Exploring the limits of toughness enhancers for 3D printed photopolymers as bone replacement materials

Vinyl esters (VEs) are well-examined monomers for additive manufacturing technology in tissue engineering. They display benefits like low cytotoxicity, good biocompatibility and favorable degradation behavior. Nevertheless, mechanical properties of crosslinked VEs are poor, as they show high brittleness. A previous study showed, that covalent incorporation of high molecular weight additive into an established vinyl ester-thiol network circumvents these problems. In this work, additives based on poly(epsilon-caprolactone) are modified with photopolymerizable end groups to improve the mechanical properties focusing on the toughness and to allow the application in digital light processing stereolithography. The different toughness enhancing additives and their influence on the photochemical and (thermo)mechanical characteristics are studied. As well, the impact of a commercial, flexible and a synthesized rigid thiol on these properties are investigated. It was shown that without forfeiting photoreactivity, the covalently incorporated toughness enhancers led to materials with excellent mechanical properties, above all the tensile toughness, which could be tripled.