Showing papers in "Journal of The Mechanical Behavior of Biomedical Materials in 2008"

Mechanical biocompatibilities of titanium alloys for biomedical applications.

Abstract: Young's modulus as well as tensile strength, ductility, fatigue life, fretting fatigue life, wear properties, functionalities, etc., should be adjusted to levels that are suitable for structural biomaterials used in implants that replace hard tissue. These factors may be collectively referred to as mechanical biocompatibilities. In this paper, the following are described with regard to biomedical applications of titanium alloys: the Young's modulus, wear properties, notch fatigue strength, fatigue behaviour on relation to ageing treatment, improvement of fatigue strength, fatigue crack propagation resistance and ductility by the deformation-induced martensitic transformation of the unstable beta phase, and multifunctional deformation behaviours of titanium alloys.

Relationship between surface properties (roughness, wettability and morphology) of titanium and dental implant removal torque

Abstract: The biological properties of titanium depend on its surface oxide film. Several mechanical and chemical treatments have been used to modify the surface morphology and properties of titanium dental implants. One possible method of improving dental implant biocompatibility is to increase surface roughness and decrease the contact angle. In the present work, the biological properties of dental implants were investigated through in vivo and in vitro tests. The effects of surface roughness, contact angle and surface morphology on titanium dental implant removal torque were investigated. Machined dental implants and discs made with commercially pure titanium ASTM grade 4 were submitted to sandblasting treatments, acid etching and anodizing. The sample surface morphologies were characterized by SEM, the surface roughness parameters were quantified using a laser non-contact profilometer, and a contact angle measurement was taken. Dental implants were placed in the tibia of rabbits and removed 12 weeks after the surgery. It was found that: (i) acid etching homogenized the surface roughness parameters; (ii) the anodized surface presented the smallest contact angle; (iii) the in vivo test suggested that, in similar conditions, the surface treatment had a beneficial effect on the implant biocompatibility measured through removal torque; and (iv) the anodized dental implant presented the highest removal torque.

Nanomechanics of collagen fibrils under varying cross-link densities: atomistic and continuum studies.

Abstract: Collagen is a protein material with intriguing mechanical properties - it is highly elastic, shows large fracture strength and plays a crucial role in making Nature's structural materials tough. Collagen based tissues consist of collagen fibrils, each of which is composed out of a staggered array of ultra-long tropocollagen molecules extending to several hundred nanometers. Albeit the macroscopic properties of collagen based tissues have been studied extensively, less is known about the nanomechanical properties of tropocollagen molecules and collagen fibrils, their elementary building blocks. In particular, the relationship between molecular properties and tissue properties remains a scarcely explored aspect of the science of collagen materials. Results of molecular multi-scale modeling of the nanomechanical properties of the large-strain deformation regime of collagen fibrils under varying cross-link densities are reported in this paper. The results confirm the significance of cross-links in collagen fibrils in improving its mechanical strength. Further, it is found that cross-links influence the nature of its large-deformation and fracture behavior. Cross-link deficient collagen fibrils show a highly dissipative deformation behavior with large yield regimes. Increasing cross-link densities lead to stronger fibrils that display an increasingly brittle deformation character. The simulation results are compared with recent nanomechanical experiments at the scale of tropocollagen molecules and collagen fibrils.

Structure and Mechanical Properties of Selected Biological Materials

Abstract: Mineralized biological tissues offer insight into how nature has evolved these components to optimize multifunctional purposes. These mineral constituents are weak by themselves, but interact with the organic matrix to produce materials with unexpected mechanical properties. The hierarchical structure of these materials is at the crux of this enhancement. Microstructural features such as organized, layered organic/inorganic structures and the presence of porous and fibrous elements are common in many biological components. The organic and inorganic portions interact at the molecular and micro-levels synergistically to enhance the mechanical function. In this paper, we report on recent progress on studies of the abalone and Araguaia river clam shells, arthropod exoskeletons, antlers, tusks, teeth and bird beaks.

