Chapter 10: Interface (Cell, Gel, Surface) and Biocompatibility in Gel Processing

Extrusion-based bioprinting has tremendous potential in delivering functional constructs for tissue engineering. The process generally involves the deposition of a cell-laden hydrogel precursor solution (the bioink) that undergoes post-printing stabilization through polymer crosslinking. The main hurdle to clinical application is related to the optimization of the “interface” between the polymeric material, cells, and the dispensing apparatus during the process. An optimal mutual interaction is needed to deposit constructs that exhibit both high printing resolution and fidelity and sound cell viability. After a brief introduction to the process, herein we discuss the main features of the bioink and the dispensing system that play a key role in optimal interface and related to the use of stem cells. The natural and synthetic macromolecules, usually employed as the polymeric part of the bioink, as well as the main polymer gelation mechanisms are reviewed, highlighting their effect on the “interface”. Finally, the progress from single polymer-bioinks, only compromising printing quality and cell activity, to more advanced formulations is discussed. Emphasis is put on the most promising bioink designs combining the use of injectable (crosslinked) hydrogels as the polymeric component with dual crosslinking strategies.