11.2.2　Hemostatic hydrogel dressings

A direct result of skin trauma is the occurrence of bleeding.Excessive blood loss is the main cause of death.The use of appropriate hemostatic equipment for first aid treatment can effectively reduce casualties.Since the application of tourniquets in parts of the human body other than the limbs is often limited，rapid hemostatic materials have always been a hot topic in the field of first aid.Currently，the common types of hemostatic dressings mainly include rubber dressings，foam dressings，electrospun fiber dressings，membrane dressings，hydrogel dressings，etc.Among these dressings，hydrogels are of great importance in the application of hemostatic dressings due to their specific crosslinked network structure，semipermeable，bacterial invasion blockage，wound infection prevention，and allow for the passage of oxygen and water.

Hemostatic hydrogel dressings can be obtained by introducing hemostatic factors（e.g.，hemostatic polypeptides，hemostatic drugs）into the gel or via a strong physical barrier.For example，Paul Slezak et al.used click chemistry to graft thrombin receptor agonist peptide-6（TRAP-6）onto poly（vinyl alcohol）（PVA）to obtain a hemostatic polypeptide modified PVA-TRAP-6 hydrogel.Since TRAP-6 has a significant function ofactivating platelets，the hemostatic hydrogel not only exhibits a good biocompatibility，but also significantly shortens the clotting time，and can be used as a hemostatic dressing for wounds and bleeding in tissues and organs（Figure 11-4）.Ouyang et al.designed a light-responsive adhesive that mimicked the composition of the extracellular matrix（ECM），which could quickly gel and fix after ultraviolet irradiation，and adhered and sealed the bleeding artery and myocardial wall.The adhered hydrogel could withstand blood pressure up to 290 mmHg，which is significantly higher than the blood pressure in most clinical settings.This hydrogel can prevent 4-5 mm porcine carotid artery incisions and 6 mm diameter heart penetration holes in the porcine heart.The treated pigs survived after using this hydrogel for hemostatic treatment，which is well tolerated and has significant clinical advantages as a wound sealant.(https://www.daowen.com)

In addition，the introduction of inorganic nanoparticles（NPs）（e.g.，silica，clays）with hemostatic function into hydrogels is also an effective manner to obtain hemostatic hydrogel dressings.The negatively charged silicate can effectively condense the coagulation factors in the blood，and the fast water absorption of inorganic nanoparticles can effectively concentrate blood components.Hartgerink et al.prepared a nanocomposite hydrogel and the result showed that through the synergistic effect of silicate and collagen，the nanocomposite hydrogel has multiple functions of efficiently enriching coagulation factors and rapidly concentrating blood components，and can achieve rapid hemostasis.