Calvarial Bone Repair with Porous D,L-Polylactide

Abstract

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 ≤ 100 μm, ≤ 200 μm, and ≤ 350 μm; 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 ≤350 μm had the greatest quantity of bone ingrowth (≤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.