Bio-Medical Materials and Engineering - Volume 11, issue 1

Authors: Hedia, H.S.

Article Type: Research Article

Abstract: It is acknowledged that bone resorption and fatigue fracture of cement in total hip replacement may cause feature problems. The solution is frequently sought associated with the stiffness of cement and stem. The purpose of this paper is firstly to describe the effect of changes in modulus of elasticity of the cement material for the implanted prosthesis on the fatigue notch factor (Kf ). The paper further describes a method of numerical optimisation to determine the optimal stiffness characteristics of cement and stem materials, which minimises the probability of fatigue fracture of cement at all interfaces with the stem …and the bone, while limiting the amount of bone resorbed. The parameters describing the elastic moduli of cement and stem were considered as design variables. The method was applied to an equivalent 2D finite element model of femoral hip replacement in combination with an optimisation procedure using the ANSYS program. The results of the first study suggest that lower modulus of elasticity of cement material decreases Kf in the cement at all interfaces and proximal bone while higher values increase Kf . For the second aim, Young's moduli of about 0.6 and 22 GPa are optimal for cement and stem materials, respectively. These characteristics decreased the probability of fatigue fracture of cement at all interfaces with the stem and the bone as a result of decreasing Kf in cement at all interfaces, while limiting the amount of bone resorbed as a result of increasing Kf in the proximal bone. Show more

Keywords: Cement, stem, hip replacement, finite element, optimisation, fatigue notch factor

Citation: Bio-Medical Materials and Engineering, vol. 11, no. 1, pp. 1-10, 2001

Authors: Otsuka, M. | Fujita, H. | Nakamura, T. | Kokubo, T.

Article Type: Research Article

Abstract: The purpose of this study was to elucidate the effect of amount of ceramic cement powder on drug release from bioactive bone cement. The associated bone‐bonding strength was also investigated. The bioactive bone cement under investigation consisted of bisphenol‐α‐glycidyl methacrylate (Bis‐GMA), triethylene‐glycol dimethacrylate (TEGDMA) resin and a combination of apatite‐ and wollastonite‐containing glass‐ceramic (A‐W GC) powder. A‐W GC powder (50%, 70% and 80% w/w) containing 5% cephalexin (CEX) powder hardened within 5 min after mixing with Bis‐GMA/TEGDMA resin. The compressive strength of the cement with or without drug increased with increasing the amount of ceramic powder. The compressive strength of …the 80% ceramic cement without the incorporation of cephalexin was 194 MPa. This compressive strength was about 3 times higher than that for polymethylmethacrylate cement. After the cement was implanted in the proximal metaphysis of the tibiae of male rabbits, the failure load for the cement was found to increase with increasing of the amount of ceramic powder. This finding suggested that the cement formed a bonding with bone. In vitro CEX release from bioactive bone cement pellets in a simulated body fluid at pH 7.25 and 37○ C continued for more than 2 weeks. Drug release profile followed the Higuchi equation initially, but not at later stages. The drug release rate increased with increasing amount of ceramic powder in the mixture. Since the pore volume of the cement increased with increasing of amount of ceramic powder, the drug diffused in the pores between the ceramics particle and polymer matrix. As hydroxyapatite precipitated on the cement surface, the drug release rate decreased, as observed at the later release stage. These results suggest that varying the amount of ceramic powder in the cement system could control the drug release rate from bioactive bone cement. Show more

Keywords: Antibiotics, cephalexin, bioactive glass ceramics, bone cement, Bis‐GMA resin, drug delivery system

Citation: Bio-Medical Materials and Engineering, vol. 11, no. 1, pp. 11-22, 2001

Authors: Endo, M.M. | Barbour, P.S.M. | Barton, D.C. | Fisher, J. | Tipper, J.L. | Ingham, E. | Stone, M.H.

Article Type: Research Article

Abstract: The wear debris generated from ultra high molecular weight polyethylene (UHMWPE) have been recognised as one of the major causes of failure in total hip replacements (THR). It is essential to reduce the wear debris generated from UHMWPE acetabular cups in order to minimise this problem. Debris in the submicron size range is believed to have greater osteolytic potential [1]. It is now known that crosslinked UHMWPE acetabular cups have reduced volumetric wear rates but little is known about the influence of crosslinking on the size and morphology of the wear debris. In this study, the wear of grade GUR …1020 crosslinked (vacuum gamma irradiated), GUR 1120 crosslinked (acetylene enhanced irradiated) and non cross linked (ethylene oxide sterilised) GUR 1020 UHMWPE was compared in multidirectional pin‐on‐plate wear tests under three different counterface conditions (smooth, isotropically rough and scratched counterfaces). Multidirectional motion was chosen because this motion was closer to the relative motion in the natural hip. From this study, better wear resistance of crosslinked UHMWPE compared with non‐crosslinked UHMWPE was demonstrated for the smooth counterface conditions. However, in the rough and scratched counterface conditions, the vacuum gamma irradiated crosslinked material produced significantly higher wear rates than the non‐crosslinked material. The analysis of the wear debris showed that the majority of the volume of the acetylene enhanced crosslinked UHMWPE wear debris was in the most biologically active size range (0.1 to 0.5 μm). In contrast, the non‐crosslinked material and the vacuum gamma irradiated crosslinked material had a greater proportion of the volume of the debris in the larger size ranges which are less biologically active. This has important implications for its osteolytic potential. Show more

Citation: Bio-Medical Materials and Engineering, vol. 11, no. 1, pp. 23-35, 2001

Authors: Voice, A.M. | Vale, M.C. | Fisher, J.

