Spatiotemporal control of tendon healing through modular, injectable hydrogel composites - PROJECT SUMMARY Biomaterials-based approaches have potential for treating tendon injury, the chronic sequelae of which include pain, diminished function, and heightened risk of reinjury due to aberrant scar formation. Unfortunately, the undefined origin and function of numerous cellular players involved in the tendon injury response have made it difficult to identify biological mechanisms of these poor outcomes. As a result, therapeutic targets for biomaterials-mediated tendon repair approaches have not been established. Recently, it has been shown that neonatal mice fully regenerate completely transected tendons. Key differences in their injury response compared to that of adults suggest that recruitment of progenitor cells and their subsequent tenogenic differentiation can lead to regenerative healing. Thus, the long-term goal of the proposed work is to develop a biomaterial therapy capable of coordinating multiple, distinct phases of tendon healing. Toward this end, we aim to design a synthetic, hydrogel-based composite scaffold that integrates physical (mechanical and topographical) and soluble cues to 1) recruit specific progenitor cell populations to the injury site and 2) direct tenogenic progenitor cell differentiation and de novo matrix synthesis of the appropriate composition and organization following tendon injury. Our central hypothesis is that spatiotemporal presentation of combinatorial microenvironmental cues can control the abundance and identity of reparative cells entering the injury site and promote their differentiation and matrix remodeling activity, both of which will improve the adult tendon healing response. Our preliminary data establishes a material that is permissive to tendon progenitor cell (TPC) migration and tenogenic differentiation; moreover, we have established a tunable soluble factor release system enabling gradual release of chemotactic cues and cell-triggered release of differentiation factors. We have already found that physical and microgel- delivered soluble cues synergistically enhance TPC recruitment into these composite hydrogels. Therefore, in Aim 1, we will optimize microenvironmental cues for driving robust tenogenic differentiation in vitro. In Aim 2, this dextran vinyl sulfone-based material system will be tested in a murine Achilles tendon injury model to study the effects of these cues on recruitment of TPCs to the wound site, subsequent tenogenesis, and matrix deposition/organization. The extent of tenogenic differentiation will be quantified through the expression of a panel of tenogenic factors, deposition of organized de novo matrix supporting tenogenesis, and functional analysis of regenerated tendons. This work will establish a novel, injectable, modular hydrogel scaffold capable of driving a robust tendon healing response in adult mice. Moreover, this work will provide a deeper understanding of the microenvironmental cues regulating tenogenesis, information critical to the advancement of biomaterial therapeutics geared toward connective tissue regeneration.
