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Abstract

Fibrin is a natural biomaterial that plays an essential role in hemostasis upon injury, as being the main component of the blood clot. In the clinic, fibrin is widely used in regenerative medicine as a hemostatic agent to prevent blood leakage and as a sealant agent to glue tissues. In addition, fibrin-based biomaterials have been extensively explored as delivery carriers for therapeutics, including growth factors (GFs), to improve tissue regeneration. In these applications, premature degradation of fibrin, called fibrinolysis, leads to recurrent bleeding, tissue dehiscence and limited regenerative efficacy, which strongly hindered the potential of fibrin. Physiologically, fibrinolysis is slowed by α2-antiplasmin (α2PI), a protease inhibitor that crosslinks into fibrin during polymerization and prevent proteolytic degradation by plasmin. In this thesis, we first engineered fibrin biomaterials with human α2PI to protect them from fibrinolysis. We highlighted the clinical translation potential of α2PI as a recombinant protein drug, as well as its superiority as compared to the current clinical drug aprotinin, a bovine-derived fibrinolysis inhibitor. We additionally showed that α2PI can protect fibrin materials made of low fibrinogen concentration, which could substantially reduce their cost and manufacturing challenges. Moreover, this could further support the development of patient-derived fibrin biomaterials using unpurified plasma, in which fibrinogen concentration is naturally low as compared to the clinical fibrinogen. Indeed, we then demonstrated that α2PI can be used to effectively prevent fibrinolysis of endogenous fibrin in healthy and diabetic conditions. We particularly explored the use of α2PI-engineered fibrin as a carrier material for the delivery of growth factors in skin diabetic wound healing. We found that α2PI co-delivered with engineered variants of the vascular endothelial growth factor-A (VEGF-A) and the platelet-derived growth factor-BB (PDGF-BB) in exogenous fibrin or directly from the endogenous fibrin clot can significantly improve the healing of diabetic wounds, despite their high proteolytic environment. In addition of these two GFs, we aimed to engineered a potent chemokine called the stromal-derived factor-1 (SDF-1), broadly involved in tissue regeneration and blood vessel formation, for increased affinity to fibrin and other extracellular matrix proteins. We found that fibrin-mediated delivery of SDF-1 increased angiogenesis in diabetic wounds, although the chemokine remained challenging to engineer and produce. As another application of endogenous fibrin protection, we evaluated the hemostatic efficacy of α2PI to reduce bleeding during surgery. Indeed, the excessive activity of plasmin during coronary artery bypass graft surgery (CABG) is known to lead to excess of blood loss which increase the need of patient blood transfusion. We here proved that α2PI was able to reduce bleeding time and volume as effectively as the clinical aprotinin. Based on these findings, we believe that engineering of fibrin biomaterials and endogenous fibrin with α2PI and growth factors can have a strong impact in regenerative medicine, leading to improvements in the clinical use of fibrin.

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