Surface Functionalization of Thermoplastic Polyurethane Scaffolds to Enhance Microparticle Attachment

While the use of polymer micro- and nanoparticles for drug delivery has been demonstrated for diverse biomedical applications, not all techniques have allowed for the precise localization of the drug that is needed to support surrounding tissues. Herein, we report a biocompatible thermoplastic polyurethane silk fibroin composite drug delivery platform for localized drug release. The work leverages two distinct materials, combining the biocompatibility of silk fibroin protein particles as a drug carrier with the modularity of a thermoplastic polyurethane scaffold, whose mechanical properties are tuned by composition. Two different particle attachment strategies were investigated; a Michael addition reaction was found to result in a high number of particles attached and a more complete surface coverage than carbodiimide coupling that is often employed with silk-based materials. The attachment of silk fibroin microparticles allows localized delivery of molecules, and the incorporation of poly(tetrahydrofuran) (pTHF) into polyurethane was found to tailor phase separation of the hard and soft segments that, in turn, affects the crystallinity and stiffness of the scaffold. The hard segment crystallinity of unprocessed powders (range: 16.26-35.51%) and slow-cooled films (range: 9.04-37.29%) increased as the pTHF content increased, indicating an increase in phase separation. The Young's modulus of thermoplastic polyurethanes (TPUs) also increased with increasing pTHF, from 9.02 to 14.49 MPa. In vitro cytocompatibility testing with human dermal fibroblasts showed >85% viability and no significant changes in cell growth with respect to composition. This platform demonstrates a promising strategy by combining two distinct materials to provide localized drug delivery with potential application for longer-term biocompatible medical implants.