ultimate stress have been determined using tensile and shear tests. Using Dynamical Mechanical Analysis (DMA), the activation energy for transitions that appear in polyester matrix as well as the complex elastic modulus can be determined, function of temperature.

Effects of various plasticizers and nanoclays on the mechanical properties of red algae film.

PubMed

Jang, S A; Shin, Y J; Seo, Y B; Song, K B

2011-04-01

To manufacture red algae (RA) film, we used various plasticizers such as glycerol, sorbitol, sucrose, fructose, and polypropylene glycol (PPG), and then determined the mechanical properties of the RA films. The tensile strength (TS), elongation at break (E), and water vapor permeability (WVP) of the films containing various plasticizers ranged between 0.43 to 9.10 MPa, 10.93% to 47.17%, and 1.28 to 1.42 ng m/m2sPa, respectively. RA films containing fructose as a plasticizer had the best mechanical properties of all the films evaluated. Incorporation of nanoclay (Cloisite Na+ and 30B) improved the mechanical properties of the films. RA film with 3% Cloisite Na+ had a TS of 10.89, while RA film with 30B had a TS of 10.85 MPa; these films also had better E and WVP values than the other RA films evaluated. These results suggest that RA/nanoclay composite films are suitable for use as food packaging materials.   Edible RE/nanoclay composite films prepared in the present investigation can be applied in food packaging.

Novel matrix resins for composites for aircraft primary structures, phase 1

NASA Technical Reports Server (NTRS)

Woo, Edmund P.; Puckett, P. M.; Maynard, S.; Bishop, M. T.; Bruza, K. J.; Godschalx, J. P.; Mullins, M. J.

1992-01-01

The objective of the contract is the development of matrix resins with improved processability and properties for composites for primarily aircraft structures. To this end, several resins/systems were identified for subsonic and supersonic applications. For subsonic aircraft, a series of epoxy resins suitable for RTM and powder prepreg was shown to give composites with about 40 ksi compressive strength after impact (CAI) and 200 F/wet mechanical performance. For supersonic applications, a thermoplastic toughened cyanate prepreg system has demonstrated excellent resistance to heat aging at 360 F for 4000 hours, 40 ksi CAI and useful mechanical properties at greater than or equal to 310 F. An AB-BCB-maleimide resin was identified as a leading candidate for the HSCT. Composite panels fabricated by RTM show CAI of approximately 50 ksi, 350 F/wet performance and excellent retention of mechanical properties after aging at 400 F for 4000 hours.

Injection Molding and Mechanical Properties of Bio-Based Polymer Nanocomposites.

PubMed

Mistretta, Maria Chiara; Botta, Luigi; Morreale, Marco; Rifici, Sebastiano; Ceraulo, Manuela; La Mantia, Francesco Paolo

2018-04-17

The use of biodegradable/bio-based polymers is of great importance in addressing several issues related to environmental protection, public health, and new, stricter legislation. Yet some applications require improved properties (such as barrier or mechanical properties), suggesting the use of nanosized fillers in order to obtain bio-based polymer nanocomposites. In this work, bionanocomposites based on two different biodegradable polymers (coming from the Bioflex and MaterBi families) and two different nanosized fillers (organo-modified clay and hydrophobic-coated precipitated calcium carbonate) were prepared and compared with traditional nanocomposites with high-density polyethylene (HDPE) as matrix. In particular, the injection molding processability, as well as the mechanical and rheological properties of the so-obtained bionanocomposites were investigated. It was found that the processability of the two biodegradable polymers and the related nanocomposites can be compared to that of the HDPE-based systems and that, in general, the bio-based systems can be taken into account as suitable alternatives.

Injection Molding and Mechanical Properties of Bio-Based Polymer Nanocomposites

PubMed Central

Mistretta, Maria Chiara; Rifici, Sebastiano; Ceraulo, Manuela

2018-01-01

The use of biodegradable/bio-based polymers is of great importance in addressing several issues related to environmental protection, public health, and new, stricter legislation. Yet some applications require improved properties (such as barrier or mechanical properties), suggesting the use of nanosized fillers in order to obtain bio-based polymer nanocomposites. In this work, bionanocomposites based on two different biodegradable polymers (coming from the Bioflex and MaterBi families) and two different nanosized fillers (organo-modified clay and hydrophobic-coated precipitated calcium carbonate) were prepared and compared with traditional nanocomposites with high-density polyethylene (HDPE) as matrix. In particular, the injection molding processability, as well as the mechanical and rheological properties of the so-obtained bionanocomposites were investigated. It was found that the processability of the two biodegradable polymers and the related nanocomposites can be compared to that of the HDPE-based systems and that, in general, the bio-based systems can be taken into account as suitable alternatives. PMID:29673143

Determining the Mechanical Properties of Lattice Block Structures

NASA Technical Reports Server (NTRS)

Wilmoth, Nathan

2013-01-01

Lattice block structures and shape memory alloys possess several traits ideal for solving intriguing new engineering problems in industries such as aerospace, military, and transportation. Recent testing at the NASA Glenn Research Center has investigated the material properties of lattice block structures cast from a conventional aerospace titanium alloy as well as lattice block structures cast from nickel-titanium shape memory alloy. The lattice block structures for both materials were sectioned into smaller subelements for tension and compression testing. The results from the cast conventional titanium material showed that the expected mechanical properties were maintained. The shape memory alloy material was found to be extremely brittle from the casting process and only compression testing was completed. Future shape memory alloy lattice block structures will utilize an adjusted material composition that will provide a better quality casting. The testing effort resulted in baseline mechanical property data from the conventional titanium material for comparison to shape memory alloy materials once suitable castings are available.

Physics of Cancer

NASA Astrophysics Data System (ADS)

Mierke, Claudia Tanja

2015-09-01

Physics of Cancer focuses on the mechanical properties of cancer cells and their role in cancer disease and metastasis. It discusses the role of the mechanical properties of interacting cells and the connective tissue microenvironment and describes the role of an inflammation during cancer disease. This outstanding book is the first to describe cancer disease from a biophysical point of view without being incomplete in describing the biological site of cancer. Originating in part from the author's own courses on tumor biology and cellular biophysics, this book is suitable for both students and researchers in this dynamic interdisciplinary field, be they from a physical, biological or medical sciences background.

3D printed porous stainless steel for potential use in medicine

NASA Astrophysics Data System (ADS)

Fousová, M.; Kubásek, J.; Vojtěch, D.; Fojt, J.; Čapek, J.

2017-02-01

3D printing technologies like Selective Laser Melting (SLM) or Electron Beam Melting (EBM) produce components of very complicated shapes from various kinds of materials. In this work a highly porous (porosity of almost 90 vol. %) stainless steel component was manufactured by SLM. The material was characterized in terms of structure, surface chemistry and mechanical properties. It was observed that mechanical properties of the material were similar to those of trabecular human bone. The tests realized in this work confirmed suitability of the porous material prepared by SLM for the use in medicine, for example, for scaffolds designed to repair bone defects.

Improved simulation method of automotive spot weld failure with an account of the mechanical properties of spot welds

NASA Astrophysics Data System (ADS)

Wu, H.; Meng, X. M.; Fang, R.; Huang, Y. F.; Zhan, S.

2017-12-01

In this paper, the microstructure and mechanical properties of spot weld were studied, the hardness of nugget and heat affected zone (HAZ) were also tested by metallographic microscope and microhardness tester. The strength of the spot weld with the different parts' area has been characterized. According to the experiments result, CAE model of spot weld with HAZ structure was established, and simulation results of different lap-shear CAE models were analyzed. The results show that the spot weld model which contained the HAZ has good performance and more suitable for engineering application in spot weld simulation.

New Soft Tissue Implants Using Organic Elastomers

NASA Astrophysics Data System (ADS)

Ku, David N.

Typical biomaterials are stiff, difficult to manufacture, and not initially developed for medical implants. A new biomaterial is proposed that is similar to human soft tissue. The biomaterial provides mechanical properties similar to soft tissue in its mechanical and physical properties. Characterization is performed for modulus of elasticity, ultimate strength and wear resistance. The material further exhibits excellent biocompatibility with little toxicity and low inflammation. The material can be molded into a variety of anatomic shapes for use as a cartilage replacement, heart valve, and reconstructive implant for trauma victims. The biomaterial may be suitable for several biodevices of the future aimed at soft-tissue replacements.

Supplementation of exogenous adenosine 5'-triphosphate enhances mechanical properties of 3D cell-agarose constructs for cartilage tissue engineering.

PubMed

Gadjanski, Ivana; Yodmuang, Supansa; Spiller, Kara; Bhumiratana, Sarindr; Vunjak-Novakovic, Gordana

2013-10-01

Formation of tissue-engineered cartilage is greatly enhanced by mechanical stimulation. However, direct mechanical stimulation is not always a suitable method, and the utilization of mechanisms underlying mechanotransduction might allow for a highly effective and less aggressive alternate means of stimulation. In particular, the purinergic, adenosine 5'-triphosphate (ATP)-mediated signaling pathway is strongly implicated in mechanotransduction within the articular cartilage. We investigated the effects of transient and continuous exogenous ATP supplementation on mechanical properties of cartilaginous constructs engineered using bovine chondrocytes and human mesenchymal stem cells (hMSCs) encapsulated in an agarose hydrogel. For both cell types, we have observed significant increases in equilibrium and dynamic compressive moduli after transient ATP treatment applied in the fourth week of cultivation. Continuous ATP treatment over 4 weeks of culture only slightly improved the mechanical properties of the constructs, without major changes in the total glycosaminoglycan (GAG) and collagen content. Structure-function analyses showed that transiently ATP-treated constructs, and in particular those based on hMSCs, had the highest level of correlation between compositional and mechanical properties. Transiently treated groups showed intense staining of the territorial matrix for GAGs and collagen type II. These results indicate that transient ATP treatment can improve functional mechanical properties of cartilaginous constructs based on chondrogenic cells and agarose hydrogels, possibly by improving the structural organization of the bulk phase and territorial extracellular matrix (ECM), that is, by increasing correlation slopes between the content of the ECM components (GAG, collagen) and mechanical properties of the construct.

Advances in vascular tissue engineering.

PubMed

Thomas, Anita C; Campbell, Gordon R; Campbell, Julie H

2003-01-01

Coronary and peripheral artery bypass grafting is commonly used to relieve the symptoms of vascular deficiencies, but the supply of autologous artery or vein may not be sufficient or suitable for multiple bypass or repeat procedures, necessitating the use of other materials. Synthetic materials are suitable for large bore arteries but often thrombose when used in smaller arteries. Suitable replacement grafts must have appropriate characteristics, including resistance to infection, low immunogenicity and good biocompatability and thromboresistance, with appropriate mechanical and physiological properties and cheap and fast manufacture. Current avenues of graft development include coating synthetic grafts with either biological chemicals or cells with anticoagulatory properties. Matrix templates or acellular tubes of extracellular matrix (such as collagen) may be coated or infiltrated with cultured cells. Once placed into the artery, these grafts may become colonised by host cells and gain many of the properties of normal artery. "Tissue-engineered blood vessels" may also be formed from layers of human vascular cells grown in culture. These engineered vessels have many of the characteristics of arteries formed in vivo. "Artificial arteries" may be also be derived from peritoneal granulation tissue in body "bioreactors" by adapting the body's natural wound healing response to produce a hollow tube.

Insoluble elastin reduces collagen scaffold stiffness, improves viscoelastic properties, and induces a contractile phenotype in smooth muscle cells.

PubMed

Ryan, Alan J; O'Brien, Fergal J

2015-12-01

Biomaterials with the capacity to innately guide cell behaviour while also displaying suitable mechanical properties remain a challenge in tissue engineering. Our approach to this has been to utilise insoluble elastin in combination with collagen as the basis of a biomimetic scaffold for cardiovascular tissue engineering. Elastin was found to markedly alter the mechanical and biological response of these collagen-based scaffolds. Specifically, during extensive mechanical assessment elastin was found to reduce the specific tensile and compressive moduli of the scaffolds in a concentration dependant manner while having minimal effect on scaffold microarchitecture with both scaffold porosity and pore size still within the ideal ranges for tissue engineering applications. However, the viscoelastic properties were significantly improved with elastin addition with a 3.5-fold decrease in induced creep strain, a 6-fold increase in cyclical strain recovery, and with a four-parameter viscoelastic model confirming the ability of elastin to confer resistance to long term deformation/creep. Furthermore, elastin was found to result in the modulation of SMC phenotype towards a contractile state which was determined via reduced proliferation and significantly enhanced expression of early (α-SMA), mid (calponin), and late stage (SM-MHC) contractile proteins. This allows the ability to utilise extracellular matrix proteins alone to modulate SMC phenotype without any exogenous factors added. Taken together, the ability of elastin to alter the mechanical and biological response of collagen scaffolds has led to the development of a biomimetic biomaterial highly suitable for cardiovascular tissue engineering. Copyright © 2015 Elsevier Ltd. All rights reserved.

Difference in suitable mechanical properties of three-dimensional, synthetic scaffolds for self-renewing mouse embryonic stem cells of different genetic backgrounds.

PubMed

Lee, Myungook; Ahn, Jong Il; Ahn, Ji Yeon; Yang, Woo Sub; Hubbell, Jeffrey A; Lim, Jeong Mook; Lee, Seung Tae

2017-11-01

We evaluated whether the genetic background of embryonic stem cells (ESCs) affects the properties suitable for three-dimensional (3D) synthetic scaffolds for cell self-renewal. Inbred R1 and hybrid B6D2F1 mouse ESC lines were cultured for 7 days in hydrogel scaffolds with different properties derived from conjugating 7.5, 10, 12.5, or 15% (wt/vol) vinylsulfone-functionalized three-, four-, or eight-arm polyethylene glycol (PEG) with dicysteine-containing crosslinkers with an intervening matrix metalloproteinase-specific cleavage sites. Cell proliferation and expression of self-renewal-related genes and proteins by ESCs cultured in feeder-free or containing 2D culture plate or 3D hydrogel were monitored. As a preliminary experiment, the E14 ESC-customized synthetic 3D microenvironment did not maintain self-renewal of either the R1 or B6D2F1 ESCs. The best R1 cell proliferation (10.04 vs. 0.16-4.39; p < 0.0001) was observed in the four-arm 7.5% PEG-based hydrogels than those with other properties, whereas the F1 ESCs showed better proliferation when they were embedded in the three-arm 10% hydrogels. Self-renewal-related gene and protein expression by ESCs after feeder-free 3D culture was generally maintained compared with the feeder-containing 2D culture, but expression patterns and quantities differed. However, the feeder-free 3D culture yielded better expression than the feeder-free 2D culture. In conclusion, genetic background determined the suitability of hydrogel scaffolds for self-renewal of ESCs, which requires customization for the mechanical properties of each cell line. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2261-2268, 2017. © 2016 Wiley Periodicals, Inc.

Effects of La2O3 Content and Rolling on Microstructure and Mechanical Properties of ODS Molybdenum Alloys

NASA Astrophysics Data System (ADS)

Ma, Jingling; Li, Wuhui; Wang, Guangxin; Li, Yaqiong; Guo, Hongbo; Zhao, Zeliang; Li, Wei

2017-10-01

In order to study the effects of La2O3 content and rolling on microstructure and mechanical properties of Mo-La2O3 alloys, Mo-0.5% (1%) La2O3 alloys were prepared by liquid-solid doping technique, subsequently rolled either by a single-direction rolling or a cross-rolling. As a result, three different materials were prepared for this study. After being annealed at 1800 °C, the single-directionally rolled Mo-1% La2O3 alloy shows the best mechanical properties in terms of strength, hardness, and sagging deformation among the three materials. This is attributed to the observation that the alloy is only recovered with a microstructure of subgrains and dislocations. The single-directionally rolled Mo-0.5% La2O3 exhibits the worst mechanical property among the three materials. In this material, coarse grains, but no subgrains and dislocations, can be observed after annealing, indicating that it is fully recrystallized. For the cross-rolled Mo-1% La2O3 alloy, grains of dispersed sizes, but no dislocations, are visible after annealing, implying that this alloy is partially recrystallized. Accordingly, the mechanical property of this material is in between the other two materials. Thus, the mechanical properties of the three materials can be well understood based on OM, SEM, and TEM results. Overall, the single-directionally rolled Mo-1% La2O3 alloy possesses good mechanical properties and is more suitable for high-temperature applications.

Synthesis, growth, structure, mechanical and optical properties of a new semi-organic 2-methyl imidazolium dihydrogen phosphate single crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nagapandiselvi, P., E-mail: nagapandiselvip@ssn.edu.in; Baby, C.; Gopalakrishnan, R.

2016-09-15

Highlights: • 2MIDP crystals were grown by slow evaporation solution growth technique. • Single crystal XRD revealed self-assembled supramolecular framework. • Z scan technique is employed for third order nonlinear optical susceptibility. • Structure-property correlation is established. - Abstract: A new semi-organic compound, 2-methyl imidazolium dihydrogen phosphate (2MIDP), was prepared and good quality single crystals of 2MIDP were grown by slow evaporation solution growth technique. Crystal structure elucidated using Single crystal XRD showed that 2MIDP crystallizes in monoclinic system with P2{sub 1}/c space group. FT-IR, UV-Vis-NIR, Fluorescence and FT-NMR spectra confirm the molecular structure of 2MIDP. The UV-Vis-NIR spectra establishedmore » the suitability of the compound for NLO applications. TG-DSC showed that 2MIDP is thermally stable up to 200 °C. Mechanical characteristics like hardness number (H{sub v}), stiffness constant (C{sub 11}), yield strength (σ{sub v}), fracture toughness (K{sub c}) and brittleness index (B{sub i}) were assessed using Vicker’s microhardness tester. Third order nonlinear optical properties determined from Z-scan measurement using femto and picosecond lasers showed two photon reverse saturable absorption. The enhancement of nonlinear optical properties in femto second laser, revealed the suitability of 2MIDP for optical limiting applications.« less

Properties and Applications of High Emissivity Composite Films Based on Far-Infrared Ceramic Powder

PubMed Central

Xiong, Yabo; Huang, Shaoyun; Wang, Wenqi; Liu, Xinghai; Li, Houbin

2017-01-01

Polymer matrix composite materials that can emit radiation in the far-infrared region of the spectrum are receiving increasing attention due to their ability to significantly influence biological processes. This study reports on the far-infrared emissivity property of composite films based on far-infrared ceramic powder. X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray powder diffractometry were used to evaluate the physical properties of the ceramic powder. The ceramic powder was found to be rich in aluminum oxide, titanium oxide, and silicon oxide, which demonstrate high far-infrared emissivity. In addition, the micromorphology, mechanical performance, dynamic mechanical properties, and far-infrared emissivity of the composite were analyzed to evaluate their suitability for strawberry storage. The mechanical properties of the far-infrared radiation ceramic (cFIR) composite films were not significantly influenced (p ≥ 0.05) by the addition of the ceramic powder. However, the dynamic mechanical analysis (DMA) properties of the cFIR composite films, including a reduction in damping and shock absorption performance, were significant influenced by the addition of the ceramic powder. Moreover, the cFIR composite films showed high far-infrared emissivity, which has the capability of prolonging the storage life of strawberries. This research demonstrates that cFIR composite films are promising for future applications. PMID:29186047

Properties and Applications of High Emissivity Composite Films Based on Far-Infrared Ceramic Powder.

PubMed

Xiong, Yabo; Huang, Shaoyun; Wang, Wenqi; Liu, Xinghai; Li, Houbin

2017-11-29

Polymer matrix composite materials that can emit radiation in the far-infrared region of the spectrum are receiving increasing attention due to their ability to significantly influence biological processes. This study reports on the far-infrared emissivity property of composite films based on far-infrared ceramic powder. X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray powder diffractometry were used to evaluate the physical properties of the ceramic powder. The ceramic powder was found to be rich in aluminum oxide, titanium oxide, and silicon oxide, which demonstrate high far-infrared emissivity. In addition, the micromorphology, mechanical performance, dynamic mechanical properties, and far-infrared emissivity of the composite were analyzed to evaluate their suitability for strawberry storage. The mechanical properties of the far-infrared radiation ceramic (cFIR) composite films were not significantly influenced ( p ≥ 0.05) by the addition of the ceramic powder. However, the dynamic mechanical analysis (DMA) properties of the cFIR composite films, including a reduction in damping and shock absorption performance, were significant influenced by the addition of the ceramic powder. Moreover, the cFIR composite films showed high far-infrared emissivity, which has the capability of prolonging the storage life of strawberries. This research demonstrates that cFIR composite films are promising for future applications.

pH-Induced Modulation of One- and Two-Photon Absorption Properties in a Naphthalene-Based Molecular Probe.

PubMed

Murugan, N Arul; Kongsted, Jacob; Ågren, Hans

2013-08-13

Presently, there is a great demand for small probe molecules that can be used for two-photon excitation microscopy (TPM)-based monitoring of intracellular and intraorganelle activity and pH. The candidate molecules should ideally possess a large two-photon absorption cross section with optical properties sensitive to pH changes. In the present work, we investigate the potential of a methoxy napthalene (MONAP) derivative for its suitability to serve as a pH sensor using TPM. Using an integrated approach rooted in hybrid quantum mechanics/molecular mechanics, the structures, dynamics, and the one- and two-photon properties of the probe in dimethylformamide solvent are studied. It is found that the protonated form is responsible for the optical property of MONAP at moderately low pH, for which the calculated pH-induced red shift is in good agreement with experiments. A 2-fold increase in the two-photon absorption cross section in the IR region of the spectrum is predicted for the moderately low pH form of the probe, suggesting that this can be a potential probe for pH monitoring of living cells. We also propose some design principles aimed at obtaining control of the absorption spectral range of the probe by structural tuning. Our work indicates that the integrated approach employed is capable of capturing the pH-induced changes in structure and optical properties of organic molecular probes and that such in silico tools can be used to draw structure-property relationships to design novel molecular probes suitable for a specific application.

Shape tailoring to enhance and tune the properties of graphene nanomechanical resonators

NASA Astrophysics Data System (ADS)

Miller, David; Alemán, Benjamín

2017-06-01

The shape of a nanomechanical resonator profoundly affects its mechanical properties and determines its suitability for various applications, such as ultra-sensitive mass and force detection. Despite the promise of 2D nanomechanical systems in such applications, full control over the shape of suspended 2D materials, such as graphene, has not been achieved. We present an effective, single-step method to shape pre-suspended graphene into nanomechanical resonators with arbitrary geometries leading to enhanced properties in comparison to conventional drumheads. Our technique employs focused ion beam milling and achieves feature sizes ranging from a few tens of nanometers to several microns, while obtaining near perfect yield. We compare the mechanical properties of the shaped devices to unmodified drumheads, and find that low-tension, singly-clamped graphene cantilevers display a 20 fold increase in the mechanical quality factor (Q) with a factor 100 reduction in the mechanical damping. Importantly, we achieve these results while simultaneously removing mass, which enables state-of-the-art force sensitivity for a graphene mechanical resonator at room temperature. Our approach opens up a unique, currently inaccessible regime in graphene nanomechanics, one characterized by low strain, low frequency, small mass, and high Q, and facilitates tailoring of non-linearity and damping in mechanical structures composed of graphene and other 2D crystals.

Synthesis of Foam-Shaped Nanoporous Zeolite Material: A Simple Template-Based Method

ERIC Educational Resources Information Center

Saini, Vipin K.; Pires, Joao

2012-01-01

Nanoporous zeolite foam is an interesting crystalline material with an open-cell microcellular structure, similar to polyurethane foam (PUF). The aluminosilicate structure of this material has a large surface area, extended porosity, and mechanical strength. Owing to these properties, this material is suitable for industrial applications such as…

A quest for 2D lattice materials for actuation

NASA Astrophysics Data System (ADS)

Pronk, T. N.; Ayas, C.; Tekõglu, C.

2017-08-01

In the last two decades, most of the studies in shape morphing technology have focused on the Kagome lattice materials, which have superior properties such as in-plane isotropy, high specific stiffness and strength, and low energy requirement for actuation of its members. The Kagome lattice is a member of the family of semi-regular tessellations of the plane. Two fundamental questions naturally arise: i-) What makes a lattice material suitable for actuation? ii-) Are there other tessellations more effective than the Kagome lattice for actuation? The present paper tackles both questions, and provides a clear answer to the first one by comparing an alternative lattice material, the hexagonal cupola, with the Kagome lattice in terms of mechanical/actuation properties. The second question remains open, but, hopefully easier to challenge owing to a newly-discovered criterion: for an n-dimensional (n = 2 , 3) in-plane isotropic lattice material to be suitable for actuation, its pin-jointed equivalent must obey the generalised Maxwell's rule, and must possess M = 3(n - 1) non strain-producing finite kinematic mechanisms.

Carbon nanotube-poly(methyl methacrylate) hybrid films: preparation using diazonium salt chemistry and mechanical properties.

PubMed

Mammeri, Fayna; Teyssandier, Joan; Darche-Dugaret, Clément; Debacker, Sabine; Le Bourhis, Eric; Chehimi, Mohamed Mehdi

2014-11-01

The poor miscibility of carbon nanotubes (CNTs) in common organic solvents and organic monomers requires their modification by suitable functional (reactive or not) groups prior to their incorporation in thermoplastic polymers. Dispersion behavior of carbon nanotubes and mechanical properties of various CNT-poly(methylmethacrylate) (PMMA) nanocomposites were investigated. We studied the influence of the surface chemistry through the use of diazonium salts as an elegant and environmentally friendly platform to provide a suitable sidewall functionalization by methyl methacrylate functions. We used either a molecular size functional group through the grafting of methacryloxypropyltrimethoxysilane or a macromolecular size one, consisting in PMMA brushes grown by SI-ATRP in order to study the influence of the length of methacrylate function on the dispersion of CNT in PMMA. The hardness and the elastic indentation modulus of all hybrid films were obtained through nanoindentation measurements and found to increase, using ATRP-modified CNTs, suggesting a better dispersion of CNTs in PMMA due to optimal inorganic-organic interactions promoted by the short chains of PMMA. Copyright © 2014 Elsevier Inc. All rights reserved.

In Vivo Corrosion of Two Novel Magnesium Alloys ZEK100 and AX30 and Their Mechanical Suitability as Biodegradable Implants

PubMed Central

Huehnerschulte, Tim Andreas; Angrisani, Nina; Rittershaus, Dina; Bormann, Dirk; Windhagen, Henning; Meyer-Lindenberg, Andrea

2011-01-01

In magnesium alloys, the components used modify the alloy properties. For magnesium implants in contact with bone, rare earths alloys are commonly examined. These were shown to have a higher corrosion resistance than other alloys and a high mechanical strength, but their exact composition is hard to predict. Therefore a reduction of their content could be favorable. The alloys ZEK100 and AX30 have a reduced content or contain no rare earths at all. The aim of the study was to investigate their in vivo degradation and to assess the suitability of the in vivo µCT for the examination of their corrosion. Implants were inserted in rabbit tibiae. Clinical examinations, X-rays and in vivo µCT scans were done regularly. Afterwards implants were analyzed with REM, electron dispersive X-ray (EDX), weighing and mechanical testing. The in vivo µCT is of great advantage, because it allows a quantification of the corrosion rate and qualitative 3D assessment of the corrosion morphology. The location of the implant has a remarkable effect on the corrosion rate. Due to its mechanical characteristics and its corrosion behavior, ZEK100 was judged to be suitable, while AX30, which displays favorable degradation behavior, has too little mechanical strength for applications in weight bearing bones. PMID:28879972

Computational Screening of 2D Materials for Photocatalysis.

PubMed

Singh, Arunima K; Mathew, Kiran; Zhuang, Houlong L; Hennig, Richard G

2015-03-19

Two-dimensional (2D) materials exhibit a range of extraordinary electronic, optical, and mechanical properties different from their bulk counterparts with potential applications for 2D materials emerging in energy storage and conversion technologies. In this Perspective, we summarize the recent developments in the field of solar water splitting using 2D materials and review a computational screening approach to rapidly and efficiently discover more 2D materials that possess properties suitable for solar water splitting. Computational tools based on density-functional theory can predict the intrinsic properties of potential photocatalyst such as their electronic properties, optical absorbance, and solubility in aqueous solutions. Computational tools enable the exploration of possible routes to enhance the photocatalytic activity of 2D materials by use of mechanical strain, bias potential, doping, and pH. We discuss future research directions and needed method developments for the computational design and optimization of 2D materials for photocatalysis.

Joining of aluminum and stainless steel using AlSi10 brazing filler: Microstructure and mechanical properties

NASA Astrophysics Data System (ADS)

Fedorov, Vasilii; Uhlig, Thomas; Wagner, Guntram

2017-07-01

Joining of dissimilar materials like stainless steel and aluminum is of special interest for automotive applications. Due to the different properties of these materials, suitable joining techniques are required. Brazing offers the possibilities to manufacture high performance joints in one step and at low joining temperatures. However, these joints often need to withstand a high number of high cyclic loads during application. Therefore, in addition to the monotonic properties, the fatigue behavior of the produced joints must be considered and evaluated. In the present work, specimens are manufactured by induction brazing using an AlSi10 filler and a non-corrosive flux. The mechanical properties are determined by tensile shear tests as well as in fatigue tests at ambient and elevated temperatures. The microstructure of the brazed joints and the fracture surfaces of the tested samples are investigated by SEM.

Influence of the simultaneous addition of bentonite and cellulose fibers on the mechanical and barrier properties of starch composite-films.

PubMed

de Moraes, J Oliveira; Müller, C M O; Laurindo, J B

2012-02-01

The addition of nanoclay or cellulose fibers has been presented in the literature as a suitable alternative for reinforcing starch films. The aim of the present work was to evaluate the effect of the simultaneous incorporation of nanoclay (bentonite) and cellulose fibers on the mechanical and water barrier properties of the resultant composite-films. Films were prepared by casting with 3% in weight of cassava starch, using glycerol as plasticizer (0.30 g per g of starch), cellulose fibers at a concentration of 0.30 g of fibers per g of starch and nanoclay (0.05 g clay per g starch and 0.10 g clay per g starch). The addition of cellulose fibers and nanoclay increased the tensile strength of the films 8.5 times and the Young modulus 24 times but reduced the elongation capacity 14 times. The water barrier properties of the composite-films to which bentonite and cellulose fibers were added were approximately 60% inferior to those of starch films. Diffractograms showed that the nanoclay was intercalated in the polymeric matrix. These results indicate that the simultaneous addition of bentonite and cellulose fibers is a suitable alternative to increase the tensile strength of the films and decrease their water vapor permeabilities.

Poly(dimethylsiloxane) coatings for controlled drug release--polymer modifications.

PubMed

Schulze Nahrup, J; Gao, Z M; Mark, J E; Sakr, A

2004-02-11

Modifications of endhydroxylated poly(dimethylsiloxane) (PDMS) formulations were studied for their ability to be applied onto tablet cores in a spray-coating process and to control drug release in zero-order fashion. Modifications of the crosslinker from the most commonly used tetraethylorthosilicate (TEOS) to the trifunctional 3-(2,3-epoxypropoxy)propyltrimethoxysilane (SIG) and a 1:1 mixture of the two were undertaken. Addition of methylpolysiloxane-copolymers were studied. Lactose, microcrystalline cellulose (MCC) and polyethylene glycol 8000 (PEG) were the channeling agents applied. The effects on dispersion properties were characterized by particle size distribution and viscosity. Mechanical properties of resulting free films were studied to determine applicability in a pan-coating process. Release of hydrochlorothiazide (marker drug) was studied from tablets coated in a lab-size conventional coating pan. All dispersions were found suitable for a spray-coating process. Preparation of free films showed that copolymer addition was not possible due to great decline in mechanical properties. Tablets coated with formulations containing PEG were most suitable to control drug release, at only 5% coating weight. Constant release rates could be achieved for formulations with up to 25% PEG; higher amounts resulted in a non-linear release pattern. Upon adding 50% PEG, a drug release of 63% over 24 h could be achieved.

Micro-CT based finite element models for elastic properties of glass-ceramic scaffolds.

PubMed

Tagliabue, Stefano; Rossi, Erica; Baino, Francesco; Vitale-Brovarone, Chiara; Gastaldi, Dario; Vena, Pasquale

2017-01-01

In this study, the mechanical properties of porous glass-ceramic scaffolds are investigated by means of three-dimensional finite element models based on micro-computed tomography (micro-CT) scan data. In particular, the quantitative relationship between the morpho-architectural features of the obtained scaffolds, such as macroscopic porosity and strut thickness, and elastic properties, is sought. The macroscopic elastic properties of the scaffolds have been obtained through numerical homogenization approaches using the mechanical characteristics of the solid walls of the scaffolds (assessed through nanoindentation) as input parameters for the numerical simulations. Anisotropic mechanical properties of the produced scaffolds have also been investigated by defining a suitable anisotropy index. A comparison with morphological data obtained through the micro-CT scans is also presented. The proposed study shows that the produced glass-ceramic scaffolds exhibited a macroscopic porosity ranging between 29% and 97% which corresponds to an average stiffness ranging between 42.4GPa and 36MPa. A quantitative estimation of the isotropy of the macroscopic elastic properties has been performed showing that the samples with higher solid fractions were those closest to an isotropic material. Copyright © 2016 Elsevier Ltd. All rights reserved.

Nanoindentation of HMX and Idoxuridine to Determine Mechanical Similarity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burch, Alexandra; Yeager, John; Bahr, David

Assessing the mechanical behavior (elastic properties, plastic properties, and fracture phenomena) of molecular crystals is often complicated by the difficulty in preparing samples. Pharmaceuticals and energetic materials in particular are often used in composite structures or tablets, where the individual grains can strongly impact the solid behavior. Nanoindentation is a convenient method to experimentally assess these properties, and it is used here to demonstrate the similarity in the mechanical properties of two distinct systems: individual crystals of the explosive cyclotetramethylene tetranitramine (HMX) and the pharmaceutical idoxuridine were tested in their as-precipitated state, and the effective average modulus and hardness (whichmore » can be orientation dependent) were determined. Both exhibit a hardness of 1.0 GPa, with an effective reduced modulus of 25 and 23 GPa for the HMX and idoxuridine, respectively. They also exhibit similar yield point behavior. This indicates idoxuridine may be a suitable mechanical surrogate (or “mock”) for HMX. While the methodology to assess elastic and plastic properties was relatively insensitive to specific crystal orientation (i.e., a uniform distribution in properties was observed for all random crystals tested), the indentation-induced fracture properties appear to be much more sensitive to tip-crystal orientation, and an unloading slope analysis is used to demonstrate the need for further refinement in relating toughness to orientation in these materials with relatively complex slip systems and crystal structures. View Full-Text« less

Nanoindentation of HMX and Idoxuridine to Determine Mechanical Similarity

DOE PAGES

Burch, Alexandra; Yeager, John; Bahr, David

2017-11-01

Assessing the mechanical behavior (elastic properties, plastic properties, and fracture phenomena) of molecular crystals is often complicated by the difficulty in preparing samples. Pharmaceuticals and energetic materials in particular are often used in composite structures or tablets, where the individual grains can strongly impact the solid behavior. Nanoindentation is a convenient method to experimentally assess these properties, and it is used here to demonstrate the similarity in the mechanical properties of two distinct systems: individual crystals of the explosive cyclotetramethylene tetranitramine (HMX) and the pharmaceutical idoxuridine were tested in their as-precipitated state, and the effective average modulus and hardness (whichmore » can be orientation dependent) were determined. Both exhibit a hardness of 1.0 GPa, with an effective reduced modulus of 25 and 23 GPa for the HMX and idoxuridine, respectively. They also exhibit similar yield point behavior. This indicates idoxuridine may be a suitable mechanical surrogate (or “mock”) for HMX. While the methodology to assess elastic and plastic properties was relatively insensitive to specific crystal orientation (i.e., a uniform distribution in properties was observed for all random crystals tested), the indentation-induced fracture properties appear to be much more sensitive to tip-crystal orientation, and an unloading slope analysis is used to demonstrate the need for further refinement in relating toughness to orientation in these materials with relatively complex slip systems and crystal structures. View Full-Text« less

Corrosion behaviour of electropolished AISI 316L austenitic biomaterial in physiological solution

NASA Astrophysics Data System (ADS)

Zatkalíková, V.; Markovičová, L.; Škorvanová, M.

2017-11-01

Due to suitable mechanical properties, satisfactory corrosion resistance and relatively low cost, austenitic stainless steels are important biomaterials for manufacture of implants and various medical instruments and devices. Their corrosion properties and biocompatibility are significantly affected by protective passive surface film quality, which depends on used mechanical and chemical surface treatment. This article deals with corrosion resistance of AISI 316L stainless steel, which is the most widely used Cr-Ni-Mo austenitic biomaterial. Corrosion behaviour of five various surfaces (original, electropolished, three surfaces with combined treatment finished by electropolishing) is evaluated on the bases of cyclic potentiodynamic polarization tests performed in physiological solution at the temperature of 37± 0.5 °C.

The microstructure of petroleum vacuum residue films for bituminous concrete: a microscopy approach.

PubMed

Sourty, E D; Tamminga, A Y; Michels, M A J; Vellinga, W-P; Meijer, H E H

2011-02-01

Selected carbon-rich refinery residues ('binders') mixed with mineral particles can form composite materials ('bituminous concrete') with bulk mechanical properties comparable to those of cement concrete. The microstructural mechanism underlying the remarkable composite properties has been related to the appearance of a rigid percolating network consisting of asphaltenes and mineral particles [Wilbrink M. et al. (2005) Rigidity percolation in dispersions with a structured visco-elastic matrix. Phys. Rev. E71, 031402]. In this paper, we explore the microstructure of thin binder films of varying thickness with a number of microscopic characterization techniques, and attempt to relate the observed microstructure to the distinctive mechanical behaviour. Two binders, only one of which has been proven to be suitable for bituminous concrete were investigated, and their microstructure compared. Both binders show the formation of asphaltene aggregates. The binder suitable for bituminous concrete is distinguished by the fact that the asphaltenes show a stronger tendency towards such aggregation, due to a higher concentration and less stabilization in the maltene phase. They also show a clear affinity to other species (such as waxes) and may act as nucleation sites for crystals and aggregates of those species. © 2010 The Authors Journal compilation © 2010 The Royal Microscopical Society.

The Feasibility of Sugar Palm (Arenga pinnata) Trunk for Raw Material of Parquet (Wood Flooring)

NASA Astrophysics Data System (ADS)

Nuryawan, A.; Tarigan, A.; Hakim, L.

2017-03-01

In the market, parquet was made from high density wood such as teak, merbau, kempas, ulin, oak, lime, maple, or other high density wood. Parquet has been used for flooring in specific buildings, for instance sport hall, library, commercial building (i.e hotel lobby, hypermarket), and office building. Because of the scarcity of high density wood nowadays and in order to find out the alternative material for wood flooring, the utilization of sugar palm trunk was considered. In this contribution, unproductive sugar palm tree was cut down and divided into three sections using chain saw, namely bottom, middle, and tip. For each section, physical and mechanical samples testing were made according to British Standard 373:1957 for small clear specimen. Investigation of both properties was done in ambient temperature with at least three replications. Instron UTM (Universal Testing Machine) was used to evaluate the mechanical properties. Results of the physical testing (density, moisture content and tangential shrinkage) showed the entire trunk was suitable for raw material of parquet. However, the results of mechanical testing (hardness, MOE/modulus of elasticity, MOR/modulus of rupture, and compression perpendicular to grain) showed only bottom and middle parts were suitable for raw material of parquet while the upper part was vice versa.

Mechanical strength of ceramic scaffolds reinforced with biopolymers is comparable to that of human bone.

PubMed

Henriksen, S S; Ding, M; Juhl, M Vinther; Theilgaard, N; Overgaard, S

2011-05-01

Eight groups of calcium-phosphate scaffolds for bone implantation were prepared of which seven were reinforced with biopolymers, poly lactic acid (PLA) or hyaluronic acid in different concentrations in order to increase the mechanical strength, without significantly impairing the microarchitecture. Controls were un-reinforced calcium-phosphate scaffolds. Microarchitectural properties were quantified using micro-CT scanning. Mechanical properties were evaluated by destructive compression testing. Results showed that adding 10 or 15% PLA to the scaffold significantly increased the mechanical strength. The increase in mechanical strength was seen as a result of increased scaffold thickness and changes to plate-like structure. However, the porosity was significantly lowered as a consequence of adding 15% PLA, whereas adding 10% PLA had no significant effect on porosity. Hyaluronic acid had no significant effect on mechanical strength. The novel composite scaffold is comparable to that of human bone which may be suitable for transplantation in specific weight-bearing situations, such as long bone repair.

Properties of Galvanized and Galvannealed Advanced High Strength Hot Rolled Steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

V.Y. Guertsman; E. Essadiqi; S. Dionne

2008-04-01

The objectives of the project were (i) to develop the coating process information to achieve good quality coatings on 3 advanced high strength hot rolled steels while retaining target mechanical properties, (ii) to obtain precise knowledge of the behavior of these steels in the various forming operations and (iii) to establish accurate user property data in the coated conditions. Three steel substrates (HSLA, DP, TRIP) with compositions providing yield strengths in the range of 400-620 MPa were selected. Only HSLA steel was found to be suitable for galnaizing and galvannealing in the hot rolled condition.

Review of Relationship Between Particle Deformation, Coating Microstructure, and Properties in High-Pressure Cold Spray

NASA Astrophysics Data System (ADS)

Rokni, M. R.; Nutt, S. R.; Widener, C. A.; Champagne, V. K.; Hrabe, R. H.

2017-08-01

In the cold spray (CS) process, deposits are produced by depositing powder particles at high velocity onto a substrate. Powders deposited by CS do not undergo melting before or upon impacting the substrate. This feature makes CS suitable for deposition of a wide variety of materials, most commonly metallic alloys, but also ceramics and composites. During processing, the particles undergo severe plastic deformation and create a more mechanical and less metallurgical bond with the underlying material. The deformation behavior of an individual particle depends on multiple material and process parameters that are classified into three major groups—powder characteristics, geometric parameters, and processing parameters, each with their own subcategories. Changing any of these parameters leads to evolution of a different microstructure and consequently changes the mechanical properties in the deposit. While cold spray technology has matured during the last decade, the process is inherently complex, and thus, the effects of deposition parameters on particle deformation, deposit microstructure, and mechanical properties remain unclear. The purpose of this paper is to review the parameters that have been investigated up to now with an emphasis on the existent relationships between particle deformation behavior, microstructure, and mechanical properties of various cold spray deposits.

Tissue Regeneration: A Silk Road.

PubMed

Jao, Dave; Mou, Xiaoyang; Hu, Xiao

2016-08-05

Silk proteins are natural biopolymers that have extensive structural possibilities for chemical and mechanical modifications to facilitate novel properties, functions, and applications in the biomedical field. The versatile processability of silk fibroins (SF) into different forms such as gels, films, foams, membranes, scaffolds, and nanofibers makes it appealing in a variety of applications that require mechanically superior, biocompatible, biodegradable, and functionalizable biomaterials. There is no doubt that nature is the world's best biological engineer, with simple, exquisite but powerful designs that have inspired novel technologies. By understanding the surface interaction of silk materials with living cells, unique characteristics can be implemented through structural modifications, such as controllable wettability, high-strength adhesiveness, and reflectivity properties, suggesting its potential suitability for surgical, optical, and other biomedical applications. All of the interesting features of SF, such as tunable biodegradation, anti-bacterial properties, and mechanical properties combined with potential self-healing modifications, make it ideal for future tissue engineering applications. In this review, we first demonstrate the current understanding of the structures and mechanical properties of SF and the various functionalizations of SF matrices through chemical and physical manipulations. Then the diverse applications of SF architectures and scaffolds for different regenerative medicine will be discussed in detail, including their current applications in bone, eye, nerve, skin, tendon, ligament, and cartilage regeneration.

A computational modeling approach for the characterization of mechanical properties of 3D alginate tissue scaffolds.

PubMed

Nair, K; Yan, K C; Sun, W

2008-01-01

Scaffold guided tissue engineering is an innovative approach wherein cells are seeded onto biocompatible and biodegradable materials to form 3-dimensional (3D) constructs that, when implanted in the body facilitate the regeneration of tissue. Tissue scaffolds act as artificial extracellular matrix providing the environment conducive for tissue growth. Characterization of scaffold properties is necessary to understand better the underlying processes involved in controlling cell behavior and formation of functional tissue. We report a computational modeling approach to characterize mechanical properties of 3D gellike biomaterial, specifically, 3D alginate scaffold encapsulated with cells. Alginate inherent nonlinearity and variations arising from minute changes in its concentration and viscosity make experimental evaluation of its mechanical properties a challenging and time consuming task. We developed an in silico model to determine the stress-strain relationship of alginate based scaffolds from experimental data. In particular, we compared the Ogden hyperelastic model to other hyperelastic material models and determined that this model was the most suitable to characterize the nonlinear behavior of alginate. We further propose a mathematical model that represents the alginate material constants in Ogden model as a function of concentrations and viscosity. This study demonstrates the model capability to predict mechanical properties of 3D alginate scaffolds.

Evaluation of material properties and compression characteristics of Assam Bora rice flours as a directly compressible vehicle in tablet formulation.

PubMed

Ahmad, Mohammad Zaki; Akhter, Sohail; Dhiman, Ishita; Sharma, Poonam; Verma, Reena

2013-02-01

The mechanical properties and compaction characteristics of different varieties of Assam Bora rice flours (ABRFs) were evaluated and compared with those of official Starch 1500®. The material properties and compression characteristics of Assam Bora rice flours were studied by Heckel and Kawakita analysis. The influences of physical and geometrical properties of ABRFs were evaluated with regard to their compression properties. The mechanical properties, such as toughness and Young's modulus of ABRFs were also compared with that of Starch 1500®. The novel ABRFs reflect better physical characteristics such as higher bulk and tap densities, less porosity, better powder packing ability, large surface area, and improved flowability. ABRFs were the least sensitive material to magnesium stearate, and blending time did not affect its compactibility. Their onset of plastic deformation and strain rate sensitivity as compared to that of Starch 1500® demonstrate its potential use as a directly compressible vehicle for tablet. The experimental ABRFs showed superior properties to official Starch 1500® in many cases and could serve as suitable alternatives for particular purposes.

Pyrolytic graphite collector development program

NASA Technical Reports Server (NTRS)

Wilkins, W. J.

1982-01-01

Pyrolytic graphite promises to have significant advantages as a material for multistage depressed collector electrodes. Among these advantages are lighter weight, improved mechanical stiffness under shock and vibration, reduced secondary electron back-streaming for higher efficiency, and reduced outgassing at higher operating temperatures. The essential properties of pyrolytic graphite and the necessary design criteria are discussed. This includes the study of suitable electrode geometries and methods of attachment to other metal and ceramic collector components consistent with typical electrical, thermal, and mechanical requirements.

The Effect of a Two-Stage Heat-Treatment on the Microstructural and Mechanical Properties of a Maraging Steel

PubMed Central

Sun, Lin; Galvin, Deri Rhys; Hill, Paul; Rawson, Martin; Gilbert, Elliot Paul; Bhadeshia, Harshad; Perkins, Karen

2017-01-01

Maraging steels gain many of their beneficial properties from heat treatments which induce the precipitation of intermetallic compounds. We consider here a two-stage heat-treatment, first involving austenitisation, followed by quenching to produce martensite and then an ageing treatment at a lower temperature to precipitation harden the martensite of a maraging steel. It is shown that with a suitable choice of the initial austenitisation temperature, the steel can be heat treated to produce enhanced toughness, strength and creep resistance. A combination of small angle neutron scattering, scanning electron microscopy, electron back-scattered diffraction, and atom probe tomography were used to relate the microstructural changes to mechanical properties. It is shown that such a combination of characterisation methods is necessary to quantify this complex alloy, and relate these microstructural changes to mechanical properties. It is concluded that a higher austenitisation temperature leads to a greater volume fraction of smaller Laves phase precipitates formed during ageing, which increase the strength and creep resistance but reduces toughness. PMID:29168800

Effect of Different Thermomechanical Processes on the Microstructure, Texture, and Mechanical Properties of API 5L X70 Steel

NASA Astrophysics Data System (ADS)

Masoumi, Mohammad; Echeverri, Edwan Anderson Ariza; Silva, Cleiton Carvalho; Béreš, Miloslav; de Abreu, Hamilton Ferreira Gomes

2018-03-01

A commercial API 5L X70 steel plate was subjected to different thermomechanical processes to propose a novel thermomechanical rolling path to achieve improved mechanical properties. Scanning electron microscopy, electron backscatter diffraction, and x-ray texture analysis were employed for microstructural characterization. The results showed that strain-free recrystallized {001} ferrite grains that developed at higher rolling temperature could not meet the American Petroleum Institute (API) requirements. Also, refined and work-hardened grains that have formed in the intercritical region with high stored energy do not provide suitable tensile properties. However, fine martensite-austenite constituents dispersed in ferrite matrix with grains having predominantly {111} and {110} orientations parallel to the normal direction that developed under isothermal rolling at 850 °C provided an outstanding combination of tensile strength and ductility.

Effect of cold drawing on mechanical properties of biodegradable fibers.

PubMed

La Mantia, Francesco Paolo; Ceraulo, Manuela; Mistretta, Maria Chiara; Morreale, Marco

2017-01-26

Biodegradable polymers are currently gaining importance in several fields, because they allow mitigation of the impact on the environment related to disposal of traditional, nonbiodegradable polymers, as well as reducing the utilization of oil-based sources (when they also come from renewable resources). Fibers made of biodegradable polymers are of particular interest, though, it is not easy to obtain polymer fibers with suitable mechanical properties and to tailor these to the specific application. The main ways to tailor the mechanical properties of a given biodegradable polymer fiber are based on crystallinity and orientation control. However, crystallinity can only marginally be modified during processing, while orientation can be controlled, either during hot drawing or cold stretching. In this paper, a systematic investigation of the influence of cold stretching on the mechanical and thermomechanical properties of fibers prepared from different biodegradable polymer systems was carried out. Rheological and thermal characterization helped in interpreting the orientation mechanisms, also on the basis of the molecular structure of the polymer systems. It was found that cold drawing strongly improved the elastic modulus, tensile strength and thermomechanical resistance of the fibers, in comparison with hot-spun fibers. The elastic modulus showed higher increment rates in the biodegradable systems upon increasing the draw ratio.

41 CFR 102-75.1185 - What are suitability criteria?

Code of Federal Regulations, 2014 CFR

2014-01-01

... 41 Public Contracts and Property Management 3 2014-01-01 2014-01-01 false What are suitability criteria? 102-75.1185 Section 102-75.1185 Public Contracts and Property Management Federal Property... DISPOSAL Use of Federal Real Property to Assist the Homeless Suitability Criteria § 102-75.1185 What are...

41 CFR 102-75.1185 - What are suitability criteria?

Code of Federal Regulations, 2010 CFR

2010-07-01

... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false What are suitability criteria? 102-75.1185 Section 102-75.1185 Public Contracts and Property Management Federal Property... DISPOSAL Use of Federal Real Property to Assist the Homeless Suitability Criteria § 102-75.1185 What are...

[A study on alpha-tricalcium phosphate bone cement carbon fiber-reinforced].

PubMed

Wu, Wenjin; Yang, Weizhong; Zhou, Dali; Ma, Jiang; Xiao, Bin

2006-06-01

In order to improve the mechanical properties of alpha-tricalcium phosphate (alpha-TCP), we prepared surface-modified carbon fibers (CF) reinforced alpha-TCP composite bone cement. Bone cement was soaked in Ringer's body solution to test its capacity of fast formation of hydroxyapatite crystals and self-solidification. Scan electronic microscope (SEM) observation and compressive strength measurement were taken to analyze the mechanical properties and the micro- morphological structure of CF reinforced alpha-TCP bone cement. The results showed that the bone cement was transferred into hydroxyapatite plates after being soaked in Ringer's simulated body fluid for 5 days. Suitable amount of carbon fibers could well spread in and bond with the matrix of the bone cement. The mechanical properties of the bone cement have been improved by CF reinforcing; the compressive strength reaches 46.7 MPa when the amount of carbon fibers is 0.5% in weight percent, which is 22% higher than that of the non-reinforced alpha-TCP bone cement.

Effect of multiple forming tools on geometrical and mechanical properties in incremental sheet forming

NASA Astrophysics Data System (ADS)

Wernicke, S.; Dang, T.; Gies, S.; Tekkaya, A. E.

2018-05-01

The tendency to a higher variety of products requires economical manufacturing processes suitable for the production of prototypes and small batches. In the case of complex hollow-shaped parts, single point incremental forming (SPIF) represents a highly flexible process. The flexibility of this process comes along with a very long process time. To decrease the process time, a new incremental forming approach with multiple forming tools is investigated. The influence of two incremental forming tools on the resulting mechanical and geometrical component properties compared to SPIF is presented. Sheets made of EN AW-1050A were formed to frustums of a pyramid using different tool-path strategies. Furthermore, several variations of the tool-path strategy are analyzed. A time saving between 40% and 60% was observed depending on the tool-path and the radii of the forming tools while the mechanical properties remained unchanged. This knowledge can increase the cost efficiency of incremental forming processes.

Ultrasonic alignment of microparticles in nozzle-like geometries

NASA Astrophysics Data System (ADS)

Whittaker, Molly A.; Dauson, Erin R.; Parra-Raad, Jaime; Heard, Robert A.; Oppenheim, Irving J.

