Development of a human-derived bioink based on keratin methacrylate for corneal bioprinting

The development of suitable bioinks for bioprinting is still a key issue in the field of tissue engineering. Most of the biomaterials used are derived from animal sources. A novel bioink for corneal stroma bioprinting based on chemically modified keratin derived from human hair waste was developed and evaluated. To confirm the successful functionalization of methacrylated keratin (KerMA), various characterization methods such as ¹H-NMR, IR as well as a cytotoxity assay were performed. The newly developed biomaterial KerMA was mixed with methacrylated hyaluronic acid and bioprinted with cells as a corneal stroma substitute. Two different cell types were encapsulated in the bioink, immortalized corneal keratocytes and human corneal fibroblasts. The printed constructs were crosslinked under UV light and cultured for up to four weeks. The bioprinted constructs were monitored for four weeks for optical transparency, cell viability (live/dead staining), biomechanical properties and protein expression by indirect immunofluorescence. Furthermore, human corneal epithelial cells were seeded on top of the bioprinted constructs and demonstrated high cell viability. The bioprinted constructs showed good optical transparency and decent biomechanical properties. The addition of KerMA to methacrylated hyaluronic acid led to an improvement in cell viability and protein expression. This bioink approach offers a sustainable, ethically sourced alternative to animal-derived materials. It forms the basis for future in vitro and in vivo studies on the development of corneal tissue.