In Situ Crosslinkable Gelatin Hydrogels For Vasculogenic Delivery of Mesenchymal Stem Cells

Abstract

Gelatin is a hydrolyzed and denatured form of collagen, which comprises the majority of extracellular matrix. Despite its numerous advantages for tissue engineering, its use as a thermostable hydrogel has been achieved only recently by conjugating hydroxyphenyl propionic acid to the gelatin backbone, resulting in injectable in situ crosslinking hydrogels through a H2O2- and peroxidase-mediated reaction. Gelatin hydrogels gelled rapidly, and exhibited excellent biocompatibility in vitro where mesenchymal stem cells (MSCs) were encapsulated over 15 days. Furthermore, MSCs organized into tubular network and differentiated into an endothelial lineage purely by material effects. Finally, 2-week long subcutaneous implantation of gelatin hydrogels delivering MSCs in vivo confirmed the vasculogenic and angiogenic effect where implanted MSCs expressed Flk-1, an endothelial cell marker, and increased blood vessel formation was observed via microangiography. Histology showed no fibrous capsule formation around the gelatin hydrogel, and qPCR also confirmed favorable host macrophage responses by up-regulating MRC1, a reparative/regenerative macrophage marker, and down-regulating iNOS, an inflammatory macrophage marker. Based on these observations, we conclude that injectable in situ crosslinking gelatin hydrogel is a promising biomaterial for tissue engineering/regenerative medicine where robust angiogenesis and favorable host immune response are required.