Poly(Thioketal Urethane) Autograft Extenders in an Intertransverse Process Model of Bone Formation

Iliac crest autograft (AG) is the gold standard for bone grafting. Due to the limited supply of autograft, synthetic materials such as ceramics and polymers have been proposed as AG extenders to minimize the volume of AG required for induction of new bone formation. However, the feasibility of reactive polymers for use as settable AG extenders has not been previously investigated. In this study, a reactive oxygen species-degradable poly(thioketal urethane) (PTKUR) was evaluated as a settable AG extender. AG was anticipated to enhance infiltration of cells into the defect and induce new bone formation. Histological analysis of a preliminary study in a rat femoral segmental defect model showed that cells infiltrated PTKUR/AG implants at 4 weeks. In a second experiment, implantation into an intertransverse process model of bone formation showed bone remodeling from the superior and inferior transverse processes. Histological analysis combining data from stains and fluorochrome injections showed lamellar bone formation ongoing near the base of the transverse processes after 8 weeks. Similar findings were observed for a second group, in which 35% of the AG was replaced with calcium phosphate granules. These observations highlight the potential of PTKUR for use as a settable AG extender. The development of autograft extenders is a significant clinical need in bone tissue engineering. We report new settable poly(thioketal urethane)-based autograft extenders that have bone-like mechanical properties and handling properties comparable to calcium phosphate bone cements. These settable autograft extenders remodeled to form new bone in a biologically stringent intertransverse process model of bone formation that does not heal when treated with calcium phosphate bone void fillers or cements alone. This is the first study to report settable autograft extenders with bone-like strength and handling properties comparable to ceramic bone cements, which have the potential to improve treatment of bone fractures and other orthopedic conditions.