Joris van Dongen

215 PRP enriched facial lipofilling formation of human umbilical vein endothelial cells both in vitro as well as in a nude mouse model 39 . PRP induces changes on endothelial cells that can contribute to (neo) angiogenesis of the fat graft and thereby enhance fat graft survival 44 . These findings however, fail to make a significant impact in the majority of available clinical PRP- lipofilling studies 45, 46 , thus questioning clinical use of PRP addition to lipofilling for this reason. PRP speeds up patient recovery Patient reported recovery time was significantly reduced by the addition of PRP in this study. This finding is in line with previous data from our retrospective study 11 and current literature on aesthetic procedures like fractional carbon dioxide laser resurfacing treatment 47, 48 . Dermal- and wound closure effects observed after PRP injection might be explained by the effect from PRP on fibroblasts. In vitro study of Ramos-Torrecillas et al. 49 eases the growth of fibroblasts and induces their differentiation into myofibroblasts, thus playing a key part in wound contracture 22 . Collagen 1 and extracellular matrix remodeling by fibroblast is also affected by PRP. Fibroblast exposed to PRP lysate in vitro up regulates the expression of Matrix metalloproteinase (MMP)-1 24 , which in its turn plays a key role in collagen remodeling. Also, type 1 collagen expression is increased under these circumstances 50 . Increased fibroblast activity, along with changes in collagen production and a potentially stronger inflammation response 51 could also play a role in our observed reduced recovery time after surgery when the lipograft was combined with PRP. The concentration paradox: Less is more? Apotential pitfall in evaluating the effect of PRP is the lack of uniformconcentrations of created PRP. The studies of Yamaguchi et al. 52, 53 were the first publications that showed that a higher concentration of PRP (or more platelets) may produce counterproductive effects, possibly by unwanted cell differentiation. Most commercially available PRP kits capture a percentage of available platelets fromwhole blood, not a certain quantitative number of platelets. Considering the fact that normal human platelet counts are defined within a wide range and show large daily variations, the cumulative amount of growth factors in kit-isolated PRP is inconsistent 54 . This variation can inadvertently influence its effect in a way as is observed in vitro on different cell types 22 . Regarding cells present in the lipograft, PRP concentration alters ASC proliferation, function