The Composition Analysis Of Lipoaspirate-derived Fibrous Connective Tissue And Effects On The Survival Quality And Mechanical Properties Of Fat Grafts

During the clinical purification of lipoaspirates,the fibrous connective tissue(fiber for short)is usually removed to obtain fat for transplantation.However,the fiber contains the extracellular matrix of adipose tissue,which performs structural support for tissues and cells.The protein component in the fiber affects the migration,proliferation and differentiation of cells;moreover,the extracellular matrix of adipose tissue is the location of stromal vascular fractions(SVF),in which the stem cells play an important role during adipogenesis and angiogenesis after lipotransfer.Theorically,fiber removal will affect survival quality and mechanical properties of fat grafts.However,there is still no clear evidence in vivo and vitro about how the fiber affects the fat grafts.Objectives:1.To obtain basic data on the expression and content of protein and the number of SVF cells in the fiber from lipoaspirates to provide evidence for further research and mechanism discussion.2.To investigate the difference of survival quality and mechanical properties of grafts with different proportions of the fat and fiber in nude mice to provide data references for clinical practice.Methods:Obtain lipoaspirates from the patients under abdominal liposuction and pick out the fibers under the naked eye.Western blot and ELISA were used to detect the expression and content of Collagen Ⅰ,Laminin,Collagen Ⅳ,Fibronectin,and Myosin.The SVF in fat and fiber of equal volume was obtained by collagenase digestion for cell counting and comparison.0.3 ml of grafts from the fat group(100%fat),the mixed group(50%fat,50%fiber in volume ratio),and the fiber group(100%fiber)were injected into 3 different sites of the mice dorsum.A total of 27 mice were injected and 9 nude mice were sacrified for sample collection at 4,8,and 12 weeks after injection.The grafts were taken for the following tests:volume retention rate,histological analysis,and elasticity modulus.Results:The fiber contains Collagen Ⅰ(5.122±4.581 μg/L),Laminin(15.876±0.385 μg/L),Collagen Ⅳ(4.488±4.822 μg/L)and Fibronectin(10.55±8.403 μg/L).The number of SVF cells in fat(1.27 ±0.45×105/ml)was significantly higher than that in fibers(3.42±1.34×104/ml),P<0.01.Graft volume retention rate:at week 4,the fiber group>the mixed group>the fat group,and the difference among three groups was statistically significant;at week 8,the fiber group>the mixed group>the fat group,and the difference between the fiber group and the fat group was statistically significant,while the remaining comparisons were not statistically significant;at week 12,the differences among three groups were not statistically significant.Histological analysis:the parameter of intact adipocytes at each time point:the fat group>the mixed group>the fiber group,and the difference between the fat group and the mixed group was not statistically significant,while the remaining comparisons were statistically significant.The parameter of cyst,fibrosis and inflammation:the fat group>the mixed group>the fiber group,and the difference among three groups at each time point was statistically significant.Capillary density:there was no significant difference among three groups at week 4 and 8;at week 12,the fat group>the mixed group>the fiber group,and the difference among three groups was statistically significant.Elasticity modulus:at week 4,the fat group>the mixed group>the fiber group,and the differences between the fat group and the fiber group and between the fat group and the mixed group were statistically significant;at week 8,the fat group>the mixed group>the fiber group,and the difference between the fat group and the fiber group was statistically significant,while the remaining comparisons were not statistically significant;at week 12,the difference among three groups was not statistically significant.Conclusions1.The main component of the fiber is extracellular matrix,which contains Collagen Ⅰ,Laminin,Collagen Ⅳ and Fibronectin.The SVF cells in the fiber is less than that in the fat of equal volume.2.The fiber content in the graft does not affect the long-term volume retention rate and elasticity modulus.The increase of fiber content in the graft reduces the degree of fibrosis and inflammation,the number of cysts,the intact adipocytes and the capillary density.