Hydrogel-based 3D ECM mimics must contain cell-responsive sites (cell-binding motifs), which exist in natural ECM materials (such as collagens), so the cells can attach and grow in the matrix. As one type of hydrogel-based ECM mimics, GelMA is prepared by functionalizing gelatin with unsaturated methacryloyl groups. Gelatin is denatured and partially hydrolyzed collagens. Therefore, cells attach on GelMA in a similar way as they attach on collagen.

Question: could you estimate which concentration of collagen contains similar cell-binding site density as 8% GelMA?