Mechanical strength of abalone nacre: Role of the soft organic layer

Abstract: The nacreous portion of the abalone shell is composed of calcium carbonate crystals interleaved with layers of viscoelastic proteins. The resulting structure yields unique mechanical properties. In this study, we focus on the thin viscoelastic layers between the tiles and on their role on the mechanical properties of the shell. Both SEM and AFM show that the thin (approximately 30 nm) organic layer is porous, containing holes with diameter of approximately 50 nm. These holes enable the formation of mineral bridges between adjacent tile layers. The mineral bridges play a pivotal role in growth and ensure the maintenance of the same crystallographic relationship through tile growth in the 'terraced cone' mode. The existence of mineral bridges is consistent with the difference between tensile and compressive strength of the abalone. Mechanical tests with loading applied perpendicular to the plane of the organic layers reveal a tensile strength lower than 10 MPa, whereas the compressive strength is approximately 300-500 MPa. These nanoscale bridges have, by virtue of their dimensions (50 nm diameter x 30 nm length), a strength that reaches their theoretical value. The calculated tensile strength based on the theoretical strength predicts a bridge density of approximately 2.25/microm(2). A major conclusion of this investigation is that the role of the organic layer is primarily to subdivide the CaCO(3) matrix into platelets with thickness of 0.5 microm. Its intrinsic effect in providing a glue between adjacent tiles may not be significant.

Fatigue and durability of Nitinol stents

Abstract: Nitinol self-expanding stents are effective in treating peripheral artery disease, including the superficial femoral, carotid, and renal arteries. However, fracture occurrences of up to 50% have been reported in some stents after one year. These stent fractures are likely due to in vivo cyclic displacements. As such, the cyclic fatigue and durability properties of Nitinol-based endovascular stents are discussed in terms of an engineering-based experimental testing program. In this paper, the combined effects of cardiac pulsatile fatigue and stent-vessel oversizing are evaluated for application to both stents and stent subcomponents. In particular, displacement-controlled fatigue tests were performed on stent-like specimens processed from Nitinol microtubing. Fatigue data were collected with combinations of simulated oversizing conditions and pulsatile cycles that were identified by computer modeling of the stent that mimic in vivo deformation conditions. These data are analyzed with non-linear finite element computations and are illustrated with strain-life and strain-based constant-life diagrams. The utility of this approach is demonstrated in conjunction with 10 million cycle pulsatile fatigue tests of Cordis SMART Control((R)) Nitinol self-expanding stents to calculate fatigue safety factors and thereby predict in vivo fatigue resistance. These results demonstrate the non-linear constant fatigue-life response of Nitinol stents, whereby, contrary to conventional engineering materials, the fatigue life of Nitinol is observed to increase with increasing mean strain.

Understanding the mechanical behaviour of human enamel from its structural and compositional characteristics.

Abstract: As the hardest and one of the most durable load-bearing tissues of the body, enamel has attracted considerable interest from both material scientists and clinical practitioners due to its excellent mechanical properties. In this paper, possible mechanisms responsible for the excellent mechanical properties of enamel are explored and summarized, which primarily include its hierarchical structure and the nanomechanical properties of the minor protein macromolecular component. Furthermore, additional experimental and numerical evidences to support the assumptions are presented. For example, enamel shows lower elastic modulus, higher energy absorption ability and greater indentation creep behaviour than sintered hydroxyapatite material. All the data indicate that the structural and compositional characteristics of the minor protein component significantly regulate the mechanical properties of enamel to better match its functional needs.

Engineering functionally graded tissue engineering scaffolds.

