Joost Peerbooms

11 General Introduction chemotaxis, cell differentiation, and angiogenesis. Therefore, PRP is used to promote new tissue growth, preserve remaining tissue, reduce pain, and improve function. 9 History of PRP The concept and description of PRP originate from haematology. The term PRP was first used by Kingsley in 1954 to earmark platelet concentrate during blood coagulation experiments in the field of transfusion medicine. 10 In the 1970s, the term PRP was used to describe plasma with a platelet count higher than that of peripheral blood. This product was also investigated in a rat model to improve skin tissue healing. 11 In the following years, researchers established the role of platelets in enhancing tissue healing during the treatment of skin ulcers in humans. 12 Approximately 10 years later, PRP was studied in bone repair by Marx et al. 5 , who reported the beneficial effect of platelet-rich product on bone healing after maxillofacial surgery. Over the last decade, the popularity of PRP has increased, leading to much publicity about its use as a biological treatment for athletic injuries. Moreover, its application has grown exponentially in orthopaedics. Different Types of PRP When considering the use of PRP, health care practitioners should understand that the treatment has various forms. When whole blood is centrifuged, the different components of the blood are separated. Different protocols for the separation of blood components exist. On one end of the spectrum, hardly any separation of leukocytes and platelets occurs. On the other end of the spectrum, the platelets and leukocytes are (mostly) separated. If separation is limited, this technique is called buffy coat-based separation. If more separation between the cells is created, this is known as a plasma- based technique. 13-15 Because every commercially available product is made according to a different protocol (centrifugation time and speed, number of times the process is repeated, and G-forces used), a great deal of variation exists among the different products. The plasma-based technique yields leukocyte-poor PRP (LP-PRP), while the buffy coat- based technique creates leukocyte-rich PRP (LR-PRP). The fluid that remains after centrifuging the platelets and removing the leukocytes and erythrocytes is called platelet-poor plasma (PPP). For this thesis, we used a buffy coat-based preparation system and hence used LR-PRP in all studies. PPP was used alongside LR-PRP to investigate wound healing. Furthermore, there are different techniques for initiating platelet degranulation and the subsequent release of growth factors. 16 One such technique is to rely on the patient’s collagen to release thrombin in vivo and to start the degranulation of the platelets. Other available techniques use bovine thrombin or calcium chloride to antagonise the anticoagulant in donated blood. 17 The different PRP preparation methods could potentially affect the characteristics and therapeutic efficacy of the resulting product, 1