Incorporation of polylactide-polyglycolide in a cortical defect: neoangiogenesis and blood supply in a bone chamber.

Erodible polymers are an alternative to metals for fracture fixation (for example, in the malleolus) and for maxillofacial reconstruction. In this study, the vascular response to eroding polylactide-polyglycolide copolymer threads was observed chronically in a bone chamber implant, with use of intravital microscopy. A bone chamber implant loaded with 100 microns thick polylactide-polyglycolide threads was implanted into the right tibia in 15 mature female New Zealand White rabbits. Periodic intravital microscopic observations were performed from the third to the tenth or twelfth week after implantation. Vascularization, blood flow, and trabecular growth into the chambers from the medial cortex were recorded on videotape and analyzed using digital image processing. A statistically significant delay of neo-osteogenesis in the presence of this copolymer was described in an earlier report. The present report describes the measures of neoangiogenesis and blood supply; there was a significant delay in neoangiogenesis. It is suggested that both delayed angiogenesis and osteogenesis were secondary consequences of the macrophage response to slowly eroding poly-L-lactide crystal nanoparticles and the influence of reduced nutrient exchange. The lesser effect on blood supply and vascular volume fraction was seen to be linked to the slowing down of angiogenesis, as the latter allowed vessels to mature, with a widening of their calibers. This homeostatic adjustment was interpreted as being only partially successful in restoring control levels of oxygen delivery, because resulting increases in vessel surface area did not reach control levels. Thus, in the presence of eroding polylactide-polyglycolide, the oxygen supply and extravasation of other nutrients may be below normal during healing phases when the need is critical.