Osteoconductivity and Mechanical Properties of a New Bioactive Bone Cement

摘要

Osteoconductivity and mechanical properties of a new bioactive bone cement (designated-GBC) consisting of high molecular weight polymethyl methacrylate (PMMA) as an organic matrix and bioactive glass beads as an inorganic filler have been evaluated. The bioactive beads consisting of MgO-CaO-SiO_2-P_2O_5, CaF_2 glass, have been newly designed and a novel PMMA powder was selected. The aim of the present study is to compare GBC's osteoconductivity and mechanical properties with cement consisting of the same matrix as GBC and either apatite- and wollastonite-containing glass-ceramic (AW-GC) powder (designated AWC) or sintered hydroxyapatite (HA) powder (designated HAC) and to examine effects of the amount of the bioactive glass beads filler added to GBC, and to decide the most suitable amount of the filler content The bioactive glass beads added to the cements amounted 30,40,50,60, and 70 wt percent and AW-GC powder and HA powder added to the cements amounted 70 wt percent. Each cement was designated respectively GBC30, 40,50,60,70, AWC70, and HAC70. The bending strength of GBC70 was significantly higher than that of AWC70 and HAC70. The compressive strength and the elastic modulus of bending of GBC increased as the glass beads content increased. The handling property of each GBC was comparable with that of conventional PMMA bone cement. Cements were packed into intramedullar canals of rat tibiae in order to evaluate osteoconductivity determined by an affinity index. Rats were sacrificed at 4 and 8 weeks after operation. The affinity index was calculated for each cement, which equaled the length of bone in direct contact with the cement expressed as a percentage of the total length of the cement surface. At each time interval studied, GBC70 showed a significantly higher affinity index than AWC70 or HAC70. Increasing trend in the affinity index of GBC was found with increasing glass beads filler content. The value for each GBC, AWC70, and HAC70 increased significantly with time up to 8 weeks. Histologically, new bone had formed on each GBC, AWC70, and HAC70 surface within 4 weeks, even on GBC30 coating glass beads at only 30 wt percent. Our study revealed that a higher osteoconductivity of GBC was due to a higher bioactivity of the glass beads at the cement surface and to a lower solubility of the novel PMMA powder to MMA monomer. Since no significant increase of affinity index was indicated between GBC60 and GBC70 and a "low signal layer" observed only at the bone-cement interface of GBC7O might be a sign of degradation, GBC60 was the best from a viewpoint of osteoconductivity. In addition, it was found that a smaller spherical shape and glassy phase of the glass beads gave GBC strong enough mechanical properties. And, in order to keep a higher compressive strength and a lower modulus, GBC60 was the best also from a viewpoint of mechanical properties. In conclusion, GBC60 was the best and showed excellent enough osteoconductivity and strong enough mechanical properties as an alternative with improved properties to conventional PMMA bone cement.