Enzymatically cross-linked injectable gelatin gel as osteoblast delivery vehicle

Injectable and degradable hydrogels are potential candidates as cell delivery vehicles for the regeneration of osseous defects. We evaluated the potential of injectable enzymatically cross-linked gelatin gel as an osteoblast delivery vehicle using murine preosteoblast MC3T3-E1 cells. Injectable hydrogels were prepared by enzymatic cross-linking of the phenol derivatives of gelatin (tyramine-modified) in the presence of hydrogen peroxide (H2O2) and horseradish peroxidase. The effect of gelatin concentration on gel morphology and in supporting the adhesion and spreading of encapsulated MC3T3-E1 cells, activation of intercellular signaling in MC3T3-E1 cells by extracellular signal-regulated kinase phosphorylation, beta-catenin and Runx2 was evaluated. Both tyramine-modified and unmodified gelatins as well as gelatin gels did not activate intercellular signaling pathways in MC3T3-E1 cells. The encapsulated cells in gelatin gel showed extracellular signal-regulated kinase phosphorylation and active beta-catenin expression in the presence of inductive molecules such as insulin and LiCl. The gelatin gels formed from 10 to 25 mg/mL tyramine-modified gelatin supported the adhesion, spreading, and three-dimensional growth of MC3T3-E1 cells. However, the lack of activation of intercellular signaling in the gelatin gel indicates the need to add exogenous bioactive molecules to modulate the osteogenic functions of the encapsulated cells.