Joris van Dongen

329 General discussion and future perspectives GENERAL DISCUSSION AND FUTURE PERSPECTIVES Transplantation of adipose tissue i.e. lipofilling has been used to restore volume defects due to ageing as well as due to congenital or traumatic deviations for decades. 1 Adipose tissue, similar to almost all tissues, comprises of parenchyme (adipocytes) and supporting tissue. Obviously, the filler feature of adipose tissue is to be attributed to the 90% volume effect of adipocytes. In the past decades it has become clear that supporting tissue holds potency to support tissue repair and regeneration. Supporting tissue comprises connective tissue cells and vasculature that is embedding in an extracellular matrix. This is called the stromal vascular fraction of tissue (SVF). The current dogma is that the regenerative engine of adipose tissue comprises of adipose tissue-derived stromal cells (ASCs). ASCs reside in the SVF attached around vessels as precursor cell types e.g. pericytes and supra-adventitial cells. 2,3 Zuk et al. was the first to culture ASCs from enzymatically isolated adipose tissue and showed the multilineages differentiation capacity of ASCs in vitro e.g. ectodermal, endodermal and mesodermal. 4 During culture, ASCs secrete a plethora of growth factors, cytokines and proteins which are in potential able to support regeneration of damaged tissue. 5 Therefore, in order to make full use of the regenerative capacity of SVF, isolation procedures are warranted that yield all components. However, for reasons of simplicity, intra-operative enzymatic isolation procedures have been developed to isolate a single cell suspension of SVF cells containing ASCs by degrading all intercellular connections including extracellular matrix. 6 Nowadays, this single cell suspension of SVF cells is used for a variety of different clinical indications e.g. skin rejuvenation, scar remodeling, osteoarthritis or wound healing to mention a few. 7-9 However, clinical use of intra- operative enzymatic isolation procedures is expensive and time-consuming. Therefore, mechanical isolation procedures were developed to be faster and less expensive, although mechanical isolation procedures are not capable of disrupting all adipocytes in contrast to enzymatic isolation procedures that separate all adipocytes from SVF cells. For instance, the mechanical Lipogems procedure is able to process up to 130 ml of lipoaspirate to isolate about 60-100 ml of SVF, while 90% of the volume of adipose tissue is contributed by adipocytes. 10 Hence, a large number of adipocytes remain intact after performing the Lipogems procedure. Therefore, we have developed a mechanical isolation procedure to isolate SVF cells by effectively disrupting adipocytes. 11,12 This mechanical isolation procedure is called the Fractionation of Adipose Tissue (FAT) procedure yields SVF that is devoid of almost all adipocytes while preserving vasculature and SVF cells as well as cell-cell communications, extracellular matrix and cell- matrix interactions. Moreover, a large fraction of ASCs was present, which were phenotypically as well as functionally intact. The volume of the obtained SVF was