Studies on Equine Platelet-Rich Plasma: Preparation and Activation Methods, Composition, In Vivo Effects, and Material Properties

Platelet-rich plasma (PRP) is an autologous biological product used to improve the quality of tissue repair at sites of injury, by virtue of the growth factors contained in platelet alpha granules. PRP is most often applied by percutaneous intra-lesional injection, but can also be used in a gel form during open surgical applications. Clinical practices of PRP use vary widely for both horses and people, based on variables such as preparation method, platelet activation, platelet concentration, and physical form of the product. This dissertation is comprised of 6 studies that were undertaken to examine these variables and generate recommendations for the clinical use of PRP in horses. The key findings of this work are as follows: 1. Platelet activation, which is required for growth factor delivery to tissues, may not occur simply as a result of the injection process or exposure to collagen. Exogenous PRP activation is likely to improve growth factor delivery. 2. Activation methods differ in terms of growth factor release. Calcium chloride and bovine thrombin are superior to autologous thrombin or freeze-thaw cycles in terms of growth factor release from equine PRP. 3. Growth factor concentrations are directly correlated to platelet concentration in equine PRP. 4. When used intra-articularly, PRP induces a transient inflammatory response in the synovial fluid, which differs according to activation method. 5. Growth factor concentrations in synovial fluid did not change significantly after intra-articular injection of PRP, but inflammatory cytokines did increase significantly over 6-24 hours. However, when examined in vitro, platelets appear to activate spontaneously upon exposure to synovial fluid, causing significant increases in growth factor concentrations in the synovial fluid but without any increase in inflammatory cytokines. 6. The material properties of fibrin gels are altered by the inclusion of platelets. Platelet-rich fibrin gels may confer structural and functional advantages over conventional fibrin gels when used as a biomaterial in tissue engineering and regenerative medicine.