UC Santa Barbara

Additive Manufacturing, also commonly known as 3D Printing, has significant potential for personalized medicine and biomedical devices, owing to its streamlined design-to-production workflow. Unlike traditional manufacturing techniques, 3D printing allows for the creation of highly tailored products that can be precisely designed to meet the specific needs of individual patients. Current printable biomaterials are limited to synthetic and biological polymers and their range in material properties. Although synthetic polymers are tunable, they lack degradability. Unlike synthetic polymers, biopolymers are biodegradable, but their properties are limited to those found in nature. Therefore, there is a need for tunable and biodegradable materials in 3D printing to help expand its capability. In Chapter 1, the 3D printing hydrogel literature is surveyed, and polypeptides based on N-carboxyanhydride (NCA) are recognized as a potential feedstock that can diversify the printable material palette. In Chapter 2 and Appendix A, a library of star block copolypeptide composed of a consistent inner hydrophilic block and different β-sheet outer blocks were synthesized. By varying the β-sheet forming domains, shear-processable hydrogels with diverse microstructure and mechanical properties were prepared and structure-function relationships were determined. The versatile synthesis of these star block copolypeptides provides a robust platform to tune material properties based solely on molecular design. Utilizing these systems in 3D printing, specifically Direct Ink Writing (DIW), eliminates the necessity for additives and provides a synthetic handle to tailor its functionality. In Chapter 3 and Appendix B, photocrosslinkable groups were facilely integrated into the star block copolypeptide scaffold to allow subsequent chemical crosslinking with visible light after DIW. Escherichia Coli was integrated into these hydrogel inks and biological composites with complex geometries were achieved in these bioinert printing conditions. Furthermore, the tunable properties of different copolypeptide networks enable control over proliferation and colony formation for embedded microbes as demonstrated based on green fluorescent protein (GFP) expression. Opening the possibility of controlling integrated biological behavior through the molecular design of the star copolypeptide matrix. To demonstrate the ease of use of these star copolypeptides, Chapter 4 and Appendix C delve into their utilization as rheological modifiers within the widely used Gelatin Methacrylamide (GelMA) bioinks. The temperature stability of the star copolypeptide networks allows these GelMA hybrids to be extruded at physiological temperatures, facilitating their utilization for integrating mammalian cells for bioprinting. In contrast to conventional rheological modifiers, the star copolypeptide participates in photochemical crosslinking with GelMA while preserving its natural biodegradability. This approach, employing star copolypeptides as rheological modifiers for DIW, showcases the prospective integration of bioactive materials and fluids, paving the way for modular bioinks. This thesis aims to unveil the unexplored capabilities of star copolypeptides as a tailorable material, propelling the frontier of bioprinting.