Calvarial bone repair with porous D,L-polylactide.

Bone is a storehouse of biologic factors enabling it to regenerate without scar formation. Recombinant technology has made many of these factors available in significant quantity for therapeutic applications. However, a system to deliver recombinant bone-regenerating factors is needed. Biodegradable, biocompatible polymers have shown promise for delivering bone regenerative factors, such as bone morphogenetic protein. The polymer we selected to investigate was racemic D,L-polylactide. Our immediate objective was to engineer porous D,L-polylactide to promote bone ingrowth (osteoconduction). We tested the hypothesis that porous D,L-polylactide implanted in a standard intraosseous calvarial wound would not hinder but would support bone regeneration. Therefore porous polylactide disks (65% void volume) were manufactured with pores < or = 100 microns, < or = 200 microns, and < or = 350 microns; implanted in rabbits' calvariae, and retrieved 1, 2, 4, and 6 months after insertion. Quantitative histomorphometry revealed a possible relationship in the amount of bone ingrowth with increasing pore size over time. The D,L-polylactide disks < or = 350 microns had the greatest quantity of bone ingrowth (< or = 0.05). However, a disturbing finding was the multinucleated giant cell response associated with all implanted disks. We speculate these cells may have produced an inhospitable environment stifling osteoconduction. Consequently, postsynthesis engineering refinements of D,L-polylactide to eliminate the giant cell response are crucial before loading with bone morphogenetic protein.