Bio-Medical Materials and Engineering - Volume 6, issue 3

Authors: Hedia, H.S. | Barton, D.C. | Fisher, J. | Elmidany, T.T.

Article Type: Research Article

Abstract: The load transferred through the hip joint is one of the major forces occurring in the human body. After the replacement of this joint in THR arthoplasty, the load is transferred through the implant to the femoral bone. Loosening of the fixation of the implant and the fatigue failure of prosthetic stems create problems for both patient and surgeon. Both problems can be reduced by the use of Finite Element (FE) analysis to predict stresses and fatigue lifes but the results are sensitive to assumptions regarding the loading conditions and the idealisation of the components. Consequently the stress distributions and …resulting fatigue notch factors in the human femur with an endoprosthesis have been determined for different assumptions regarding the form of the idealisation, the load conditions, and the interface conditions. The FE results show that a realistic loading condition without a tension banding force always produces the highest fatigue notch factor and von Mises stresses. An equivalent 2D plane stress model obtained by varying the thickness is likely to give more realistic stresses because it predicts more realistic strains than other 2D approximations. The full bonded interface is a satisfactory. approximation for the real interface conditions because it predicts stress distributions of the correct form without excessive stress concentration. Show more

Keywords: Von Mises stress, fatigue notch factor, loading conditions, interface conditions

DOI: 10.3233/BME-1996-6301

Citation: Bio-Medical Materials and Engineering, vol. 6, no. 3, pp. 135-152, 1996

Authors: Sabrià, J. | Cortada, M. | Giner, L. | Gil, F.J. | Fernández, E. | Manero, J.M. | Planell, J.A.

Article Type: Research Article

Abstract: NiTi alloy used in dental prosthetic fixators shows pseudoelastic behaviour and exhibits a great potential in dental and orthopaedic applications where constant correcting loads are required. In order to use such materials in dental prosthetic fixators, where the device is cyclically deformed, it is necessary to investigate the effect of the cyclic straining upon the transformation stresses and temperatures of the material. The aim of this work is to study the load cycling of a pseudoelastic NiTi shape memory alloy to be applied in the making of dental prosthetic fixators.

Keywords: Pseudoelasticity, NiTi, fatigue, shape memory alloy, prosthetic, fixator

DOI: 10.3233/BME-1996-6302

Citation: Bio-Medical Materials and Engineering, vol. 6, no. 3, pp. 153-157, 1996

Authors: Kim, Jeong K. | Park, Joon B.

Article Type: Research Article

Abstract: In order to alleviate fixation-related problems of cemented total hip arthroplasty (THA), a wire coil was incorporated within the cement mantle at the distal end of femoral prosthesis in a sectioned human cadaver specimen. Mechanical push-out test results showed that the wire reinforcement reduces the hoop strain by 50% at the exterior surface of the bone. The reinforced specimen also showed less axial stem displacement. The use of wire coil within the cement mantle could reduce hoop strain and axial stem displacement in the femoral prosthesis of total hip joint implants.

DOI: 10.3233/BME-1996-6303

Citation: Bio-Medical Materials and Engineering, vol. 6, no. 3, pp. 159-164, 1996

Authors: Mohanty, Mira

Article Type: Research Article

Abstract: In recent times, loosening of joint prosthesis resulting in failure, is of grave concern to orthopedicians. It is estimated that 50% of total hip replacements become loose after 15 years, and most of them require either revision surgery or resection orthoplasty. Neither, newer operative techniques, change in design, use of novel materials, nor surface modifications have helped to circumvent the problem. It is in this context, that attention has been focussed on the role of tissue surrounding the implant, in the loosening of the prosthesis. Tissue response around prosthesis results in either formation of a fibrous layer around the …implant, ingrowth into fenestrations on implant or direct bone apposition on prosthesis. Long-term implantation results in implant debris being released into surrounding tissue. These particles initiate a chronic granulonatous inflammation with a significant number of activated macrophages and foreign body type of giant cells, all engaged in attempts to get rid of the debris. These features have been found to be invariably associated with peri-prosthetic lysis of bone. Since such bone resorption is also observed around non-cemented prosthesis, possibly causes other than cement are responsible for the osteolysis. Retrospective studies on failed implants suggest that peri-prosthetic osteolysis is mediated by activated macrophages. Cytokines are capable of stimulating bone resorbing cells, the osteoclasts. Bone resorption results in further loosening of the prosthesis, changes in stress, frictional wear, release of more wear debris and recruitment of more macrophages. Bone death and proliferation of macrophages, thus appear to be the cause for pain and loosening of prosthesis. Show more

Keywords: Joint prosthesis, loosening, wear, cytokines

DOI: 10.3233/BME-1996-6304

Citation: Bio-Medical Materials and Engineering, vol. 6, no. 3, pp. 165-172, 1996

Authors: Wen, Xuejun | Wang, Xiaoxiang | Zhang, Ning

Article Type: Research Article

Abstract: In this paper, four aspects of microrough surface of metallic biomaterials are reviewed: i.e., the preparation of microrough surface, the technology of surface roughness measurement, the parameters of roughness and the bio-effect of microrough surface. Microrough surfaces (roughness below 50 μm) are easily prepared and conveniently detected in practice. Microrough surfaces allow early better adhesion of mineral ions or atoms, biomolecules, and cells, form firmer fixation of bone or connective tissue, result in thinner tissue-reaction-layer with inflammatory cells decreased or absent, and prevent microorganism adhesion and plaque accumulation, when compared with the smooth surfaces.

