ABSTRACT
A novel composite femoral stem has been developed to match cortical stiffness and achieve fixation by osseointegration with the primary goal to reduce cortical bone loss associated with stress shielding. The femoral stem consists of three distinct material layers: the first is a long carbon fiber (CF) in a polyamide 12 (PA12) polymer matrix (PA12/CF); the second is a PA12/HA (hydroxyapatite) interface; and the third is a plasma-sprayed coating of HA. In vitro studies with MG63 cells indicated that the HA surface supported improved proliferation and differentiation of osteoblast-like cells as determined by alkaline phosphatase activity and osteocalcin production when compared with Ti-6Al-4V (Ti64). In vivo studies comparing the composite and Ti64 rods in the rabbit femur demonstrated significantly higher bone apposition to the composite than Ti64 rods. The results of this study indicate that the invasion of surrounding bone cells and thus osteointegration together with its bone-matching mechanical properties make the PA12/CF/HA stem a promising hip replacement candidate.
Subject(s)
Carbon/chemistry , Coated Materials, Biocompatible/chemistry , Hip Prosthesis , Osseointegration , Alkaline Phosphatase/metabolism , Animals , Carbon Fiber , Cell Adhesion , Cell Line , Cell Proliferation , Cell Survival , Collagen/metabolism , Durapatite/chemistry , Femur/surgery , Femur/ultrastructure , Fibroblasts/cytology , Humans , Male , Mice , Osteoblasts/cytology , Osteoblasts/metabolism , Osteocalcin/metabolism , RabbitsABSTRACT
Hydroxyapatite (HA) and HA-alumina (HA/Al2O3) composites, with Al2O3 contents of 5, 10, 20, and 30%, were synthesized using a wet precipitation method and sintered at 900 and 1300 degrees C. We investigated the effect of sintering temperature and relative concentration of HA and Al2O3 on the chemical composition, surface morphology, and cytotoxicity of the composite powders. The XRD results show that in the 1300 degrees C composites, HA partially decomposed into CaO which combined with Al2O3 to form different calcium aluminates. For the 900 degrees C composites the CaO phase was not detected, though a Ca/P ratio larger than 1.67 measured by XPS suggests that CaO was present in trace amounts. SEM-EDX analysis indicated that the HA microstructure was affected by the sintering temperature, and this HA is present on the surface of Al2O3 particles. The cytotoxicity of the composites was assessed indirectly using the MTT assay. The short-term effect of leachables was quantified by exposing a L929 mouse fibroblast cell line to the degradation products released by the composites after immersion in the cell culture medium. Degradation products were less toxic to L-929 at lower extract concentrations (10, 50%) than at 100% concentration. Cell viability was also influenced by leachable size.
