Fat tissue, Harvesting techniques and processing of fat graft
Adipose tissue is remarkably complex and has a profound role in nutrient homeostasis and is, due to adipose-derived serum factors like adipsin, TNF-α and leptin seen as a separate endocrine organ(21). Fat tissue further has a necessary role in thermogenesis and insulation and protects important organs like the eyes mechanically (22). Fat tissue therefore contains a high quantity of cell types. Adipose-derived stem cells (ASCs) can differentiate into adipocytes, fibroblasts, neurons, muscles or endothelial cells (8). Zuk et al found regenerative and stem cells in the stromal vascular fraction (SVF) of fat (23). SVFcells have been shown to have regenerative effects, like angiogenesis and reduction of inflammation in facial aesthetics. There are reports on regenerative effects on elastin and collagen fibers and an elevation of capillary density (24).
Every step in the process of AFG from the choice of the donor site, donor site preparation, to harvesting over processing to injection has the potential to influence graft outcome and volume retention (19). Tuin et al analysed 35 studies to identify the optimal processing technique. Their outcome was adipocyte viability, ASC survival and growth factors in vitro, volume of the graft in animal studies and volume retention in human studies. They discovered no superior processing technique could be identified based on clinical outcome (25). Lee et al found no differences in histology and weight with high versus low aspiration pressure in lipoaspirates injected in nude mice. Shear stress had a high impact on graft viability, therefore slowly injected fat grafts outperformed injection with high shear stress (26).