The biocompatibility of biodegradable glycine containing polyphosphazenes: A comparative study in bone

Polyphosphazenes have gained considerable attention as biomaterials for use in tissue engineering and orthopaedic reconstruction. In this paper we examined the polyphosphazenes' in vivo biocompatibility and degradation by studying their ability to repair bone in a rabbit metaphyseal distal femur defect model. Matrices constructed from poly[(50% p-methylphenoxy)-(50%ethyl glycinato) phosphazene] (PPHOS-50) and poly[bis(ethyl glycinato) phosphazene] (PPHOS-100), were surgically implanted into a metaphyseal rabbit defect of the distal femur as constructs for tissue regeneration. Poly(lactide-co-glycolide) (PLAGA) implants, which are the biodegradable polymers most widely used clinically, and defects without polymers were used as controls in this experiment. Histological studies demonstrated that both PPHOS-50 and PPHOS-100 appeared to support bone growth comparable to the control PLAGA. By 12 weeks, femurs with polyphosphazene implants showed evidence of bone in-growth and a mild fibrous response. The PPHOS-50 implants were found to have a local tissue response that was more favorable than PPHOS-100 and similar to PLAGA. Biodegradable polyphosphazenes are a novel class of polymers which have been observed to facilitate bone growth in vivo.