Photo‐Crosslinking Aided Hierarchical Assembly of Recombinant Collagen Hydrogels for 3D Bio‐Printing

Collagen is a critical structural and functional protein in extracellular matrix. Recombinant collagen provides key benefits such as virus-free safety, low immunogenicity, solubility, and quality consistency. However, it is still challenge to induce recombinant collagen to form self-supported hydrogels while retaining integrity of triple helix structures and fiber morphology. Here we developed photo-crosslinking assisted hierarchical assembly of recombinant collagen fibers to hydrogel. The processing order of methacryloylation prior to inducing fiber formation of recombinant collagen not only made hydrogel with higher substitution degree, higher storage modulus (G') and initial shear-thinning stress, but also retained triple helix structure and fiber morphology similar to D-periodic banding pattern of Type I collagen. Under the same concentration, photo-crosslinked methacryloylated recombinant collagen (RCMA) hydrogel presented typical viscoelastic solid behavior with a storage modulus G' of 102 Pa, while GelMA behaved as a viscous solution without sol-gel transition. Further, the RCMA hydrogel demonstrated robust printability in 3D bio-printing, showing potential for constructing intricate biological architectures. Moreover, NIH-3T3 cell culture demonstrated excellent biocompatibility and negligible cytotoxicity of the RCMA hydrogel, with no adverse effects on cell adhesion or proliferation. In summary, these properties underscore the significant potential of RCMA hydrogel for applications in biomedicine and tissue engineering.