3D Bioprinting and Natural Bioinks: Principles and Applications

Currently, 3D bioprinting as an additive manufacturing technique for building 3D constructs with desired geometries is broadly employed in tissue engineering and drug screening applications. Bioprinting enables the fabrication of living tissues using cell aggregates or cells encapsulated in biomaterials—all of which can be referred to as bioink. Research on novel bioinks with appropriate printability, biocompatibility, and mechanical properties akin to the target tissue is an essential prerequisite toward advancing 3D bioprinting applications in regenerative medicine. The only class of materials capable of providing an environment similar to the human body and maintaining cell viability during encapsulation is hydrogels. Among the two categories of natural and synthetic hydrogels employed as bioinks, natural materials are much more widely used than synthetic ones due to their better biocompatibility, lower risk of immune rejection, more similarity to native tissues, and the possibility of laboratory modification and combination with other materials to obtain optimal properties. In this article, first, a review of 3D bioprinting technology and its defined modalities is presented. Next, bioink biomaterials and their cross-linking mechanism are discussed. Finally, a summary of studies on some of the most widely used natural bioinks (including collagen, gelatin, silk, alginate, hyaluronic acid, chitosan and extracellular matrix) is reported. Research results indicate that recreating organs using 3D bioprinting necessitates precise placement of specific cells, materials, and bioactive factors to induce functional tissue formation. Attempting to meet these requirements for more complex tissues highlights the need for more tissue-specific, biologically and mechanically tunable bioinks.