Shape Memory Polymer Bioglass Composite Scaffolds to Heal Complex Bone Defects

Craniomaxillofacial (CMF) defects are generally treated with autografts, but difficulty achieving a conformal fit with can lead to premature graft resorption. Thus, we have developed shape memory polymer (SMP) scaffolds that can “self-fit” into irregularly shaped CMF defects. These are formed from biodegradable <i>linear</i>-poly(e-caprolactone) diacrylate (<i>linear</i>-PCL-DA), with crystalline lamellae serving as switching segments (T_m= ~55 deg C) and crosslinks acting as netpoints. After exposure to warm saline (~55 deg C), the scaffold becomes malleable, allowing press-fitting into an irregular defect before cooling to body temperature restores its rigid state. Herein, SMP scaffold composition was systematically tailored to enhance thermal tissue safety, degradation rate, modulus, and bioactivity. <i>Star</i>-architectures of constituent polymers and inclusion of bioactive Bioglass (BG) were utilized to achieve these properties. To reduce the self-fitting temperature, SMP scaffolds were be formed from <i>star</i>-PCL-tetraacrylate (<i>star</i>-PCL-TA; T_m = ~45 deg C). Furthermore, to accelerate degradation and tune modulus, semi-interpenetrating networks (semi-IPNs) were formed by including <i>linear-</i> or <i>star-</i>poly(l-lactic acid) (PLLA). 45S5 BG is known to induce hydroxyapatite (HAp) mineralization that subsequently promotes osteogenic differentiation (i.e., osteoinductivity) as well as osseointegration. Scaffolds were prepared from <i>linear</i>-PCL-DA or <i>star</i>-PCL-DA, as well as each with <i>linear</i>- or <i>star</i>-PLLA (75:25 wt% ratio). BG was incorporated at varying levels into scaffolds (up to 30 wt%) during fabrication. The BG content was confirmed using thermal gravimetric analysis (TGA). The compressive mechanical properties of the scaffolds were evaluated, as well as the <i>in vitro</i> degradation behavior. Notably, composite scaffolds exhibited rapid formation (24 hours) of HAp when exposed to simulated body fluid (SBF) as confirmed by SEM/EDS. Overall, these composite SMP scaffolds are expected to provide enhanced healing of complex bone defects.