Mechanical properties and osteoconductivity of new bioactive composites consisting of partially crystallized glass beads and poly(methyl methacrylate)

New bioactive composites consisting of partially crystallized glass beads as inorganic fillers and poly(methyl methacrylate) (PMMA) as an organic matrix were developed. Two kinds of partially crystallized glass beads, designated Cry820 and Cry850, were newly prepared by the heating of MgO-CaO-SiO2-P2O5 glass at 820 and 850degreesC, respectively. The glass beads were mixed with PMMA to form two new composites designated Cry820C and Cry850C, respectively. The goal of this study was to produce a highly osteoconductive and mechanically strong composite cement with these new fillers. A previously reported composite cement designated AWC, which was composed of apatite- and wollastonite-containing glass ceramic (AW-GC) as a powder filler and the same PMMA polymer used in the new composites, was used as a reference material. The quantity of filler added to each composite was 70 wt %. The bending strength of Cry820C was significantly higher than that of Cry850C. Composites were packed into intramedullary canals of rat tibiae to evaluate their osteoconductivity, a's determined by an affinity index. The affinity index, which equaled the length of bone in direct contact with the composite surface expressed as a percentage of the total length of the composite surface, was calculated for each composite. The rats were euthanized at 4, 8, and 25 weeks after implantation. At each time interval studied, Cry820C showed a significantly higher affinity index than AWC up to 25 weeks after implantation. Cry850C showed a significantly higher affinity index than AWC up to 8 weeks and a higher affinity index than AWC at 25 weeks, although the difference was not significant. The values for each composite increased significantly with time up to 25 weeks. Our study revealed that the higher osteoconductivity of the new composites was due to the larger quantity of the glassy phase of the crystallized glass beads at the composite surface and the lower solubility of the PMMA powder to methyl methacrylate monomer. In addition, the spherical shape of the crystallized glass beads gave the new composites strong enough mechanical properties to be useful under weight-bearing conditions. The new composites show promise as alternatives, with improved properties, to conventional PMMA bone cement. (C) 2002 Wiley Periodicals, Inc.