In Vivo Aging Test for Bioactive Bone Cements Composed of Glass Bead and PMMA

The degradation of a bioactive bone cement (GBC), consisting of bioact ive MgO-CaO-SiO2-P2O5-CaF2 glass beads and high-molecular-weight polymethyl methacrylate (hPMMA) was evaluated in an in vivo aging test. Hardened rectangular specimens were prepared from two GBC formulations (containing 50%w/w [GBC50] or 60%w/w [GBC60] bioactive beads) and a conventional PMMA bone cement control (CMW-1). Initial bending stre ngths were measured using the three-point bending method. Specimens of all three cements we re then implanted into the dorsal subcutaneous tissue of rats, removed after 3, 6 or 12 months, and test ed for bending strength. The bending strengths (MPa) of GBC50 at baseline (0 months), 3, 6 and 12 mont hs were 136 ±1, 119±3, 106±5 and 104±5, respectively. Corresponding values were 138 ±3, 120±3, 110±2 and 109±5 for GBC60, and 106 ±5, 97±5, 92±4 and 88±4 for CMW-1. Although the bending strengths of all three cements decreased significantly ( p<0.05) from 0 to 6 months, those of GBC50 and GBC60 did not change significantly thereafter, whereas that of CMW-1 declined significantly between 6 and 12 months. Thus, degradation of GBC50 and GBC60 does not appear to continue after 6 months, whereas CMW-1 degrades progressively over 12 months. Moreover, the bending strengths of GBC50 and GBC60 (especially GBC60) were significantly higher than that of CMW-1 throughout. We believe that GBC60 is strong enough for use under weight-bearing conditions and that its mechanical strength is retained in vivo.