PROJECT SUMMARY/ABSTRACT Post-traumatic elbow contracture is a debilitating complication characterized by joint immobility and caused by thickening and stiffening of the joint capsule. Surgical capsular release is performed when contractures do not respond to nonsurgical intervention. Capsular release, however, generally only improves (but not normalize) elbow range of motion. Furthermore, additional fibrosis and contraction often recurs, all of which necessitates the need to develop better treatment strategies. Joint capsules from post-traumatic elbow contractures have been found to contain activated myofibroblasts expressing alpha smooth muscle actin (α-SMA) and increased collagen deposition. In other wound healing scenarios, myofibroblasts exert contractile forces on the ECM and synthesize collagen in a manner that is modulated in part by mechanical forces and biochemical factors present in and around the wound. These components interact with the myofibroblasts in a reciprocal and dynamic manner, such that wound healing proceeds as a mechano-chemical feedback loop that resolves with either normal or pathological healing. We hypothesize that this feedback loop is also operational in the injured joint capsule and contributes to capsule thickening and contracture. Our strategy is to interrupt this feedback loop by temporarily blocking NMMII-actin engagement, and thus the ability of myofibroblasts to generate and sense force at critical points during wound healing by delivering the drug blebbistatin (or its derivatives) to the wound site via poly(lactide-co-gylcolide) (PLGA) particles. This project has two major aims that are centered on developing a mechanistic understanding of the feedback loop in the joint capsule and assessing the feasibility of using small molecules to interrupt this feedback loop and reduce/eliminate fibrosis and contracture. In aim 1, we will perform a series of in vitro experiments where we compare blebbistatin and para-nitroblebbistatin PLGA particle compositions and release kinetics to remodeling outcomes, such as myofibroblast activation, force generation, myofibroblast activation, collagen production, and ECM remodeling/tissue stiffness. In aim 2, we will test the ability of blebbistatin or para-nitroblebbistatin to mitigate joint capsule thickening/stiffening, contracture, and fibrosis in a validated rat model of elbow joint contracture. We envision that inhibition of NMMII activity with blebbistatin/para-blebbistatin can be used adjunctively to capsule release surgery. We hypothesize that the controlled-release of drug will temper myofibroblast behavior so that more normal healing follows and larger gains in post-operative ROM are maintained. The knowledge gained here will also have implications for other joints (e.g., knee, ankle, finger) and fibrotic conditions.