Abstract: Tissue Engineering (TE) aims to create biological substitutes to repair or replace failing organs or tissues due to trauma or ageing. One of the more promising approaches in TE is to grow cells on biodegradable scaffolds, which act as temporary supports for the cells to attach, proliferate and differentiate; after which the scaffold will degrade, leaving behind a healthy regenerated tissue. Tissues in nature, including human tissues, exhibit gradients across a spatial volume, in which each identifiable layer has specific functions to perform so that the whole tissue/organ can behave normally. Such a gradient is termed a functional gradient. A good TE scaffold should mimic such a gradient, which fulfils the biological and mechanical requirements of the target tissue. Thus, the design and fabrication process of such scaffolds become more complex and the introduction of computer-aided tools will lend themselves well to ease these challenges. This paper reviews the needs and characterization of these functional gradients and the computer-aided systems used to ease the complexity of the scaffold design stage. These include the fabrication techniques capable of building functionally graded scaffolds (FGS) using both conventional and rapid prototyping (RP) techniques. They are able to fabricate both continuous and discrete types of FGS. The challenge in fabricating continuous FGS using RP techniques lies in the development of suitable computer aided systems to facilitate continuous FGS design. What have been missing are the appropriate models that relate the scaffold gradient, e.g. pore size, porosity or material gradient, to the biological and mechanical requirements for the regeneration of the target tissue. The establishment of these relationships will provide the foundation to develop better computer-aided systems to help design a suitable customized FGS.

Computational predictions of the tensile properties of electrospun fibre meshes: effect of fibre diameter and fibre orientation.

Abstract: The mechanical properties of biomaterial scaffolds are crucial for their efficacy in tissue engineering and regenerative medicine. At the microscopic scale, the scaffold must be sufficiently rigid to support cell adhesion, spreading, and normal extracellular matrix deposition. Concurrently, at the macroscopic scale the scaffold must have mechanical properties that closely match those of the target tissue. The achievement of both goals may be possible by careful control of the scaffold architecture. Recently, electrospinning has emerged as an attractive means to form fused fibre scaffolds for tissue engineering. The diameter and relative orientation of fibres affect cell behaviour, but their impact on the tensile properties of the scaffolds has not been rigorously characterized. To examine the structure-property relationship, electrospun meshes were made from a polyurethane elastomer with different fibre diameters and orientations and mechanically tested to determine the dependence of the elastic modulus on the mesh architecture. Concurrently, a multiscale modelling strategy developed for type I collagen networks was employed to predict the mechanical behaviour of the polyurethane meshes. Experimentally, the measured elastic modulus of the meshes varied from 0.56 to 3.0 MPa depending on fibre diameter and the degree of fibre alignment. Model predictions for tensile loading parallel to fibre orientation agreed well with experimental measurements for a wide range of conditions when a fitted fibre modulus of 18 MPa was used. Although the model predictions were less accurate in transverse loading of anisotropic samples, these results indicate that computational modelling can assist in design of electrospun artificial tissue scaffolds.

Phenomena and mechanisms of crack propagation in glass-ceramics.

Abstract: Lithium disilicate, leucite and apatite glass-ceramics have become state-of-the-art framework materials in the fabrication of all-ceramic dental restorative materials. The goal of this study was to examine the crack propagation behaviour of these three known glass-ceramic materials after they have been subjected to Vickers indentation and to characterize their crack opening profiles ( δ meas vs. ( a − r ) ). For this purpose, various methods of optical examination were employed. Optical microscopy investigations were performed to examine the crack phenomena at a macroscopic level, while high-resolution techniques, such as scanning electron microscopy (SEM) and atomic force microscopy (AFM), were employed to investigate the crack phenomena at a microscopic level. The crack patterns of the three glass-ceramics vary from fairly straightforward to more complex, depending on the amount of residual glass matrix present in the material. The high-strength lithium disilicate crystals feature a high degree of crosslinking, thereby preventing crack propagation. In this material, the crack propagates only through the residual glass phase, which constitutes 30%–40% by volume. Having a high glass content of more than 65% by volume, the leucite and apatite glass-ceramics show far more complex crack patterns. Cracks in the leucite glass-ceramic propagate through both the glass and crystal phase. The apatite glass-ceramic shows a similar crack behaviour as an inorganic–organic composite material containing nanoscale fillers, which are pulled out in the surroundings of the crack tip. The observed crack behaviour and the calculated K tip values of the three types of glass-ceramics were compared to the K I C values determined according to the SEVNB method.