2018-03-01

Additive manufacturing (3-D printing) is presently limited by the mechanical properties of the materials, such as polymer resins, that are otherwise efficient and economical for part-forming. Reinforcing the resin with microscale fibers and/or particles would be an effective mechanism to achieve desired mechanical properties such as strength and ductility. Our work combines standing wave ultrasonics and microfluidics to align microparticles in devices that can act as print nozzles, based in part on our prior work with cell sorting. In this paper three different approaches are presented illustrating different engineering tradeoffs, and demonstrating laboratory results of particle alignment. First acoustic resonators are discussed, in which the ultrasonic standing waves result mostly from the mechanical properties of the microfluidic structure, excited by a piezoceramic transducer. Next non-resonant microfluidic structures are discussed, in which ultrasonic standing waves are produced directly by symmetrical transducer deployment. Finally, devices that combine nozzle-like structures, which themselves are suitable acoustic resonators, subjected to symmetrical ultrasonic excitation are presented. We will show that all three configurations will align microparticles, and discuss the tradeoffs among them for subsequent configuration of a print nozzle.

Technical features and criteria in designing fiber-reinforced composite materials: from the aerospace and aeronautical field to biomedical applications.

PubMed

Gloria, Antonio; Ronca, Dante; Russo, Teresa; D'Amora, Ugo; Chierchia, Marianna; De Santis, Roberto; Nicolais, Luigi; Ambrosio, Luigi

2011-01-01

Polymer-based composite materials are ideal for applications where high stiffness-to-weight and strength-to-weight ratios are required. From aerospace and aeronautical field to biomedical applications, fiber-reinforced polymers have replaced metals, thus emerging as an interesting alternative. As widely reported, the mechanical behavior of the composite materials involves investigation on micro- and macro-scale, taking into consideration micromechanics, macromechanics and lamination theory. Clinical situations often require repairing connective tissues and the use of composite materials may be suitable for these applications because of the possibility to design tissue substitutes or implants with the required mechanical properties. Accordingly, this review aims at stressing the importance of fiber-reinforced composite materials to make advanced and biomimetic prostheses with tailored mechanical properties, starting from the basic principle design, technologies, and a brief overview of composites applications in several fields. Fiber-reinforced composite materials for artificial tendons, ligaments, and intervertebral discs, as well as for hip stems and mandible models will be reviewed, highlighting the possibility to mimic the mechanical properties of the soft and hard tissues that they replace.

Fabrication and characterization of magnesium scaffold using different processing parameters

NASA Astrophysics Data System (ADS)

Toghyani, Saeid; Khodaei, Mohammad

2018-03-01

Structural and mechanical properties of scaffolds are important for hard tissue reconstruction. In this study, magnesium scaffolds were fabricated using space holder method for bone tissue reconstruction and the effect of cold compaction pressure and also volume percent of porosity on structural and mechanical properties of scaffolds were investigated using scanning electron microscopy (SEM) and uniaxial compression test. The carbamide spacer agent was also removed after pellet compaction, using NaOH solution and ethanol for the first time and their effect on phases present in scaffold after sintering was investigated using x-ray diffraction (XRD) analysis. Based on the results of mechanical and structural assessments, the optimum cold compaction pressure was selected 350 MPa for pellet compaction. The elastic modulus and strength of magnesium scaffolds including 67 vol.% porosity were in the range of 0.20–0.28 GPa and 4–4.25 MPa, respectively which is comparable to cancellous bone tissue. The mechanical properties of magnesium scaffolds decreased by increasing the porosity. The results also revealed that ethanol is a more suitable liquid for carbamide removal compared to NaOH solution.

Theoretical investigation of the structures and properties of CL-20/DNB cocrystal and associated PBXs by molecular dynamics simulation.

PubMed

Hang, Gui-Yun; Yu, Wen-Li; Wang, Tao; Li, Zhen

2018-03-19

In this work, a CL-20/DNB cocrystal explosive model was established and six different kinds of fluoropolymers, i.e., PVDF, PCTFE, F 2311 , F 2312 , F 2313 and F 2314 were added into the (1 0 0), (0 1 0), (0 0 1) crystal orientations to obtain the corresponding polymer bonded explosives (PBXs). The influence of fluoropolymers on PBX properties (energetic property, stability and mechanical properties) was investigated and evaluated using molecular dynamics (MD) methods. The results reveal a decrease in engineering moduli, an increase in Cauchy pressure (i.e., rigidity and stiffness is lessened), and an increase in plastic properties and ductility, thus indicating that the fluoropolymers have a beneficial influence on the mechanical properties of PBXs. Of all the PBXs models tested, the mechanical properties of CL-20/DNB/F 2311 were the best. Binding energies show that CL-20/DNB/F 2311 has the highest intermolecular interaction energy and best compatibility and stability. Therefore, F 2311 is the most suitable fluoropolymer for PBXs. The mechanical properties and binding energies of the three crystal orientations vary in the order (0 1 0) > (0 0 1) > (1 0 0), i.e., the mechanical properties of the (0 1 0) crystal orientation are best, and this is the most stable crystal orientation. Detonation performance results show that the density and detonation parameters of PBXs are lower than those of the pure CL-20 and CL-20/DNB cocrystal explosive. The power and energetic performance of PBXs are thus weakened; however, these PBXs still have excellent detonation performance and are very promising. The results and conclusions provide some helpful guidance and novel instructions for the design and manufacture of PBXs.

Stress adapted embroidered meshes with a graded pattern design for abdominal wall hernia repair

NASA Astrophysics Data System (ADS)

Hahn, J.; Bittrich, L.; Breier, A.; Spickenheuer, A.

2017-10-01

Abdominal wall hernias are one of the most relevant injuries of the digestive system with 25 million patients in 2013. Surgery is recommended primarily using allogenic non-absorbable wrap-knitted meshes. These meshes have in common that their stress-strain behaviour is not adapted to the anisotropic behaviour of native abdominal wall tissue. The ideal mesh should possess an adequate mechanical behaviour and a suitable porosity at the same time. An alternative fabrication method to wrap-knitting is the embroidery technology with a high flexibility in pattern design and adaption of mechanical properties. In this study, a pattern generator was created for pattern designs consisting of a base and a reinforcement pattern. The embroidered mesh structures demonstrated different structural and mechanical characteristics. Additionally, the investigation of the mechanical properties exhibited an anisotropic mechanical behaviour for the embroidered meshes. As a result, the investigated pattern generator and the embroidery technology allow the production of stress adapted mesh structures that are a promising approach for hernia reconstruction.

Determination of the axial and circumferential mechanical properties of the skin tissue using experimental testing and constitutive modeling.

PubMed

Karimi, Alireza; Navidbakhsh, Mahdi; Haghighatnama, Maedeh; Haghi, Afsaneh Motevalli

2015-01-01

The skin, being a multi-layered material, is responsible for protecting the human body from the mechanical, bacterial, and viral insults. The skin tissue may display different mechanical properties according to the anatomical locations of a body. However, these mechanical properties in different anatomical regions and at different loading directions (axial and circumferential) of the mice body to date have not been determined. In this study, the axial and circumferential loads were imposed on the mice skin samples. The elastic modulus and maximum stress of the skin tissues were measured before the failure occurred. The nonlinear mechanical behavior of the skin tissues was also computationally investigated through a suitable constitutive equation. Hyperelastic material model was calibrated using the experimental data. Regardless of the anatomic locations of the mice body, the results revealed significantly different mechanical properties in the axial and circumferential directions and, consequently, the mice skin tissue behaves like a pure anisotropic material. The highest elastic modulus was observed in the back skin under the circumferential direction (6.67 MPa), while the lowest one was seen in the abdomen skin under circumferential loading (0.80 MPa). The Ogden material model was narrowly captured the nonlinear mechanical response of the skin at different loading directions. The results help to understand the isotropic/anisotropic mechanical behavior of the skin tissue at different anatomical locations. They also have implications for a diversity of disciplines, i.e., dermatology, cosmetics industry, clinical decision making, and clinical intervention.

Evaluation of suitable porosity for sintered porous {beta}-tricalcium phosphate as a bone substitute

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Jin-Hong; Bae, Ji-Yong; Shim, Jaebum

2012-09-15

Structural and mechanical characterization is performed for sintered porous beta tricalcium phosphate ({beta}-TCP) to determine the appropriate porosity for use as a bone substitute. Four different types of porous {beta}-TCP specimen with different porosities are fabricated through a sintering process. For structural characterization, scanning electron microscopy and a Microfocus X-ray computed tomography system are used to investigate the pore openings on the specimen's surface, pore size, pore distribution, and pore interconnections. Compression tests of the specimens are performed, and mechanical properties such as the elastic modulus and compressive strength are obtained. Also, the geometric shape and volume of the {beta}-TCPmore » around the contact region of two pores, which need to be initially resolved after implantation in order to increase the size of the pore openings, are evaluated through simple calculations. The results show that porous {beta}-TCP with 42.1% porosity may be a suitable bone substitute candidate in terms of sustaining external loads, and inducing and cultivating bone cells. - Highlights: Black-Right-Pointing-Pointer Structural and mechanical characterization was performed for sintered porous {beta}-TCP specimens. Black-Right-Pointing-Pointer For structural characterization, SEM and Microfocus X-ray CT system were used. Black-Right-Pointing-Pointer For mechanical characterization, compression tests were performed. Black-Right-Pointing-Pointer Porous {beta}-TCP with 42.1% porosity may be a suitable bone substitute.« less

Mechanically activated fly ash as a high performance binder for civil engineering

NASA Astrophysics Data System (ADS)

Rieger, D.; Kullová, L.; Čekalová, M.; Novotný, P.; Pola, M.

2017-01-01

This study is aimed for investigation of fly ash binder with suitable properties for civil engineering needs. The fly ash from Czech brown coal power plant Prunerov II was used and mechanically activated to achieve suitable particle size for alkaline activation of hardening process. This process is driven by dissolution of aluminosilicate content of fly ash and by subsequent development of inorganic polymeric network called geopolymer. Hardening kinetics at 25 and 30 °C were measured by strain controlled small amplitude oscillatory rheometry with strain of 0.01 % and microstructure of hardened binder was evaluated by scanning electron microscopy. Strength development of hardened binder was investigated according to compressional and flexural strength for a period of 180 days. Our investigation finds out, that mechanically activated fly ash can be comparable to metakaolin geopolymers, according to setting time and mechanical parameters even at room temperature curing. Moreover, on the bases of long time strength development, achieved compressional strength of 134.5 after 180 days is comparable to performance of high grade Portland cement concretes.

Porous Nb-Ti-Ta alloy scaffolds for bone tissue engineering: Fabrication, mechanical properties and in vitro/vivo biocompatibility.

PubMed

Liu, Jue; Ruan, Jianming; Chang, Lin; Yang, Hailin; Ruan, Wei

2017-09-01

Porous Nb-Ti-Ta (at.%) alloys with the pore size of 100-600μm and the porosity of 50%-80% were fabricated by the combination of the sponge impregnation technique and sintering method. The results revealed that the pores were well connected with three-dimensional (3D) network structure, which showed morphological similarity to the anisotropic porous structure of human bones. The results also showed that the alloys could provide the compressive Young's modulus of 0.11±0.01GPa to 2.08±0.09GPa and the strength of 17.45±2.76MPa to 121.67±1.76MPa at different level of porosity, indicating that the mechanical properties of the alloys are similar to those of human bones. Pore structure on the compressive properties was also discussed on the basis of the deformation mode. The relationship between compressive properties and porosity was well consistent with the Gibson-Ashby model. The mechanical properties could be tailored to match different requirements of the human bones. Moreover, the alloys had good biocompatibility due to the porous structure with higher surface, which were suitable for apatite formation and cell adhesion. In conclusion, the porous Nb-Ti-Ta alloy is potentially useful in the hard tissue implants for the appropriate mechanical properties as well as the good biocompatible properties. Copyright © 2017. Published by Elsevier B.V.

Fabrication of Titanium-Niobium-Zirconium-Tantalium Alloy (TNZT) Bioimplant Components with Controllable Porosity by Spark Plasma Sintering

PubMed Central

Rechtin, Jack; Torresani, Elisa; Ivanov, Eugene; Olevsky, Eugene

2018-01-01

Spark Plasma Sintering (SPS) is used to fabricate Titanium-Niobium-Zirconium-Tantalum alloy (TNZT) powder—based bioimplant components with controllable porosity. The developed densification maps show the effects of final SPS temperature, pressure, holding time, and initial particle size on final sample relative density. Correlations between the final sample density and mechanical properties of the fabricated TNZT components are also investigated and microstructural analysis of the processed material is conducted. A densification model is proposed and used to calculate the TNZT alloy creep activation energy. The obtained experimental data can be utilized for the optimized fabrication of TNZT components with specific microstructural and mechanical properties suitable for biomedical applications. PMID:29364165

Bio-Functional Design, Application and Trends in Metallic Biomaterials

PubMed Central

Yang, Ke; Zhou, Changchun; Fan, Hongsong; Fan, Yujiang; Jiang, Qing; Song, Ping; Fan, Hongyuan; Chen, Yu; Zhang, Xingdong

2017-01-01

Introduction of metals as biomaterials has been known for a long time. In the early development, sufficient strength and suitable mechanical properties were the main considerations for metal implants. With the development of new generations of biomaterials, the concepts of bioactive and biodegradable materials were proposed. Biological function design is very import for metal implants in biomedical applications. Three crucial design criteria are summarized for developing metal implants: (1) mechanical properties that mimic the host tissues; (2) sufficient bioactivities to form bio-bonding between implants and surrounding tissues; and (3) a degradation rate that matches tissue regeneration and biodegradability. This article reviews the development of metal implants and their applications in biomedical engineering. Development trends and future perspectives of metallic biomaterials are also discussed. PMID:29271916

Bio-Functional Design, Application and Trends in Metallic Biomaterials.

PubMed

Yang, Ke; Zhou, Changchun; Fan, Hongsong; Fan, Yujiang; Jiang, Qing; Song, Ping; Fan, Hongyuan; Chen, Yu; Zhang, Xingdong

2017-12-22

Introduction of metals as biomaterials has been known for a long time. In the early development, sufficient strength and suitable mechanical properties were the main considerations for metal implants. With the development of new generations of biomaterials, the concepts of bioactive and biodegradable materials were proposed. Biological function design is very import for metal implants in biomedical applications. Three crucial design criteria are summarized for developing metal implants: (1) mechanical properties that mimic the host tissues; (2) sufficient bioactivities to form bio-bonding between implants and surrounding tissues; and (3) a degradation rate that matches tissue regeneration and biodegradability. This article reviews the development of metal implants and their applications in biomedical engineering. Development trends and future perspectives of metallic biomaterials are also discussed.

Microstructure evolution and tensile properties of Zr-2.5wt%Nb pressure tubes processed from billets with different microstructures

NASA Astrophysics Data System (ADS)

Kapoor, K.; Saratchandran, N.; Muralidharan, K.

1999-02-01

Starting with identical ingots, billets having different microstructures were obtained by three different processing methods for fabrication of Zr-2.5wt%Nb pressure tubes. The billets were further processed by hot extrusion and cold Pilger tube reducing to the finished product. Microstructural characterization was done at each stage of processing. The effects of the initial billet microstructure on the intermediate and final microstructure and mechanical property results were determined. It was found that the structure at each stage and the final mechanical properties depend strongly on the initial billet microstructure. The structure at the final stage consists of elongated alpha zirconium grains with a network of metastable beta zirconium phase. Some of this metastable phase transforms into stable beta niobium during thermomechanical processing. Billets with quenched structure resulted in less beta niobium at the final stage. The air cooled billets resulted in a large amount of beta niobium. The tensile properties, especially the percentage elongation, were found to vary for the different methods. Higher percentage elongation was observed for billets having quenched structure. Extrusion and forging did not produce any characteristic differences in the properties. The results were used to select a process flow sheet which yields the desired mechanical properties with suitable microstructure in the final product.

Process for derivatizing carbon nanotubes with diazonium species and compositions thereof

NASA Technical Reports Server (NTRS)

Bahr, Jeffrey L. (Inventor); Tour, James M. (Inventor); Yang, Jiping (Inventor)

2011-01-01

Methods for the chemical modification of carbon nanotubes involve the derivatization of multi- and single-wall carbon nanotubes, including small diameter (ca. 0.7 nm) single-wall carbon nanotubes, with diazonium species. The method allows the chemical attachment of a variety of organic compounds to the side and ends of carbon nanotubes. These chemically modified nanotubes have applications in polymer composite materials, molecular electronic applications, and sensor devices. The methods of derivatization include electrochemical induced reactions, thermally induced reactions, and photochemically induced reactions. Moreover, when modified with suitable chemical groups, the derivatized nanotubes are chemically compatible with a polymer matrix, allowing transfer of the properties of the nanotubes (such as, mechanical strength or electrical conductivity) to the properties of the composite material as a whole. Furthermore, when modified with suitable chemical groups, the groups can be polymerized to form a polymer that includes carbon nanotubes.

Discovery of a Small Molecule Probe That Post-Translationally Stabilizes the Survival Motor Neuron Protein for the Treatment of Spinal Muscular Atrophy.

PubMed

Rietz, Anne; Li, Hongxia; Quist, Kevin M; Cherry, Jonathan J; Lorson, Christian L; Burnett, Barrington G; Kern, Nicholas L; Calder, Alyssa N; Fritsche, Melanie; Lusic, Hrvoje; Boaler, Patrick J; Choi, Sungwoon; Xing, Xuechao; Glicksman, Marcie A; Cuny, Gregory D; Androphy, Elliot J; Hodgetts, Kevin J

2017-06-08

Spinal muscular atrophy (SMA) is the leading genetic cause of infant death. We previously developed a high-throughput assay that employs an SMN2-luciferase reporter allowing identification of compounds that act transcriptionally, enhance exon recognition, or stabilize the SMN protein. We describe optimization and characterization of an analog suitable for in vivo testing. Initially, we identified analog 4m that had good in vitro properties but low plasma and brain exposure in a mouse PK experiment due to short plasma stability; this was overcome by reversing the amide bond and changing the heterocycle. Thiazole 27 showed excellent in vitro properties and a promising mouse PK profile, making it suitable for in vivo testing. This series post-translationally stabilizes the SMN protein, unrelated to global proteasome or autophagy inhibition, revealing a novel therapeutic mechanism that should complement other modalities for treatment of SMA.

Alginate nanobeads interspersed fibrin network as in situ forming hydrogel for soft tissue engineering.

PubMed

Deepthi, S; Jayakumar, R

2018-06-01

Hydrogels are a class of materials that has the property of injectability and in situ gel formation. This property of hydrogels is manipulated in this study to develop a biomimetic bioresorbable injectable system of alginate nanobeads interspersed in fibrin network. Alginate nanobeads developed by calcium cross-linking yielded a size of 200-500 nm. The alginate nanobeads fibrin hydrogel was formed using dual syringe apparatus. Characterization of the in situ injectable hydrogel was done by SEM, FTIR and Rheometer. The developed hydrogel showed mechanical strength of 19 kPa which provides the suitable compliance for soft tissue engineering. Cytocompatibility studies using human umbilical cord blood derived mesenchymal stem cells showed good attachment, proliferation and infiltration within the hydrogel similar to fibrin gel. The developed in situ forming hydrogel could be a suitable delivery carrier of stem cells for soft tissue regeneration.

G-CSF loaded nanofiber/nanoparticle composite coated with collagen promotes wound healing in vivo.

PubMed

Tanha, Shima; Rafiee-Tehrani, Morteza; Abdollahi, Mohamad; Vakilian, Saeid; Esmaili, Zahra; Naraghi, Zahra Safaei; Seyedjafari, Ehsan; Javar, Hamid Akbari

2017-10-01

Sustained release of functional growth factors can be considered as a beneficial methodology for wound healing. In this study, recombinant human granulocyte colony-stimulating factor (G-CSF)-loaded chitosan nanoparticles were incorporated in Poly(ε-caprolactone) (PCL) nanofibers, followed by surface coating with collagen type I. Physical and mechanical properties of the PCL nanofibers containing G-CSF loaded chitosan nanoparticles PCL/NP(G-CSF) and in vivo performance for wound healing were investigated. G-CSF structural stability was evaluated through SDS_PAGE, reversed phase (RP) HPLC and size-exclusion chromatography, as well as circular dichroism. Nanofiber/nanoparticle composite scaffold was demonstrated to have appropriate mechanical properties as a wound dresser and a sustained release of functional G-CSF. The PCL/NP(G-CSF) scaffold showed a suitable proliferation and well-adherent morphology of stem cells. In vivo study and histopathological evaluation outcome revealed that skin regeneration was dramatically accelerated under PCL/NP(G-CSF) as compared with control groups. Superior fibroblast maturation, enhanced collagen deposition and minimum inflammatory cells were also the beneficial properties of PCL/NP(G-CSF) over the commercial dressing. The synergistic effect of extracellular matrix-mimicking nanofibrous membrane and G-CSF could develop a suitable supportive substrate in order to extensive utilization for the healing of skin wounds. © 2017 Wiley Periodicals Inc. J Biomed Mater Res Part A: 105A: 2830-2842, 2017. © 2017 Wiley Periodicals, Inc.

Biomedical Applications of Mulberry Silk and its Proteins: A Review

NASA Astrophysics Data System (ADS)

Nivedita, S.; Sivaprasad, V.

2014-04-01

Silk is a natural fibre used mainly for aesthetic purposes. It has also been used for making surgical sutures for centuries. The recent rediscovery of silk's biological properties have led to new areas of research and utilization in cosmetic, health and medical fields. The silk proteins, fibroin and sericin are processed into biomaterials because of bio-compatibility, bio-degradability, excellent mechanical properties, thermo tolerance and UV protective properties. Silk proteins could be obtained as pure liquids and regenerated in different forms suitable for tissue engineering applications. This paper presents some of the biomedical products and biomaterials made from native, degraded and regenerated silk and their fabrication techniques.

Choline chloride based ionic liquid analogues as tool for the fabrication of agar films with improved mechanical properties

USDA-ARS?s Scientific Manuscript database

In the present paper, we test the suitability of Choline-Cl/urea (DES-U) and Choline-Cl/glycerol (DES-G) eutectic mixtures at 1:2 molar ratios for the production of agar biodegradable films. A three-step process is proposed: pre-solubilization of polymer in DES followed by compression-molding and s...

Silicone nanocomposite coatings for fabrics

NASA Technical Reports Server (NTRS)

Lee, Stein S. (Inventor); Ou, Runqing (Inventor); Eberts, Kenneth (Inventor); Singhal, Amit (Inventor)

2011-01-01

A silicone based coating for fabrics utilizing dual nanocomposite fillers providing enhanced mechanical and thermal properties to the silicone base. The first filler includes nanoclusters of polydimethylsiloxane (PDMS) and a metal oxide and a second filler of exfoliated clay nanoparticles. The coating is particularly suitable for inflatable fabrics used in several space, military, and consumer applications, including airbags, parachutes, rafts, boat sails, and inflatable shelters.

High-performance coatings for micromechanical mirrors.

PubMed

Gatto, Alexandre; Yang, Minghong; Kaiser, Norbert; Heber, Jörg; Schmidt, Jan Uwe; Sandner, Thilo; Schenk, Harald; Lakner, Hubert

2006-03-01

High-performance coatings for micromechanical mirrors were developed. The high-reflective metal systems can be integrated into the technology of MOEMS, such as spatial light modulators and microscanning mirrors from the near-infrared down to the vacuum-ultraviolet spectral regions. The reported metal designs permit high optical performances to be merged with suitable mechanical properties and fitting complementary metal-oxide semiconductor compatibility.

MEMS Reliability Assurance Guidelines for Space Applications

NASA Technical Reports Server (NTRS)

Stark, Brian (Editor)

1999-01-01

This guide is a reference for understanding the various aspects of microelectromechanical systems, or MEMS, with an emphasis on device reliability. Material properties, failure mechanisms, processing techniques, device structures, and packaging techniques common to MEMS are addressed in detail. Design and qualification methodologies provide the reader with the means to develop suitable qualification plans for the insertion of MEMS into the space environment.

Research on materials for advanced electronic and aerospace application. [including optical and magnetic data processing, stress corrosion and H2 interaction, and polymeric systems

NASA Technical Reports Server (NTRS)

1975-01-01

Development and understanding of materials most suitable for use in compact magnetic and optical memory systems are discussed. Suppression of metal deterioration by hydrogen is studied. Improvement of mechanical properties of polymers is considered, emphasizing low temperature ductility and compatibility with high modulus fiber materials.

Special Considerations in Selection of Fabric Film Laminates for Use in Inflatable Structures

NASA Technical Reports Server (NTRS)

Said, Magdi A.

1999-01-01

Inflatable structures are gaining wide support in planetary scientific missions as well as commercial applications. For such applications a new class of fabric/film laminates is being considered for use as a structural gas envelope. The emerging composite materials are a result of recent advances in the manufacturing of lightweight, high strength fibers, fabrics and scrims. The lamination of these load-carrying members with the proper gas barriers results in a wide range of materials suitable for various loading and environmental conditions. Polyester-based woven fabrics laminated to thin homogenous film of polyester are an example of this class. This fabric/film laminate is being considered for the development of a material suitable for building large gas envelopes for use in the NASA ultra long duration balloon program (ULDB). Compared to commercial homogenous films, the material provides relatively high strength to weight ratio as well as better resistance to crack and tear propagation, The mechanical, creep and viscoelastic properties of these fabric film laminates have been studied to form a material model. Preliminary analysis indicates that the material is highly viscoelastic. The mechanical properties of this class of materials will be discussed in some details.

Fabrication and Characterization of Electrospun PCL-MgO-Keratin-Based Composite Nanofibers for Biomedical Applications

PubMed Central

Boakye, Maame A. D.; Rijal, Nava P.; Adhikari, Udhab; Bhattarai, Narayan

2015-01-01

Polymeric nanofibers are of great interest in biomedical applications, such as tissue engineering, drug delivery and wound healing, due to their ability to mimic and restore the function of natural extracellular matrix (ECM) found in tissues. Electrospinning has been heavily used to fabricate nanofibers because of its reliability and effectiveness. In our research, we fabricated poly(ε-caprolactone)-(PCL), magnesium oxide-(MgO) and keratin (K)-based composite nanofibers by electrospinning a blend solution of PCL, MgO and/or K. The electrospun nanofibers were analyzed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), mechanical tensile testing and inductively-coupled plasma optical emission spectroscopy (ICP-OES). Nanofibers with diameters in the range of 0.2–2.2 µm were produced by using different ratios of PCL/MgO and PCL-K/MgO. These fibers showed a uniform morphology with suitable mechanical properties; ultimate tensile strength up to 3 MPa and Young’s modulus 10 MPa. The structural integrity of nanofiber mats was retained in aqueous and phosphate buffer saline (PBS) medium. This study provides a new composite material with structural and material properties suitable for potential application in tissue engineering. PMID:28793426

Bio-based topical system for enhanced salicylic acid delivery: preparation and performance of gels.

PubMed

Langasco, Rita; Spada, Gianpiera; Tanriverdi, Sakine Tuncay; Rassu, Giovanna; Giunchedi, Paolo; Özer, Özgen; Gavini, Elisabetta

2016-08-01

New salicylic acid (SA)-loaded gels were developed using excipients made from renewable materials, and our goal was to improve drug permeation in the topical treatment of acne vulgaris. We studied the preparation parameters to obtain suitable gel formulations. Only naturally occurring polymers were used as gelling agents. Two hydrogels and three lipogels were selected and characterized in terms of drug loading, pH, viability cells, rheology, mechanical properties and in vitro permeation; these hydrogels and lipogels were compared with the traditional ointment. We also evaluated skin parameters before and after gel application. The formulations that we studied are non-Newtonian fluids; they have high drug loading and suitable mechanical properties. Lipogels exhibit a slower and more linear in vitro permeation profile compared with hydrogels. The different vehicles that we used affected drug permeation and improve patient compliance. Cytotoxicity studies suggest that all of the formulations are non-toxic. Lipogels demonstrate appropriate technological features and improved performance compared with the traditional ointment with regard to their composition. Lipogels may represent a new bio-based topical system for SA delivery. The use of 'green' excipients leads to 'skin-friendly' formulations that are able to satisfy environmental safety. © 2016 Royal Pharmaceutical Society.

Non-Contact Measurement of Thermal Diffusivity in Ion-Implanted Nuclear Materials

NASA Astrophysics Data System (ADS)

Hofmann, F.; Mason, D. R.; Eliason, J. K.; Maznev, A. A.; Nelson, K. A.; Dudarev, S. L.

2015-11-01

Knowledge of mechanical and physical property evolution due to irradiation damage is essential for the development of future fission and fusion reactors. Ion-irradiation provides an excellent proxy for studying irradiation damage, allowing high damage doses without sample activation. Limited ion-penetration-depth means that only few-micron-thick damaged layers are produced. Substantial effort has been devoted to probing the mechanical properties of these thin implanted layers. Yet, whilst key to reactor design, their thermal transport properties remain largely unexplored due to a lack of suitable measurement techniques. Here we demonstrate non-contact thermal diffusivity measurements in ion-implanted tungsten for nuclear fusion armour. Alloying with transmutation elements and the interaction of retained gas with implantation-induced defects both lead to dramatic reductions in thermal diffusivity. These changes are well captured by our modelling approaches. Our observations have important implications for the design of future fusion power plants.

Non-Contact Measurement of Thermal Diffusivity in Ion-Implanted Nuclear Materials

DOE PAGES

Hofmann, F.; Mason, D. R.; Eliason, J. K.; ...

2015-11-03

Knowledge of mechanical and physical property evolution due to irradiation damage is essential for the development of future fission and fusion reactors. Ion-irradiation provides an excellent proxy for studying irradiation damage, allowing high damage doses without sample activation. Limited ion-penetration-depth means that only few-micron-thick damaged layers are produced. Substantial effort has been devoted to probing the mechanical properties of these thin implanted layers. Yet, whilst key to reactor design, their thermal transport properties remain largely unexplored due to a lack of suitable measurement techniques. Here we demonstrate non-contact thermal diffusivity measurements in ion-implanted tungsten for nuclear fusion armour. Alloying withmore » transmutation elements and the interaction of retained gas with implantation-induced defects both lead to dramatic reductions in thermal diffusivity. These changes are well captured by our modelling approaches. Our observations have important implications for the design of future fusion power plants.« less

Non-Contact Measurement of Thermal Diffusivity in Ion-Implanted Nuclear Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hofmann, F.; Mason, D. R.; Eliason, J. K.

Knowledge of mechanical and physical property evolution due to irradiation damage is essential for the development of future fission and fusion reactors. Ion-irradiation provides an excellent proxy for studying irradiation damage, allowing high damage doses without sample activation. Limited ion-penetration-depth means that only few-micron-thick damaged layers are produced. Substantial effort has been devoted to probing the mechanical properties of these thin implanted layers. Yet, whilst key to reactor design, their thermal transport properties remain largely unexplored due to a lack of suitable measurement techniques. Here we demonstrate non-contact thermal diffusivity measurements in ion-implanted tungsten for nuclear fusion armour. Alloying withmore » transmutation elements and the interaction of retained gas with implantation-induced defects both lead to dramatic reductions in thermal diffusivity. These changes are well captured by our modelling approaches. Our observations have important implications for the design of future fusion power plants.« less

Non-Contact Measurement of Thermal Diffusivity in Ion-Implanted Nuclear Materials

PubMed Central

Hofmann, F.; Mason, D. R.; Eliason, J. K.; Maznev, A. A.; Nelson, K. A.; Dudarev, S. L.

2015-01-01

Knowledge of mechanical and physical property evolution due to irradiation damage is essential for the development of future fission and fusion reactors. Ion-irradiation provides an excellent proxy for studying irradiation damage, allowing high damage doses without sample activation. Limited ion-penetration-depth means that only few-micron-thick damaged layers are produced. Substantial effort has been devoted to probing the mechanical properties of these thin implanted layers. Yet, whilst key to reactor design, their thermal transport properties remain largely unexplored due to a lack of suitable measurement techniques. Here we demonstrate non-contact thermal diffusivity measurements in ion-implanted tungsten for nuclear fusion armour. Alloying with transmutation elements and the interaction of retained gas with implantation-induced defects both lead to dramatic reductions in thermal diffusivity. These changes are well captured by our modelling approaches. Our observations have important implications for the design of future fusion power plants. PMID:26527099

Novel preparation and characterization of human hair-based nanofibers using electrospinning process.

PubMed

Park, Mira; Shin, Hye Kyoung; Panthi, Gopal; Rabbani, Mohammad Mahbub; Alam, Al-Mahmnur; Choi, Jawun; Chung, Hea-Jong; Hong, Seong-Tshool; Kim, Hak-Yong

2015-05-01

Human hair-based biocomposite nanofibers (NFs) have been fabricated by an electrospinning technique. Aqueous keratin extracted from human hair was successfully blended with poly(vinyl alcohol) (PVA). The focus here is on transforming into keratin/PVA nanofibrous membranes and insoluble property of electrospun NFs. The resulting hair-based NFs were characterized using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning colorimetry (DSC), and thermogravimetric analysis (TGA). Toward the potential use of these NFs after cross-linking with various weight fractions of glyoxal, its physicochemical properties, such as morphology, mechanical strength, crystallinity, and chemical structure were investigated. Keratin/PVA ratio of 2/1 NFs with 6 wt%-glyoxal showed good uniformity in fiber morphology and suitable mechanical properties, and excellent antibacterial activity providing a potential application of hair-based NFs in biomedical field. Copyright © 2015 Elsevier B.V. All rights reserved.

Recycling of engineering plastics from waste electrical and electronic equipments: influence of virgin polycarbonate and impact modifier on the final performance of blends.

PubMed

Ramesh, V; Biswal, Manoranjan; Mohanty, Smita; Nayak, Sanjay K

2014-05-01

This study is focused on the recovery and recycling of plastics waste, primarily polycarbonate, poly(acrylonitrile-butadiene-styrene) and high impact polystyrene, from end-of-life waste electrical and electronic equipments. Recycling of used polycarbonate, acrylonitrile-butadiene-styrene, polycarbonate/acrylonitrile-butadiene-styrene and acrylonitrile-butadiene-styrene/high impact polystrene material was carried out using material recycling through a melt blending process. An optimized blend composition was formulated to achieve desired properties from different plastics present in the waste electrical and electronic equipments. The toughness of blended plastics was improved with the addition of 10 wt% of virgin polycarbonate and impact modifier (ethylene-acrylic ester-glycidyl methacrylate). The mechanical, thermal, dynamic-mechanical and morphological properties of recycled blend were investigated. Improved properties of blended plastics indicate better miscibility in the presence of a compatibilizer suitable for high-end application.

Characterization of polymer composites during autoclave manufacturing by Fourier transform Raman spectroscopy

NASA Astrophysics Data System (ADS)

Farquharson, Stuart; Smith, Wayne W.; Rigas, Elias J.; Granville, Dana

2001-02-01

12 The superior engineering properties of fiber reinforced polymer matrix composites, primarily the high strength-to- weight ratio, make them suitable to applications ranging from sporting goods to aircraft components (e.g. helicopter blades). Unfortunately, consistent fabrication of components with desired mechanical properties has proven difficult, and has led to high production costs. This is largely due to the inability to monitor and control polymer cure, loosely defined as the process of polymer chain extension and cross- linking. Even with stringent process control, slight variations in the pre-polymer formulations (e.g. prepreg) can influence reaction rates, reaction mechanisms, and ultimately, product properties. In an effort to optimize the performance of thermoset composite, we have integrated fiber optic probes between the plies of laminates and monitored cure by Raman spectroscopy, with the eventual goal of process control. Here we present real-time measurements of two high performance aerospace companies cured within an industrial autoclave.

DEVELOPMENT OF FERRITIC STEELS FOR HIGH TEMPERATURE SODIUM SERVICE. PART II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, W.J.; Sheffield, G.S.; Birkle, A.J.

1963-11-30

The suitability of modified 2.25 Cr--1 Mo alloy steels for sodium service was investigated. Eleven modifications were examined to establish heat treatment behavior, mechanical properties, resistance to decarburization in liquid sodium, and weldability. Two of the alloys, 4S8 (2.25 Cr--1 Mo--0.6 V-- 0.1 Cb) and 4S4 (2.25 Cr--1 Mo-0.8 V), were found to have the best combination of properties. When heat treated by normalizing and tempering, their mechanical properties to 1200 deg F were found to be comparable to those of Type 304 stainless steel. A low chromium, nickel-base alloy was developed for welding the steels, to give either fullymore » heat treatable joints or to apply the butter-weld technique useful in field welding. It provides high joint efficiency without sacrifice in joint ductility. (auth)« less

In-situ polymerized cellulose nanocrystals (CNC)-poly(l-lactide) (PLLA) nanomaterials and applications in nanocomposite processing.

PubMed

Miao, Chuanwei; Hamad, Wadood Y

2016-11-20

CNC-PLLA nanomaterials were synthesized via in-situ ring-opening polymerization of l-lactide in the presence of CNC, resulting in hydrophobic, homogeneous mixture of PLLA-grafted-CNC and free PLLA homopolymer. The free PLLA serves two useful functions: as barrier to further prevent PLLA-g-CNC from forming aggregates, and in creating improved interfacial properties when these nanomaterials are blended with other polymers, hence enhancing their performance. CNC-PLLA nanomaterials can be used for medical or engineering applications as-they-are or by compounding with suitable biopolymers using versatile techniques, such as solution casting, co-extrusion or injection molding, to form hybrid nanocomposites of tunable mechanical properties. When compounded with commercial-grade PLA, the resulting CNC-PLA nanocomposites appear transparent and have tailored (dynamic and static) mechanical and barrier properties, approaching those of poly(ethylene terephthalate), PET. The effect of reaction conditions on the properties of CNC-PLLA nanomaterials have been carefully studied and detailed throughout the paper. Copyright © 2016 Elsevier Ltd. All rights reserved.

Mechanical Properties of Optimized Diamond Lattice Structure for Bone Scaffolds Fabricated via Selective Laser Melting.

PubMed

Liu, Fei; Zhang, David Z; Zhang, Peng; Zhao, Miao; Jafar, Salman

2018-03-03

Developments in selective laser melting (SLM) have enabled the fabrication of periodic cellular lattice structures characterized by suitable properties matching the bone tissue well and by fluid permeability from interconnected structures. These multifunctional performances are significantly affected by cell topology and constitutive properties of applied materials. In this respect, a diamond unit cell was designed in particular volume fractions corresponding to the host bone tissue and optimized with a smooth surface at nodes leading to fewer stress concentrations. There were 33 porous titanium samples with different volume fractions, from 1.28 to 18.6%, manufactured using SLM. All of them were performed under compressive load to determine the deformation and failure mechanisms, accompanied by an in-situ approach using digital image correlation (DIC) to reveal stress-strain evolution. The results showed that lattice structures manufactured by SLM exhibited comparable properties to those of trabecular bone, avoiding the effects of stress-shielding and increasing longevity of implants. The curvature of optimized surface can play a role in regulating the relationship between density and mechanical properties. Owing to the release of stress concentration from optimized surface, the failure mechanism of porous titanium has been changed from the pattern of bottom-up collapse by layer (or cell row) to that of the diagonal (45°) shear band, resulting in the significant enhancement of the structural strength.

Production and mechanical properties of Ti-5Al-2.5Fe-xCu alloys for biomedical applications.

PubMed

Yamanoglu, Ridvan; Efendi, Erdinc; Kolayli, Fetiye; Uzuner, Huseyin; Daoud, Ismail

2018-01-30

In this study, the mechanical, antibacterial properties and cell toxicity response of Ti-5Al2.5Fe alloy with different copper contents were investigated. The alloys were prepared by high-energy ball milling using elemental Ti, Al, Fe, and Cu powders and consolidated by a uniaxial vacuum hot press. Staphylococcus aureus strain ATCC 29213 and Escherichia coli strain ATCC 25922 were used to determine the antibacterial properties of the sintered alloys. The in vitro cytotoxicity of the samples was evaluated with HeLa (ATTC, CCL-2) cells using thiazolyl blue tetrazolium bromide. The mechanical behavior of the samples was determined as a function of hardness and bending tests and analyzed by scanning electron microscopy, energy dispersive x-ray spectroscopy, optical microscopy and x-ray diffraction (XRD). The results showed that the Cu content significantly improved the antibacterial properties. Cu addition prevented the formation of E. coli and S. aureus colonies on the surface of the samples. All samples exhibited very good cell biocompatibility. The alloys with different copper contents showed different mechanical properties, and the results were correlated by microstructural and XRD analyses in detail. Our results showed that Cu has a great effect on the Ti5Al2.5Fe alloy and the alloy is suitable for biomedical applications with enhanced antibacterial activity.

Mechanical Properties of Optimized Diamond Lattice Structure for Bone Scaffolds Fabricated via Selective Laser Melting

PubMed Central

Zhang, David Z.; Zhang, Peng; Zhao, Miao; Jafar, Salman

2018-01-01

Developments in selective laser melting (SLM) have enabled the fabrication of periodic cellular lattice structures characterized by suitable properties matching the bone tissue well and by fluid permeability from interconnected structures. These multifunctional performances are significantly affected by cell topology and constitutive properties of applied materials. In this respect, a diamond unit cell was designed in particular volume fractions corresponding to the host bone tissue and optimized with a smooth surface at nodes leading to fewer stress concentrations. There were 33 porous titanium samples with different volume fractions, from 1.28 to 18.6%, manufactured using SLM. All of them were performed under compressive load to determine the deformation and failure mechanisms, accompanied by an in-situ approach using digital image correlation (DIC) to reveal stress–strain evolution. The results showed that lattice structures manufactured by SLM exhibited comparable properties to those of trabecular bone, avoiding the effects of stress-shielding and increasing longevity of implants. The curvature of optimized surface can play a role in regulating the relationship between density and mechanical properties. Owing to the release of stress concentration from optimized surface, the failure mechanism of porous titanium has been changed from the pattern of bottom-up collapse by layer (or cell row) to that of the diagonal (45°) shear band, resulting in the significant enhancement of the structural strength. PMID:29510492

Fabrication and mechanical evaluation of hydroxyapatite/oxide nano-composite materials.

PubMed

Mohamed, Khaled R; Beherei, Hanan H; El Bassyouni, Gehan T; El Mahallawy, Nahed

2013-10-01

In the current study, the semiconducting metal oxides such as nano-ZnO and SiO2 powders were prepared via sol-gel technique and conducted on nano-hydroxyapatite (nHA) which was synthesized by chemical precipitation. The properties of fabricated nano-structured composites containing different ratios of HA, ZnO and SiO2 were examined using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The effect of the variation of ratios between the three components on mechanical, microstructure and in-vitro properties was assessed to explore the possibility of enhancing these properties. The results proved that the mechanical properties exhibited an increment with increasing the ZnO content at the extent of HA. In-vitro study proved the formation and nucleation of apatite onto the surface of the fabricated composites after one week of immersion. It is concluded that HA composites containing SiO2 or SiO2/ZnO content had a suitable mechanical properties and ability to form apatite particles onto the composite surface. Based on bioactivity behavior, Si-HA is more bioactive than pure hydroxyapatite and nano-arrangements will provide an interface for better bone formation. Therefore, these nano-composites will be promising as bone substitutes especially in load bearing sites. Copyright © 2013 Elsevier B.V. All rights reserved.

Microstructure, mechanical behavior and biocompatibility of powder metallurgy Nb-Ti-Ta alloys as biomedical material.

PubMed

Liu, Jue; Chang, Lin; Liu, Hairong; Li, Yongsheng; Yang, Hailin; Ruan, Jianming

2017-02-01

Microstructures, mechanical properties, apatite-forming ability and in vitro experiments were studied for Nb-25Ti-xTa (x=10, 15, 20, 25, 35at.%) alloys fabricated by powder metallurgy. It is confirmed that the alloys could achieve a relative density over 80%. Meanwhile, the increase in Ta content enhances the tensile strength, elastic modulus and hardness of the as-sintered alloys. When increasing the sintering temperatures, the microstructure became more homogeneous for β phase, resulting in a decrease in the modulus and strength. Moreover, the alloys showed a good biocompatibility due to the absence of cytotoxic elements, and were suitable for apatite formation and cell adhesion. In conclusion, Nb-25Ti-xTa alloys are potentially useful in biomedical applications with their mechanical and biological properties being evaluated in this work. Copyright © 2016 Elsevier B.V. All rights reserved.

Preparation and characterization of a novel willemite bioceramic.

PubMed

Zhang, Meili; Zhai, Wanyin; Chang, Jiang

2010-04-01

Willemite (Zn(2)SiO(4)) ceramics were prepared by sintering the willemite green compacts. The effects of sintering temperature on the linear shrinkage, porosity and mechanical strength of the ceramics were examined. With the sintering temperature increased, the linear shrinkage of the ceramics increased and the porosity decreased. When sintered at 1,300 degrees C, willemite ceramics showed mechanical properties of the same order of magnitude as values for human cortical bone, as measured by bending strength (91.2 +/- 4.2 MPa) and Young's modulus (37.5 +/- 1.5 GPa). In addition, the adhesion and proliferation of rabbit bone marrow stromal cells (BMSCs) on willemite ceramics was investigated. The results showed that the ceramics supported cell adhesion and stimulated the proliferation. All these findings suggest that willemite ceramics possess suitable mechanical properties and favorable biocompatibility and might be a promising biomaterial for bone implant applications.

Comparison of mechanical properties for several electrical spring contact alloys. [Beryllium-nickel alloy 440 (Ni--1. 95 Be--0. 5 Ti); comparison with Neyoro G and Paliney 7

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nordstrom, T.V.

Purpose was to determine whether beryllium--nickel alloy 440 (Ni-1.95 Be-0.5 Ti) had mechanical properties which made it suitable as a substitute for the presently used precious metal contact alloys Paliney 7 and Neyoro G, in certain electrical contact applications. Possible areas of applicability for the alloy were where extremely low contact resistance was not necessary or in components encountering elevated temperatures above those presently seen in weapons applications. Evaluation of the alloy involved three major experimental areas: (1) measurement of the room temperature microplastic (epsilon approximately 10/sup -6/) and macroplastic (epsilon approximately 10/sup -3/) behavior of alloy 440 in variousmore » age hardening conditions, (2) determination of applied stress effects on stress relaxation or contact force loss, and (3) measurement of elevated temperature mechanical properties and stress relaxation behavior. Similar measurements were also made on Neyoro G and Paliney 7 for comparison. Results show that beryllium-nickel alloy 440 is equal or superior to the presently used Paliney 7 and Neyoro G for normal Sandia requirements. For elevated temperature applications, alloy 440 has clearly superior mechanical properties. 12 fig.« less

Study of thermal, flammability and mechanical properties of intumescent flame retardant PP/kenaf nanocomposites

NASA Astrophysics Data System (ADS)

Subasinghe; Das; Bhattacharyya

2016-07-01

Detrimental physical and mechanical properties are common problems for composites when their flame retardancy is improved through filler additions. An increased interest of the synergistic nanoparticle addition to improve the flame retardancy of natural fiber composites is the aim of this work. The paper investigates the synergistic effect of two different nanoparticles (halloysite nanotubes (HNTs) and montmorillonite (MMT) nanoclay) on the flame and mechanical properties in an intumescent ammonium polyphosphate (APP)-based polypropylene (PP)/kenaf composite system. First, the nature of nanoparticle dispersion in PP through X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveals that under twin screw compounding process, the partial exfoliation and intercalation have taken place within the nanocomposites. An increase in the decomposition temperature was observed under thermogravimetric analysis (TGA), with the presence of HNT. However, MMT tends to lower the maximum decomposition temperature under inert atmosphere. The flammability analysis in an intumescent flame retardant (IFR) system shows that the suitable amount of high aspect ratio nanoparticles with their exfoliation characteristics effectively helps to reduce the sustained combustion. Even though, improved stiffness properties can be observed with the presence of increased filler content, particle agglomeration tends to reduce the mechanical strengths of these composites due to low compatibilization and crack propagation.

Ultrasonic evaluation of the physical and mechanical properties of granites.

PubMed

Vasconcelos, G; Lourenço, P B; Alves, C A S; Pamplona, J

2008-09-01

Masonry is the oldest building material that survived until today, being used all over the world and being present in the most impressive historical structures as an evidence of spirit of enterprise of ancient cultures. Conservation, rehabilitation and strengthening of the built heritage and protection of human lives are clear demands of modern societies. In this process, the use of nondestructive methods has become much common in the diagnosis of structural integrity of masonry elements. With respect to the evaluation of the stone condition, the ultrasonic pulse velocity is a simple and economical tool. Thus, the central issue of the present paper concerns the evaluation of the suitability of the ultrasonic pulse velocity method for describing the mechanical and physical properties of granites (range size between 0.1-4.0 mm and 0.3-16.5 mm) and for the assessment of its weathering state. The mechanical properties encompass the compressive and tensile strength and modulus of elasticity, and the physical properties include the density and porosity. For this purpose, measurements of the longitudinal ultrasonic pulse velocity with distinct natural frequency of the transducers were carried out on specimens with different size and shape. A discussion of the factors that induce variations on the ultrasonic velocity is also provided. Additionally, statistical correlations between ultrasonic pulse velocity and mechanical and physical properties of granites are presented and discussed. The major output of the work is the confirmation that ultrasonic pulse velocity can be effectively used as a simple and economical nondestructive method for a preliminary prediction of mechanical and physical properties, as well as a tool for the assessment of the weathering changes of granites that occur during the serviceable life. This is of much interest due to the usual difficulties in removing specimens for mechanical characterization.

Investigation of Wear and Friction Properties Under Sliding Conditions of Some Materials Suitable for Cages of Rolling-Contact Bearings

NASA Technical Reports Server (NTRS)

Johnson, Robert L; Swikert, Max A; Bisson, Edmond E

1952-01-01

An investigation of wear and friction properties of a number of materials sliding against SAE 52100 steel was conducted. These materials included brass, bronze, beryllium copper, monel, nichrome v, 24s-t aluminum, nodular iron, and gray cast iron. The metals investigated may be useful as possible cage (separator or retainer) materials for rolling-contact bearings of high-speed turbine engines. The ability of materials to form surface films that prevent welding is a most important factor in both dry friction and boundary lubrication. On the basis of wear and resistance to welding only, the cast irons were the most promising materials investigated; they showed the least wear and the least tendency to surface failure when run dry, and when boundary lubricated they showed the highest load capacity. On the basis of mechanical properties, nodular iron is superior to gray cast iron. Bronze had the lowest friction coefficient under dry sliding conditions. The results with brass, beryllium copper, and aluminum were poor and these materials do not appear, with regard to friction and wear, to be suitable for cages.

Characterization and selection of suitable grades of lactose as functional fillers for capsule filling: part 1.

PubMed

Moolchandani, Vikas; Augsburger, Larry L; Gupta, Abhay; Khan, Mansoor; Langridge, John; Hoag, Stephen W

2015-01-01

The purpose of this work is to characterize thermal, physical and mechanical properties of different grades of lactose and better understand the relationships between these properties and capsule filling performance. Eight grades of commercially available lactose were evaluated: Pharmatose 110 M, 125 M, 150 M, 200 M, 350 M (α-lactose monohydrate), AL (anhydrous lactose containing ∼80% β-AL), DCL11 (spray dried α-lactose monohydrate containing ∼15% amorphous lactose) and DCL15 (granulated α-lactose monohydrate containing ∼12% β-AL). In this study, different lactose grades were characterized by thermal, solid state, physical and mechanical properties and later evaluated using principal component analysis (PCA) to assess the inter-relationships among some of these properties. The lactose grades were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), moisture sorption/desorption isotherms, particle size distribution; the flow was characterized by Carr Index (CI), critical orifice diameter (COD) and angle of friction. Plug mechanical strength was estimated from its diametric crushing strength. The first and second principal components (PC) captured 47.6% and 27.4% of variation in the physical and mechanical property data, respectively. The PCA plot grouped together 110 M, AL, DCL11 and DCL15 on the one side of plot which possessed superior properties for capsule formulation and these grades were selected for future formulation development studies (part II of this work).

Microstructure evolution and tensile properties of Zr-2.5 wt.% Nb pressure tubes processed from billets with different microstructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kapoor, K.; Saratchandran, N.; Muralidharan, K.

1999-02-01

Pressurized heavy water reactors (PHWR) use zirconium-base alloys for their low neutron-absorption cross section, good mechanical strength, low irradiation creep, and high corrosion resistance in reactor atmospheres. Starting with identical ingots, billets having different microstructures were obtained by three different processing methods for fabrication of Zr-2.5 wt%Nb pressure tubes., The billets were further processed by hot extrusion and cold Pilger tube reducing to the finished product. Microstructural characterization was done at each stage of processing. The effects of the initial billet microstructure on the intermediate and final microstructure and mechanical property results were determined. It was found that the structuremore » at each stage and the final mechanical properties depend strongly on the initial billet microstructure. The structure at the final stage consists of elongated alpha zirconium grains with a network of metastable beta zirconium phase. Some of this metastable phase transforms into stable beta niobium during thermomechanical processing. Billets with quenched structure resulted in less beta niobium at the final stage. The air cooled billets resulted in a large amount of beta niobium. The tensile properties, especially the percentage elongation, were found to vary for the different methods. Higher percentage elongation was observed for billets having quenched structure. Extrusion and forging did not produce any characteristic differences in the properties. The results were used to select a process flow sheet which yields the desired mechanical properties with suitable microstructure in the final product.« less

Ab initio calculations of the magnetic properties of TM (Ti, V)-doped zinc-blende ZnO

NASA Astrophysics Data System (ADS)

Goumrhar, F.; Bahmad, L.; Mounkachi, O.; Benyoussef, A.

2018-01-01

In order to promote suitable material to be used in spintronics devices, this study purposes to evaluate the magnetic properties of the titanium and vanadium-doped zinc-blende ZnO from first-principles. The calculations of these properties are based on the Korringa-Kohn-Rostoker (KKR) method combined with the coherent potential approximation (CPA), using the local density approximation (LDA). We have calculated and discussed the density of states (DOSs) in the energy phase diagrams for different concentration values, of the dopants. We have also investigated the magnetic and half-metallic properties of this doped compound. Additionally, we showed the mechanism of the exchange coupling interaction. Finally, we estimated and studied the Curie temperature for different concentrations.

