PEER-REVIEW | FACIAL AESTHETICS | The platelet cytoplasm contains an open, canalicular


system that increases the effective surface area for intake of stimulatory agonists and the discharge of effector secretions. The sub-membrane region contains microfilaments of actin and myosin that mediate morphologic alterations5


. These cells possess a


tricarboxylic acid cycle and use glucose by means of the glycolytic and hexose monophosphate shunt pathways4 Their function is closely linked to their metabolic activity.


.


PRP preparation A small volume of blood (ideally 20 ml) is taken by venipuncture from the patient and inserted into the correct size of tube to be centrifuged. Platelet concentration (growth factors) will be dependant on: ■ The amount of whole-blood used ■ Platelet recovery efficiency ■ The final volume of plasma in which platelets are suspended.


For these reasons, to homogenate the value of the


acceleration, which is of importance to the self-activation of the liquid, it is better to work with wide and short tubes. It is also important to choose a concentration factor of less than 4 to avoid a final concentration that is too high, which would be detrimental owing to a high risk of self-activation (premature). Self-activation in such cases is usually the result of an increase in concentration and platelet aggregation that follows their physical proximity. It has been established that excessive acceleration will


decrease the integrity of the platelet membrane, some of which are then activated10


400 G, 5% of platelets are activated11 It is well known


that the wound healing process is complex and typically divided into three phases; inflammatory, regeneration, and remodelling.


platelets activated at 3000 G12


. Thus, for values of more than , and 40–70% of will be .


The results obtained


with systems using a double centrifugation are similar to those that use a single centrifuge, but injections are more painful


and inflammatory13 , owing to


the ratio between platelets, leukocytes and plasma, as well as the increased amount of


manipulations. Furthermore, even if the desired concentrations are higher, the risk of self-activation will increase. PRP contains large numbers of cellular microparticles, including annexin V+


microparticles,


which are lost to varying degrees when PRP is double centrifuged to remove platelets. Platelet fragmentation during processing should be


avoided, because it is the process of activation that results in the completion of the tertiary structure of some


Table 1


GROWTH FACTORS (PDGF) ■ Chemo-attractive to


Fundamental growth factors PLATELET-DERIVED


mesenchymal stem cells and endothelial cells


■ Differentiation for fibroblasts and osteoblasts


■ Up-regulate effects of other growth factors on


cells such as macrophages ■ Mitogens of


mesenchymal stem cells promote the synthesis of the extracellular matrix


TRANSFORMING GROWTH FACTORS (TGF) ALPHA AND BETA


■ Promote cell mitosis ■ Significantly increase


type I collagen production in the tendons


■ Favour the synthesis of collagen


■ Sheath fibroblast ■ Stimulation of DNA


synthesis, proliferation of various types of cell


VASCULAR ENDOTHELIAL GROWTH FACTORS (VEGF)


■ Stimulate angiogenesis


■ Chemo-attractive for osteoblasts


EPIDERMAL GROWTH FACTORS (EGF)


■ Important role in the


regulation of cell growth, proliferation, and


differentiation by binding to its receptor EGFR


■ Induce epithelial


development and promote angiogenesis


■ Stimulate proliferation and differentiation of epidermis cells, co-


stimulating angionegesis


INSULIN-LIKE GROWTH FACTORS (IGF) 1 AND 2


■ Stimulate the proliferation and differentiation of osteoblasts


of the secretory proteins. As a result, such fragmentation during processing could result in the release of high levels of proteins with compromised bioactivity. The integrity of the platelet membrane can be preserved through the use of low gravity forces during the centrifugation process. Growth factors released from activated platelets initiate and modulate wound healing in both soft and hard tissue. There are a number of different PRP harvesting kits


available, but some contain thrombin — either from bovine or human origin — and therefore the end product cannot be categorised as autologous. Others use a chemical buffer to separate the plasma and red cells, and do not deliver pure PRP as a result. The separation should be physical, not chemical.


How does it work? It is well known that the wound healing process is complex and typically divided into three phases; inflammatory, regeneration, and remodelling (Figure 1). A number of proteins are contained within the platelet’s alpha-granules. Collectively, these proteins are members of the families of growth factors, cytokines and chemokines, which are broadly referred to as secretory proteins. They are of prime importance in the realisation of this entire process as each step of the healing cascade is under the influence of specific growth factors/ cytokines14


should achieve a 3- to 5-fold increase in platelet concentration over baseline5, 10, 15


. Owing to the presence of high concentrations of growth


factors, apart from the wide use to accelerate wound healing, PRP has been used in a wide variety of surgical procedures and clinical treatments. Indeed, there is substantial clinical evidence regarding its use in other medical fields14, 16


. The substantial concentration of platelets,


compared with normal blood, certainly represents a unique source of growth factors. Following subcutaneous injection, these proteins and growth factors interact with the basal cells in the subcutaneous tissue, including fibroblasts, endothelial cells, and subcutaneous stem cells. PRP is also used in the aesthetic field for the stimulation of the superficial dermis, as well as the deep layers of the dermis. It has been proven that PRP application both augments the skin and increases its volume17, 18


. Fitzpatrick published a study proving that topical


application of growth factors stimulate the rejuvenation of photoaged facial skin, improving its clinical appearance and inducing new collagen synthesis19, 20


, and another


research study showed that PRP actually induces increased expression of G1 cell cycle regulators, type I collagen, and matrix metalloproteinase (MMP)-1 in human dermal fibroblasts21


.


Cells, osteoblasts, fibroblasts, endothelial cells, and epidermal cells express the cell membrane receptors


. Some investigators have suggested that PRP


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