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Platelet-Rich Plasma (PRP): What Is PRP and What Is Not PRP?

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Platelet-Rich Plasma (PRP): What Is PRP and What Is Not PRP? Reprinted from IMPLANT DENTISTRY Vol.10No.4 2001 Copyright@ 2001 by Lippincott Williams & Wilkins Printed in U.S.A. Platelet-Rich Plasma (PRP): What Is PRP and What Is Not PRP? Robert E. Marx, DDS Iatelet-rich plasma (PRP) has been a break- factors_ Recombinant growth factors are pure hu­ through in the stimulation and acceleration man growth factors, but they are not native P of bone and soft tissue healing. It represents growth factors. Human cells such as platelets do a relatively new biotechnology that is part of the not synthesize them. Instead they are synthesized growing interest in tissue engineering and cellular usually by a culture of Chinese hamster ovarian therapy today. Because of its newness, there is a cells that have a human gene inserted into their potential for misunderstanding, misuse, and applica­ nucleus through a bacterial plasmid vector. Re­ tion ofwhat the practitioner may incorrectly think is combinant growth factors are single growth factors PRP. The purpose of this paper is to discuss the def­ and are delivered in high doses within either a inition of PRP, its safety, its proper development, synthetic carrier or a carrier derived from pro­ and its most efficacious means of application. cessed animal proteins. PRP is the combination of seven native growth factors within a normal clot as the carrier. The clot is composed of fibrin, fi­ bronectin, and vitronectin, which are cell adhesion Platelet-rich plasma is just that; it is a volume of autologous plasma that has a platelet concentra­ molecules required for cell migration such as is tion above baseline. Normal platelet counts in seen in osteoconduction, wound epithelialization, blood range between 150,000/1J.1 and 350,000/1J.1 and osseointegration. PRP, however, contains only and average about 200,000/1J.1. Because the scien­ the same concentrations of these cell adhesion tific proof of bone and soft tissue healing en­ molecules as does a normal blood clot (200 IJ.g­ hancement has been shown using PRP with 400 IJ.g/ml). Therefore, PRP is not a fibrin glue. 1,000,000 platelets/lJ.l, it is this concentration of Platelet Rich Plasma is also not osteoinductive. It cannot induce new bone formation de noyo. Only platelets in a 5-ml volume of plasma which is the working definition of PRP today. Lesser concen­ the bone morphogenetic proteins (BMPs) are known to induce bone de novo. However, the pro­ trations cannot be relied upon to enhance wound healing, and greater concentrations have not yet been longed length of time required by recombinant shown to further enhance wound healing (Fig. I). BMP to produce de novo new bone formation and its immature osteoid nature suggest an opportunity WHAT IS PRP IN RELAnON TO for PRP to accelerate BMP activity in the future. RECOMBINANT GROWTH FACTORS? PRP acts on healing capable cells to increase their numbers (mitogenesis) and stimulate vascular Because PRP is developed from autologous ingrowth (angiogenesis). Therefore, it is unlikely blood, it is inherently safe and is free from trans­ to significantly promote bone substitutes and other missible diseases such as HIV and hepatitis. non-cellular graft materials. However, because it Within PRP, the increased number ofplatelets has been shown to stimulate autogenous marrow delivers an increased number of growth factors to grafts, it is likely to enhance the bone formation the surgical area. The seven known growth factors when applied to combinations of cellular autoge­ in PRP are: platelet derived growth factor as nous bone and non-cellular bone substitutes. (PDGFaa), PDGFbb, PDGFab, transforming growth factor beta-, (TGF-b,), TGF-b2. vascular TERMINOLOGY endothelial growth factor (VEGF), and epithelial ------------- ._------------------------­ growth factor (EGF). These are native growth fac­ There has already bCt:n some mistaken termi­ tors in their biologically determined ratios. This is nology related to PRP. Some have advanced the what distinguishes PRP from recombinant growth term "platelet concentrate." This is not correct because a platelet concentrate is a solid composi­ tion of platelets without plasma. which would ISSN 1056-616~/01l01004-225$~_OO Implant Dentistry therefore not clot. The clinically useful product is Volume 10 • Number 4 Copyright © 2001 by Lippincott Williams & Wilkins, Inc. a concentration of platelets in a small volume of IMPLANT DENTISTRY I VOLUME 10, NUMBER 4 2001 225 Human Platelet Derived Growth Factor AB (PDGF-AB) • lI • • • • • • • 200 400 600 800 1000 1200 t400 1800 1800 3 Platelet Count (xI0 /pl) Fig. I. Human platelet-derived growth factor AB (PDG-AB). Graph ofPDGF-ab versus platelet count indicates growth factors available to tissues as directly proportional to the concentration of platelets. plasma and is therefore a "platelet-rich plasma." blood, the