Effect of geometric size on mechanical properties of dielectric elastomers based on an improved visco-hyperelastic film model

NASA Astrophysics Data System (ADS)

Chang, Mengzhou; Wang, Zhenqing; Tong, Liyong; Liang, Wenyan

2017-03-01

Dielectric polymers show complex mechanical behaviors with different boundary conditions, geometry size and pre-stress. A viscoelastic model suitable for inhomogeneous deformation is presented integrating the Kelvin-Voigt model in a new form in this work. For different types of uniaxial tensile test loading along the length direction of sample, single-step-relaxation tests, loading-unloading tests and tensile-creep-relaxation tests the improved model provides a quite favorable comparison with the experiment results. Moreover, The mechanical properties of test sample with several length-width ratios under different boundary conditions are also invested. The influences of the different boundary conditions are calculated with a stress applied on the boundary point and the result show that the fixed boundary will increase the stress compare with homogeneous deformation. In modeling the effect of pre-stress in the shear test, three pre-stressed mode are discussed. The model validation on the general mechanical behavior shows excellent predictive capability.

Physical and mechanical properties of PLA, and their functions in widespread applications - A comprehensive review.

PubMed

Farah, Shady; Anderson, Daniel G; Langer, Robert

2016-12-15

Poly(lactic acid) (PLA), so far, is the most extensively researched and utilized biodegradable aliphatic polyester in human history. Due to its merits, PLA is a leading biomaterial for numerous applications in medicine as well as in industry replacing conventional petrochemical-based polymers. The main purpose of this review is to elaborate the mechanical and physical properties that affect its stability, processability, degradation, PLA-other polymers immiscibility, aging and recyclability, and therefore its potential suitability to fulfill specific application requirements. This review also summarizes variations in these properties during PLA processing (i.e. thermal degradation and recyclability), biodegradation, packaging and sterilization, and aging (i.e. weathering and hygrothermal). In addition, we discuss up-to-date strategies for PLA properties improvements including components and plasticizer blending, nucleation agent addition, and PLA modifications and nanoformulations. Incorporating better understanding of the role of these properties with available improvement strategies is the key for successful utilization of PLA and its copolymers/composites/blends to maximize their fit with worldwide application needs. Copyright © 2016 Elsevier B.V. All rights reserved.

Wear-resistant ball bearings for space applications

NASA Technical Reports Server (NTRS)

Boving, H.; Hintermann, H. E.; Hanni, W.; Bondivenne, E.; Boeto, M.; Conde, E.

1977-01-01

Ball bearings consisting of steel parts of which the rings are coated with hard, wear resistant, chemical vapor deposited TiC are described. Experiments conducted in ultrahigh vacuum, using cages of various materials with self-lubricating properties, show that such bearings are suitable for space applications. The results of laboratory tests on the ESA Meteosat Radiometer Focalizing mechanism, which contains six coated bearings, are summarized.

Mechanical properties of carbon nanotubes

NASA Astrophysics Data System (ADS)

Salvetat, J.-P.; Bonard, J.-M.; Thomson, N. H.; Kulik, A. J.; Forró, L.; Benoit, W.; Zuppiroli, L.

A variety of outstanding experimental results on the elucidation of the elastic properties of carbon nanotubes are fast appearing. These are based mainly on the techniques of high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) to determine the Young's moduli of single-wall nanotube bundles and multi-walled nanotubes, prepared by a number of methods. These results are confirming the theoretical predictions that carbon nanotubes have high strength plus extraordinary flexibility and resilience. As well as summarising the most notable achievements of theory and experiment in the last few years, this paper explains the properties of nanotubes in the wider context of materials science and highlights the contribution of our research group in this rapidly expanding field. A deeper understanding of the relationship between the structural order of the nanotubes and their mechanical properties will be necessary for the development of carbon-nanotube-based composites. Our research to date illustrates a qualitative relationship between the Young's modulus of a nanotube and the amount of disorder in the atomic structure of the walls. Other exciting results indicate that composites will benefit from the exceptional mechanical properties of carbon nanotubes, but that the major outstanding problem of load transfer efficiency must be overcome before suitable engineering materials can be produced.

Exposure to buffer solution alters tendon hydration and mechanics.

PubMed

Safa, Babak N; Meadows, Kyle D; Szczesny, Spencer E; Elliott, Dawn M

2017-08-16

A buffer solution is often used to maintain tissue hydration during mechanical testing. The most commonly used buffer solution is a physiological concentration of phosphate buffered saline (PBS); however, PBS increases the tissue's water content and decreases its tensile stiffness. In addition, solutes from the buffer can diffuse into the tissue and interact with its structure and mechanics. These bathing solution effects can confound the outcome and interpretation of mechanical tests. Potential bathing solution artifacts, including solute diffusion, and their effect on mechanical properties, are not well understood. The objective of this study was to measure the effects of long-term exposure of rat tail tendon fascicles to several concentrations (0.9-25%) of NaCl, sucrose, polyethylene glycol (PEG), and SPEG (NaCl+PEG) solutions on water content, solute diffusion, and mechanical properties. We found that with an increase in solute concentration the apparent water content decreased for all solution types. Solutes diffused into the tissue for NaCl and sucrose, however, no solute diffusion was observed for PEG or SPEG. The mechanical properties changed for both NaCl solutions, in particular after long-term (8h) incubation the modulus and equilibrium stress decreased compared to short-term (15min) for 25% NaCl, and the cross sectional area increased for 0.9% NaCl. However, the mechanical properties were unchanged for both PEG and SPEG except for minor alterations in stress relaxation parameters. This study shows that NaCl and sucrose buffer solutions are not suitable for long-term mechanical tests. We therefore propose using PEG or SPEG as alternative buffer solutions that after long-term incubation can maintain tissue hydration without solute diffusion and produce a consistent mechanical response. Copyright © 2017 Elsevier Ltd. All rights reserved.

The effect of platelet lysate supplementation of a dextran-based hydrogel on cartilage formation.

PubMed

Moreira Teixeira, Liliana S; Leijten, Jeroen C H; Wennink, Jos W H; Chatterjea, Anindita G; Feijen, Jan; van Blitterswijk, Clemens A; Dijkstra, Pieter J; Karperien, Marcel

2012-05-01

In situ gelating dextran-tyramine (Dex-TA) injectable hydrogels have previously shown promising features for cartilage repair. Yet, despite suitable mechanical properties, this system lacks intrinsic biological signals. In contrast, platelet lysate-derived hydrogels are rich in growth factors and anti-inflammatory cytokines, but mechanically unstable. We hypothesized that the advantages of these systems may be combined in one hydrogel, which can be easily translated into clinical settings. Platelet lysate was successfully incorporated into Dex-TA polymer solution prior to gelation. After enzymatic crosslinking, rheological and morphological evaluations were performed. Subsequently, the effect of platelet lysate on cell migration, adhesion, proliferation and multi-lineage differentiation was determined. Finally, we evaluated the integration potential of this gel onto osteoarthritis-affected cartilage. The mechanical properties and covalent attachment of Dex-TA to cartilage tissue during in situ gel formation were successfully combined with the advantages of platelet lysate, revealing the potential of this enhanced hydrogel as a cell-free approach. The addition of platelet lysate did not affect the mechanical properties and porosity of Dex-TA hydrogels. Furthermore, platelet lysate derived anabolic growth factors promoted proliferation and triggered chondrogenic differentiation of mesenchymal stromal cells. Copyright © 2012 Elsevier Ltd. All rights reserved.

The Role of Ambient Gas and Pressure on the Structuring of Hard Diamond-Like Carbon Films Synthesized by Pulsed Laser Deposition

PubMed Central

Popescu, Andrei C.; Stan, George E.; Duta, Liviu; Nita, Cristina; Popescu, Camelia; Surdu, Vasile-Adrian; Husanu, Marius-Adrian; Bita, Bogdan; Ghisleni, Rudy; Himcinschi, Cameliu; Craciun, Valentin

2015-01-01

Hard carbon thin films were synthesized on Si (100) and quartz substrates by the Pulsed Laser Deposition (PLD) technique in vacuum or methane ambient to study their suitability for applications requiring high mechanical resistance. The deposited films’ surface morphology was investigated by scanning electron microscopy, crystalline status by X-ray diffraction, packing and density by X-ray reflectivity, chemical bonding by Raman and X-ray photoelectron spectroscopy, adherence by “pull-out” measurements and mechanical properties by nanoindentation tests. Films synthesized in vacuum were a-C DLC type, while films synthesized in methane were categorized as a-C:H. The majority of PLD films consisted of two layers: one low density layer towards the surface and a higher density layer in contact with the substrate. The deposition gas pressure played a crucial role on films thickness, component layers thickness ratio, structure and mechanical properties. The films were smooth, amorphous and composed of a mixture of sp3-sp2 carbon, with sp3 content ranging between 50% and 90%. The thickness and density of the two constituent layers of a film directly determined its mechanical properties.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shanaghi, Ali, E-mail: alishanaghi@gmail.com; Rouhaghdam, Ali Reza Sabour, E-mail: sabour01@modares.ac.ir; Ahangarani, Shahrokh, E-mail: sh.ahangarani@gmail.com

Highlights: ► The TiC{sub x} nanostructure coatings have been deposited by PACVD method. ► Dominant mechanism of growth structure at 490 °C is island-layer type. ► TiC{sub x} nanostructure coating applied at 490 °C, exhibits lowest friction coefficient. ► Young's moduli are 289.9, 400 and 187.6 GPa for 470, 490 and 510 °C, respectively. ► This higher elastic modulus and higher hardness of nanocoating obtain at 490 °C. -- Abstract: The structure, composition, and mechanical properties of nanostructured titanium carbide (TiC) coatings deposited on H{sub 11} hot-working tool steel by pulsed-DC plasma assisted chemical vapor deposition at three different temperaturesmore » are investigated. Nanoindentation and nanoscratch tests are carried out by atomic force microscopy to determine the mechanical properties such as hardness, elastic modulus, surface roughness, and friction coefficient. The nanostructured TiC coatings prepared at 490 °C exhibit lower friction coefficient (0.23) than the ones deposited at 470 and 510 °C. Increasing the deposition temperature reduces the Young's modulus and hardness. The overall superior mechanical properties such as higher hardness and lower friction coefficient render the coatings deposited at 490 °C suitable for wear resistant applications.« less

Investigation on Suitability of Natural Fibre as Replacement Material for Table Tennis Blade

NASA Astrophysics Data System (ADS)

Arifin, A. M. T.; Fahrul Hassan, M.; Ismail, A. E.; Zulafif Rahim, M.; Rasidi Ibrahim, M.; Haq, R. H. Abdul; Rahman, M. N. A.; Yunos, M. Z.; Amin, M. H. M.

2017-08-01

This paper presents an investigation of suitability natural fibre as replacement material for table tennis blade, due to low cost, lightweight and apparently environmentally. Nowadays, natural fibre are one of the materials often used in replaced the main material on manufacturing sector, such as automotive, and construction. The objective of this study is to investigate and evaluate the suitability natural fiber materials to replace wood as a structure on table tennis blade. The mechanical properties of the different natural fibre material were examined, and correlated with characteristic of table tennis blade. The natural fibre selected for the study are kenaf (Hibiscus Cannabinus), jute, hemp, sisal (Agave Sisalana) and ramie. A further comparison was made with the corresponding properties of each type of natural fiber using Quality Function Deployment (QFD) and Theory of Inventive Problem Solving (TRIZ). TRIZ has been used to determine the most appropriate solution in producing table tennis blade. The results showed the most appropriate solution in producing table tennis blade using natural fibre is kenaf natural fibre. The selected on suitability natural fibre used as main structure on table tennis blade are based on the characteristics need for good performance of table tennis blade, such as energy absorption, lightweight, strength and hardness. Therefore, it shows an opportunity for replacing existing materials with a higher strength, lower cost alternative that is environmentally friendly.

Experimental Study on Dissimilar Friction Stir welding of Aluminium Alloys (5083-H111 and 6082-T6) to investigate the mechanical properties

NASA Astrophysics Data System (ADS)

Kumar, H. M. Anil; Venkata Ramana, V.; Pawar, Mayur

2018-03-01

Friction stir welding is an innovative technology in the joining realm of metals and alloys. This technique is highly economical and suitable especially for non ferrous alloys compared to ferrous alloys. It finds many applications in various fields of aeronautics, automobile, ship building industries etc. The paper presents the comparative results of mechanical properties such as tensile strength, microstructure, macro structure and hardness on the similar and dissimilar aluminum alloys AA5083-H111 and AA6082-T6 under certain selected variables - constant tool rotational speed, its tilt angle, welding speed using friction stir welding process. It is observed from the experimental results that joint efficiency of dissimilar aluminium alloys is higher than the similar aluminum alloys.

Soil quality as a factor of the distribution of damages at the meizoseismal area of the Kozani-Grevena 1995 earthquake, in Greece ( Ms = 6.6)

NASA Astrophysics Data System (ADS)

Christaras, B.; Dimitriou, An; Lemoni, Hel

The physical and mechanical properties of the soil formations were related to the damages observed in Kozani and Grevena area, in Northern Greece, after the earth-quake of 13th May 1995 ( Ms = 6.6). Properties such as grain size distribution, plasticity, shear strength, compression index, permeability and ultrasonic velocity were measured in order to classify the suitability of the soil formations, for urban planning, and correlate their mechanical behaviour with the damages observed in the construction. According to our observations, a great number of recent buildings were damaged also in areas far away from the seismotectonic zones, where silty and clayey soils dominate, presenting very low permeability, low ultrasonic velocity together with high plasticity and compressibility.

Improving Mechanical Properties of Molded Silicone Rubber for Soft Robotics Through Fabric Compositing.

PubMed

Wang, Yue; Gregory, Cherry; Minor, Mark A

2018-06-01

Molded silicone rubbers are common in manufacturing of soft robotic parts, but they are often prone to tears, punctures, and tensile failures when strained. In this article, we present a fabric compositing method for improving the mechanical properties of soft robotic parts by creating a fabric/rubber composite that increases the strength and durability of the molded rubber. Comprehensive ASTM material tests evaluating the strength, tear resistance, and puncture resistance are conducted on multiple composites embedded with different fabrics, including polyester, nylon, silk, cotton, rayon, and several blended fabrics. Results show that strong fabrics increase the strength and durability of the composite, valuable in pneumatic soft robotic applications, while elastic fabrics maintain elasticity and enhance tear strength, suitable for robotic skins or soft strain sensors. Two case studies then validate the proposed benefits of the fabric compositing for soft robotic pressure vessel applications and soft strain sensor applications. Evaluations of the fabric/rubber composite samples and devices indicate that such methods are effective for improving mechanical properties of soft robotic parts, resulting in parts that can have customized stiffness, strength, and vastly improved durability.

A review of experimental techniques to produce a nacre-like structure.

PubMed

Corni, I; Harvey, T J; Wharton, J A; Stokes, K R; Walsh, F C; Wood, R J K

2012-09-01

The performance of man-made materials can be improved by exploring new structures inspired by the architecture of biological materials. Natural materials, such as nacre (mother-of-pearl), can have outstanding mechanical properties due to their complicated architecture and hierarchical structure at the nano-, micro- and meso-levels which have evolved over millions of years. This review describes the numerous experimental methods explored to date to produce composites with structures and mechanical properties similar to those of natural nacre. The materials produced have sizes ranging from nanometres to centimetres, processing times varying from a few minutes to several months and a different range of mechanical properties that render them suitable for various applications. For the first time, these techniques have been divided into those producing bulk materials, coatings and free-standing films. This is due to the fact that the material's application strongly depends on its dimensions and different results have been reported by applying the same technique to produce materials with different sizes. The limitations and capabilities of these methodologies have been also described.

Multiscale design and synthesis of biomimetic gradient protein/biosilica composites for interfacial tissue engineering.

PubMed

Guo, Jin; Li, Chunmei; Ling, Shengjie; Huang, Wenwen; Chen, Ying; Kaplan, David L

2017-11-01

Continuous gradients present at tissue interfaces such as osteochondral systems, reflect complex tissue functions and involve changes in extracellular matrix compositions, cell types and mechanical properties. New and versatile biomaterial strategies are needed to create suitable biomimetic engineered grafts for interfacial tissue engineering. Silk protein-based composites, coupled with selective peptides with mineralization domains, were utilized to mimic the soft-to-hard transition in osteochondral interfaces. The gradient composites supported tunable mineralization and mechanical properties corresponding to the spatial concentration gradient of the mineralization domains (R5 peptide). The composite system exhibited continuous transitions in terms of composition, structure and mechanical properties, as well as cytocompatibility and biodegradability. The gradient silicified silk/R5 composites promoted and regulated osteogenic differentiation of human mesenchymal stem cells in an osteoinductive environment in vitro. The cells differentiated along the composites in a manner consistent with the R5-gradient profile. This novel biomimetic gradient biomaterial design offers a useful approach to meet a broad range of needs in regenerative medicine. Copyright © 2017 Elsevier Ltd. All rights reserved.

Emerging bone tissue engineering via Polyhydroxyalkanoate (PHA)-based scaffolds.

PubMed

Lim, Janice; You, Mingliang; Li, Jian; Li, Zibiao

2017-10-01

Polyhydroxyalkanoates (PHAs) are a class of biodegradable polymers derived from microorganisms. On top of their biodegradability and biocompatibility, different PHA types can contribute to varying mechanical and chemical properties. This has led to increasing attention to the use of PHAs in numerous biomedical applications over the past few decades. Bone tissue engineering refers to the regeneration of new bone through providing mechanical support while inducing cell growth on the PHA scaffolds having a porous structure for tissue regeneration. This review first introduces the various properties PHA scaffold that make them suitable for bone tissue engineering such as biocompatibility, biodegradability, mechanical properties as well as vascularization. The typical fabrication techniques of PHA scaffolds including electrospinning, salt-leaching and solution casting are further discussed, followed by the relatively new technology of using 3D printing in PHA scaffold fabrication. Finally, the recent progress of using different types of PHAs scaffold in bone tissue engineering applications are summarized in intrinsic PHA/blends forms or as composites with other polymeric or inorganic hybrid materials. Copyright © 2017 Elsevier B.V. All rights reserved.

The role of retinal bipolar cell in early vision: an implication with analogue networks and regularization theory.

PubMed

Yagi, T; Ohshima, S; Funahashi, Y

1997-09-01

A linear analogue network model is proposed to describe the neuronal circuit of the outer retina consisting of cones, horizontal cells, and bipolar cells. The model reflects previous physiological findings on the spatial response properties of these neurons to dim illumination and is expressed by physiological mechanisms, i.e., membrane conductances, gap-junctional conductances, and strengths of chemical synaptic interactions. Using the model, we characterized the spatial filtering properties of the bipolar cell receptive field with the standard regularization theory, in which the early vision problems are attributed to minimization of a cost function. The cost function accompanying the present characterization is derived from the linear analogue network model, and one can gain intuitive insights on how physiological mechanisms contribute to the spatial filtering properties of the bipolar cell receptive field. We also elucidated a quantitative relation between the Laplacian of Gaussian operator and the bipolar cell receptive field. From the computational point of view, the dopaminergic modulation of the gap-junctional conductance between horizontal cells is inferred to be a suitable neural adaptation mechanism for transition between photopic and mesopic vision.

Surface modification of carbon nanotubes using 3-aminopropyltriethoxysilane to improve mechanical properties of nanocomposite based polymer matrix: Experimental and Density functional theory study

NASA Astrophysics Data System (ADS)

Hamed Mashhadzadeh, A.; Fereidoon, Ab.; Ghorbanzadeh Ahangari, M.

2017-10-01

In current study we combined theoretical and experimental studies to evaluate the effect of functionalization and silanization on mechanical behavior of polymer-based/CNT nanocomposites. Epoxy was selected as thermoset polymer, polypropylene and poly vinyl chloride were selected as thermoplastic polymers. The whole procedure is divided to two sections . At first we applied density functional theory (DFT) to analyze the effect of functionalization on equilibrium distance and adsorption energy of unmodified, functionalized by sbnd OH group and silanized epoxy/CNT, PP/CNT and PVC/CNT nanocomposites and the results showed that functionalization increased adsorption energy and reduced the equilibrium distance in all studied nanocomposites and silanization had higher effect comparing to OH functionalizing. Then we prepared experimental samples of all mentioned nanocomposites and tested their tensile and flexural strength properties. The obtained results showed that functionalization increased the studied mechanical properties in all evaluated nanocomposites. Finally we compared the results of experimental and theoretical sections with each other and estimated a suitable agreement between these parts.

Graphene oxide based nanohybrid proton exchange membranes for fuel cell applications: An overview.

PubMed

Pandey, Ravi P; Shukla, Geetanjali; Manohar, Murli; Shahi, Vinod K

2017-02-01

In the context of many applications, such as polymer composites, energy-related materials, sensors, 'paper'-like materials, field-effect transistors (FET), and biomedical applications, chemically modified graphene was broadly studied during the last decade, due to its excellent electrical, mechanical, and thermal properties. The presence of reactive oxygen functional groups in the grapheme oxide (GO) responsible for chemical functionalization makes it a good candidate for diversified applications. The main objectives for developing a GO based nanohybrid proton exchange membrane (PEM) include: improved self-humidification (water retention ability), reduced fuel crossover (electro-osmotic drag), improved stabilities (mechanical, thermal, and chemical), enhanced proton conductivity, and processability for the preparation of membrane-electrode assembly. Research carried on this topic may be divided into protocols for covalent grafting of functional groups on GO matrix, preparation of free-standing PEM or choice of suitable polymer matrix, covalent or hydrogen bonding between GO and polymer matrix etc. Herein, we present a brief literature survey on GO based nano-hybrid PEM for fuel cell applications. Different protocols were adopted to produce functionalized GO based materials and prepare their free-standing film or disperse these materials in various polymer matrices with suitable interactions. This review article critically discussed the suitability of these PEMs for fuel cell applications in terms of the dependency of the intrinsic properties of nanohybrid PEMs. Potential applications of these nanohybrid PEMs, and current challenges are also provided along with future guidelines for developing GO based nanohybrid PEMs as promising materials for fuel cell applications. Copyright © 2016 Elsevier B.V. All rights reserved.

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors.

PubMed

Wilgosz, Karolina; Chen, Xuecheng; Kierzek, Krzysztof; Machnikowski, Jacek; Kalenczuk, Ryszard J; Mijowska, Ewa

2012-05-29

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors.

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors

NASA Astrophysics Data System (ADS)

Wilgosz, Karolina; Chen, Xuecheng; Kierzek, Krzysztof; Machnikowski, Jacek; Kalenczuk, Ryszard J.; Mijowska, Ewa

2012-05-01

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors.

Heterobimetallic Complexes for Theranostic Applications.

PubMed

Fernández-Moreira, Vanesa; Gimeno, M Concepción

2018-03-07

The design of more efficient anticancer drugs requires a deeper understanding of their biodistribution and mechanism of action. Cell imaging agents could help to gain insight into biological processes and, consequently, the best strategy for attaining suitable scaffolds in which both biological and imaging properties are maximized. A new concept arises in this field that is the combination of two metal fragments as collaborative partners to provide the precise emissive properties to visualize the cell as well as the optimum cytotoxic activity to build more potent and selective chemotherapeutic agents. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanical properties of shape memory polymers for morphing aircraft applications

NASA Astrophysics Data System (ADS)

Keihl, Michelle M.; Bortolin, Robert S.; Sanders, Brian; Joshi, Shiv; Tidwell, Zeb

2005-05-01

This investigation addresses basic characterization of a shape memory polymer (SMP) as a suitable structural material for morphing aircraft applications. Tests were performed for monotonic loading in high shear at constant temperature, well below, or just above the glass transition temperature. The SMP properties were time-and temperature-dependent. Recovery by the SMP to its original shape needed to be unfettered. Based on the testing SMPs appear to be an attractive and promising component in the solution for a skin material of a morphing aircraft. Their multiple state abilities allow them to easily change shape and, once cooled, resist large loads.

Polymers for hydrogen infrastructure and vehicle fuel systems :

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barth, Rachel Reina; Simmons, Kevin L.; San Marchi, Christopher W.

2013-10-01

This document addresses polymer materials for use in hydrogen service. Section 1 summarizes the applications of polymers in hydrogen infrastructure and vehicle fuel systems and identifies polymers used in these applications. Section 2 reviews the properties of polymer materials exposed to hydrogen and/or high-pressure environments, using information obtained from published, peer-reviewed literature. The effect of high pressure on physical and mechanical properties of polymers is emphasized in this section along with a summary of hydrogen transport through polymers. Section 3 identifies areas in which fuller characterization is needed in order to assess material suitability for hydrogen service.

Dermal-epidermal membrane systems by using human keratinocytes and mesenchymal stem cells isolated from dermis.

PubMed

Salerno, Simona; Messina, Antonietta; Giordano, Francesca; Bader, Augustinus; Drioli, Enrico; De Bartolo, Loredana

2017-02-01

Dermal-epidermal membrane systems were developed by co-culturing human keratinocytes with Skin derived Stem Cells (SSCs), which are Mesenchymal Stem Cells (MSCs) isolated from dermis, on biodegradable membranes of chitosan (CHT), polycaprolactone (PCL) and a polymeric blend of CHT and PCL. The membranes display physico-chemical, morphological, mechanical and biodegradation properties that could satisfy and fulfil specific requirements in skin tissue engineering. CHT membrane exhibits an optimal biodegradation rate for acute wounds; CHT-PCL for the chronic ones. On the other hand, PCL membrane in spite of its very slow biodegradation rate exhibits mechanical properties similar to in vivo dermis, a lower hydrophilic character, and a surface roughness, all properties that make it able to sustain cell adhesion and proliferation for in vitro skin models. Both CHT-PCL and PCL membranes guided epidermal and dermal differentiation of SSCs as pointed out by the expression of cytokeratins and the deposition of the ECM protein fibronectin, respectively. In the dermal-epidermal membrane systems, a more suitable microenvironment for the SSCs differentiation was promoted by the interactions and the mutual interplay with keratinocytes. Being skin tissue-biased stem cells committed to their specific final dermal and/or epidermal cell differentiation, SSCs are more suitable for skin tissue engineering than other adult MSCs with different origin. For this reason, they represent a useful autologous cell source for engineering skin substitutes for both in vivo and in vitro applications. Copyright © 2016 Elsevier B.V. All rights reserved.

Low-Temperature Variation of Acoustic Velocity in PDMS for High-Frequency Applications.

PubMed

Streque, Jeremy; Rouxel, Didier; Talbi, Abdelkrim; Thomassey, Matthieu; Vincent, Brice

2018-05-01

Polydimethylsiloxane (PDMS) and other related silicon-based polymers are among the most widely employed elastomeric materials in microsystems, owing to their physical and chemical properties. Meanwhile, surface acoustic wave (SAW) and bulk acoustic wave (BAW) sensors and filters have been vastly explored for sensing and wireless applications. Many fields could benefit from the combined use of acoustic wave devices, and polydimethylsiloxane-based soft-substrates, microsystems, or packaging elements. The mechanical constants of PDMS strongly depend on frequency, similar to rubber materials. This brings to the exploration of the specific mechanical properties of PDMS encountered at high frequency, required for its exploitation in SAW or BAW devices. First, low-frequency mechanical behavior is confirmed from stress strain measurements, remaining useful for the exploitation of PDMS as a soft substrate or packaging material. The study, then, proposes a temperature-dependent, high-frequency mechanical study of PDMS based on Brillouin spectroscopy to determine the evolution of the longitudinal acoustic velocity in this material, which constitutes the main mechanical parameter for the design of acoustic wave devices. The PDMS glass transition is then retrieved by differential scanning calorimetry in order to confirm the observations made by Brillouin spectroscopy. This paper validates Brillouin spectroscopy as a very suitable characterization technique for the retrieval of longitudinal mechanical properties at low temperature, as a preliminary investigation for the design of acoustic wave devices coupled with soft materials.

Flame and acid resistant polymide fibers

NASA Technical Reports Server (NTRS)

Stringham, R. S.; Toy, M. S.

1977-01-01

Economical process improves flame resistance and resistance to acids of polyamide fibers, without modifying colors of mechanical properties. Process improves general safety of garments and other items made from polyamide fibers and makes them suitable for applications requiring exposure to oxygen-rich atmosphere or corrosive acids. Halo-olefins are added to surface of fibers by photoadditon in sealed chamber. Process could be used with films and other forms of polyamide.

Polyurethane foam/nano hydroxyapatite composite as a suitable scaffold for bone tissue regeneration.

PubMed

Meskinfam, M; Bertoldi, S; Albanese, N; Cerri, A; Tanzi, M C; Imani, R; Baheiraei, N; Farokhi, M; Farè, S

2018-01-01

In bone tissue regeneration, the use of biomineralized scaffolds to create the 3D porous structure needed for well-fitting with defect size and appropriate cell interactions, is a promising alternative to autologous and heterologous bone grafts. Biomineralized polyurethane (PU) foams are here investigated as scaffold for bone tissue regeneration. Biomineralization of the foams was carried out by activation of PU surface by a two steps procedure performed for different times (1 to 4 weeks). Scaffolds were investigated for morphological, chemico-physical and mechanical properties, as well as for in vitro interaction with rat Bone Marrow Mesenchymal Stem Cells (BMSCs). Untreated and biomineralized PU samples showed a homogenous morphology and regular pore size (average Ø=407μm). Phase and structure of formed calcium phosphates (CaPs) layer onto the PU foam were analyzed by Fourier Transform Infrared spectroscopy and X-ray diffraction, proving the formation of bone-like nano hydroxyapatite. Biomineralization caused a significant increase of mechanical properties of treated foams compared to untreated ones. Biomineralization also affected the PU scaffold cytocompatibility providing a more appropriate surface for cell attachment and proliferation. Considering the obtained results, the proposed scaffold can be considered suitable for bone tissue regeneration. Copyright © 2017 Elsevier B.V. All rights reserved.

High biocompatibility and improved osteogenic potential of novel Ca-P/titania composite scaffolds designed for regeneration of load-bearing segmental bone defects.

PubMed

Cunha, Carla; Sprio, Simone; Panseri, Silvia; Dapporto, Massimiliano; Marcacci, Maurilio; Tampieri, Anna

2013-06-01

Regeneration of load-bearing bone segments is still an open challenge due to the lack of biomaterials mimicking natural bone with a suitable chemicophysical and mechanical performance. This study proposes ceramic bone scaffolds made of β-tricalcium phosphate (β-TCP) and titania (TiO2 ), developed from hydroxyapatite (HA) and TiO2 starting nanopowders, which exhibit high and interconnected macroporosity (>70 vol %). The scaffold composition was designed to achieve a synergistic effect of bioactivity/resorbability and mechanical properties suitable for load-bearing regenerative applications. The analysis of the morphology, structure, and mechanical strength of the scaffolds resulted in compression strength nearly twice that of commercially available HA bone grafts with similar structure (Engipore(®)). Biological characterization was carried out for human MG-63 osteoblast-like cells proliferation, activity, attachment, and viability. β-TCP/TiO2 scaffolds show high proliferation rate, high viability, and high colonization rates. Moreover, an increased activity of the osteogenic marker alkaline phosphatase (ALP) was found. These results demonstrate that β-TCP/TiO2 scaffolds have good potential as osteogenically active load-bearing scaffolds; moreover, given the high and interconnected macroporosity as well as the resorbability properties of β-TCP, these scaffolds may enhance in vivo osteointegration and promote the formation of new organized bone, thus resulting in very promising biomimetic scaffolds for long bone regeneration. Copyright © 2012 Wiley Periodicals, Inc.

Neuronal Differentiation Modulated by Polymeric Membrane Properties.

PubMed

Morelli, Sabrina; Piscioneri, Antonella; Drioli, Enrico; De Bartolo, Loredana

2017-01-01

In this study, different collagen-blend membranes were successfully constructed by blending collagen with chitosan (CHT) or poly(lactic-co-glycolic acid) (PLGA) to enhance their properties and thus create new biofunctional materials with great potential use for neuronal tissue engineering and regeneration. Collagen blending strongly affected membrane properties in the following ways: (i) it improved the surface hydrophilicity of both pure CHT and PLGA membranes, (ii) it reduced the stiffness of CHT membranes, but (iii) it did not modify the good mechanical properties of PLGA membranes. Then, we investigated the effect of the different collagen concentrations on the neuronal behavior of the membranes developed. Morphological observations, immunocytochemistry, and morphometric measures demonstrated that the membranes developed, especially CHT/Col30, PLGA, and PLGA/Col1, provided suitable microenvironments for neuronal growth owing to their enhanced properties. The most consistent neuronal differentiation was obtained in neurons cultured on PLGA-based membranes, where a well-developed neuronal network was achieved due to their improved mechanical properties. Our findings suggest that tensile strength and elongation at break are key material parameters that have potential influence on both axonal elongation and neuronal structure and organization, which are of fundamental importance for the maintenance of efficient neuronal growth. Hence, our study has provided new insights regarding the effects of membrane mechanical properties on neuronal behavior, and thus it may help to design and improve novel instructive biomaterials for neuronal tissue engineering. © 2017 S. Karger AG, Basel.

41 CFR 102-75.450 - What type of property is suitable or desirable for use as a historic monument?

Code of Federal Regulations, 2010 CFR

2010-07-01

... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false What type of property is... Historic Monuments § 102-75.450 What type of property is suitable or desirable for use as a historic... Property Management Federal Property Management Regulations System (Continued) FEDERAL MANAGEMENT...

41 CFR 102-75.450 - What type of property is suitable or desirable for use as a historic monument?

Code of Federal Regulations, 2011 CFR

2011-01-01

... 41 Public Contracts and Property Management 3 2011-01-01 2011-01-01 false What type of property is... Historic Monuments § 102-75.450 What type of property is suitable or desirable for use as a historic... Property Management Federal Property Management Regulations System (Continued) FEDERAL MANAGEMENT...

41 CFR 102-75.450 - What type of property is suitable or desirable for use as a historic monument?

Code of Federal Regulations, 2012 CFR

2012-01-01

... 41 Public Contracts and Property Management 3 2012-01-01 2012-01-01 false What type of property is... Historic Monuments § 102-75.450 What type of property is suitable or desirable for use as a historic... Property Management Federal Property Management Regulations System (Continued) FEDERAL MANAGEMENT...

41 CFR 102-75.450 - What type of property is suitable or desirable for use as a historic monument?

Code of Federal Regulations, 2013 CFR

2013-07-01

... 41 Public Contracts and Property Management 3 2013-07-01 2013-07-01 false What type of property is... Historic Monuments § 102-75.450 What type of property is suitable or desirable for use as a historic... Property Management Federal Property Management Regulations System (Continued) FEDERAL MANAGEMENT...

41 CFR 102-75.450 - What type of property is suitable or desirable for use as a historic monument?

Code of Federal Regulations, 2014 CFR

2014-01-01

... 41 Public Contracts and Property Management 3 2014-01-01 2014-01-01 false What type of property is... Historic Monuments § 102-75.450 What type of property is suitable or desirable for use as a historic... Property Management Federal Property Management Regulations System (Continued) FEDERAL MANAGEMENT...

Biodegradable magnesium-hydroxyapatite metal matrix composites.

PubMed

Witte, Frank; Feyerabend, Frank; Maier, Petra; Fischer, Jens; Störmer, Michael; Blawert, Carsten; Dietzel, Wolfgang; Hort, Norbert

2007-04-01

Recent studies indicate that there is a high demand to design magnesium alloys with adjustable corrosion rates and suitable mechanical properties. An approach to this challenge might be the application of metal matrix composite (MMC) based on magnesium alloys. In this study, a MMC made of magnesium alloy AZ91D as a matrix and hydroxyapatite (HA) particles as reinforcements have been investigated in vitro for mechanical, corrosive and cytocompatible properties. The mechanical properties of the MMC-HA were adjustable by the choice of HA particle size and distribution. Corrosion tests revealed that HA particles stabilised the corrosion rate and exhibited more uniform corrosion attack in artificial sea water and cell solutions. The phase identification showed that all samples contained hcp-Mg, Mg(17)Al(12), and HA before and after immersion. After immersion in artificial sea water CaCO3 was found on MMC-HA surfaces, while no formation of CaCO3 was found after immersion in cell solutions with and without proteins. Co-cultivation of MMC-HA with human bone derived cells (HBDC), cells of an osteoblasts lineage (MG-63) and cells of a macrophage lineage (RAW264.7) revealed that RAW264.7, MG-63 and HBDC adhere, proliferate and survive on the corroding surfaces of MMC-HA. In summary, biodegradable MMC-HA are cytocompatible biomaterials with adjustable mechanical and corrosive properties.

Evaluation of structural and mechanical properties of electrospun nano-micro hybrid of poly hydroxybutyrate-chitosan/silk scaffold for cartilage tissue engineering

PubMed Central

Karbasi, Saeed; Fekrat, Farnoosh; Semnani, Daryoush; Razavi, Shahnaz; Zargar, Elham Naghash

2016-01-01

Background: One of the new methods of scaffold fabrication is a nano-micro hybrid structure in which the properties of the scaffold are improved by introducing nanometer and micrometer structures. This method could be suitable for scaffold designing if some features improve. Materials and Methods: In this study, electrospun nanofibers of 9% weight solution of poly (3-hydroxybutyrate) (P3HB) and a 15% weight of chitosan by trifluoroacetic acid were coated on both the surface of a silk knitted substrate in the optimum condition to improve the mechanical properties of scaffolds for cartilage tissue engineering application. These hybrid nano-micro fibrous scaffolds were characterized by structural and mechanical evaluation methods. Results: Scanning electron microscopy values and porosity analysis showed that average diameter of nanofibers was 584.94 nm in electrospinning part and general porosity was more than 80%. Fourier transform infrared spectroscopy results indicated the presence of all elements without pollution. The tensile test also stated that by electrospinning, as well as adding chitosan, both maximum strength and maximum elongation increased to 187 N and 10 mm. It means that the microfibrous part of scaffold could affect mechanical properties of nano part of the hybrid scaffold, significantly. Conclusions: It could be concluded that P3HB-chitosan/silk hybrid scaffolds can be a good candidate for cartilage tissue engineering. PMID:28028520

Evaluation of structural and mechanical properties of electrospun nano-micro hybrid of poly hydroxybutyrate-chitosan/silk scaffold for cartilage tissue engineering.

PubMed

Karbasi, Saeed; Fekrat, Farnoosh; Semnani, Daryoush; Razavi, Shahnaz; Zargar, Elham Naghash

2016-01-01

One of the new methods of scaffold fabrication is a nano-micro hybrid structure in which the properties of the scaffold are improved by introducing nanometer and micrometer structures. This method could be suitable for scaffold designing if some features improve. In this study, electrospun nanofibers of 9% weight solution of poly (3-hydroxybutyrate) (P3HB) and a 15% weight of chitosan by trifluoroacetic acid were coated on both the surface of a silk knitted substrate in the optimum condition to improve the mechanical properties of scaffolds for cartilage tissue engineering application. These hybrid nano-micro fibrous scaffolds were characterized by structural and mechanical evaluation methods. Scanning electron microscopy values and porosity analysis showed that average diameter of nanofibers was 584.94 nm in electrospinning part and general porosity was more than 80%. Fourier transform infrared spectroscopy results indicated the presence of all elements without pollution. The tensile test also stated that by electrospinning, as well as adding chitosan, both maximum strength and maximum elongation increased to 187 N and 10 mm. It means that the microfibrous part of scaffold could affect mechanical properties of nano part of the hybrid scaffold, significantly. It could be concluded that P3HB-chitosan/silk hybrid scaffolds can be a good candidate for cartilage tissue engineering.

[Influence on mechanical properties and microstructure of nano-zirconia toughened alumina ceramics with nano-zirconia content].

PubMed

Wang, Guang-Kui; Kang, Hong; Bao, Guang-Jie; Lv, Jin-Jun; Gao, Fei

2006-10-01

To investigate the mechanical properties and microstructure of nano -zirconia toughened alumina ceramics with variety of nano-zirconia content in centrifugal infiltrate casting processing of dental all-ceramic. Composite powder with different ethanol-water ratio, obtained serosity from ball milling and centrifugal infiltrate cast processing of green, then sintered at 1 450 degrees C for 8 h. The physical and mechanical properties of the sintered sample after milling and polishing were tested. Microstructures of the surface and fracture of the sintered sample were investigated by SEM. The experimental results showed that there had statistical significience (P < 0.01) on static three-point flexure strength and Vickers Hardness in three kinds of different nano-zirconia content sintered sample. Fracture toughness of 20% group was different from other two groups, while 10% group had not difference from 30% group (P < 0.05). The mechanical properties of this ceramic with 20% nano-zirconia was the best of the three, the static three-point flexure strength was (433 +/- 19) MPa and fracture toughness was (7.50 +/- 0.56) MPa x min 1/2. The intra/inter structure, fracture of intragranular and intergranular on the surface and fracture of sintered sample in microstrucre was also found. Intra/inter structure has strengthen toughness in ceramics. It has better toughness with 20% nano-zirconia, is suitable dental all-ceramic restoratives.

Microcomputed tomography and microfinite element modeling for evaluating polymer scaffolds architecture and their mechanical properties.

PubMed

Alberich-Bayarri, Angel; Moratal, David; Ivirico, Jorge L Escobar; Rodríguez Hernández, José C; Vallés-Lluch, Ana; Martí-Bonmatí, Luis; Estellés, Jorge Más; Mano, Joao F; Pradas, Manuel Monleón; Ribelles, José L Gómez; Salmerón-Sánchez, Manuel

2009-10-01

Detailed knowledge of the porous architecture of synthetic scaffolds for tissue engineering, their mechanical properties, and their interrelationship was obtained in a nondestructive manner. Image analysis of microcomputed tomography (microCT) sections of different scaffolds was done. The three-dimensional (3D) reconstruction of the scaffold allows one to quantify scaffold porosity, including pore size, pore distribution, and struts' thickness. The porous morphology and porosity as calculated from microCT by image analysis agrees with that obtained experimentally by scanning electron microscopy and physically measured porosity, respectively. Furthermore, the mechanical properties of the scaffold were evaluated by making use of finite element modeling (FEM) in which the compression stress-strain test is simulated on the 3D structure reconstructed from the microCT sections. Elastic modulus as calculated from FEM is in agreement with those obtained from the stress-strain experimental test. The method was applied on qualitatively different porous structures (interconnected channels and spheres) with different chemical compositions (that lead to different elastic modulus of the base material) suitable for tissue regeneration. The elastic properties of the constructs are explained on the basis of the FEM model that supports the main mechanical conclusion of the experimental results: the elastic modulus does not depend on the geometric characteristics of the pore (pore size, interconnection throat size) but only on the total porosity of the scaffold. (c) 2009 Wiley Periodicals, Inc.

Manufacturing of biodegradable polyurethane scaffolds based on polycaprolactone using a phase separation method: physical properties and in vitro assay

PubMed Central

Asefnejad, Azadeh; Khorasani, Mohammad Taghi; Behnamghader, Aliasghar; Farsadzadeh, Babak; Bonakdar, Shahin

2011-01-01

Background Biodegradable polyurethanes have found widespread use in soft tissue engineering due to their suitable mechanical properties and biocompatibility. Methods In this study, polyurethane samples were synthesized from polycaprolactone, hexamethylene diisocyanate, and a copolymer of 1,4-butanediol as a chain extender. Polyurethane scaffolds were fabricated by a combination of liquid–liquid phase separation and salt leaching techniques. The effect of the NCO:OH ratio on porosity content and pore morphology was investigated. Results Scanning electron micrographs demonstrated that the scaffolds had a regular distribution of interconnected pores, with pore diameters of 50–300 μm, and porosities of 64%–83%. It was observed that, by increasing the NCO:OH ratio, the average pore size, compressive strength, and compressive modulus increased. L929 fibroblast and chondrocytes were cultured on the scaffolds, and all samples exhibited suitable cell attachment and growth, with a high level of biocompatibility. Conclusion These biodegradable polyurethane scaffolds demonstrate potential for soft tissue engineering applications. PMID:22072874

Effects of charge symmetry on heavy ion reaction mechanisms

NASA Astrophysics Data System (ADS)

Colonna, M.; di Toro, M.; Fabbri, G.; Maccarone, S.

1998-03-01

We suggest several possibilities to study the properties of the symmetry term in the nuclear equation of state from radioactive beam experiments. Collision simulations with a stochastic transport approach, where asymmetry effects are suitably introduced, are presented. The dynamical response of an interacting highly asymmetric nuclear matter can be studied, taking advantage of the neutron skin structure. The main reaction mechanisms, from fusion to deep inelastic and fragmentation, appear quite sensitive to the form of the symmetry term of the effective force used, opening some new appealing experimental perspectives. Finally new features of fragment production are presented, due to the onset of chemical plus mechanical instabilities in dilute asymmetric nuclear matter.

Microhardness and In Vitro Corrosion of Heat-Treated Mg–Y–Ag Biodegradable Alloy

PubMed Central

Vlček, Marián; Lukáč, František; Kudrnová, Hana; Smola, Bohumil; Stulíková, Ivana; Luczak, Monika; Szakács, Gábor; Hort, Norbert; Willumeit-Römer, Regine

2017-01-01

Magnesium alloys are promising candidates for biodegradable medical implants which reduce the necessity of second surgery to remove the implants. Yttrium in solid solution is an attractive alloying element because it improves mechanical properties and exhibits suitable corrosion properties. Silver was shown to have an antibacterial effect and can also enhance the mechanical properties of magnesium alloys. Measurements of microhardness and electrical resistivity were used to study the response of Mg–4Y and Mg–4Y–1Ag alloys to isochronal or isothermal heat treatments. Hardening response and electrical resistivity annealing curves in these alloys were compared in order to investigate the effect of silver addition. Procedures for solid solution annealing and artificial aging of the Mg–4Y–1Ag alloy were developed. The corrosion rate of the as-cast and heat-treated Mg–4Y–1Ag alloy was measured by the mass loss method. It was found out that solid solution heat treatment, as well artificial aging to peak hardness, lead to substantial improvement in the corrosion properties of the Mg–4Y–1Ag alloy. PMID:28772414

Mechanical properties of Haynes Alloy 188 after exposure to LiF-22CaF2, air, and vacuum at 1093 K for periods up to 10,000 hours

NASA Technical Reports Server (NTRS)

Whittenberger, J. D.

1992-01-01

As part of a program to provide reassurance that the cobalt-base superalloy Haynes Alloy 188 can adequately contain a LiF-CaF2 eutectic thermal energy storage salt, 4900- and 10,000-hr exposures of Haynes Alloy 188 to LiF-22CaF2, its vapor, vacuum, and air at 1093 K have been undertaken. Following such exposures, the microstructure has been characterized and the 77 to 1200 K tensile properties measured. In addition, 1050 K vacuum creep-rupture testing of as-received and molten salt- and vacuum-exposed samples has been undertaken. Although slight degradation of the mechanical properties of Haynes Alloy 188 due to prior exposure was observed, basically none of the losses could be ascribed to a particular environment. Hence, observed decreases in properties are due to thermal aging effects, not corrosive attack. In view of these findings, Haynes Alloy 188 is still deemed to be suitable for containment of the eutectic LiF-CaF2 thermal energy storage media.

Ultrasound elastography to determine the layered mechanical properties of articular cartilage and the importance of such structural characteristics under load.

PubMed

McCredie, Alexandra J; Stride, Eleanor; Saffari, Nader

2009-01-01

Articular cartilage is an important load bearing surface in joints. Prone to damage and with limited self-repair ability, it is of interest to tissue engineers. Tissue implant design requires full mechanical characterisation of healthy native tissue. A layered organisation of reinforcing collagen fibrils exists in healthy articular cartilage and is believed to be important for correct tissue function. However, the effect of this on the local depth-dependent elasticity is poorly characterised. In this study, quasi-static ultrasound elastography is used both to compare the depth-dependent elastic properties of cartilage structures with two different fibril arrangements and to monitor changes in the elastic properties of engineered samples during development. Results show global and local elastic properties of the native tissues and highlight the differences caused by fibril architecture. At increasing culture periods, results from the engineered tissue demonstrate an increase in elastic stiffness and the time taken to reach equilibrium under a quasi-static displacement. The study suggests suitability of ultrasound elastography for design and monitoring engineered articular cartilage.

Dosimetric evaluation of Plastic Water Diagnostic-Therapy.

PubMed

Ramaseshan, Ramani; Kohli, Kirpal; Cao, Fred; Heaton, Robert K

2008-04-29

High-precision radiotherapy planning and quality assurance require accurate dosimetric and geometric phantom measurements. Phantom design requires materials with mechanical strength and resilience, and dosimetric properties close to those of water over diagnostic and therapeutic ranges. Plastic Water Diagnostic Therapy (PWDT: CIRS, Norfolk, VA) is a phantom material designed for water equivalence in photon beams from 0.04 MeV to 100 MeV; the material has also good mechanical properties. The present article reports the results of computed tomography (CT) imaging and dosimetric studies of PWDT to evaluate the suitability of the material in CT and therapy energy ranges. We characterized the water equivalence of PWDT in a series of experiments in which the basic dosimetric properties of the material were determined for photon energies of 80 kVp, 100 kVp, 250 kVp, 4 MV, 6 MV, 10 MV, and 18 MV. Measured properties included the buildup and percentage depth dose curves for several field sizes, and relative dose factors as a function of field size. In addition, the PWDT phantom underwent CT imaging at beam qualities ranging from 80 kVp to 140 kVp to determine the water equivalence of the phantom in the diagnostic energy range. The dosimetric quantities measured with PWDT agreed within 1.5% of those determined in water and Solid Water (Gammex rmi, Middleton, WI). Computed tomography imaging of the phantom was found to generate Hounsfield numbers within 0.8% of those generated using water. The results suggest that PWDT material is suitable both for regular radiotherapy quality assurance measurements and for intensity-modulated radiation therapy (IMRT) verification work. Sample IMRT verification results are presented.

Functional similarities in the mechanical design of the aorta in lower vertebrates and mammals.

PubMed

Gibbons, C A; Shadwick, R E

1989-12-01

The mechanical properties of the aorta from the toad Bufo marinus, the lizard Gekko gecko and the garter snake Thamnophis radix were compared to those of the rat, by inflation of vessel segments in vitro. The arteries of the lower vertebrates, like those of mammals, were compliant, highly resilient, and non-linearly elastic. The elastic modulus of the artery wall was similar in the lower vertebrates and mammals, at their respective mean physiological pressures. We conclude that the aorta in each of these animals is suitably designed to function effectively as an elastic pulse smoothing component in the circulation; differences in the pressure wave transmission characteristics of lower vertebrates and mammals do not result from dissimilarities in arterial elastic properties, but from substantial differences in heart rate of these two groups.

Cellular-level surgery using nano robots.

PubMed

Song, Bo; Yang, Ruiguo; Xi, Ning; Patterson, Kevin Charles; Qu, Chengeng; Lai, King Wai Chiu

2012-12-01

The atomic force microscope (AFM) is a popular instrument for studying the nano world. AFM is naturally suitable for imaging living samples and measuring mechanical properties. In this article, we propose a new concept of an AFM-based nano robot that can be applied for cellular-level surgery on living samples. The nano robot has multiple functions of imaging, manipulation, characterizing mechanical properties, and tracking. In addition, the technique of tip functionalization allows the nano robot the ability for precisely delivering a drug locally. Therefore, the nano robot can be used for conducting complicated nano surgery on living samples, such as cells and bacteria. Moreover, to provide a user-friendly interface, the software in this nano robot provides a "videolized" visual feedback for monitoring the dynamic changes on the sample surface. Both the operation of nano surgery and observation of the surgery results can be simultaneously achieved. This nano robot can be easily integrated with extra modules that have the potential applications of characterizing other properties of samples such as local conductance and capacitance.

Physico-functional and mechanical properties of chitosan and calcium salts incorporated fish gelatin scaffolds.

PubMed

Jeevithan, E; Jeya Shakila, R; Varatharajakumar, A; Jeyasekaran, G; Sukumar, D

2013-09-01

Four types of fish gelatin scaffolds viz. gelatin (G), gelatin-chitosan (GC), gelatin-calcium acetate (GCA) and gelatin-chitosan-calcium acetate (GCCA) prepared were investigated for their functional properties, biomechanical strength, microstructural changes in relation to biodegradation. GC scaffold was superior with pH 3.15 and viscosity 9.40 cP. Chitosan and calcium acetate improved tensile strength (TS) and Young's modulus (YM), but lowered elongation at break (EAB). GCCA scaffold possessed moderate TS of 19.6 MPa, EAB of 4.76% and YM of 185 MPa. Foaming ability ratio of GC scaffold was high (3.41). GCA and GCCA scaffolds remained for 4 days before complete in vitro biodegradation. GC scaffold had larger cavities (180-300 μm) that were responsible for low swelling ratios and shrinkage factor. GCCA scaffold with moderate swelling rates, mechanical, functional properties and lowered biodegradation rate were found more suitable for biomedical applications. Copyright © 2013 Elsevier B.V. All rights reserved.

Bio-functionalization of biomedical metals.

PubMed

Xiao, M; Chen, Y M; Biao, M N; Zhang, X D; Yang, B C

2017-01-01

Bio-functionalization means to endow biomaterials with bio-functions so as to make the materials or devices more suitable for biomedical applications. Traditionally, because of the excellent mechanical properties, the biomedical metals have been widely used in clinic. However, the utilized functions are basically supporting or fixation especially for the implantable devices. Nowadays, some new functions, including bioactivity, anti-tumor, anti-microbial, and so on, are introduced to biomedical metals. To realize those bio-functions on the metallic biomedical materials, surface modification is the most commonly used method. Surface modification, including physical and chemical methods, is an effective way to alter the surface morphology and composition of biomaterials. It can endow the biomedical metals with new surface properties while still retain the good mechanical properties of the bulk material. Having analyzed the ways of realizing the bio-functionalization, this article briefly summarized the bio-functionalization concepts of six hot spots in this field. They are bioactivity, bony tissue inducing, anti-microbial, anti-tumor, anticoagulation, and drug loading functions. Copyright © 2016. Published by Elsevier B.V.

