Joris van Dongen

150 Chapter 7 In this review the authors, both clinicians and biologist, try to bridge the gap between both worlds, provide a review of recent literature and summarize possible mechanism behind the anti-scarring effect of adipose tissue and its adipose-derived stem/stromal cells. LIPOFILLING ON A CELLULAR LEVEL Liposuction simply implicates the harvest of adipose tissue under negative pressure with small-bore suction cannulas. By this, the architecture of the fat tissue is disrupted and small lumps of adipose tissue are harvested and collected in a sterile environment (bag or collector), which can then be used for lipofilling subsequently. Inevitably, some degree of hypoxia occurs around the grafting of the lipoaspirate. In the recipient, the integration of the graft requires extensive (re)vascularization, which is primed by the occurring hypoxia as well as by the pre-existing microvasculature in the graft. Too large ‘lumps’ of lipograft obviously develop necrotic cores due to diffusion insufficiency, as a result of which the graft ‘take’ may be reduced 11-13 . Adipocytes are sensitive to hypoxia and as a consequence prone to apoptosis 11,12,14 . Depending on the technique and time that is required for harvesting and lipofilling 15,16 , 40-90% of the injected lipograft volume will remain 17 , while the rest is resorbed within months after grafting. Oily cysts may remain in the grafted area as a consequence of this fat necrosis. To improve fat graft survival, different processing techniques are used (e.g. centrifugation, decantation, gauze-towel technique). In a systematic review, these techniques are compared for viability of the fat graft as a whole 18 in terms of number of viable cells and in terms of graft volume survival in human and animal models. For fat graft survival, the gauze- towel processing technique is found to be superior to centrifugation or decantation. However, if the focus lies on the number of ADSC in adipose grafts, centrifugation improves the number of ADSC that can be isolated, compared to a non-centrifuged fat 19 . Thus, depending on the goal of lipofilling, different fat processing techniques need to be considered carefully. Adipose tissue, the energy storehouse of the human body, consists of a parenchymal mass of adipocytes that is structurally supported by connective tissue and perfused by blood vessels. All non-adipocyte tissue is called stroma or stromal tissue. Adipocytes are the main volumetric component of adipose tissue although they only comprise up to 20% of all cells 20 . Adipocytes consist of a thin layer of cytoplasm with an eccentric nucleus, while most of the volume is made up by the large central vacuole in which triglycerides predominantly are stored 21 .