Keywords: Metallic biomaterials, microrough surface, surface roughness, biocompatibility, surface modification, surface analysis

DOI: 10.3233/BME-1996-6305

Citation: Bio-Medical Materials and Engineering, vol. 6, no. 3, pp. 173-189, 1996

Authors: Ueyama, Keishi | Jones, James W. | Varvitsiotis, Poseidon S. | LaFuente, Javier A. | Thornby, John I. | Raskin, Steven A. | Beall, Jr., Arthur C.

Article Type: Research Article

Abstract: Heat exchange methods must be efficient in order to minimize the patient's pump time. However, comparisons of heat exchangers have been rare. Therefore, the in vivo functions of the most popular, currently available heat exchangers, Sarns, Cobe, Medtronics Maxima, and an experimental model manufactured by Haemonetics were compared. Thirty-two pigs weighing between 63–74 kg were placed on cardiopulmonary bypass with right atrial and ascending aorta cannulation through a right thoracotomy. Thermocouples were placed in the pump tubing before and after the heat exchangers, in the water line before and after the heat exchangers, in the inlet and outlet line …of the pump, and the esophagus, brain, bladder, rectum, liver, myocardium, and tympanic membranes of the pigs. They were cooled until the bladder temperature was reduced to 14°C, and maintained at that temperature for 10 minutes. Rewarming was begun until the bladder temperature became 37°C. The pump flow was maintained between 50–60 ml/kg/min with standard ventilation. Cobe, Sarns, Maxima, and Haemonetics heat exchangers were tested and their function determined by comparing the time necessary for rewarming. The Haemonetics heat exchanger required a significant shorter time than the others to rewarm the pigs to normal bladder temperature (Cobe 82.0 ± 12.0, Sams 80.3 ± 15.4, Maxima 89.0± 13.9, Haemonetics 68.7 ± 13.4, p < 0.05). The principal advantage was seen at the lowest temperatures between the Haemonetics experimental heat exchanger and the other heat exchangers. No statistically significant superiority was seen at higher temperatures. The current heat exchangers are relatively comparable but improved performance is possible with available technology. Show more

Keywords: Heat exchanger, Cardiopulmonary Bypass (CPB), extracorporeal circulation, hypothermia, rewarming

DOI: 10.3233/BME-1996-6306

Citation: Bio-Medical Materials and Engineering, vol. 6, no. 3, pp. 191-197, 1996

Authors: Hedia, H.S. | Barton, D.C. | Fisher, J. | Ibrahim, A.

Article Type: Research Article

Abstract: The femoral component of the artificial hip joint implanted in a patient's femur is subjected to a complex set of forces exerted due to normal life activities. It is thought that high values of stress in the cement in a cemented prosthesis can lead to fractures of the cement mantle and loosening of the stem. The incidence of such problems may be diminished by reduction of the fatigue notch factor in the cement, such that stress concentrations are avoided and the crack initiation time maximised. This study describes a method for numerical shape optimisation to determine an optimal shape for …the femoral stem of a hip prosthesis in order to minimise the fatigue notch factor in the cement layer at the interfaces with the bone and stem whilst at the same time maintaining or increasing the stress levels in the proximal medial femoral bone to help prevent stress shielding. The method when used to optimise the shape of a stainless steel Charnley stem was found to be extremely efficient and effective. The resulting optimal shape was heavily waisted in the proximal region below the neck but distally was quite similar to the original design. The fatigue notch factors in the cement were reduced by 16% and 19% for medial and lateral cement/stem interfaces, respectively, and by 8% and 2% for the corresponding cement/bone interfaces. The fatigue notch factor in the proximal medial bone was increased by 57% which indicates that the general stress level in this region is markedly increased. Thus the optimised design should increase the fatigue life of the cement and at the same time reduce stress shielding in the proximal bone. Both of these effects may help prevent loosening of the femoral component and hence reduce the need for early revision operations. Show more

DOI: 10.3233/BME-1996-6307

Citation: Bio-Medical Materials and Engineering, vol. 6, no. 3, pp. 199-217, 1996

Authors: Pintar, Frank A. | Schlick, Michael B. | Yoganandan, Narayan | Maiman, Dennis J.

Article Type: Research Article

Abstract: Spinal cord injuries continue to generate large individual and societal costs. The study of spinal cord injury has been undertaken from the perspective of animal studies to understand cord functioning, and from the use of cadaver material to understand ligamentous column failure. The present study was conducted to develop a tool to link results from both these methods of research. An instrumented artificial spinal cord was designed, constructed, and evaluated under different testing scenarios. Properties of the in vivo animal cord were obtained using the dorsal impact method and reproduced in a collagen-encased gelatin physical model. The cord was instrumented …in seven places using thin, non-invasive piezo-electric pressure sensors. The instrumented artificial cord was then evaluated in the canal of a human cadaver head-neck column under dynamic loading conditions. A C5 compression fracture correlated to high local pressure changes. These results demonstrate the feasibility of using this new tool to understand the mechanisms of spinal cord injury. Show more

Keywords: Spinal cord injury, biomechanics, cervical spine, spinal fractures, trauma

DOI: 10.3233/BME-1996-6308

Citation: Bio-Medical Materials and Engineering, vol. 6, no. 3, pp. 219-229, 1996