Bio-Medical Materials and Engineering - Volume 4, issue 3
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Bio-Medical Materials and Engineering is to promote the welfare of humans and to help them keep healthy. This international journal is an interdisciplinary journal that publishes original research papers, review articles and brief notes on materials and engineering for biological and medical systems.
Articles in this peer-reviewed journal cover a wide range of topics, including, but not limited to: Engineering as applied to improving diagnosis, therapy, and prevention of disease and injury, and better substitutes for damaged or disabled human organs; Studies of biomaterial interactions with the human body, bio-compatibility, interfacial and interaction problems; Biomechanical behavior under biological and/or medical conditions; Mechanical and biological properties of membrane biomaterials; Cellular and tissue engineering, physiological, biophysical, biochemical bioengineering aspects; Implant failure fields and degradation of implants. Biomimetics engineering and materials including system analysis as supporter for aged people and as rehabilitation; Bioengineering and materials technology as applied to the decontamination against environmental problems; Biosensors, bioreactors, bioprocess instrumentation and control system; Application to food engineering; Standardization problems on biomaterials and related products; Assessment of reliability and safety of biomedical materials and man-machine systems; and Product liability of biomaterials and related products.
Abstract: Artificial roots must carry multiple forces during mastication. Stress distribution around a root depends upon the shape, material, and function of the root. Therefore, for biomechanical studies on artificial roots, triad research on the material, shape, and functional effect upon surrounding tissue is essential. For dental implants, there are two different functional systems against the masticatory force, i.e., gomphosis and ankylosis on osseointegration. Stress analyses of functioning new type (gomphosis) artificial roots were carried out in mandibular and maxilla models to study the triad effect using finite element analysis. The authors have already reported histological and biomechanical studies…on the shape and functional effect. To observe the material effect biomechanically, artificial roots made of sintered hydroxyapatite and zirconium oxide were analyzed in the models. Thereafter, animal experiments using dogs were carried out to observe bone formation around artificial roots made of hydroxyapatite and zirconium oxide in the mandible and maxilla. The following results were obtained: The patterns of stress distribution around artificial roots of two different materials were not too different, and were exclusively dependent upon the root shape and structure of the jawbone. Around the artificial roots, bone formation coincided with a moderate stress distributing zone and principal stress trajectories. Through these experiments, the following conclusions were obtained: (a) Osteogenesis around artificial roots coincides with the stress distribution patterns. (b) Stress distribution patterns are dependent very little upon material properties but upon both the artificial root shape and the structure of the jawbone. (c) Optimization of the artificial root shape can be obtained by FEA in the models.
Keywords: artificial root, finite element analysis, shape effect, optimization, periimplantium
Abstract: Regarding the junction of bioceramics with original bone, which have quite different material constants of Young's modulus and Poisson's ratio from each other, synostosis (ankylosis) cannot be obtained under severe loading conditions. Therefore, it is necessary to introduce a new junction system for the interface between the biomaterial mechanical organ and original bone. The jointing system of dental root to jawbone reflects on the function against mastication. The interface between different mechanical organs with different materials necessitates a specific juncture system under severe loading because of the disparity of material constants. The authors already reported the result of studies on…the shape effect of artificial roots in functioning jawbone by means of finite element analysis. Studies on the functional effect of artificial roots in undulated shape were carried out biomechanically by means of finite element analysis using models to investigate an effective juncture system between bone and biomaterials. The results of finite element analysis were compared with the findings obtained from histological specimens. To observe the juncture state of bioceramics with tubular bone cortex, tubular apatite artificial bone was implanted in the femur of a dog. From these studies, the following results and conclusions were obtained: (a) The fibrous juncture system around bioceramics has an important role, after which the principal stress trajectories are converted; and (b) optimal undulated morphology compatible to the artificial bone's juncture system by means of fibrous ligament is essential for remodeling of the bone around the artificial skeletal bone.