device must use a double centrifugation Some have advanced the term "platelet gel." This technique. The first spin (called the hard spin) will is also incorrect because PRP is nothing more than separate the red blood cells from the plasma, a human blood clot with increased platelet num­ which contains the platelets, the white blood cells, bers. The clot by virtue of its cell adhesion mole­ and the clotting factors. The second spin (called cules has additional biologic activity, whereas a the soft spin) finely separates the platelets and gel does nol. Still others have reversed the term white blood cells together with a few red blood platelet-rich plasma into plasma rich in platelets, cells from the plasma. This soft spin produces the plasma very rich in platelets, and even plasma PRP and separates it from the platelet poor plasma very very rich in platelets. The ludicrousness of (PPP) free from the obstruction provided by a this terminology is obvious and is more reminis­ large number of red blood cells. To attempt PRP cent of a coffee house than a clinical science. with a single spin would not produce a true PRP. Instead, it would produce a mixture ofPRP and PROCESSING PRP AND PRP DEVICES PPP and have disappointingly low platelet counts. The professions have already seen numerous Regardless of the rate of centrifugation or the time individuals and corporations promoting devices to of centrifugation, a single spin cannot adequately processes PRP for either cost savings or economic concentrate platelets, because the red blood cells rewards. The practitioner should keep in mind that will interfere with the fine separation of the plate­ any PRP device should process a concentration of lets. This is germane to those who may use a lab­ at least 1,000,000 platelets/f.l.l in a 5-ml volume, oratory centrifuge to develop PRP or may pur­ process viable undamaged platelets, and process chase a device that is merely a modification of PRP in a sterile fashion and be pyrogen free. Lia­ Iaboratory centrifuge. Such centrifuges are de­ bility, consent, and licensing must be discussed signed for diagnostic purposes-not PRP develop­ because both patient and auxiliary staff safety is­ ment. They may not produce a sufficient platelet sues are pertinent. It should be noted that "sterile" yield, they may damage platelets, they may not and "pyrogen free" are not the same. Sterile use pyrogen free test tubes, and they are not FDA means the absence of microorganism. Pyrogen cleared. Therefore, they should not be used. free means the absence of any microorgan ism The FDA clearance is indeed important. Al­ products or foreign body particle that might pro­ though the patient is protected from transmissible duce a fever. Therefore, the PRP device must use diseases because of the autologous nature of PRP, only certified pyrogen free disposable materials. the practitioner and the auxiliary staff are not. De­ To truly concentrate platelets from autologous vices that leak blood or have the potential to mal­ 226 WHITE PAPER function from centrifuge misbalance, or design characteristic intended for diagnostic blood work, are a real health, medical, and legal risk. Practitio­ ners are recommended to look to devices that have the simple FDA clearance to process PRP from autologous whole blood. Further FDA clearances to mix PRP with autologous grafts and bone sub­ stitutes is an advanced security of some devices. No dental practitioner or medical practitioner is licensed to infuse or re-infuse blood or blood products systemically in an office setting. How­ Fig. 2. Platelet-rich plasma (PRP) membrane is an ever, it is within the licensure of each to apply activation of the clotting mechanism. which in turn activates platelets and stimulates the release of their growth factors. blood products topically in the office as is done with PRP. Office devices that produce PRP use only 45 ml to 60 ml of blood, which is insignifi­ study PRP but are actually studying growth factor cant related to a normal 4- to 5-L blood volume. depleted clots or supernatants. Complete PRP is There is no reason to re-infuse the blood that is both a fresh clot and the supernatant. not used, and it would be risky to do so. This knowledge is germane to those who have advanced the concept of developing PRP from APPLICATIONS OF PRP clotted blood or to companies that have promoted PRP may be mixed into a bone graft, layered "serum separator tubes." Serum is not plasma and in as the graft is placed, sprayed on a soft tissue contains almost no platelets. It is impossible to surface, applied on top of a graft, or used as a develop PRP from clotted whole blood. Because biologic membrane. However, clotting of the PRP the two functional roles of platelets in nature are should be done only at the time of use. Clotting initiation of healing and hemostasis, platelets be­ activates platelets, which begin secreting their come part of the physical blood clot and, there­ growth factors immediately (Fig.
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