Bio-Medical Materials and Engineering - Volume 14, issue 1

Authors: Murdoch, A.H. | Mathias, K.J. | Shepherd, D.E.T.

Article Type: Research Article

Abstract: When testing medical implants it is very important to be able to test the implant using a suitable material. In the case of orthopaedic implants the optimum material is bone. Beech wood is considered a suitable substitute for bone as it has a similar Young's modulus in tension. Although it is widely used, no actual comparison of the two materials has been undertaken. The aim of this study was to compare the material properties of beech wood and cortical bone using conventional compression tests. Cortical bone samples 4 mm in diameter and 20 mm in length, were prepared from the …tibia of an amputated leg. Beech wood samples were prepared to the same specifications. In compression, the Young's modulus for cortical bone was found to be 27±9.9 GPa (mean ± standard deviation) and for beech wood 2.6±1.7 GPa. The failure load for cortical bone was 911±207 N and 732±62 N for beech wood. Although beech wood has been used as a substitute for bone in some studies, this study has shown that there are significant differences in the properties of the two materials when they are subjected to compression. Show more

Keywords: Beech wood, cortical bone, compression, Young's modulus

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 1-4, 2004

Authors: Wang, C.X. | Zhou, X. | Wang, M.

Article Type: Research Article

Abstract: The mechanism of bone‐like apatite formation on the surface of pure titanium pretreated with NaOH solution is still being investigated. The apatite formation may depend on the solution that is used. In the present study, several types of solutions such as simulated body fluid (SBF), calcium aqueous solution (CAS), and phosphate aqueous solution (PAS) were used to investigate bone‐like apatite formation on alkali‐treated titanium. In order to observe the effect of hydrolysis on the apatite formation, experiments of pretreated titanium immersed in distilled water before the immersion in SBF were also conducted. The results showed that the mechanism of apatite …formation was the hydrolysis reaction of sodium titanate which induced the apatite formation. The pre‐precipitation of either calcium or phosphate could prevent the apatite formation on the surface of alkaline treated titanium. Show more

Keywords: Alkaline treatment, pure titanium, bone‐like apatite

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 5-11, 2004

Authors: Wu, John Z. | Brumfield, Anne | Miller, Gerald R. | Metheny, Rebecca | Cutlip, Robert G.

Article Type: Research Article

Abstract: Tendon injuries may result in variations of its mechanical properties. The published data of the tendon stiffness of small animals, such as mouse and rat, are exclusively obtained by measuring grip‐to‐grip (g‐t‐g) displacement. Local strain concentration and relative sliding of the specimens in the clamps might significantly affect the measured tendon deformation. In the present study, the mechanical properties of the rat tibialis anterior tendon measured using the proposed tendon mark method were compared to those evaluated using the g‐t‐g displacement method. Five male Sprague Dawley rats (∼418 g) were used in this study. For the proposed method, reference marks …were made on the tendons using permanent ink. A microscope video system was customized to observe and record the tendon deformation. Pattern recognition software was developed to obtain the displacement time‐histories of the reference marks. The distance between the grips was approximately 7 mm; and the distance between the reference marks used for the data processing was approximately 5 mm. The cross‐section areas of the specimens were measured using a custom‐made slot gauge and by applying a constant compressive stress (0.15 MPa). The tendons were clamped between two custom‐made metal grips and stretched on a testing machine at a constant speed (1 mm/s) up to failure. Throughout the tests, the tendon specimens were submerged in a PBS bath at 22°C. The deformation of the specimens was evaluated using the g‐t‐g displacement method and the proposed method. The stress/strain curves obtained by using the g‐t‐g displacement can be characterized by an initial toe zone, a quasi‐linear zone, and a final failure stage. The stress/strain curves determined using the proposed method are quite different from those obtained using the g‐t‐g displacement: it has a smaller toe zone and a stress‐hardening transition, over which the tendon stiffness increases dramatically with the increasing strain. The tendon stiffness measured by using the g‐t‐g displacement method may underestimate the actual mechanical properties of tendon by approximately 43%. Show more

