Abstract: BACKGROUND: Due to the sudden release and the rapid removal by proteases, platelet-rich plasma hydrogel leads to shorter residence times of growth factors at the wound site. In recent years, researchers have focused on the use of hydrogels to encapsulate platelet-rich plasma in order to improve the deficiency of platelet-rich plasma hydrogels.
OBJECTIVE: To prepare self-assembled polypeptide-platelet-rich plasma hydrogel and to explore its effects on the release of bioactive factors of platelet-rich plasma. 
METHODS: The self-assembled polypeptide was synthesized by the solid-phase synthesis method, and the solution was prepared by D-PBS. Hydrogels were prepared by mixing different volumes of polypeptide solutions with platelet-rich plasma and calcium chloride/thrombin solutions, so that the final mass fraction of polypeptides in the system was 0.1%, 0.3%, and 0.5%, respectively. The hydrogel state was observed, and the release of growth factors in platelet-rich plasma was detected in vitro. The polypeptide self-assembly was stimulated by mixing 1% polypeptide solution with 1% human serum albumin solution, so that the final mass fraction of the polypeptide was 0.1%, 0.3%, and 0.5%, respectively. The flow state of the liquid was observed, and the rheological mechanical properties of the self-assembled polypeptide were tested. The microstructure of polypeptide (mass fraction of 0.1% and 0.001%) -human serum albumin solution was observed by scanning electron microscope and transmission electron microscope.
RESULTS AND CONCLUSION: (1) Hydrogels could be formed between different volumes of polypeptide solution and platelet-rich plasma. Compared with platelet-rich plasma hydrogels, 0.1% and 0.3% polypeptide-platelet-rich plasma hydrogels could alleviate the sudden release of epidermal growth factor and vascular endothelial growth factor, and extend the release time to 48 hours. (2) After the addition of human serum albumin, the 0.1% polypeptide group still exhibited a flowing liquid, the 0.3% polypeptide group was semi-liquid, and the 0.5% polypeptide group stimulated self-assembly to form hydrogel. It was determined that human serum albumin in platelet-rich plasma could stimulate the self-assembly of polypeptides. With the increase of the mass fraction of the polypeptide, the higher the storage modulus of the self-assembled polypeptide, the easier it was to form glue. (3) Transmission electron microscopy exhibited that the polypeptide nanofibers were short and disordered before the addition of human serum albumin. After the addition of human serum albumin, the polypeptide nanofibers became significantly longer and cross-linked into bundles, forming a dense fiber network structure. Under a scanning electron microscope, the polypeptides displayed a disordered lamellar structure before adding human serum albumin. After the addition of human serum albumin, the polypeptides self-assembled into cross-linked and densely arranged porous structures. (4) In conclusion, the novel polypeptide can self-assemble triggered by platelet-rich plasma and the self-assembly effect can be accurately adjusted according to the ratio of human serum albumin to polypeptide. This polypeptide has a sustained release effect on the growth factors of platelet-rich plasma, which can be used as a new biomaterial for tissue repair.  

Key words: tissue engineering, platelet-rich plasma hydrogel, polypeptide, self-assembly, nanofiber, porous network, growth factor, sustained-release