Joris van Dongen

241 tSVF enriched facial lipofilling with PRP physiological process where elastin gradually degrades due to ultraviolet exposure and wear-and-tear with no substantial changes in a short period of time. These changes over time cause no significant release of cytokines and thus transplanted ASCs are probably not sufficiently triggered by host environment to regenerate tissue. To induce a regeneration trigger, host environment might be damaged deliberately prior treatment using trichloroacetic (TCA) peeling. Aging related skin modifications cannot be considered damaged tissue and therefore lipofilling for skin rejuvenation is not a suitable indication and should only be used for a volumizing effect of the facial fat compartments in the aging face. In contrast, pathological processes are accompanied by a burst release of growth factors and cytokines initiating inflammation, a disturbance in extracellular matrix remodeling and reducing angiogenesis. These growth factors and cytokines trigger ASCs to release anti-inflammatory and pro-angiogenic cytokines as well as metalloproteinase to remodel extracellular matrix. 41 Thus far, several clinical studies have shown that autologous lipofilling might increase scar remodeling. 42 Although, PRP contains a large number of pro-angiogenic growth factor and metalloproteinases, clinical data of skin rejuvenation remains insufficient. 8,43 A systematic review by Maisel-Campbell et al. evaluated studies using PRP as a monotherapy for skin rejuvenation. 43 In total, ten studies treating 180 patients with PRP showed improvement in satisfaction, skin texture, hydration and pigmentation. However, almost all studies used non-validated and subjective outcome measurements and most studies failed to report the concentration of platelets in PRP or baseline blood samples. It is well-known that platelet concentrations highly variable during the day and most PRP preparation devices use relatively increased number of platelets compared to the baseline at the moment of preparation. Studies have shown that high concentrations of PRP increases proliferation of ASCs but may also induces undesirable differentiation. 10,11 High concentrations of PRP may change ASCs towards a more fibrotic phenotype with a less angiogenic capacity as well. 9 Hence, the concentration of PRP was reduced from six to eight times above threshold in our previous study to four times above threshold in this study. 12 However, most suitable concentration of PRP to maximize tissue regeneration by ASCs remains unknown in vivo which is one of the limitations of this study as well. Yet, baseline concentration of platelets was comparable between both study groups. Similarly, the ratio of SVF/lipofilling is still on debate. In this study, a ratio of 1:6 for respectively tSVF and superficial lipofilling was used based on pragmatic reasons. Ni et al. showed that a ratio of 1:3 for respectively cSVF and lipofilling was ideal in terms of volume maintenance in comparison with lower ratios in a rabbit model three months after injection. 44 Other studies confirmed the aforementioned results and showed that