The influence of heat treatment on properties of cold rolled alloyed steel and nickel superalloys sheets used in aircraft industry

NASA Astrophysics Data System (ADS)

Zaba, K.; Dul, I.; Puchlerska, S.

2017-02-01

Superalloys based on nickel and selected steels are widely used in the aerospace industry, because of their excellent mechanical properties, heat resistance and creep resistance. Metal sheets of these materials are plastically deformed and applied, inter alia, to critical components of aircraft engines. Due to their chemical composition these materials are hardly deformable. There are various methods to improve the formability of these materials, including plastic deformation at an elevated or high temperature, or a suitable heat treatment before forming process. The paper presents results of the metal sheets testing after heat treatment. For the research, sheets of two types of nickel superalloys type Inconel and of three types of steel were chosen. The materials were subjected to multivariate heat treatment at different temperature range and time. After this step, mechanical properties were examined according to the metal sheet rolling direction. The results were compared and the optimal type of pre-trial softening heat treatment for each of the materials was determined.

Microstructural Characterization of Semi-Interpenetrating Polymer Networks by Positron Lifetime Spectroscopy

NASA Technical Reports Server (NTRS)

Singh, Jag J.; Pater, Ruth H.; Eftekhari, Abe

1996-01-01

Thermoset and thermoplastic polyimides have complementary physical and mechanical properties. Whereas thermoset polyimides are brittle and generally easier to process, thermoplastic polyimides are tough but harder to process. A combination of these two types of polyimides may help produce polymers more suitable for aerospace applications. Semi-Interpenetrating Polymer Networks (S-IPN) of thermoset LaRC(TM)-RP46 and thermoplastic LaRC(TM)-IA polyimides were prepared in weight percent ratios ranging from 100:0 to 0:100. Positron lifetime measurements were made in these samples to correlate their free volume features with physical and mechanical properties. As expected, positronium atoms are not formed in these samples. The second lifetime component has been used to infer the positron trap dimensions. The 'free volume' goes through a minimum at a ratio of about 50:50, and this suggests that S-IPN samples are not merely solid solutions of the two polymers. These data and related structural properties of the S-IPN samples are discussed.

Microstructure and Mechanical Properties of Microwave Post-processed Ni Coating

NASA Astrophysics Data System (ADS)

Zafar, Sunny; Sharma, Apurbba Kumar

2017-03-01

Flame-sprayed coatings are widely used in the industries attributed to their low cost and simple processing. However, the presence of porosity and poor adhesion with the substrate requires suitable post-processing of the as-sprayed deposits. In the present work, post-processing of the flame-sprayed Ni-based coating has been successfully attempted using microwave hybrid heating. Microwave post-processing of the flame-sprayed coatings was carried out at 2.45 GHz in a 1 kW multimode industrial microwave applicator. The microwave-processed and as-sprayed deposits were characterized for their microstructure, porosity, fracture toughness and surface roughness. The properties of the coatings were correlated with their abrasive wear behavior using a sliding abrasion test on a pin-on-disk tribometer. Microwave post-processing led to healed micropores and microcracks, thus causing homogenization of the microstructure in the coating layer. Therefore, microwave post-processed coating layer exhibits improved mechanical and tribological properties compared to the as-sprayed coating layer.

Mechanical performance of hybrid polyester composites reinforced Cloisite 30B and kenaf fibre

NASA Astrophysics Data System (ADS)

Bonnia, N. N.; Surip, S. N.; Ratim, S.; Mahat, M. M.

2012-06-01

Hybridization of rubber toughened polyester-kenaf nanocomposite was prepared by adding various percentage of kenaf fiber with 4% Cloisite 30B in unsaturated polyester resin. Composite were prepared by adding filler to modified polyester resin subsequently cross-linked using methyl ethyl ketone peroxide and the accelerator cobalt octanoate 1%. Three per hundred rubbers (phr) of liquid natural rubber (LNR) were added in producing this composite. This composite expected to be applied in the interior of passenger cars and truck cabins. This is a quality local product from a combination of good properties polyester and high performance natural fiber, kenaf that is suitable for many applications such as in automotive sector and construction sector. The mechanical and thermal properties of composite were characterized using Durometer Shore-D hardness test, Izod impact test, Scanning electron microscopy, thermogravimetry (TGA) and differential scanning calorimetry (DSC). Result shows that addition of LNR give good properties on impact, flexural and hardness compare to without LNR composite. DSC curve shows that all composition of composites is fully cured and good in thermal properties. Addition of higher percentage of kenaf will lead the composite to elastic behavior and decrease the toughened properties of the composite. Hybrid system composite showed the flexural properties within the flexural properties of kenaf - polyester and Cloisite 30B.

Microstructure and Mechanical Properties of Additively Manufactured Parts with Staircase Feature

NASA Astrophysics Data System (ADS)

Keya, Tahmina

This thesis focuses on a part with staircase feature that is made of Inconel 718 and fabricated by SLM process. The objective of the study was to observe build height effect on the microstructure and mechanical properties of the part. Due to the nature of SLM, there is possibility of different microstructure and mechanical properties in different locations depending on the design of the part. The objective was to compare microstructure and mechanical properties from different location and four comparison groups were considered: 1. Effect of thermal cycle; 2. External and internal surfaces; 3. Build height effect and 4. Bottom surfaces. To achieve the goals of this research, standard metallurgical procedure has been performed to prepare samples. Etching was done to reveal the microstructure of SLM processed Inconel 718 parts. Young's modulus and hardness were measured using nanoindentation technique. FEM analysis was performed to simulate nanoindentation. The conclusions drawn from this research are: 1. The microstructure of front and side surface of SLM processed Inconel 718 consists of arc shaped cut ends of melt pools with intermetallic phase at the border of the melt pool; 2. On top surface, melted tracks and scanning patterns can be observed and the average width of melted tracks is 100-150 microm; 3. The microstructure looks similar at different build height; 4. Microstructure on the top of a stair is more defined and organized than the internal surface; 5. The mechanical properties are highest at the bottom. OM images revealed slight difference in microstructure in terms of build height for this specific part, but mechanical properties seem to be vary noticeably. This is something to be kept in mind while designing or determining build orientation. External and internal surfaces of a stair at the same height showed difference in both microstructure and mechanical properties. To minimize that effect and to make it more uniform, gradual elevation can be considered when suitable as far as design modification is concerned. Above all, this study reveals important information about the pattern of microstructure, thus heat transfer mechanism inside a part which is useful to understand the SLM process.

Thermally Sprayed High Temperature Sandwich Structures: Physical Properties and Mechanical Performance

NASA Astrophysics Data System (ADS)

Salavati, Saeid

Metallic foam core sandwich structures have been of particular interest for engineering applications in recent decades due to their unique physical and mechanical properties. One of the potential applications of open pore metallic foam core sandwich structures is in heat exchangers. An investigation of sandwich structures fabricated from materials suitable for application at high temperatures and in corrosive environments was undertaken in this project. A novel method for fabrication of metallic foam core sandwich structures is thermal spray deposition of the faces on the prepared surfaces of the metallic foam substrate. The objective of the current study was to optimize the twin wire arc spray process parameters for the deposition of alloy 625 faces with controllable porosity content on the nickel foam substrate, and to characterize the physical and mechanical properties of the sandwich structure. The experimental investigations consisted of microstructural evaluation of the skin material and the foam substrate, investigation of the effect of alloying on the mechanical and thermal properties of the nickel foam, optimization of the grit-blasting and arc spray processes, observation of mechanical properties of the alloy 625 deposit by tensile testing and evaluation of the overall mechanical properties of the sandwich structure under flexural loading condition. The optimization of arc spraying process parameters allowed deposition of alloy 625 faces with a porosity of less than 4% for heat exchanger applications. Modification of the arc spraying process by co-deposition of polyester powder enabled 20% porosity to be obtained in the deposited faces for heat shield applications with film cooling. The effects of nickel foam alloying and heat treatment on the flexural rigidity of the sandwich structures were investigated and compared with as-received foam and as-fabricated sandwich structures. Available analytical models were employed to describe the effect of constituents' mechanical properties on the overall mechanical performance of the sandwich structures. Finite element modeling using ANSYS Structural was used to simulate the behaviour of the sandwich structures in four-point bending. The analytical and simulation results were compared with the experimental results obtained from the flexural tests.

Structure and Mechanical Properties of As-Cast Ti-5Sn-xMo Alloys.

PubMed

Yu, Hsing-Ning; Hsu, Hsueh-Chuan; Wu, Shih-Ching; Hsu, Shih-Kuang; Ho, Wen-Fu

2017-04-27

Ti-5Sn- x Mo ( x = 0, 1, 3, 5, 7.5, 10, 12.5, 15, 17.5, and 20 wt %) alloys were designed and prepared for application as implant materials with superior mechanical properties. The results demonstrated that the crystal structure and mechanical properties of Ti-5Sn- x Mo alloys are highly affected by their Mo content. The as-cast microstructures of Ti-5Sn- x Mo alloys transformed in the sequence of phases α' → α″ → β, and the morphologies of the alloys changed from a lath structure to an equiaxed structure as the Mo content increased. The α″-phase Ti-5Sn-7.5Mo (80 GPa) and β-phase Ti-5Sn-10Mo (85 GPa) exhibited relatively low elastic moduli and had excellent elastic recovery angles of 27.4° and 37.8°, respectively. Furthermore, they exhibited high ductility and moderate strength, as evaluated using the three-point bending test. Search for a more suitable implant material by this study, Ti-5Sn- x Mo alloys with 7.5 and 10 wt % Mo appear to be promising candidates because they demonstrate the optimal combined properties of microhardness, ductility, elastic modulus, and elastic recovery capability.

Physical and mechanical properties by utilizing empty fruit bunch into fired clay brick

NASA Astrophysics Data System (ADS)

Kadir, Aeslina Abdul; Sarani, Noor Amira; Mokhtar, Siti Zulaikha; Abdullah, Mohd Mustafa Al Bakri

2017-04-01

Palm oil plantation has become one of the country's success stories in agricultural development which also generates the highest number of waste among the agricultural waste. In this study, the investigation on the possibility to utilize the empty fruit bunch (EFB) waste into the fired clay brick was carried out. The main purpose of this study is to determine the physical and mechanical properties of bricks incorporated with different percentages of EFB. In this study, bricks with four different percentages of EFB (0 %, 1 %, 5 % and 10 %) were manufactured. Manufactured bricks were fired at 1050 °C with heating rate of 1 °C/min. Physical and mechanical properties including shrinkage, density, Initial Rate of Suction (IRS) and compressive strength were reported and discussed. Since shrinkage for each mixing is below than 8 %, then a good brick was manufactured. Bricks become more porous due to the organic content of EFB are burnt away and voids are formed in the specimen, giving it a lighter appearance and were produced lightweight brick which is suitable for non-loading purposes. As a conclusion, the incorporation of EFB into fired clay brick gives some advantages to the brick properties and also provides an alternative solution to disposed EFB waste.

Multifaceted prospects of nanocomposites for cardiovascular grafts and stents

PubMed Central

Vellayappan, Muthu Vignesh; Balaji, Arunpandian; Subramanian, Aruna Priyadarshini; John, Agnes Aruna; Jaganathan, Saravana Kumar; Murugesan, Selvakumar; Supriyanto, Eko; Yusof, Mustafa

2015-01-01

Cardiovascular disease is the leading cause of death across the globe. The use of synthetic materials is indispensable in the treatment of cardiovascular disease. Major drawbacks related to the use of biomaterials are their mechanical properties and biocompatibility, and these have to be circumvented before promoting the material to the market or clinical setting. Revolutionary advancements in nanotechnology have introduced a novel class of materials called nanocomposites which have superior properties for biomedical applications. Recently, there has been a widespread recognition of the nanocomposites utilizing polyhedral oligomeric silsesquioxane, bacterial cellulose, silk fibroin, iron oxide magnetic nanoparticles, and carbon nanotubes in cardiovascular grafts and stents. The unique characteristics of these nanocomposites have led to the development of a wide range of nanostructured copolymers with appreciably enhanced properties, such as improved mechanical, chemical, and physical characteristics suitable for cardiovascular implants. The incorporation of advanced nanocomposite materials in cardiovascular grafts and stents improves hemocompatibility, enhances antithrombogenicity, improves mechanical and surface properties, and decreases the microbial response to the cardiovascular implants. A thorough attempt is made to summarize the various applications of nanocomposites for cardiovascular graft and stent applications. This review will highlight the recent advances in nanocomposites and also address the need of future research in promoting nanocomposites as plausible candidates in a campaign against cardiovascular disease. PMID:25897223

Fabrication of low-cost beta-type Ti-Mn alloys for biomedical applications by metal injection molding process and their mechanical properties.

PubMed

Santos, Pedro Fernandes; Niinomi, Mitsuo; Liu, Huihong; Cho, Ken; Nakai, Masaaki; Itoh, Yoshinori; Narushima, Takayuki; Ikeda, Masahiko

2016-06-01

Titanium and its alloys are suitable for biomedical applications owing to their good mechanical properties and biocompatibility. Beta-type Ti-Mn alloys (8-17 mass% Mn) were fabricated by metal injection molding (MIM) as a potential low cost material for use in biomedical applications. The microstructures and mechanical properties of the alloys were evaluated. For up to 13 mass% Mn, the tensile strength (1162-938MPa) and hardness (308-294HV) of the MIM fabricated alloys are comparable to those of Ti-Mn alloys fabricated by cold crucible levitation melting. Ti-9Mn exhibits the best balance of ultimate tensile strength (1046MPa) and elongation (4.7%) among the tested alloys, and has a Young's modulus of 89GPa. The observed low elongation of the alloys is attributed to the combined effects of high oxygen content, with the presence of interconnected pores and titanium carbides, the formation of which is due to carbon pickup during the debinding process. The elongation and tensile strength of the alloys decrease with increasing Mn content. The Ti-Mn alloys show good compressive properties, with Ti-17Mn showing a compressive 0.2% proof stress of 1034MPa, and a compressive strain of 50%. Copyright © 2016 Elsevier Ltd. All rights reserved.

Dielectric, thermal and mechanical properties of zirconium silicate reinforced high density polyethylene composites for antenna applications.

PubMed

Varghese, Jobin; Nair, Dinesh Raghavan; Mohanan, Pezholil; Sebastian, Mailadil Thomas

2015-06-14

A low cost and low dielectric loss zirconium silicate (ZrSiO4) reinforced HDPE (high-density polyethylene) composite has been developed for antenna applications. The 0-3 type composite is prepared by dispersing ZrSiO4 fillers for various volume fractions (0.1 to 0.5) in the HDPE matrix by the melt mixing process. The composite shows good microwave dielectric properties with a relative permittivity of 5.6 and a dielectric loss of 0.003 at 5 GHz at the maximum filler loading of 0.5 volume fraction. The composite exhibits low water absorption, excellent thermal and mechanical properties. It shows a water absorption of 0.03 wt%, a coefficient of thermal expansion of 70 ppm per °C and a room temperature thermal conductivity of 2.4 W mK(-1). The composite shows a tensile strength of 22 MPa and a microhardness of 13.9 kg mm(-2) for the filler loading of 0.5 volume fraction. The HDPE-ZrSiO4 composites show good dielectric, thermal and mechanical properties suitable for microwave soft substrate applications. A microstrip patch antenna is designed and fabricated using the HDPE-0.5 volume fraction ZrSiO4 substrate and the antenna parameters are investigated.

Graphene oxide/alginate beads as adsorbents: Influence of the load and the drying method on their physicochemical-mechanical properties and adsorptive performance.

PubMed

Platero, Emiliano; Fernandez, Maria Emilia; Bonelli, Pablo Ricardo; Cukierman, Ana Lea

2017-04-01

Graphene oxide/alginate beads were prepared from lab-synthesized graphene oxide, varying its content within the beads (0.05, 0.125, and 0.25wt.%). Ethanol-drying and lyophilization were compared as drying methods to obtain suitable adsorbents which were later tested to the removal of a model organic molecule (methylene blue). The morphological and textural properties of all the beads were characterized by scanning electron microscopy and N 2 adsorption/desorption isotherms at -196°C, respectively. Limited porosity was obtained for all cases (S BET <60m 2 /g). Uniaxial compression tests were performed to assess the mechanical properties of the beads. Ethanol-dried ones exhibited higher Young's elasticity modulus (E=192kPa) than the lyophilized samples (twice at 0.25wt.% graphene oxide loading), which disclosed breakage points at lower deformation percentages. Adsorption experiments were conducted and dye adsorption isotherms were obtained for the beads with the best removal performance. The experimental data were better fitted by the Langmuir model. The highest maximum adsorption capacity (4.25mmol/g) was obtained for the lyophilized beads with the highest graphene oxide content. Mechanical properties were found to be affected also by the dye adsorption. Copyright © 2016 Elsevier Inc. All rights reserved.

Structure and Mechanical Properties of As-Cast Ti–5Sn–xMo Alloys

PubMed Central

Yu, Hsing-Ning; Hsu, Hsueh-Chuan; Wu, Shih-Ching; Hsu, Shih-Kuang; Ho, Wen-Fu

2017-01-01

Ti–5Sn–xMo (x = 0, 1, 3, 5, 7.5, 10, 12.5, 15, 17.5, and 20 wt %) alloys were designed and prepared for application as implant materials with superior mechanical properties. The results demonstrated that the crystal structure and mechanical properties of Ti–5Sn–xMo alloys are highly affected by their Mo content. The as-cast microstructures of Ti–5Sn–xMo alloys transformed in the sequence of phases α′ → α″ → β, and the morphologies of the alloys changed from a lath structure to an equiaxed structure as the Mo content increased. The α″-phase Ti–5Sn–7.5Mo (80 GPa) and β-phase Ti–5Sn–10Mo (85 GPa) exhibited relatively low elastic moduli and had excellent elastic recovery angles of 27.4° and 37.8°, respectively. Furthermore, they exhibited high ductility and moderate strength, as evaluated using the three-point bending test. Search for a more suitable implant material by this study, Ti–5Sn–xMo alloys with 7.5 and 10 wt % Mo appear to be promising candidates because they demonstrate the optimal combined properties of microhardness, ductility, elastic modulus, and elastic recovery capability. PMID:28772820

[Structure and properties of colored dental tetragonal zirconia stabilized by yttrium ceramics].

PubMed

Yi, Yuan-fu; Wang, Chen; Wen, Ning; Lin, Yong-zhao; Tian, Jie-mo

2009-10-01

To investigate the structure, mechanical and low temperature aging properties of colored dental zirconia ceramics. 5 graded colored dental zirconia ceramics were made by adding colorants and their combinations into a 3Y-TZP (tetragonal zirconia stabilized by 3mol% yttrium) powder, the green body were compacted at 200 MPa, pre-sinter at 1,050 degrees C and maintained for 2 h, then densely sintered at 1,500 degrees C for 2 h. Specimens were cut from each of the 5 graded colored blocks. Physical, mechanical properties as well as chemical stability were tested, microstructure were observed, crystalline phase were identified by X-ray diffraction (XRD), aging properties were assessed by measurement of the relative content of monoclinic phase and bending strength testing. The overall density of colored zirconia ceramics was over 99.7%, linear shrinkage was about 20%, while thermal expansion coefficient was about 11 x 10(-6) x degrees C(-1), the crystalline phase was tetragonal, bending strength was over 900 MPa which was slightly lowered than that of the uncolored zirconia, fracture toughness was slightly higher. Good chemical stability in acetic acid was observed. After aging treatment, tetragonal-to-monoclinic phase transformation was detected up to 40%, while bending strength was not significantly degraded. The results showed that colored 3Y-TZP ceramics presented good mechanical properties even after aging treatments, and was suitable for dental clinical use.

Composites Based on Conducting Polymers and Carbon Nanomaterials for Heavy Metal Ion Sensing (Review).

PubMed

Deshmukh, Megha A; Shirsat, Mahendra D; Ramanaviciene, Almira; Ramanavicius, Arunas

2018-07-04

Current review signifies recent trends and challenges in the development of electrochemical sensors based on organic conducting polymers (OCPs), carbon nanotubes (CNTs) and their composites for the determination of trace heavy metal ions in water are reviewed. OCPs and CNTs have some suitable properties, such as good electrical, mechanical, chemical and structural properties as well as environmental stability, etc. However, some of these materials still have significant limitations toward selective and sensitive detection of trace heavy metal ions. To overcome the limitations of these individual materials, OCPs/CNTs composites were developed. Application of OCPs/CNTs composite and their novel properties for the adsorption and detection of heavy metal ions outlined and discussed in this review.

Evaluation of Aluminum Alloy 2050-T84 Microstructure and Mechanical Properties at Ambient and Cryogenic Temperatures

NASA Technical Reports Server (NTRS)

Hafley, Robert A.; Domack, Marcia S.; Hales, Stephen J.; Shenoy, Ravi N.

2011-01-01

Aluminum alloy 2050 is being considered for the fabrication of cryogenic propellant tanks to reduce the mass of future heavy-lift launch vehicles. The alloy is available in section thicknesses greater than that of the incumbent aluminum alloy, 2195, which will enable designs with greater structural efficiency. While ambient temperature design allowable properties are available for alloy 2050, cryogenic properties are not available. To determine its suitability for use in cryogenic propellant tanks, tensile, compression and fracture tests were conducted on 4 inch thick 2050-T84 plate at ambient temperature and at -320degF. Various metallurgical analyses were also performed in order to provide an understanding of the compositional homogeneity and microstructure of 2050.

Actuators Based on Liquid Crystalline Elastomer Materials

PubMed Central

Jiang, Hongrui; Li, Chensha; Huang, Xuezhen

2013-01-01

Liquid crystalline elastomers (LCEs) exhibit a number of remarkable physical effects, including the unique, high-stroke reversible mechanical actuation when triggered by external stimuli. This article reviews some recent exciting developments in the field of LCEs materials with an emphasis on their utilization in actuator applications. Such applications include artificial muscles, industrial manufacturing, health and microelectromechanical systems (MEMS). With suitable synthetic and preparation pathways and well-controlled actuation stimuli, such as heat, light, electric and magnetic field, excellent physical properties of LCE materials can be realized. By comparing the actuating properties of different systems, general relationships between the structure and the property of LCEs are discussed. How these materials can be turned into usable devices using interdisciplinary techniques is also described. PMID:23648966

Actuators based on liquid crystalline elastomer materials

NASA Astrophysics Data System (ADS)

Jiang, Hongrui; Li, Chensha; Huang, Xuezhen

2013-05-01

Liquid crystalline elastomers (LCEs) exhibit a number of remarkable physical effects, including the unique, high-stroke reversible mechanical actuation when triggered by external stimuli. This article reviews some recent exciting developments in the field of LCE materials with an emphasis on their utilization in actuator applications. Such applications include artificial muscles, industrial manufacturing, health and microelectromechanical systems (MEMS). With suitable synthetic and preparation pathways and well-controlled actuation stimuli, such as heat, light, electric and magnetic fields, excellent physical properties of LCE materials can be realized. By comparing the actuating properties of different systems, general relationships between the structure and the properties of LCEs are discussed. How these materials can be turned into usable devices using interdisciplinary techniques is also described.

Mechanical properties of orthodontic wires made of super engineering plastic.

PubMed

Maekawa, Minami; Kanno, Zuisei; Wada, Takahiro; Hongo, Toshio; Doi, Hisashi; Hanawa, Takao; Ono, Takashi; Uo, Motohiro

2015-01-01

Most orthodontic equipment is fabricated from alloys such as stainless steel, Co-Cr and Ni-Ti because of their excellent elastic properties. In recent years, increasing esthetic demands, metal allergy and interference of metals with magnetic resonance imaging have driven the development of non-metallic orthodontic materials. In this study, we assessed the feasibility of using three super engineering plastics (PEEK, PES and PVDF) as orthodontic wires. PES and PVDF demonstrated excellent esthetics, although PEEK showed the highest bending strength and creep resistance. PEEK and PVDF showed quite low water absorption. Because of recent developments in coloration of PEEK, we conclude that PEEK has many advantageous properties that make it a suitable candidate for use as an esthetic metal-free orthodontic wire.

Development of polysilsesquioxane composites

NASA Technical Reports Server (NTRS)

Srinivasan, K.; Tiwari, S. N.

1990-01-01

Polymer composites are increasingly being required to operate for prolonged durations at higher temperatures than in the past. Hence there have been increased efforts devoted to synthesizing and characterizing polymers capable of withstanding temperatures greater than 300 C for long periods. Several such organic polymers have been investigated in recent times. This research effort seeks to enquire if inorganic polymers can be utilized to provide the same result. Ceramics have long been recognized as providing superior thermal properties for demanding applications. However, the extremely high softening temperatures preclude their being shaped into complex shapes through melt processing techniques common to organic polymers. One approach towards solving this problem has been through the development of preceramic polymers. These are capable of being processed in the polymeric state with ease, and subsequently being pyrolyzed to ceramic structures. This experimental study is aimed at studying the feasibility of using preceramic polymers (that have not been subject to the pyrolysis step) as high performance composite matrices for high temperature applications. A preliminary study of this nature is not geared towards optimizing mechanical properties suitable for such composites. Rather, this study attempts to process such resins in composite form and suitably characterize their properties.

Formulation development and evaluation of metformin chewing gum with bitter taste masking

PubMed Central

Mostafavi, Sayed Abolfazl; Varshosaz, Jaleh; Arabian, Saber

2014-01-01

Background: Medicated gums are intended to be chewed and act either locally, absorbed via the buccal mucosa or swallowed with saliva. We prepared the metformin gum to overcome its side effects including vomiting, diarrhea, and abdomen discomfort. Furthermore, it could be useful for those who have swallowing problems. Materials and Methods: Metformin hydrochloride (250 mg) with suitable sweeteners was mixed manually for 5 min. This mixture was spray dried, freeze dried, or directly mixed with chewing gum base. Glycerin, xylitol, and menthol were added and the produced paste was kept in the freezer for 2 h to be stable. As the metformin shows bitter taste, we tried to mask this unpleasant taste with using different methods explained. The releasing pattern was evaluated by using a mechanical chewing machine. The best formulation with the optimized releasing pattern, suitable physicochemical properties and pleasant taste were selected. Content uniformity, releasing percent, and other physicochemical properties were identified as well. Taste, flavor, and appearance characteristics were evaluated by using a self-made questionnaire based on the hedonic test method. Results: The chewing gum dosage content was about 86.2%. The release rate of metformin chewing gum was about 70% after 5 min of mastication. Masking the bitter taste of drug was achieved by using acesulfame-isomalt as sweeteners and prepared it by freeze drying equipment. Conclusion: Metfornin chewing gum had suitable appearance and appropriate invitro characteristics that fallow the pharmacopeia suggestions. This chewable gum showed bitterness suppression with a suitable release rate. PMID:24800181

Why Do Silver Trimers Intercalated in DNA Exhibit Unique Nonlinear Properties That Are Promising for Applications?

PubMed

Bonačić-Koutecký, Vlasta; Perić, Martina; Sanader, Željka

2018-05-17

Our investigation of one-photon absorption (OPA) and nonlinear optical (NLO) properties such as two-photon absorption (TPA) of silver trimer intercalated in DNA based on TDDFT approach allowed us to propose a mechanism responsible for large TPA cross sections of such NLO-phores. We present a concept that illustrates the key role of quantum cluster as well as of nucleotide bases from the immediate neighborhood. For this purpose, different surroundings consisting of guanine-cytosine and adenine-thymine such as (GCGC) and (ATAT) have been investigated that are exhibiting substantially different values of TPA cross sections. This has been confirmed by extending the immediate surroundings as well as using the two-layer quantum mechanics/molecular mechanics (QM/MM) approach. We focus on the cationic closed-shell system and illustrate that the neutral open-shell system shifts OPA spectra into the NIR regime, which is suitable for applications. Thus, in this contribution, we propose novel NLO-phores inducing large TPA cross sections, opening the route for multiphoton imaging.

Effect of sonication frequency on the disruption of algae.

PubMed

Kurokawa, Masaki; King, Patrick M; Wu, Xiaoge; Joyce, Eadaoin M; Mason, Timothy J; Yamamoto, Ken

2016-07-01

In this study, the efficiency of ultrasonic disruption of Chaetoceros gracilis, Chaetoceros calcitrans, and Nannochloropsis sp. was investigated by applying ultrasonic waves of 0.02, 0.4, 1.0, 2.2, 3.3, and 4.3 MHz to algal suspensions. The results showed that reduction in the number of algae was frequency dependent and that the highest efficiency was achieved at 2.2, 3.3, and 4.3MHz for C. gracilis, C. calcitrans, and Nannochloropsis sp., respectively. A review of the literature suggested that cavitation, rather than direct effects of ultrasonication, are required for ultrasonic algae disruption, and that chemical effects are likely not the main mechanism for algal cell disruption. The mechanical resonance frequencies estimated by a shell model, taking into account elastic properties, demonstrated that suitable disruption frequencies for each alga were associated with the cell's mechanical properties. Taken together, we consider here that physical effects of ultrasonication were responsible for algae disruption. Copyright © 2015 Elsevier B.V. All rights reserved.

Theoretical Investigations on the Influence of Artificially Altered Rock Mass Properties on Mechanical Excavation

NASA Astrophysics Data System (ADS)

Hartlieb, Philipp; Bock, Stefan

2018-03-01

This study presents a theoretical analysis of the influence of the rock mass rating on the cutting performance of roadheaders. Existing performance prediction models are assessed for their suitability for forecasting the influence of pre-damaging the rock mass with alternative methods like lasers or microwaves, prior to the mechanical excavation process. Finally, the RMCR model was chosen because it is the only reported model incorporating a range of rock mass properties into its calculations. The results show that even very tough rocks could be mechanically excavated if the occurrence, orientation and condition of joints are favourable for the cutting process. The calculated improvements in the cutting rate (m3/h) are up to 350% for the most favourable cases. In case of microwave irradiation of hard rocks with an UCS of 200 MPa, a reasonable improvement in the performance by 120% can be achieved with as little as an extra 0.7 kWh/m3 (= 1% more energy) compared to cutting only.

Detergent-enzymatic decellularization of swine blood vessels: insight on mechanical properties for vascular tissue engineering.

PubMed

Pellegata, Alessandro F; Asnaghi, M Adelaide; Stefani, Ilaria; Maestroni, Anna; Maestroni, Silvia; Dominioni, Tommaso; Zonta, Sandro; Zerbini, Gianpaolo; Mantero, Sara

2013-01-01

Small caliber vessels substitutes still remain an unmet clinical need; few autologous substitutes are available, while synthetic grafts show insufficient patency in the long term. Decellularization is the complete removal of all cellular and nuclear matters from a tissue while leaving a preserved extracellular matrix representing a promising tool for the generation of acellular scaffolds for tissue engineering, already used for various tissues with positive outcomes. The aim of this work is to investigate the effect of a detergent-enzymatic decellularization protocol on swine arteries in terms of cell removal, extracellular matrix preservation, and mechanical properties. Furthermore, the effect of storage at -80°C on the mechanical properties of the tissue is evaluated. Swine arteries were harvested, frozen, and decellularized; histological analysis revealed complete cell removal and preserved extracellular matrix. Furthermore, the residual DNA content in decellularized tissues was far low compared to native one. Mechanical testings were performed on native, defrozen, and decellularized tissues; no statistically significant differences were reported for Young's modulus, ultimate stress, compliance, burst pressure, and suture retention strength, while ultimate strain and stress relaxation of decellularized vessels were significantly different from the native ones. Considering the overall results, the process was confirmed to be suitable for the generation of acellular scaffolds for vascular tissue engineering.

Influence of carbon nanoparticle modification on the mechanical and electrical properties of epoxy in small volumes.

PubMed

Leopold, Christian; Augustin, Till; Schwebler, Thomas; Lehmann, Jonas; Liebig, Wilfried V; Fiedler, Bodo

2017-11-15

The influence of nanoparticle morphology and filler content on the mechanical and electrical properties of carbon nanoparticle modified epoxy is investigated regarding small volumes. Three types of particles, representing spherical, tubular and layered morphologies are used. A clear size effect of increasing true failure strength with decreasing volume is found for neat and carbon black modified epoxy. Carbon nanotube (CNT) modified epoxy exhibits high potential for strength increase, but dispersion and purity are critical. In few layer graphene modified epoxy, particles are larger than statistically distributed defects and initiate cracks, counteracting any size effect. Different toughness increasing mechanisms on the nano- and micro-scale depending on particle morphology are discussed based on scanning electron microscopy images. Electrical percolation thresholds in the small volume fibres are significantly higher compared to bulk volume, with CNT being found to be the most suitable morphology to form electrical conductive paths. Good correlation between electrical resistance change and stress strain behaviour under tensile loads is observed. The results show the possibility to detect internal damage in small volumes by measuring electrical resistance and therefore indicate to the high potential for using CNT modified polymers in fibre reinforced plastics as a multifunctional, self-monitoring material with improved mechanical properties. Copyright © 2017. Published by Elsevier Inc.

Optical mass memories

NASA Technical Reports Server (NTRS)

Bailey, G. A.

1976-01-01

Optical and magnetic variants in the design of trillion-bit read/write memories are compared and tabulated. Components and materials suitable for a random access read/write nonmoving memory system are examined, with preference given to holography and photoplastic materials. Advantages and deficiencies of photoplastics are reviewed. Holographic page composer design, essential features of an optical memory with no moving parts, fiche-oriented random access memory design, and materials suitable for an efficient photoplastic fiche are considered. The optical variants offer advantages in lower volume and weight at data transfer rates near 1 Mbit/sec, but power drain is of the same order as for the magnetic variants (tape memory, disk memory). The mechanical properties of photoplastic film materials still leave much to be desired.

Fabrication and characterization of carbon nanotube turfs

NASA Astrophysics Data System (ADS)

Qiu, Anqi

Carbon nanotube turfs are vertically aligned, slightly tortuous and entangled functional nanomaterials that exhibit high thermal and electrical properties. CNT turfs exhibit unique combinations of thermal and electrical conductivity, energy absorbing capability, low density and adhesive behavior. The objective of this study is to fabricate, measure, manipulate and characterize CNT turfs and thus determine the relationship between a turf's properties and its morphology, and provide guidance for developing links between turf growth conditions and of the subsequent turf properties. Nanoindentation was utilized to determine the mechanical and in situ electrical properties of CNT turfs. Elastic properties do not vary significantly laterally within a single turf, quantifying for the first time the ability to treat the turf as a mechanical continuum throughout. The use of the average mechanical properties for any given turf should be suitable for design purpose without the necessity of accounting for lateral spatial variation in structure. Properties variation based on time dependency, rate dependency, adhesive behavior and energy absorption and dissipation behavior have been investigated for these CNT turfs. Electrical properties measurements of CNT turfs have been carried out and show that a constant electrical current at a constant penetration depth indicates that a constant number of CNTs in contact with the tip; combining with the results that adhesive load increased with an increasing penetration hold time, thus we conclude that during a hold period of nanoindentation, individual tubes increase their individual attachment to the tip. CNT turfs show decreased adhesion and modulus after exposure to an electron beam due to carbon deposition and subsequent oxidation. To increase the modulus of the turf, axial compression and solvent capillary were used to increase the density of the turf by up to 15 times. Structure-property relationships were determined from the density and tortuosity measurements carried out through in situ electrical measurements and directionality measurements. Increasing density increases the mechanical properties as well as electrical conductivity. The modulus increased with a lower tortuosity, which may be related to the compressive buckling positioning.

Comparative studies of physical properties of kinesiotapes.

PubMed

Gołąb, Agnieszka; Kulesa-Mrowiecka, Małgorzata; Gołąb, Marek

2017-01-01

Nowadays we observe growing popularity of kinesiotaping as a supportive method in physiotherapy. In documents available on kinesiotaping we can find that mechanical properties of tapes are similar to the ones of a human skin, but usually there is hardly any numerical data characterizing these properties. Therefore, testing and comparing physical properties of commercially available kinesiotapes seems to be important. Physical properties of five commercially available kinesiotapes were examined. Strain vs. stress data was collected up to 15 N. Program Origin 9.0 was used for data analysis. The obtained results show that up to about 2 N the strain vs. stress characteristics of the tested tapes are similar while for greater stress they differ essentially. An alternative, to commonly used, way of defining relative strain is proposed. This definition could be more suitable in those cases when desired tape tensions are higher than 50% i.e. in ligament and tendon techniques.

Comparative acoustic performance and mechanical properties of silk membranes for the repair of chronic tympanic membrane perforations.

PubMed

Allardyce, Benjamin J; Rajkhowa, Rangam; Dilley, Rodney J; Xie, Zhigang; Campbell, Luke; Keating, Adrian; Atlas, Marcus D; von Unge, Magnus; Wang, Xungai

2016-12-01

The acoustic and mechanical properties of silk membranes of different thicknesses were tested to determine their suitability as a repair material for tympanic membrane perforations. Membranes of different thickness (10-100μm) were tested to determine their frequency response and their resistance to pressure loads in a simulated ear canal model. Their mechanical rigidity to pressure loads was confirmed by tensile testing. These membranes were tested alongside animal cartilage, currently the strongest available myringoplasty graft as well as paper, which is commonly used for simpler procedures. Silk membranes showed resonant frequencies within the human hearing range and a higher vibrational amplitude than cartilage, suggesting that silk may offer good acoustic energy transfer characteristics. Silk membranes were also highly resistant to simulated pressure changes in the middle ear, suggesting they can resist retraction, a common cause of graft failure resulting from chronic negative pressures in the middle ear. Part of this strength can be explained by the substantially higher modulus of silk films compared with cartilage. This allows for the production of films that are much thinner than cartilage, with superior acoustic properties, but that still provide the same level of mechanical support as thicker cartilage. Together, these in vitro results suggest that silk membranes may provide good hearing outcomes while offering similar levels of mechanical support to the reconstructed middle ear. Copyright © 2016 Elsevier Ltd. All rights reserved.

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors

PubMed Central

2012-01-01

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors. PMID:22643113

The influence of high temperatures on selected properties of calcium aluminous composites

NASA Astrophysics Data System (ADS)

KoÅáková, Dana; KoÅ¥átková, Jaroslava; Čáchová, Monika; Vejmelková, Eva; Čechmánek, René; Reiterman, Pavel; Černý, Robert

2017-07-01

The article compares different types of aluminate cements with the reference Portland cement, used in refractory composites. The rate of influence of elevated temperatures (400 °C and 1000 °C) is studied. The investigated parameters are basic physical characteristics and mechanical properties. Results show the best behaviour of the mixture containing Portland cement for the reference state (in the means of all studied parameters); which however after exposition to 1000 °C has the worst performance. Both aluminate cements behave better after heating, which proves its suitability for refractory composites. It is concluded, that the mixture with Gorkal cement achieves the best results.

Corundum ceramic materials modified with silica nanopowders: structure and mechanical properties

NASA Astrophysics Data System (ADS)

Kostytsyn, M. A.; Muratov, D. S.; Lysov, D. V.; Chuprunov, K. O.; Yudin, A. G.; Leybo, D. V.

2016-01-01

Filtering elements are often used in the metallurgy of rare earth metals. Corundum ceramic is one of the most suitable materials for this purpose. The process of formation and the properties of nanomodified ceramic materials, which are proposed as filtering materials with tunable effective porosity, are described. A silica nanopowder is used as a porosity-increasing agent. Vortex layer apparatus is used for mixing of precursor materials. The obtained results show that nanomodification with the vortex layer apparatus using 0.04 wt. % silica nanopowder as a modifying agent leads to an increase in the compression strength of corundum ceramic by the factor of 1.5.

Influence of Inherent Surface and Internal Defects on Mechanical Properties of Additively Manufactured Ti6Al4V Alloy: Comparison between Selective Laser Melting and Electron Beam Melting

PubMed Central

Fousová, Michaela; Vojtěch, Dalibor; Doubrava, Karel; Daniel, Matěj; Lin, Chiu-Feng

2018-01-01

Additive manufacture (AM) appears to be the most suitable technology to produce sophisticated, high quality, lightweight parts from Ti6Al4V alloy. However, the fatigue life of AM parts is of concern. In our study, we focused on a comparison of two techniques of additive manufacture—selective laser melting (SLM) and electron beam melting (EBM)—in terms of the mechanical properties during both static and dynamic loading. All of the samples were untreated to focus on the influence of surface condition inherent to SLM and EBM. The EBM samples were studied in the as-built state, while SLM was followed by heat treatment. The resulting similarity of microstructures led to comparable mechanical properties in tension, but, due to differences in surface roughness and specific internal defects, the fatigue strength of the EBM samples reached only half the value of the SLM samples. Higher surface roughness that is inherent to EBM contributed to multiple initiations of fatigue cracks, while only one crack initiated on the SLM surface. Also, facets that were formed by an intergranular cleavage fracture were observed in the EBM samples. PMID:29614712

Influence of Inherent Surface and Internal Defects on Mechanical Properties of Additively Manufactured Ti6Al4V Alloy: Comparison between Selective Laser Melting and Electron Beam Melting.

PubMed

Fousová, Michaela; Vojtěch, Dalibor; Doubrava, Karel; Daniel, Matěj; Lin, Chiu-Feng

2018-03-31

Additive manufacture (AM) appears to be the most suitable technology to produce sophisticated, high quality, lightweight parts from Ti6Al4V alloy. However, the fatigue life of AM parts is of concern. In our study, we focused on a comparison of two techniques of additive manufacture-selective laser melting (SLM) and electron beam melting (EBM)-in terms of the mechanical properties during both static and dynamic loading. All of the samples were untreated to focus on the influence of surface condition inherent to SLM and EBM. The EBM samples were studied in the as-built state, while SLM was followed by heat treatment. The resulting similarity of microstructures led to comparable mechanical properties in tension, but, due to differences in surface roughness and specific internal defects, the fatigue strength of the EBM samples reached only half the value of the SLM samples. Higher surface roughness that is inherent to EBM contributed to multiple initiations of fatigue cracks, while only one crack initiated on the SLM surface. Also, facets that were formed by an intergranular cleavage fracture were observed in the EBM samples.

Reuse of steel slag in bituminous paving mixtures.

PubMed

Sorlini, Sabrina; Sanzeni, Alex; Rondi, Luca

2012-03-30

This paper presents a comprehensive study to evaluate the mechanical properties and environmental suitability of electric arc furnace (EAF) steel slag in bituminous paving mixtures. A variety of tests were executed on samples of EAF slag to characterize the physical, geometrical, mechanical and chemical properties as required by UNI EN specifications, focusing additionally on the volumetric expansion associated with hydration of free CaO and MgO. Five bituminous mixtures of aggregates for flexible road pavement were designed containing up to 40% of EAF slag and were tested to determine Marshall stability and indirect tensile strength. The leaching behaviour of slag samples and bituminous mixtures was evaluated according to the UNI EN leaching test. The tested slag showed satisfactory physical and mechanical properties and a release of pollutants generally below the limits set by the Italian code. Tests on volume stability of fresh materials confirmed that a period of 2-3 months is necessary to reduce effects of oxides hydration. The results of tests performed on bituminous mixtures with EAF slag were comparable with the performance of mixtures containing natural aggregates and the leaching tests provided satisfactory results. Copyright © 2012 Elsevier B.V. All rights reserved.

Influence of copper composition on mechanical properties of biodegradable material Mg-Zn-Cu for orthopedic application

NASA Astrophysics Data System (ADS)

Purniawan, A.; Maulidiah, H. M.; Purwaningsih, H.

2018-04-01

Implant is usually used as a treatment of bone fracture. At the moment, non-biodegradable implants is still widely employed in this application. Non-biodegradable implant requires re-surgery to retrieve implants that are installed in the body. It increase the cost and it is painful for the patient itself. In order to solve the problem, Mg-based biodegradable metals is developing so that the material will be compatible with body and gradually degrade in patient's body. However, magnesium has several disadvantages such as high degradation rates and low mechanical properties when compared to the mechanical properties of natural bone. Therefore, it is necessary to add elements into the magnesium alloy. In this research, copper (Cu) was alloyed in Mg alloy based biodegradable material. In addition, Cu is not only strengthening the structure but also for supporting element for the immune system, antibacterial and antifungal. The purpose of this research is to improve mechanical properties of Mg-based biodegradable material using Cu alloying. Powder metallurgy method was used to fabricate the device. The variation used in this research is the composition of Cu (0.5, 1, and 1.5% Cu). The porosity test was performed using apparent porosity test, compressive test and hardness test to know the mechanical properties of the alloy, and the weightless test to find out the material degradation rate. Based on the results can be conclude that Mg-Zn-Cu alloy material with 1% Cu composition is the most suitable specimen to be applied as a candidate for orthopedic devices material with hardness value is 393.6 MPa. Also obtained the value of the compressive test is 153 MPa.

A new tensile impact test for the toughness characterization of sheet material

NASA Astrophysics Data System (ADS)

Könemann, Markus; Lenz, David; Brinnel, Victoria; Münstermann, Sebastian

2018-05-01

In the past, the selection of suitable steels has been carried out primarily based on the mechanical properties of different steels. One of these properties is the resistance against crack propagation. For many constructions, this value plays an important role, because it can compare the impact toughness of different steel grades easily and gives information about the loading capacity of the specific materials. For thin sheets, impact toughness properties were usually not considered. One of the reasons for this is that the Charpy-impact test is not applicable for sheets with thicknesses below 2 mm. For a long time, this was not relevant because conventional steels had a sufficient impact toughness in a wide temperature range. However, since new multiphase steel grades with improved mechanical property exploitations are available, it turned out that impact toughness properties need to be considered during the component design phase, as the activation of the cleavage fracture mechanism is observed under challenging loading conditions. Therefore, this work aims to provide a new and practical testing procedure for sheet material or thin walled structures. The new testing procedure is based on tensile tests conducted in an impact pendulum similar to the Charpy impact hammer. A new standard geometry is provided, which enables a comparison between different steels or steel grades. A connection to the conventional Charpy test is presented using a damage mechanics model, which predicts material failure with consideration of to the stress state at various temperatures. Different specimen geometries are analysed to cover manifold stress states. A special advantage of the damage mechanics model is also the possibility to predict the materials behaviour in the transition area. To verify the method a conventional steel was tested in Charpy tests as well as in the new tensile impact test.

Methodologies in determining mechanical properties of thin films using nanoindentation

NASA Astrophysics Data System (ADS)

Han, Seung Min Jane

Thin films are critical components of microelectronic and MEMS devices, and evaluating their mechanical properties is of current interest. As the dimensions of the devices become smaller and smaller, however, understanding the mechanical properties of materials at sub-micron length scales becomes more challenging. The conventional methods for evaluating strengths of materials in bulk form cannot be applied, and new methodologies are required for accurately evaluating mechanical properties of thin films. In this work, development of methodologies using the nanoindenter was pursued in three parts: (1) creation of a new method for extracting thin film hardness, (2) use of combinatorial methods for determining compositions with desired mechanical properties, and (3) use of microcompression testing of sub-micron sized pillars to understand plasticity in Al-Sc multilayers. The existing nanoindentation hardness model by Oliver & Pharr is unable to accurately determine the hardness of thin films on substrates with an elastic mismatch. Thus, a new method of analysis for extracting thin film hardness from film/substrate systems, that eliminates the effect of elastic mismatch of the underlying substrate, surface roughness, and also pile-up/sink-in, is needed. Such a method was developed in the first part of this study. The feasibility of using the nanoindentation hardness together with combinatorial methods to efficiently scan through mechanical properties of Ti-Al metallic alloys was examined in the second part of this study. The combinatorial approach provides an efficient method that can be used to determine alloy compositions that might merit further exploration and development as bulk materials. Finally, the mechanical properties of Al-Al3Sc multilayers with bilayer periods ranging from 6-100 nm were examined using microcompression. The sub-micron sized pillars were prepared using the focused ion beam (FIB) and compression tested with the flat tip of the nanoindenter. The measured yield strengths show the trend of increasing strength with decreasing bilayer period, and agree with the nanoindentation hardness results using the suitable Tabor correction factor. Strain softening was observed at large strains, and a new model for the true stress and true strain was developed to account for the inhomogeneous deformation geometry.

Properties of poly(lactic acid)/hydroxyapatite composite through the use of epoxy functional compatibilizers for biomedical application.

PubMed

Monmaturapoj, Naruporn; Srion, Autcharaporn; Chalermkarnon, Prasert; Buchatip, Suthawan; Petchsuk, Atitsa; Noppakunmongkolchai, Warobon; Mai-Ngam, Katanchalee

2017-08-01

A composite of 70/30 poly(lactic acid)/hydroxyapatite was systematically prepared using various amounts of glycidyl methacrylate as reactive compatibilizer or Joncryl ADR®-4368 containing nine glycidyl methacrylate functions as a chain extension/branching agent to improve the mechanical and biological properties for suitable usage as internal bone fixation devices. The effect of glycidyl methacrylate/Joncryl on mechanical properties of poly(lactic acid)/hydroxyapatite was investigated through flexural strength. Cell proliferation and differentiation of osteoblast-like MC3T3-E1 cells cultured on the composite samples were determined by Alamar Blue assay and alkaline phosphatase expression, respectively. Result shows that flexural strength tends to decrease, as glycidyl methacrylate content increases except for 1 wt.% glycidyl methacrylate. With an addition of dicumyl peroxide, the flexural strength shows an improvement than that of without dicumyl peroxide probably due to the chemical bonding of the hydroxyapatite and poly(lactic acid) as revealed by FTIR and NMR, whereas the composite with 5 wt.% Joncryl shows the best result, as the flexural strength increases getting close to pure poly(lactic acid). The significant morphology change could be seen in composite with Joncryl where the uniform agglomeration of hydroxyapatite particles oriented in poly(lactic acid) matrix. Addition of the epoxy functional compatibilizers at suitable percentages could also have benefits to cellular attachment, proliferation, differentiation and mineralization. So that, this poly(lactic acid)/hydroxyapatite composite could be a promising material to be used as internal bone fixation devices such as screws, pins and plates.

Physical and antibacterial properties of açaí edible films formulated with thyme essential oil and apple skin polyphenols.

PubMed

Espitia, Paula J P; Avena-Bustillos, Roberto J; Du, Wen-Xian; Chiou, Bor-Sen; Williams, Tina G; Wood, Delilah; McHugh, Tara H; Soares, Nilda F F

2014-05-01

Thyme essential oil (TEO) and apple skin polyphenols (ASP) are natural compounds considered as generally recognized as safe by FDA, with biological effects against bacteria and fungi. This work aimed to evaluate physical and antimicrobial properties of açaí edible films formulated with TEO and ASP at 3% and 6% (w/w) individually or combined at 3% (w/w) each. Physical properties studied include mechanical resistance, water vapor permeability (WVP), color, and thermal resistance. Antimicrobial activity against Listeria monocytogenes was determined using the overlay diffusion test. Addition of ASP resulted in improved mechanical properties. TEO at 6% (w/w) resulted in increased elongation. ASP films had significant higher WVP than control film. ASP films were lighter and had more red color than other films. Incorporation of ASP resulted in improved film thermal stability, whereas TEO caused rapid thermal decomposition. Presence of clusters was observed on the surface of films. Addition of ASP resulted in a smoother surface, whereas addition of TEO led to the formation of crater-like pits on the film surface. Açaí edible film incorporated with 6% (w/w) TEO presented the highest antimicrobial activity. However, both antimicrobials are necessary in the açaí films in order to obtain edible films with suitable physical-mechanical properties. The results of the present study showed that TEO and ASP can be used to prepare açaí edible films with adequate physical-mechanical properties and antimicrobial activity for food applications by direct contact. Developed açaí edible films presented antimicrobial activity against L. monocytogenes and good physical-mechanical properties, showing the potential use of açaí edible films in food preservation. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Thermomechanical Properties of Polylactic Acid-Graphene Composites: A State-of-the-Art Review for Biomedical Applications

PubMed Central

2017-01-01

Due to its biodegradable and bioabsorbable characteristics polylactic acid (PLA) has attracted considerable attention for numerous biomedical applications. Moreover, a number of tissue engineering problems for function restoration of impaired tissues have been addressed by using PLA and its copolymers due to their biocompatibility and distinctive mechanical properties. Recent studies on various stereocomplex formation between enantiomeric PLA, poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) indicated that stereocomplexation enhances the mechanical properties as well as the thermal- and hydrolysis-resistance of PLA polymers. On the other hand, biomedical application of graphene is a relatively new front with significant potential. Many recent reports have indicated that understanding of graphene-cell (or tissue, organ) interactions; particularly the cellular uptake mechanisms are still challenging. Therefore, use of graphene or graphene oxide properly embedded in suitable PLA matrices can positively impact and accelerate the growth, differentiation, and proliferation of stem cells, conceivably minimizing concerns over cytotoxicity of graphene. As such, PLA-graphene composites hold great promise in tissue engineering, regenerative medicine, and in other biomedical fields. However, since PLA is classified as a hard bio-polyester prone to hydrolysis, understanding and engineering of thermo-mechanical properties of PLA-graphene composites are very crucial for such cutting-edge applications. Hence, this review aims to present an overview of current advances in the preparation and applications of PLA-graphene composites and their properties with focus on various biomedical uses such as scaffolds, drug delivery, cancer therapy, and biological imaging, together with a brief discussion on the challenges and perspectives for future research in this field. PMID:28773109

Bundles of Spider Silk, Braided into Sutures, Resist Basic Cyclic Tests: Potential Use for Flexor Tendon Repair

PubMed Central

Hennecke, Kathleen; Redeker, Joern; Kuhbier, Joern W.; Strauss, Sarah; Allmeling, Christina; Kasper, Cornelia; Reimers, Kerstin; Vogt, Peter M.

