Cell-Free Fat Extract (Ceffe) Combined with GelMA Hydrogel to Improve the Survival Rate of Random Skin Flaps in Mice

Enhancing flap survival is essential in flap surgery. Cell-free fat extract (Ceffe), a "natural cocktail" of bioactive compounds derived from adipocytes, has demonstrated the potential to improve flap viability. However, direct local injection of Ceffe is limited by its quick leakage and short duration of effectiveness. To address these limitations, this study encapsulated Ceffe in a gelatin methacrylate (GelMA) hydrogel to develop a more stable releasing system. The role of Ceffe in promoting angiogenesis and facilitating flap repair was evaluated by using CCK-8 assays, scratch assays, and tube formation assays. Its antioxidative stress effect was first assessed using flow cytometry and further validated through subsequent experiments employing immunofluorescence and PCR. Scanning electron microscopy (SEM) confirmed that Ceffe@GelMA retained a porous structure, while rheological testing demonstrated its injectability. Drug release assays indicated that GelMA, containing a high concentration of Ceffe, was capable of sustained Ceffe release beneath the flap, thereby promoting flap repair. The biocompatibility of GelMA was assessed using Phalloidin staining, live-dead staining, CCK-8 assays, hemolysis tests, and subcutaneous degradation assay, all of which demonstrated favorable biocompatibility. In a murine random skin flap model, temperature measurements of the flap suggested that Ceffe@GelMA exhibited significant pro-repair activity. Histological analysis through HE and Masson's trichrome staining revealed the presence of abundant neovessels. Immunofluorescence analysis of endothelial marker CD31, vascular endothelial growth factor (VEGF), and smooth muscle actin (α-SMA) further supported that the Ceffe@GelMA treatment group exhibited enhanced pro-angiogenic potential. This study provides substantial evidence supporting Ceffe's therapeutic efficacy in flap necrosis prevention and establishes a Ceffe-incorporated hydrogel system, representing a significant advancement in clinical treatment strategies.