Chemically Crosslinked Amphiphilic Degradable Shape Memory Polymer Nanocomposites with Readily Tuned Physical, Mechanical, and Biological Properties

Abstract

Facile surgical delivery and stable fixation of synthetic scaffolds play roles just as critically as degradability and bioactivity in ensuring successful scaffold-guided tissue regeneration. Properly engineered shape memory polymers (SMPs) may meet these challenges. Polyhedral oligomeric silsesquioxanes (POSSs) can be covalently integrated with urethane-crosslinked polylactide (PLA) to give high-strength, degradable SMPs around physiological temperatures. To explore their potential for guided bone regeneration, here we tune their hydrophilicity, degradability, cytocompatibility, and osteoconductivity/osteoinductivity by crosslinking star-branched POSS-PLA with hydrophilic polyethylene glycol diisocyanates of different lengths and up to 60 wt % hydroxyapatite (HA). The composites exhibit high compliance, toughness, up to gigapascal storage moduli, and excellent shape recovery (>95%) at safe triggering temperatures. Water swelling ratios and hydrolytic degradation rates positively correlated with the hydrophilic crosslinker lengths, while the negative impact of degradation on the proliferation and osteogenesis of bone marrow stromal cells was mitigated with HA incorporation. Macroporous composites tailored for a rat femoral segmental defect were fabricated, and their ability to stably retain and sustainedly release recombinant osteogenic bone morphogenetic protein-2 and support cell attachment and osteogenesis was demonstrated. These properties combined make these amphiphilic osteoconductive degradable SMPs promising candidates as next-generation synthetic bone grafts.