2013-01-01

Repair success for injuries to the flexor tendon in the hand is often limited by the in vivo behaviour of the suture used for repair. Common problems associated with the choice of suture material include increased risk of infection, foreign body reactions, and inappropriate mechanical responses, particularly decreases in mechanical properties over time. Improved suture materials are therefore needed. As high-performance materials with excellent tensile strength, spider silk fibres are an extremely promising candidate for use in surgical sutures. However, the mechanical behaviour of sutures comprised of individual silk fibres braided together has not been thoroughly investigated. In the present study, we characterise the maximum tensile strength, stress, strain, elastic modulus, and fatigue response of silk sutures produced using different braiding methods to investigate the influence of braiding on the tensile properties of the sutures. The mechanical properties of conventional surgical sutures are also characterised to assess whether silk offers any advantages over conventional suture materials. The results demonstrate that braiding single spider silk fibres together produces strong sutures with excellent fatigue behaviour; the braided silk sutures exhibited tensile strengths comparable to those of conventional sutures and no loss of strength over 1000 fatigue cycles. In addition, the braiding technique had a significant influence on the tensile properties of the braided silk sutures. These results suggest that braided spider silk could be suitable for use as sutures in flexor tendon repair, providing similar tensile behaviour and improved fatigue properties compared with conventional suture materials. PMID:23613793

Microstructure, mechanical properties, bio-corrosion properties and cytotoxicity of as-extruded Mg-Sr alloys.

PubMed

Zhao, Chaoyong; Pan, Fusheng; Zhang, Lei; Pan, Hucheng; Song, Kai; Tang, Aitao

2017-01-01

In this study, as-extruded Mg-Sr alloys were studied for orthopedic application, and the microstructure, mechanical properties, bio-corrosion properties and cytotoxicity of as-extruded Mg-Sr alloys were investigated by optical microscopy, scanning electron microscopy with an energy dispersive X-ray spectroscopy, X-ray diffraction, tensile and compressive tests, immersion test, electrochemical test and cytotoxicity test. The results showed that as-extruded Mg-Sr alloys were composed of α-Mg and Mg 17 Sr 2 phases, and the content of Mg 17 Sr 2 phases increased with increasing Sr content. As-extruded Mg-Sr alloy with 0.5wt.% Sr was equiaxed grains, while the one with a higher Sr content was long elongated grains and the grain size of the long elongated grains decreased with increasing Sr content. Tensile and compressive tests showed an increase of both tensile and compressive strength and a decrease of elongation with increasing Sr content. Immersion and electrochemical tests showed that as-extruded Mg-0.5Sr alloy exhibited the best anti-corrosion property, and the anti-corrosion property of as-extruded Mg-Sr alloys deteriorated with increasing Sr content, which was greatly associated with galvanic couple effect. The cytotoxicity test revealed that as-extruded Mg-0.5Sr alloy did not induce toxicity to cells. These results indicated that as-extruded Mg-0.5Sr alloy with suitable mechanical properties, corrosion resistance and good cytocompatibility was potential as a biodegradable implant for orthopedic application. Copyright © 2016 Elsevier B.V. All rights reserved.

Indium telluride nanotubes: Solvothermal synthesis, growth mechanism, and properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Liyan; Yan, Shancheng, E-mail: yansc@njupt.edu.cn; School of Geography and Biological Information, Nanjing University of Posts and Telecommunications, Nanjing 210046

2014-03-15

A convenient solvothermal approach was applied for the first time to synthesize In{sub 2}Te{sub 3} nanotubes. The morphology of the resultant nanotubes was studied by scanning electron microscopy and transmission electron microscopy. Nanotubes with a relatively uniform diameter of around 500 nm, tube wall thickness of 50–100 nm, and average length of tens of microns were obtained. X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy were used to study the crystal structures, composition, and optical properties of the products. To understand the growth mechanism of the In{sub 2}Te{sub 3} nanotubes, we studied the influences of temperature, reaction time, and polyvinylpyrrolidonemore » (PVP) and ethylene diamine (EDA) dosages on the final products. Based on the experimental results, a possible growth mechanism of In{sub 2}Te{sub 3} nanotubes was proposed. In this mechanism, TeO{sub 3}{sup −2} is first reduced to allow nucleation. Circumferential edges of these nucleated molecules attract further deposition, and nanotubes finally grow rapidly along the c-axis and relatively slowly along the circumferential direction. The surface area of the products was determined by BET and found to be 137.85 m{sup 2} g{sup −1}. This large surface area indicates that the nanotubes may be suitable for gas sensing and hydrogen storage applications. The nanotubes also showed broad light detection ranging from 300 nm to 1100 nm, which covers the UV–visible–NIR regions. Such excellent optical properties indicate that In{sub 2}Te{sub 3} nanotubes may enable significant advancements in new photodetection and photosensing applications. -- Graphical abstract: A convenient solvothermal approach was applied to synthesize In{sub 2}Te{sub 3} nanotubes, which has not been reported in the literature for our knowledge. Surface area of this material is 137.85 m{sup 2} g{sup −1} from the BET testing, and such a high value makes it probably suitable for gas sensing and hydrogen storage, compared with the nanowires. The nanotube device also has a broad light detection range from 300 nm to 1100 nm, covering the UV–visible–NIR region. This good performance of In{sub 2}Te{sub 3} nanotubes may enable significant advancements of new photodetection and photosensing applications. Highlights: • The In{sub 2}Te{sub 3} nanotube device also has a broad light detection range from 300 nm to 1100 nm. • The nanotube is 137.85 m{sup 2} g{sup −1}, which makes it suitable for gas sensing and hydrogen storage. • A possible growth mechanism of the indium telluride nanotubes was proposed. • In addition, no In{sub 2}Te{sub 3} nanotubes have been reported until now.« less

Fibrin gels exhibit improved biological, structural, and mechanical properties compared with collagen gels in cell-based tendon tissue-engineered constructs.

PubMed

Breidenbach, Andrew P; Dyment, Nathaniel A; Lu, Yinhui; Rao, Marepalli; Shearn, Jason T; Rowe, David W; Kadler, Karl E; Butler, David L

2015-02-01

The prevalence of tendon and ligament injuries and inadequacies of current treatments is driving the need for alternative strategies such as tissue engineering. Fibrin and collagen biopolymers have been popular materials for creating tissue-engineered constructs (TECs), as they exhibit advantages of biocompatibility and flexibility in construct design. Unfortunately, a few studies have directly compared these materials for tendon and ligament applications. Therefore, this study aims at determining how collagen versus fibrin hydrogels affect the biological, structural, and mechanical properties of TECs during formation in vitro. Our findings show that tendon and ligament progenitor cells seeded in fibrin constructs exhibit improved tenogenic gene expression patterns compared with their collagen-based counterparts for approximately 14 days in culture. Fibrin-based constructs also exhibit improved cell-derived collagen alignment, increased linear modulus (2.2-fold greater) compared with collagen-based constructs. Cyclic tensile loading, which promotes the maturation of tendon constructs in a previous work, exhibits a material-dependent effect in this study. Fibrin constructs show trending reductions in mechanical, biological, and structural properties, whereas collagen constructs only show improved tenogenic expression in the presence of mechanical stimulation. These findings highlight that components of the mechanical stimulus (e.g., strain amplitude or time of initiation) need to be tailored to the material and cell type. Given the improvements in tenogenic expression, extracellular matrix organization, and material properties during static culture, in vitro findings presented here suggest that fibrin-based constructs may be a more suitable alternative to collagen-based constructs for tissue-engineered tendon/ligament repair.

Fibrin Gels Exhibit Improved Biological, Structural, and Mechanical Properties Compared with Collagen Gels in Cell-Based Tendon Tissue-Engineered Constructs

PubMed Central

Dyment, Nathaniel A.; Lu, Yinhui; Rao, Marepalli; Shearn, Jason T.; Rowe, David W.; Kadler, Karl E.; Butler, David L.

2015-01-01

The prevalence of tendon and ligament injuries and inadequacies of current treatments is driving the need for alternative strategies such as tissue engineering. Fibrin and collagen biopolymers have been popular materials for creating tissue-engineered constructs (TECs), as they exhibit advantages of biocompatibility and flexibility in construct design. Unfortunately, a few studies have directly compared these materials for tendon and ligament applications. Therefore, this study aims at determining how collagen versus fibrin hydrogels affect the biological, structural, and mechanical properties of TECs during formation in vitro. Our findings show that tendon and ligament progenitor cells seeded in fibrin constructs exhibit improved tenogenic gene expression patterns compared with their collagen-based counterparts for approximately 14 days in culture. Fibrin-based constructs also exhibit improved cell-derived collagen alignment, increased linear modulus (2.2-fold greater) compared with collagen-based constructs. Cyclic tensile loading, which promotes the maturation of tendon constructs in a previous work, exhibits a material-dependent effect in this study. Fibrin constructs show trending reductions in mechanical, biological, and structural properties, whereas collagen constructs only show improved tenogenic expression in the presence of mechanical stimulation. These findings highlight that components of the mechanical stimulus (e.g., strain amplitude or time of initiation) need to be tailored to the material and cell type. Given the improvements in tenogenic expression, extracellular matrix organization, and material properties during static culture, in vitro findings presented here suggest that fibrin-based constructs may be a more suitable alternative to collagen-based constructs for tissue-engineered tendon/ligament repair. PMID:25266738

Prediction of trabecular bone qualitative properties using scanning quantitative ultrasound

PubMed Central

Qin, Yi-Xian; Lin, Wei; Mittra, Erik; Xia, Yi; Cheng, Jiqi; Judex, Stefan; Rubin, Clint; Müller, Ralph

2012-01-01

Microgravity induced bone loss represents a critical health problem in astronauts, particularly occurred in weight-supporting skeleton, which leads to osteopenia and increase of fracture risk. Lack of suitable evaluation modality makes it difficult for monitoring skeletal status in long term space mission and increases potential risk of complication. Such disuse osteopenia and osteoporosis compromise trabecular bone density, and architectural and mechanical properties. While X-ray based imaging would not be practical in space, quantitative ultrasound may provide advantages to characterize bone density and strength through wave propagation in complex trabecular structure. This study used a scanning confocal acoustic diagnostic and navigation system (SCAN) to evaluate trabecular bone quality in 60 cubic trabecular samples harvested from adult sheep. Ultrasound image based SCAN measurements in structural and strength properties were validated by μCT and compressive mechanical testing. This result indicated a moderately strong negative correlations observed between broadband ultrasonic attenuation (BUA) and μCT-determined bone volume fraction (BV/TV, R2=0.53). Strong correlations were observed between ultrasound velocity (UV) and bone’s mechanical strength and structural parameters, i.e., bulk Young’s modulus (R2=0.67) and BV/TV (R2=0.85). The predictions for bone density and mechanical strength were significantly improved by using a linear combination of both BUA and UV, yielding R2=0.92 for BV/TV and R2=0.71 for bulk Young’s modulus. These results imply that quantitative ultrasound can characterize trabecular structural and mechanical properties through measurements of particular ultrasound parameters, and potentially provide an excellent estimation for bone’s structural integrity. PMID:23976803

Prediction of trabecular bone qualitative properties using scanning quantitative ultrasound

NASA Astrophysics Data System (ADS)

Qin, Yi-Xian; Lin, Wei; Mittra, Erik; Xia, Yi; Cheng, Jiqi; Judex, Stefan; Rubin, Clint; Müller, Ralph

2013-11-01

Microgravity induced bone loss represents a critical health problem in astronauts, particularly occurred in weight-supporting skeleton, which leads to osteopenia and increase of fracture risk. Lack of suitable evaluation modality makes it difficult for monitoring skeletal status in long term space mission and increases potential risk of complication. Such disuse osteopenia and osteoporosis compromise trabecular bone density, and architectural and mechanical properties. While X-ray based imaging would not be practical in space, quantitative ultrasound may provide advantages to characterize bone density and strength through wave propagation in complex trabecular structure. This study used a scanning confocal acoustic diagnostic and navigation system (SCAN) to evaluate trabecular bone quality in 60 cubic trabecular samples harvested from adult sheep. Ultrasound image based SCAN measurements in structural and strength properties were validated by μCT and compressive mechanical testing. This result indicated a moderately strong negative correlations observed between broadband ultrasonic attenuation (BUA) and μCT-determined bone volume fraction (BV/TV, R2=0.53). Strong correlations were observed between ultrasound velocity (UV) and bone's mechanical strength and structural parameters, i.e., bulk Young's modulus (R2=0.67) and BV/TV (R2=0.85). The predictions for bone density and mechanical strength were significantly improved by using a linear combination of both BUA and UV, yielding R2=0.92 for BV/TV and R2=0.71 for bulk Young's modulus. These results imply that quantitative ultrasound can characterize trabecular structural and mechanical properties through measurements of particular ultrasound parameters, and potentially provide an excellent estimation for bone's structural integrity.

Mechanical properties of haynes alloy 188 after 22,500 hours of exposure to LiF-22CaF2 and vacuum at 1093 K

NASA Astrophysics Data System (ADS)

Whittenberger, J. D.

1994-12-01

As a continuation of a study of a space-based thermal energy storage system centered on a LiF-CaF2 eutectic salt contained by Haynes alloy 188, this Co-base superalloy was subjected to molten salt, its vapor, and vacuum for 22,500 h at 1093 K. Samples from all three exposure conditions were tensile tested between 77 to 1200 K; in addition, vacuum and molten-salt exposed specimens were vacuum creep rupture tested at 1050 K. Comparison of these mechanical properties with those measured for the as-received alloy reveals no evidence for degradation beyond that ascribed to simple thermal aging of Haynes alloy 188. This behavior is identical to the 10,000 h results (Ref 3); hence, Haynes alloy 188 is a suitable containment material for an eutectic LiF-CaF2 thermal energy storage salt.

Synthesis, crystal growth, structural, thermal, optical and mechanical properties of solution grown 4-methylpyridinium 4-hydroxybenzoate single crystal.

PubMed

Sudhahar, S; Krishna Kumar, M; Sornamurthy, B M; Mohan Kumar, R

2014-01-24

Organic nonlinear optical material, 4-methylpyridinium 4-hydroxybenzoate (4MPHB) was synthesized and single crystal was grown by slow evaporation solution growth method. Single crystal and powder X-ray diffraction analyses confirm the structure and crystalline perfection of 4MPHB crystal. Infrared, Raman and NMR spectroscopy techniques were used to elucidate the functional groups present in the compound. TG-DTA analysis was carried out in nitrogen atmosphere to study the decomposition stages, endothermic and exothermic reactions. UV-visible and Photoluminescence spectra were recorded for the grown crystal to estimate the transmittance and band gap energy respectively. Linear refractive index, birefringence, and SHG efficiency of the grown crystal were studied. Laser induced surface damage threshold and mechanical properties of grown crystal were studied to assess the suitability of the grown crystals for device applications. Copyright © 2013 Elsevier B.V. All rights reserved.

Towards the miniaturization of monolithic folded pendulums: a new approach to the implementation of small and light sensors for ground, space, and marine applications

NASA Astrophysics Data System (ADS)

Barone, F.; Giordano, G.

2018-03-01

The UNISA Folded Pendulum technological platform is very promising for the implementation of high sensitive, large band miniaturized mechanical seismometers and accelerometers in different materials. In fact, the symmetry of its mechanical architecture allows to take full advantage of one of the most relevant properties of the folded pendulum, that is the scalability. This property is very useful for the design of folded pendulums of small size and weight, provided with a suitable combination of physical and geometrical parameters. Using a lagrangian simplified model of folded pendulum, we present and discuss this idea, showing different possible approaches that may lead to the miniaturization of a folded pendulum. Finally we present a first prototype of miniaturized folded pendulum, discussing its characteristics and limitations, in connection with scientific ground, marine and space applications.

Improved Mechanical Properties of Various Fabric-Reinforced Geocomposite at Elevated Temperature

NASA Astrophysics Data System (ADS)

Samal, Sneha; Phan Thanh, Nhan; Petríková, Iva; Marvalová, Bohadana

2015-07-01

This article signifies the improved performance of the various types of fabric reinforcement of geopolymer as a function of physical, thermal, mechanical, and heat-resistant properties at elevated temperatures. Geopolymer mixed with designed Si:Al ratios of 15.6 were synthesized using three different types of fabric reinforcement such as carbon, E-glass, and basalt fibers. Heat testing was conducted on 3-mm-thick panels with 15 × 90 mm surface exposure region. The strength of carbon-based geocomposite increased toward a higher temperature. The basalt-reinforced geocomposite strength decreased due to the catastrophic failure in matrix region. The poor bridging effect and dissolution of fabric was observed in the E-glass-reinforced geocomposite. At an elevated temperature, fiber bridging was observed in carbon fabric-reinforced geopolymer matrix. Among all the fabrics, carbon proved to be suitable candidate for the high-temperature applications in thermal barrier coatings and fire-resistant panels.

Comparison of physical and mechanical properties of river sand concrete with quarry dust concrete

NASA Astrophysics Data System (ADS)

Opara, Hyginus E.; Eziefula, Uchechi G.; Eziefula, Bennett I.

2018-03-01

This study compared the physical and mechanical properties of river sand concrete with quarry dust concrete. The constituent materials were batched by weight. The water-cement ratio and mix ratio selected for the experimental investigation were 0.55 and 1:2:4, respectively. The specimens were cured for 7, 14, 21 and 28 days. Slump, density and compressive strength tests were carried out. The results showed that river sand concrete had greater density and compressive strength than quarry dust concrete for all curing ages. At 28 days of curing, river sand concrete exceeded the target compressive strength by 36%, whereas quarry dust concrete was less than the target compressive strength by 12%. Both river sand concrete and quarry dust concrete for the selected water/cement ratio and mix ratio are suitable for non-structural applications and lightly-loaded members where high strength is not a prerequisite.

Preparation and characterization of malonic acid cross-linked chitosan and collagen 3D scaffolds: an approach on non-covalent interactions.

PubMed

Mitra, Tapas; Sailakshmi, G; Gnanamani, A; Mandal, A B

2012-05-01

The present study emphasizes the influence of non-covalent interactions on the mechanical and thermal properties of the scaffolds of chitosan/collagen origin. Malonic acid (MA), a bifuncitonal diacid was chosen to offer non-covalent cross-linking. Three dimensional scaffolds was prepared using chitosan at 1.0% (w/v) and MA at 0.2% (w/v), similarly collagen 0.5% (w/v) and MA 0.2% (w/v) and characterized. Results on FT-IR, TGA, DSC, SEM and mechanical properties (tensile strength, stiffness, Young's modulus, etc.) assessment demonstrated the existence of non-covalent interaction between MA and chitosan/collagen, which offered flexibility and high strength to the scaffolds suitable for tissue engineering research. Studies using NIH 3T3 fibroblast cells suggested biocompatibility nature of the scaffolds. Docking simulation study further supports the intermolecular hydrogen bonding interactions between MA and chitosan/collagen.

Biomimetic Silk Scaffolds with an Amorphous Structure for Soft Tissue Engineering.

PubMed

Sang, Yonghuan; Li, Meirong; Liu, Jiejie; Yao, Yuling; Ding, Zhaozhao; Wang, Lili; Xiao, Liying; Lu, Qiang; Fu, Xiaobing; Kaplan, David L

2018-03-21

Fine tuning physical cues of silk fibroin (SF) biomaterials to match specific requirements for different soft tissues would be advantageous. Here, amorphous SF nanofibers were used to fabricate scaffolds with better hierarchical extracellular matrix (ECM) mimetic microstructures than previous silk scaffolds. Kinetic control was introduced into the scaffold forming process, resulting in the direct production of water-stable scaffolds with tunable secondary structures and thus mechanical properties. These biomaterials remained with amorphous structures, offering softer properties than prior scaffolds. The fine mechanical tunability of these systems provides a feasible way to optimize physical cues for improved cell proliferation and enhanced neovascularization in vivo. Multiple physical cues, such as partly ECM mimetic structures and optimized stiffness, provided suitable microenvironments for tissue ingrowth, suggesting the possibility of actively designing bioactive SF biomaterials. These systems suggest a promising strategy to develop novel SF biomaterials for soft tissue repair and regenerative medicine.

Dry-Spun Silk Produces Native-Like Fibroin Solutions

PubMed Central

2016-01-01

Silk’s outstanding mechanical properties and energy efficient solidification mechanisms provide inspiration for biomaterial self-assembly as well as offering a diverse platform of materials suitable for many biotechnology applications. Experiments now reveal that the mulberry silkworm Bombyx mori secretes its silk in a practically “unspun” state that retains much of the solvent water and exhibits a surprisingly low degree of molecular order (β-sheet crystallinity) compared to the state found in a fully formed and matured fiber. These new observations challenge the general understanding of silk spinning and in particular the role of the spinning duct for structure development. Building on this discovery we report that silk spun in low humidity appears to arrest a molecular annealing process crucial for β-sheet formation. This, in turn, has significant positive implications, enabling the production of a high fidelity reconstituted silk fibroin with properties akin to the gold standard of unspun native silk. PMID:27526078

Mechanical suitability of glycerol-preserved human dura mater for construction of prosthetic cardiac valves.

PubMed

McGarvey, K A; Lee, J M; Boughner, D R

1984-03-01

We have examined the tensile viscoelastic properties of fresh and glycerol-preserved human dura mater, and correlated the results with structural information from the scanning electron microscope. The interwoven laminar structure of dura produces rather high flexural stiffness, while the crossed-fibrillar laminae produce planar mechanical isotropy. Glycerol storage shifts the stress-strain curve to lower strain, reduces stress relaxation and creep, and lowers the ultimate tensile strength and strain at fracture. These changes may be due to glyceraldehyde crosslinking, or to increased interfibrillar friction. The latter hypothesis suggests that glycerol storage may reduce the fatigue lifetime of the tissue.

Fabrication and researching of weathering resistant double cladding power delivery fiber

NASA Astrophysics Data System (ADS)

Rong, Liang; Ren, Junjiang; Li, Rundong; Wang, Lianping; Zou, Huan

2016-01-01

A novel well weathering resistant power delivery fiber which is of double cladding and high optical energy transmitting ability is developed via fluoroplastic out sheath extruding process. The fiber has been comprehensively evaluated including optical performance, mechanical performance, environmental suitability and laser transmitting property. It is shown that the fiber has not only low attenuation, high numerical aperture and better mechanical bending performance, but also outstanding weathering resistance and high power laser transmitting performance, which implies the qualification of the fiber for various kinds of applying situations, such as laser ignition, laser induced expanding sound underwater, ship-based and airborne laser weapon.

Viscous and thermal modelling of thermoplastic composites forming process

NASA Astrophysics Data System (ADS)

Guzman, Eduardo; Liang, Biao; Hamila, Nahiene; Boisse, Philippe

2016-10-01

Thermoforming thermoplastic prepregs is a fast manufacturing process. It is suitable for automotive composite parts manufacturing. The simulation of thermoplastic prepreg forming is achieved by alternate thermal and mechanical analyses. The thermal properties are obtained from a mesoscopic analysis and a homogenization procedure. The forming simulation is based on a viscous-hyperelastic approach. The thermal simulations define the coefficients of the mechanical model that depend on the temperature. The forming simulations modify the boundary conditions and the internal geometry of the thermal analyses. The comparison of the simulation with an experimental thermoforming of a part representative of automotive applications shows the efficiency of the approach.

Mechanical Properties for the Grasp of a Robotic Hand

DTIC Science & Technology

1984-09-01

qf. The object is treated as a rigid body and consequently, a small motion , db, of the object in the (x.yz) system produces a displacement of the...several fingers, Asada addresses the problem of choosing a suitable finger configuration, He treats the held object as a rigid body and models the...modcled as elastic structures and the object as a rigid body . This is usually a good approximation for robots assembling parts or holding tools since

The choice of iron-containing filling for composite radioprotective material

NASA Astrophysics Data System (ADS)

Matyukhin, P. V.

2018-03-01

The paper presents the data the composition of modern composite building materials including materials which in addition to high physical-mechanical have radio-protective properties. The article presents infrared researches and differential thermal data of fine-grained magnetite and hematite beneficiated iron-ore concentrates. The choice of the most suitable filling for new composite radio-protective building material engineering and development was made basing on the magnetite and hematite data presented in the paper.

Strontium-based glass polyalkenoate cements for luting applications in the skeleton.

PubMed

Clarkin, O; Boyd, D; Towler, M R

2010-02-01

Glass Polyalkenoate Cements (GPCs) based on strontium calcium zinc silicate (Sr-Ca-Zn-SiO2) glasses and high molecular weight poly(acrylic acid) (PAA) have been shown to exhibit suitable mechanical properties for orthopaedic arthroplasty applications, however for vertebroplasty and other medical luting applications these cements have working and setting times which are unsuitable for such applications. In this study GPCs based on Sr-Ca-Zn-SiO2 glasses and low molecular weight PAA were evaluated for orthopaedic luting applications. GPCs based on four different glasses; BT100 (0.16CaO, 0.36ZnO, 0.48SiO2), BT101 (0.04SrO, 0.12CaO, 0.36ZnO, 0.48SiO2), BT102 (0.08SrO 0.08CaO, 0.36ZnO, 0.48SiO2) and BT103 (0.12SrO 0.04CaO, 0.36ZnO, 0.48SiO2) and two PAAs (MW; 12,700 and 25,700) were examined. These cement formulations exhibited handling properties potentially suitable for luting applications as well as mechanical strengths which were similar to those of trabecular bone. Upon immersion in simulated body fluid, the GPCs showed sustained growth of a calcium phosphate layer on the surface of the cement indicating that these cements were bioactive in nature.

Morphological effects of porous poly-d,l-lactic acid/hydroxyapatite scaffolds produced by supercritical CO2 foaming on their mechanical performance.

PubMed

Rouholamin, Davood; van Grunsven, William; Reilly, Gwendolen C; Smith, Patrick J

2016-08-01

A novel supercritical CO2 foaming technique was used to fabricate scaffolds of controllable morphology and mechanical properties, with the potential to tailor the scaffolds to specific tissue engineering applications. Biodegradable scaffolds are widely used as temporary supportive structures for bone regeneration. The scaffolds must provide a sufficient mechanical support while allowing cell attachment and growth as well as metabolic activities. In this study, supercritical CO2 foaming was used to prepare fully interconnected porous scaffolds of poly-d,l-lactic acid and poly-d,l-lactic acid/hydroxyapatite. The morphological, mechanical and cell behaviours of the scaffolds were measured to examine the effect of hydroxyapatite on these properties. These scaffolds showed an average porosity in the range of 86%-95%, an average pore diameter of 229-347 µm and an average pore interconnection of 103-207 µm. The measured porosity, pore diameter, and interconnection size are suitable for cancellous bone regeneration. Compressive strength and modulus of up to 36.03 ± 5.90 and 37.97 ± 6.84 MPa were measured for the produced porous scaffolds of various compositions. The mechanical properties presented an improvement with the addition of hydroxyapatite to the structure. The relationship between morphological and mechanical properties was investigated. The matrices with different compositions were seeded with bone cells, and all the matrices showed a high cell viability and biocompatibility. The number of cells attached on the matrices slightly increased with the addition of hydroxyapatite indicating that hydroxyapatite improves the biocompatibility and proliferation of the scaffolds. The produced poly-d,l-lactic acid/hydroxyapatite scaffolds in this study showed a potential to be used as bone graft substitutes. © IMechE 2016.

Calculation of wave-functions with frozen orbitals in mixed quantum mechanics/molecular mechanics methods. II. Application of the local basis equation.

PubMed

Ferenczy, György G

2013-04-05

The application of the local basis equation (Ferenczy and Adams, J. Chem. Phys. 2009, 130, 134108) in mixed quantum mechanics/molecular mechanics (QM/MM) and quantum mechanics/quantum mechanics (QM/QM) methods is investigated. This equation is suitable to derive local basis nonorthogonal orbitals that minimize the energy of the system and it exhibits good convergence properties in a self-consistent field solution. These features make the equation appropriate to be used in mixed QM/MM and QM/QM methods to optimize orbitals in the field of frozen localized orbitals connecting the subsystems. Calculations performed for several properties in divers systems show that the method is robust with various choices of the frozen orbitals and frontier atom properties. With appropriate basis set assignment, it gives results equivalent with those of a related approach [G. G. Ferenczy previous paper in this issue] using the Huzinaga equation. Thus, the local basis equation can be used in mixed QM/MM methods with small size quantum subsystems to calculate properties in good agreement with reference Hartree-Fock-Roothaan results. It is shown that bond charges are not necessary when the local basis equation is applied, although they are required for the self-consistent field solution of the Huzinaga equation based method. Conversely, the deformation of the wave-function near to the boundary is observed without bond charges and this has a significant effect on deprotonation energies but a less pronounced effect when the total charge of the system is conserved. The local basis equation can also be used to define a two layer quantum system with nonorthogonal localized orbitals surrounding the central delocalized quantum subsystem. Copyright © 2013 Wiley Periodicals, Inc.

Production, characterization, and modeling of mineral filled polypropylene filaments

NASA Astrophysics Data System (ADS)

George, Brian Robert

1999-11-01

This research produced mineral filled polypropylene filaments using a variety of fillers, characterized these filaments, and attempted to model their mechanical properties with current composite models. Also, these filaments were compared with bone to determine if they are suitable for modeling the mechanical properties of bone. Fillers used consist of wollastonite, talc, calcium carbonate, titanium dioxide, and hydroxyapatite. Fillers and polypropylene chips were combined and extruded into rods with the use of a mixer. The rods were chipped up and then formed into filaments through melt extrusion utilizing a piston extruder. Filaments with volume fractions of filler of 0.05, 0.10, 0.15, and 0.20 were produced. Additionally, some methods of trying to improve the properties of these filaments were attempted, but did not result in any significant property improvements. The fillers and filaments were visually characterized with a scanning electron microscope. Cross-sections, filament outer surfaces, fracture surfaces, and longitudinal cut open surfaces were viewed in this manner. Those filaments with anisotropic filler had some oriented filler particles, while all filaments suffered from poor adhesion between the polypropylene and the filler as well as agglomerations of filler particles. Twenty specimens of each filament were tensile tested and the average tenacity, strain, and modulus were calculated. Filaments containing talc, talc and wollastonite, titanium dioxide, or hydroxyapatite suffered from a drastic transition from ductile to brittle with the addition of 0.05 volume fraction of filler. This is evidenced by the sharp decrease in strain at this volume fraction of filler when compared to the strain of the unfilled polypropylene filament. Additionally, these same filaments suffered a sharp decrease in tenacity at the same volume fraction. These instant decreases are attributed to the agglomerations of filler in the filament. Generally, the modulus of the filaments increased with the increase in concentration of filler. The tensile tenacity, strain, and modulus were modeled with current composite models for particulate filled composites. The tenacity and strain models did not accurately predict the properties of the filaments, while the modulus models were more accurate, perhaps because the agglomerations of filler did not affect the modulus as much as it affected the tenacity and strain of the filaments. Production, characterization, and modeling of these filaments indicates that there are many areas for improvements, such as improved mixing of the filler and polypropylene, increased adhesion between matrix and filler, and decreased agglomerations of filler. Mechanically, these filaments can not match the properties of bone. However, they do have many structural similarities at the micro-mechanical level, so with some improvements in properties these filaments may be suitable models for modeling bone behavior.

Design of optical mirror structures

NASA Technical Reports Server (NTRS)

Soosaar, K.

1971-01-01

The structural requirements for large optical telescope mirrors was studied with a particular emphasis placed on the three-meter Large Space Telescope primary mirror. Analysis approaches through finite element methods were evaluated with the testing and verification of a number of element types suitable for particular mirror loadings and configurations. The environmental conditions that a mirror will experience were defined and a candidate list of suitable mirror materials with their properties compiled. The relation of the mirror mechanical behavior to the optical performance is discussed and a number of suitable design criteria are proposed and implemented. A general outline of a systematic method to obtain the best structure for the three-meter diffraction-limited system is outlined. Finite element programs, using the STRUDL 2 analysis system, were written for specific mirror structures encompassing all types of active and passive mirror designs. Parametric studies on support locations, effects of shear deformation, diameter to thickness ratios, lightweight and sandwich mirror configurations, and thin shell active mirror needs were performed.

Microstructure-Mechanical Property Relationships for a Fe/Mn/Cr Rock Bolt Reinforcing Steel

NASA Astrophysics Data System (ADS)

Panigrahi, B. K.

2010-08-01

The influence of low chromium additions to a 0.25C-1.5Mn semikilled steel on microstructure, and tensile and impact behaviors of high strength rock bolt reinforcing bars has been investigated. Although chromium imparted adequate tensile properties at ambient temperature (yield stress: 624 MPa; ultimate tensile stress: 819 MPa; elongation: 12.5%) by forming transformation products such as tempered martensite, lower and upper bainite, and small amounts of acicular ferrite, it increased the ductile-to-brittle transition temperature due to coarser upper bainite in the core region of bar having larger unit crack paths. The synthesized steel is considered to be effective in realizing the desired tensile properties, and suitable for application in rock bolt, as well as other reinforced concrete structures.

Non-linear Mechanics of Three-dimensional Architected Materials; Design of Soft and Functional Systems and Structures

NASA Astrophysics Data System (ADS)

Babaee, Sahab

In the search for materials with new properties, there have been significant advances in recent years aimed at the construction of architected materials whose behavior is governed by structure, rather than composition. Through careful design of the material's architecture, new mechanical properties have been demonstrated, including negative Poisson's ratio, high stiffness to weight ratio and mechanical cloaking. However, most of the proposed architected materials (also known as mechanical metamaterials) have a unique structure that cannot be recon figured after fabrication, making them suitable only for a specific task. This thesis focuses on the design of architected materials that take advantage of the applied large deformation to enhance their functionality. Mechanical instabilities, which have been traditionally viewed as a failure mode with research focusing on how to avoid them, are exploited to achieve novel and tunable functionalities. In particular I demonstrate the design of mechanical metamaterials with tunable negative Poisson ratio, adaptive phononic band gaps, acoustic switches, and reconfigurable origami-inspired waveguides. Remarkably, due to large deformation capability and full reversibility of soft materials, the responses of the proposed designs are reversible, repeatable, and scale independent. The results presented here pave the way for the design of a new class of soft, active, adaptive, programmable and tunable structures and systems with unprecedented performance and improved functionalities.

A novel approach for preparation and in situ tensile testing of silica glass membranes in the TEM

NASA Astrophysics Data System (ADS)

Mačković, Mirza; Przybilla, Thomas; Dieker, Christel; Herre, Patrick; Romeis, Stefan; Stara, Hana; Schrenker, Nadine; Peukert, Wolfgang; Spiecker, Erdmann

2017-04-01

The mechanical behavior of glasses in the micro- and/or nanometer regime increasingly gains importance in nowadays modern technology. However, suitable small scale preparation and mechanical testing approaches for a reliable assessment of the mechanical properties of glasses still remain a big challenge. In the present work, a novel approach for site-specific preparation and quantitative in situ tensile testing of thin silica glass membranes in the transmission electron microscope is presented. Thereby, advanced focused ion beam techniques are used for the preparation of nanoscale dog bone shaped silica glass specimens suitable for in situ tensile testing. Small amounts of gallium are detected on the surface of the membranes resulting from redeposition effects during the focused ion beam preparation procedure. Possible structural changes of silica glass upon irradiation with electrons and gallium ions are investigated by controlled irradiation experiments, followed by a structural analysis using Raman spectroscopy. While moderate electron beam irradiation does not alter the structure of silica glass, ion beam irradiation results in minor densification of the silica glass membranes. In situ tensile testing of membranes under electron beam irradiation results in distinctive elongations without fracture confirming the phenomenon of superplasticity. In contrast, in situ tensile testing in the absence of the electron beam reveals an elastic/plastic deformation behavior, and finally leads to fracture of the membranes. The Young’s moduli of the glass membranes pulled at beam off conditions in the TEM are comparable with values known for bulk fused silica, while the tensile strength is in the range of values reported for silica glass fibers with comparable dimensions. The impact of electron beam irradiation on the mechanical properties of silica glass membranes is further discussed. The results of the present work open new avenues for dedicated preparation and nanomechanical characterization of silica glasses, and further contribute to a fundamental understanding of the mechanical behavior of such glasses when being scaled down to the nanometer regime.

77 FR 47861 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2012-08-10

... Notice to identify Federal buildings and other real property that HUD has reviewed for suitability for... landholding agencies regarding unutilized and underutilized buildings and real property controlled by such... landholding agencies at the following addresses: COE: Mr. Scott Whiteford, Army Corps of Engineers, Real...

Ten Deg Off-Axis Test for Shear Properties in Fiber Composites

NASA Technical Reports Server (NTRS)

Chamis, C. C.; Sinclair, J. H.

1977-01-01

A combined theoretical and experimental investigation was conducted to assess the suitability of the 10 deg off-axis tensile test specimen for the intralaminar shear characterization of unidirectional composites. Composite mechanics, a combined-stress failure criterion, and a finite variation across the specimen width and the relative stress and strain magnitudes at the 10 deg plane. Strain gages were used to measure the strain variation across the specimen width at specimen midlength and near the end tabs. Specimens from Mod-I/epoxy, T-300/epoxy, and S-glass/epoxy were used in the experimental program. It was found that the 10 deg off-axis tensile test specimen is suitable for intralaminar shear characterization, and it is recommended that it should be considered as a possible standard test specimen for such a characterization.

Degraded and osteogenic properties of coated magnesium alloy AZ31; an experimental study.

PubMed

Zhuang, Jinpeng; Jing, Yongbin; Wang, Yaming; Zhang, Jinghuai; Xie, Huanxin; Yan, Jinglong

2016-03-14

Degraded and osteogenic property of coated magnesium alloy was evaluated for the fracture fixation in rabbits. Magnesium alloy AZ31 with a different coating thickness by microarc oxidation was used, and the bilateral radial fracture model was created by the bite bone clamp. Thirty-six New Zealand white rabbits in weight of 2.5~3.0 kg were randomly divided into A, B, and C groups at four time points and other 3 rabbits as the control group without magnesium alloy. Coated magnesium alloy AZ31 was implanted on the fracture and fixed with silk thread. Indexes such as general observation, histology, X-ray, hematology, and mechanical properties were observed and detected at 2nd, 4th, 8th, and 12th week after implantation. Fracture in each rabbit was healed at 12th week after implantation. Among the three groups, the best results of general observation, histology, and X-ray appeared in A group without coating. However, A group showed the worst results from the perspective of mechanical properties about tensile strength and flexural strength, which failed to reach that of the natural bone at the 12th week. Comprehensive results displayed that C group with 20-μm coating was better than others in mechanical properties, while there is no difference between B and C groups in hematology. Degradation rate is inversely proportional to the coating thickness. And magnesium alloy with a 20-μm coating is more suitable for the fracture fixation.

Design of exceptionally strong and conductive Cu alloys beyond the conventional speculation via the interfacial energy-controlled dispersion of γ-Al2O3 nanoparticles

PubMed Central

Zeon Han, Seung; Kim, Kwang Ho; Kang, Joonhee; Joh, Hongrae; Kim, Sang Min; Ahn, Jee Hyuk; Lee, Jehyun; Lim, Sung Hwan; Han, Byungchan

2015-01-01

The development of Cu-based alloys with high-mechanical properties (strength, ductility) and electrical conductivity plays a key role over a wide range of industrial applications. Successful design of the materials, however, has been rare due to the improvement of mutually exclusive properties as conventionally speculated. In this paper, we demonstrate that these contradictory material properties can be improved simultaneously if the interfacial energies of heterogeneous interfaces are carefully controlled. We uniformly disperse γ-Al2O3 nanoparticles over Cu matrix, and then we controlled atomic level morphology of the interface γ-Al2O3//Cu by adding Ti solutes. It is shown that the Ti dramatically drives the interfacial phase transformation from very irregular to homogeneous spherical morphologies resulting in substantial enhancement of the mechanical property of Cu matrix. Furthermore, the Ti removes impurities (O and Al) in the Cu matrix by forming oxides leading to recovery of the electrical conductivity of pure Cu. We validate experimental results using TEM and EDX combined with first-principles density functional theory (DFT) calculations, which all consistently poise that our materials are suitable for industrial applications. PMID:26616045

Design of exceptionally strong and conductive Cu alloys beyond the conventional speculation via the interfacial energy-controlled dispersion of γ-Al2O3 nanoparticles.

PubMed

Han, Seung Zeon; Kim, Kwang Ho; Kang, Joonhee; Joh, Hongrae; Kim, Sang Min; Ahn, Jee Hyuk; Lee, Jehyun; Lim, Sung Hwan; Han, Byungchan

2015-11-30

The development of Cu-based alloys with high-mechanical properties (strength, ductility) and electrical conductivity plays a key role over a wide range of industrial applications. Successful design of the materials, however, has been rare due to the improvement of mutually exclusive properties as conventionally speculated. In this paper, we demonstrate that these contradictory material properties can be improved simultaneously if the interfacial energies of heterogeneous interfaces are carefully controlled. We uniformly disperse γ-Al2O3 nanoparticles over Cu matrix, and then we controlled atomic level morphology of the interface γ-Al2O3//Cu by adding Ti solutes. It is shown that the Ti dramatically drives the interfacial phase transformation from very irregular to homogeneous spherical morphologies resulting in substantial enhancement of the mechanical property of Cu matrix. Furthermore, the Ti removes impurities (O and Al) in the Cu matrix by forming oxides leading to recovery of the electrical conductivity of pure Cu. We validate experimental results using TEM and EDX combined with first-principles density functional theory (DFT) calculations, which all consistently poise that our materials are suitable for industrial applications.

A novel sample preparation method to avoid influence of embedding medium during nano-indentation

NASA Astrophysics Data System (ADS)

Meng, Yujie; Wang, Siqun; Cai, Zhiyong; Young, Timothy M.; Du, Guanben; Li, Yanjun

2013-02-01

The effect of the embedding medium on the nano-indentation measurements of lignocellulosic materials was investigated experimentally using nano-indentation. Both the reduced elastic modulus and the hardness of non-embedded cell walls were found to be lower than those of the embedded samples, proving that the embedding medium used for specimen preparation on cellulosic material during nano-indentation can modify cell-wall properties. This leads to structural and chemical changes in the cell-wall constituents, changes that may significantly alter the material properties. Further investigation was carried out to detect the influence of different vacuum times on the cell-wall mechanical properties during the embedding procedure. Interpretation of the statistical analysis revealed no linear relationships between vacuum time and the mechanical properties of cell walls. The quantitative measurements confirm that low-viscosity resin has a rapid penetration rate early in the curing process. Finally, a novel sample preparation method aimed at preventing resin diffusion into lignocellulosic cell walls was developed using a plastic film to wrap the sample before embedding. This method proved to be accessible and straightforward for many kinds of lignocellulosic material, but is especially suitable for small, soft samples.

Method to Prepare Processable Polymides with Reactive Endgroups using 1,3-Bis (3-Aminophenoxy) Benzene

NASA Technical Reports Server (NTRS)

Jensen, Brian J. (Inventor)

2000-01-01

Polyimide copolymers were obtained containing 1,3-bis(3-aminophenoxy)benzene (APB) and other diamines and dianhydrides and terminating with the appropriate amount of reactive endcapper. The reactive endcappers studied include but should not be limited to 4-phenylethynyl phthalic anhydride (PEPA ), 3-aminophenoxy- 4'-phenylethynylbenzophenone (3-APEB), maleic anhydride (MA) and nadic anhydride (5-norbomene-2,3-dicarboxylic anhydride, NA). Homopolymers containing only other diamines and dianhydrides which are not processable under conditions described previously can be made processable by incorporating various amounts of APB, depending on the chemical structures of the diamines and dianhydrides used. By simply changing the ratio of APB to the other diamine in the polyimide backbone, a material with a unique combination of solubility, Tg, Tm, melt viscosity, toughness and elevated temperature mechanical properties can be prepared. The copolymers that result from using APB to enhance processability have a unique combination of properties that include low pressure processing (200 psi and below), long term melt stability (several hours at 300 C. for the phenylethynyl terminated polymers), high toughness, improved solvent resistance, improved adhesive properties, and improved composite mechanical properties. These copolyimides are eminently suitable as adhesives, composite matrices, moldings, films and coatings.

Characterization of Polycaprolactone and Rice Husk Silica Composite (PCL-SiO2) by E-Spinning to Apply Supporter for Drug Release

NASA Astrophysics Data System (ADS)

Song, Sinae; Hilonga, Askwar; Taik Kim, Hee

2018-03-01

Polycaprolactone (PCL) is an interesting material to apply biomedical field owing to its biodegradability and biocompatibility which is suitable for a specific site with longer healing times. Blending the polymer with other materials has degradation property improved with the effective and economic method. This study was conducted to fabricate supporter based on Polycaprolactone and Rice husk silica (PCL-SiO2) by using electrospinning. Nano-porous silica in the composite was synthesized from rice husk having properties of economic, eco-friendly and high surface area. It drew to enhance the amount of drug loading in the carrier. Electrospinning technique is used to fabricate fibrous component by optimization condition obtained from previous mechanical properties experiments. Release experiment was carried out by the degree of dye absorbance at 544nm by ultraviolet–visible spectroscopy, the RhB in SiO2 alternative drug for modelling of drug release was released for 1 ~ 20 days at 37°C in phosphate buffer. Furthermore, the Mechanical property was confirmed by DSC, TGA. Morphology and degree of biodegradation were shown as SEM images and EDS.

The effect of bacterial cellulose on the shape memory behavior of polyvinyl alcohol nanocomposite hydrogel

NASA Astrophysics Data System (ADS)

Pirahmadi, Pegah; Kokabi, Mehrdad

2018-01-01

Most research on shape memory polymers has been confined to neat polymers in their dry state, while, some hydrogel networks are known for their shape memory properties. Hydrogels have low glass transition temperatures which are below 100°C depend on the content of water. But they are usually weak and brittle, and not suitable for structural applications due to their low mechanical strengths because of these materials have large amount of water (>50%), so they could not remember original shape perfectly. Bacterial cellulose nanofibers with perfect properties such as high water holding capacity, high crystallinity, high tensile strength and good biocompatibility can dismiss all the drawbacks. In the present study, polyvinyl alcohol/bacterial cellulose nanocomposite hydrogel prepared by repetitive freezing-thawing method. The bacterial cellulose was used as reinforcement to improve the mechanical properties and stimuli response. Differential scanning calorimetry was employed to obtain the glass transition temperature. Nanocomposite morphology was characterized by field-emission scanning electron microscopy and mechanical properties were investigated by standard tensile test. Finally, the effect of bacterial cellulose nanofiber on shape memory behavior of polyvinyl alcohol/bacterial cellulose nanocomposite hydrogel was investigated. It is found that switching temperature of this system is the glass transition temperature of the nano domains formed within the system. The results also show increase of shape recovery, and shape recovery speed due to presence of bacterial cellulose.

Effect of Heat Treatment on the Properties of CoCrMo Alloy Manufactured by Selective Laser Melting

NASA Astrophysics Data System (ADS)

Guoqing, Zhang; Junxin, Li; Xiaoyu, Zhou; Jin, Li; Anmin, Wang

2018-04-01

To obtain medical implants with better mechanical properties, it is necessary to conduct studies on the heat treatment process of the selective laser melting (SLM) manufacturing parts. The differential scanning calorimetry method was used to study the heat treatment process of the phase transition of SLM CoCrMo alloy parts. The tensile properties were tested with a tensile test machine, the quantity of carbide precipitated after heat treatment was measured by energy-dispersive x-ray spectroscopy, and the tensile fracture morphology of the parts was investigated using SEM. The obtained results were: Mechanical properties in terms of elongation and tensile strength of CoCrMo alloy manufactured by SLM that had been heat-treated at 1200 °C for 2 h followed by cooling with water were not only higher than the national standard but also higher than the experimental results of the same batch of castings. The mechanism of fracture of parts manufactured by SLM without heat treatment was brittle fracture, whereas parts which had been heat-treated at 1200 °C for 2 h combined with water cooling and at 1200 °C for 1 h with furnace cooling suffered ductile fracture. This study provides the basis for defining the applications for which CoCrMo alloys manufactured by SLM are suitable within the field of medical implants.

Effect of Heat Treatment on the Properties of CoCrMo Alloy Manufactured by Selective Laser Melting

NASA Astrophysics Data System (ADS)

Guoqing, Zhang; Junxin, Li; Xiaoyu, Zhou; Jin, Li; Anmin, Wang

2018-05-01

To obtain medical implants with better mechanical properties, it is necessary to conduct studies on the heat treatment process of the selective laser melting (SLM) manufacturing parts. The differential scanning calorimetry method was used to study the heat treatment process of the phase transition of SLM CoCrMo alloy parts. The tensile properties were tested with a tensile test machine, the quantity of carbide precipitated after heat treatment was measured by energy-dispersive x-ray spectroscopy, and the tensile fracture morphology of the parts was investigated using SEM. The obtained results were: Mechanical properties in terms of elongation and tensile strength of CoCrMo alloy manufactured by SLM that had been heat-treated at 1200 °C for 2 h followed by cooling with water were not only higher than the national standard but also higher than the experimental results of the same batch of castings. The mechanism of fracture of parts manufactured by SLM without heat treatment was brittle fracture, whereas parts which had been heat-treated at 1200 °C for 2 h combined with water cooling and at 1200 °C for 1 h with furnace cooling suffered ductile fracture. This study provides the basis for defining the applications for which CoCrMo alloys manufactured by SLM are suitable within the field of medical implants.

Synthesis and photoluminescence study in Eu3+:Y2WO6 phosphors

NASA Astrophysics Data System (ADS)

Sonali, Mondal, Manisha; Rai, Vineet Kumar

2018-05-01

Eu3+ doped Y2WO6 phosphors were synthesized by solid state reaction method. The photoluminescence properties of the Eu3+:Y2WO6 phosphors were studied for different concentration of Eu3+ ions. The luminescence intensity is found maximum at 0.3 mol% of Eu3+ ions. The excitation spectra monitored at ˜617 nm lies in the 220 - 350 nm region occurs due to charge transfer state (CTS) band of the europium-oxygen interactions, which is caused by an electron transfer from oxygen 2p orbital to an empty 4f shell of europium ions. The phosphors effectively excited by ˜393 nm near-ultraviolet (NUV) light gives efficient red emission band (˜ 617 nm) corresponding to 5D0 → 7F2 transition. The concentration dependence photoluminescence study and the mechanisms behind the photoluminescence properties have been explored with the help of suitable energy level diagram. Moreover, the CIE colour coordinate lie in the near white region so the prepared phosphors can be suitably use in making visible downconverter and in making visible light display devices.

Improved interface growth and enhanced flux pinning in YBCO films deposited on an advanced IBAD-MgO based template

NASA Astrophysics Data System (ADS)

Khan, M. Z.; Zhao, Y.; Wu, X.; Malmivirta, M.; Huhtinen, H.; Paturi, P.

2018-02-01

The growth mechanism is studied from the flux pinning point of view in small-scale YBa2Cu3O6+x (YBCO) thin films deposited on a polycrystalline hastelloy with advanced IBAD-MgO based buffer layer architecture. When compared the situation with YBCO films grown on single crystal substrates, the most critical issues that affect the suitable defect formation and thus the optimal vortex pinning landscape, have been studied as a function of the growth temperature and the film thickness evolution. We can conclude that the best critical current property in a wide applied magnetic field range is observed in films grown at relatively low temperature and having intermediate thickness. These phenomena are linked to the combination of the improved interface growth, to the film thickness related crystalline relaxation and to the formation of linear array of edge dislocations that forms the low-angle grain boundaries through the entire film thickness and thus improve the vortex pinning properties. Hence, the optimized buffer layer structure proved to be particularly suitable for new coated conductor solutions.

Microstructure and mechanical properties of NiCoCrAlYTa alloy processed by press and sintering route

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pereira, J.C., E-mail: jpereira@uc.edu.ve; Centro de Investigaciones en Mecánica, Facultad de Ingeniería, Universidad de Carabobo; Zambrano, J.C.

2015-03-15

Nickel-based superalloys such as NiCoCrAlY are widely used in high-temperature applications, such as gas turbine components in the energy and aerospace industries, due to their strength, high elastic modulus, and high-temperature oxidation resistance. However, the processing of these alloys is complex and costly, and the alloys are currently used as a bond coat in thermal barrier coatings. In this work, the effect of cold press and sintering processing parameters on the microstructure and mechanical properties of NiCoCrAlY alloy were studied using the powder metallurgy route as a new way to obtain NiCoCrAlYTa samples from a gas atomized prealloyed powder feedstock.more » High mechanical strength and adequate densification up to 98% were achieved. The most suitable compaction pressure and sintering temperature were determined for NiCoCrAlYTa alloy through microstructure characterization. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive spectroscopy microanalysis (EDS) were performed to confirm the expected γ-Ni matrix and β-NiAl phase distribution. Additionally, the results demonstrated the unexpected presence of carbides and Ni–Y-rich zones in the microstructure due to the powder metallurgy processing parameters used. Thus, microhardness, nanoindentation and uniaxial compression tests were conducted to correlate the microstructure of the alloy samples with their mechanical properties under the different studied conditions. The results show that the compaction pressure did not significantly affect the mechanical properties of the alloy samples. In this work, the compaction pressures of 400, 700 and 1000 MPa were used. The sintering temperature of 1200 °C for NiCoCrAlYTa alloy was preferred; above this temperature, the improvement in mechanical properties is not significant due to grain coarsening, whereas a lower temperature produces a decrease in mechanical properties due to high porosity and poor solid-state diffusion. - Graphical abstract: Display Omitted - Highlights: • We made NiCoCrAlYTa alloy by a conventional powder metallurgy route. • High densification and adequate strength were observed. • The presence of unexpected carbides found along γ/γ and γ/β grain boundaries was detected. • The effect of cold press and sintering processing parameters on the microstructure and mechanical properties were studied.« less

Nuclear Instruments and Methods in Physics Research. Section B; Microstructural Characterization of Semi-Interpenetrating Polymer Networks by Positron Lifetime Spectroscopy

NASA Technical Reports Server (NTRS)

Singh, Jag J.; Pater, Ruth H.; Eftekhari, Abe

1998-01-01

Thermoset and thermoplastic polyimides have complementary physical/mechanical properties. Whereas thermoset polyimides are brittle and generally easier to process, thermoplastic polyimides are tough but harder to process. It is expected that a combination of these two types of polyimides may help produce polymers more suitable for aerospace applications. Semi-Interpenetrating Polymer Networks (S-IPNs) of thermoset LaRC(Trademark)-RP46 and thermoplastic LARC(Trademark)-IA polyimides were prepared in weight percent ratios ranging from 100:0 to 0: 100. Positron lifetime measurements were made in these samples to correlate their free volume features with physical/mechanical properties. As expected, positronium atoms are not formed in these samples. The second life time component has been used to infer the positron trap dimensions. The "free volume" goes through a minimum at about 50:50 ratio, suggesting that S-IPN samples are not merely solid solutions of the two polymers. These data and related structural properties of the S-IPN samples have been discussed in this paper.

