Regarding autologous fat transplantation and filling, I have divided it into six aspects, such as donor area selection, fat acquisition, fat out, transplantation method, additives and stem cells. I. Donor area selection There has been no clear scientific conclusion on the ideal donor area for autologous adipose tissue extraction. Studies of subcutaneous adipose tissue in various parts of the body have revealed that there is little difference in the viability of adipocytes and no significant difference in the weight, volume and histomorphology of the grafts after transplantation. However, the highest numbers of adipocytes and adipose stem cells were found in the adipose tissue of the lower abdomen and inner thighs, and adipocytes in these areas have alpha2 receptors, which are resistant to lipolysis and less responsive to nutrients, and have a higher probability of survival after transplantation. Adipose stem cells then help to reduce cell death in the early stages of transplantation and maintain long-lasting transplantation results. Therefore, most scholars currently consider the lower abdomen and inner thighs as the best donor areas. Second, fat acquisition The use of swelling technique + negative pressure liposuction technique to extract fat has become a consensus, but there is still a controversy on how to obtain the fat with the least impact on the vitality of adipose tissue. Currently, the commonly used methods are syringe method and mechanical extraction method. Studies have shown that there is no significant difference in the cell proliferation capacity of traditional negative pressure liposuction compared with syringe method. The use of smaller volume syringes or low negative pressure devices for extraction is more effective in maintaining the viability and metabolic function of fat cells than the traditional liposuction method or larger volume syringes. However, it has also been shown that the syringe method is superior to negative pressure liposuction, with the former losing only 5% of adipocytes compared to up to 90% loss in the latter. Morphological studies of adipocytes in adipose tissue obtained using different negative pressures have shown that when the negative pressure is higher than -700 mmHg (-93.1 kPa), the adipocytes rupture due to damage. The adipose tissue extracted using the negative pressure liposuction method has weak adipocyte function and is not easily survived after transplantation, although it maintains normal tissue structure and the number of viable adipocytes that approximate normal adipose tissue. By comparing the Coleman method with the traditional negative pressure liposuction method, it was found that the former method can obtain a larger number of viable fat cells with good function, and therefore the Coleman method is considered the most suitable method for fat acquisition. Regarding the selection of the liposuction needle and syringe for harvesting, it is believed that the larger the diameter of the needle, the greater the number of viable fat cells. Therefore, most doctors recommend using blunt-tipped liposuction needles with a diameter of 3 to 4 mm for liposuction retrieval with the lowest negative pressure. However, some studies have confirmed that using a 2mm diameter liposuction needle with a blunt tip with several side holes and a 10mL syringe is more beneficial than a 3mm diameter liposuction needle connected to a 60mL syringe for retrieval. Third, fat treatment The purpose of fat treatment is to remove inactivated cells, cell debris, blood, free lipids, swelling fluid, etc., in order to purify the adipose tissue and to benefit the survival of the transplanted fat. Although different opinions still exist, it has become a consensus that adipose tissue must be treated before transplantation, and static sedimentation, filtration and centrifugation are the common clinical treatment methods used today. Some studies have shown that there is no difference in the outcome of adipose tissue treated by these three methods one year after transplantation, and there is no difference in the percentage of adipocyte breakdown with or without centrifugation and the conditions used. So what method of treatment causes the least damage to the fat tissue? Studies have shown that the speed of centrifugation has a linear relationship with the viability of fat grafts, with faster speeds resulting in lower viability. When the centrifugation speed reaches 4000r/min, the fat cells will rupture; when the centrifugation speed is 1500-3000r/min and the centrifugation time is more than 5min; or when the centrifugation speed is 5000r/min and the centrifugation time is 1min, the survival rate of fat cells are very low. Therefore, it is proposed that 3 min at 1500-3000 r/min is the optimum condition for treating fat. It was found that there was no significant difference in the survival rate of transplanted fat between adipose tissue treated with cotton pad filtration or gauze filtration and those treated by centrifugation; and after treatment by static sedimentation method, more blood cells remained in the grafts, and the number of stem cells was very small. It has been suggested that centrifugal treatment is only applicable to small injections, but not for large numbers of grafts. Therefore, there