Abstract: BACKGROUND: Autologous fat is an ideal filler that repairs soft tissue defects, but the long-term survival rate of adipose tissue after transplantation has uncertainty. We explored the effect of adipose tissue structure on the survival of fat transplantation, providing theoretical basis for improving the clinical effect of fat transplantation.  
OBJECTIVE: To investigate the viability of different fat derivatives in vitro and the outcome after transplantation.
METHODS:  The adipose tissue obtained after liposuction was prepared into four kinds of adipose derivatives: large granular adipose tissue, medium granular adipose tissue, small granular adipose tissue and stromal vascular fraction gel. Fat acquisition rate and histological structural integrity, content, activity and migration ability of adipose-derived stem cells were compared. Four groups of adipose derivatives were randomly injected into the back of nude mice. The survival rate of the grafts, tissue structure observation and CD31 immunohistochemical staining were performed 1 and 12 weeks after transplantation.  
RESULTS AND CONCLUSION: (1) The volume acquisition rates of large, medium, small granular fat and stromal vascular fraction gel were (71.43±2.87)%, (57.14±3.11)%, (45.72±3.97)%, and (11.30±2.33)%, respectively. The fat histological structure of the large particles was the most complete, followed by the medium and small granular fat groups, and the tissue structure of stromal vascular fraction gel was basically completely destroyed. (2) The contents of adipose stem cells obtained from large, medium, small granular fat and stromal vascular fraction gel were (5.03±0.56)×107 L-1, (3.77±0.46)×107 L-1, (2.01±0.64)×107 L-1, and (14.84±1.09)×107 L-1, respectively, with significant differences (P < 0.05). (3) The proliferation ability of adipose stem cells in large granular fat group was the best, followed by medium and small granular fat groups; the proliferation ability of stromal vascular fraction gel group was the worst. (4) The migration ability of adipose stem cells in large granular fat group was the best, followed by medium granular fat group, while that in the small granular fat group and stromal vascular fraction gel group was poor. (5) After transplantation, the volume retention rate of stromal vascular fraction gel group was the highest, followed by large granular fat group, while small granular fat group was the worst. (6) After 12 weeks of fat transplantation, fat cells in large granular fat group were partially destroyed; cells in medium granular fat group and small granular fat group were largely destroyed and some vesicles were formed; a large number of mature fat cells were formed in stromal vascular fraction gel group. (7) At 12 weeks after transplantation, the formation of blood vessels in large granular fat group and stromal vascular fraction gel group was more than that in medium granular fat group, while small granular fat group was the least, with significant differences (P < 0.05). There was no significant difference between the large granular fat group and stromal vascular fraction gel group (P > 0.05). (8) Results show that structural integrity of adipose tissue affects adipose stem cell production, vitality and adipose tissue survival rate after transplantation. Suitable options are made according to the characteristics of different fat derivatives to achieve the best filling effect.

Key words: granular fat, stromal vascular fraction gel, fat transplantation, fat derivatives, structural integrity, survival rate