Mechanical Compatibility Research Articles

Low Temperature Synthesis of Lanthanum Silicate Apatite Type by Modified Sol Gel Process

Rare earth silicate apatite type is a very important and promising material for application as an electrolyte in IT-SOFC (Intermediate Temperature Solid Oxide Fuel Cell). Lanthanum silicate apatite, La9,33Si6O26, exhibits high conductivity and has high efficiency, long term stability, fuel flexibility, low emissions and relatively low cost compared to yttria stabilized zirconia (YSZ - yttria stabilized zirconia), at temperatures between 600 to 800 °C. One of the problems of YSZ is its high operating temperature which results in long starting times and problems of mechanical and chemical compatibility. The interest of investigating lanthanum silicate apatite as an electrolyte is to overcome the problems caused by high temperature operation required by YSZ electrolyte. In the present study, sol-gel method was used to synthesize La9,33Si6O26. Initially, the reagents (sodium silicate and lanthanum nitrate) were mixed to obtain colloidal silica. Then, this gel containing lanthanum nitrate was thermally treated to allow the melting of lanthanum nitrate salt distributed on colloidal silica. The aim of this study was to verify if this method permits the formation of La9,33Si6O26 pure apatite phase, in order to obtain fine powders and uniform particles for further processing and obtaining a ceramic body.

TR method: a practical tool to analyze focal mechanisms and identify the ‘real’ seismogenic fault of an extensional or compressional shallow earthquake sequence

The recently proposed TR method that separates heterogeneous fault-slip data in extensional and compressional stress regimes is applied on focal mechanisms of a number of earthquake sequences aiming to identify the main seismogenic fault plane. The method only requires the earthquake sequence to be classified as related to an extensional or compressional stress regime. In particular, the nodal planes of the compressional or extensional focal mechanisms have been subdivided into two opposite dipping groups taking into account the average trend of their horizontal P or T axis. In the TR diagrams where we plot the slip deviation (from the dip-slip activation) of the nodal plane versus the angle between the dip direction of the nodal plane and the average trend of the P or T axis, the comparison of the geometric, kinematic, dynamic and mechanical compatibility of the two opposite nodal plane groups is possible. Moreover, a quality number (TRn) is devised in order to assess the two opposite facing groups quantitatively. Five earthquake sequences related with an extensional stress regime, and two related with a compressional stress regime, are processed in order to demonstrate and validate the potential and efficiency of the method. These cases indicate that the TR method can be fairly used as a practical tool to assess which nodal planes are more likely to identify the main seismogenic fault plane. The main advantages of the method are (a) the assessment of the nodal plane groups without the necessity to determine all the parameters of the driving stress tensor, i.e., stress axes and stress ratio, (b) the consideration of the slip tendency.

Mo doped DLC nanocomposite coatings with improved mechanical and blood compatibility properties

Abstract Mo (molybdenum) doped diamond like carbon (Mo-DLC) coatings with improved mechanical and blood compatibility properties were deposited by closed field unbalanced magnetron sputtering. The undoped and Mo-doped DLC coatings were analyzed by various characterization techniques such as Raman spectra, Atomic force microscopy, and temperature-dependent frictional wear testing. The results showed that the Mo-DLC coating with low Mo concentration was a effective protective coating with reduced residual stress and increased cohesive strength, and kept good wear resistance at the ambient temperature of 500 °C. The blood compatibility of Mo-DLC coatings was investigated by platelet adhesion. The results showed that the amount of thrombus on the Mo-DLC nanocomposite coatings was much less than that of thrombus on pyrolytic carbon films. The Mo-DLC nanocomposite coatings would be a new kind of promising materials applied to artificial heart valve and endovascula stent.

