Development of a Human Recombinant Collagen for Vat Polymerization‐Based Bioprinting

ABSTRACT In light‐based 3D‐bioprinting, gelatin methacrylate (GelMA) is one of the most widely used materials, as it supports cell attachment, and shows good biocompatibility and degradability in vivo. However, as an animal‐derived material, it also causes safety concerns when used in medical applications. Gelatin is a partial hydrolysate of collagen, containing high amounts of hydroxyproline. This causes the material to form a thermally induced gel at ambient temperatures, a behavior also observed in GelMA. This temperature‐dependent gelation requires precise temperature control during the bioprinting process to prevent the gelation of the material. To avoid safety concerns associated with animal‐derived materials and reduce potential issues caused by thermal gelation, a recombinant human alpha‐1 collagen I fragment was expressed in Komagataella phaffii without hydroxylation. The resulting protein was successfully modified with methacryloyl groups and underwent rapid photopolymerization upon ultraviolet light exposure. The developed material exhibited slightly slower polymerization and lower storage modulus compared to GelMA, while it showed higher stretchability. However, unlike the latter, the material did not undergo physical gelation at ambient temperatures, but only when cooled down to below 10°C, a characteristic that has not been described for comparable materials so far. This gelation was not caused by the formation of triple‐helical structures, as shown by the absence of the characteristic peak at 220 nm in CD spectra. Moreover, the developed recombinant material facilitated cell adherence with high cell viability after crosslinking via light to a 3D structure. Furthermore, desired geometries could be easily printed on a stereolithographic bioprinter. Graphical and Lay Summary We expressed a human collagen fragment without hydroxylation. In contrast to gelatin the resulting material did not show thermal gelation at ambient temperatures but allowed for rapid photopolymerisation following addition of methacryloyl groups. The thereby generated hydrogel showed promising mechanical properties as well as cell adhesion.