Background:Fat grafting technologies are popularly used in plastic and reconstructive surgery.Due to its size limitation,it is hard to directly inject untreated fat tissue into the dermal layer.Nanofat,which was introduced by Tonnard,solves this problem by mechanically emulsifying fat tissue.However,the viability of the cells was greatly destroyed.In this study,we reported a new method by gentlydigesting the fat tissue to produce viable adipocytes,progenitors,and stromal stem cells using collagenase I digestion and centrifugation.This was named Vivo nanofat.Methods:Human liposuction aspirates were obtained from five healthy female donors with mean age of 28.7 ± 5.6 years.Colony-forming assay,flow cytometry analysis,and adipogenic and osteogenic induction of the adherent cells from the Vivo nanofat were used to characterize the adipose mesenchymal stem cells (MSCs).To investigate in vivo survival,we respectively injected Vivo nanofat and nanofat subcutaneously to the back of 8-week-old male BALB/c nude mice.Samples were harvested 2 days,2 weeks,and 4 weeks postinjection for measurement,hematoxylin and eosin staining,and immunostaining.Results:Our results showed that the Vivo nanofat contained a large number of colony-forming cells.These cells expressed MSC markers and had multi-differentiative potential.In vivo transplantation showed that the Vivo nanofat had lower resorption ratio than that of nanofat.The size of the transplanted nanofat was obviously smaller than that of Vivo nanofat 4 weeks postinjection (0.50 ± 0.17 cm vs.0.81 ± 0.07 cm,t =-5783,P =0.01).Conclusion:Vivo nanofat may serve as a cell fraction injectable through a fine needle;this could be used for cosmetic applications.