The Synergetic Roles of Stromal Vascular Fraction (SVF) and Extracellular Matrix (ECM) on Fat Graft Retention in Nude Mice

Background. Both stromal vascular fraction (SVF) and extracellular matrix (ECM) are of great concern to adipogenesis and angiogenesis. SVF and ECM are rich in adipose tissue and may provide structural and biochemical support and form a microenvironment for free granular fat. The present study was to investigate whether SVF-gel, a mixture of SVF and ECM harvested by mechanical emulsification, could improve the long-term volume retention of fat grafts. Methods. Human SVF-gel of different percentages was mixed with microfat. According to the percentages of SVF-gel into microfat, 4 groups were included in the study; they are the microfat group, 10% gel group, 30% gel group, and gel group. The fat grafts were transplanted in the subcutaneous layer on each flank in nude mice. The sample volume was measured to evaluate the fat retention rate 90 days post-transplantation. Tissue integrity, collagen content, numbers of viable adipocytes, and density of blood vessels were examined by further detection. Results. The retention volume rates in the 30% gel group and gel group were significantly higher than the microfat group and the 10% gel group (p < 0.05). Equivalent fat integrity was observed in the four groups. Higher collagen volume, enhanced mRNA expression of VEGF, TNF-α and adiponectin, more CD31-positive blood vessels, and more regenerative adipocytes were observed in the 30% gel group and the gel group. The fat tissue in the 30% gel group showed similar structures as the normal fat tissue, while almost of the tissue in the gel group exhibited as fibrous tissue. Conclusion. SVF-gel could improve fat graft retention while it came to a certain ratio into microfat via proangiogenic effect and fat regeneration which may be provided by SVF and ECM synergistically. SVF-gel-assisted fat grafting is a promising strategy to be used in clinical operations.