PROJECT SUMMARY – Lower Extremity Bypass Graft With Physiologic Longitudinal Pre-Stretch Despite years of improvements and refinements in technologies and pharmacological adjuncts, failure rates remain high for lower extremity prosthetic grafts, particularly when grafts cross the knee joint. Though much work has been done focusing on pathological processes associated with infrainguinal synthetic graft failure, the underlying mechanisms remain incompletely understood. The main artery of the lower extremity, the femoropopliteal artery (FPA), demonstrates significantly different structural features and mechanical properties compared to other arteries. The specialized arrangement of its extracellular matrix components creates longitudinal tension, also known as longitudinal pre-stretch (LPS). In young arteries that are pre-stretched in situ like a rubber band under tension, LPS prevents arterial buckling during limb movement, but in older FPAs, LPS is significantly reduced, which results in more severe bending, kinking, high intramural stresses, and disturbed flow in the bent limb, promoting deleterious cellular and biochemical responses that may culminate in both primary disease development and reconstruction failure. While reduced LPS in PAD patients likely cannot be restored, it can be engineered into bypass grafts used to treat them. We have developed a method of manufacturing nanofibrillar elastomeric bypass (NEB) graft fabrics with nonlinear compliance that can be tuned to match that of blood vessels. By electrospinning biomedical grade elastomers, we made fabrics that can produce low resistance to physiological deformations while protecting the material from overstretching at elevated loads. Our preliminary data using a swine model demonstrate that the NEB graft fabric maintains its compliance, undergoes rapid endothelialization, and gets quickly incorporated into the arterial wall. In this application, we propose to decouple longitudinal and circumferential compliances of our material to fully mimic the complexity of human FPA biomechanics, and test the hypothesis that FPA-tuned NEB grafts with LPS produce less tortuosity, improved hemodynamics, and better in vivo healing responses compared with grafts without LPS. This hypothesis will be tested through three specific aims, whereby we will first optimize the manufacturing method and develop an empirical framework for making compliant anisotropic grafts. Second, we will develop NEB grafts tuned to healthy human FPAs and test them for their mechanical properties, suture retention, water permeability, burst strength, cytotoxicity, platelet adhesion characteristics, implantability, biomechanics, and flow characteristics using in silico and in vitro methods. Lastly, we will test the performance of pre-stretched and non-pre-stretched NEB grafts in a preclinical swine model. This project will demonstrate whether incorporating LPS into lower extremity bypass grafts to reduce bending and tortuosity of...