Alkaline activation of endogenous latent TGFβ1 by an injectable hydrogel directs cell homing for in situ complex tissue regeneration

Utilization of the body's regenerative potential for tissue repair is known as in situ tissue regeneration. However, the use of exogenous growth factors requires delicate control of the dose and delivery strategies and may be accompanied by safety, efficacy and cost concerns. In this study, we developed, for the first time, a biomaterial-based strategy to activate endogenous transforming growth factor beta 1 (TGFβ1) under alkaline conditions for effective in situ tissue regeneration. We demonstrated that alkaline-activated TGFβ1 from blood serum, bone marrow fluids and soaking solutions of meniscus and tooth dentin was capable of increasing cell recruitment and early differentiation, implying its broad practicability. Furthermore, we engineered an injectable hydrogel (MS-Gel) consisting of gelatin microspheres for loading strong alkaline substances and a modified gelatin matrix for hydrogel click crosslinking. In vitro models showed that alkaline MS-Gel controllably and sustainably activated endogenous TGFβ1 from tooth dentin for robust bone marrow stem cell migration. More importantly, infusion of in vivo porcine prepared root canals with alkaline MS-Gel promoted significant pulp-dentin regeneration with neurovascular stroma and mineralized tissue by endogenous proliferative cells. Therefore, this work offers a new bench-to-beside translation strategy using biomaterial-activated endogenous biomolecules to achieve in situ tissue regeneration without the need for cell or protein delivery.