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In Vivo Comparison Of Adipose Particle Size On Autologous Fat Graft Retention In A Rodent
Xiaonan Yang, MD, PhD1,2, Francesco M. Egro1, Taraneh Jones1, Vincent Nerone1, Jeffrey A. Gusenoff1, J. Peter Rubin1, Lauren Kokai1.
1Department of Plastic Surgery, University of Pittsburgh School of Medicine, PITTSBURGH, PA, USA, 2Plastic Surgery Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China.

Background: Unpredictable retention outcomes remain a significant issue in autologous fat grafting procedures. Liposuction cannula variation leads to variability in fat particle size. Recent data suggest that the size of fat particles is closely related to graft healing outcomes, however this remains a point of contention due to potential confounding variables such as tissue trauma with harvest. The aim of this study was to compare autologous fat grafting outcomes with variable fat particle sizes in an animal model which isolated fat particle size as the primary experimental variable. The overall goal of this work is to determine if reducing fat particle size is an effective method for enhancing graft retention in autologous fat grafting.
Methods: The range of fat particle diameter harvested by four common liposuction cannulas was quantified to define relevant small and large particle target diameters. To determine if particle size impacted nutrient and oxygen permeability, small and large particles were incubated in vitro in a spinner flask with an abundance of culture media and VEGF secretion was measured with ELISA. Finally, small and large fat grafts were prepared from subcutaneous mouse fat pads and syngeneically grafted in Balb/CJ mice. Weight and volume retention were evaluated at 1,4, 8, and 12 weeks. Histological analysis with Massonís trichrome and perilipin immunofluorescent staining was performed. qRT-PCR was performed for adipogenic, inflammatory and apoptotic genes.
Results: The range of fat particle diameters harvested with four commonly used cannulas was 2-7 mm. In vitro studies showed that 5-7mm particles had significantly increased VEGF secretion normalized to weight, indicating increased tissue hypoxia in these particles compared to 2-4mm. Surprisingly, in vivo comparison in two unique studies showed 2-4mm and 5-7mm fat particles had comparable graft retention (p=0.5329). Massonís trichrome staining revealed increased extracellular matrix and fibrosis in the 5-7 mm particle group (p=0.0115). Adipocyte survival with perilipin demonstrated comparable viability. Gene expression showed large particles experienced increased inflammation and apoptosis at 1 week after grafting, but overall there were no significant differences between groups.
Conclusions: The ideal fat particle size should be large enough to contain adequate mesenchyme while not so thick as to preclude imbibition. This study suggests that despite changes in hypoxia and VEGF levels, differing fat particles (2-4mm and 5-7mm) can achieve similar graft retention.


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