Platelet-Rich Plasma in Tissue Engineering: Hype and Hope
Authors: Lang Siegmund , Loibl Markus , Herrmann Marietta 
Published: September 2018

<b><i>Background:</i></b> Platelet-rich plasma (PRP) refers to an enriched platelet suspension in plasma. In addition to the clinical application of PRP in the context of various orthopedic diseases and beyond, PRP and platelet lysate (PL) have been in focus in the field of tissue engineering. In this review, we discuss the application of PRP as a cell culture supplement and as part of tissue engineering strategies, particularly emphasizing current hurdles and ambiguities regarding the efficacy of PRP in these approaches. <b><i>Summary:</i></b> As a putative autologous replacement for animal-derived supplements such as fetal calf serum (FCS), PRP has been applied as cell culture supplement for the expansion of stem and progenitor cells for tissue engineering applications and cell therapies. Attributed to the high content of growth factors in platelets, PRP has been shown to promote cell growth, which was mostly superior to standard cultures supplemented with FCS, while the differentiation capacity of progenitor cells seems not to be affected. However, it was also suggested that cultivation of cells with PRP significantly alters the protein expression profile in cells in comparison to FCS, indicating that the influence of PRP on cell behavior should be thoroughly investigated. Moreover, different PRP preparation methods and donor variations have to be considered for the use of PRP under good manufacturing practice conditions. PRP has been used for various tissue engineering applications in the context of bone, cartilage, skin, and soft tissue repair, where most studies were conducted in the field of bone tissue engineering. These approaches take either advantage of the release of chemoattractive, angiogenic, proliferative, and putatively pro-regenerative growth factors from PRP, and/or the hydrogel properties of activated PRP, making it suitable as a cell delivery vehicle. In many of these studies, PRP is combined with biomaterials, cells, and in some cases recombinant growth factors. Although the experimental design often does not allow conclusions on the pro-regenerative effect of PRP itself, most publications report beneficial effects if PRP is added to the tissue-engineered construct. Furthermore, it was demonstrated that the release of growth factors from PRP may be tailored and controlled when PRP is combined with materials able to capture growth factors. <b><i>Key Messages:</i></b> Platelet-derived preparations such as PRP and PL represent a promising source of autologous growth factors, which may be applied as cell culture supplement or to promote regeneration in tissue-engineered constructs. Furthermore, activated PRP is a promising candidate as an autologous cell carrier. However, the studies investigating PRP in these contexts often show conflicting results, which most likely can be attributed to the lack of standardized preparation methods, particularly with regard to the platelet content and donor variation of PRP. Ultimately, the use of PRP has to be tailored for the individual application.