Optimization of a Nanofiber-Hydrogel Composite for Improved Fat Graft Survival
Deepa Bhat, MD1,2, Bart Kachniarz, MD1, Michelle Seu, B.S.1, Russell Martin, PhD1, Xiaowei Li, Phd1, Brian Cho, MD1, Sashank Reddy, MD PhD1, Hai-Quan Mao, PhD1, Justin Sacks, MD MBA1.
1Johns Hopkins University, Baltimore, MD, USA, 2University of Illinois-Metropolitan Group Hospitals, Chicago, IL, USA.
PURPOSE: Autologous fat grafting is a commonly performed procedure in the field of plastic surgery. However, it is imperfect and oftentimes fraught with complications. High resorption rates, oil cyst formation, fat necrosis/calcification, and need for multiple procedures can occur. We have developed a nanofiber-hydrogel composite that can be injected along with the patient’s own fat in order to promote graft retention and vascularization, serving as a tissue scaffold that mimics native extra-cellular matrix. The purpose of this study was to characterize the mechanical/rheological properties of our soft-tissue scaffold when combined with adipose tissue. In addition, we compared adipose tissue survival with and without composite in in-vitro cell culture studies, with the intention of implanting this into an in-vivo murine model.
METHODS: Varying ratios of fat and composite were mixed into pre-formed molds and allowed to gel. The different groups were tested using the rheometer to assess their individual storage moduli (G’), which is a measure of a material’s flow and deformation characteristics (Pa). Fat and a mixture of 75% fat and 25% composite were then cultured in-vitro with growth media to assess viability over a period of seven days. Alamar Blue was used to quantify relative amounts of cell survival. The Live/Dead assay was employed for fluorescence images and absolute cell count. Immunohistochemistry was performed to analyze adipocyte morphology and composite integration on a cellular level.
RESULTS: Figure 1 summarizes the rheology data. A ratio of 75% fat and 25% composite greatly increases storage modulus, as compared to the other groups. Figure 2 shows cell viability over a period of 7 days using the Alamar Blue test, demonstrating that our composite is benign and does not harm adipose tissue cells. Figure 3 demonstrates the integration of our nanofiber tissue scaffold with human adipose tissue on a cellular level using immunohistochemistry techniques.
CONCLUSION: When combined in a 75%:25% fat to composite ratio, the storage modulus (G’) of the combined materials increases in a synergistic manner. This is important because the storage modulus is a measure of how deformable a material is. With higher storage moduli, the fat/composite combination is less deformable and thus stronger/less susceptible to shear forces. Previous research has demonstrated that this translates to less lipolysis and higher adipocyte survival. Thus, it can reasonably be inferred that having a fat-composite combination with a high storage modulus would translate to improved adipocyte and fat graft survival in-vivo. This has strong clinical implications, as this translates to less morbidity and fewer procedures for the patient undergoing fat grafting for soft tissue reconstruction.
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