Bio-Medical Materials and Engineering - Volume 16, issue 5

Authors: Even-Tzur, Nurit | Weisz, Ety | Hirsch-Falk, Yifat | Gefen, Amit

Article Type: Research Article

Abstract: Modern sport shoes are designed to attenuate mechanical stress waves, mainly through deformation of the viscoelastic midsole which is typically made of ethylene vinyl acetate (EVA) foam. Shock absorption is obtained by flow of air through interconnected air cells in the EVA during shoe deformation under body-weight. However, when the shoe is overused and air cells collapse or thickness of the EVA is reduced, shock absorption capacity may be affected, and this may contribute to running injuries. Using lumped system and finite element models, we studied heel pad stresses and strains during heel-strike in running, considering the viscoelastic constitutive behavior …of both the heel pad and EVA midsole. In particular, we simulated wear cases of the EVA, manifested in the modeling by reduced foam thickness, increased elastic stiffness, and shorter stress relaxation with respect to new shoe conditions. Simulations showed that heel pad stresses and strains were sensitive to viscous damping of the EVA. Wear of the EVA consistently increased heel pad stresses, and reduced EVA thickness was the most influential factor, e.g., for a 50% reduction in thickness, peak heel pad stress increased by 19%. We conclude that modeling of the heel–shoe interaction should consider the viscoelastic properties of the tissue and shoe components, and the age of the studied shoe. Show more

Keywords: Finite element analysis, foot biomechanics, footwear, sport shoes, viscoelasticity

Citation: Bio-Medical Materials and Engineering, vol. 16, no. 5, pp. 289-299, 2006

Authors: Wang, Jung-Pin | Zhong, Zheng-Cheng | Cheng, Cheng-Kung | Chen, Chen-Sheng | Yu, Chung-hung | Chang, Ting-Kuo | Wei, Shun-Hwa

Article Type: Research Article

Abstract: Spondylolysis is a fracture of the bone lamina in the pars interarticularis and has a high risk of developing spondylolisthesis, as well as traction on the spinal cord and nerve root, leading to spinal disorders or low back pain when the lumbar spine is subjected to high external forces. Previous studies mostly investigated the mechanical changes of the endplate in spondylolysis. However, little attention has been focused on the entire structural changes that occur in spondylolysis. Therefore, the purpose of this study was to evaluate the biomechanical changes in posterior ligaments, disc, endplate, and pars interarticularis between the intact lumbar …spine and spondylolysis. A total of three finite element models, namely the intact L2-L4 lumbar spine, lumbar spine with unilateral pars defect and with bilateral pars defect were established using a software ANSYS 6.0. A loading of 10 N·m in flexion, extension, left torsion, right torsion, left lateral bending, and right lateral bending respectively were imposed on the superior surface of the L2 body. The bottom of the L4 vertebral body was completely constrained. The finite element models estimated that the lumbar spine with a unilateral pars defect was able to maintain spinal stability as the intact lumbar spine, but the contralateral pars experienced greater stress. For the lumbar spine with a bilateral pars defect, the rotation angle, the vertebral body displacement, the disc stress, and the endplate stress, was increased more when compared to the intact lumbar spine under extension or torsion. Show more

Keywords: Pars defect, spondylolysis, finite element method, biomechanics

Citation: Bio-Medical Materials and Engineering, vol. 16, no. 5, pp. 301-308, 2006

Authors: Chen, Nian-Zhong | Lee, Winson C.C. | Zhang, Ming

Article Type: Research Article

Abstract: Lower-limb prostheses are used to restore amputee's walking. Monolimb is one of the designs referring to socket and the shank being molded into one piece of thermoplastic material. Appropriate shank flexibility of a monolimb can improve gait of an amputee. However, during the fabrication, the variations of design variables are inevitably produced which may lead the unexpected shank deflection and directly influence on gait efficiency of an amputee. This paper presents a robust design procedure for improvement of quality of the monolimb by simultaneously minimizing performance variations caused by variations in design variables and bringing the mean value of performance …on target. The robust design procedure embodies the integration of response surface methodology with genetic algorithms. Response surface models are developed for the responses of monolimb as functions of design variables over the region of interest and genetic algorithms are employed to find the robust solution. A robust design of monolimb is performed for an amputee subject and the results show that the robust design can design a “robust” monolimb which provides specified performance targets that are minimally sensitive to the variations of design variables. This indicates that robust design may have the potential application in improving the quality of the prescribed prosthesis. Show more

Keywords: Lower-limb prosthesis, monolimb, robust design, finite element analysis, response surface methodology, genetic algorithms

Citation: Bio-Medical Materials and Engineering, vol. 16, no. 5, pp. 309-318, 2006

Authors: Lewis, Gladius | Duggineni, Rajesh

Article Type: Research Article

Abstract: A finite element analysis of the stresses in a construct, comprising a three-dimensional model of the proximal human femur in which the stem of a total hip joint replacement was cemented, was performed. The one-legged standing condition was used, with all applied forces on the proximal femur being considered. These forces were the resultant hip joint reaction force and the forces due to the activation of the abductor, ilio-psoas, and ilio-tibialis muscles. The cortical and cancellous bones were assigned anisotropic elastic properties. It was found that the mean value of the strain energy density at each of the regions considered …was considerably higher when debonding was considered at both the cancellous bone–acrylic bone cement and bone cement–stem interfaces (represented using surface-to-surface Coulomb friction, coefficient of friction=0.22) compared to when perfect bonding conditions were taken to exist at these interfaces. The significance of this finding, together with the study limitations, is discussed. Show more

Keywords: Finite element analysis, total hip joint replacement, Coulomb friction, strain energy density

Citation: Bio-Medical Materials and Engineering, vol. 16, no. 5, pp. 319-327, 2006

Authors: Jagannath, J.H. | Radhika, M.

