The amount of HC to be incorporated into the HAD was chosen by monitoring the formation of fibrin (at 405 nm) in the platelet poor plasma (PPP) over time (Fig. 3, A and B). California2+ was used as a control because it plays an important role in blood clotting (47). The relative absorption of the plasma coagulation curve shows that with the increase in the concentration of HC from 0.25 to 2.0 mg / ml, the corresponding relative slope also increased. Since the slope did not change above 1.0 mg / ml HC concentration (Figure 3B), 1.0 mg / ml was chosen as the optimal dose of HC incorporated into the HAD. In Figure 3C, we also studied the release of HC from HAD by the potency relationship. During the first 3 minutes, 0.25 mg HC was released from 1 ml of HAD, and after 30 minutes the released HC reached 0.65 mg. The released HC was also bioactive to convert fibrinogen to fibrin. The haemostatic capacity of HAD was assessed by monitoring the clotting time of blood in contact with the hydrogel surface in a 96-well plate (Fig. 3D and film S1). Under normal conditions without any intervention, the blood will clot within 5 to 6 minutes (48, 49). As expected, the clotting time of the control group was 5.61 ± 0.51 min (Fig. 3, D and E). The HC and GelMA groups significantly reduced clotting times, with 3.74 ± 0.32 min and 2.13 ± 0.23 min, respectively. As a positive control, the clotting time with fibrin glue was 1.29 ± 0.13 min. HC accelerated coagulation by converting fibrinogen to fibrin, and the HAD group showed an unexpected decrease in clotting time to 0.76 ± 0.05 min. We have also studied the morphology of blood with different contact times by SEM. For the GelMA group, red blood cells (RBCs) began to aggregate on the surface of the adhesive, but there was no sign of fibrin formation at 1 min (Fig. 3F). A certain fibrin mesh was observed little after 2 and 3 min of contacts on the GelMA (Fig. 3, G and H). Compared to the GelMA group, the aggregation of red blood cells on HAD at 1 min was accompanied by a loose fibrin mesh (Fig. 3I). After 2 and 3 minutes of contact with the HAD, the density of the fibrin mesh covering the red blood cells increased (Fig. 3, J and K), indicating that the HAD accelerated the formation of the fibrin mesh. We also quantified the morphology of fibrin via the analysis of SEM images. California2+, GelMA and HC were used as controls. As shown in fig. S2, the average fibrin fiber size in Ca2+, HC, GelMA and HAD were 107.59, 142.50, 103.77 and 196.91 nm, respectively. The average fibrin mesh pore size for Ca2+, HC, GelMA and HAD were 266.52, 316.53, 392.45 and 223.88 nm, respectively. Fibrin incubated with Ca2+ has a similar fiber size of about 100 nm to GelMA, but the GelMA group generated less fibrin. The fibrin incubated with HAD was significantly thicker, indicating that the combination of HC and GelMA was a plus for fibrin generation. In SEM images of coagulation (Fig. 3, F to K), there was no clear sign of whole blood platelet aggregation in both the GelMA group and the HAD group. Therefore, platelet rich plasma (PRP) was prepared to study platelet interactions with HAD. The adsorption of platelets on the HAD is shown in fig. S3A, which demonstrated the strong adhesion of platelets to HAD. Activated platelets adhered to the surface of the ADH and fibrin was found (Fig. S3B). These results demonstrated that the rapid clot formation was attributed to the synergy between GelMA and HC, where activated platelets and red blood cells adhered to the adhesive, and the HC in HAD converted fibrinogen to fibrin. Collectively, these in vitro clot data showed that the HC in GelMA can dramatically reduce blood clotting time.