Bioinks for Three-Dimensional Printing in Regenerative Medicine

Traditional three-dimensional printing technologies, originally meant for synthetic materials, have been adapted for biotechnology and regenerative medicine. The technology works but there is high variability in the resins needed for successful integration with biological components. We define these print resins as bioinks, which encompass printable materials that interface with biocomponents during or after the actual print or are involved in the structural construction of scaffolds that will interface with biocomponents. Although synthetic materials are traditionally accepted as mechanically robust, are finely tunable, and are processed using commercially available methods, natural materials have inherent biochemical cues that induce cell attachment and differentiation. The balance of the strong properties of these materials has led to combined technologies such as co-printing and hybrid bioinks, and the development of specialized resins such cell-laden, sacrificial, and support bioinks. Here, we review the evolution of bioinks from traditional methods and materials to highly complex and specialized resins that have been used successfully for in vitro and in vivo bioengineering applications.