Mechanically Robust Shape Memory Polyurethane Nanocomposites for Minimally Invasive Bone Repair

Shape memory polymers (SMPs) have great potential utility in the area of minimally invasive surgery; however, insufficient mechanical properties hinder their applications for bone defect repair, particularly in high load-bearing locations. In this study, hydroxyapatite (HA)/reduced graphene oxide (rGO) nanofillers were incorporated into a shape memory polyurethane (SMPU) to enhance its mechanical properties. Then the nanocomposite was further modified using arginyl-glycyl-aspartic acid (RGD peptide) to improve its cellular adhesion toward promoting neotissue formation and integration with surrounding bone tissue. The physical and biological properties in terms of their chemical structure, surface wettability, mechanical behaviors, shape memory performance, and cell adhesion were systematically investigated. The results demonstrated that the multimodified SMPU/HA/rGO/RGD nanocomposite significantly enhanced mechanical properties (e.g., ∼200% increase in Young's modulus and >300% enhancement in tensile strength compared with the unmodified SMPU), which might be attributed to the intercalated structure and metal affinity inside the nanocomposite. Adhesion of rabbit bone mesenchymal stem cells was clearly demonstrated on an RGD-immobilized SMPU nanocomposite surface. With an excellent shape memory behavior (e.g., 97.3% of shape fixity ratio and 98.2% of shape recovery ratio), we envision that our SMPU/HA/rGO/RGD nanocomposite can be implanted into a bone defect with a minimally invasive surgery.