Goals/Purpose: Autologous fat transplantation is a widely used technique for soft tissue augmentation in both aesthetic and reconstructive surgery. Volume maintenance is thought to be maximized by the injection of small amounts of fat in multiple areas thus enhancing rapid neovascularization. In spite of meticulous efforts, fat graft take can be unpredictable. Carriers and matrix design have been suggested to provide a favorable environment for cell growth and angiogenesis. Hyaluronan has been shown to be a promising cell carrier in adipose tissue engineering.
Methods/Technique: Fat was harvested from the groins of 27 rats, rinsed with lactated Ringer's solution, left to drain on Telfa and meticulously cut into very small injectable pieces. The processed fat was injected using 1 cc Luer-Lok™ syringes and a 16 gauge angiocatheter in multiple passes beneath the rat's dorsum forming two implants (0.8 cc each). The first implant contained fat alone and the second contained fat and hyaluronan (HA 4 mg/ml concentration) in 1:1 mix (Fat-HA). CT scan of the implants in vivo was performed at base line and at 4 weeks (n=8), 12 weeks (n=8) and 20 weeks (n=9). Scans were performed with a GE Locus high resolution small animal CT scanner using a soft tissue protocol. Fat and hyaluronan densities were determined by scanning a tube containing rat fat and another containing the hyaluronan material that had the same concentration used in this study. Volumetric analysis was performed of all implants. Fat-HA implants volume was measured as a whole. In addition, the fat component's volume was measured based on the difference in density between fat and hyaluronan. Rats were sacrificed in three groups at the same time intervals and histological studies were performed with hematoxylin and eosin and CD 31 stains. Wilcoxon signed rank tests were performed to evaluate changes within animal, and the Kruskal-Wallis test followed by the Steel-Dwass multiple comparison procedure was used to compare sacrifice times. A p-value of 0.05 was considered statistically significant.
Results/Complications: One rat died from anesthesia and another from the 12-week group was excluded from volumetric analysis due to incomplete image capture of the implants. All grafts in all animal groups were clinically viable. Fat volume change (as measured by CT scan analysis), measured as percentage change from baseline was significantly different (smaller) for both fat and Fat-HA measures, at all time intervals. However, at 20 weeks, the fat component of the Fat-HA implant had significantly less volume loss than the fat only implant (p=0.008). Overall, fat necrosis was significantly less in the Fat-HA measures as compared to the fat alone measures (p<0.001). This difference was most profound at 4 weeks (p=0.008). However, differences at 12 and at 20 weeks did not reach statistical significance. At 12 weeks, the blood density measures for the Fat-HA implants were significantly greater than fat alone (p=0.016). However, this did not reach statistical significance at 4 or at 20 weeks. No significant correlations were observed between blood vessel density and the development of fat necrosis in each implant.
Conclusion: Hyaluronan was compatible with adipose tissue and may act as a carrier to enhance cell viability, and angiogenesis. Although resorption was observed in both implants, the Fat-HA showed more fat volume maintenance at long term follow up. This technology may provide technical advancements in small volume fat grafting of contour defects in facial and breast reconstruction. Further research is needed using human adipose tissue and different hyaluronan concentrations.
Table 1: Differences in the changes in fat necrosis (%) by sacrifice time are shown. Medians and quartiles are provided.
|
| Week 4 | Week 12 | Week 20 | Group | |||
Factor | Total | N | Median (IQR) | N | Median (IQR) | N | Median (IQR) | p value |
Fat Necrosis (%) | 26 | 8 | 60.00 (47.50, 63.75) | 9 | 5.00 (0.00, 5.00) | 9 | 5.00 (1.00, 10.00) | < 0.001 |
Fat-HA Necrosis (%) | 24 | 8 | 5.00 (3.75, 13.75) | 7 | 0.00 (0.00, 0.00) | 9 | 0.00 (0.00, 1.00) | 0.042 |
Difference Between Sides - Necrosis | 24 | 8 | -50.00 (-55.00, -43.75) | 7 | 0.00 (-5.00, 0.00) | 9 | -5.00 (-9.00, -1.00) | < 0.001 |
* Fat only represents the fat component in the Fat-HA graft, i.e. (Fat-HA) – HA.
Figure 1, Fat and hyaluronan in a Luer-Lok™ Tip syringe.
Figure 2, Fat and hyaluronan in a Luer-Lok™ Tip syringe after mixing.
Figure 3, Fat alone in a Luer-Lok™ Tip syringe after mixing.
Figure 4, Rat dorsum immediately after injection of fat alone and fat mixed with hyaluronan on either side of the midline.
Figure 5, Fat + hyaluronan graft after harvest at 4 weeks.
Figure 6, Fat + hyaluronan graft after harvest at 4 weeks with cross section. Notice clinical viability of fat well incorporated within hyaluronan gel.
Figure 7, Fat alone graft after harvest at 4 weeks.
Figure 8, CT scan image of fat + hyaluronan implant with 3 D reconstruction.