Photopolymers based on boronic esters for the enhanced degradation of 3D-printed scaffolds

Abstract

Lithography-based additive manufacturing technologies have become a valuable tool in tissue engineering for the fabrication of biocompatible and biodegradable bone regeneration scaffolds. Currently employed photopolymers based on (meth)acrylates, vinyl esters, or vinyl carbonates display undesirable properties such as irritancy or cytotoxicity of residual monomers, degradation via autocatalytic bulk erosion leading to implant failure, or insufficient degradation speed in vivo. This work investigates monomers containing boronic ester bonds as a potential alternative to these state-of-the-art compounds. Next to a facile synthesis, significantly lower cytotoxicity was shown for this generation of biocompatible allyl ether monomers compared to commonly utilized (meth)acrylates. Photopolymerization via the thiol-ene reaction showed that rigid boronic esters led to sufficient photoreactivity for 3D structuring, and materials with reduced shrinkage and excellent mechanical properties can be obtained. Additionally, degradation studies revealed significantly accelerated degradation via the desired surface erosion under physiological and acidic conditions. Ultimately, a 3D test structure out of a boronic ester-based formulation was successfully stereolithography-printed, showing the great potential of these monomers as precursors for photopolymers used for 3D-printed implants with improved degradation behavior without forfeiting good mechanical properties.