The effect of pressure and shear on autologous fat grafting.

BACKGROUND: Fat grafting has become routine in plastic surgery because of low donor-site morbidity, a low complication rate, and fast recovery time. The optimal technique, however, has yet to be defined. Two critical variables are pressure and shear, both defined as force divided by area. In this study, the authors examined the effect of pressure and shear on human fat grafts in a nude mouse model. METHODS: For negative pressure, tumescent liposuction was performed on fresh panniculectomy specimens. Suction pressure was either -15 inHg or -25 inHg. Lipoaspirate was centrifuged at 1200 g and injected into the flanks of nude mice. For positive pressure, positive pressure was applied to lipoaspirate up to 6 atm for up to 3 minutes and then injected into nude mice. For shear stress, lipoaspirate was centrifuged at 1200 g for 3 minutes and then injected with a fast flow rate (3 to 5 cc/second) or slow flow rate (0.5 to 1 cc/second). After 4 weeks, the fat grafts were analyzed for weight and histology. RESULTS: For negative pressure, there were no differences in weight or histology with high versus low suction pressures. For positive pressure, application of positive pressures up to 6 atm for up to 3 minutes did not create a significant difference in graft weight or histology at 4 weeks. For shear stress, in vivo, a slow injection pressure yielded a 38 percent increase in weight (p < 0.001) compared with fast injection. Histology was similarly affected. CONCLUSIONS: Higher aspiration pressures up to -0.83 atm did not affect fat graft viability in vivo. Positive pressure up to 6 atm also did not affect fat graft viability. The degree of shear stress, which is a function of flow rate, did significantly affect fat graft viability. Fat grafts injected slowly with low shear stress significantly outperformed fat injected with high shear stress. These data suggest that shear stress is a more important variable regarding fat graft viability than pressure.

Micro-mechanical fractional skin rejuvenation.

BACKGROUND: The most commonly performed skin rejuvenation procedure, laser resurfacing, is associated with adverse events and significant expense. The authors have developed a novel device that uses micro-coring needles to remove tissue in a fractional pattern and avoid the side effects of laser therapy. The authors compare the efficacy of these needles to standard needles in a pig model. METHODS: One swine was treated with three needle types: standard hypodermic, solid hypodermic, and the authors' novel coring needles. Thirty-two 1 × 1-inch sites per flank received either 20 or 40 percent treatment coverage. Photographs were taken and punch biopsies were performed at days 0, 7, 28, 56, and 84. Biopsy specimens were evaluated for histology and collagen content. RESULTS: All treatment sites healed quickly, with no evidence of scarring or infection. Coring sites were easily identified and contained increased fibroblast activity and newly synthesized collagen. At 1 month, the papillary dermis and epidermis of the coring sites were up to 196 percent thicker compared with controls (p < 0.001). The coring sites had enhanced undulating rete ridges-consistent with regeneration. At 3 months, a pronounced increase in collagen fibers and newly organized and augmented elastic fibers was seen. Enzyme-linked immunosorbent assay confirmed an 89 percent increase in collagen content in these coring sites (p < 0.001). CONCLUSIONS: This novel approach to skin rejuvenation was found to effectively induce the microscopic and biological endpoints of skin rejuvenation. This may provide a new modality for the safe and cost-effective treatment of age-related rhytides, skin laxity, photodamage, scarring, and striae.

A novel approach to adipocyte analysis.

BACKGROUND: Fat grafting bench research is difficult because many traditional endpoints cannot be used reliably with adipocytes. Manual cell counting with trypan blue is a common method of measuring cell viability. There are, however, multiple known limitations, including human error, inability to analyze cell size, overestimation of adipocyte viability, and labor intensity. In this study, the authors demonstrate the effectiveness of an improved method of accurate adipocyte analysis using an automated cell counter. METHODS: Human lipoaspirate was obtained, centrifuged, and digested. Samples were analyzed using a hemocytometer and an automated cell counter with two viability dyes. Results were then optimized by novel methods of preparation using carboxymethyl cellulose and formalin. RESULTS: Manual trypan blue cell counts ranged from 2,750,000 to 19,200,000 live cells/ml. Automated cell counts significantly reduced variability (3,230,000 to 4,290,000 cells/ml). Counting cells between 40 and 150 µm, which is more specific to adipocytes, yielded 1,040,000 to 1,420,000 viable cells/ml. Using a second viability dye, CellTiter Blue, cell counts ranged between 993,000 and 1,340,000 live cells/ml. Adding carboxymethyl cellulose substantially decreased sampling variability by 80 percent, and the use of formalin prevented the decrease in cell counts over 4 hours from 432,000 to 7,000 cells/ml. CONCLUSIONS: This novel method utilizing automated cell counters can more accurately identify the viable adipocyte population without the limitations of traditional cell counting. In addition, the use of carboxymethyl cellulose and formalin in the preparation process can decrease variability and stabilize cell counts over time. This is an efficient, specific, and reliable method of adipocyte analysis.