Medium density fibreboard production by hot pressing without adhesive using Triarrhena sacchariflora residue bio-pretreated by white-rot fungus Coriolus versicolor.

PubMed

Wu, J G; Zhang, X; Liu, J; Xiong, M; Lu, X Y; Fan, H D; Wang, X F; Zhang, X Y

2016-08-01

To produce fibreboard with Triarrhena sacchariflora residue (TSR) without adhesive and understand the relationship between bio-pretreatment and mechanical property of fibreboard. White-rot fungus Coriolus versicolor was used to pretreat TSR, and biochemical and physical analysis were investigated by ultraviolet spectrophotometry, Fourier transform infrared spectroscopy and environmental scanning electron microscopy method. TSR was suitable to produce fibreboard without adhesive by bio-pretreatment with C. versicolor. The property of fibreboard became stronger by optimization of bio-pretreatment parameters, and the moduli of rupture and elasticity of fibreboard were increased to 18·12 MPa and 4·3 GPa, respectively, which were close to national standard of medium-density fibreboard with adhesive. Bio-pretreated TSR increased the mechanical properties of fibreboard because of 1·4-fold content of polysaccharide and 1·15 U g(-1) laccase, more hydroxyl group and more porous surface structure than that of untreated TSR. TSR-based fibreboard production without adhesive eliminated potential formaldehyde gas emission. © 2016 The Society for Applied Microbiology.

The Effects of Adding Elements of Zinc and Magnesium on Ag-Cu Eutectic Alloy for Warming Acupuncture

PubMed Central

Park, Il Song; Kim, Keun Sik; Lee, Min Ho

2013-01-01

The warming acupuncture for hyperthermia therapy is made of STS304. However, its needle point cannot be reached to a desirable temperature due to heat loss caused by low thermal conductivity, and the quantification of stimulation condition and the effective standard establishment of warming acupuncture are required as a heat source. Accordingly, in this study, after Ag-Cu alloys with different composition ratios were casted and then mixed with additives to improve their physical and mechanical properties, the thermal conductivity and biocompatibility of the alloy specimens were evaluated for selecting suitable material. Ag-Cu binary alloys and ternary alloys added 5 wt% Zn or 2 wt% Mg were casted and then cold drawn to manufacture needles for acupuncture, and their physical properties, thermal conductivity, and biocompatibility were evaluated for their potential use in warming acupuncture. The results of this study showed that the physical and mechanical properties of the Ag-Cu alloys were improved by additives and that the thermal conductivity, machinability, and biocompatibility of the Ag-Cu alloys were improved by Mg addition. PMID:24078827

The effects of adding elements of zinc and magnesium on ag-cu eutectic alloy for warming acupuncture.

PubMed

Kim, Yu Kyoung; Park, Il Song; Kim, Keun Sik; Lee, Min Ho

2013-01-01

The warming acupuncture for hyperthermia therapy is made of STS304. However, its needle point cannot be reached to a desirable temperature due to heat loss caused by low thermal conductivity, and the quantification of stimulation condition and the effective standard establishment of warming acupuncture are required as a heat source. Accordingly, in this study, after Ag-Cu alloys with different composition ratios were casted and then mixed with additives to improve their physical and mechanical properties, the thermal conductivity and biocompatibility of the alloy specimens were evaluated for selecting suitable material. Ag-Cu binary alloys and ternary alloys added 5 wt% Zn or 2 wt% Mg were casted and then cold drawn to manufacture needles for acupuncture, and their physical properties, thermal conductivity, and biocompatibility were evaluated for their potential use in warming acupuncture. The results of this study showed that the physical and mechanical properties of the Ag-Cu alloys were improved by additives and that the thermal conductivity, machinability, and biocompatibility of the Ag-Cu alloys were improved by Mg addition.

Structure characterization and wear performance of NiTi thermal sprayed coatings

NASA Astrophysics Data System (ADS)

Cinca, N.; Isalgué, A.; Fernández, J.; Guilemany, J. M.

2010-08-01

NiTi shape memory alloy (SMA) has been studied for many years for its shape memory and pseudoelastic properties, as well as its biocompatibility, which make it suitable for many biomedical applications. However, SMA NiTi is also interesting for relevant wear resistance near the transition temperature which, along with its high oxidation and corrosion resistance, suggests its use as a coating to increase the lifetime of some components. Also, whereas bulk material properties have been characterized in respect of the nominal composition, manufacturing methods and thermo-mechanical treatments, NiTi overlays have been investigated much less. Most existent works in this field specifically deal with magnetron sputtering technology for thin films and its use in micro-devices (micro-electro-mechanical systems, MEMS), just some works refer to vacuum plasma spraying (VPS) for thicker coatings. The present paper explores and compares the microstructure and wear-related properties of coatings obtained from atomized NiTi powders, by VPS as well as by atmospheric plasma spraying (APS) and high velocity oxygen fuel (HVOF) techniques. In the present case, the wear behaviour of the NiTi deposits has been studied by rubber-wheel equipment and ball-on-disk tests. The results obtained at room temperature show that the APS-quenched coatings exhibit a preferential dry sliding wear mechanism, while the VPS and HVOF coatings show an abrasive mechanism.

Comparison between PCL/hydroxyapatite (HA) and PCL/halloysite nanotube (HNT) composite scaffolds prepared by co-extrusion and gas foaming.

PubMed

Jing, Xin; Mi, Hao-Yang; Turng, Lih-Sheng

2017-03-01

In this work, three-dimensional poly(caprolactone) (PCL) tissue engineering scaffolds were prepared by co-extrusion and gas foaming. Biocompatible hydroxyapatite (HA) and halloysite nanotubes (HNT) were added to the polymer matrix to enhance the mechanical properties and bioactivity of the composite scaffolds. The effects of HA and HNT on the rheological behavior, microstructure, and mechanical properties of the composite scaffolds were systematically compared. It was found that the HNT improved viscosity more significantly than HA, and reduced the pore size of scaffolds, while the mechanical performance of PCL/HNT scaffolds was higher than PCL/HA scaffolds with the same filler content. Human mesenchymal stem cells (hMSCs) were used as the cell model to compare the biological properties of two composite scaffolds. The results demonstrated that cells could survive on all scaffolds, and showed a more flourishing living state on the composite scaffolds. The cell differentiation for 5% HA and 1% HNT scaffolds were significantly higher than other scaffolds, while the differentiation of 5% HNT scaffolds was lower than that of 1% HNT scaffolds mainly because of the reduced pore size and pore interconnectivity. Therefore, this study suggested that, with proper filler content and control of microstructure through processing, HNT could be a suitable substitute for HA for bone tissue engineering to reduce the cost and improve mechanical performance. Copyright © 2016. Published by Elsevier B.V.

Ultrafast Self-Healing Nanocomposites via Infrared Laser and Their Application in Flexible Electronics.

PubMed

Wu, Shuwen; Li, Jinhui; Zhang, Guoping; Yao, Yimin; Li, Gang; Sun, Rong; Wong, Chingping

2017-01-25

The continuous evolution toward flexible electronics with mechanical robust property and restoring structure simultaneously places high demand on a set of polymeric material substrate. Herein, we describe a composite material composed of a polyurethane based on Diels-Alder chemistry (PU-DA) covalently linked with functionalized graphene nanosheets (FGNS), which shows mechanical robust and infrared (IR) laser self-healing properties at ambient conditions and is therefore suitable for flexible substrate applications. The mechanical strength can be tuned by varying the amount of FGNS and breaking strength can reach as high as 36 MPa with only 0.5 wt % FGNS loading. On rupture, the initial mechanical properties are restored with more than 96% healing efficiency after 1 min irradiation time by 980 nm IR laser. Especially, this is the highest value of healing efficiency reported in the self-healable materials based on DA chemistry systems until now, and the composite exhibits a high volume resistivity up to 5.6 × 10 11 Ω·cm even the loading of FGNS increased to 1.0 wt %. Moreover, the conductivity of the broken electric circuit which was fabricated by silver paste drop-cast on the healable composite substrate was completely recovered via IR laser irradiating bottom substrate mimicking human skin. These results demonstrate that the FGNS-PU-DA nanocomposite can be used as self-healing flexible substrate for the next generation of intelligent flexible electronics.

Radiopaque UHMWPE sublaminar cables for spinal deformity correction: Preclinical mechanical and radiopacifier leaching assessment.

PubMed

Roth, Alex K; Boon-Ceelen, Karlien; Smelt, Harold; van Rietbergen, Bert; Willems, Paul C; van Rhijn, Lodewijk W; Arts, Jacobus J

2018-02-01

Polymeric sublaminar cables have a number of advantages over metal cables in the field of spinal deformity surgery, with decreased risk of neurological injury and potential for higher correction forces as the two most predominant. However, currently available polymer cables are radiolucent, precluding postoperative radiological assessment of instrumentation stability and integrity. This study provides a preclinical assessment of a woven UHMWPE cable made with radiopaque UHMWPE fibers. Our primary goal was to determine if the addition of a radiopacifier negatively affects the mechanical properties of UHMWPE woven cables. Tensile mechanical properties were determined and compared to suitable controls. Radiopacity was evaluated and radiopacifier leaching was assessed in vitro and in vivo. Finally, in vivo bismuth organ content was quantified after a 24-week implantation period in sheep. Results show that the mechanical properties of woven UHMWPE cables were not deleteriously affected by the addition of homogenously dispersed bismuth oxide particles within each fiber. Limited amounts of bismuth oxide were released in vitro, well below the toxicological threshold. Tissue concentrations lower than generally accepted therapeutic dosages for use against gastrointestinal disorders, well below toxic levels, were discovered in vivo. These results substantiate controlled clinical introduction of these radiopaque UHMWPE cables. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 771-779, 2018. © 2017 Wiley Periodicals, Inc.

Optical properties of hydroxyapatite obtained by mechanical alloying

NASA Astrophysics Data System (ADS)

Silva, C. C.; Thomazini, D.; Pinheiro, A. G.; Lanciotti, F.; Sasaki, J. M.; Góes, J. C.; Sombra, A. S. B.

2002-09-01

Calcium phosphate based bioceramics, mainly in the form of hydroxyapatite (HA), have been in use in medicine and dentistry for the last 20 years. Applications include coatings of orthopaedic and dental implants, alveolar ridge augmentation, maxillofacial surgery, otolaryngology, and scaffolds for bone growth and as powders in total hip and knee surgery. These materials exhibit several problems of handling and fabrication, which can be overcome by mixing with a suitable binder. In this paper, mechanical alloying has been used successfully to produce nanocrystalline powders of HA using five different experimental procedures. The milled HA were studied by X-ray powder diffraction, infrared and Raman scattering spectroscopy. For four different procedures, HA was obtained after a couple of hours of milling (on an average, 20 h of milling depending on the reaction procedure). The XRD patterns indicate that the grain size is within the range of 29-103 nm. This milling process, used to produce HA, presents the advantage that melting is not necessary and the powder obtained is nanocrystalline with extraordinary mechanical properties. The material can be compacted and transformed in solid ceramic samples. The high efficiency of the process opens a way to produce commercial amount of nanocrystalline HA. Due to the nanocrystalline character of this powder, their mechanical properties have changed and for this reason a pressure of 1 GPa is enough to shape the sample into any geometry.

Fabrication, morphology and mechanical properties of Ti and metastable Ti-based alloy foams for biomedical applications.

PubMed

Rivard, J; Brailovski, V; Dubinskiy, S; Prokoshkin, S

2014-12-01

Metallic foams with porosity ranging from 0.25 to 0.65 have been produced from TiCp, Ti-Nb-Zr and Ti-Nb-Ta prealloyed powder by using the space-holder technique, and analysed from both the pore morphology and mechanical properties' points of view. For all the foams, the most suitable porosity range for bone ingrowth appears to be 0.35 to 0.45, since these porosities lead to a pore size that is globally encompassed in the recommended 100-600 μm range. From the mechanical behavior point of view, all of the as-sintered foams demonstrate similar compression behavior in terms of their apparent Young's modulus and critical stresses. In the recommended 0.3-0.45 porosity range, their Young's modulus varies from 15 to 8 GPa, whilst their yield stress varies from 300 to 150 MPa. The first characteristic comes close to that of cortical bone, whilst the second significantly exceeds bone resistance. Compared to Ti foams, the mechanical properties of metastable TNZ and TNT alloy foams can also be regulated within a ±20% range, by selecting an appropriate post-sintering thermal treatment. This effect, which is initiated by activating reversible stress-induced β to α″ martensitic transformation, is strongly perceptible for TNZ foams, whilst much less pronounced for TNT foams. Copyright © 2014 Elsevier B.V. All rights reserved.

Silk coating on a bioactive ceramic scaffold for bone regeneration: effective enhancement of mechanical and in vitro osteogenic properties towards load-bearing applications.

PubMed

Li, Jiao Jiao; Roohani-Esfahani, Seyed-Iman; Kim, Kyungsook; Kaplan, David L; Zreiqat, Hala

2017-06-01

Bioactive ceramic scaffolds represent competitive choices for clinical bone reconstruction, but their widespread use is restricted by inherent brittleness and weak mechanical performance under load. This study reports the development of strong and tough bioactive scaffolds suitable for use in load-bearing bone reconstruction. A strong and bioactive ceramic scaffold (strontium-hardystonite-gahnite) is combined with single and multiple coating layers of silk fibroin to enhance its toughness, producing composite scaffolds which match the mechanical properties of cancellous bone and show enhanced capacity to promote in vitro osteogenesis. Also reported for the first time is a comparison of the coating effects obtained when a polymeric material is coated on ceramic scaffolds with differing microstructures, namely the strontium-hardystonite-gahnite scaffold with high-density struts as opposed to a conventional ceramic scaffold, such as biphasic calcium phosphate, with low-density struts. The results show that silk coating on a unique ceramic scaffold can lead to simple and effective enhancement of its mechanical and biological properties to suit a wider range of applications in clinical bone reconstruction, and also establish the influence of ceramic microstructure on the effectiveness of silk coating as a method of reinforcement when applied to different types of ceramic bone graft substitutes. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

Fast parametric relationships for the large-scale reservoir simulation of mixed CH 4-CO 2 gas hydrate systems

DOE PAGES

Reagan, Matthew T.; Moridis, George J.; Seim, Katie S.

2017-03-27

A recent Department of Energy field test on the Alaska North Slope has increased interest in the ability to simulate systems of mixed CO 2-CH 4 hydrates. However, the physically realistic simulation of mixed-hydrate simulation is not yet a fully solved problem. Limited quantitative laboratory data leads to the use of various ab initio, statistical mechanical, or other mathematic representations of mixed-hydrate phase behavior. Few of these methods are suitable for inclusion in reservoir simulations, particularly for systems with large number of grid elements, 3D systems, or systems with complex geometric configurations. In this paper, we present a set ofmore » fast parametric relationships describing the thermodynamic properties and phase behavior of a mixed methane-carbon dioxide hydrate system. We use well-known, off-the-shelf hydrate physical properties packages to generate a sufficiently large dataset, select the most convenient and efficient mathematical forms, and fit the data to those forms to create a physical properties package suitable for inclusion in the TOUGH+ family of codes. Finally, the mapping of the phase and thermodynamic space reveals the complexity of the mixed-hydrate system and allows understanding of the thermodynamics at a level beyond what much of the existing laboratory data and literature currently offer.« less

Process for derivatizing carbon nanotubes with diazonium species

NASA Technical Reports Server (NTRS)

Tour, James M. (Inventor); Bahr, Jeffrey L. (Inventor); Yang, Jiping (Inventor)

2007-01-01

The invention incorporates new processes for the chemical modification of carbon nanotubes. Such processes involve the derivatization of multi- and single-wall carbon nanotubes, including small diameter (ca. 0.7 nm) single-wall carbon nanotubes, with diazonium species. The method allows the chemical attachment of a variety of organic compounds to the side and ends of carbon nanotubes. These chemically modified nanotubes have applications in polymer composite materials, molecular electronic applications and sensor devices. The methods of derivatization include electrochemical induced reactions thermally induced reactions (via in-situ generation of diazonium compounds or pre-formed diazonium compounds), and photochemically induced reactions. The derivatization causes significant changes in the spectroscopic properties of the nanotubes. The estimated degree of functionality is ca. 1 out of every 20 to 30 carbons in a nanotube bearing a functionality moiety. Such electrochemical reduction processes can be adapted to apply site-selective chemical functionalization of nanotubes. Moreover, when modified with suitable chemical groups, the derivatized nanotubes are chemically compatible with a polymer matrix, allowing transfer of the properties of the nanotubes (such as, mechanical strength or electrical conductivity) to the properties of the composite material as a whole. Furthermore, when modified with suitable chemical groups, the groups can be polymerized to form a polymer that includes carbon nanotubes ##STR00001##.

Fast parametric relationships for the large-scale reservoir simulation of mixed CH4-CO2 gas hydrate systems

NASA Astrophysics Data System (ADS)

Reagan, Matthew T.; Moridis, George J.; Seim, Katie S.

2017-06-01

A recent Department of Energy field test on the Alaska North Slope has increased interest in the ability to simulate systems of mixed CO2-CH4 hydrates. However, the physically realistic simulation of mixed-hydrate simulation is not yet a fully solved problem. Limited quantitative laboratory data leads to the use of various ab initio, statistical mechanical, or other mathematic representations of mixed-hydrate phase behavior. Few of these methods are suitable for inclusion in reservoir simulations, particularly for systems with large number of grid elements, 3D systems, or systems with complex geometric configurations. In this work, we present a set of fast parametric relationships describing the thermodynamic properties and phase behavior of a mixed methane-carbon dioxide hydrate system. We use well-known, off-the-shelf hydrate physical properties packages to generate a sufficiently large dataset, select the most convenient and efficient mathematical forms, and fit the data to those forms to create a physical properties package suitable for inclusion in the TOUGH+ family of codes. The mapping of the phase and thermodynamic space reveals the complexity of the mixed-hydrate system and allows understanding of the thermodynamics at a level beyond what much of the existing laboratory data and literature currently offer.

Fast parametric relationships for the large-scale reservoir simulation of mixed CH 4-CO 2 gas hydrate systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reagan, Matthew T.; Moridis, George J.; Seim, Katie S.

A recent Department of Energy field test on the Alaska North Slope has increased interest in the ability to simulate systems of mixed CO 2-CH 4 hydrates. However, the physically realistic simulation of mixed-hydrate simulation is not yet a fully solved problem. Limited quantitative laboratory data leads to the use of various ab initio, statistical mechanical, or other mathematic representations of mixed-hydrate phase behavior. Few of these methods are suitable for inclusion in reservoir simulations, particularly for systems with large number of grid elements, 3D systems, or systems with complex geometric configurations. In this paper, we present a set ofmore » fast parametric relationships describing the thermodynamic properties and phase behavior of a mixed methane-carbon dioxide hydrate system. We use well-known, off-the-shelf hydrate physical properties packages to generate a sufficiently large dataset, select the most convenient and efficient mathematical forms, and fit the data to those forms to create a physical properties package suitable for inclusion in the TOUGH+ family of codes. Finally, the mapping of the phase and thermodynamic space reveals the complexity of the mixed-hydrate system and allows understanding of the thermodynamics at a level beyond what much of the existing laboratory data and literature currently offer.« less

A first demonstration of audio-frequency optical coherence elastography of tissue

NASA Astrophysics Data System (ADS)

Adie, Steven G.; Alexandrov, Sergey A.; Armstrong, Julian J.; Kennedy, Brendan F.; Sampson, David D.

2008-12-01

Optical elastography is aimed at using the visco-elastic properties of soft tissue as a contrast mechanism, and could be particularly suitable for high-resolution differentiation of tumour from surrounding normal tissue. We present a new approach to measure the effect of an applied stimulus in the kilohertz frequency range that is based on optical coherence tomography. We describe the approach and present the first in vivo optical coherence elastography measurements in human skin at audio excitation frequencies.

Space Environment Stability and Physical Properties of New Materials for Space Power and Commercial Applications

NASA Technical Reports Server (NTRS)

Hambourger, Paul D.

1997-01-01

To test and evaluate suitability of materials for use in space power systems and related space and commercial applications, and to achieve sufficient understanding of the mechanisms by which, the materials perform in their intended applications. Materials and proposed applications included but were not limited to: Improved anodes for lithium ion batteries, highly-transparent arc-proof solar array coatings, and improved surface materials for solar dynamic concentrators and receivers. Cooperation and interchange of data with industrial companies as appropriate.

Overview of zirconia with respect to gas turbine applications

NASA Technical Reports Server (NTRS)

Cawley, J. D.

1984-01-01

Phase relationships and the mechanical properties of zirconia are examined as well as the thermal conductivity, deformation, diffusion, and chemical reactivity of this refractory material. Observations from the literature particular to plasma-sprayed material and implications for gas turbine engine applications are discussed. The literature review indicates that Mg-PSZ (partially stabilized zirconia) and Ca-PSZ are unsuitable for advanced gas turbine applications; a thorough characterization of the microstructure of plasma-sprayed zirconia is needed. Transformation-toughened zirconia may be suitable for use in monolithic components.

Breast Tissue Stromal Cells Preferentially Promote Generation of M2 Macrophages: A Novel Mechanism for Tumor Supportive Properties of Breast Microenvironment

DTIC Science & Technology

2011-08-01

macrophages (MQs), on growth of breast tumor cells, and (2) to test the hypothesis that MSCs of non -breast adipose tissues, in contrast to MSCs of...macrophages in normal and malignant tissues. In contrast to all studies focused on the role of breast tissue microenvironment in growth of primary breast...the phenotype of macrophages, provide an immune environment suitable for growth of breast cancer cells, but MSCs present in non -breast adipose

75 FR 70941 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-11-19

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-45] Federal Property Suitable as... homeless. FOR FURTHER INFORMATION CONTACT: Kathy Ezzell, Department of Housing and Urban Development, 451...-site use only Land California Drill Site 3A null Ford City CA 93268 Landholding Agency: GSA Property...

Cell mechanics as a marker for diseases: Biomedical applications of AFM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rianna, Carmela; Radmacher, Manfred, E-mail: mr@biophysik.uni-bremen.de

Many diseases are related to changes in cell mechanics. Atomic Force Microscopy (AFM) is one of the most suitable techniques allowing the investigation of both topography and mechanical properties of adherent cells with high spatial resolution under physiological conditions. Over the years the use of this technique in medical and clinical applications has largely increased, resulting in the notion of cell mechanics as a biomarker to discriminate between different physiological and pathological states of cells. Cell mechanics has proven to be a biophysical fingerprint able discerning between cell phenotypes, unraveling processes in aging or diseases, or even detecting and diagnosingmore » cellular pathologies. We will review in this report some of the works on cell mechanics investigated by AFM with clinical and medical relevance in order to clarify the state of research in this field and to highlight the role of cell mechanics in the study of pathologies, focusing on cancer, blood and cardiovascular diseases.« less

Apatite glass-ceramics: a review

NASA Astrophysics Data System (ADS)

Duminis, Tomas; Shahid, Saroash; Hill, Robert Graham

2016-12-01

This article is a review of the published literature on apatite glass-ceramics (GCs). Topics covered include crystallization mechanisms of the various families of the apatite GCs and an update on research and development on apatite GCs for applications in orthopedics, dentistry, optoelectronics and nuclear waste management. Most apatite GCs crystallize through a homogenous nucleation and crystallization mechanism, which is aided by a prior liquid-liquid phase separation. Careful control of the base glass composition and heat-treatment conditions, which determine the nature and morphology of the crystal phases in the GC can produce GC materials with exceptional thermal, mechanical, optical and biological properties. The GCs reviewed for orthopedic applications exhibit suitable mechanical properties and can chemically bond to bone and stimulate its regeneration. The most commercially successful apatite GCs are those developed for dental veneering. These materials exhibit excellent translucency and clinical esthetics, and mimic the natural tooth mineral. Due to the ease of solid solution of the apatite lattice, rare earth doped apatite GCs are discussed for potential applications in optoelectronics and nuclear waste management. One of the drawbacks of the commercial apatite GCs used in orthopedics is the lack of resorbability, therefore the review provides a direction for future research in the field.

Sol-Gel Derived Hydroxyapatite Coating on Mg-3Zn Alloy for Orthopedic Application

NASA Astrophysics Data System (ADS)

Singh, Sanjay; Manoj Kumar, R.; Kuntal, Kishor Kumar; Gupta, Pallavi; Das, Snehashish; Jayaganthan, R.; Roy, Partha; Lahiri, Debrupa

2015-04-01

In recent years, magnesium and its alloys have gained a lot of interest as orthopedic implant constituents because their biodegradability and mechanical properties are closer to that of human bone. However, one major concern with Mg in orthopedics is its high corrosion rate that results in the reduction of mechanical integrity before healing the bone tissue. The current study evaluates the sol-gel-derived hydroxyapatite (HA) coating on a selected Mg alloy (Mg-3Zn) for decreasing the corrosion rate and increasing the bioactivity of the Mg surface. The mechanical integrity of the coating is established as a function of the surface roughness of the substrate and the sintering temperature of the coating. Coating on a substrate roughness of 15-20 nm and sintering at 400°C shows the mechanical properties in similar range of bone, thus making it suitable to avoid the stress-shielding effect. The hydroxyapatite coating on the Mg alloy surface also increases corrosion resistance very significantly by 40 times. Bone cells are also found proliferating better in the HA-coated surface. All these benefits together establish the candidature of sol-gel HA-coated Mg-3Zn alloy in orthopedic application.

MEMS-based wide-bandwidth electromagnetic energy harvester with electroplated nickel structure

NASA Astrophysics Data System (ADS)

Sun, Shi; Dai, Xuhan; Sun, Yunna; Xiang, Xiaojian; Ding, Guifu; Zhao, Xiaolin

2017-11-01

A novel nickel-based nonlinear electromagnetic energy harvester has been designed, fabricated, and characterized in this work. Electroplated nickel is very suitable for a stretching-based mechanism to broaden the bandwidth due to its good process and mechanical properties. A strong hardening nonlinearity is induced due to the large deformation of the thin nickel based guided-beam structure. Combining the merits of both the mechanical properties and guided-beam structure, the energy harvester shows good bandwidth performance. It is found that increasing the thickness of the central platform could guarantee nonlinearity. Static and dynamic models of the energy harvester are simulated and validated. Test results show that the energy harvester has good repeatability without any destruction under a large deformation condition. At the acceleration of 0.5 g, comparative large bandwidths of 129 and 59 Hz are obtained for displacement and RMS output voltage, respectively. Power output of 3.4 µW and normalized power density of 125.92 µW cm-3 g-2 are achieved with the load resistance of 38 Ω.

Iron oxide nanoparticles as dielectric and piezoelectric enhancers for silicone elastomers

NASA Astrophysics Data System (ADS)

Iacob, Mihail; Tugui, Codrin; Tiron, Vasile; Bele, Adrian; Vlad, Stelian; Vasiliu, Tudor; Cazacu, Maria; Vasiliu, Ana-Lavinia; Racles, Carmen

2017-10-01

Iron oxide nanoparticles were prepared using an alkaline precipitation method to tune the reaction time so as to afford ferrihydrite with spherical morphology or goethite nanorods. These two nanoparticle types, surface-treated with a surfactant (Pluronic L81), were each incorporated in 10, 20 and 30 wt% within a polydimethylsiloxane-α,ω-diol (Mn = 60 000 g mol-1). The mixtures were processed as films and crosslinked by condensation with tetraethoxysilane at room temperature. The aged films were investigated concerning filler distribution (by SEM coupled with an energy-dispersive x-ray spectroscopy module), mechanical (tensile strength, elongation and Young’s modulus), and dielectric properties (permittivity, loss, conductivity and strength). The results show that the fillers have a relatively homogeneous distribution within the matrix and, dependent on the filler nature and amount, generally manifest a mechanical reinforcing effect and act as dielectric permittivity and strength enhancers. In addition, it has been found that the crystalline nanoparticles induce a piezoelectric response, emphasized by piezoelectric force microscopy. The improved properties of the composites make them suitable for applications in mechanical/electrical energy conversion, as theoretical estimates showed.

The Influence of Welding Parameters on the Nugget Formation of Resistance Spot Welding of Inconel 625 Sheets

NASA Astrophysics Data System (ADS)

Rezaei Ashtiani, Hamid Reza; Zarandooz, Roozbeh

2015-09-01

A 2D axisymmetric electro-thermo-mechanical finite element (FE) model is developed to investigate the effect of current intensity, welding time, and electrode tip diameter on temperature distributions and nugget size in resistance spot welding (RSW) process of Inconel 625 superalloy sheets using ABAQUS commercial software package. The coupled electro-thermal analysis and uncoupled thermal-mechanical analysis are used for modeling process. In order to improve accuracy of simulation, material properties including physical, thermal, and mechanical properties have been considered to be temperature dependent. The thickness and diameter of computed weld nuggets are compared with experimental results and good agreement is observed. So, FE model developed in this paper provides prediction of quality and shape of the weld nuggets and temperature distributions with variation of each process parameter, suitably. Utilizing this FE model assists in adjusting RSW parameters, so that expensive experimental process can be avoided. The results show that increasing welding time and current intensity lead to an increase in the nugget size and electrode indentation, whereas increasing electrode tip diameter decreases nugget size and electrode indentation.

Polyurethane/fluor-hydroxyapatite nanocomposite scaffolds for bone tissue engineering. Part I: morphological, physical, and mechanical characterization

PubMed Central

Asefnejad, Azadeh; Behnamghader, Aliasghar; Khorasani, Mohammad Taghi; Farsadzadeh, Babak

2011-01-01

In this study, new nano-fluor-hydroxyapatite (nFHA)/polyurethane composite scaffolds were fabricated for potential use in bone tissue engineering. Polyester urethane samples were synthesized from polycaprolactone, hexamethylene diisocyanate, and 1,4-butanediol as chain extender. Nano fluor-hydroxyapatite (nFHA) was successfully synthesized by sol-gel method. The solid–liquid phase separation and solvent sublimation methods were used for preparation of the porous composites. Mechanical properties, chemical structure, and morphological characteristics of the samples were investigated by compressive test, Fourier transform infrared, and scanning electron microscopy (SEM) techniques, respectively. The effect of nFHA powder content on porosity and pore morphology was investigated. SEM images demonstrated that the scaffolds were constituted of interconnected and homogeneously distributed pores. The pore size of the scaffolds was in the range 50–250 μm. The result obtained in this research revealed that the porosity and pore average size decreased and compressive modulus increased with nFHA percentage. Considering morphological, physical, and mechanical properties, the scaffold with a higher ratio of nFHA has suitable potential use in tissue regeneration. PMID:21289986

Transparent Metal-Salt-Filled Polymeric Radiation Shields

NASA Technical Reports Server (NTRS)

Edwards, David; Lennhoff, John; Harris, George

2003-01-01

"COR-RA" (colorless atomic oxygen resistant -- radiation shield) is the name of a transparent polymeric material filled with x-ray-absorbing salts of lead, bismuth, cesium, and thorium. COR-RA is suitable for use in shielding personnel against bremsstrahlung radiation from electron-beam welding and industrial and medical x-ray equipment. In comparison with lead-foil and leaded-glass shields that give equivalent protection against x-rays (see table), COR-RA shields are mechanically more durable. COR-RA absorbs not only x-rays but also neutrons and rays without adverse effects on optical or mechanical performance. The formulation of COR-RA with the most favorable mechanical-durability and optical properties contains 22 weight percent of bismuth to absorb x-rays, plus 45 atomic percent hydrogen for shielding against neutrons.

On the characterization of the heterogeneous mechanical response of human brain tissue.

PubMed

Forte, Antonio E; Gentleman, Stephen M; Dini, Daniele

2017-06-01

The mechanical characterization of brain tissue is a complex task that scientists have tried to accomplish for over 50 years. The results in the literature often differ by orders of magnitude because of the lack of a standard testing protocol. Different testing conditions (including humidity, temperature, strain rate), the methodology adopted, and the variety of the species analysed are all potential sources of discrepancies in the measurements. In this work, we present a rigorous experimental investigation on the mechanical properties of human brain, covering both grey and white matter. The influence of testing conditions is also shown and thoroughly discussed. The material characterization performed is finally adopted to provide inputs to a mathematical formulation suitable for numerical simulations of brain deformation during surgical procedures.

Identifying mechanical property parameters of planetary soil using in-situ data obtained from exploration rovers

NASA Astrophysics Data System (ADS)

Ding, Liang; Gao, Haibo; Liu, Zhen; Deng, Zongquan; Liu, Guangjun

2015-12-01

Identifying the mechanical property parameters of planetary soil based on terramechanics models using in-situ data obtained from autonomous planetary exploration rovers is both an important scientific goal and essential for control strategy optimization and high-fidelity simulations of rovers. However, identifying all the terrain parameters is a challenging task because of the nonlinear and coupling nature of the involved functions. Three parameter identification methods are presented in this paper to serve different purposes based on an improved terramechanics model that takes into account the effects of slip, wheel lugs, etc. Parameter sensitivity and coupling of the equations are analyzed, and the parameters are grouped according to their sensitivity to the normal force, resistance moment and drawbar pull. An iterative identification method using the original integral model is developed first. In order to realize real-time identification, the model is then simplified by linearizing the normal and shearing stresses to derive decoupled closed-form analytical equations. Each equation contains one or two groups of soil parameters, making step-by-step identification of all the unknowns feasible. Experiments were performed using six different types of single-wheels as well as a four-wheeled rover moving on planetary soil simulant. All the unknown model parameters were identified using the measured data and compared with the values obtained by conventional experiments. It is verified that the proposed iterative identification method provides improved accuracy, making it suitable for scientific studies of soil properties, whereas the step-by-step identification methods based on simplified models require less calculation time, making them more suitable for real-time applications. The models have less than 10% margin of error comparing with the measured results when predicting the interaction forces and moments using the corresponding identified parameters.

Evaluation of Flexural Strength of Polymethyl Methacrylate modified with Silver Colloidal Nanoparticles subjected to Two Different Curing Cycles: An in vitro Study.

PubMed

Munikamaiah, Ranganath L; Jain, Saket K; Pal, Kapil S; Gaikwad, Ajay

2018-03-01

Silver colloidal nanoparticles have been incorporated into acrylic resins to induce antimicrobial properties. However, as additives, they can influence the mechanical properties of the final product. Mechanical properties are also dependent on different curing cycles. The aim of this study was to evaluate flexural strength of a denture base resin incorporated with different concentrations of silver colloidal nanoparticles subjected to two different curing cycles. Lucitone 199 denture base resin was used into which silver colloidal nanoparticles were incorporated at 0.5 and 5% by polymer mass. Specimens devoid of nanoparticles were used as controls. A total of 60 specimens were fabricated and divided into two groups. Each group was divided into three subgroups consisting of 10 specimens each. The specimens were fabricated according to American Dental Association (ADA) specification No. 12 and tested for flexural strength using universal testing machine. Silver colloidal nanoparticle incorporation at 0.5% concentration increased the mean flexural strength in both curing cycles by 7.5 and 4.4%, respectively, when compared with the control group. The study suggested that the mean flexural strength value of 0.5% silver colloidal nanoparticles in denture base resin was above the value of the control group both in short and long curing cycles, which makes it clinically suitable as a denture base material. However, at 5% concentration, the statistically significant amount of decrease in flexural strength compared with the value of control group both in short and long curing cycles gives it a questionable prognosis. The specimens incorporated with the antimicrobial agent 0.5% silver colloidal nanoparticles and processed by long curing cycles showed significant increase in its flexural strength compared with the control group, which makes it clinically suitable as a denture base material.

Modelling and simulation of cure in pultrusion processes

NASA Astrophysics Data System (ADS)

Tucci, F.; Rubino, F.; Paradiso, V.; Carlone, P.; Valente, R.

2017-10-01

Trial and error approach is not a suitable method to optimize the pultrusion process because of the high times required for the start up and the wide range of possible combinations of matrix and reinforcement. On the other hand, numerical approaches can be a suitable solution to test different parameter configuration. One of the main tasks in pultrusion processes is to obtain a complete and homogeneous resin polymerization. The formation of cross-links between polymeric chains is thermally induced but it leads to a strong exothermic heat generation, hence the thermal and the chemical phenomena are mutually affected. It requires that the two problems have to be modelled in coupled way. The mathematical model used in this work considers the composite as a lumped material, whose thermal and mechanical properties are evaluated as function of resin and fibers properties. The numerical pattern is based on a quasi-static approach in a three-dimensional Eulerian domain, which describes both thermal and chemical phenomena. The data obtained are used in a simplified C.H.I.L.E. (Cure Hardening Instantaneous Linear Elastic) model to compute the mechanical properties of the resin fraction in the pultruded. The two combined approaches allow to formulate a numerical model which takes into account the normal (no-penetration) and tangential (viscosity/friction) interactions between die and profile, the pulling force and the hydrostatic pressure of the liquid resin to evaluate the stress and strain fields induced by the process within the pultruded. The implementation of the numerical models has been carried out using the ABAQUS finite element suite, by means of several user subroutines (in Fortran language) which improve the basic software potentialities.

Environmental Suitability for Leasing Property

EPA Pesticide Factsheets

This is a Memorandum of Understanding between the U.S. Environmental Protection Agency and the U.S. Department of Defense, regarding the procedures to determine environmental suitability for leasing property available as a result of a base closure or realignment.

76 FR 34093 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2011-06-10

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Association of Alpha Tocopherol and Ag Sulfadiazine Chitosan Oleate Nanocarriers in Bioactive Dressings Supporting Platelet Lysate Application to Skin Wounds.

PubMed

Bonferoni, Maria Cristina; Sandri, Giuseppina; Rossi, Silvia; Dellera, Eleonora; Invernizzi, Alessandro; Boselli, Cinzia; Cornaglia, Antonia Icaro; Del Fante, Claudia; Perotti, Cesare; Vigani, Barbara; Riva, Federica; Caramella, Carla; Ferrari, Franca

2018-02-09

Chitosan oleate was previously proposed to encapsulate in nanocarriers some poorly soluble molecules aimed to wound therapy, such as the anti-infective silver sulfadiazine, and the antioxidant α tocopherol. Because nanocarriers need a suitable formulation to be administered to wounds, in the present paper, these previously developed nanocarriers were loaded into freeze dried dressings based on chitosan glutamate. These were proposed as bioactive dressings aimed to support the application to wounds of platelet lysate, a hemoderivative rich in growth factors. The dressings were characterized for hydration capacity, morphological aspect, and rheological and mechanical behavior. Although chitosan oleate nanocarriers clearly decreased the mechanical properties of dressings, these remained compatible with handling and application to wounds. Preliminary studies in vitro on fibroblast cell cultures demonstrated good compatibility of platelet lysate with nanocarriers and bioactive dressings. An in vivo study on a murine wound model showed an accelerating wound healing effect for the bioactive dressing and its suitability as support of the platelet lysate application to wounds.

Association of Alpha Tocopherol and Ag Sulfadiazine Chitosan Oleate Nanocarriers in Bioactive Dressings Supporting Platelet Lysate Application to Skin Wounds

PubMed Central

Bonferoni, Maria Cristina; Dellera, Eleonora; Invernizzi, Alessandro; Cornaglia, Antonia Icaro; Perotti, Cesare; Vigani, Barbara; Caramella, Carla; Ferrari, Franca

2018-01-01

Chitosan oleate was previously proposed to encapsulate in nanocarriers some poorly soluble molecules aimed to wound therapy, such as the anti-infective silver sulfadiazine, and the antioxidant α tocopherol. Because nanocarriers need a suitable formulation to be administered to wounds, in the present paper, these previously developed nanocarriers were loaded into freeze dried dressings based on chitosan glutamate. These were proposed as bioactive dressings aimed to support the application to wounds of platelet lysate, a hemoderivative rich in growth factors. The dressings were characterized for hydration capacity, morphological aspect, and rheological and mechanical behavior. Although chitosan oleate nanocarriers clearly decreased the mechanical properties of dressings, these remained compatible with handling and application to wounds. Preliminary studies in vitro on fibroblast cell cultures demonstrated good compatibility of platelet lysate with nanocarriers and bioactive dressings. An in vivo study on a murine wound model showed an accelerating wound healing effect for the bioactive dressing and its suitability as support of the platelet lysate application to wounds. PMID:29425164

Studies on the growth, structural, optical, mechanical properties of 8-hydroxyquinoline single crystal by vertical Bridgman technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prabhakaran, SP.; Babu, R. Ramesh, E-mail: rampap2k@yahoo.co.in; Velusamy, P.

2011-11-15

Highlights: {yields} Growth of bulk single crystal of 8-hydroxyquinoline (8-HQ) by vertical Bridgman technique for the first time. {yields} The crystalline perfection is reasonably good. {yields} The photoluminescence spectrum shows that the material is suitable for blue light emission. -- Abstract: Single crystal of organic nonlinear optical material, 8-hydroxyquinoline (8-HQ) of dimension 52 mm (length) x 12 mm (dia.) was grown from melt using vertical Bridgman technique. The crystal system of the material was confirmed by powder X-ray diffraction analysis. The crystalline perfection of the grown crystal was examined by high-resolution X-ray diffraction study. Low angular spread around 400'' ofmore » the diffraction curve and the low full width half maximum values show that the crystalline perfection is reasonably good. The recorded photoluminescence spectrum shows that the material is suitable for blue light emission. Optical transmittance for the UV and visible region was measured and mechanical strength was estimated from Vicker's microhardness test along the growth face of the grown crystal.« less

Substrate stiffness affects skeletal myoblast differentiation in vitro

NASA Astrophysics Data System (ADS)

Romanazzo, Sara; Forte, Giancarlo; Ebara, Mitsuhiro; Uto, Koichiro; Pagliari, Stefania; Aoyagi, Takao; Traversa, Enrico; Taniguchi, Akiyoshi

2012-12-01

To maximize the therapeutic efficacy of cardiac muscle constructs produced by stem cells and tissue engineering protocols, suitable scaffolds should be designed to recapitulate all the characteristics of native muscle and mimic the microenvironment encountered by cells in vivo. Moreover, so not to interfere with cardiac contractility, the scaffold should be deformable enough to withstand muscle contraction. Recently, it was suggested that the mechanical properties of scaffolds can interfere with stem/progenitor cell functions, and thus careful consideration is required when choosing polymers for targeted applications. In this study, cross-linked poly-ɛ-caprolactone membranes having similar chemical composition and controlled stiffness in a supra-physiological range were challenged with two sources of myoblasts to evaluate the suitability of substrates with different stiffness for cell adhesion, proliferation and differentiation. Furthermore, muscle-specific and non-related feeder layers were prepared on stiff surfaces to reveal the contribution of biological and mechanical cues to skeletal muscle progenitor differentiation. We demonstrated that substrate stiffness does affect myogenic differentiation, meaning that softer substrates can promote differentiation and that a muscle-specific feeder layer can improve the degree of maturation in skeletal muscle stem cells.

Polyad breaking phenomenon associated with a local-to-normal mode transition and suitability to estimate force constants

NASA Astrophysics Data System (ADS)

Bermúdez-Montaña, M.; Lemus, R.; Castaños, O.

2017-12-01

In a system of two interacting harmonic oscillators a local-to-normal mode transition is manifested as a polyad breaking phenomenon. This phenomenon is associated with the suitability to estimate zeroth-order force constants in the framework of a local mode description. This transition is also exhibited in two interacting Morse oscillators. To study this case, an appropriate parameterisation going from a molecule with local mode behaviour (H2O) to a molecule presenting a normal mode behaviour (CO2) is introduced. Concepts from quantum mechanics like fidelity, entropy and probability density, as well from nonlinear classical mechanics like Poincaré sections are used to detect the transition region. It is found that fidelity and entropy are sensitive complementary properties to detect the local-to-normal transition. Poincaré sections allow the local-to-normal transition to be detected through the appearance of chaos as a consequence of the polyad breaking phenomenon. In addition, two kinds of avoided energy crossings are identified in accordance with the different regions of the spectrum.

Fabrication of Bioceramic Bone Scaffolds for Tissue Engineering

NASA Astrophysics Data System (ADS)

Liu, Fwu-Hsing

2014-10-01

In this study, microhydroxyapatite and nanosilica sol were used as the raw materials for fabrication of bioceramic bone scaffold using selective laser sintering technology in a self-developed 3D Printing apparatus. When the fluidity of ceramic slurry is matched with suitable laser processing parameters, a controlled pore size of porous bone scaffold can be fabricated under a lower laser energy. Results shown that the fabricated scaffolds have a bending strength of 14.1 MPa, a compressive strength of 24 MPa, a surface roughness of 725 nm, a pore size of 750 μm, an apparent porosity of 32%, and a optical density of 1.8. Results indicate that the mechanical strength of the scaffold can be improved after heat treatment at 1200 °C for 2 h, while simultaneously increasing surface roughness conducive to osteoprogenitor cell adhesion. MTT method and SEM observations confirmed that bone scaffolds fabricated under the optimal manufacturing process possess suitable biocompatibility and mechanical properties, allowing smooth adhesion and proliferation of osteoblast-like cells. Therefore, they have great potential for development in the field of tissue engineering.

Synthesis and photopolymerization of low shrinkage methacrylate monomers containing bulky substituent groups.

PubMed

Ge, Junhao; Trujillo, Marianela; Stansbury, Jeffrey

2005-12-01

This study was conducted to determine whether novel photopolymerizable formulations based on dimethacrylate monomers with bulky substituent groups could provide low polymerization shrinkage without sacrifice to degree of conversion, and mechanical properties of the polymers. Relatively high molecular weight dimethacrylate monomers were prepared from rigid bisphenol A core groups. Photopolymerization kinetics and shrinkage as well as flexural strength and glass transition temperatures were evaluated for various comonomer compositions. Copolymerization of the bulky monomers with TEGDMA show higher conversion but similar shrinkage compared with Bis-GMA/TEGDMA controls. The resulting polymers have suitable mechanical strength properties for potential dental restorative materials applications. When copolymerized with PEGDMA, the bulky monomers show lower shrinkage, comparable conversion, and more homogeneous polymeric network structures compared with Bis-EMA/PEGDMA systems. The novel dimethacrylate monomers with reduced reactive group densities can decrease the polymerization shrinkage as anticipated, but there is no significant evidence that the bulky substituent groups have any additional effect on reducing shrinkage based on the physical interactions as polymer side chains. The bulky groups improve the double bond conversion and help maintain the mechanical properties of the resulting polymer, which would otherwise decrease rapidly due to the reduced crosslinking density. Further, it was found that bulky monomers help produce more homogeneous copolymer networks.

3D Printing of Photocurable Cellulose Nanocrystal Composite for Fabrication of Complex Architectures via Stereolithography.

PubMed

Palaganas, Napolabel B; Mangadlao, Joey Dacula; de Leon, Al Christopher C; Palaganas, Jerome O; Pangilinan, Katrina D; Lee, Yan Jie; Advincula, Rigoberto C

2017-10-04

The advantages of 3D printing on cost, speed, accuracy, and flexibility have attracted several new applications in various industries especially in the field of medicine where customized solutions are highly demanded. Although this modern fabrication technique offers several benefits, it also poses critical challenges in materials development suitable for industry use. Proliferation of polymers in biomedical application has been severely limited by their inherently weak mechanical properties despite their other excellent attributes. Earlier works on 3D printing of polymers focus mainly on biocompatibility and cellular viability and lack a close attention to produce robust specimens. Prized for superior mechanical strength and inherent stiffness, cellulose nanocrystal (CNC) from abaca plant is incorporated to provide the necessary toughness for 3D printable biopolymer. Hence, this work demonstrates 3D printing of CNC-filled biomaterial with significant improvement in mechanical and surface properties. These findings may potentially pave the way for an alternative option in providing innovative and cost-effective patient-specific solutions to various fields in medical industry. To the best of our knowledge, this work presents the first successful demonstration of 3D printing of CNC nanocomposite hydrogel via stereolithography (SL) forming a complex architecture with enhanced material properties potentially suited for tissue engineering.

Biodegradable HEMA-based hydrogels with enhanced mechanical properties.

PubMed

Moghadam, Mohamadreza Nassajian; Pioletti, Dominique P

2016-08-01

Hydrogels are widely used in the biomedical field. Their main purposes are either to deliver biological active agents or to temporarily fill a defect until they degrade and are followed by new host tissue formation. However, for this latter application, biodegradable hydrogels are usually not capable to sustain any significant load. The development of biodegradable hydrogels presenting load-bearing capabilities would open new possibilities to utilize this class of material in the biomedical field. In this work, an original formulation of biodegradable photo-crosslinked hydrogels based on hydroxyethyl methacrylate (HEMA) is presented. The hydrogels consist of short-length poly(2-hydroxyethyl methacrylate) (PHEMA) chains in a star shape structure, obtained by introducing a tetra-functional chain transfer agent in the backbone of the hydrogels. They are cross-linked with a biodegradable N,O-dimethacryloyl hydroxylamine (DMHA) molecule sensitive to hydrolytic cleavage. We characterized the degradation properties of these hydrogels submitted to mechanical loadings. We showed that the developed hydrogels undergo long-term degradation and specially meet the two essential requirements of a biodegradable hydrogel suitable for load bearing applications: enhanced mechanical properties and low molecular weight degradation products. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1161-1169, 2016. © 2015 Wiley Periodicals, Inc.

Graphene and its elemental analogue: A molecular dynamics view of fracture phenomenon

NASA Astrophysics Data System (ADS)

Rakib, Tawfiqur; Mojumder, Satyajit; Das, Sourav; Saha, Sourav; Motalab, Mohammad

2017-06-01

Graphene and some graphene like two dimensional materials; hexagonal boron nitride (hBN) and silicene have unique mechanical properties which severely limit the suitability of conventional theories used for common brittle and ductile materials to predict the fracture response of these materials. This study revealed the fracture response of graphene, hBN and silicene nanosheets under different tiny crack lengths by molecular dynamics (MD) simulations using LAMMPS. The useful strength of these two dimensional materials are determined by their fracture toughness. Our study shows a comparative analysis of mechanical properties among the elemental analogues of graphene and suggested that hBN can be a good substitute for graphene in terms of mechanical properties. We have also found that the pre-cracked sheets fail in brittle manner and their failure is governed by the strength of the atomic bonds at the crack tip. The MD prediction of fracture toughness shows significant difference with the fracture toughness determined by Griffth's theory of brittle failure which restricts the applicability of Griffith's criterion for these materials in case of nano-cracks. Moreover, the strengths measured in armchair and zigzag directions of nanosheets of these materials implied that the bonds in armchair direction have the stronger capability to resist crack propagation compared to zigzag direction.

Evolution of the mechanical and tribological properties of DLC thin films doped with low-concentration hafnium on 316L steel

NASA Astrophysics Data System (ADS)

Qi, Meng; Xiao, Jianrong; Gong, Chenyang; Jiang, Aihua; Chen, Yong

2018-01-01

Low concentrations (<1 at%) of hafnium doped into diamond-like thin films (Hf-DLC) were deposited on 316L stainless steel and silicon (1 0 0) substrates by magnetron sputtering to attain superior mechanical and tribological properties. Ar and CH4 were used as source gases. The microstructure, chemical composition, and morphology of the Hf-DLC thin films in various concentrations were analyzed using x-ray diffraction, Raman spectroscopy, x-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy. Results showed that Hf species transferred from the particulate microstructure to Hf carbide phases, and the surface roughness increased monotonically with increasing Hf concentration. Moreover, the hardness and elastic modulus exhibited high values when the doped Hf concentration was 0.42 at%. Similarly, the tribological behaviors and wear life of Hf-DLC thin films had a low friction coefficient and excellent wear resistance at 0.42 at% Hf concentration. Therefore, 0.42 at% Hf is an optimal doping concentration to improve the mechanical and tribological properties of DLC thin films. Generally, the use of low-concentration Hf doping into DLC thin films is novel, and the present results provide guidance for the selection of suitable and effective concentration to optimize Hf-DLC thin films with superior performance.

Mechanical and biological evaluations of beta-tricalcium phosphate/silicone rubber composite as a novel soft-tissue implant.

PubMed

Zhang, Yi-ming; Wang, Shao-liang; Lei, Ze-yuan; Fan, Dong-li

2009-09-01

Although silicone rubber (SR) implants are most commonly used and effective for soft-tissue augmentation, they still have been implicated in many adverse reactions. To overcome this problem, a novel composite beta-tricalcium phosphate/silicone rubber (beta-TCP/SR) was prepared by adding beta-TCP into a SR matrix. This study was to evaluate its application potential by investigating the mechanical properties and biocompatibility of beta-TCP/SR. Mechanical properties, including Shore A hardness and tensile strength, were evaluated with 3-mm-thick samples and a universal testing machine. Cytocompatibility tests were conducted in vitro using 0.2-mm-thick beta-TCP/SR samples by seeding fibroblasts onto different samples. Soft-tissue response to beta-TCP/SR and pull-out measurements were investigated 4 weeks and 24 weeks after implantation. The main mechanical properties were all significantly changed after mixing beta-TCP into the SR matrix, except for tearing strength. The cytocompatibility test showed enhanced adhesion and proliferation of fibroblasts onto beta-TCP/SR. Fibrous tissue ingrowth after resorption of beta-TCP was observed by in vivo histologic analysis. The peri-implant capsules in the beta-TCP/SR group were thinner than in the SR group 24 weeks after implantation. In a 24-week test, the maximum force required to pull out the beta-TCP/SR sheet was about six times greater than that needed for SR. Although some mechanical properties were significantly changed, the results of the cytocompatibility test and in vivo animal study still suggest that beta-TCP/SR may be more suitable as a soft-tissue implant than SR and has the potential to be used in plastic surgery.

