Assessment of the Effects of Energy Density in Crosslinking of Keratin-Based Photo-Sensitive Resin

Keratin, a natural fibrous structural protein that can be found in hair and skin, can self-assemble or be crosslinked into hydrogels that are physiologically biodegradable and provide adequate cell support. We have formulated a keratin-based photocrosslinkable resin that can be used to cast or 3D print keratin under an ultra-violet (UV) light source. The resin was used to produce keratin hydrogels, assessing how the amount of energy projected during curing (4 to 200 mJ/mm ³ ) defines the network's crosslinking degree, and thus the system's physicochemical properties. The energy density was proven to regulate the dityrosine chemical reaction needed to crosslink keratin, and it determines the extent to which the hydrogel network crosslinks. As expected it follows a saturation trend, limited by the amount of tyrosine available in keratin. The crosslinking degree, and its saturation nature, determines microstructural properties of the hydrogel, including swelling capacity and degradation trends. The relation between energy density and crosslinking degree was further elucidated with the differences observed in both the thermal degradation profiles (using DSC) and the infrared profiles (using FTIR). Understanding the effects of energy density on the creation of the crosslinked network allowed us to further optimize printing parameters, particularly UV intensity, of the photo-sensitive resin in a cDLP 3D printing system.