Synthesis, mechanical properties, biocompatibility, and biodegradation of polyurethane networks from lysine polyisocyanates

Bone defects, such as compressive fractures in the vertebral bodies, are frequently treated with acrylic bone cements (e.g., PMMA). Although these biomaterials have sufficient mechanical properties for fixing the fracture, they are non-degradable and do not remodel or integrate with host tissue. In an alternative approach, biodegradable polyurethane (PUR) networks have been synthesized that are designed to integrate with host tissue and degrade to non-cytotoxic decomposition products. PUR networks have been prepared by two-component reactive liquid molding of low-viscosity quasi-prepolymers derived from lysine polyisocyanates and poly(epsilon-caprolactone-co-DL-lactide-co-glycolide) triols. The composition, thermal transitions, and mechanical properties of the biomaterials were measured. The values of Young's modulus ranged from 1.20-1.43 GPa, and the compressive yield strength varied from 82 to 111 MPa, which is comparable to the strength of PMMA bone cements. In vitro, the materials underwent controlled biodegradation to non-cytotoxic decomposition products, and supported the attachment and proliferation of MC3T3 cells. When cultured in osteogenic medium on the PUR networks, MC3T3 cells deposited mineralized extracellular matrix, as evidenced by von Kossa staining and tetracycline labeling. Considering the favorable mechanical and biological properties, as well as the low-viscosity of the reactive intermediates used to prepare the PUR networks, these biomaterials are potentially useful as injectable, biodegradable bone cements for fracture healing.