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 13-22, 2004

Authors: Yang, Cheng‐Huei | Luo, Ching‐Hsing | Yang, Cheng‐Hong | Chuang, Li‐Yeh

Article Type: Research Article

Abstract: Morse code is now being harnessed for use in rehabilitation applications of augmentative‐alternative communication and assistive technology, including mobility, environmental control and adapted worksite access. In this paper, Morse code is selected as a communication adaptive device for disabled persons who suffer from muscle atrophy, cerebral palsy or other severe handicaps. A stable typing rate is strictly required for Morse code to be effective as a communication tool. This restriction is a major hindrance. Therefore, a switch adaptive automatic recognition method with a high recognition rate is needed. The proposed system combines counter‐propagation networks with a variable degree variable step …size LMS algorithm. It is divided into five stages: space recognition, tone recognition, learning process, adaptive processing, and character recognition. Statistical analyses demonstrated that the proposed method elicited a better recognition rate in comparison to alternative methods in the literature. Show more

Keywords: Morse code, adaptive signal processing, counter‐propagation network, least‐mean‐square algorithm

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 23-32, 2004

Authors: Lewis, Gladius | Janna, Si

Article Type: Research Article

Abstract: The goal of the present work was to investigate the influence of the viscosity classification of an acrylic bone cement on its in vitro fatigue performance, as determined in fully‐reversed tension–compression (±15 MPa) fatigue tests. The test matrix comprised six commercially available bone cements [Orthoset® 1, (OS1), Orthoset® 3 (OS3), Cemex® RX (CRX), Cemex® XL (CXL), Palacos® R (PR) and Osteopal® (OP)], two methods of mixing the cement constituents (hand‐mixing and vacuum‐mixing), two methods of fabricating the test specimens (direct molding and molding followed by machining), two specimen cross‐sectional shapes (rectangular or “flat” and circular or “round”), and four test …frequencies (1, 2, 5, and 10 Hz). In total, 185 specimens, distributed among 20 sets, were tested. The test results (number of fatigue stress cycles, Nf ) were processed using the linearized transformation of the three‐parameter Weibull distribution, whence estimates of the Weibull mean, NWM , were obtained. Statistical analysis of the ln Nf results (Mann–Whitney test; α<0.05) and a comparison of the NWM estimates for specimen sets in which the formulations have essentially the same composition but different viscosity classification (namely, OS1 versus OS3, CRX versus CXL, and PR versus OP) showed that, in the majority of the comparisons carried out, the viscosity classification of a bone cement does not exert a significant influence on its in vitro fatigue performance. Show more

Keywords: Acrylic bone cement, cement viscosity, fatigue life, three‐parameter Weibull equation

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 33-42, 2004

Authors: Lewis, Gladius

Article Type: Research Article

Abstract: The study utilized the geometric element analysis method to investigate the effect of three variables (head diameter, d; head material; and neck material) on the y‐direction displacement, due to fretting (Δ), in a model of the head‐neck connection in a modular version of the femoral component of a hip implant, subjected to a resultant hip joint force only. It was found that while d and neck material exerted a strong effect on Δ, the head material had practically no such effect. The implications of this finding for design and materials selection issues for this connection are discussed.

Keywords: Hip implant, fretting, geometric element modeling and analysis

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 43-51, 2004

Authors: Chen, X. | Aoki, H. | Fukui, Y.

Article Type: Research Article

Abstract: We have investigated the effect of exercise on the bone strength, bone mineral density (BMD), and metal content in rat femurs. Five Wister rats acting as an exercised group (E group) were exercised at intervals on a treadmill every day for four weeks. Another five rats were fed in a cage, acting as a control group (C group), without any exercise. After four weeks, the bend strength, Young's modulus, BMD value, and metal content of the femurs were measured using a three‐point bend test, Dual‐Energy X‐ray Absorptiometry (DEXA), and chemical analysis. The bend strength of the E group was 101±5 …MPa, and that of the C group was 86±7 MPa. The Young's modulus was 1.16±0.03 GPa for the E group, and 0.98±0.06 GPa for the C group. The BMD values were 0.179±0.002 g/cm2 for the E group, and 0.166±0.002 g/cm2 for the C group. The Ca concentration was 230,600 ± 1,500 μg/g for the E group, and 223,000 ± 2,700 μg/g for the C group. The Zn concentration was 160 ± 7 μg/g for the E group, and 188 ± 8 μg/g for the C group. Show more

Keywords: Exercise, rat femurs, bone strength, BMD, metal mineral content

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 53-59, 2004

Authors: Najman, S. | Savic, V. | Djordjevic, Lj. | Ignjatovic, N. | Uskokovic, D.