Keywords: junction system, material property, functional effect, finite element method, principal stress trajectory
Abstract: Transplanted and replanted autogenous teeth or implanted artificial roots become easily ankylotic. However, if adequate functional loads are applied to them continuously postop with proper fixation, ankylosis can be prevented. The author found this fact through studies on autogenous tooth replantation 20 years ago. Therefore, not only can tooth transplantation, replantation, and artificial root implantation be done successfully with adequate functional loads, but surgical orthodontics as well as plastic operation of jaw deformity can also benefit in the same way. This therapeutic method is called functional surgery. The ankylotic process can be more effectively prevented by applying bioceramic granules. Using…these methods, (a) 30 vital teeth in 23 patients were transplanted or replanted. Follow-up duration was 6 to 96 months. (b) Artificial roots made of compact sintered hydroxyapatite (apatite) were implanted under the new concept of functional surgery. In all, 57 artificial roots in 19 patients were implanted and observed for over 5 years. (c) Masticatory skeletal deformities of the viscerocranium were treated with the new concept of functional surgery applying sintered apatite. For this purpose, artificial bone implantation or simple gnathoplasty, tooth transplantation, and artificial root implantation was carried out in 15 patients, after which mastication training was applied with concomitant corrections of function inclination, i.e., oral-perioral habits. In these clinical experiments, excellent favorable results were obtained. The following conclusion was obtained: Introducing the new concept of functional surgery using bioceramics, not only tooth transplantation, as well as artificial root therapeutics, but deformity of the jaw can be steadily treated.
Abstract: The present work is a study of the effects of soft segment molecular weight and chemical structure on the fatigue crack propagation of model copoly (ether-urethane-urea)s (PEUU). The PEUU were synthesized using polypropylene glycol (PPG), polytetramethylene glycol (PTMG), and polyethylene glycol (PEG) as the soft segment component. The number average molecular weights of the polyethers were within the range of 1000 ~ 2000. Methylene bis (4-phenylisocyanate) (MOl) and ethylene diamine were used as the diisocyanate and the chain extender, respectively. The cyclic loading experiments were carried out using a computerized film stretcher that can conduct sinusoidal operation at a…constant strain amplitude, strain rate, and frequency. The Rivlin-Thomas tearing energy, T, and the fatigue crack propagation (FCP) rate were selected to characterize the fatigue behavior of the model polyurethanes. An empirical equation was applied to define the fatigue properties of model polyurethanes and to evaluate the fatigue resistance. To investigate the effect of molecular variables on the FCP, the morphological changes caused by structural differences and cyclic stress were determined using dynamic viscoelastometer (Rheovibron), Small Angle X-ray Scattering (SAXS), and Fourier-Transform Infrared (FT-IR) spectroscopy. Mooney-Rivlin plot was used to determine the crosslink density variation. In addition the orientation behavior at the crack tip was characterized by IR dichroism technique using a polarized FT -IR microscope. The results indicated a reasonable relationship between the FCP rates and the hard segment content, crosslink density, and deformation property at the crack tip. However, the initial stage of phase separation and domain disruption behavior did not show a good correlation with the FCP properties of model polyurethanes. Among the model polyurethanes tested, the PEUU with PTMG (Mn =1000) exhibited the best fatigue resistance at given test condition.
Abstract: Silica-coatings prepared by sol-gel method was coated on CP-titania cones and discs. Thin coatings of less than approximately 0.3 μm were produced, The greatest advantage with the Si-gel coatings is that the densification of the gel takes place at already 500°C, thus not changing the character of the metal surface. The coatings showed to passivate the surface of the CP-titania specimen, provided that the thickness did not exceed 0.3 μm. That seemed to be the critical thickness for a smooth and intact coating. Thicker coatings of Si-gel scales easily off.