Processing nanoengineered scaffolds through electrospinning and mineralization suitable for biomimetic bone tissue engineering.

Abstract: Processing scaffolds that mimic the extracellular matrix (ECM) of natural bone in structure and chemical composition is a potential promising option for engineering physiologically functional bone tissue. In this article, we report a novel method, by combining electrospinning and mineralization, to process a series of nano-fibrous scaffolding systems with desirable characteristics suitable for biomimetic bone tissue engineering. We have chosen two types of polymers, namely collagen and poly (lactic-co-glycolic acid) (PLGA), natural and synthetic of its kind, respectively, to electrospin into nano-fibrous scaffolds. The electrospun scaffolds have high surface area, high porosity and well connected open pore network. In order to mimic the chemical composition of native bone ECM, the electrospun scaffolds were subjected to mineralization under optimal conditions. From the experimental results, we observed that the formation of bone-like apatite into collagen was relatively abundant and significantly more uniform than PLGA. The major finding of this study has suggested that the surface functional groups of the scaffolding material, such as carboxyl and carbonyl groups of collagen, are important for the mineralization in vitro. In addition, this study revealed that the mineralization process predominantly induce the formation of nanosize carbonated hydroxyapatite (CHA) during collagen mineralization, whilst nanosize hydroxyapatite (HA) is formed during PLGA mineralization. These findings are critically important while selecting the material for processing bone scaffolding system.

Investigating load relaxation mechanics in tendon

Abstract: Tendons are hierarchical fibre composite materials, designed for the efficient transfer of force from muscles to the skeleton. As such, they exhibit high tensile strength, as well as complex viscoelastic and anisotropic characteristics. Although the viscoelastic behaviour has received considerable attention, the mechanisms by which the tendon structure facilitates this behaviour are less well understood. This study examines viscoelasticity within isolated tendon fascicles, using stress relaxation tests to examine how the matrix acts to dissipate load during the relaxation period. The fascicle behaviour during incremental and direct load relaxation tests was examined, using mechanical testing and confocal microscopy to assess the load and structural responses of the tendon, respectively. Results provide further evidence of the highly viscoelastic nature of tendon, and also demonstrate that relaxation behaviour within isolated tendon fascicles is dominated by fibre sliding mechanisms. These data indicate an important functional role for proteoglycans, in controlling the viscoelastic behaviour and the mechanisms of strain transfer within tendon.

Fatigue of mineralized tissues: cortical bone and dentin.

Abstract: Gaining a mechanistic understanding of the mechanical properties of mineralized tissues, such as dentin and cortical bone, is important from the perspective of developing a framework for predicting and preventing failure of teeth and whole bones, particularly with regard to understanding the effects of microstructural modifications from factors such as aging, disease, or medical treatments. Accordingly, considerable research efforts have been made to determine the specific mechanisms involved in the fatigue and fracture of mineralized tissues, and to discover how these mechanisms relate to features within the respective microstructures. This article seeks to review the progress that has been made specifically in the area of fatigue, focusing on the research that moves our understanding beyond simple fatigue life (S/N) concepts and instead addresses the separate mechanisms for microdamage initiation, crack propagation, and in the case of bone, repair and remodeling.

Titanium–nickel shape memory alloy foams for bone tissue engineering

Abstract: Titanium–nickel (TiNi) shape memory alloy (SMA) foams with an open-cell porous structure were fabricated by space-holder sintering process and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The mechanical properties and shape memory properties of the TiNi foam samples were investigated using compressive test. Results indicate that the plateau stresses and elastic moduli of the foams under compression decrease with the increase of their porosities. The plateau stresses and elastic moduli are measured to be from 1.9 to 38.3 MPa and from 30 to 860 MPa for the TiNi foam samples with porosities ranged from 71% to 87%, respectively. The mechanical properties of the TiNi alloy foams can be tailored to match those of bone. The TiNi alloy foams exhibit shape memory effect (SME), and it is found that the recoverable strain due to SME decreases with the increase of foam porosity.

