In vivo aging test for a bioactive bone cement consisting of glass bead filler and PMMA matrix.

Abstract

The degradation of a new bioactive bone cement (GBC), comprised of an inorganic filler (bioactive MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) glass beads) and an organic matrix [high-molecular-weight polymethyl methacrylate (PMMA)], was evaluated in an in vivo aging test. Hardened rectangular specimens (20 x 4 x 3 mm) 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 strengths were measured with the use of the three-point bending method. Specimens of all three cements were then implanted into the dorsal subcutaneous tissue of rats, removed after 3, 6, or 12 months, and tested for bending strength. The bending strengths (MPa) of GBC50 at baseline (0 months), 3, 6, and 12 months 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 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. It is believed that GBC60 is strong enough for use under weight-bearing conditions and that its mechanical strength is retained in vivo; however, its dynamic fatigue behavior will need assessment before application in the clinical setting.