is no consensus on fat treatment. Fourth, transplantation methods There are various methods of fat transplantation, including syringe method, injection gun method, spiral push injection method, thread push injection method, pneumatic push injection method, electric push injection method, etc. Each method has its own characteristics, and the key is how to inject to ensure the survival of transplanted fat! Studies have shown that the recipient area can only provide nutrients to the transplanted fat (1.5±0.5) mm away from it through plasma leaching, and only 40% of the transplanted fat can survive by this route. Coleman advocates the use of 1mL or 2mL syringes connected to 17-gauge needles to graft smaller amounts of fat into numerous areas in multiple tunnels. Studies on the effect of injection plane on the survival of transplanted fat have found that injection into the superficial surface of the muscle has a higher survival rate than subcutaneous and deep surface of the muscle, and subcutaneous injection has a better long-term effect, so multiple planes of injection are advocated, and a blunt-tipped needle with a diameter of 2 mm should be used to inject in a fan shape while retracting the needle, and each tunnel should be injected with 1/30 mL to obtain 82% survival rate. and advocate 30% to 50% correction to the right. In summary, according to a large number of experimental and clinical studies, the consensus of fat grafting technology recognized by most scholars is the principle of “three low and three more”, namely low-pressure aspiration, low-speed centrifugation, low-volume injection; multi-tunnel, multi-plane, multi-point injection. V. Role of additives in improving the survival rate of autologous fat transplantation In response to the various factors affecting the survival of autologous fat transplantation, in addition to the aforementioned selection of the donor area and improvement of the extraction, purification treatment and transplantation methods, studies have been conducted at home and abroad to promote vascularization, reduce inflammatory reactions and improve colloid osmotic pressure in order to improve the survival rate of autologous fat transplantation, including the addition of platelet-rich plasma (PRP), albumin, and other protein to the transplanted fat tissue. (PRP), albumin, growth factors, insulin, vitamin E, thyroxine, and non-steroidal anti-inflammatory drugs. PRP can improve the survival rate by increasing the vascularization rate of the transplanted adipose tissue, allowing long-term survival of the transplanted adipocytes and precursor cells. In addition, various growth factors such as PDGF, FGF, VEGF, and TGF-β accumulate in platelet alpha granules and play their corresponding roles as platelet activation and degranulation are released. Albumin can prevent adipocyte osmotic pressure imbalance shock due to the decrease of soluble protein molecule concentration in swelling anesthesia and purification treatment. Insulin can enhance the metabolic capacity of adipocytes and inhibit lipolysis, and vitamin E plays an important role in this process. In addition, insulin can induce fibroblasts to acquire lipids produced by lipolysis and thus transform into adipocytes, etc. VI. Role of stem cells and other adjuvant techniques in improving the survival rate of autologous fat transplantation Cell-assisted fat transplantation technique is a new method of autologous fat transplantation, which is a mixture of adipose stem cells and adipose tissue. Adipose stem cells are dual stem cells, which are the source of adipocytes and angiogenic cells. The roles of adipose stem cells in CAL: 1) differentiate into adipocytes and promote adipose tissue regeneration; 2) differentiate into vascular endothelial cells and vessel wall cells to promote neovascularization and graft survival; 3) release vascular endothelial growth factor; 4) exist partially as original adipose stem cells. The amount of adipose stem cells in the autologous adipose tissue obtained by aspiration is only 50% of the original amount in vivo. The purpose of using CAL technology is to restore the ratio of adipose stem cells to mature cells in autologous adipose tissue as much as possible by replenishing adipose stem cells. Studies have shown that this move can increase the volume or weight of surviving adipose tissue. The stromal vascular component is a mixture of different cell types obtained by collagenase digestion of adipose tissue to form a cellular mass. These cellular components are mainly mesenchymal cells, vascular endothelial cells and mural cells without adipocytes. The addition of a vascular matrix component is a way to supplement the adipose stem cell content of the transplanted adipose tissue and has been widely used in clinical practice. Tip: Autologous fat grafting is a safe and effective technique commonly used in the field of cosmetic surgery and restoration and reconstruction. However, fat grafting is not yet able to be filled at once, but still needs to be filled in small amounts several times, and there are still some urgent problems to be solved in terms of graft survival rate. It is believed that there will be new improvements and enhancements through further research and exploration in the future.