D. A. Atashroo1, T. Wearda1, J. Raphel2, K. Paik1, E. Zielins1, G. Walmsley1, M. Hu1, K. Senarath-Yapa1, S. Menon1, A. Luan1, R. Tevlin1, D. Duscher1, Z. Maan1, G. Gurtner1, D. Wan1, S. Heilshorn2, M. T. Longaker1 2Stanford,Material Science,Stanford, CA, USA 1Stanford,Plastic Surgery,Stanford, CA, USA
Introduction:
Based on it’s abundant availability, ease of harvest, and biocompatability, fat grafting has grown tremendously in popularity. Even so, it suffers from unpredictable outcomes. At this point, little is known about how specific components in a fat grafting algorithm affect graft quality and survival. In this study, we use rheology, the study of material flow and deformation, to quantify the effects that cannula diameter, length, and shape, flow rate, and extensional flow have on the integrity of fat.
Methods:
Lipoaspirate was harvested from cosmetic surgery patients using suction assisted liposuction. To prepare lipoaspirate for grafting, it was allowed to settle and then centrifuged and filtered to remove blood, oil, and debris. To test the effects of cannula size and length, a syringe pump was used to inject fat at a controlled flow rate through various gauge (g) cannulas ranging from 8 to 25 cm in length. All other variables were then held constant, and fat was injected at variable flow rates ranges from .1 ml/sec to greater than 2 ml/sec. The effects of extensional flow, a rheological concept where pulling of a material causes it to deform in the absence of shear, was then tested with specially designed cannulas. After injection, all processed samples were then tested in triplicate on a rheometer to measure their viscoelastic properties. Fat grafts from representative groups were then placed into the scalps of CD1 athymic nude mice. Volume of fat grafts was assessed by micro-CT at baseline and after 8 weeks when grafts were explanted, weighed, and sectioned for histology.
Results:
In general fat grafts injected through larger, shorter, straight cannulas and at slower flow rates exhibited less shear thinning. Importantly, clear breakpoints existed for these variables. The storage modulus (G’) of fat processed with 14g and larger cannulas was significantly higher than for fat processed with smaller gauge cannulas (*p < .05). Similarly, the 8 cm cannula group had a significantly greater G’ than the 25 cm cannula group (*p < .05). The optimal flow rate was .5ml sec, and this group had a significantly improved integrity compared to the 1 ml/sec and faster groups (*p < .05). Interestingly, the .1 ml/sec group, even though the slowest flow rate, tended to break down more than the .5 ml/sec group (p = .08). In-vivo results comparing graft survival recapitulated the rheological findings in representative groups.
Conclusions:
Surgeon choice of fat grafting algorithm has a significant impact on the final integrity of placed fat. This study outlines specific alterations that surgeons may make to respect the damaging effects of shear forces and thereby optimize placement outcomes.
