Joris van Dongen

216 Chapter 9 and behavior. High PRP concentrations increase proliferation, but also changes ASC into a fibroblast like phenotype, with increased collagen RNA expression and altered paracrine signaling that negatively influences endothelial vessel formation 55, 56 . Although platelet counts were normal within our well-defined healthy patient cohort, combined with comparable fat-graft-PRP-or-placebo mixture ratios, our study is potentially biased and weakened by this concentration-depended effect. Moreover, this phenomenon could explain the failure of clinical studies. Local growth factor conditions after lipofilling are also an issue that remains unclear; in a healthy patient, the release of platelets and pro-inflammatory factors due to damage caused by the lipofilling procedure itself could be of such an extent that the addition of PRP actually is insignificant and/or redundant or even too high. CONCLUSION This randomized double-blinded, placebo-controlled study clearly has shown that PRP significantly reduces post-operative recovery time but does not improve patient outcome when looking at skin elasticity, improvement of the nasolabial fold nor patient satisfaction. The reversal of the correlation between age and elasticity might indicate for some effect on skin, but requires more power of future studies. Thus far, the use of PRP as an additive in lipofilling has shown great promises in vitro. These beneficiary effects, however, have only partially been reproduced in a clinical setting. A growing number of studies report a concentration depended effect of PRP in vitro, making optimal use in a clinical setting delicate and complex. Further studies of PRP interactions on both the lipograft as well as the receptor host site involved cells seems to be of paramount importance to determine the optimal use and concentrations of PRP in a clinical setting.