Self-deploying shape memory polymer scaffolds for grafting and stabilizing complex bone defects: A mouse femoral segmental defect study

Treatment of complex bone defects places a significant burden on the US health care system. Current strategies for treatment include grafting and stabilization using internal metal plates/screws, intramedullary rods, or external fixators. Here, we introduce the use of shape memory polymer (SMP) materials for grafting and adjunct stabilization of segmental defects. Self-deploying SMP grafts and SMP sleeves capable of expanding and contracting, respectively, under intraoperative conditions were developed and evaluated in a mouse segmental defect model in vivo. Integration between grafts/sleeves and native bone was assessed using x-ray radiography, microcomputed tomography, and torsional mechanical testing. We found that SMP grafts were able to integrate with the native bone after 12 weeks, maintain defect stability, and provide torsional mechanical properties comparable to an allograft alone treatment; however no gross de novo bone formation was observed. SMP sleeves did not inhibit bony bridging at the margins, and limbs treated with a sleeve/allograft combination had torsional mechanical properties comparable to limbs treated with an allograft alone. In vitro torsional and bending tests suggest sleeves may provide additional torsional stability to defects. Incorporation of shape memory into synthetic bone graft substitutes and adjunct stabilization devices is anticipated to enhance functionality of synthetic materials employed in both applications.