Hierarchical structures of β-TCP/45S5 bioglass hybrid scaffolds prepared by gelcasting.

PubMed

Lopes, João Henrique; Magalhães, Jéssica Aparecida; Gouveia, Rubia Figueredo; Bertran, Celso Aparecido; Motisuke, Mariana; Camargo, Samira E A; Trichês, Eliandra de Sousa

2016-09-01

This paper investigates the microstructure and the mechanical properties of β-tricalcium phosphate (β-TCP) three-dimensional (3D) porous materials reinforced with 45S5 bioactive glass (BG). β-TCP and β-TCP/x%-BG scaffolds with interconnected pores networks, suitable for bone regeneration, were fabricated by gel-casting method. Mechanical properties, porosity, and morphological characteristics were evaluated by compressive strength test, scanning electron microscopy (SEM) and X-ray microtomography analysis, whereas the structures were fully explored by XRD, and Raman spectroscopy. To the best of our knowledge, this is the first time where the mechanism for understanding the effect of bioglass on the mechanical properties and microstruture of β-TCP/45S5-BG scaffolds has been systematically studied. The findings showed that ionic product lixiviated from 45S5 bioactive glass, rich in silicon species and sodium ion, catalyzes a phase transition from β-TCP to Si-TCP by replacement of phosphorus for silicon and contributes to the improvement of scaffolds mechanical properties. The compressive strength of β-TCP/5%-BG and β-TCP/7.5%-BG was improved around 200% in comparison to pure β-TCP. Osteoblast-like cells (MG 63) were exposed to the materials for 24h through the use of medium conditioned by β-tricalcium phosphate/bioactive glass. Cell viability was measured by MTT assay in the cells and the data obtained were submitted to ANOVA, Tukey׳s multiple comparison (p<0.05). The β-TCP/7.5-BG promoted an increase of cell proliferation. The results suggest that compositions and processing method studied may provide appropriate materials for tissue engineering. Copyright © 2016 Elsevier Ltd. All rights reserved.

A combinaison of UV curing technology with ATL process

NASA Astrophysics Data System (ADS)

Balbzioui, I.; Hasiaoui, B.; Barbier, G.; L'hostis, G.; Laurent, F.; Ibrahim, A.; Durand, B.

2017-10-01

In order to reduce the time and the cost of manufacturing composite, UV curing technology combined with automated tape placement process (ATL) based on reverse approach by working with a fixed head was studied in this article. First, a brief description of the developed head placement is presented. Mechanical properties are then evaluated by varying process parameters, including compaction force and tape placement speed. Finally, a parametric study is carried out to identify suitable materials and process parameters to manufacture a photo composite material with high mechanical performances. The obtained results show that UV curing is a very good alternative for thermal polymerization because of its fast cure speed due to less dependency on temperature.

Shear thickening regimes of dense non-Brownian suspensions.

PubMed

Ness, Christopher; Sun, Jin

2016-01-21

We propose a unifying rheological framework for dense suspensions of non-Brownian spheres, predicting the onsets of particle friction and particle inertia as distinct shear thickening mechanisms, while capturing quasistatic and soft particle rheology at high volume fractions and shear rates respectively. Discrete element method simulations that take suitable account of hydrodynamic and particle-contact interactions corroborate the model predictions, demonstrating both mechanisms of shear thickening, and showing that they can occur concurrently with carefully selected particle surface properties under certain flow conditions. Microstructural transitions associated with frictional shear thickening are presented. We find very distinctive divergences of both microstructural and dynamic variables with respect to volume fraction in the thickened and non-thickened states.

Adjustment of Part Properties for an Elastomeric Laser Sintering Material

NASA Astrophysics Data System (ADS)

Wegner, A.; Ünlü, T.

2018-03-01

Laser sintering of polymers is gaining more and more importance within the field of small series productions. Polyamide 12 is predominantly used, although a variety of other materials are also available for the laser sintering process. For example, elastomeric, rubberlike materials offer very different part property profiles. Those make the production of flexible parts like, e.g., sealings, flexible tubes or shoe soles possible because they offer high part ductility and low hardness. At the chair for manufacturing technology, a new elastomeric laser sintering material has been developed and then commercialized by a spin-off from university. The aim of the presented study was the analysis of the new material's properties. Proof was found that Shore hardness can be modified by varying the parameter settings. Therefore, the correlation between process parameters, energy input, Shore hardness and other part properties like mechanical properties were analyzed. Based on these results, suitable parameter settings were established which lead to the possibility of producing parts with different Shore hardnesses.

Bio-functionalisation of polyether ether ketone using plasma immersion ion implantation

NASA Astrophysics Data System (ADS)

Wakelin, Edgar; Yeo, Giselle; Kondyurin, Alexey; Davies, Michael; McKenzie, David; Weiss, Anthony; Bilek, Marcela

2015-12-01

Plasma immersion ion implantation (PIII) is used here to improve the surface bioactivity of polyether ether ketone (PEEK) by modifying the chemical and mechanical properties and by introducing radicals. Modifications to the chemical and mechanical properties are characterised as a function of ion fluence (proportional to treatment time) to determine the suitability of the treated surfaces for biological applications. Radical generation increases with treatment time, where treatments greater than 400 seconds result in a high concentration of long-lived radicals. Radical reactions are responsible for oxidation of the surface, resulting in a permanent increase in the polar surface energy. The nano-scale reduced modulus was found to increase with treatment time at the surface from 4.4 to 5.2 GPa. The macromolecular Young's modulus was also found to increase, but by an amount corresponding to the volume fraction of the ion implanted region. The treated surface layer exhibited cracking under cyclical loads, associated with an increased modulus due to dehydrogenation and crosslinking, however it did not show any sign of delamination, indicating that the modified layer is well integrated with the substrate - a critical factor for bioactive surface coatings to be used in-vivo. Protein immobilisation on the PIII treated surfaces was found to saturate after 240 seconds of treatment, indicating that there is room to tune surface mechanical properties for specific applications without affecting the protein coverage. Our findings indicate that the modification of the chemical and mechanical properties by PIII treatments as well as the introduction of radicals render PEEK well suited for use in orthopaedic implantable devices.

Chemical, Mechanical, and Durability Properties of Concrete with Local Mineral Admixtures under Sulfate Environment in Northwest China.

PubMed

Nie, Qingke; Zhou, Changjun; Shu, Xiang; He, Qiang; Huang, Baoshan

2014-05-13

Over the vast Northwest China, arid desert contains high concentrations of sulfate, chloride, and other chemicals in the ground water, which poses serious challenges to infrastructure construction that routinely utilizes portland cement concrete. Rapid industrialization in the region has been generating huge amounts of mineral admixtures, such as fly ash and slags from energy and metallurgical industries. These industrial by-products would turn into waste materials if not utilized in time. The present study evaluated the suitability of utilizing local mineral admixtures in significant quantities for producing quality concrete mixtures that can withstand the harsh chemical environment without compromising the essential mechanical properties. Comprehensive chemical, mechanical, and durability tests were conducted in the laboratory to characterize the properties of the local cementitious mineral admixtures, cement mortar and portland cement concrete mixtures containing these admixtures. The results from this study indicated that the sulfate resistance of concrete was effectively improved by adding local class F fly ash and slag, or by applying sulfate resistance cement to the mixtures. It is noteworthy that concrete containing local mineral admixtures exhibited much lower permeability (in terms of chloride ion penetration) than ordinary portland cement concrete while retaining the same mechanical properties; whereas concrete mixtures made with sulfate resistance cement had significantly reduced strength and much increased chloride penetration comparing to the other mixtures. Hence, the use of local mineral admixtures in Northwest China in concrete mixtures would be beneficial to the performance of concrete, as well as to the protection of environment.

Chemical, Mechanical, and Durability Properties of Concrete with Local Mineral Admixtures under Sulfate Environment in Northwest China

PubMed Central

Nie, Qingke; Zhou, Changjun; Shu, Xiang; He, Qiang; Huang, Baoshan

2014-01-01

Over the vast Northwest China, arid desert contains high concentrations of sulfate, chloride, and other chemicals in the ground water, which poses serious challenges to infrastructure construction that routinely utilizes portland cement concrete. Rapid industrialization in the region has been generating huge amounts of mineral admixtures, such as fly ash and slags from energy and metallurgical industries. These industrial by-products would turn into waste materials if not utilized in time. The present study evaluated the suitability of utilizing local mineral admixtures in significant quantities for producing quality concrete mixtures that can withstand the harsh chemical environment without compromising the essential mechanical properties. Comprehensive chemical, mechanical, and durability tests were conducted in the laboratory to characterize the properties of the local cementitious mineral admixtures, cement mortar and portland cement concrete mixtures containing these admixtures. The results from this study indicated that the sulfate resistance of concrete was effectively improved by adding local class F fly ash and slag, or by applying sulfate resistance cement to the mixtures. It is noteworthy that concrete containing local mineral admixtures exhibited much lower permeability (in terms of chloride ion penetration) than ordinary portland cement concrete while retaining the same mechanical properties; whereas concrete mixtures made with sulfate resistance cement had significantly reduced strength and much increased chloride penetration comparing to the other mixtures. Hence, the use of local mineral admixtures in Northwest China in concrete mixtures would be beneficial to the performance of concrete, as well as to the protection of environment. PMID:28788648

Emerging transparent electrodes based on thin films of carbon nanotubes, graphene, and metallic nanostructures.

PubMed

Hecht, David S; Hu, Liangbing; Irvin, Glen

2011-04-05

Transparent electrodes are a necessary component in many modern devices such as touch screens, LCDs, OLEDs, and solar cells, all of which are growing in demand. Traditionally, this role has been well served by doped metal oxides, the most common of which is indium tin oxide, or ITO. Recently, advances in nano-materials research have opened the door for other transparent conductive materials, each with unique properties. These include CNTs, graphene, metal nanowires, and printable metal grids. This review will explore the materials properties of transparent conductors, covering traditional metal oxides and conductive polymers initially, but with a focus on current developments in nano-material coatings. Electronic, optical, and mechanical properties of each material will be discussed, as well as suitability for various applications. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Embedded atom method potential for studying mechanical properties of binary Cu–Au alloys

NASA Astrophysics Data System (ADS)

Gola, Adrien; Pastewka, Lars

2018-07-01

We present an embedded atom method (EAM) potential for the binary Cu–Au system. The unary phases are described by two well-tested unary EAM potentials for Cu and Au. We fitted the interaction between Cu and Au to experimental properties of the binary intermetallic phases Cu3Au, CuAu and CuAu3. Particular attention has been paid to reproducing stacking fault energies in order to obtain a potential suitable for studying deformation in this binary system. The resulting energies, lattice constant, elastic properties and melting points are in good agreement with available experimental data. We use nested sampling to show that our potential reproduces the phase boundaries between intermetallic phases and the disordered face-centered cubic solid solution. We benchmark our potential against four popular Cu–Au EAM parameterizations and density-functional theory calculations.

Pharmaceutical solvates, hydrates and amorphous forms: A special emphasis on cocrystals.

PubMed

Healy, Anne Marie; Worku, Zelalem Ayenew; Kumar, Dinesh; Madi, Atif M

2017-08-01

Active pharmaceutical ingredients (APIs) may exist in various solid forms, which can lead to differences in the intermolecular interactions, affecting the internal energy and enthalpy, and the degree of disorder, affecting the entropy. Differences in solid forms often lead to differences in thermodynamic parameters and physicochemical properties for example solubility, dissolution rate, stability and mechanical properties of APIs and excipients. Hence, solid forms of APIs play a vital role in drug discovery and development in the context of optimization of bioavailability, filing intellectual property rights and developing suitable manufacturing methods. In this review, the fundamental characteristics and trends observed for pharmaceutical hydrates, solvates and amorphous forms are presented, with special emphasis, due to their relative abundance, on pharmaceutical hydrates with single and two-component (i.e. cocrystal) host molecules. Copyright © 2017 Elsevier B.V. All rights reserved.

Nano/micro hybrid scaffold of PCL or P3HB nanofibers combined with silk fibroin for tendon and ligament tissue engineering.

PubMed

Naghashzargar, Elham; Farè, Silvia; Catto, Valentina; Bertoldi, Serena; Semnani, Dariush; Karbasi, Saeed; Tanzi, Maria Cristina

2015-07-04

A novel biodegradable nano/micro hybrid structure was obtained by electrospinning P3HB or PCL nanofibers onto a twisted silk fibroin (SF) structure, with the aim of fabricating a suitable scaffold for tendon and ligament tissue engineering. The electrospinning (ES) processing parameters for P3HB and PCL were optimized on 2D samples, and applied to produce two different nano/micro hybrid constructs (SF/ES-PCL and SF/ES-P3HB).Morphological, chemico-physical and mechanical properties of the novel hybrid scaffolds were evaluated by SEM, ATR FT-IR, DSC, tensile and thermodynamic mechanical tests. The results demonstrated that the nanofibers were tightly wrapped around the silk filaments, and the crystallinity of the SF twisted yarns was not influenced by the presence of the electrospun polymers. The slightly higher mechanical properties of the hybrid constructs confirmed an increase of internal forces due to the interaction between nano and micro components. Cell culture tests with L929 fibroblasts, in the presence of the sample eluates or in direct contact with the hybrid structures, showed no cytotoxic effects and a good level of cytocompatibility of the nano/micro hybrid structures in term of cell viability, particularly at day 1. Cell viability onto the nano/micro hybrid structures decreased from the first to the third day of culture when compared with the control culture plastic, but appeared to be higher when compared with the uncoated SF yarns. Although additional in vitro and in vivo tests are needed, the original fabrication method here described appears promising for scaffolds suitable for tendon and ligament tissue engineering.

A novel method for single sample multi-axial nanoindentation of hydrated heterogeneous tissues based on testing great white shark jaws.

PubMed

Ferrara, Toni L; Boughton, Philip; Slavich, Eve; Wroe, Stephen

2013-01-01

Nanomechanical testing methods that are suitable for a range of hydrated tissues are crucial for understanding biological systems. Nanoindentation of tissues can provide valuable insights into biology, tissue engineering and biomimetic design. However, testing hydrated biological samples still remains a significant challenge. Shark jaw cartilage is an ideal substrate for developing a method to test hydrated tissues because it is a unique heterogeneous composite of both mineralized (hard) and non-mineralized (soft) layers and possesses a jaw geometry that is challenging to test mechanically. The aim of this study is to develop a novel method for obtaining multidirectional nanomechanical properties for both layers of jaw cartilage from a single sample, taken from the great white shark (Carcharodon carcharias). A method for obtaining multidirectional data from a single sample is necessary for examining tissue mechanics in this shark because it is a protected species and hence samples may be difficult to obtain. Results show that this method maintains hydration of samples that would otherwise rapidly dehydrate. Our study is the first analysis of nanomechanical properties of great white shark jaw cartilage. Variation in nanomechanical properties were detected in different orthogonal directions for both layers of jaw cartilage in this species. The data further suggest that the mineralized layer of shark jaw cartilage is less stiff than previously posited. Our method allows multidirectional nanomechanical properties to be obtained from a single, small, hydrated heterogeneous sample. Our technique is therefore suitable for use when specimens are rare, valuable or limited in quantity, such as samples obtained from endangered species or pathological tissues. We also outline a method for tip-to-optic calibration that facilitates nanoindentation of soft biological tissues. Our technique may help address the critical need for a nanomechanical testing method that is applicable to a variety of hydrated biological materials whether soft or hard.

A multimethod Global Sensitivity Analysis to aid the calibration of geomechanical models via time-lapse seismic data

NASA Astrophysics Data System (ADS)

Price, D. C.; Angus, D. A.; Garcia, A.; Fisher, Q. J.; Parsons, S.; Kato, J.

2018-03-01

Time-lapse seismic attributes are used extensively in the history matching of production simulator models. However, although proven to contain information regarding production induced stress change, it is typically only loosely (i.e. qualitatively) used to calibrate geomechanical models. In this study we conduct a multimethod Global Sensitivity Analysis (GSA) to assess the feasibility and aid the quantitative calibration of geomechanical models via near-offset time-lapse seismic data. Specifically, the calibration of mechanical properties of the overburden. Via the GSA, we analyse the near-offset overburden seismic traveltimes from over 4000 perturbations of a Finite Element (FE) geomechanical model of a typical High Pressure High Temperature (HPHT) reservoir in the North Sea. We find that, out of an initially large set of material properties, the near-offset overburden traveltimes are primarily affected by Young's modulus and the effective stress (i.e. Biot) coefficient. The unexpected significance of the Biot coefficient highlights the importance of modelling fluid flow and pore pressure outside of the reservoir. The FE model is complex and highly nonlinear. Multiple combinations of model parameters can yield equally possible model realizations. Consequently, numerical calibration via a large number of random model perturbations is unfeasible. However, the significant differences in traveltime results suggest that more sophisticated calibration methods could potentially be feasible for finding numerous suitable solutions. The results of the time-varying GSA demonstrate how acquiring multiple vintages of time-lapse seismic data can be advantageous. However, they also suggest that significant overburden near-offset seismic time-shifts, useful for model calibration, may take up to 3 yrs after the start of production to manifest. Due to the nonlinearity of the model behaviour, similar uncertainty in the reservoir mechanical properties appears to influence overburden traveltime to a much greater extent. Therefore, reservoir properties must be known to a suitable degree of accuracy before the calibration of the overburden can be considered.

Fatigue and quasi‐static mechanical behavior of bio‐degradable porous biomaterials based on magnesium alloys

PubMed Central

Ahmadi, S. M.; Lietaert, K.; Tümer, N.; Li, Y.; Amin Yavari, S.; Zadpoor, A. A.

2018-01-01

Abstract Magnesium and its alloys have the intrinsic capability of degrading over time in vivo without leaving toxic degradation products. They are therefore suitable for use as biodegradable scaffolds that are replaced by the regenerated tissues. One of the main concerns for such applications, particularly in load‐bearing areas, is the sufficient mechanical integrity of the scaffold before sufficient volumes of de novo tissue is generated. In the majority of the previous studies on the effects of biodegradation on the mechanical properties of porous biomaterials, the change in the elastic modulus has been studied. In this study, variations in the static and fatigue mechanical behavior of porous structures made of two different Mg alloys (AZ63 and M2) over different dissolution times ( 6, 12, and 24 h) have been investigated. The results showed an increase in the mechanical properties obtained from stress–strain curve (elastic modulus, yield stress, plateau stress, and energy absorption) after 6–12 h and a sharp decrease after 24 h. The initial increase in the mechanical properties may be attributed to the accumulation of corrosion products in the pores of the porous structure before degradation has considerably proceeded. The effects of mineral deposition was more pronounced for the elastic modulus as compared to other mechanical properties. That may be due to insufficient integration of the deposited particles in the structure of the magnesium alloys. While the bonding of the parts being combined in a composite‐like material is of great importance in determining its yield stress, the effects of bonding strength of both parts is much lower in determining the elastic modulus. The results of the current study also showed that the dissolution rates of the studied Mg alloys were too high for direct use in human body. © 2018 Authors Journal of Biomedical Materials Research Part A Published by Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1798–1811, 2018. PMID:29468807

Micromechanical finite element modeling and experimental characterization of the compressive mechanical properties of polycaprolactone:hydroxyapatite composite scaffolds prepared by selective laser sintering for bone tissue engineering

PubMed Central

Eshraghi, Shaun; Das, Suman

2012-01-01

Bioresorbable scaffolds with mechanical properties suitable for bone tissue engineering were fabricated from polycaprolactone (PCL) and hydroxyapatite (HA) by selective laser sintering (SLS) and modeled by finite element analysis (FEA). Both solid gage parts and scaffolds having 1-D, 2-D and 3-D orthogonal, periodic porous architectures were made with 0, 10, 20 and 30% HA by volume. PCL:HA scaffolds manufactured by SLS had nearly full density (99%) in the designed solid regions and had excellent geometric and dimensional control. Through optimization of the SLS process, the compressive moduli for our solid gage parts and scaffolds are the highest reported in the literature for additive manufacturing. The compressive moduli of solid gage parts were 299.3, 311.2, 415.5 and 498.3 MPa for PCL:HA loading at 100:0, 90:10, 80:20 and 70:30 respectively. The compressive effective stiffness tended to increase as the loading of HA was increased and the designed porosity was lowered. In the case of the most 3-D porous scaffold, the compressive modulus more than doubled from 14.9 MPa to 36.2 MPa when changing the material from 100:0 to 70:30 PCL:HA. A micromechanical finite element analysis (FEA) model was developed to investigate the reinforcement effect of HA loading on the compressive modulus of the bulk material. Using a first-principles based approach, the random distribution of HA particles in a solidified PCL matrix was modeled for any loading of HA to predict the bulk mechanical properties of the composites. The bulk mechanical properties were also used for FEA of the scaffold geometries. Results of the FEA were found to be in good agreement with experimental mechanical testing. The development of patient and site-specific composite tissue engineering constructs with tailored properties can be seen as a direct extension of this work on computational design, a priori modeling of mechanical properties and direct digital manufacturing. PMID:22522129

Micromechanical finite-element modeling and experimental characterization of the compressive mechanical properties of polycaprolactone-hydroxyapatite composite scaffolds prepared by selective laser sintering for bone tissue engineering.

PubMed

Eshraghi, Shaun; Das, Suman

2012-08-01

Bioresorbable scaffolds with mechanical properties suitable for bone tissue engineering were fabricated from polycaprolactone (PCL) and hydroxyapatite (HA) by selective laser sintering (SLS) and modeled by finite-element analysis (FEA). Both solid gage parts and scaffolds having 1-D, 2-D and 3-D orthogonal, periodic porous architectures were made with 0, 10, 20 and 30 vol.% HA. PCL:HA scaffolds manufactured by SLS had nearly full density (99%) in the designed solid regions and had excellent geometric and dimensional control. Through optimization of the SLS process, the compressive moduli for our solid gage parts and scaffolds are the highest reported in the literature for additive manufacturing. The compressive moduli of solid gage parts were 299.3, 311.2, 415.5 and 498.3 MPa for PCL:HA loading at 100:0, 90:10, 80:20 and 70:30, respectively. The compressive effective stiffness tended to increase as the loading of HA was increased and the designed porosity was lowered. In the case of the most 3-D porous scaffold, the compressive modulus more than doubled from 14.9 to 36.2 MPa when changing the material from 100:0 to 70:30 PCL:HA. A micromechanical FEA model was developed to investigate the reinforcement effect of HA loading on the compressive modulus of the bulk material. Using a first-principles based approach, the random distribution of HA particles in a solidified PCL matrix was modeled for any HA loading to predict the bulk mechanical properties of the composites. The bulk mechanical properties were also used for FEA of the scaffold geometries. The results of the FEA were found to be in good agreement with experimental mechanical testing. The development of patient- and site-specific composite tissue-engineering constructs with tailored properties can be seen as a direct extension of this work on computational design, a priori modeling of mechanical properties and direct digital manufacturing. Copyright © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Study of thermo-hydro-mechanical processes at a potential site of an Indian nuclear waste repository

NASA Astrophysics Data System (ADS)

Maheshwar, Sachin; Verma, A. K.; Singh, T. N.; Bajpai, R. K.

2015-12-01

A detailed scientific study is required for the disposal of high-level radioactive wastes because they generate extremely high heat during their half-life period. Although, several methods have been proposed for the disposal of nuclear wastes, deep underground repository is considered to be a suitable option. In this paper, field investigation has been done near to Bhima basin of peninsular India. Detailed fracture analysis near the borehole shows very prominent maxima of fractures striking N55∘E coinciding with the trace of master basement cover metasediment fault. Physico-mechanical properties of rocks have been determined in the laboratory. The host rock chosen is granite and engineered barrier near the canister is proposed to be clay. A thermo-hydro-mechanical (THM) analysis has been done to study the effect of heat on deformations, stresses and pore-pressure variation in granite and clay barriers. For this purpose, finite difference method has been used. Suitable rheological models have been used to model elastic canister and elasto-plastic engineered barrier and host rock. It has been found that both temperature and stresses at any point in the rockmass is below the design criteria which are 100∘C for temperature and 0.2 for damage number.

Application of C30B15N15 heterofullerene in the isoniazid drug delivery: DFT studies

NASA Astrophysics Data System (ADS)

Hazrati, Mehrnoosh Khodam; Bagheri, Zargham; Bodaghi, Ali

2017-05-01

Using density functional theory, we have investigated the potential application of a C30B15N15 heterofullerene in anti-cancer isoniazid drug delivery. It was found that isoniazid prefers to attach via its -NH2 group to a boron atom of the C30B15N15 with releasing a large energy of about 21.91 kcal/mol. Our partial density of states analysis demonstrates that the boron atoms significantly contribute in generation of virtual orbitals of C30B15N15 fullerene, indicating that these atoms will be suitable for nucleophilic attack rather than carbon atoms. In addition to the large released energy, the electronic properties C30B15N15 are significantly sensitive to the isoniazid attachment which can recognize the drug trajectory by affecting the fluorescence emission properties. Unlike, different nanostructures whose structures need to be manipulated to be suitable for drug delivery, the C30B15N15 fullerene can be used in the pristine form. We proposed a drug release mechanism in cancer tissues, representing that in the low pH of the cancer cells the drug and C30B15N15 fullerene are considerably protonated, thereby separating the drug from the surface of the fullerene. The reaction mechanism of the drug with the fullerene is changed from covalence in natural environment to hydrogen bonding in acidic cancer cells.

3D bioprinting of methacrylated hyaluronic acid (MeHA) hydrogel with intrinsic osteogenicity.

PubMed

Poldervaart, Michelle T; Goversen, Birgit; de Ruijter, Mylene; Abbadessa, Anna; Melchels, Ferry P W; Öner, F Cumhur; Dhert, Wouter J A; Vermonden, Tina; Alblas, Jacqueline

2017-01-01

In bone regenerative medicine there is a need for suitable bone substitutes. Hydrogels have excellent biocompatible and biodegradable characteristics, but their visco-elastic properties limit their applicability, especially with respect to 3D bioprinting. In this study, we modified the naturally occurring extracellular matrix glycosaminoglycan hyaluronic acid (HA), in order to yield photo-crosslinkable hydrogels with increased mechanical stiffness and long-term stability, and with minimal decrease in cytocompatibility. Application of these tailor-made methacrylated hyaluronic acid (MeHA) gels for bone tissue engineering and 3D bioprinting was the subject of investigation. Visco-elastic properties of MeHA gels, measured by rheology and dynamic mechanical analysis, showed that irradiation of the hydrogels with UV light led to increased storage moduli and elastic moduli, indicating increasing gel rigidity. Subsequently, human bone marrow derived mesenchymal stromal cells (MSCs) were incorporated into MeHA hydrogels, and cell viability remained 64.4% after 21 days of culture. Osteogenic differentiation of MSCs occurred spontaneously in hydrogels with high concentrations of MeHA polymer, in absence of additional osteogenic stimuli. Addition of bone morphogenetic protein-2 (BMP-2) to the culture medium further increased osteogenic differentiation, as evidenced by increased matrix mineralisation. MeHA hydrogels demonstrated to be suitable for 3D bioprinting, and were printed into porous and anatomically shaped scaffolds. Taken together, photosensitive MeHA-based hydrogels fulfilled our criteria for cellular bioprinted bone constructs within a narrow window of concentration.

3D bioprinting of methacrylated hyaluronic acid (MeHA) hydrogel with intrinsic osteogenicity

PubMed Central

Poldervaart, Michelle T.; Goversen, Birgit; de Ruijter, Mylene; Abbadessa, Anna; Melchels, Ferry P. W.; Öner, F. Cumhur; Dhert, Wouter J. A.; Vermonden, Tina

2017-01-01

In bone regenerative medicine there is a need for suitable bone substitutes. Hydrogels have excellent biocompatible and biodegradable characteristics, but their visco-elastic properties limit their applicability, especially with respect to 3D bioprinting. In this study, we modified the naturally occurring extracellular matrix glycosaminoglycan hyaluronic acid (HA), in order to yield photo-crosslinkable hydrogels with increased mechanical stiffness and long-term stability, and with minimal decrease in cytocompatibility. Application of these tailor-made methacrylated hyaluronic acid (MeHA) gels for bone tissue engineering and 3D bioprinting was the subject of investigation. Visco-elastic properties of MeHA gels, measured by rheology and dynamic mechanical analysis, showed that irradiation of the hydrogels with UV light led to increased storage moduli and elastic moduli, indicating increasing gel rigidity. Subsequently, human bone marrow derived mesenchymal stromal cells (MSCs) were incorporated into MeHA hydrogels, and cell viability remained 64.4% after 21 days of culture. Osteogenic differentiation of MSCs occurred spontaneously in hydrogels with high concentrations of MeHA polymer, in absence of additional osteogenic stimuli. Addition of bone morphogenetic protein-2 (BMP-2) to the culture medium further increased osteogenic differentiation, as evidenced by increased matrix mineralisation. MeHA hydrogels demonstrated to be suitable for 3D bioprinting, and were printed into porous and anatomically shaped scaffolds. Taken together, photosensitive MeHA-based hydrogels fulfilled our criteria for cellular bioprinted bone constructs within a narrow window of concentration. PMID:28586346

Suitability of live and fire-killed small-diameter ponderosa and lodgepole pine trees for manufacturing a new structural wood composite.

PubMed

Linton, J M; Barnes, H M; Seale, R D; Jones, P D; Lowell, E C; Hummel, S S

2010-08-01

Finding alternative uses for raw material from small-diameter trees is a critical problem throughout the United States. In western states, a lack of markets for small-diameter ponderosa pine (Pinus ponderosa) and lodgepole pine (Pinus contorta) can contribute to problems associated with overstocking. To test the feasibility of producing structural composite lumber (SCL) beams from these two western species, we used a new technology called steam-pressed scrim lumber (SPSL) based on scrimming technology developed in Australia. Both standing green and fire-killed ponderosa and lodgepole pine logs were used in an initial test. Fire-killed logs of both species were found to be unsuitable for producing SPSL but green logs were suitable for producing SPSL. For SPSL from green material, ponderosa pine had significantly higher modulus of rupture and work-to-maximum load values than did SPSL from lodgepole pine. Modulus of elasticity was higher for lodgepole pine. The presence of blows was greater with lodgepole pine than with ponderosa. Blows had a negative effect on the mechanical properties of ponderosa pine but no significant effect on the mechanical properties of SPSL from lodgepole pine. An evaluation of non-destructive testing methods showed that X-ray could be used to determine low density areas in parent beams. The use of a sonic compression wave tester for NDE evaluation of modulus of rupture showed some promise with SPSL but requires further research. (c) 2010 Elsevier Ltd. All rights reserved.

Hybrid chitosan-ß-glycerol phosphate-gelatin nano-/micro fibrous scaffolds with suitable mechanical and biological properties for tissue engineering.

PubMed

Lotfi, Marzieh; Bagherzadeh, Roohollah; Naderi-Meshkin, Hojjat; Mahdipour, Elahe; Mafinezhad, Asghar; Sadeghnia, Hamid Reza; Esmaily, Habibollah; Maleki, Masoud; Hasssanzadeh, Halimeh; Ghayaour-Mobarhan, Majid; Bidkhori, Hamid Reza; Bahrami, Ahmad Reza

2016-03-01

Scaffold-based tissue engineering is considered as a promising approach in the regenerative medicine. Graft instability of collagen, by causing poor mechanical properties and rapid degradation, and their hard handling remains major challenges to be addressed. In this research, a composite structured nano-/microfibrous scaffold, made from a mixture of chitosan-ß-glycerol phosphate-gelatin (chitosan-GP-gelatin) using a standard electrospinning set-up was developed. Gelatin-acid acetic and chitosan ß-glycerol phosphate-HCL solutions were prepared at ratios of 30/70, 50/50, 70/30 (w/w) and their mechanical and biological properties were engineered. Furthermore, the pore structure of the fabricated nanofibrous scaffolds was investigated and predicted using a theoretical model. Higher gelatin concentrations in the polymer blend resulted in significant increase in mean pore size and its distribution. Interaction between the scaffold and the contained cells was also monitored and compared in the test and control groups. Scaffolds with higher chitosan concentrations showed higher rate of cell attachment with better proliferation property, compared with gelatin-only scaffolds. The fabricated scaffolds, unlike many other natural polymers, also exhibit non-toxic and biodegradable properties in the grafted tissues. In conclusion, the data clearly showed that the fabricated biomaterial is a biologically compatible scaffold with potential to serve as a proper platform for retaining the cultured cells for further application in cell-based tissue engineering, especially in wound healing practices. These results suggested the potential of using mesoporous composite chitosan-GP-gelatin fibrous scaffolds for engineering three-dimensional tissues with different inherent cell characteristics. © 2015 Wiley Periodicals, Inc.

Neurotoxicity and risk assessment of brominated and alternative flame retardants.

PubMed

Hendriks, Hester S; Westerink, Remco H S

2015-01-01

Brominated flame retardants (BFRs) are widely used chemicals that prevent or slow the onset and spreading of fire. Unfortunately, many of these compounds pose serious threats for human health and the environment, indicating an urgent need for safe(r) and less persistent alternative flame retardants (AFRs). As previous research identified the nervous system as a sensitive target organ, the neurotoxicity of past and present flame retardants is reviewed. First, an overview of the neurotoxicity of BFRs in humans and experimental animals is provided, and some common in vitro neurotoxic mechanisms of action are discussed. The combined epidemiological and toxicological studies clearly underline the need for replacing BFRs. Many potentially suitable AFRs are already in use, despite the absence of a full profile of their environmental behavior and toxicological properties. To prioritize the suitability of some selected halogenated and non-halogenated organophosphorous flame retardants and inorganic halogen-free flame retardants, the available neurotoxic data of these AFRs are discussed. The suitability of the AFRs is rank-ordered and combined with human exposure data (serum concentrations, breast milk concentrations and house dust concentrations) and physicochemical properties (useful to predict e.g. bioavailability and persistence in the environment) for a first semi-quantitative risk assessment of the AFRs. As can be concluded from the reviewed data, several BFRs and AFRs share some neurotoxic effects and modes of action. Moreover, the available neurotoxicity data indicate that some AFRs may be suitable substitutes for BFRs. However, proper risk assessment is hampered by an overall scarcity of data, particularly regarding environmental persistence, human exposure levels, and the formation of breakdown products and possible metabolites as well as their toxicity. Until these data gaps in environmental behavioral and toxicological profiles are filled, large scale use of these chemicals should be cautioned.

A deep learning approach to estimate chemically-treated collagenous tissue nonlinear anisotropic stress-strain responses from microscopy images.

PubMed

Liang, Liang; Liu, Minliang; Sun, Wei

2017-11-01

Biological collagenous tissues comprised of networks of collagen fibers are suitable for a broad spectrum of medical applications owing to their attractive mechanical properties. In this study, we developed a noninvasive approach to estimate collagenous tissue elastic properties directly from microscopy images using Machine Learning (ML) techniques. Glutaraldehyde-treated bovine pericardium (GLBP) tissue, widely used in the fabrication of bioprosthetic heart valves and vascular patches, was chosen to develop a representative application. A Deep Learning model was designed and trained to process second harmonic generation (SHG) images of collagen networks in GLBP tissue samples, and directly predict the tissue elastic mechanical properties. The trained model is capable of identifying the overall tissue stiffness with a classification accuracy of 84%, and predicting the nonlinear anisotropic stress-strain curves with average regression errors of 0.021 and 0.031. Thus, this study demonstrates the feasibility and great potential of using the Deep Learning approach for fast and noninvasive assessment of collagenous tissue elastic properties from microstructural images. In this study, we developed, to our best knowledge, the first Deep Learning-based approach to estimate the elastic properties of collagenous tissues directly from noninvasive second harmonic generation images. The success of this study holds promise for the use of Machine Learning techniques to noninvasively and efficiently estimate the mechanical properties of many structure-based biological materials, and it also enables many potential applications such as serving as a quality control tool to select tissue for the manufacturing of medical devices (e.g. bioprosthetic heart valves). Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A set of hypotheses on tribology of mammalian herbivore teeth

NASA Astrophysics Data System (ADS)

Kaiser, Thomas M.; Clauss, Marcus; Schulz-Kornas, Ellen

2016-03-01

Once erupted, mammal cheek teeth molars are continuously worn. Contact of molar surfaces with ingesta and with other teeth contribute to this wear. Microscopic wear features (dental surface texture) change continuously as new wear overprints old texture features. These features have been debated to indicate diet. The general assumption in relating occlusal textures to diet is that they are independent of masticatory movements and forces. If this assumption is not accepted, one needs to propose that occlusal textures comprise signals not only from the ‘last supper’ but also from masticatory events that represent ecological, species- or taxon-specific adaptations, and that occlusal textures therefore give a rather unspecific, somehow diet-related signal that is functionally inadequately understood. In order to test for mechanical mechanisms of wear, we created a hypothesis matrix that related sampled individuals with six tribological variables. Three variables represent mechanically relevant ingesta properties, and three represent animal-specific characteristics of the masticatory system. Three groups of mammal species (free ranging Cetartiodactyla and Perissodactyla, free ranging primates, and artificially fed rabbits) were investigated in terms of their 3D dental surface textures, which were quantified employing ten ISO 25178 surface texture parameters. We first formulated a set of specific predictions based on theoretical reflections on the effects of diet properties and animal characteristics, and subsequently performed discriminant analysis to test which parameters actually followed these predictions. We found that parameters Vvc, Vmc, Sp, Sq allowed the prediction of both, ingesta properties and properties of the masticatory system, if combined with other parameters. Sha, Sda and S5v had little predictive power in our dataset. Spd seemed rather unrelated to ingesta properties and made this parameter a suitable indicator of masticatory system properties.

Effect of various additives on microstructure, mechanical properties, and in vitro bioactivity of sodium oxide-calcium oxide-silica-phosphorus pentoxide glass-ceramics.

PubMed

Li, H C; Wang, D G; Hu, J H; Chen, C Z

2013-09-01

The partial substitution of MgO, TiO2, or CaF2 for CaO in the Na2O-CaO-SiO2-P2O5 (45S5) system was conducted by the sol-gel method and a comparative study on structural, mechanical properties, and bioactivity of the glasses was reported. Based on thermogravimetric and differential thermal analysis, the gels were sintered with a suitable heat treatment procedure. The glass-ceramic properties were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and so on, and the bioactivity of the glass-ceramic was evaluated by in vitro assays in simulated body fluid (SBF). Results indicate that with the partial substitution of MgO, TiO2, CaF2 for CaO in glass composition, the mechanical properties of the glass-ceramics have been significantly improved. Furthermore, CaF2 promotes glass crystallization and the crystallization does not inhibit the glass-ceramic bioactivity. All samples possess bioactivity; however, the bioactivity of these glass-ceramics is quite different. Compared with 45S5, the introduction of MgO decreases the ability of apatite induction. The addition of TiO2 does not significantly improve the bioactivity, and the replacement of CaO by CaF2 shows a higher bioactivity. Copyright © 2013 Elsevier Inc. All rights reserved.

Mechanical properties of an experimental soft lining material based on urethane oligomer.

PubMed

Kanie, Takahito; Kadokawa, Akihiko; Arikawa, Hiroyuki; Fujii, Koichi; Ban, Seiji

2005-09-01

The purpose of this study was to investigate the apparent viscosities and mechanical properties of two experimental light-curing soft lining materials (SLM-1 and SLM-2) based on soft-type urethane oligomers, as well as the shear bond strength and dye penetration between the denture base resin and the polymerized SLMs after storage in water. The apparent viscosities of SLM-1 and SLM-2 were 144.0-146.9 and 1.9 Pa x s respectively. After storage in water for two prescribed periods (one day and three months), the mechanical properties of the SLMs on the overall were 10.6-20.6 MPa for elastic modulus, 69.3-72.1 for hardness, and 3.8-4.0 MPa for adhesive strength. Tensile strength was observed to decrease after three months' storage in water, when compared to that after one-day storage (p < 0.01). Water sorption rates also differed significantly (p < 0.05)--namely 3.0 and 2.8 mg/cm2 for SLM-1 after one day and three months respectively, and 2.0 and 2.2 mg/cm2 for SLM-2. As for dye penetration, no infiltration was observed at the denture base resin-SLM interface after three months' storage. Based on the results of this study, it seemed like the SLMs possess many suitable properties for use with a new technique that we recently developed for preparing denture base resin and soft lining material.

Hollow fibers of poly(lactide-co-glycolide) and poly(ε-caprolactone) blends for vascular tissue engineering applications.

PubMed

Diban, Nazely; Haimi, Suvi; Bolhuis-Versteeg, Lydia; Teixeira, Sandra; Miettinen, Susanna; Poot, André; Grijpma, Dirk; Stamatialis, Dimitrios

2013-05-01

At present the manufacture of small-diameter blood vessels is one of the main challenges in the field of vascular tissue engineering. Currently available vascular grafts rapidly fail due to development of intimal hyperplasia and thrombus formation. Poly(lactic-co-glycolic acid) (PLGA) hollow fiber (HF) membranes have previously been proposed for this application, but as we show in the present work, they have an inhibiting effect on cell proliferation and rather poor mechanical properties. To overcome this we prepared HF membranes via phase inversion using blends of PLGA with poly(ε-caprolactone) (PCL). The influence of polymer composition on the HF physicochemical properties (topography, water transport and mechanical properties) and cell attachment and proliferation were studied. Our results show that only the ratio PCL/PLGA of 85/15 (PCL/PLGA85/15) yielded a miscible blend after processing. A higher PLGA concentration in the blend led to immiscible PCL/PLGA phase-separated HFs with an inhomogeneous morphology and variation in the cell culture results. In fact, the PCL/PLGA85/15 blend, which had the most homogeneous morphology and suitable pore structure, showed better human adipose stem cell (hASC) attachment and proliferation compared with the homopolymers. This, combined with the good mechanical and transport properties, makes them potentially useful for the development of small-caliber vascular grafts. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Extrinsic Fluorescent Dyes as Tools for Protein Characterization

PubMed Central

Hawe, Andrea; Sutter, Marc

2008-01-01

Noncovalent, extrinsic fluorescent dyes are applied in various fields of protein analysis, e.g. to characterize folding intermediates, measure surface hydrophobicity, and detect aggregation or fibrillation. The main underlying mechanisms, which explain the fluorescence properties of many extrinsic dyes, are solvent relaxation processes and (twisted) intramolecular charge transfer reactions, which are affected by the environment and by interactions of the dyes with proteins. In recent time, the use of extrinsic fluorescent dyes such as ANS, Bis-ANS, Nile Red, Thioflavin T and others has increased, because of their versatility, sensitivity and suitability for high-throughput screening. The intention of this review is to give an overview of available extrinsic dyes, explain their spectral properties, and show illustrative examples of their various applications in protein characterization. PMID:18172579

Effect of Poly(Vinyl Alcohol) Addition on the Properties of Hydrothermal Derived Calcium Phosphate Cement for Bone Filling Materials

NASA Astrophysics Data System (ADS)

Razali, N. N.; Sopyan, I.; Mel, M.; Salleh, H. M.; Rahman, M. M.; Singh, R.

2017-06-01

The effect of addition of poly(vinyl alcohol) on hydrothermal derived calcium phosphate cement has been studied. The precursors used to prepare the cement were calcium oxide (CaO) and ammonium dihydrogen phosphate (NH4H2PO4); the reaction was conducted in water at 80-100°C. To improve properties of CPC, poly(vinyl alcohol) (PVA) of 1wt% and 2wt% was added to the liquid phase of CPC and the results were compared to CPC without PVA addition. The addition of PVA was proved to bring remarkable effects on cohesion, setting time and mechanical strength of CPC which make it suitable physically for injectable bone filler applications.

Electrochemical properties of tin oxide anodes for sodium-ion batteries

NASA Astrophysics Data System (ADS)

Lu, Ying Ching; Ma, Chuze; Alvarado, Judith; Kidera, Takafumi; Dimov, Nikolay; Meng, Ying Shirley; Okada, Shigeto

2015-06-01

Few tin (Sn)-oxide based anode materials have been found to have large reversible capacity for both sodium (Na)-ion and lithium (Li)-ion batteries. Herein, we report the synthesis and electrochemical properties of Sn oxide-based anodes for sodium-ion batteries: SnO, SnO2, and SnO2/C. Among them, SnO is the most suitable anode for Na-ion batteries with less first cycle irreversibility, better cycle life, and lower charge transfer resistance. The energy storage mechanism of the above-mentioned Sn oxides was studied, which suggested that the conversion reaction of the Sn oxide anodes is reversible in Na-ion batteries. The better anode performance of SnO is attributed by the better conductivity.

Investigation of new semiinsulating behavior of III-V compounds

NASA Technical Reports Server (NTRS)

Lagowski, Jacek

1990-01-01

The investigation of defect interactions and properties related to semiinsulating behavior of III-V semiconductors resulted in about twenty original publications, six doctoral thesis, one masters thesis and numerous conference presentations. The studies of new compensation mechanisms involving transition metal impurities have defined direct effects associated with deep donor/acceptor levels acting as compensating centers. Electrical and optical properties of vanadium and titanium levels were determined in GaAs, InP and also in ternary compounds InGaAs. The experimental data provided basis for the verification of chemical trends and the VRBE method. They also defined compositional range for III-V mixed crystals whereby semiinsulating behavior can be achieved using transition elements deep levels and a suitable codoping with shallow donor/acceptor impurities.

Fast Setting Silk Fibroin Bioink for Bioprinting of Patient-Specific Memory-Shape Implants.

PubMed

Costa, João B; Silva-Correia, Joana; Oliveira, Joaquim M; Reis, Rui L

2017-11-01

The pursuit for the "perfect" biomimetic and personalized implant for musculoskeletal tissue regeneration remains a big challenge. 3D printing technology that makes use of a novel and promising biomaterials can be part of the solution. In this study, a fast setting enzymatic-crosslinked silk fibroin (SF) bioink for 3D bioprinting is developed. Their properties are fine-tuned and different structures with good resolution, reproducibility, and reliability can be fabricated. Many potential applications exist for the SF bioinks including 3D bioprinted scaffolds and patient-specific implants exhibiting unique characteristics such as good mechanical properties, memory-shape feature, suitable degradation, and tunable pore architecture and morphology. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigation of dielectric substrates on electrical and optical performance of wafer-scale graphene using non-contact methods

NASA Astrophysics Data System (ADS)

Wang, Dong; Ning, Jing; Zhang, Jincheng; Guo, Lixin; Hao, Yue

2017-10-01

Here we systemically discussed the influence of dielectric substrates on the surface morphology, electrical and optical performance of transferred graphene. The electrical properties were investigated using a microwave-probing technique without metal-graphene contact. We found that a complex mechanism governed the influence of the surface properties of the dielectric substrates, such as morphology, hydrophilicity, crystallinity, and polarization, on the performance of the graphene. We also found that graphene on r-Al2O3 was more effective for graphene-based devices with a high carrier mobility of ˜5000 cm2 V-1 s-1. This provides a new method to choose the most suitable substrate for fabricating graphene-based devices.

Anisotropy of Photopolymer Parts Made by Digital Light Processing

PubMed Central

Monzón, Mario; Ortega, Zaida; Hernández, Alba; Paz, Rubén; Ortega, Fernando

2017-01-01

Digital light processing (DLP) is an accurate additive manufacturing (AM) technology suitable for producing micro-parts by photopolymerization. As most AM technologies, anisotropy of parts made by DLP is a key issue to deal with, taking into account that several operational factors modify this characteristic. Design for this technology and photopolymers becomes a challenge because the manufacturing process and post-processing strongly influence the mechanical properties of the part. This paper shows experimental work to demonstrate the particular behavior of parts made using DLP. Being different to any other AM technology, rules for design need to be adapted. Influence of build direction and post-curing process on final mechanical properties and anisotropy are reported and justified based on experimental data and theoretical simulation of bi-material parts formed by fully-cured resin and partially-cured resin. Three photopolymers were tested under different working conditions, concluding that post-curing can, in some cases, correct the anisotropy, mainly depending on the nature of photopolymer. PMID:28772426

Design Concepts, Fabrication and Advanced Characterization Methods of Innovative Piezoelectric Sensors Based on ZnO Nanowires.

PubMed

Araneo, Rodolfo; Rinaldi, Antonio; Notargiacomo, Andrea; Bini, Fabiano; Pea, Marialilia; Celozzi, Salvatore; Marinozzi, Franco; Lovat, Giampiero

2014-12-08

Micro- and nano-scale materials and systems based on zinc oxide are expected to explode in their applications in the electronics and photonics, including nano-arrays of addressable optoelectronic devices and sensors, due to their outstanding properties, including semiconductivity and the presence of a direct bandgap, piezoelectricity, pyroelectricity and biocompatibility. Most applications are based on the cooperative and average response of a large number of ZnO micro/nanostructures. However, in order to assess the quality of the materials and their performance, it is fundamental to characterize and then accurately model the specific electrical and piezoelectric properties of single ZnO structures. In this paper, we report on focused ion beam machined high aspect ratio nanowires and their mechanical and electrical (by means of conductive atomic force microscopy) characterization. Then, we investigate the suitability of new power-law design concepts to accurately model the relevant electrical and mechanical size-effects, whose existence has been emphasized in recent reviews.

SchNet - A deep learning architecture for molecules and materials

NASA Astrophysics Data System (ADS)

Schütt, K. T.; Sauceda, H. E.; Kindermans, P.-J.; Tkatchenko, A.; Müller, K.-R.

2018-06-01

Deep learning has led to a paradigm shift in artificial intelligence, including web, text, and image search, speech recognition, as well as bioinformatics, with growing impact in chemical physics. Machine learning, in general, and deep learning, in particular, are ideally suitable for representing quantum-mechanical interactions, enabling us to model nonlinear potential-energy surfaces or enhancing the exploration of chemical compound space. Here we present the deep learning architecture SchNet that is specifically designed to model atomistic systems by making use of continuous-filter convolutional layers. We demonstrate the capabilities of SchNet by accurately predicting a range of properties across chemical space for molecules and materials, where our model learns chemically plausible embeddings of atom types across the periodic table. Finally, we employ SchNet to predict potential-energy surfaces and energy-conserving force fields for molecular dynamics simulations of small molecules and perform an exemplary study on the quantum-mechanical properties of C20-fullerene that would have been infeasible with regular ab initio molecular dynamics.

Experimental Investigation of Mechanical Properties of Welded Corten Steel A588 Grade Plate Using ER70S - 6 Filler Material for Construction Application

NASA Astrophysics Data System (ADS)

Deepak, J. R.; Bupesh Raja, V. K.; Janardhan Guptha, Mittapalli; Durga Prasad, Palaparthi Hari; Sriram, V.

2017-05-01

ASTM A588 Grade A steel plate is a high strength, low alloy structural steel with 0.19 % of carbon content. When exposed to the atmosphere, A588 Grade A is suitable for construction in the bare (paint - free) condition. The main problems are lack of fusion, lack of penetration and corrosion on heat affected zone. In this research work Corten ASTM A588 Grade steel of 3mm thickness is electroplated with copper and then both raw and copper electroplated are welded by GMAW welding process with ER70S-6 as a filler material. The welded ASTM A588 is cut according to ASTM size for further testing of mechanical properties. Considering its welding strength after the process of electroplating, this research clearly states the metal can be utilized for better results in any given field. Here both the tensile and hardness are higher in copper electroplated welded when compare to raw welded.

Rice stubble as a new biopolymer source to produce carboxymethyl cellulose-blended films.

PubMed

Rodsamran, Pattrathip; Sothornvit, Rungsinee

2017-09-01

Rice stubble is agricultural waste consisting of cellulose which can be converted to carboxymethyl cellulose from rice stubble (CMCr) as a potential biomaterial. Plasticizer types (glycerol and olive oil) and their contents were investigated to provide flexibility for use as food packaging material. Glycerol content enhanced extensibility, while olive oil content improved the moisture barrier of films. Additionally, CMCr showed potential as a replacement for up to 50% of commercial CMC without any changes in mechanical and permeability properties. A mixture of plasticizers (10% glycerol and 10% olive oil) provided blended film with good water barrier and mechanical properties comparable with 20% individual plasticizer. Principle component (PC) analysis with 2 PCs explained approximately 81% of the total variance, was a useful tool to select a suitable plasticizer ratio for blended film production. Therefore, CMCr can be used to form edible film and coating as a renewable environmentally friendly packaging material. Copyright © 2017 Elsevier Ltd. All rights reserved.