Article Type: Research Article

Abstract: Histopathologic analysis of the tissue with HAp/PLLA implants was made and the leukocyte formula and chemiluminescence response of peritoneal phagocytes 2, 7 and 12 weeks after intraperitoneal implantation studied. Implants were made of HAp/PLLA biocomposites with PLLA molecular weights of 50,000 (HAp/PLLA(50)) and 430,000 g/mol (HAp/PLLA(430)) and of crushed devitalized femur bone of a young Wistar rat. Leukocyte formula and chemiluminescence of peritoneal phagocytes showed no systemic inflammatory response. The studied implants caused locally weak inflammatory reaction. The resorption of implants ranges in intensity (polymer resorption, i.e. disappearance rate), from the highest with the bone implants, low with HAp/PLLA(50), to …the lowest with the HAp/PLLA(430) implants. Good resorption of the biocomposites and its mutual ingrowth with connective tissue prove their good biocompatibility. Show more

Keywords: Hydroxyapatite/poly‐L‐lactide composite biomaterial, bone implants, in vivo, intraperitoneal implantation

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 61-70, 2004

Authors: Haher, Thomas | Ottaviano, Danielle | Lapman, Peter | Goldfarb, Brian | Merola, Andrew | Valdevit, Antonio

Article Type: Research Article

Abstract: Use of 4.0 mm and 5.0 mm steel rods have resulted in proximal screw pullout. Titanium rods, which encompass a reduced yield point, may increase the effective stiffness of the construct when used with segmental anchors. Seven human thoracic spines were loaded in axial compression, axial torsion, flexion, extension, and lateral bending. Testing was performed on intact, discectomy and simulated bony fusion specimens. Specimens were randomly instrumented with 4.0 mm and 5.0 mm steel, and 4.5 mm CP Ti rods. In compression and torsion, the intact spine demonstrated increased stiffness with respect to all instrumentation employed in a discectomy condition. …No significant differences between the intact and the instrumentation systems were detected for torsion or compression under simulation of fusion. Under flexural loading, no significant differences were detected between the intact specimen and the instrumentation systems. When used in conjunction with segmental force anchors, the use of CPTi rods which posses reduced yield points can provide sufficient rigidity as compared to stainless steel rods of comparable diameter. Implants of reduced yield point will permit permanent deformation with low force. Screw pullout may result when high yield materials are employed in conjunction with anchors. Show more

Keywords: Stiffness, titanium, steel, thoracic, loading

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 71-77, 2004

Authors: Haher, Thomas R. | Ottaviano, Danielle | DeFrancis, Jason G. | Merola, Andrew | Valdevit, Antonio

Article Type: Research Article

Abstract: The in vitro biomechanical models using a cadaveric spine specimen have long been used in understanding normal and abnormal functions of spines as well as for strength and stability testing of the spine specimen or spinal construct. Little effort has been made to describe the similarities or differences between UHMWPE and cadaveric models. Eight cadaveric lumbar spines were harvested generating six FSU and three corpectomy models. Six UHMWPE blocks were fabricated to form FSU and corpectomy models. All were tested intact, with posterior instrumentation, and with anterior instrumentation consisting of Moss‐Miami 4.0 mm stainless steel rods, uni‐axial stainless steel screws …and DePuy Harm's cages. All models were tested in axial compression. The cadaveric model and UHMPWE model yielded axial stiffness values of comparable magnitude with respect to instrumentation applied using the posterior approach (P>0.05). Under an FSU configuration, only in the case of anterior instrumentation without the addition of a Harm's cage did both the cadaveric and UHMPWE models provide comparable axial stiffness results (P>0.05). While in vitro cadaveric models are considered the gold standard for biomechanical testing of the spine, the data suggests that under specific approaches and surgical models UHMWPE can be used to infer mechanical performance of instrumentation in cadaveric material. Show more

Keywords: UHMWPE, stiffness, loading, corpectomy, FSU

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 79-85, 2004

Authors: Chu, K.T. | Oshida, Y. | Hancock, E.B. | Kowolik, M.J. | Barco, T. | Zunt, S.L.