Type of Failure of Zirconia-Based Ceramics in Dental Laboratory in Misurata, Libya

Zirconia (ZrO2) is used to fix restorations as a core material because of its mechanical properties, aesthetics, and compatibility. This study aims to analyze the failure types in ZrO2-based restoration fabricated in a dental laboratory in Misurata, Libya. Data were collected from laboratory records for a 30-day period with follow-up for five months. About 6% of the total restorations had defects with different percentages, 46% of which were fractures, 29% of which had weak bonding between ZrO2frameworks and veneers, 18% of which had cracks, and 7% of which had shade defects. Although ZrO2is a suitable material for dental restorations, defects may occur and lead to the failure of dental restorations. A thorough study is necessary to analyze the cause of failurein zirconia-based restorationsand to improve the properties to produce a versatile dental restorative material.

Numerically robust spectral methods for crystal plasticity simulations of heterogeneous materials

Efficient spectral methods are developed to predict the micromechanical behaviour of plastically deforming heterogeneous materials. The direct and mixed variational conditions for mechanical equilibrium and strain compatibility are formulated in a framework that couples them to a general class of non-linear solution methods. Locally evolving micromechanical fields in a sheared polycrystalline material governed by a phenomenological crystal plasticity constitutive law are used to validate the methods, and their performance at varying material heterogeneities is benchmarked. The results indicate that the solution method has a dominant influence on performance and stability at large material heterogeneities, and significant improvements over the conventional fixed-point approach are obtained when higher-order solution methods are employed. Optimal solution strategies are devised based on this and applied to an idealised dual-phase polycrystalline aggregate.

Synthesis of calcium phosphate-zirconia scaffold and human endometrial adult stem cells for bone tissue engineering

To address the hypothesis that using a zirconia (ZrO2)/ β-tricalcium phosphate (β-TCP) composite might improve both the mechanical properties and cellular compatibility of the porous material, we fabricated ZrO2/β-TCP composite scaffolds with different ZrO2/β-TCP ratios, and evaluated their physical and mechanical characteristics, also the effect of three-dimensional (3D) culture (ZrO2/β-TCP scaffold) on the behavior of human endometrial stem cells. Results showed the porosity of a ZrO2/β-TCP scaffold can be adjusted from 65% to 84%, and the compressive strength of the scaffold increased from 4.95 to 6.25 MPa when the ZrO2 content increased from 30 to 50 wt%. The cell adhesion and proliferation in the ZrO2/β-TCP scaffold was greatly improved when ZrO2 decreased. Moreover, in vitro study showed that an osteoblasts-loaded ZrO2/β-TCP scaffold provided a suitable 3D environment for osteoblast survival and enhanced bone regeneration. We thus showed that a porous ZrO2/β-TCP composite scaffold has excellent mechanical properties, and cellular/tissue compatibility, and would be a promising substrate to achieve both bone reconstruction and regeneration needed during in vivo study for treatment of large bone defects.

Nucleus Pulposus Replacement: Hydrogel or Scaffold?—An Organ Culture Study under Dynamic Load

IntroductionNucleus pulposus (NP) replacement offers a minimally invasive disc regeneration treatment alternative to traditional fusion or total disc replacement. An ideal NP replacement material s...

Effect of design parameters on thin film bulk acoustic resonator performance

Film bulk acoustic resonators (FBARs) have received considerable attention for micro-electromechanical systems (MEMS) applications such as RF filters, resonators, and recently, bio-sensors. FBARs consisting of a piezoelectric thin film and an acoustic reflector for acoustic isolation from the surrounding medium are advantageous due to the intrinsic high sensitivity to mechanical, chemical, or electrical perturbation and compatibility with standard CMOS processing. In this work, we investigated the resonance characteristics of acoustic Bragg reflector-type FBARs by the model-based parametric analysis. The effect of various thicknesses and materials of electrodes and structural variation of acoustic Bragg reflectors on the key performance characteristics was studied to identify optimal design parameters for high performance FBAR devices. The key performance characteristics of FBARs include impedance characteristics, reflection coefficients, electro-mechanical coupling coefficients, and Q factors. These results not only offer new insights into design guidelines for high performance FBAR devices but also help better understanding of the fundamental physical phenomenon at resonances of the device.

