PhotoCol™-IRG bioink kit consists of purified methacrylated Type I bovine collagen as the core component with other support reagents. The methacrylated Type I collagen is produced from telo-peptide intact bovine collagen where the collagen has been modified by reacting the free amines, primarily the ε-amines groups of the lysine residues as well as the a-amines groups on the N-termini. Over 20% of the total lysine residues of the collagen molecule have been methacrylated. A bottle of 20 mM acetic acid solution is provided to solubilize the lyophilized methacrylated collagen at concentrations ranging from 3 to 8 mg/ml. The neutralization solution consists of an alkaline 10X phosphate buffered saline (PBS) solution which provides physiological salts and pH in the final mixture. The photoinitiator consists of Irgacure 2959 to be formulated in methanol (methanol not included), which allows UV crosslinking of the printed structure at 365 nm. PhotoCol™-IRG provides native-like 3D collagen gels, and the final gel stiffness can be customized by changing collagen concentrations and crosslinking.