Design Concepts, Fabrication and Advanced Characterization Methods of Innovative Piezoelectric Sensors Based on ZnO Nanowires

PubMed Central

Araneo, Rodolfo; Rinaldi, Antonio; Notargiacomo, Andrea; Bini, Fabiano; Pea, Marialilia; Celozzi, Salvatore; Marinozzi, Franco; Lovat, Giampiero

2014-01-01

Micro- and nano-scale materials and systems based on zinc oxide are expected to explode in their applications in the electronics and photonics, including nano-arrays of addressable optoelectronic devices and sensors, due to their outstanding properties, including semiconductivity and the presence of a direct bandgap, piezoelectricity, pyroelectricity and biocompatibility. Most applications are based on the cooperative and average response of a large number of ZnO micro/nanostructures. However, in order to assess the quality of the materials and their performance, it is fundamental to characterize and then accurately model the specific electrical and piezoelectric properties of single ZnO structures. In this paper, we report on focused ion beam machined high aspect ratio nanowires and their mechanical and electrical (by means of conductive atomic force microscopy) characterization. Then, we investigate the suitability of new power-law design concepts to accurately model the relevant electrical and mechanical size-effects, whose existence has been emphasized in recent reviews. PMID:25494351

Development of COPVS for High pressure, In-Space, Cryogenic Fuel Storage

NASA Technical Reports Server (NTRS)

DeLay, Tom; Schneider, Judy; Dyess, Mark; Hastings, Chad; Noorda, Ryan; Noorda, Jared; Patterson, James

2008-01-01

Polymeric composite overwrapped pressure vessels (COPVs) provide an attractive material system to support developing commercial launch business and alternate fuel ventures. However to be able to design with these materials, the mechanical behavior of the materials must be understood with regards to processing, performance, damage tolerance, and environment. For the storage of cryogenic propellants, it is important to evaluate the materials performance and impact damage resistance at cryogenic temperatures in order to minimize weight and to ensure safety and reliability. To evaluate the ultimate performance, various polymeric COPV's have been statically burst tested at cryogenic conditions before and after exposure to irradiation. Materials selected for these COPVs were based on the measured mechanical properties of candidate resin systems and fibers that were also tested at cryogenic conditions before and after exposure to irradiation. The correlation of COPV burst pressures with the constituent material properties has proven to be a valuable screening method for selection of suitable candidate materials with resistance to material degradation due to exposure to temperature and radiation.

Mechanical and optoelectric properties of post-annealed fluorine-doped tin oxide films by ultraviolet laser irradiation

NASA Astrophysics Data System (ADS)

Tseng, Shih-Feng; Hsiao, Wen-Tse; Chiang, Donyau; Huang, Kuo-Cheng; Chou, Chang-Pin

2011-06-01

The fluorine-doped tin oxide (FTO) thin film deposited on a soda-lime glass substrate was annealed by a defocus ultraviolet (UV) laser irradiation at ambient temperature. The mechanical and optoelectric properties of FTO films annealed by using the various laser processing parameters were reported. After the FTO films were subjected to laser post-annealing, the microhardness were slightly less but the reduced modulus values were larger than that of unannealed FTO films, respectively. The average optical transmittance in the visible waveband slightly increased with increasing the laser annealing energy and scan speed. Moreover, all the sheet resistance of laser annealed films was less than that of the unannealed ones. We found that the sheet resistance decrease was obviously influenced by annealing. The suitable annealing conditions could maintain the film thickness and relief the internal stress generated in the film preparation process to improve the electrical conductivity via decreasing laser energy or increasing scan speed.

PVA bio-nanocomposites: a new take-off using cellulose nanocrystals and PLGA nanoparticles.

PubMed

Rescignano, N; Fortunati, E; Montesano, S; Emiliani, C; Kenny, J M; Martino, S; Armentano, I

2014-01-01

The formation of a new generation of hybrid bio-nanocomposites is reported: these are intended at modulating the mechanical, thermal and biocompatibility properties of the poly(vinyl alcohol) (PVA) by the combination of cellulose nanocrystals (CNC) and poly (D,L-lactide-co-glycolide) (PLGA) nanoparticles (NPs) loaded with bovine serum albumin fluorescein isothiocynate conjugate (FITC-BSA). CNC were synthesized from microcrystalline cellulose by hydrolysis, while PLGA nanoparticles were produced by a double emulsion with subsequent solvent evaporation. Firstly, binary bio-nanocomposites with different CNC amounts were developed in order to select the right content of CNC. Next, ternary PVA/CNC/NPs bio-nanocomposites were developed. The addition of CNC increased the elongation properties without compromising the other mechanical responses. Thermal analysis underlined the nucleation effect of the synergic presence of cellulose and nanoparticles. Remarkably, bio-nanocomposite films are suitable to vehiculate biopolymeric nanoparticles to adult bone marrow mesenchymal stem cells successfully, thus representing a new tool for drug delivery strategies. Copyright © 2013 Elsevier Ltd. All rights reserved.

Additive Manufacturing of Fuel Injectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sadek Tadros, Dr. Alber Alphonse; Ritter, Dr. George W.; Drews, Charles Donald

Additive manufacturing (AM), also known as 3D-printing, has been shifting from a novelty prototyping paradigm to a legitimate manufacturing tool capable of creating components for highly complex engineered products. An emerging AM technology for producing metal parts is the laser powder bed fusion (L-PBF) process; however, industry manufacturing specifications and component design practices for L-PBF have not yet been established. Solar Turbines Incorporated (Solar), an industrial gas turbine manufacturer, has been evaluating AM technology for development and production applications with the desire to enable accelerated product development cycle times, overall turbine efficiency improvements, and supply chain flexibility relative to conventionalmore » manufacturing processes (casting, brazing, welding). Accordingly, Solar teamed with EWI on a joint two-and-a-half-year project with the goal of developing a production L-PBF AM process capable of consistently producing high-nickel alloy material suitable for high temperature gas turbine engine fuel injector components. The project plan tasks were designed to understand the interaction of the process variables and their combined impact on the resultant AM material quality. The composition of the high-nickel alloy powders selected for this program met the conventional cast Hastelloy X compositional limits and were commercially available in different particle size distributions (PSD) from two suppliers. Solar produced all the test articles and both EWI and Solar shared responsibility for analyzing them. The effects of powder metal input stock, laser parameters, heat treatments, and post-finishing methods were evaluated. This process knowledge was then used to generate tensile, fatigue, and creep material properties data curves suitable for component design activities. The key process controls for ensuring consistent material properties were documented in AM powder and process specifications. The basic components of the project were: • Powder metal input stock: Powder characterization, dimensional accuracy, metallurgical characterization, and mechanical properties evaluation. • Process parameters: Laser parameter effects, post-printing heat-treatment development, mechanical properties evaluation, and post-finishing technique. • Material design curves: Room and elevated temperature tensiles, low cycle fatigue, and creep rupture properties curves generated. • AM specifications: Key metal powder characteristics, laser parameters, and heat-treatment controls identified.« less

Numerical simulations of mechanical properties of innovative pothole patching materials featuring high toughness, low viscosity nano-molecular resins

NASA Astrophysics Data System (ADS)

Yuan, K. Y.; Yuan, W.; Ju, J. W.; Yang, J. M.; Kao, W.; Carlson, L.

2012-04-01

As asphalt pavements age and deteriorate, recurring pothole repair failures and propagating alligator cracks in the asphalt pavements have become a serious issue to our daily life and resulted in high repairing costs for pavement and vehicles. To solve this urgent issue, pothole repair materials with superior durability and long service life are needed. In the present work, revolutionary pothole patching materials with high toughness, high fatigue resistance that are reinforced with nano-molecular resins have been developed to enhance their resistance to traffic loads and service life of repaired potholes. In particular, DCPD resin (dicyclopentadiene, C10H12) with a Rhuthinium-based catalyst is employed to develop controlled properties that are compatible with aggregates and asphalt binders. In this paper, a multi-level numerical micromechanics-based model is developed to predict the mechanical properties of these innovative nanomolecular resin reinforced pothole patching materials. Coarse aggregates in the finite element analysis are modeled as irregular shapes through image processing techniques and randomly-dispersed coated particles. The overall properties of asphalt mastic, which consists of fine aggregates, asphalt binder, cured DCPD and air voids are theoretically estimated by the homogenization technique of micromechanics. Numerical predictions are compared with suitably designed experimental laboratory results.

Stability and carrier transport properties of phosphorene-based polymorphic nanoribbons

NASA Astrophysics Data System (ADS)

Kaur, Sumandeep; Kumar, Ashok; Srivastava, Sunita; Pandey, Ravindra; Tankeshwar, K.

2018-04-01

Few-layer black phosphorene has recently attracted significant interest in the scientific community. In this paper, we consider several polymorphs of phosphorene nanoribbons (PNRs) and employ deformation potential theory within the effective mass approximation, together with density functional theory, to investigate their structural, mechanical and electronic properties. The results show that the stability of a PNR strongly depends on the direction along which it can be cut from its 2D counterpart. PNRs also exhibit a wide range of line stiffnesses ranging from 6 × 1010 eV m-1 to 18 × 1011 eV m-1, which has little dependence on the edge passivation. Likewise, the calculated electronic properties of PNRs show them to be either a narrow-gap semiconductor (E g < 1 eV) or a wide-gap semiconductor (E g > 1 eV). The carrier mobility of PNRs is found to be comparable to that of black phosphorene. Some of the PNRs show an n-type (p-type) semiconducting character owing to their higher electron (hole) mobility. Passivation of the edges leads to n-type ↔ p-type transition in many of the PNRs considered. The predicted novel characteristics of PNRs, with a wide range of mechanical and electronic properties, make them potentially suitable for use in nanoscale devices.

Effect of metallurgical structure and properties on adhesion and friction behavior of cobalt alloys

NASA Technical Reports Server (NTRS)

Keller, D. V., Jr.; Shatynski, S.; Vedamanikam, P. M.

1972-01-01

The metallurgical structure and some of the mechanical properties of two cobalt alloys, cobalt-50% iron and cobalt-25% molybdenum-10% chromium, were determined under various heat treated conditions. The mechanical properties of the bcc disordered Co-50Fe alloy, which was found to be very brittle, indicated an exceedingly low fracture strength, low hardness, and very weak grain boundary strength. Ordering by suitable heat treatment only produced a more brittle material with a lower fracture strength and a slightly higher hardness value. Work hardening was found to produce a finer grain structure and a greater grain boundary strength. Tensile properties were examined. It was found that the Co-25Mo-10Cr alloy was difficult to place in the alpha Co solid solution condition, which limited the ability to use precipitation as a hardening reaction. Over two hundred adhesion cycles from zero contact load, to maximum load, to fracture were conducted between couples for each of the above alloys in an ultrahigh vacuum system which would permit the sample surfaces to be cleaned of all contaminant layers. In the Co-50Fe case, the calculated fracture stress from the adhesion tests showed values in the range of 80 to 150 k.s.i., which is about ten times greater than the values from tension tests.

Investigation on the Crack Behaviour in Kevlar 49 Based Composite Materials using Extended Finite Element Method for Aerospace Applications

NASA Astrophysics Data System (ADS)

Handa, Danish; Sekhar Dondapati, Raja; Kumar, Abhinav

2017-08-01

Ductile to brittle transition (DTBT) is extensively observed in materials under cryogenic temperatures, thereby observing brittle failure due to the non-resistance of crack propagation. Owing to its outstanding mechanical and thermal properties, Kevlar 49 composites are widely used in aerospace applications under cryogenic temperatures. Therefore, in this paper, involving the assumption of linear elastic fracture mechanics (LEFM), mechanical characterization of Kevlar 49 composite is done using Extended Finite Element Method (X-FEM) technique in Abaqus/CAE software. Further, the failure of Kevlar 49 composites due to the propagation of crack at room temperature and the cryogenic temperature is investigated. Stress, strain and strain energy density as a function of the width of the Kevlar specimen is predicted, indicates that Kevlar 49 composites are suitable for use under cryogenic temperatures.

Microstructure, nickel suppression and mechanical characteristics of electropolished and photoelectrocatalytically oxidized biomedical nickel titanium shape memory alloy.

PubMed

Chu, C L; Guo, C; Sheng, X B; Dong, Y S; Lin, P H; Yeung, K W K; Chu, Paul K

2009-07-01

A new surface modification protocol encompassing an electropolishing pretreatment (EP) and subsequent photoelectrocatalytic oxidation (PEO) has been developed to improve the surface properties of biomedical nickel titanium (NiTi) shape memory alloy (SMA). Electropolishing is a good way to improve the resistance to localized breakdown of NiTi SMA whereas PEO offers the synergistic effects of advanced oxidation and electrochemical oxidation. Our results indicate that PEO leads to the formation of a sturdy titania film on the EP NiTi substrate. There is an Ni-free zone near the top surface and a graded interface between the titania layer and NiTi substrate, which bodes well for both biocompatibility and mechanical stability. In addition, Ni ion release from the NiTi substrate is suppressed, as confirmed by the 10-week immersion test. The modulus and hardness of the modified NiTi surface increase with larger indentation depths, finally reaching plateau values of about 69 and 3.1GPa, respectively, which are slightly higher than those of the NiTi substrate but much lower than those of a dense amorphous titania film. In comparison, after undergoing only EP, the mechanical properties of NiTi exhibit an inverse change with depth. The deformation mechanism is proposed and discussed. Our results indicate that surface modification by dual EP and PEO can notably suppress Ni ion release and improve the biocompatibility of NiTi SMA while the surface mechanical properties are not compromised, making the treated materials suitable for hard tissue replacements.

76 FR 46149 - Financial Assistance: Wildlife Restoration, Sport Fish Restoration, Hunter Education and Safety

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-01

... changes for personal property, we moved the examples of real property from the proposed Sec. 80.20(b)(1... during the license period, or (2) At the time of sale as if it were a single-payment annuity, which is an... proposed Sec. 80.50(a)(4) to read, ``Acquire real property suitable or capable of being made suitable for...

Incorporation of nisin in poly (ethylene-co-vinyl acetate) films by melt processing: a study on the antimicrobial properties.

PubMed

Scaffaro, Roberto; Botta, Luigi; Marineo, Sandra; Puglia, Anna Maria

2011-07-01

Both industry and academia have shown a growing interest in materials with antimicrobial properties suitable for food packaging applications. In this study, we prepared and characterized thin films of ethylene-co-vinyl acetate (EVA) copolymer with antimicrobial properties. The films were prepared with a film blowing process by incorporating a nisin preparation as an antimicrobial agent in the melt. Two grades of EVA containing 14 and 28% (wt/wt) vinyl acetate (EVA 14 and EVA 28, respectively) and two commercial formulations of nisin with different nominal activities were used. The effect of the nisin concentration also was evaluated. The films with the highest antimicrobial activity were those formulated with nisin at the highest activity and EVA with the highest content of vinyl acetate. The use of the commercial formulation of nisin with high activity in the EVA films allowed reduction in the amount of nisin needed to provide antimicrobial properties. Consequently, the mechanical properties of these films were only slightly inferior to those of the pure polymers. In contrast, films prepared by incorporating more of the nisin with lower activity had poor mechanical properties. The effect of different processing temperatures used in the preparation of the films on the antimicrobial properties of the films also was evaluated. The materials displayed antimicrobial properties even when they were prepared at temperatures as high as 160 °C, probably because of the very short processing time (60 to 90 s) required for preparation. Copyright ©, International Association for Food Protection

Mechanical behaviour of degradable phosphate glass fibres and composites-a review.

PubMed

Colquhoun, R; Tanner, K E

2015-12-23

Biodegradable materials are potentially an advantageous alternative to the traditional metallic fracture fixation devices used in the reconstruction of bone tissue defects. This is due to the occurrence of stress shielding in the surrounding bone tissue that arises from the absence of mechanical stimulus to the regenerating bone due to the mismatch between the elastic modulus of bone and the metal implant. However although degradable polymers may alleviate such issues, these inert materials possess insufficient mechanical properties to be considered as a suitable alternative to current metallic devices at sites of sufficient mechanical loading. Phosphate based glasses are an advantageous group of materials for tissue regenerative applications due to their ability to completely degrade in vivo at highly controllable rates based on the specific glass composition. Furthermore the release of the glass's constituent ions can evoke a therapeutic stimulus in vivo (i.e. osteoinduction) whilst also generating a bioactive response. The processing of these materials into fibres subsequently allows them to act as reinforcing agents in degradable polymers to simultaneously increase its mechanical properties and enhance its in vivo response. However despite the various review articles relating to the compositional influences of different phosphate glass systems, there has been limited work summarising the mechanical properties of different phosphate based glass fibres and their subsequent incorporation as a reinforcing agent in degradable composite materials. As a result, this review article examines the compositional influences behind the development of different phosphate based glass fibre compositions intended as composite reinforcing agents along with an analysis of different potential composite configurations. This includes variations in the fibre content, matrix material and fibre architecture as well as other novel composites designs.

Graphene oxide/oxidized carbon nanofiber/mineralized hydroxyapatite based hybrid composite for biomedical applications

NASA Astrophysics Data System (ADS)

Murugan, N.; Sundaramurthy, Anandhakumar; Chen, Shen-Ming; Sundramoorthy, Ashok K.

2017-12-01

Hydroxyapatite (Ca10(PO4)6(OH)2, HAP), a multi-mineral substituted calcium phosphate is the main mineral component of tooth enamel and bone, has become an important biomaterial for biomedical applications. However, as-synthesized HAP has poor mechanical properties and inferior wear resistance, so it is not suitable to use in bone tissue engineering applications. We report the successful incorporation of oxidized carbon nanofibers (O-CNF) and graphene oxide (GO) into the mineralized hydroxyapatite (M-HAP) which showed excellent mechanical and biological properties. GO improved the high mechanical strength and corrosion protection of the substrate in simulated body fluid (SBF) solution and promoted the viability of osteoblasts MG63 cells. As-prepared M-HAP/O-CNF/GO composite showed materials characteristics that similar to natural bone (M-HAP) with high mechanical strength. The resultant M-HAP/O-CNF/GO composite was characterized out by x-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and Fourier-transform infrared spectroscopy (FT-IR), respectively. The mechanical strength of the material was determined by Vicker’s micro-hardness method and it was found that M-HAP/O-CNF/GO (468  ±  4 Hv) composite has superior mechanical properties than M-HAP (330  ±  3 Hv) and M-HAP/GO (425  ±  5 Hv) samples. In addition, antibacterial activity of the composite was studied against Staphylococcus aureus and Escherichia coli. Furthermore, the cell viability of the composite was observed in vitro against osteoblast cells. All these studies confirmed that the M-HAP/O-CNF/GO composite can be considered as potential candidate for dental and orthopedic applications.

45 CFR 12a.4 - Suitability determination.

Code of Federal Regulations, 2010 CFR

2010-10-01

... underutilized will be reviewed for suitability no earlier than six months prior to the expected date when the... following: (1) The suitability determination for a particular piece of property, and the reasons for that...

Zirconia in dental implantology: A review

PubMed Central

Apratim, Abhishek; Eachempati, Prashanti; Krishnappa Salian, Kiran Kumar; Singh, Vijendra; Chhabra, Saurabh; Shah, Sanket

2015-01-01

Background: Titanium has been the most popular material of choice for dental implantology over the past few decades. Its properties have been found to be most suitable for the success of implant treatment. But recently, zirconia is slowly emerging as one of the materials which might replace the gold standard of dental implant, i.e., titanium. Materials and Methods: Literature was searched to retrieve information about zirconia dental implant and studies were critically analyzed. PubMed database was searched for information about zirconia dental implant regarding mechanical properties, osseointegration, surface roughness, biocompatibility, and soft tissue health around it. The literature search was limited to English language articles published from 1975 to 2015. Results: A total of 45 papers met the inclusion criteria for this review, among the relevant search in the database. Conclusion: Literature search showed that some of the properties of zirconia seem to be suitable for making it an ideal dental implant, such as biocompatibility, osseointegration, favourable soft tissue response and aesthetics due to light transmission and its color. At the same time, some studies also point out its drawbacks. It was also found that most of the studies on zirconia dental implants are short-term studies and there is a need for more long-term clinical trials to prove that zirconia is worth enough to replace titanium as a biomaterial in dental implantology. PMID:26236672

Plackett-Burman experimental design to facilitate syntactic foam development

DOE PAGES

Smith, Zachary D.; Keller, Jennie R.; Bello, Mollie; ...

2015-09-14

The use of an eight-experiment Plackett–Burman method can assess six experimental variables and eight responses in a polysiloxane-glass microsphere syntactic foam. The approach aims to decrease the time required to develop a tunable polymer composite by identifying a reduced set of variables and responses suitable for future predictive modeling. The statistical design assesses the main effects of mixing process parameters, polymer matrix composition, microsphere density and volume loading, and the blending of two grades of microspheres, using a dummy factor in statistical calculations. Responses cover rheological, physical, thermal, and mechanical properties. The cure accelerator content of the polymer matrix andmore » the volume loading of the microspheres have the largest effects on foam properties. These factors are the most suitable for controlling the gel point of the curing foam, and the density of the cured foam. The mixing parameters introduce widespread variability and therefore should be fixed at effective levels during follow-up testing. Some responses may require greater contrast in microsphere-related factors. As a result, compared to other possible statistical approaches, the run economy of the Plackett–Burman method makes it a valuable tool for rapidly characterizing new foams.« less

Cobalt ferrite based magnetostrictive materials for magnetic stress sensor and actuator applications

NASA Technical Reports Server (NTRS)

Jiles, David C. (Inventor); Paulsen, Jason A. (Inventor); Snyder, John E. (Inventor); Lo, Chester C. H. (Inventor); Ring, Andrew P. (Inventor); Bormann, Keith A. (Inventor)

2008-01-01

Magnetostrictive material based on cobalt ferrite is described. The cobalt ferrite is substituted with transition metals (such manganese (Mn), chromium (Cr), zinc (Zn) and copper (Cu) or mixtures thereof) by substituting the transition metals for iron or cobalt to form substituted cobalt ferrite that provides mechanical properties that make the substituted cobalt ferrite material effective for use as sensors and actuators. The substitution of transition metals lowers the Curie temperature of the material (as compared to cobalt ferrite) while maintaining a suitable magnetostriction for stress sensing applications.

Novel shape memory alloy optical fibre connection method

NASA Astrophysics Data System (ADS)

Trouillard, G.; Zivojinovic, P.; Cerutti, R.; Godmaire, X. Pruneau; Weynant, E.

2010-02-01

In this paper, the capacity and quality of a shape memory alloy device is demonstrated for installation and connection of 125-μm to 1000-μm optical fibres. The new mechanical splice has the particularity of using a very simple tool for aligning and holding the cladding of fibres itself without the need of glue. Optimend main characteristics are its small dimensions (few millimetres), reusability, glueless, ruggedness, low temperature variation, heat dissipation and ease of use. These properties are very suitable for many optical fibre applications where both quick and reliable connections are desirable.

Resin/graphite fiber composites

NASA Technical Reports Server (NTRS)

Cavano, P. J.; Jones, R. J.; Vaughan, R. W.

1972-01-01

High temperature resin matrices suitable for use in advanced graphite fiber composites for jet engine applications were evaluated. A series of planned, sequential screening experiments with resin systems in composite form were performed to reduce the number of candidates to a single A-type polyimide resin that repetitively produced void-free, high strength and modulus composites acceptable for use in the 550 F range for 1000 hours. An optimized processing procedure was established for this system. Extensive mechanical property studies characterized this single system, at room temperature, 500 F, 550 F and 600 F, for various exposure times.

Influence of Codium tomentosum Extract in the Properties of Alginate and Chitosan Edible Films

PubMed Central

Dias, Juliana R.; Alves, Nuno M.; Pedrosa, Rui; Silva, Susana F. J.

2018-01-01

The growing search for natural alternatives to synthetic food packaging materials and additives has increased, and seaweed extracts’ bioactivity has made them suitable candidates for incorporation in novel edible films. This study aims to investigate the effect of Codium tomentosum seaweed extract (SE) incorporation in alginate and chitosan edible films. Alginate- and chitosan-based films with and without the incorporation of 0.5% SE were characterized according to their physical, optical, mechanical, and thermal properties. Seaweed extract incorporation in chitosan films resulted in an increase of film solubility (50%), elasticity (18%), and decrease of puncture strength (27%) and energy at break (39%). In alginate films, the extract incorporation significantly decreased film solubility (6%), water vapour permeability (46%), and elasticity (24%), and had no effect on thermal properties. Depending on the type of application, the addition of SE in edible films can bring advantages for food conservation. PMID:29614782

Assessment of Technologies for the Space Shuttle External Tank Thermal Protection System and Recommendations for Technology Improvement - Part III: Material Property Characterization, Analysis, and Test Methods

NASA Technical Reports Server (NTRS)

Gates, Thomas S.; Johnson, Theodore F.; Whitley, Karen S.

2005-01-01

The objective of this report is to contribute to the independent assessment of the Space Shuttle External Tank Foam Material. This report specifically addresses material modeling, characterization testing, data reduction methods, and data pedigree. A brief description of the External Tank foam materials, locations, and standard failure modes is provided to develop suitable background information. A review of mechanics based analysis methods from the open literature is used to provide an assessment of the state-of-the-art in material modeling of closed cell foams. Further, this report assesses the existing material property database and investigates sources of material property variability. The report presents identified deficiencies in testing methods and procedures, recommendations for additional testing as required, identification of near-term improvements that should be pursued, and long-term capabilities or enhancements that should be developed.

The Effect of Gravity on the Combustion Synthesis of Porous Biomaterials

NASA Technical Reports Server (NTRS)

Castillo, M.; Zhang, X.; Moore, J. J.; Schowengerdt, F. D.; Ayers, R. A.

2003-01-01

Production of highly porous composite materials by traditional materials processing is limited by difficult processing techniques. This work investigates the use of self propagating high temperature (combustion) synthesis (SHS) to create porous tricalcium phosphate (Ca3(PO4)2), TiB-Ti, and NiTi in low and microgravity. Combustion synthesis provides the ability to use set processing parameters to engineer the required porous structure suitable for bone repair or replacement. The processing parameters include green density, particle size, gasifying agents, composition, and gravity. The advantage of the TiB-Ti system is the high level of porosity achieved together with a modulus that can be controlled by both composition (TiB-Ti) and porosity. At the same time, NiTi exhibits shape memory properties. SHS of biomaterials allows the engineering of required porosity coupled with resorbtion properties and specific mechanical properties into the composite materials to allow for a better biomaterial.

Heat treatment condition of EN AW-7075 influencing the anodic oxidation process and coating properties

NASA Astrophysics Data System (ADS)

Morgenstern, R.; Scharf, I.; Lampke, T.

2018-06-01

The age-hardenable aluminium alloy EN AW-7075 exhibits outstanding specific mechanical properties and therefore offers a high potential for lightweight construction. Anodising in aqueous oxalic acid solutions is suitable to produce a protective oxide ceramic conversion layer on this alloy. This study examines the influence of the precipitation state of the substrate alloy on microstructure and properties of anodic oxide layers. Therefore, EN AW-7075 sheets in the heat treatment conditions T4, T6 and T73 were anodized in 0.8 M oxalic acid solution at constant voltage. The current efficiency was determined on the basis of the electrical charge quantity, coating thickness and coating mass. Instrumented indentation tests were applied in order to evaluate the coating hardness. The microstructure of the anodic oxide layer was illustrated using field emission electron microscopy. It was shown that the current efficiency strongly depends on the heat treatment condition.

Comparative assessment of the microhardness and plastic degradation mechanism of deposited modulated coatings on mild steel

NASA Astrophysics Data System (ADS)

Fayomi, O. S. I.; Anawe, P. A. L.; Inegbenebor, A. O.; Udoye, N. E.

2018-05-01

Zinc based coatings modified with aluminium and tin inclusions were electrodeposited in chloride zinc sulfate electrolytes containing a metallic powder of titanium. It was found that presence of these particulates is suitable to obtain ZnAlSn-Ti composites coating that could help increase the microhardnesss characteristics and wear properties. The hardness and wear properties of the deposited coatings were examined with diamond base micro-hardness tester and CETR reciprocating sliding tester respectively. The structural properties were examined with the help of scanning electron microscope. It was observed that structural coating surface impact on the hardness propagation with increases from 33.4 to 299 kgf mm-2 (HVN40), and shows a considerably higher wear resistance from 2.351g/min to 0.002g/min. It is obvious that plastic deformation of the working steel structure is dependent on protective coating and the concentration of the individual particulate.

Well-balanced high-order solver for blood flow in networks of vessels with variable properties.

PubMed

Müller, Lucas O; Toro, Eleuterio F

2013-12-01

We present a well-balanced, high-order non-linear numerical scheme for solving a hyperbolic system that models one-dimensional flow in blood vessels with variable mechanical and geometrical properties along their length. Using a suitable set of test problems with exact solution, we rigorously assess the performance of the scheme. In particular, we assess the well-balanced property and the effective order of accuracy through an empirical convergence rate study. Schemes of up to fifth order of accuracy in both space and time are implemented and assessed. The numerical methodology is then extended to realistic networks of elastic vessels and is validated against published state-of-the-art numerical solutions and experimental measurements. It is envisaged that the present scheme will constitute the building block for a closed, global model for the human circulation system involving arteries, veins, capillaries and cerebrospinal fluid. Copyright © 2013 John Wiley & Sons, Ltd.

Properties of Josephson Junction Fabricated on Bicrystal Substrate with Different Misorientation Angles

NASA Astrophysics Data System (ADS)

Minotani, Tadashi; Kawakami, Satoru; Kuroki, Yukinori; Enpuku, Keiji

1998-06-01

In order to develop YBa2Cu3O7-δ bicrystal junctions suitable for high-performance superconducting quantum interference device (SQUID), the relationship between the junction properties and the misorientation angle of the bicrystal substrate is studied experimentally. Misorientation angles of 24°, 27°, 30°, 33° and 36.8° are used, and the angular dependencies of junction resistance Rs and critical current Io are investigated. It is shown that values of Rs and Io approximately follow the relation IoRs1.5=const. in these junctions. The obtained results are analyzed in terms of the direct and resonant tunneling mechanisms. It is also shown that values of Rs≈10 Ω and Io≈20 µA can be obtained rather reproducibly when we use the 30° junctions. The properties of this junction are very promising for the development of high-performance SQUID.

Healing of skin wounds with a chitosan-gelatin sponge loaded with tannins and platelet-rich plasma.

PubMed

Lu, Bitao; Wang, Tianyou; Li, Zhiquan; Dai, Fangying; Lv, Lingmei; Tang, Fengling; Yu, Kun; Liu, Jiawei; Lan, Guangqian

2016-01-01

A chitosan-gelatin sponge (CSGT) was prepared using a chitosan/ascorbic acid solution blend containing gelatin, followed by crosslinking with tannin acid and freeze-drying, thereby combining the chitosan sponge and gelatin sponge. The structure of the CSGT was observed by scanning electron microscopy and was shown to have uniform and abundant pores measuring about 145-240μm in size. We also characterized the sponges by infrared spectroscopy, thermogravimetric analysis, mechanical property tests, swelling behavior analysis, water retention capacity tests, antibacterial property analysis, and cytotoxicity tests. Our data showed that the CSGT had good thermostability and mechanical properties as well as efficient water absorption and retention capacities. Moreover, the CSGT could effectively inhibit the growth of Escherichia coli and Staphylococcus aureus with low toxicity. In animal experiments, macroscopic observations and histological examinations showed that the wound covered by the CSGT healed quickly. Additionally, loading of the CSGT with platelet-rich plasma resulted in further acceleration of wound healing. Therefore, the CSGT and the CSGT with platelet-rich plasma were suitable for application as a wound dressing and may have potential for use in various biomedical applications. Copyright © 2015 Elsevier B.V. All rights reserved.

Effect of milling time on microstructure and mechanical properties of Cu-Ni-graphite composites

NASA Astrophysics Data System (ADS)

Wang, Yiran; Gao, Yimin; Li, Yefei; Zhang, Chao; Huang, Xiaoyu; Zhai, Wenyan

2017-09-01

Cu-Ni-graphite composites are intended for application in switch slide baseplate materials. The microstructure of the composites depends strongly on the ball milling time, and a suitable time can significantly improve the properties of the Cu-Ni-graphite composites. In this study, a two-step milling method was employed. The morphology evolution and microstructural features of the powder was characterized at different milling times. Afterwards, the Cu-Ni-graphite composites were prepared in the process of cold pressing, sintering, re-pressing and re-sintering as a function of the different milling times. Finally, both the microstructure and mechanical properties of the Cu-Ni-graphite composites are discussed. The results show that no new phase was generated during the milling process. The morphology evolution of the mixture of Cu/Ni powder changed from spherical-like to cubic-like, plate-like and flake-like with an increasing milling time. The microstructure of the composites consisted of α-phase and graphite. The boundary area and quantity of pores changed as the milling time increased. The relative density, hardness and flexural strength reached maximum values at 15 h of milling time.

Completion of evaluation of manufacturing processes for B/Al composites containing 0.2mm diameter boron fibers

NASA Technical Reports Server (NTRS)

Moore, T. J.; Moorhead, P. E.

1980-01-01

Four fabricators produced a total of 54 B/1100 Al, B/6061 Al, and B/2024 Al panels for evaluation. The 8 ply unidirectional, 45 to 50 volume percent, panels were made using 0.20 mm diameter boron fibers which were obtained from a single supplier. Hot press consolidation was carried out in vacuum except for one set of dry woven tape panels which were hot pressed in air. A single testing contractor conducted nondestructive inspection, metallography, fractography and mechanical property tests. The mechanical property tests included 21 and 260 C tensile tests and 21 C shear tests. Panel quality, as measured by nondestructive evaluation, was generally good as were the 21 C tensile properties. The panels hot pressed in air delaminated in the shear tests. Shear strength values were lower in these panels. But tensile strengths were not affected by the delaminations because of the relation between the tensile loading direction and the delaminations. Composite tensile strength was found to be proportional to the volume percent boron and the aluminum matrix rather than to the tape used or fabrication technique. Suitability of these composites for 260 C service was confirmed by tensile tests.

3D printed orodispersible films with Aripiprazole.

PubMed

Jamróz, Witold; Kurek, Mateusz; Łyszczarz, Ewelina; Szafraniec, Joanna; Knapik-Kowalczuk, Justyna; Syrek, Karolina; Paluch, Marian; Jachowicz, Renata

2017-11-30

Three dimensional printing technology is gaining in importance because of its increasing availability and wide applications. One of the three dimensional printing techniques is Fused Deposition Modelling (FDM) which works on the basis of hot melt extrusion-well known in the pharmaceutical technology. Combination of fused deposition modelling with preparation of the orodispersible film with poorly water soluble substance such as aripiprazole seems to be extra advantageous in terms of dissolution rate. 3D printed as well as casted films were compared in terms of physicochemical and mechanical properties. Moreover, drug-free films were prepared to evaluate the impact of the extrusion process and aripiprazole presence on the film properties. X-ray diffractometry and thermal analyses confirmed transition of aripiprazole into amorphous state during film preparation using 3D printing technique. Amorphization of the aripiprazole and porous structure of printed film led to increased dissolution rate in comparison to casted films, which, however have slightly better mechanical properties due to their continuous structure. It can be concluded that fused deposition modelling is suitable technique and polyvinyl alcohol is applicable polymer for orodispersible films preparation. Copyright © 2017 Elsevier B.V. All rights reserved.

Mechanical Properties of Triaxial Braided Carbon/Epoxy Composites

NASA Technical Reports Server (NTRS)

Bowman, C. L.; Roberts, G. D.; Braley, M. S.; Xie, M.; Booker, M. J.

2003-01-01

In an on-going effort to increase the safety and efficiency of turbine engines, the National Aeronautics and Space Administration is exploring lightweight alternatives to the metal containment structures that currently encase commercial jet engines. Epoxy reinforced with braided carbon fibers is a candidate structural material which may be suitable for an engine case. This paper reports flat-coupon mechanical-property experiments performed to compliment previously reported subcomponent impact testing and analytical simulation of containment structures. Triaxial-braid T700/5208 epoxy and triaxial-braid T700/M36 toughened epoxy composites were evaluated. Also, two triaxial-braid architectures (0 +/- 60 deg., 0 +/- 45 deg.) with the M36 resin were evaluated through tension, compression, and shear testing. Tensile behavior was compared between standard straight-sided specimens (ASTM D3039) and bowtie specimens. Both double-notch shear (ASTM D3846) and Iosepescu (ASTM D5379) tests were performed as well. The M36/0 +/- 45 deg. configuration yield the best response when measurements were made parallel to the axial tows. Conversely, the M36/0 +/- 60 deg. configuration was best when measurements were made perpendicular to the axial tows. The results were used to identify critical properties and to augment the analysis of impact experiments.

On the thermoelastic analysis of solar cell arrays and related material properties

NASA Technical Reports Server (NTRS)

Salama, M. A.; Bouquet, F. L.

1976-01-01

Accurate prediction of failure of solar cell arrays requires accuracy in the computation of thermally induced stresses. This was accomplished by using the finite element technique. Improved procedures for stress calculation were introduced together with failure criteria capable of describing a wide range of ductile and brittle material behavior. The stress distribution and associated failure mechanisms in the N-interconnect junction of two solar cell designs were then studied. In such stress and failure analysis, it is essential to know the thermomechanical properties of the materials involved. Measurements were made of properties of materials suitable for the design of lightweight arrays: microsheet-0211 glass material for the solar cell filter, and Kapton-H, Kapton F, Teflon, Tedlar, and Mica Ply PG-402 for lightweight substrates. The temperature-dependence of the thermal coefficient of expansion for these materials was determined together with other properties such as the elastic moduli, Poisson's ratio, and the stress-strain behavior up to failure.

Recent Prospects in the Inline Monitoring of Nanocomposites and Nanocoatings by Optical Technologies.

PubMed

Bugnicourt, Elodie; Kehoe, Timothy; Latorre, Marcos; Serrano, Cristina; Philippe, Séverine; Schmid, Markus

2016-08-19

Nanostructured materials have emerged as a key research field in order to confer materials with unique or enhanced properties. The performance of nanocomposites depends on a number of parameters, but the suitable dispersion of nanoparticles remains the key in order to obtain the full nanocomposites' potential in terms of, e.g., flame retardance, mechanical, barrier, thermal properties, etc. Likewise, the performance of nanocoatings to obtain, for example, tailored surface affinity with selected liquids (e.g., for self-cleaning ability or anti-fog properties), protective effects against flame propagation, ultra violet (UV) radiation or gas permeation, is highly dependent on the nanocoating's thickness and homogeneity. In terms of recent advances in the monitoring of nanocomposites and nanocoatings, this review discusses commonly-used offline characterization approaches, as well as promising inline systems. All in all, having good control over both the dispersion and thickness of these materials would help with reaching optimal and consistent properties to allow nanocomposites to extend their use.

Recent Prospects in the Inline Monitoring of Nanocomposites and Nanocoatings by Optical Technologies

PubMed Central

Bugnicourt, Elodie; Kehoe, Timothy; Latorre, Marcos; Serrano, Cristina; Philippe, Séverine; Schmid, Markus

2016-01-01

Nanostructured materials have emerged as a key research field in order to confer materials with unique or enhanced properties. The performance of nanocomposites depends on a number of parameters, but the suitable dispersion of nanoparticles remains the key in order to obtain the full nanocomposites’ potential in terms of, e.g., flame retardance, mechanical, barrier, thermal properties, etc. Likewise, the performance of nanocoatings to obtain, for example, tailored surface affinity with selected liquids (e.g., for self-cleaning ability or anti-fog properties), protective effects against flame propagation, ultra violet (UV) radiation or gas permeation, is highly dependent on the nanocoating’s thickness and homogeneity. In terms of recent advances in the monitoring of nanocomposites and nanocoatings, this review discusses commonly-used offline characterization approaches, as well as promising inline systems. All in all, having good control over both the dispersion and thickness of these materials would help with reaching optimal and consistent properties to allow nanocomposites to extend their use. PMID:28335278

Challenges and Opportunities for Customizing Polyhydroxyalkanoates.

PubMed

Singh, Mamtesh; Kumar, Prasun; Ray, Subhasree; Kalia, Vipin C

2015-09-01

Polyhydroxyalkanoates (PHAs) as an alternative to synthetic plastics have been gaining increasing attention. Being natural in their origin, PHAs are completely biodegradable and eco-friendly. However, consistent efforts to exploit this biopolymer over the last few decades have not been able to pull PHAs out of their nascent stage, inspite of being the favorite of the commercial world. The major limitations are: (1) the high production cost, which is due to the high cost of the feed and (2) poor thermal and mechanical properties of polyhydroxybutyrate (PHB), the most commonly produced PHAs. PHAs have the physicochemical properties which are quite comparable to petroleum based plastics, but PHB being homopolymers are quite brittle, less elastic and have thermal properties which are not suitable for processing them into sturdy products. These properties, including melting point (Tm), glass transition temperature (Tg), elastic modulus, tensile strength, elongation etc. can be improved by varying the monomeric composition and molecular weight. These enhanced characteristics can be achieved by modifications in the types of substrates, feeding strategies, culture conditions and/or genetic manipulations.

Manufacturing of tailored tubes with a process integrated heat treatment

NASA Astrophysics Data System (ADS)

Hordych, Illia; Boiarkin, Viacheslav; Rodman, Dmytro; Nürnberger, Florian

2017-10-01

The usage of work-pieces with tailored properties allows for reducing costs and materials. One example are tailored tubes that can be used as end parts e.g. in the automotive industry or in domestic applications as well as semi-finished products for subsequent controlled deformation processes. An innovative technology to manufacture tubes is roll forming with a subsequent inductive heating and adapted quenching to obtain tailored properties in the longitudinal direction. This processing offers a great potential for the production of tubes with a wide range of properties, although this novel approach still requires a suited process design. Based on experimental data, a process simulation is being developed. The simulation shall be suitable for a virtual design of the tubes and allows for gaining a deeper understanding of the required processing. The model proposed shall predict microstructural and mechanical tube properties by considering process parameters, different geometries, batch-related influences etc. A validation is carried out using experimental data of tubes manufactured from various steel grades.

Solvatochromic benzo[h] coumarins: Synthesis, solvatochromism, NLO and DFT study

NASA Astrophysics Data System (ADS)

Warde, Umesh; Sekar, Nagaiyan

2017-10-01

Three benzo[h] coumarins were synthesized and analyzed for their potential NLOphoric properties. Coumarins were synthesized using Knoevenagel condensation method by reacting hydroxyl-naphthalene aldehyde with cyano-methylelene-benzazoles containing NH, O and S elements respectively as the active methylene compounds. The absorption maxima for the coumarins are not affected by the solvent polarity but emission maxima does. Emission solvatochromism was analyzed using various solvent polarity functions which highlights the polarity dependency of the emission profile. Coumarins showed satisfactory values for first and second hyperpolarizability which are comparable using solvatochromism and DFT. NLO properties are also compared with the limits of hyperpolarizability calculated using sum rule of quantum mechanics. Results show that the NLO properties predicted by DFT are close to the upper limits of hyperpolarizability. The functional CAM-B3LYP is proven to be suitable for predicting NLO properties for these coumarins compared to functional B3LYP. The present study highlights the importance of such molecules for incorporating in advanced NLOphores.

Preparation and characterization of novel functionalized multiwalled carbon nanotubes/chitosan/β-Glycerophosphate scaffolds for bone tissue engineering.

PubMed

Gholizadeh, Shayan; Moztarzadeh, Fathollah; Haghighipour, Nooshin; Ghazizadeh, Leila; Baghbani, Fatemeh; Shokrgozar, Mohammad Ali; Allahyari, Zahra

2017-04-01

A major limitation in current tissue engineering scaffolds is that some of the most important characteristics of the intended tissue are ignored. As piezoelectricity and high mechanical strength are two of the most important characteristics of the bone tissue, carbon nanotubes are getting a lot of attention as a bone tissue scaffold component in recent years. In the present study, composite scaffolds comprised of functionalized Multiwalled Carbon Nanotubes (f-MWCNT), medium molecular weight chitosan and β-Glycerophosphate were fabricated and characterized. Biodegradability and mechanical tests indicate that while increasing f-MWCNT content can improve electrical conductivity and mechanical properties, there are some limitations for these increases, such as a decrease in mechanical properties and biodegradability in 1w/v% content of f-MWCNTs. Also, MTT cytotoxicity assay was conducted for the scaffolds and no significant cytotoxicity was observed. Increasing f-MWCNT content led to higher alkaline Phosphatase activity. The overall results show that composites with f-MWCNT content between 0.1w/v% and 0.5w/v% are the most suitable for bone tissue engineering application. Additionally, Preliminary cell electrical tests proved the efficiency of the prepared scaffolds for cell electrical applications. Copyright © 2017 Elsevier B.V. All rights reserved.

Hybrid Carbon-Based Scaffolds for Applications in Soft Tissue Reconstruction

PubMed Central

Lafdi, Khalid; Joseph, Robert M.; Tsonis, Panagiotis A.

2012-01-01

Current biomedical scaffolds utilized in surgery to repair soft tissues commonly fail to meet the optimal combination of biomechanical and tissue regenerative properties. Carbon is a scaffold alternative that potentially optimizes the balance between mechanical strength, durability, and function as a cell and biologics delivery vehicle that is necessary to restore tissue function while promoting tissue repair. The goals of this study were to investigate the feasibility of fabricating hybrid fibrous carbon scaffolds modified with biopolymer, polycaprolactone and to analyze their mechanical properties and ability to support cell growth and proliferation. Environmental scanning electron microscopy, micro-computed tomography, and cell adhesion and cell proliferation studies were utilized to test scaffold suitability as a cell delivery vehicle. Mechanical properties were tested to examine load failure and elastic modulus. Results were compared to an acellular dermal matrix scaffold control (GraftJacket® [GJ] Matrix), selected for its common use in surgery for the repair of soft tissues. Results indicated that carbon scaffolds exhibited similar mechanical maximums and capacity to support fibroblast adhesion and proliferation in comparison with GJ. Fibroblast adhesion and proliferation was collinear with carbon fiber orientation in regions of sparsely distributed fibers and occurred in clusters in regions of higher fiber density and low porosity. Overall, fibroblast adhesion and proliferation was greatest in lower porosity carbon scaffolds with highly aligned fibers. Stepwise multivariate regression showed that the variability in maximum load of carbon scaffolds and controls were dependent on unique and separate sets of parameters. These finding suggested that there were significant differences in the functional implications of scaffold design and material properties between carbon and dermis derived scaffolds that affect scaffold utility as a tissue replacement construct. PMID:22092333

Mechanical Properties, Cytocompatibility and Manufacturability of Chitosan:PEGDA Hybrid-Gel Scaffolds by Stereolithography.

PubMed

Morris, Viola B; Nimbalkar, Siddharth; Younesi, Mousa; McClellan, Phillip; Akkus, Ozan

2017-01-01

Extracellular matrix mimetic hydrogels which hybridize synthetic and natural polymers offer molecularly-tailored, bioactive properties and tunable mechanical strength. In addition, 3D bioprinting by stereolithography allows fabrication of internal pores and defined macroscopic shapes. In this study, we formulated a hybrid biocompatible resin using natural and synthetic polymers (chitosan and polyethylene glycol diacrylate (PEGDA), respectively) by controlling molecular weight of chitosan, feed-ratios, and photo-initiator concentration. Ear-shaped, hybrid scaffolds were fabricated by a stereolithographic method using a 405 nm laser. Hybrid hydrogel scaffolds of chitosan (50-190 kDa) and PEGDA (575 Da) were mixed at varying feed-ratios. Some of the cationic, amino groups of chitosan were neutralized by dialysis in acidic solution containing chitosan in excess of sodium acetate solution to inhibit quenching of newly formed photoradicals. A feed-ratio of 1:7.5 was found to be the most appropriate of the formulations considered in this study in terms of mechanical properties, cell adhesion, and printability. The biofabricated hybrid scaffold showed interconnected, homogeneous pores with a nominal pore size of 50 µm and an elastic modulus of ~400 kPa. Moreover, long-term cell viability and cell spreading was observed via actin filament staining. Printability of the biocompatible resin was confirmed by printing thresholded MR images of an ear and the feed ratio of 1:7.5 provided the most faithful reproduction of the shape. To the best of our knowledge, this is the first report of stereolithographic printing hybridizing cell-adhesive properties of chitosan with mechanical robustness of PEG in scaffolds suitable for repair of complex tissue geometries, such as those of the human ear.

A tribo-mechanical analysis of PVA-based building-blocks for implementation in a 2-layered skin model.

PubMed

Morales Hurtado, M; de Vries, E G; Zeng, X; van der Heide, E

2016-09-01

Poly(vinyl) alcohol hydrogel (PVA) is a well-known polymer widely used in the medical field due to its biocompatibility properties and easy manufacturing. In this work, the tribo-mechanical properties of PVA-based blocks are studied to evaluate their suitability as a part of a structure simulating the length scale dependence of human skin. Thus, blocks of pure PVA and PVA mixed with Cellulose (PVA-Cel) were synthesised via freezing/thawing cycles and their mechanical properties were determined by Dynamic Mechanical Analysis (DMA) and creep tests. The dynamic tests addressed to elastic moduli between 38 and 50kPa for the PVA and PVA-Cel, respectively. The fitting of the creep compliance tests in the SLS model confirmed the viscoelastic behaviour of the samples with retardation times of 23 and 16 seconds for the PVA and PVA-Cel, respectively. Micro indentation tests were also achieved and the results indicated elastic moduli in the same range of the dynamic tests. Specifically, values between 45-55 and 56-81kPa were obtained for the PVA and PVA-Cel samples, respectively. The tribological results indicated values of 0.55 at low forces for the PVA decreasing to 0.13 at higher forces. The PVA-Cel blocks showed lower friction even at low forces with values between 0.2 and 0.07. The implementation of these building blocks in the design of a 2-layered skin model (2LSM) is also presented in this work. The 2LSM was stamped with four different textures and their surface properties were evaluated. The hydration of the 2LSM was also evaluated with a corneometer and the results indicated a gradient of hydration comparable to the human skin. Copyright © 2016 Elsevier Ltd. All rights reserved.

41 CFR 51-2.4 - Determination of suitability.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 41 Public Contracts and Property Management 1 2010-07-01 2010-07-01 true Determination of suitability. 51-2.4 Section 51-2.4 Public Contracts and Property Management Other Provisions Relating to... performed and that it will have the capability to meet Government quality standards and delivery schedules...

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2012-07-06

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5601-N-26] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh Street SW., Room...

75 FR 75487 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-03

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-47] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Kathy Ezzell, Department of Housing and Urban Development, 451 Seventh Street...

76 FR 2702 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2011-01-14

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5477-N-02] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

76 FR 59150 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2011-09-23

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5477-N-38] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh Street SW., Room...

78 FR 48710 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-09

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5681-N-32] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh Street SW., Room...

75 FR 65366 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-10-22

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-41] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Kathy Ezzell, Department of Housing and Urban Development, 451 Seventh Street...

78 FR 73554 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-06

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5681-N-47] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh Street SW., Room...

77 FR 75642 - Federal Property Suitable as Facilities to Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2012-12-21

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5601-N-50] Federal Property Suitable as Facilities to Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh Street SW., Room...

77 FR 5525 - Federal Property Suitable as Facilities to Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-03

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5601-N-05] Federal Property Suitable as Facilities to Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh Street SW., Room...

78 FR 77141 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-20

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5681-N-49] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh Street SW., Room...

75 FR 68374 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-11-05

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-43] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Kathy Ezzell, Department of Housing and Urban Development, 451 Seventh Street...

41 CFR 51-2.4 - Determination of suitability.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 41 Public Contracts and Property Management 1 2011-07-01 2009-07-01 true Determination of suitability. 51-2.4 Section 51-2.4 Public Contracts and Property Management Other Provisions Relating to... performed and that it will have the capability to meet Government quality standards and delivery schedules...

78 FR 755 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2013-01-04

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5681-N-01] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

75 FR 6047 - Federal Property Suitable as Facilities to Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-02-05

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-05] Federal Property Suitable as Facilities to Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... Urban Development, 451 Seventh Street, SW., Room 7262, Washington, DC 20410; telephone (202) 708-1234...

75 FR 41510 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-07-16

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-27] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... Urban Development, 451 Seventh Street, SW., Room 7262, Washington, DC 20410; telephone (202) 708-1234...

75 FR 76999 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-10

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-48] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

75 FR 63501 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-10-15

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-40] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... Urban Development, 451 Seventh Street, SW., Room 7262, Washington, DC 20410; telephone (202) 708-1234...

76 FR 60855 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2011-09-30

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5477-N-41] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

78 FR 50078 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-16

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5681-N-33] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

77 FR 11149 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-24

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5601-N-08] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

77 FR 67389 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2012-11-09

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5601-N-44] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

78 FR 54905 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2013-09-06

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5681-N-36] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

75 FR 49512 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-08-13

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-31] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... Urban Development, 451 Seventh Street SW., Room 7262, Washington, DC 20410; telephone (202) 708-1234...

76 FR 22719 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2011-04-22

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5477-N-16] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

75 FR 57052 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-09-17

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-36] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... Urban Development, 451 Seventh Street, SW., Room 7262, Washington, DC 20410; telephone (202) 708-1234...

76 FR 75554 - Federal Property Suitable as Facilities to Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2011-12-02

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5477-N-48] Federal Property Suitable as Facilities to Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

76 FR 47606 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-05

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5477-N-31] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

76 FR 28058 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-13

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5477-N-19] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

75 FR 82409 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-30

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-51] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

77 FR 29680 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-18

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5601-N-19] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

75 FR 62414 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-10-08

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-39] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... Urban Development, 451 Seventh Street, SW., Room 7262, Washington, DC 20410; telephone (202) 708-1234...

75 FR 66774 - Federal Property Suitable as Facilities to Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-10-29

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-42] Federal Property Suitable as Facilities to Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... Urban Development, 451 Seventh Street, SW., Room 7262, Washington, DC 20410; telephone (202) 708-1234...

75 FR 80836 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-23

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-50] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

75 FR 79013 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-17

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5375-N-49] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

78 FR 70066 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2013-11-22

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5681-N-45] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

76 FR 66948 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2011-10-28

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5477-N-43] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

78 FR 37561 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2013-06-21

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5681-N-25] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

76 FR 70155 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2011-11-10

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5477-N-45] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

78 FR 65698 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2013-11-01

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5681-N-42] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

78 FR 64000 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-25

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5681-N-41] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...

78 FR 12344 - Federal Property Suitable as Facilities To Assist the Homeless

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-22

... DEPARTMENT OF HOUSING AND URBAN DEVELOPMENT [Docket No. FR-5681-N-08] Federal Property Suitable as Facilities To Assist the Homeless AGENCY: Office of the Assistant Secretary for Community Planning and... FURTHER INFORMATION CONTACT: Juanita Perry, Department of Housing and Urban Development, 451 Seventh...