Bio-Medical Materials and Engineering - Volume 13, issue 4

Authors: Li, Chaodi | Kotha, Shiva | Mason, James

Article Type: Research Article

Abstract: The exothermic polymerization of bone cement may induce thermal necrosis of bone in cemented hip arthroplasty. A finite element formulation was developed to predict the evolution of the temperature with time in the cemented hip replacement system. The developed method is capable of taking into account both the chemical reaction that generates heat during bone cement polymerization (through a kinetic model) and the physical process of heat conduction (with an energy balance equation). The possibility of thermal necrosis of bone was then evaluated based on the temperature history in the bone and an appropriate damage criterion. Specifically, we evaluate the …role of implant materials and designs on the thermal response of the system. Results indicated that the peak temperature at the bone/cement interface with a metal prosthesis was lower than that with a polymer or a composite prosthesis in hip replacement systems. Necrosis of bone was predicted to occur with a polymer or a composite prosthesis while no necrosis was predicted with a metal prosthesis in the simulated conditions. When reinforcing osteoporotic hips with injected bone cement in the cancellous core of the femur, the volume of bone cement implanted is increased which may increase the risk of thermal necrosis of bone. We evaluate whether this risk can be decreased through the use of an insulator to contain the bone cement. No thermal necrosis of bone was predicted with a 3 mm thick polyurethane insulator while more damage is predicted for the use of bone cement without the insulator. This method provides a numerical tool for the quantitative simulation of the thermal behavior of bone‐cement‐prosthesis designs and for examining and refining new designs computationally. Show more

Keywords: Bone cement, finite element, thermal behavior, prosthesis, orthopaedic

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 4, pp. 419-428, 2003

Authors: Kobayashi, Masanori | Oka, Masanori

Article Type: Research Article

Abstract: The purpose of this study was to observe and compare the effect of the behavior of different lubricating surfaces, including articular cartilage and several artificial joint materials, under the physiological loading by confocal laser scanning microscopy (CLSM) to clarify the mechanism of lubrication in natural joints and subsequently improve the quality of artificial joints. In our experiment, even with considerable loading, natural articular cartilage exhibited a synovial fluid area and an area of direct and solid contact. In the region between these two areas, a liquid crystal layer was observed. On the other hand, the materials used for artificial joints …(metal and polyethylene, which are now in use, and polyvinyl alcohol‐hydrogel polymer which is being developed), did not exhibit neither a clear fluid pool area nor the intermediary area with liquid crystal formation. These results suggest that natural articular cartilage surface has a particular characteristic which builds up a synovial pooling area and liquid crystal formation in the third area by interaction with macromolecules in synovial fluid under the loading condition. These characteristics give natural articular cartilage its excellent lubricative function. To improve the quality of artificial joints, the characteristics of the implant material surface and the synovial macromolecules must be considered. Show more

Keywords: Confocal laser scanning microscopy (CLSM), lubrication mechanism, liquid crystal, articular cartilage, artificial joint material

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 4, pp. 429-437, 2003

Authors: Dargahi, Javad | Najarian, Siamak | Amiri, Shahram

Article Type: Research Article

Abstract: The aim of this research was to investigate the optimization of the geometry of an UHMWPE type of knee implant in the sagittal plane with minimum amount of wear. Finite element analysis has been used to analyze our proposed 780 models consisting of different design parameters. Maximum stress occurring in the whole tibial component, on the surface or subsurface of the plate, was considered as a design parameter to evaluate the wear condition. By avoiding the small contact area and high stresses in the tibial part, the maximum safe flexion angles have been determined. Other effective design factors such as …implant stability, roll back distance, patella lever arm, and minimum bone resection have also been considered. Taking into account the variable parameters in the geometry of the implant parts, all possible models for the femoral component, which is made from metal, and the tibial component, which is made from UHMWPE, have been built in ANSYS and analyzed in the sagittal plane. By considering the effective mechanisms of wear in polyethylene, the results of the analyses were used to find the optimized geometry of a knee implant. This is the model, which is expected to experience the minimum wear, besides having some other properties of an ideal knee prosthesis. Show more

Keywords: Knee implant, optimization, FEA, wear, stability

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 4, pp. 439-449, 2003

Authors: Ozeki, K. | Mishima, A. | Yuhta, T. | Fukui, Y. | Aoki, H.

Article Type: Research Article

Abstract: Hydroxyapatite (HA) was coated onto titanium substrates using radio frequency sputtering, and the coated HA films were crystallized in an autoclave at 110°C using a low temperature hydrothermal method. The crystallite size, the Ca/P ratio, and the surface of the films were observed using XRD, EDS, and SEM, respectively. An immersion test was carried out in physiological saline solution, and the film‐to‐substrate adhesion strength was measured using a pull‐out test. From the XRD patterns, a sputtered film subjected to the hydrothermal treatment had crystallized after 24 h, and the crystallite size increased from 38.0±8.7 to 81.4±19.1 nm. In immersion tests, …an as‐sputtered film completely dissolved after 1 d, whereas a sputtered film subjected to the hydrothermal treatment survived to 18.7±5.8% of the initial film thickness after four weeks. In pull‐out tests, the adhesion strength of the sputtered film to the substrate increased from 1.9±0.2 to 5.3±1.6 MPa after the hydrothermal treatment. A sputtered film subjected to the hydrothermal treatment and a plasma‐sprayed coating on titanium columns were implanted in the diaphysis of the femora of six adult dogs, and a pull‐out test was carried out after two, four, and 12 weeks. The sputtered film showed higher bone bonding strength than the plasma‐sprayed coating at any period. Show more

Keywords: Sputtering, hydroxyapatite, crystallization, hydrothermal, bone bonding strength

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 4, pp. 451-463, 2003

Article Type: Other

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 4, pp. 465-470, 2003

Article Type: Other

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 4, pp. 471-472, 2003