Article Type: Research Article

Abstract: Currently PMMA is the polymer most commonly used as a bone cement for the fixation of total hip prostheses. Ideally, a bone cement material should be easy to handle, biologically compatible, nonsupporting of oral microbial growth, available in the particulate and molded forms, easy to obtain, nonallergenic, adaptable to a broad range of dental and medical applications, in possession of high compressive strength, and effective in guided tissue regenerative procedures. One of the problems associated with the conventional types of bone cement used is their unsatisfactory mechanical and exothermic reaction properties. The purpose of this in vitro study was …to investigate and compare the mechanical properties (three‐point bending strength, energy‐to‐break, and modulus of elasticity) and physical properties (setting time, water sorption, and exothermic heat) of HA/PMMA (HA group) and bovine‐bone originated HA/PMMA (BB group) composites. Composites samples were fabricated by admixing method. It was found that the addition of HA and BB particles increased the water sorption. Generally 10 v/o 20 v/o HA and 0 v/o to 10 v/o BB ratio combinations had significant beneficial effects on the mechanical properties. The heat generated during polymerization was influenced by the different admixtures. More than 40 v/o HA and 40 v/o BB should be mixed into PMMA to reduce the peak temperature. Overall evaluation indicated that the BB group had better properties than the HA group. Show more

Keywords: Hydroxyapatite, bone cement, PMMA, composites, mechanical strength, temperature raise, bovine‐bone‐originated hydroxyapatite

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 87-105, 2004

Authors: Hernandez, E.P. | Oshida, Y. | Platt, J.A. | Andres, C.J. | Barco, M.T. | Brown, D.T.

Article Type: Research Article

Abstract: The use of a provisional restoration is an important phase in the treatment of the dental prosthetic patient. A good provisional restoration should satisfy the following requirements: pulpal protection, positional stability, ease in cleaning, accurate margins, wear resistance, dimensional stability, and serve as a diagnostic aid in treatment assessment and esthetics. There is a tendency for discoloration, occlusal wear, and fracture that eventually leads to unnecessary repair. Heat‐processed and reinforced methacrylate‐based resins have been used to improve the mechanical and physical properties of provisional restorations. Among various improvements, the interpenetrating network crosslinked PMMA (IPN) has been shown to have superior …mechanical properties if manufactured through a dough compression molding process at 130°C. However, there have been no published data that relate with the use of this material for fixed provisional restorations. The objective of this study was to compare four methyl methacrylate‐based resins for provisional crowns and bridges with varying processing cycles, including JET [self‐cure], ACRALON [heat‐cured], titanium dioxide filled PMMA [heat‐cured], and IPN [heat‐cured denture tooth resin]. Properties studied included transverse strength, toughness, rigidity, and hardness. From the results of this study the following conclusions can be made: the IPN group may have had a lower degree of conversion as demonstrated by decreased strength, toughness, and hardness data as compared with Acralon. Increasing the polymerization cycle of unmodified Acralon resin causes a significant increase in strength. Show more

Keywords: Interpenetrating network crosslink, PMMA, self‐cure, heat‐cure, mechanical properties, provisional restorations

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 107-122, 2004

Authors: Fu, Weihua | Dai, Jianrong | Hu, Yimin

Article Type: Research Article

Abstract: Using higher energy photons can obtain better target dose uniformity and skin sparing for treating deep lesions, but the effect of lacking lateral scattering in the low‐density lung may degrade the target coverage. To analyze the influence of lateral electronic disequilibrium on the radiation treatment planning for lung cancer, three dimension conformal treatment (3D‐CRT) plans of using 6 MV and 18 MV X‐ray respectively for a lung cancer case have been worked out by using pencil beam algorithm and collapsed cone algorithm provided by Helax‐TMS treatment planning system for the same radiation field arrangement for both energies. Dose volume histogram …(DVH) in target and organs at risk (OARs) are used for comparison of different plans. The study shows that using pencil beam algorithm, the target DVH are similar for 6 MV and 18 MV plan. However, using collapsed cone algorithm that can make account of lateral electron scattering, the target is underdosed. The change is even more pronounced for 18 MV plan. The doses for lung and spinal cord are similar for these two energies and two algorithms. Therefore, for lung cancer, dose calculation algorithm should have the ability of handling accurately the effect of the tissue density heterogeneity. It is better to use the lower‐energy photons (6 MV) than to use the higher‐energy photons (18 MV). Show more

Keywords: Lateral electronic disequilibrium, pencil beam algorithm, collapsed cone algorithm

Citation: Bio-Medical Materials and Engineering, vol. 14, no. 1, pp. 123-126, 2004