Fabrication and characterization of plasma-sprayed HA / SiO2 coatings for biomedical application

Abstract: Fused silica powder has been mixed with hydroxyapatite (HA) powder and plasma sprayed by using gas tunnel-type plasma jet. The influence of silica content (10 wt% and 20 wt%) on the microstructure and mechanical properties of HA-silica coatings was investigated. For investigating the microstructure and mechanical properties of HA-silica coatings, SUS 304 stainless steel was used as substrate material. The spraying was carried out on roughened substrate in an atmospheric chamber. Scanning electron microscope micrographs of cross-sectioned HA/SiO(2) coatings showed that the sprayed HA coatings with 10 and 20 wt% SiO(2) have dense structure with low porosity compared to the pure HA coatings. On the other hand, as the amount of silica was increased the coatings became denser, harder and exhibited high abrasive wear resistance. The presence of silica significantly improved the adhesive strength of HA/SiO(2) coatings mainly due to the increase in bonding strength of the coating at the interface.

A 3D finite element model of ventral furrow invagination in the Drosophila melanogaster embryo.

Abstract: The paper describes a mechanical model of epithelial tissue development in Drosophila embryos to investigate a buckling phenomenon called invagination. The finite element method is used to model this ventral furrow formation in 3D by decomposing the total deformation into two parts: an imposed active deformation, and an elastic passive deformation superimposed onto the latter. The model imposes as boundary conditions (i) a constant yolk volume and (ii) a sliding contact condition of the cells against the vitelline membrane, which is interpolated as a B-Spline surface. The active deformation simulates the effects of apical constriction and apico-basal elongation of cells. This set of local cellular mechanisms leads to global shape changes of the embryo which are associated with known gene expressions. Using the model we have tested different plausible hypotheses postulated to account for the mechanical behaviour of epithelial tissues. In particular, we conclude that only certain combinations of local cell shape change can successfully reproduce the invagination process. We have quantitatively compared the model with a 2D model and shown that it exhibits a more robust invagination phenomenon. The 3D model has also revealed that invagination causes a yolk flow from the central region to the anterior and posterior ends of the embryo, causing an accordion-like global compression and expansion wave to move through the embryo. Such a phenomenon cannot be described by 2D models.

Biomechanics of the ankle joint and clinical outcomes of total ankle replacement.

Abstract: Until the 1970s ankle arthrodesis was considered to be the "gold-standard" to treat arthritis But the low fusion rate of ankle arthrodeses along with the inability to achieve normal range of motion led to the growing interest in the development of total ankle replacements Though the short-term outcomes were good, their long-term outcomes were not as promising To date, most models do not exactly mimic the anatomical functionality of a natural ankle joint Therefore, research is being conducted worldwide to either enhance the existing models or develop new models while understanding the intricacies of the joint more precisely This paper reviews the anatomical and biomechanical aspects of the ankle joint Also, the evolution and comparison of clinical outcomes of various total ankle replacements are presented

On the finite element modelling of balloon-expandable stents.

Abstract: Finite element method (FEM) has been extensively applied in the analyses of mechanical and biomechanical properties of stents. Geometrically, a closed-cell stent is an assembly of a number of repeated unit cells and exhibits periodicity in both longitudinal and circumferential directions. The objective of this paper is to study the FEM models for the analysis of stents. To this end, three models, termed respectively as the Panel, RUC (repeated unit cell) and RUC(+) (repeated unit cell with a free end) models, are proposed incorporating rotationally symmetrical, periodic and free edge conditions. The proposed models are applied to the analysis of stents of Palmaz-Schatz and sinusoidal types. The Panel model reduces the size of the numerical model from the full, half or quarter stent to a strip of it without losing the computational accuracy. The RUC model gives satisfactory results for the inner part of the stent except for the two ends. The RUC(+) model, described here for the first time, provides accurate results for both the inner part and the distal ends of the stent. In addition, it allows the prediction of the well-known phenomenon of "dog-boning", in which the balloon is excessively expanded at the two ends of the stent.

