Sustainable and Degradable Epoxy Resins from Trehalose, Cyclodextrin, and Soybean Oil Yield Tunable Mechanical Performance and Cell Adhesion

Natural product feedstocks such as carbohydrates and vegetable oils offer tremendous potential for creating sustainable cross-linked epoxy resin thermosets for numerous applications. Herein, we designed and synthesized trehalose- and β-cyclodextrin-based carboxylic acid hardeners to cure with epoxidized soybean oil forming predominantly sustainable epoxy resins. Trehalose (Tr) and β-cyclodextrin (Cd) were functionalized with heptanoyl chloride (H) and succinic anhydride (S). The resulting carboxylic acid hardeners were homogeneously formulated and cross-linked with epoxidized soy bean oil (ESO) at three different COOH/epoxide ratios. The cured resins were thermally stable up to 300 °C and stable in neutral and acidic aqueous conditions. Yet, degradation into water-soluble components could be triggered upon exposure to basic aqueous media. The physical properties of these materials are tunable based on feedstock composition and identity of the carbohydrate hardener. The glass transition temperatures (T_g) of the Tr-based epoxy polymers ranged from −3 to 3 °C, whereas the Cd-based polymers exhibited T_g values of 28–36 °C. The mechanical properties including tensile strength and Young’s moduli also varied where the Cd-thermosets offered higher performance due to the structural rigidity of the cup-like structure. Homogeneous epoxy resin films of these materials were examined for their ability to promote cell adhesion and proliferation using neonatal human dermal fibroblast (HDFn) cells. The results indicated that films composed of the Cd-based epoxy resin with a 50/50 ratio of −COOH/epoxide promoted cell adhesion and proliferation with density similar to that of the well-studied control polymer poly­(dl-lactide-co-glycolide) (PLG). Interestingly, the Tr-based epoxy films completely prevented cell adhesion and growth. The starkly different cell adhesion results and favorable physical characteristics of these predominantly sustainable epoxy resins support their promise as benign surfaces and scaffolds for a variety of applications ranging from adhesives and antifouling coatings to wound healing and tissue engineering.