Abstract: Carbon fiber reinforced polyetheretherketone (C/PEEK) composite materials are being investigated as an alternative to metal in the femoral component of a total hip arthroplasty. Wear is among the issues that must be addressed before introducing a new orthopaedic implant material. This study examines the generation of wear debris when zirconia femoral heads are mechanically attached to C/PEEK trunnions and loaded under simulated physiological conditions. Mechanical testing was performed on a trunnion/head assembly loaded from 445 to 4450N at an angle of 39° to the long axis of the trunnion. The trunnions were tested at a frequency of 20 Hz…for 10 million cycles. After completion of the fatigue test, solution from the test assembly was characterized by laser scattering and by SEM image analysis to determine the size, shape, total number, and identify of the particles. In addition, the peak load to pull the head from the trunnion was measured. The total number of particles generated during the test was in the range of 105 as indicated by both laser scattering and (SEM) image analysis. Both carbon fiber and PEEK particles were found in an average proportion of about 1:13, respectively. The carbon fiber particle size average was 153μm and the PEEK particle size average was 2.2μm. The zirconia heads remained well attached to the C/PEEK trunnions as indicated by a mean peak distraction force of 1942 ± 116N.
Keywords: composite material, hip prosthesis, wear, C/PEEK, fretting
Abstract: Carbon fiber/PEEK polymer (C/PEEK) composite materials are being developed for use as orthopaedic implant materials, Wear is an issue of increasing importance in orthopaedic implants; particulate debris generated by the wearing of biomaterials may be a causal factor leading to osteolysis and implant loosening, Therefore, numerical and ellperimental studies were completed to characterize the wear of C/PEEK composite materials in comparison to current orthopaedic implant materials. Finite element analyses (FEA) of a composite material hip stem implanted in a femur and loaded at 890 N determined that peak contact stresses will occur at the proximal-medial and distal regions of…the implant. These contact stresses were found to be below 1.0 MPa over most of the implant surface; however the peak stress in the proximal-medial region was 1.8 MPa and higher still at the distal portion of the stem, In vivo forces result in contact stress values up to 9.0 MPa, The composite implant exhibited 10–40% lower contact stresses in the distal region compared to a titanium-alloy implant of identical design. Composite material wear samples were slid against porous hydroxylapatite (HA) to simulate the stem/bone interface. An identical series of experiments was run for comparison to a current orthopaedic implant material—Ti6Al4V titanium alloy. Two domains of motion were studied; a composite ring-on-HA disc large amplitude sliding wear test; and a composite pin-on-HA disc small amplitude fretting regimen. Nominal contact pressures during testing were 1.4 MPa and 7.6 MPa for sliding and fretting tests, respectively. Fretting and sliding abrasive wear tests resulted in the composite material exhibiting a lower wear rate than the titanium-alloy. The magnitude of the difference was greatly dependent on the contact pressures, sliding amplitudes, and counterface material properties.
Keywords: composite material hip, implant, wear, C/PEEK
Abstract: The debris generated by the progressive wear of total joint replacement (TJR) devices is considered a primary cause of osteolysis, bone resorption, and premature failure of artificial hips and knees. The vast majority of this debris originates from the UHMWPE articulating surfaces caused by tribological interaction with the opposing metal or ceramic surface and hard particulates contained in the sinovial fluid. Entrapment of third body debris, such as cortical bone, PMMA cement, and titanium debris, between the articulating surfaces can cause abrasion of both the hard bearing surface and the UHMWPE. The propensity for abrasive wear is dependent on the…relationship between the hardness of the third-body debris and the hardness of the bearing surfaces. To gain a better understanding of this relationship and its effect on wear, the abrasive wear behavior of several metal and ceramic bearing surfaces was characterized in terms of the hardness of both the third-body debris and the metal or ceramic substrate. The effects of abrasion and increased surface roughness of the metal or ceramic surfaces on wear of the UHMWPE was also determined. In addition, the amount of UHMWPE wear was quantified in terms of the amount (particles/ml) of titanium fretting-type debris contained in solution. The results of this investigation showed the resistance to abrasive wear of the metal and ceramic bearing surfaces to increase with increasing surface hardness. Bone debris, PMMA cement, and titanium debris produced visible abrasion of all metal surfaces including nitrogen ion implanted Ti-6AI-4V. The ceramic bearing surfaces showed no evidence of abrasion and produced the least amount of UHMWPE wear. The wear of UHMWPE sliding against Co-Cr-Mo was found to increase with increasing levels of 1.48 μm titanium debris added to the wear test solution. The rate of UHMWPE wear increased rapidly for concentrations of titanium debris in the test solution exceeding about 105 particles/mi. These test results suggest that third-body particles, both large and small, are capable of causing increased abrasive wear of UHMWPE, and that abrasion of the hard bearing surfaces will occur if the hardness of the third-body debris exceeds the hardness of the metal or ceramic bearing surface.