Micro-computed tomography of fatigue microdamage in cortical bone using a barium sulfate contrast agent.

Abstract: Accumulation of microdamage during fatigue can lead to increased fracture susceptibility in bone. Current techniques for imaging microdamage in bone are inherently destructive and two-dimensional. Therefore, the objective of this study was to image the accumulation of fatigue microdamage in cortical bone using micro-computed tomography (micro-CT) with a barium sulfate (BaSO4) contrast agent. Two symmetric notches were machined on the tensile surface of bovine cortical bone beams in order to generate damage ahead of the stress concentrations during four-point bending fatigue. Specimens were loaded to a specified number of cycles or until one notch fractured, such that the other notch exhibited the accumulation of microdamage prior to fracture. Microdamage ahead of the notch was stained in vitro by precipitation of BaSO4 and imaged using micro-CT. Reconstructed images showed a distinct region of bright voxels around the notch tip or along propagating cracks due to the presence of BaSO4, which was verified by backscattered electron imaging and energy dispersive spectroscopy. The shape of the stained region ahead of the notch tip was consistent with principal strain contours calculated by finite element analysis. The relative volume of the stained region was correlated with the number of loading cycles by non-linear regression using a power law. This study demonstrates new methods for the non-destructive and three-dimensional detection of fatigue microdamage accumulation in cortical bone in vitro, which may be useful to gain further understanding into the role of microdamage in bone fragility.

Development of a new niobium-based alloy for vascular stent applications

Abstract: This study was performed in order to develop a new stent material that would provide reduced MR image artifact compared to current stent materials. Alloy design rationale is initially presented and following this the development of a Nb-28 Ta-3.5 W-1.3 Zr alloy is described, including the manufacture of stent tubing. Tensile testing of this new alloy showed that it had approximately twice the yield strength of current Nb-1 Zr material with a 25% higher elastic modulus. The new alloy was also confirmed to have suitably low magnetic susceptibility. Mechanical testing of demonstration coronary stents made from the new alloy were shown to have acceptable compression strength and elastic recoil performance. It is concluded that this new Nb-28 Ta-3.5 W-1.3 Zr alloy is a practical candidate stent material for both coronary applications and peripheral uses such as carotid or intracranial stenting, where reduced MR image artifact would be beneficial.

Welcome to the Journal of the Mechanical Behavior of Biomedical Materials

Abstract: ING AND INDEXING

Effects of the reinforcement morphology on the fatigue properties of hydroxyapatite reinforced polymers

Abstract: The objective of this study was to examine the effects of the hydroxyapatite (HA) reinforcement morphology and content on the fatigue behavior of HA reinforced high density polyethylene (HDPE). To this end, HDPE was reinforced with 20 and 40 vol% of either HA whiskers or an equiaxed HA powder, and tested in four-point bending fatigue under simulated physiological conditions. The fatigue life, mechanical property degradation and failure surfaces were compared between experimental groups. HDPE reinforced with HA whiskers exhibited a four- to five-fold increase ( p 0.001 , T-test) in fatigue life compared to an equiaxed powder for either the 20 and 40 vol% reinforcement level. Composites containing 40 vol% HA exhibited decreased fatigue life compared to those with 20 vol% HA for either reinforcement morphology ( p 0.0001 , ANOVA). HA whisker reinforced HDPE exhibited less stiffness loss, permanent deformation (creep) and energy dissipation at a given number of cycles compared to HA powder. Thus, HA whisker reinforced HDPE was more tolerant of fatigue damage due to either microcracking or polymer plasticity. Scanning electron microscopy of failure surfaces and surface microcracks showed evidence of toughening by uncracked ligaments, crack tip plasticity, polymer fibril bridging and HA whisker pullout. The results of this study suggest that the use of HA whiskers, in place of HA powder, is a straightforward means to improve the fatigue life and damage tolerance of HA reinforced polymers for synthetic bone substitutes.

