Engineering tough blood clots for rapid hemostasis and enhanced regeneration

Blood clots play a pivotal role for hemostasis and regeneration1, but are slow to form and mechanically weak. These limitations are attributed to complex coagulation cascades, a high content of mechanically ineffective cells, and a low content of structural polymers2. They pose a considerable risk for life-threatening hemorrhage and constrain the broader application of blood clots3-5. Overcoming these limitations is a critical challenge, as existing strategies focused on polymer networks are inapplicable to highly cellularized materials like blood clots. Here we show a strategy termed click clotting, which rapidly crosslinks living cells into tough cytogels through bioorthogonal click reactions. We demonstrate this strategy by directly crosslinking red blood cells into cytogels and incorporating them within blood clots. The resulting engineered blood clots (EBC) exhibit instantaneous clot formation (< 5 seconds), a 13-fold increase in fracture toughness, and a 4-fold improvement in adhesion energy compared to native blood clots. Experiments and computational modeling reveal a unique toughening mechanism based on cell rupture. In vivo studies show that EBC outperform clinically used products in managing non-compressible hemorrhage. Specifically, EBC can rapidly halt hemorrhage, promote tissue regeneration, mitigate inflammation and foreign body reactions, and prevent postoperative adhesion. Furthermore, our strategy is versatile and applicable to a range of cells and polymers. This work is expected to motivate the development and translation of highly cellularized materials for wound management, bleeding control, tissue repair and regeneration.