Dynamic Covalent Hydrogels for Bioprinting and Soft Material Additive Manufacturing

Abstract

Additive manufacturing has emerged as an exciting fabrication technique for creating geometrically complex soft material constructs for biomedical and environmental applications. Hydrogels, which are water-swollen polymer networks, are easily functionalized and have advantageous viscoelastic properties for biocompatible printing applications. Dynamic covalent cross-linking chemistry is frequently used in hydrogels for additive manufacturing applications. Dynamic covalent hydrogels lead to beneficial material properties such as self-healing, shear-thinning, tunable viscoelasticity, degradable networks, and stimuli-responsive behavior. In this Review, we highlight recent advances in soft material additive manufacturing and bioprinting using hydrogels with dynamic covalent cross-linking approaches. We provide an overview of the types of dynamic covalent bonds frequently used in hydrogels, with a focus on Schiff base, disulfide, boronate ester, and Diels–Alder cross-linking. We describe the rheological and printability considerations for common hydrogel additive manufacturing techniques, such as extrusion printing and lithography. We also explore emerging applications of dynamic covalent hydrogels in creating bioprinted constructs, reprocessable and recyclable networks, and other advanced material functionalities with additive manufacturing. Lastly, we describe future directions for polymeric material additive manufacturing enabled by dynamic covalent hydrogels across biomedical and environmental applications.