Physico-mechanical and performance characterization of mortars incorporating fine glass waste aggregate

The effective management of construction and demolition waste (CDW) is a major challenge for the construction sector. To address such needs, this research work focuses on a specific type of CDW – annealed plate glass – to be incorporated into cementitious renderings.Studies on glass waste are very recent, scarce, and usually limited to the alkali-silica reaction (ASR), but they tend to involve other types of glass. This work characterizes the physical–mechanical and performance of these modified mortars, something that has not yet been done. A main reason for this lack of knowledge is the serious concern that there is an ASR potential. However, a recent study [1] concluded that the approach set out in ASTM C 1260 (accelerated mortar bar test) [2] may be overly conservative for renderings because it significantly increases the cement content. That study concluded that the use of mortars containing waste glass is technically viable in terms of ASR-related durability as long as the cement type and content are controlled, as well as the size of the aggregates, which proved to be the most decisive parameter [1].In our study, mortars with a cement-to-sand volumetric ratio of 1:4 were produced with a fraction of the sand replaced by fine glass aggregates (0%, 20%, 50% and 100% by volume), while the aggregate’s size distribution in the replacement remained constant so that the material itself was the single factor under analysis.The study reveals significantly improved results, especially at the level of the mechanical performance and physical compatibility with the substrate, when these mortars are compared with similar ones containing other waste types and a conventional mortar (with only natural sand as aggregate).

Challenges and Opportunities for Design, Simulation, and Fabrication of Soft Robots

This article describes new opportunities in soft robotics and some potential avenues to overcome challenges associated with the realization of these opportunities. New opportunities include new applications that exploit novel amorphous nonrigid dynamics, a new design space due to the elimination of traditional manufacturing constraints, more opportunities for modeling and mimicry of natural systems, and increased safety and mechanical compatibility with humans. Challenges include limited simulation and design automation tools, lack of soft actuation methods, and difficulty in manufacturing and component standardization. Both computational (e.g., evolutionary design tools) and mechanical (porous and jamming materials) approaches are proposed to alleviate these needs.

Determination of Young's Modulus of Hydroxyapatite Doped with Magnesium by Vibration Method

Implants and bone reconstruction have known a great development recently. Synthesized bone tissues must have mechanical, physiological and biological properties closer to natural bone, as much as possible. Bioceramics are materials which fulfill these conditions, being biocompatible with mechanical strength similar to bone. One material widely used is hydroxyapatite. Hydroxyapatite is slightly different from bone tissue and it forms the mineral part of bone tissue. In order to improve mechanical properties and biological compatibility hydroxyapatite is doped with different compounds, mainly chemical elements. Magnesium, a chemical element present in human bone structure is one of these compounds.

Synthesis of composite gelatin-hyaluronic acid-alginate porous scaffold and evaluation for in vitro stem cell growth and in vivo tissue integration

Engineering three-dimensional (3-D) porous scaffolds with precise bio-functional properties is one of the most important issues in tissue engineering. In the present study, a three-dimensional gelatin-hyaluronic acid-alginate (GHA) polymeric composite was synthesized by freeze-drying, which was followed by ionic crosslinking using CaCl2, and evaluated for its suitability in bone tissue engineering applications. The obtained matrix showed high porosity (85%), an interconnected pore morphology and a rapid swelling behavior. The rheological analysis of GHA showed a viscoelastic characteristic, which suggested a high load bearing capacity without fractural deformation. The influence of the GHA matrix on cell growth and on modulating the differentiation ability of mesenchymal stem cells was evaluated by different biochemical and immunostaining assays. The monitoring of cells over a period of four weeks showed increased cellular proliferation and osteogenic differentiation without external growth factors, compared with control (supplemented with osteogenic differentiation medium). The in vivo matrix implantation showed higher matrix-tissue integration and cell infiltration as the duration of the implant increased. These results suggest that a porous GHA matrix with suitable mechanical integrity and tissue compatibility is a promising substrate for the osteogenic differentiation of stem cells for bone tissue engineering applications.