Article Type: Research Article

Abstract: The depth profile of oxidation index and gel fraction has been measured for two silane crosslinked poly(ethylene) (SXLPE) acetabular cups (one gamma irradiated in air, and one non‐irradiated, both with a shelf‐life of 13 years) and for two UHMWPE components (one gamma irradiated in air and one non‐irradiated, with shelf‐lives of 13 and 7 years, respectively). Only the irradiated UHMWPE exhibited any variation in these properties with depth. The oxidation profile (maximum 1 mm below surface) has been explained to result from reduced levels of diffused oxygen with depth, giving rise to a balance of alkyl and peroxyl radicals (and …hence maximum carbonyl production) just below the surface. The gel fraction profile (maximum 4 mm below surface) is also attributed to the lower levels of diffused oxygen with depth, causing crosslinking to dominate in the bulk and chain scission to dominate at the surface. The resistance to oxidative degradation in the non‐irradiated SXLPE was attributed to the use of antioxidants in the polymer processing. Show more

Citation: Bio-Medical Materials and Engineering, vol. 11, no. 1, pp. 37-41, 2001

Authors: Banerjee, R. | Bellare, Jayesh

Article Type: Research Article

Abstract: The effects of calcium, in the form of calcium chloride, at concentrations of 5 and 20 mM, were studied on the surface properties of physiologic relevance to specialised biomaterials which replace lung surfactant in Respiratory Distress Syndrome. The dynamic surface pressure, re‐spreading ratio, compressibility, hysteresis area and recruitment index of pure films of the main phospholipids of pulmonary surfactant namely dipalmitoyl phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine and of binary mixed films of these phospholipids in the ratio of 2 :3 were studied both in the presence and absence of calcium by in vitro analysis using a Wilhelmy balance. Surface excess films, of each …of the surfactant systems, with initial concentration 15 Å2 molecule were compressed at the rate of 50 seconds/cycle past collapse till a compression ratio of 4 :1. The presence of 5 mM calcium caused a significant decrease in compressibility (p<0.05 Mann–Whitney U test) of all the surfactant monolayer films. No further benefit was obtained by adding 20 mM calcium over that of 5 mM calcium. A significant beneficial effect of calcium (p<0.05 Mann–Whitney U test) on film stability was observed when analysing the materials in a pulsating bubble surfactometer, in which liposomal suspensions of 1% concentration in the presence of 5 mM calcium were pulsated at a high frequency of 40 cycles per minute, corresponding to the respiratory frequency of neonates. The ultrastructure of the liposomal suspensions were also studied using cryogenic scanning electron microscopy and longitudinal micro‐tubular structures were found on addition of 5 mM calcium, which could have resulted in the improved performance of the exogenous surfactants with respect to compressibility and stability. Show more

Keywords: Surtactant, calcium, Wilhelmy balance, pulsating bubble surfactometer

Citation: Bio-Medical Materials and Engineering, vol. 11, no. 1, pp. 43-53, 2001

Authors: Shibata, Hideyuki | Nagaoka, Masato | Takagi, Itsuko‐Kimura | Hashimoto, Shusuke | Aiyama, Ritsuo | Yokokura, Teruo

Article Type: Research Article

Abstract: This study attempted to enhance the anti‐ulcer activity of fucoidan from Cladosiphon okamuranus TOKIDA by chemical modification with a hydrophobic group. The suitable number of fucose residues in the effective compound was also clarified to obtain a compound of constant quality. Degraded fucoidans were coupled with several hydrophobic groups via Schiff bases, and their anti‐ulcer activities were determined by acetic acid‐induced ulcer models in rats. Size‐fractionated oligofucose was also modified and assayed for anti‐ulcer activity. Among the modified oligofucoses, only the oligofucose‐dodecylaniline combination (OFDA) significantly promoted ulcer healing. The effective dose was 0.2 mg/kg/d. The most suitable number of fucose …residues in the compound for the anti‐ulcer activity was determined to be around 12. We succeeded in enhancing the anti‐ulcer activity of Cladosiphon fucoidan by modification with dodecylaniline. The activity of this compound was comparable or greater than that of typical anti‐ulcer agents. By determination of the optimal OF chain length for the anti‐ulcer activity of OFDA, it became possible to obtain OFDA of constant quality. Show more

Keywords: Cladosiphon okamuranus TOKIDA, oligofucose, dodecylaniline, gastric ulcer

Citation: Bio-Medical Materials and Engineering, vol. 11, no. 1, pp. 55-61, 2001

Authors: Ozeki, K. | Yuhta, T. | Aoki, H. | Nishimura, I. | Fukui, Y.

Article Type: Research Article

Abstract: Hydroxyapatite was coated with 1 μm thickness on titanium columns of a length of 10 mm, an outer diameter of 4.0 mm by radio frequency magnetron sputtering. The hydroxyapatite coating titanium columns were implanted in the diaphysis of femora of 3 adult dogs, and push‐out test was carried out after 2, 4 and 12 weeks of implantation using a testing machine. The interface of bone/column was observed histologically after the test. At 12 weeks the push‐out strengths of coating and non‐coating columns were 3.5 and 1 MPa, respectively. Histological observation indicated a formation of thin connective tissue with 5∼30 μm …thickness at the interface of the bone/column. No inflammation was observed during the implantation periods. Show more

Keywords: Hydroxyapatite, sputtering, coating, push‐out testing

Citation: Bio-Medical Materials and Engineering, vol. 11, no. 1, pp. 63-68, 2001