Article Type: Research Article

Abstract: Polymeric bio-adhesives emulsion which is biodegradable and non-toxic containing antimicrobial agents can play an important role in preventing infection in wound covering and coating for surgical implants. Therefore a bioadhesive polymer was synthesized by semi-Interpenetrating Network process using blend of shellac, casein and polyvinyl alcohol and Maleic anhydride (MA) as reactive compatibilizer. The synthesized polymer was mixed with neem and turmeric extract and homogenized using an emulsifier. Differential scanning calorimeter (DSC) was used to measure the molecular miscibility of biopolymer components and emulsion constituents. Stability of emulsion (coating) was measured by keeping property and accelerated stability test. Antimicrobial properties were …evaluated for human pathogenic organisms namely E. coli, Staphylococcus aureus, Bacillus cereus, and Salmonella typhimurium using well diffusion assay. The results indicate that stability, miscibility and antimicrobial properties of bioadhesive was satisfactory, however further in vivo studies are required to ascertain suitability of emulsion (coating) for biomedical use. Show more

Keywords: Molecular miscibility, glass transition temperature, emulsion stability, semi-IPN, bioadhesive

Citation: Bio-Medical Materials and Engineering, vol. 16, no. 5, pp. 329-336, 2006

Authors: Najarian, Siamak | Dargahi, Javad | Firouzi, Faramarz | Afsari, Jamshid

Article Type: Research Article

Abstract: In this paper, we report on the unsteady state modeling of blood flow in an end-to-side anastomosed bypass graft, which has a stenosis upstream from the junction. In coronary artery bypass grafting/surgery (CABG), new arteries are created in order to provide blood to the heart using other blood vessels as conduits to bypass the blocked section in the patient's coronary arteries. The failure of coronary artery bypass procedures has been attributed to both intimal hyperplasia (IH) and atherosclerosis. It is believed that these two phenomena are, in turn, related to the local hemodynamic factors. In this work, a three-dimensional computational …fluid dynamics analysis is used to simulate the physiological blood flow through a model of a stenosed coronary bypass graft with the realistic assumption of non-Newtonian flow for human blood. For different flow repartitions and at different times of the cycle, both the recirculating areas and wall shear stress (WSS) are studied. Based on the different distribution of flow rates in the bypass graft and the host artery, the flow features are investigated and the influence of non-Newtonian behavior is discussed in terms of separation points, reattachment points, and the wall shear stresses. Various differences are observed based on the assumption of non-Newtonian behavior of blood, which have not been reported before when a simplified Newtonian approach is utilized. Show more

Keywords: Bypass graft, CABG, numerical simulation, physiological flow, three-dimensional

Citation: Bio-Medical Materials and Engineering, vol. 16, no. 5, pp. 337-347, 2006

Authors: Visco, A.M. | Calabrese, L. | Campo, N. | Torrisi, L. | Oteri, G. | Lo Giudice, G. | Cicciù, D.

Article Type: Research Article

Abstract: In this work composite materials, based on quartz fibers and epoxy resins, were employed with the aim to restore damaged teeth. The composite materials were chosen because they show biomechanical features very similar to that of the dentine, the main constituent of the tooth. Extracted teeth were rebuilt with two different restorative procedures: in the first, the composite material was pre-formed in a conical trunk shape abutment (PA) and then bonded to a fiber quartz post with a dental bonder. In the second rebuilt system the abutment was prepared by cross linking the resin on the fiber quartz post with …a halogen lamp (CRA). The restored teeth were then mechanically tested and observed with a Scanning Electron Microscope (SEM) with the aim to study the interaction between the reconstructive materials. Wetting and roughness measurements were also carried out in order to study the interface adhesion between the post and the abutments. Characterization analysis evidenced that the CRA restorative procedure improves the adhesion between the substitutive materials and shows higher fracture strength than the PA ones. Anyway both the rebuilt systems are able to support the masticator load. An explanation of the interfacial post–abutment interaction phenomenon is discussed. Show more

Keywords: Composite materials, teeth, restorative, bending-compressive tests, physic characterization

Citation: Bio-Medical Materials and Engineering, vol. 16, no. 5, pp. 349-358, 2006

Authors: Lewis, Gladius

Article Type: Research Article

Citation: Bio-Medical Materials and Engineering, vol. 16, no. 5, pp. 359-361, 2006