3D braid scaffolds for regeneration of articular cartilage

Regenerating articular cartilage in vivo from cultured chondrocytes requires that the cells be cultured and implanted within a biocompatible, biodegradable scaffold. Such scaffolds must be mechanically stable; otherwise chondrocytes would not be supported and patients would experience severe pain. Here we report a new 3D braid scaffold that matches the anisotropic (gradient) mechanical properties of natural articular cartilage and is permissive to cell cultivation. To design an optimal structure, the scaffold unit cell was mathematically modeled and imported into finite element analysis. Based on this analysis, a 3D braid structure with gradient axial yarn distribution was designed and manufactured using a custom-built braiding machine. The mechanical properties of the 3D braid scaffold were evaluated and compared with simulated results, demonstrating that a multi-scale approach consisting of unit cell modeling and continuum analysis facilitates design of scaffolds that meet the requirements for mechanical compatibility with tissues.

Rubber Polymers for Transdermal Drug Delivery Systems

Natural rubber latex is a colloidal dispersion of polymer particles in a liquid. It is harvested from rubber trees by a tapping process. Synthetic rubber is one type of artificial elastomer mainly synthesized from petroleum byproducts. It has good mechanical property, thermal stability, and compatibility with petroleum products. It can undergo much more elastic deformation under stress than most materials, and can return to its original size without changing permanently. Commonly, many drugs taken via the oral route are ineffective because of the first pass metabolism and drug degradation in the gastrointestinal tract. Thus, transdermal drug delivery systems can improve the disadvantage of orally taken drugs. There must be significant controlled drug release into the systemic blood circulation to target organs via the skin. In this review article, the use of rubber polymers in both natural and synthetic rubber types as a material for transdermal drug delivery systems will be reported.

Current Concepts in Biomaterials in Dental Implant

Myriads of materials have been used for replacement of missing teeth through implantation. The success of these materials depend on the ability to integrate with the host environment showing biological compatibility, mechanical compatibility, and morphological compatibility to the surrounding vital tissues. Certain materials have shown this promising property and have been used in dental implantology. With recent advances in technology, these materials are better able to improve fixation to bone through various surface modifications and bioengineering

Obtention and Characterization of Collagen and Chitosan Based Cements for Bone Regerneration. Part 1: Extraction and Characterization of Collagen

Several cements are used as biomaterials. Biopolymers such as chitosan and collagen exhibit excellent biocompatibility and can be used in the remodeling of bone tissue. The cement must have high mechanical strength and compatibility with original tissue. In this context, the objective of this study was to extract, characterize and cross-link collagen from bovine tendon, forlater associate it with chitosan and calcium phosphate to obtain cements for bone regeneration. Glutaraldehyde was used as cross-linker in 0.1, 0.5, 1.0 and 10% concentration. Infrared analysis confirmed the presence of functional groups characteristic of collagen, whereas the capacity of water absorption decreased with the increasing of cross-linking degree. Denaturation temperatures of collagen samples were obtained by Differential Scanning Calorimetry and Scanning Electron Microscopy showed the fiber structure characteristics of collagen, which were more organized for high degree of cross-linking samples.

AVALIAÇÃO DAS PROPRIEDADES MICROESTRUTURAIS E MECÂNICAS DAS LIGAS Ti-35Nb-7Zr E Ti-41,1Nb-7,1Zr PARA APLICAÇÃO BIOMÉDICA

The aim of this work was to achieve Ti-β alloys without considerable toxic elements (Al and V) with lower elastic moduli to improve the mechanical compatibility with the bone (17 GPa-35 GPa) [1,2]. Ti-35Nb-7Zr and Ti-41,1Nb-7,1Zr alloys were produced in fusion by arc melting under argon atmosphere. The ingots, with the initial diameter of 18 mm were submitted to solution heat treatment, cool rotary forging and recrystallization treatment until 6 mm of diameter. The microstructural analyses were performed using Optical Microscopy, X-ray diffraction and hardness. The mechanical characterization was evaluated through uniaxial tensile tests. The results showed that properties are dependent on the compositions studied. Microstructure results indicated that both alloys are Ti-β. Ti-35Nb-7Zr in β-solution treated condition posses the lowest value of hardness (157 HV). Vickers hardness values for alloys within 35Nb and 41,1Nb, in the recrystallization condition were very close 161 and 169 HV, respectively. The Ti-35Nb-7Zr alloy presented the lowest elastic modulus (54 GPa) and the highest ductility, based on reduction of area and elongation without change tensile strength

