Initial biocompatibility studies of a novel degradable polymeric bone substitute that hardens in situ

Clinical management of osseous defects often requires bone grafts. The standard for treatment is autogenous bone harvested from sites such as either the iliac crest or the outer table of the calvaria. In addition to the problem of donor site morbidity and the limited supply of graft material, there is the additional operating time associated with harvesting procedures. A synthetic, bone graft substitute that can match the clinical performance of autogenous bone could alleviate these deficiencies. Therefore, a polymeric bone substitute was developed that consists of a four-armed star polymer of poly(dioxanone-co-glycolide) endcapped at each termini with a biocompatible lysine-based diisocyanate crosslinker. The polymer can be mixed with inorganic fillers such as either hydroxyapatite or tricalcium phosphate to form either injectable or moldable putty. The addition of a catalyst (for example, diethylaminoethanol and water) to the polymer produces a crosslinking reaction causing the combination to harden. This reaction is nontoxic, normo-thermic and can be performed in situ. During the course of the polymerization, carbon dioxide is liberated, producing an interconnected porous network within the implant, suitable for bone ingrowth. This paper will describe a preliminary biocompatibility assay of the bone substitute.