A citric acid-based hydroxyapatite composite for orthopedic implants

We describe a novel approach to process bioceramic microparticles and poly(diol citrates) into bioceramic-elastomer composites for potential use in orthopedic surgery. The composite consists of the biodegradable elastomer poly(1,8-octanediol-citrate) (POC) and the bioceramic hydroxyapatite (HA). The objective of this work was to characterize POC-HA composites and assess the feasibility of fabricating tissue fixation devices using machining and molding techniques. The mechanical properties of POC-HA composites with HA (40, 50, 60, 65wt.%) were within the range of values reported for tissue fixation devices (for POC-HA 65wt.%, S-b = 41.4 +/- 3.1, E-b = 501.7 +/- 40.3, S-c = 74.6 +/- 9.0, E-c = 448.8 +/- 27.0, S-t = 9.7 +/- 2.3, E-t = 334.8 +/- 73.5, S-s = 27.7 +/- 2.4, T-s = 27.3 +/- 4.9, all values in MPa). At 20 weeks, the weight loss of POC HA composites ranged between 8 and 12 wt.%, with 65 wt.% HA composites degrading the slowest. Exposure of POC HA to simulated body fluid resulted in extensive mineralization in the form of calcium phosphate with Ca/P of 1.5-1.7 similar to bone. POC-HA supported osteoblast adhesion in vitro and histology results from POC-HA samples that were implanted in rabbit knees for 6 weeks suggest that the composite is biocompatible. Synthesis of POC-HA is easy and inexpensive, does not involve harsh solvents or initiators, and the mechanical properties of POC-HA with 65 wt.% HA are suitable for the fabrication of potentially osteoconductive bone screws. (c) 2006 Elsevier Ltd. All rights reserved.