Effects of strain rate and temperature on mechanical behaviour of Ti–15Mo–5Zr–3Al alloy

Abstract: This study uses the compressive split-Hopkinson pressure bar to investigate the mechanical behaviour of Ti-15 Mo-5 Zr-3 Al alloy deformed at strain rates ranging from 8 x 10(2) to 8 x 10(3) s(-1) and temperatures between 298 and 1173 K. The results indicate that the mechanical behaviour of the alloy is highly sensitive to both the strain rate and the temperature. The flow stress curves are found to include a work hardening region and a work softening region. The strain rate sensitivity parameter, m, increases with increasing strain and strain rate, but decreases with increasing temperature. The activation energy varies inversely with the flow stress, and has a low value at high deformation strain rates or low temperatures. Correlating the mechanical properties of the Ti alloy with the transmission electron microscope (TEM) observations, it is concluded that the precipitation of alpha phase dominates the fracture strain. TEM observations reveal that the amount of alpha phase increases with increasing temperature below the beta transus temperature. The maximum amount of alpha phase is formed at a temperature of 973 K and results in the minimum fracture strain observed under the current loading conditions.

Preparation and properties of an injectable scaffold of poly(lactic-co-glycolic acid) microparticles/chitosan hydrogel.

Abstract: Hydrogels are more and more attractive in biomedical fields, since they can be used as injectable scaffolds, drugs and gene carriers and smart sensors. The highly hydrated hydrogels, however, generally have low mechanical strength. In this work, a composite chitosan hydrogel was prepared by blending water soluble and crosslinkable chitosan derivative (CML) with poly(lactic-co-glycolic acid) (PLGA) particles whose surfaces were grafted with double carbon bonds containing gelatin (GM), following gelation under UV irradiation. The as-prepared composite hydrogel showed lower swelling ratio than that of the CML hydrogel, and higher elastic stiffness (i.e. storage modulus) than that of the CML hydrogel and the hydrogel filled with the same amount of PLGA particles or gelatin modified PLGA particles. Moreover, the storage modulus of the composite hydrogel was increased with the amount of GM modified PLGA particles. In vitro chondrocyte culture revealed that viability of the cells co-cultured with the GM modified PLGA particles was higher than that of the cells co-cultured with the unmodified PLGA particles. The composite hydrogel blended with the GM modified PLGA particles also showed higher cytoviability than that of the original CML hydrogel after 9d culture.

Skin biothermomechanics for medical treatments.

Abstract: Electromagnetic heating, such as microwave, radiofrequency, and laser etc., is widely used in medical treatments. Recent advances in these technologies resulted in remarkable developments of thermal treatments for a multitude of diseases and injuries involving skin tissue. The comprehension of heat transfer and related thermomechanics in skin tissue during these treatments is thus of great importance, and can contribute to the further developments of these medical applications. Biothermomechanics of skin is highly interdisciplinary, involving bioheat transfer, burn damage, biomechanics, and physiology. The aim of this study is to develop a computational approach to examine the heat transfer process, heat-induced mechanical response, as well as the associated pain level, so that the differences among the clinically applied heating modalities can be quantified. In this paper, numerical simulation with the finite difference method (FDM) was used to analyze the temperature, burn damage, and thermal stress distributions in the skin tissue subjected to various thermal treatments. The results showed that the thermomechanical behavior of skin tissue is very complex: blood perfusion has little effect on thermal damage, but a large influence on skin temperature distribution, which, in turn, influences significantly the resulting thermal stress field; for laser heating, the peak temperature is higher for lasers with shorter wavelengths, but the peak is closer to the skin surface; the thermal stress due to laser and microwave heating is mainly limited to the top epidermis layer due to the exponential decrease of heat generation along skin depth; the thin (and commonly overlooked) stratum corneum layer dominates the thermomechanical response of skin tissue.

Synthesis of polylactic acid-polyglycolic acid blends using microwave radiation.

Abstract: Degradation rates of a copolymeric PLGA can be controlled by varying the constituent amount in the copolymer. In the present study we have made an attempt to utilize microwave irradiation to blend PLLA and PGA in different concentrations. FTIR, NMR and DSC measurements clearly show the blending and cross-linking between the constituents.

