| dc.description.abstract | Thermoresponsive shape memory polymer (SMP) scaffolds afford conformal “self-fitting” into irregularly shaped craniomaxillofacial (CMF) bone defects. Grunlan and co-workers previously reported SMP scaffolds based on biodegradable poly(ε-caprolactone) (diacrylate) (PCL-DA). Later, to enhance the rate of degradation, semi-interpenetrating network (semi-IPN) scaffolds were formed with PCL-DA and thermoplastic poly(L-lactic acid) (PLLA) (75:25 wt%, respectively). Bioactivity (i.e., the ability to induce the formation of a layer of hydroxyapatite, HAp), a property integral to promoting bone regeneration, was imparted by coating scaffolds with polydopamine (PD). However, as the scaffolds erode, the PD coating is lost as is bioactivity. Furthermore, the impact of ethylene oxide (EtO) sterilization on such PD-coated scaffolds was not assessed. Grunlan and co-workers have previously observed that hydrogels containing siloxane-based polymers were bioactive. While PCL-based scaffolds had been previously prepared with a siloxane-based co-macromer, the bioactivity was not assessed.
In the first study, PD-coated PCL-DA and PCL-DA/PLLA semi-IPN scaffolds were EtO sterilized. Morphological features, in vitro bioactivity, PCL crystallinity, PLLA crystallinity, and crosslinking were all preserved. Subsequently, shape memory properties, compressive moduli, and in vitro degradation behaviors were also unchanged.
In the second study, to achieve self-fitting scaffolds with innate bioactivity, PCL/polydimethylsiloxane (PDMS) co-matrices were formed with three types of macromers to systematically alter PMDS content and crosslink density. PCL90-DA was combined with a linear-PDMS66-dimethacrylate (DMA) macromer, and a star-PDMS66-tetramethacrylate (TMA) macromer at 90:10, 75:25, and 60:40 wt % ratios. Scaffolds were also prepared with an acrylated (AcO) triblock macromer (AcO-PCL45-b-PDMS66-b-PCL45-OAc) (65:35 wt % ratio). All PCL/PDMS scaffolds displayed bioactivity in vitro, leading to significant increases in moduli. Furthermore, degradation rates increased with PDMS content.
Lastly, the impact of siloxane polymer hydrophobicity on the bioactivity of PCL-based scaffolds was investigated. Scaffolds were prepared by combining PCL90-DA with either with linear macromers: PDMS66-DMA or polymethylhydrosiloxane66-dimethacrylate (PMHS66-DMA) (90:10, 75:25, and 60:40 wt % ratios). These PMHS-containing scaffolds exhibited further increased degradation and mineralized in just two weeks. Scaffolds were also cultured with human mesenchymal stem cells (hMSCs) to assess osteoinductivity. Compared to PCL-DA scaffolds, both PCL-DA/PDMS-DMA and PCL-DA/PMHS-DMA scaffolds had increased cell viability and proliferation as well as expressed higher osteogenic protein markers. | |
