Experimental And Clinical Study Of Condensed Low Density Fat In Mega Volume Fat Graft For Breast Reconstruction

BackgroundIt is more than 100 years since the first clinical application of fat grafting.With many advantages,it has been extended to many areas of clinical practices.The morbidity of breast cancer has increased year by year.Patients who suffer breast cancer have intense willingness to reconstruct their breasts after mastectomy.However,it is difficult and traumatic to reconstruct such subunits accurately with traditional flap.While breast implants have poor hand feeling and high possibility of complications in the later period,more and more women would like to accept fat grafting for breast reconstruction.Numerous studies proved fat grafting is safe and effective for breast reconstruction.But there are still some problems in the usage of fat grafting in mega volume:1.The volume retention rate is not consistent from different literature reports.Because of the low retention of fat grafting,multiple operations will be necessary for a satistfied outcome.2.Possibilities of complications after grafting is high,such as big nodules and calcifications,which only can be removed by surgeries.It is reported that Coleman fat can be divided into high-density fat(HDF)and low density fat(LDF),according to the density of fat after centrifugation.The high-density fat contains more(stromal vascular fraction)SVF cells and(extracellular matrix)ECM components.HDF grafting have better volume retention and lower incidence of complication.However,in mega volume fat grafting,it will be a huge waste when only high-density fat is used for grafting,and a large trauma can be caused to the donor sites.Therefore,we try to explore a new method to optimize LDF for achieving better grafting effect and lesser complications.Our team found that ECM/SVF-gel has a significant improvement in volume retention and lower complications than Coleman fat.However,the ECM/SVF-gel output is pretty low,only 20%,which is not suitable for mega volume fat grafting.But the method is worth to explore for LDF optimization.Supposed LDF can be concentrated by physical shear force and centrifugation,the content of SVF cells and ECM will be increased and triglyceride will be reduced,better transplantation outcome could be achieved.The purpose of this study is to explore a reasonable and efficiency way to optimize LDF in mega volume fat grafting for breast reconstruction.Methods and resultsThe product of low density fat is named as CLDF(Condensed low density fat).The steps of this study are as below:1)Comparison of components and graft results between different density fat2)Definition of CLDF and standard protocol3)Analysis of cell subpopulation in CLDF4)Analysis of ECM in CLDF5)Experimental study of CLDF volume retention and complications in vivo6)Clinical applications of CLDF combined with HDF in breast reconstruction.The harvested fat was processed to generate Coleman fat.After centrifugation,the liquid portion was discarded.The Coleman fat was then divided into upper half layer and lower half layer by density.We found that SVF cells and ECM in HDF were the highest compared with Coleman fat and LDF and had best results.The lower fat was defined as HDF and saved for later use.The upper fat,defined as LDF,was processed by different degrees of mechanical force.The mixture was then processed by centrifugation.After centrifugation,the liquid portion and upper layer oil was removed,the substance with tight connection and elastic was defined as CLDF(Condensed low density fat).From the sedimented fat to the Coleman fat and finally to the CLDF,a standard of process has been developed.Volume of CLDF was gradually reduced as mechanical processing time increasing.Three groups with concentrations of 70%,50%,and 30%of the original LDF were obtained for intracellular and ECM composition comparison.CLDF presented a tighter tissue connection than LDF,with certain elasticity.It showed a large amount of collagen among tissue.Electron microscope showed the presence of numerous ECM with complete spatial structure and many small volume adipocytes.However,quantity and diameter of adipocytes varied with three groups of 70%,50%,and 30%concentration.The results of flow cytometry showed that SVF cells of 30%concentrated CLDF reached as 2-3 folds as LDF.ECM content of 30%concentrated CLDF was 2-3 times than LDF.Except for the content of single fat cells,other components of CLDF of 30%concentration group were close to or slightly higher than high-density fat.Fresh LDF,HDF,CLDF had been grafted on back of nude mice for 1 month and 3 months.Compared with LDF,CLDF showed more stable volume retention,and long-term retention rate was closer to high density fat in 1 and 3 months.A large number of small fat cells were found in CLDF tissue slices,similar situation in HDF.However,in LDF tissue slices,most of them were filled with cysts and fibrosis.We compared CLDF and HDF co-grafting with Coleman fat grafting to reconstruct breast in clinical.The volume retention rate of 6 months after co-grafting group was 44.06%±3.64%,which’s better than 33.00%±4.07%in Coleman fat group.The incidence of complications was about 5%in co-grafting group,while Coleman fat group was 25%.Conclusions1.CLDF concentrated ECM,SVF cells and small adipocytes only by mechanical process.2.CLDF retained small adipocytes,SVF cells and spatial complete ECM,which were good for volume retention.Large volume adipocytes were destroyed and the ineffective volume was reduced in the process for CLDF,which resulted to lower the incidence of complication.3.CLDF and HDF co-grafting in breast reconstruction has a better long-term volume retention and less complications than Coleman fat in clinical applications.4.CLDF is easy and simple to make and safe in clinical use,which meets the requirements of the current policies and regulations for clinical applications.CLDF in mega volume fat grafting has a wide clinical application prospect and is worthy of further research.