Abstract: To optimize the performance of total hip replacement, scientists and clinicians are seeking new materials and noncemented, press-fit designs that cam improve load transfer to the bone and reduce the incidence of loosening and thigh pain. Currently used Co-Cr-Mo alloy has a relatively high elastic modulus (E = 227 GPa), which limits its ability to transfer load to the surrounding bone in the proximal calcar region. Thus to improve load transfer, designs are considered with less cross-sectional area to increase flexibility, but at the expense of fit and fill, and thus stability of the implant within the bone. Should stem…loosening occur, the stem stresses may exceed the relatively low fatigue strength of the Co-Cr-Mo alloy and lead to stem breakage. To improve these conditions, lower modulus Ti-6Al-4V alloy (E = 115GPa) is being used. More recently, a new lower-modulus (E = 79 GPa) Ti-13Nb-13Zr alloy has been developed which does not contain any elemental constituents associated with adverse cell response (i.e., Co, Cr, Mo, Ni, Fe, AI, V), and which possesses comparable or superior strength and toughness to existing Ti-6Al-4V alloy. The carefully selected Nb and Zr constituents improve bone biocompatibility and corrosion resistance compared to that of currently used implant metals. Additionally, a unique diffusion hardening (DR) treatment can be conducted during the age-hardening process of this near-beta alloy to produce a hardened surface with abrasion resistance superior to that of Co-Cr-Mo alloy. This also provides an improvement in the micro-fretting tendencies that may occur within femoral head-neck taper regions and modular interfaces of other implant designs. The present study describes the metallurgy and mechanical properties of this unique low modulus Ti-13Nb-13Zr alloy, and the heat treatments used to obtain the high strength, corrosion resistance, and surface hardening that renders this biocompatible alloy well-suited for press fit hip replacement applications. Because of the relatively lower beta transus (735°C), this alloy is also much easier to net shape forge into more complex stem designs.
Abstract: An apparatus and test method were developed to determine the elastic stiffness and damping coefficient of human cartilage in compression. An underdamped, counterbalanced beam applied a sudden compressive force to a full-thickness cylindrical specimen of articular cartilage. The initial oscillatory response decayed to steady state creep after approximately 10 cycles of oscillation. The results were consistent with a Voigt phenomenological model with linear stiffness and damping terms. Standard dynamics analysis of the transient oscillatory response enabled the elastic stiffness to be determined from the frequency and the damping coefficient to be derived from the logarithmic decrement of the decay of…the oscillations. The relationship between the mechanical properties and structure of cartilage was determined by treating specimens with two specific proteolytic enzymes. Digestion and removal of proteoglycans alone with cathepsin D caused the damping coefficient to decrease with no change in elastic stiffness. The action of leukocyte elastase on collagen caused a decrease in both damping coefficient and elastic stiffness. It was concluded that the collagen fibrils in cartilage largely control the elastic response while the viscous response is controlled largely by the hydrated proteoglycans. The effects of cartilage thickness was also examined and found to be inversely proportional to the elastic stiffness. It is suggested that this method could be used to uncouple elastic and viscous properties of other viscoelastic materials.