Improvement of Wear Corrosion Characteristics of GUMMETAL in Quasi-human Body Environment by Surface Modification

Recently, the operating number of the artificial joint tends to increase gradually. Titanium alloys such as Ti-6Al-4V, Ti-6Al-7Nb and so on were well known as material used for biomedical devices. These materials were used for the reasons of having superior corrosion resistance, excellent specific strength and excellent biocompatibility. However these materials have inferior wear corrosion characteristics. For this reason, surface modification was required. GUMMETAL(Ti-23Nb-0.7Ta-2Zr-O), which is one of β titanium alloys, has low elastic modulus comparable to that of the bone, this material shows superior mechanical compatibility. At present, wear corrosion characteristics of GUMMETAL were not fully understood comprehensively both from wear and corrosion behaviors. Therefore in this study, wear corrosion characteristics of GUMMETAL were evaluated comprehensively both from wear and corrosion characters of this material and some trials for improving wear corrosion characteristics by high temperature in air oxidation were conducted. As a result, wear corrosion behavior was well understood from the viewpoint of the mutual interaction of wear and corrosion. And also, the improvement in both of wear and corrosion characteristics was recognized in case when high temperature in air oxidation was applied to the surface of specimen.

Characterization of the correlation between the interfaces and failure behaviors for particle reinforced Mg–Li composites

The interfacial microstructure of SiCp or YAl2p reinforced Mg–14Li–3Al matrix composites was comparatively characterized by scanning electron microscopy and electron probe microanalysis. A nanoindentation combined with scanning electron microscopy technique was used to characterize the interfacial mechanical properties between the reinforcements and matrix. The interfacial strength and failure behaviors for the composites were analyzed from the load–penetration curves and corresponding images. In situ tensile tests were used to observe the fracture and deformation processes with the aid of scanning electron microscopy. The results show that both the chemical and mechanical compatibilities between the YAl2 particles and LA143 matrix are better than those between the SiC particles and LA143 matrix. The interfacial breakage load for the SiC/LA143 composite is lower than that for the YAl2/LA143 composite because of the worse chemical and mechanical compatibilities between the ceramic particles and metal matrix. Interfacial breakage is the main failure mechanism for the SiC/LA143 composite, while the particle breakage and matrix crack are the main failure mechanism for the YAl2/LA143 composite. These may be related to the stronger interfacial bonding between the intermetallic particles and metal matrix.

Syntheses of La1-XSrxMnO3 Nanopowders by Hydrothermal Method

Lanthanum strontium manganese, LSM, has been considered as one of the most prospect materials for solid oxide fuel cell (SOFC) applications due to its high electrode activity for the oxygen reduction reaction, high electronic conductivity and chemical as well as mechanical compatibility with the established solid electrolytes. In this work, Sr-doped LaMnO3 was synthesized by hydrothermal method and the effect of Sr doping on lanthanum manganese (LSM) was investigated. The La1-xSrxMnO3 (0≤x≤0.4) nanopowders were prepared under different reaction conditions by hydrothermal syntheses. The synthesized nanopowders were characterized the crystalline by X-Ray diffraction. The microstructure and particle size of the nanopowders were analyzed by FE-SEM and intercept method. The particles size of LSM powders was approximately ~170nm when used KOH as a precipitant. The relative density of LSM was over 97% by Archimedes density method. The electrical conductivity of the sintered pellet was measured at 750°C in air by DC four point probe method, and the electrical conductivity was 21.3~63.85 S/cm. The physical and electrical properties of Sr-doped lanthanum manganese were discussed.