"Optimization and Standardization of the Immunodeficient Mouse Model for Assessing Fat Grafting Outcomes".

Background. Animal models are often used to assess interventions that might improve fat grafting outcomes, however, there is great variability in the models. We sought to determine the predictive value of the immunocompromised mouse model for fat grafting so that experiments could be standardized and optimized. Methods. Human lipoaspirate injections at different volumes and time points were assessed in a nude mouse model and compared with control injections of non-viable fat. Volume retention and explant histologic score were compared. In a separate study, inter-animal reproducibility was determined by implanting a highly consistent hydrogel and measuring variability in volume retention. Results. Injection volume significantly affects adipose resorption kinetics at 6 and 12 weeks. Masson's trichrome revealed that macrophages were unable to infiltrate large (1 ml) grafts, and oil cysts were not absorbed by 18 weeks, which interfered with interpretation of volume retention data. Non-viable tissue was resorbed when grafts were of 0.3mL and quantification of graft histologic viability correlated well with graft retention at all study time points. Inter-animal variability was measured to be 8.44% of the mean retention volume for small graft volumes. Conclusion. Human fat graft retention in the immunodeficient mouse correlates with graft viability in small, 0.3mL volume grafts. However, centralized oil cysts in non-viable 1.0mL grafts were not resorbed by 18 weeks and thus volume measurements were confounded and not significantly different from viable samples. Additionally, tissue injury scores increased in initially healthy fat grafts at 18 weeks, possibly due to a delayed immune reaction. (C)2017American Society of Plastic Surgeons

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