Synthesis, characterization, and in vitro cell culture viability of degradable poly(N-isopropylacrylamide-co-5,6-benzo-2-methylene-1,3-dioxepane)- based polymers and crosslinked gels

Poly(N-isopropylacrylamide-co-5,6-benzo-2-methylene-1,3-dioxepane) (poly(NIPAAm-co-BMDO)) was synthesized by atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization. Using UV-vis spectroscopy, the lower critical solution temperature (LCST) of poly (NIPAAm) and poly(NIPAAm-co-BMDO) copolymers were measured, varying with respect to the amount of incorporated BMDO. This material is degradable and possesses a LCST above room temperature and below body temperature, making it a potential candidate for use as an injectable tissue engineering scaffold to enhance fracture repair. ATRP and RAFT enabled preparation of polymers with control over molecular weight up to M_n = 50,000 g/mol and M_w/M_n < 1.2. Degradation studies were performed in basic solution and in complete Dulbecco's modified Eagle medium. The cytotoxicity of the material and its degradation products were analyzed by in vitro cell culture analyses, including cytotoxicity live/dead and CyQUANT cell proliferation assays. Cross-linked scaffolds with degradable units within the polymer backbone and at the crosslinking sites were prepared using an ester-containing diacrylate crosslinker. Furthermore, incorporation of a GRGDS peptide sequence improved cell attachment to the gels. Controlled/living radical polymerization techniques allow for precise control over macromolecular structure and are poised to become powerful tools for tissue engineering scaffold synthesis.