Microstructure, mechanical properties and cytocompatibility of stable beta Ti-Mo-Ta sintered alloys.

Abstract: We have synthesized titanium-based alloys containing molybdenum and tantalum elements by powder metallurgy. The microstructure, the residual porosity and the mechanical properties of the sintered Ti–Mo and Ti–Ta–Mo alloys were investigated by using optical and electronic microscopy, X-ray diffraction, microhardness and compression tests. The cytocompatibility of the different alloys was evaluated by the assessment of bone cell density, migration and adhesion after 14 days incubation. All the alloys present a high ductility and an excellent cytocompatibility, which make these materials useful for medical implants.

Bone material properties and fracture analysis: needle insertion for spinal surgery.

Abstract: The effectiveness of percutaneous needle-based therapy and biopsy is demonstrated in a wide variety of medical problems including spinal disorders. Combined with osteoporosis, spinal disorders are increasingly prevalent as our society ages. However, the final position of the needle depends on a complex interplay of material properties of the bone and/or pathology, as well as the shape and material of the needle, and the insertion dynamics. This paper is a survey of the literature in the area of bone material properties and needle/bone interaction in the context of needle placement. It describes research findings on bone material properties and fractures using micro-CT imaging, and integrative imaging. This review paper also discusses the feasibility of using computational methods to predict fracture by simulating needle placement on any patient-specific model with both geometrical and mechanical properties approximating those of the patient's anatomy.

Influence of femoral stem surface finish on the apparent static shear strength at the stem-cement interface.

Abstract: The stem–cement interface has long been implicated in failure of cemented total hip replacement. Much research has been performed to study the factors affecting the bond strength between the femoral stem and the bone cement. The present study aims to further investigate the influence of femoral stem surface finish on the apparent static shear strength at the stem–cement interface through a series of pull out tests, where stainless steel rods are employed to represent the femoral stem. The results demonstrated that there was a general tendency for the apparent static shear strength to be increased with the rise of surface roughness. The polished and glass bead-blasted rods illustrated a slip-stick-slip failure whereas the shot-blasted and grit-blasted rods displayed gross interface failure. Following pull out test, cement transfer films were detected on the polished rods, and there was cement debris adhered to the surface of the grit-blasted rods. Micropores, typically 120 μm in diameter, were prevalent in the cement surface interfaced with the polished rods, and the cement surfaces in contact with the shot-blasted and grit-blasted rods were greatly damaged. There was also evidence of metal debris embedding within the cement mantle originating from the tests of the grit-blasted rods, indicating an extremely strong mechanical interlocking at the interface. In summary, this present research demonstrated that the grit-blasted rods with the highest surface roughness were the best in terms of apparent static shear strength. However, it seemed to be most applicable only to the stem designs in which mechanical interlocking of the stem in the initial fixed position was essential.

Development of ZrO2/SiO2 bioinert ceramic coatings for biomedical application.

Abstract: Gas tunnel-type plasma spraying (GTPS) was employed to deposit ZrO(2)/SiO(2) bioinert ceramic composite coatings with an appropriate thickness on SUS 304 substrate. Zirconia and fused silica powders, with equal wt%, have been mixed together in ceramic pot for 30 min and internally fed in the plasma jet. The composite coatings were sprayed at two different gas flow rates (120 and 150 l/min) and constant vortex arc current of 450 A and gun current of 50 A. The microstructure of as-sprayed coatings was examined by scanning electron microscope. Elemental analysis was achieved for the composite coatings using EDS analysis unit which is attached to SEM. Phase structure was investigated by X-ray diffraction. The hardness and abrasive wear test of the coatings were investigated. The biological property of the coatings was examined by immersing the as-sprayed coatings in simulated body fluid (SBF) solution for 20 days at 36.5 degrees C. The growth of apatite (HA) on the coatings surfaces was observed by SEM and EDX analysis.