Mechanism of action of PRP

1) Release of activated growth factors to promote tissue regeneration and repair: Once PRP is activated by thrombin, it can release 5–8 types of growth factors that accelerate wound healing, including transforming growth factor-beta (TGF-β), platelet-derived growth factor (PDGF)-like factors, insulin-like growth factor (IGF), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), and others. TGF-β plays a crucial role in promoting the mitosis of fibroblasts, osteoblast precursors, and vascular endothelial cells, and is essential for cell formation, proliferation, and differentiation. It also enhances the expression of the extracellular matrix (ECM)—including collagen and fibrin—and inhibits ECM degradation. PDGF is one of the earliest growth factors to appear at the wound site. Human body tissues such as vascular endothelial cells, fibroblasts, macrophages, and bone marrow stromal stem cells all express PDGF receptors, enabling these cells to undergo mitotic division and proliferate exponentially. PDGF promotes angiogenesis, increases collagen synthesis, and activates macrophages as well as other growth factors. Once activated, macrophages efficiently clear necrotic tissue and subsequently release various other growth factors in the second phase of wound healing, playing a critical role in the later stages of tissue repair. VEGF, through autocrine or paracrine mechanisms, induces or promotes the formation of new blood vessels, creating a microenvironment favorable for bone regeneration and accelerating the healing of chronic wounds. IGF promotes cell division and further differentiation, and exhibits synergistic effects with PDGF. EGF is a potent promoter of cell division and also stimulates the synthesis and deposition of the extracellular matrix. Therefore, PRP is currently widely used in fields such as cosmetic surgery, orthopedics, diabetes management, and burn treatment.

2) Acting as a scaffold: PRP contains abundant fibrin, fibronectin, and vitronectin. These components have the ability to adhere to cells, preventing cell loss and promoting bone formation through traction.

3) Mechanism of growth factor release: Platelet granules contain large amounts of pre-synthesized, inactive growth factors. These factors are activated when platelets enter the interstitial space and, through degranulation, release substantial quantities of growth factors. PRP begins releasing growth factors within 10 minutes after clotting, and within one hour, it has already released 95% of the pre-synthesized growth factors. Moreover, PRP continues to synthesize and secrete growth factors throughout its lifespan, which lasts approximately seven days. After platelets become depleted and die, the macrophage system takes over and continues to secrete the same growth factors, thereby promoting wound healing. Immediately after secretion, growth factors bind to specific receptors on target cells. These target cells include mesenchymal stem cells, osteoblasts, fibroblasts, endothelial cells of blood vessels, and epidermal cells, among others. Growth factors activate receptors on the cell membrane, triggering signaling pathways that regulate the normal expression of cellular genes, promote cell proliferation, stimulate matrix secretion, collagen synthesis, and osteoid formation. Since growth factors do not enter the cell interior, they do not alter the genetic characteristics of target cells, do not induce tumorigenesis, and merely accelerate the natural healing process.

4) The effective concentration of PRP: The activation of mesenchymal stem cells in normal tissues is closely related to the platelet concentration. Only when the platelet concentration in PRP reaches 4 to 5 times that of whole blood does the activation of mesenchymal stem cells significantly increase. Increasing the platelet concentration in PRP can markedly enhance fibroblast proliferation and type I collagen expression. Therefore, a high-concentration PRP is crucial for achieving optimal therapeutic effects. Experimental studies have shown that a 5% PRP exhibits the strongest proliferative effect on cells, whereas a 20% concentration does not further enhance cell proliferation. In other words, the concentration of growth factors is not necessarily better at higher levels; once the upper limit of growth factor concentration is exceeded, their effectiveness actually begins to decline. Based on his many years of research, MARX concludes that the ideal platelet concentration in PRP should be approximately five times that of whole blood.

5) Regarding the activity of PRP: During the preparation of PRP, if platelets are damaged, they will no longer be able to secrete growth factors. After PRP is prepared, its viability under anticoagulated conditions can only be maintained for 8 hours; beyond this time limit, it should no longer be used.