Incorporation of Perfluorocarbons into Fat Graft May Improve Oxygenation (2017)

Sir: Fat grafting is a very common procedure in plastic surgery. However, a key limitation is unpredictable graft retention, and it is in part attributable to variable oxygenation at the recipient site. Surgeons have mitigated this problem by transplanting smaller aliquots of fat graft and in different tissue planes to reduce the oxygen diffusion distances. Despite these maneuvers, fat grafting may require multiple attempts to achieve the desired clinical result. To reduce the number of fat grafting procedures, each attempt should maximize viable fat graft volume by improving oxygen delivery. There has been little done so far to develop strategies for enhanced oxygen delivery to a fat graft. Strategies to improve oxygen delivery may include the following: (1) increasing the available oxygen partial pressure at the recipient site; and (2) increasing the oxygen permeability of the fat graft. Researchers have explored the concept of hyperbaric oxygenation, which may improve fat graft retention if used early after transplantation,1 but is probably neither practical nor cost-effective in the way the therapy could be delivered today.1,2 This represents an opportunity to develop a method or technology to enhance oxygenation at the recipient site. Furthermore, to date, there has been no attempt to enhance the oxygen permeability of a fat graft using materials that have a higher oxygen solubility, such as perfluorocarbon,3,4 which have a high oxygen solubility and are largely bioinert substances with a history of clinical use. This short communication explains the potential theoretical improvement in oxygen delivery into a fat graft should a perfluorocarbon be incorporated. Imagine a cell “product” containing harvested clusters of adipose tissue mixed in a slurry with perfluorocarbons. Using a well-accepted mathematical relation developed by Maxwell,5 the resultant improvement in oxygen permeability can be calculated. The Maxwell relation estimates the effective oxygen permeability of a continuous material (in this example, the lipoaspirate) when another immiscible material with different properties3 (such as a perfluorocarbon) is dispersed within it. Assume that the volume fraction of perfluorocarbon is 30 percent of the adipose tissue product, using the Maxwell relation the effective oxygen permeability increases by 2.2. If the volume fraction of perfluorocarbon is 50 percent, the effective oxygen permeability increases by 3.8. These values can be used to then estimate the improvement in oxygen penetration depth (L) into the fat graft from its surface using mass conservation equation in planar geometry as shown in Equation 1, where OCR is the oxygen consumption rate of the adipose tissue and (α D) is the product of oxygen solubility and diffusivity, which is oxygen permeability. As an example (Equations 2 and 3), assuming we produce an adipose tissue product containing 50 percent perfluorocarbon by volume: If From these calculations, in this example, the oxygen penetration depth doubles—which may result in a substantial improvement in oxygen delivery, depending on the original thickness of the fat graft. In conclusion, adequate oxygenation is important in improving fat graft retention. Strategies to improve oxygen availability may include increasing oxygen partial pressure at the recipient site or fat graft oxygen permeability. A possible method to improve fat graft oxygen permeability is to incorporate perfluorocarbons. DISCLOSURE The authors have no financial interest to disclose related to the work presented herein. Thomas M. Suszynski, M.D., Ph.D.Travis G. Boyd, M.D.James F. Thornton, M.D.Department of Plastic SurgeryUniversity of Texas Southwestern Medical CenterDallas, Texas