The present investigation evaluates the effects of long-term, local delivery of insulin, insulin-like growth factor-1 (IGF-1), and basic fibroblast growth factor (bFGF) on fat-graft survival using a poly (lactic-co-glycolic-acid)-polyethylene glycol (PLGA/PEG) microsphere delivery system. Twelve-micrometer PLGA/PEG microspheres incorporated separately with insulin, IGF-1, and bFGF were manufactured using a double-emulsion solvent-extraction technique. Inguinal fat from Sprague Dawley rats was harvested, diced, washed, and mixed with (1) insulin microspheres, (2) insulin-like growth factor-1 microspheres, (3) basic fibroblast growth factor microspheres, (4) a combination of the insulin and IGF-1 microspheres, and (5) a combination of insulin, IGF-1, and bFGF microspheres. The treated fat grafts were implanted autologously into subdermal pockets in six animals for each group. Animals receiving untreated fat grafts and fat grafts treated with blank microspheres constituted two external control groups (six animals per external control group). At 12 weeks, all fat-graft groups were compared on the basis of weight maintenance and a histomorphometric analysis of adipocyte area percentage, indices of volume retention and cell composition, respectively. Weight maintenance was defined as the final graft weight as a percent of the implanted graft weight. All growth factor treatments significantly increased fat-graft weight maintenance objectively, and volume maintenance grossly, in comparison with the untreated and blank microsphere-treated controls. Treatment with insulin and IGF-1, alone or in combination, was found to increase the adipocyte area percentage in comparison with fat grafts treated with bFGF alone or in combination with other growth factors. In conclusion, the findings of this study indicate that long-term, local delivery of growth factors with PLGA/PEG microspheres has the potential to increase fat-graft survival rates. Further, the type of growth factor delivered may influence the cellular/stromal composition of the grafted tissue. (Plast. Reconstr. Surg. 105: 1712, 2000.)
Autologous fat grafts have many advantages in the reconstruction for soft-tissue volume and contour defects. Fat is soft, pliable, readily available, and it can be harvested with minimal morbidity using direct excision and needle or cannula aspiration techniques. 1 However, the successful use of fat grafting is frequently limited by the sometimes low, and often unpredictable, survival rates. 2-5 This postoperative phenomenon frequently results in the need for initial overcorrection, and/or multiple operations, to meet the recipient site volume and contour requirements. 6-8
Secondary to the dissatisfaction with fat-graft survival, there have been many experimental and clinical attempts to increase survival rates. These include (1) fat concentration procedures to increase the number of living adipose cells transplanted, 9 (2) washing techniques to eliminate inflammatory mediators, 10 and (3) the utilization of reduced negative pressure liposuction harvest to decrease mechanical trauma to the grafted tissue. 11 Additionally, studies have focused on providing a more supportive biochemical milieu to the transferred adipocytes with the addition of steroids and vitamin E. 12,13 However, many of these manipulations have failed to produce results that are fully satisfactory.
In contrast, fat-graft bioactivation using dextran beads to deliver bFGF has proven to be a relative experimental success. 14-16 Postnatal adipose tissue has been shown to contain a subpopulation of preadipocytes with the potential to differentiate into mature, lipid-containing adipocytes. 17-21 Rather than focusing on the mature adipocytes, fat-graft bioactivation aims to improve fat-graft survival rates by stimulating the replacement the volume lost during the trauma of harvest and the early ischemic phase with new mature adipocytes from the differentiation of cells in the transferred preadipocyte pool that have remained viable following graft transplantation.
Insulin and IGF-1 have been shown to stimulate adipocyte proliferation, differentiation, and trophic activities in vitro. 22-27 However, the single administration of insulin in vivo does not affect fat-graft survival. 28,29 On the other hand, the clinical observation that reveals hypertrophic effect of insulin on adipose tissue is local lipohypertrophy associated with multiple injections of insulin. 30 We believe that the long-term, local delivery of insulin, IGF-1, and bFGF holds great potential for altering fat-graft survival rates.
Recently, researchers in the fields of controlled drug delivery and tissue engineering have been working with a completely biodegradable poly(lactic-co-glycolic-acid)-polyethylene glycol (PLGA/PEG) microsphere system for the long-term delivery of a variety of pharmacologic agents. 31 The in vivo use of these microspheres for delivery of insulin, IGF-1, and bFGF to adipose tissue has not yet been reported.
In the present investigation, we evaluate the effect of PLGA/PEG microsphere long-term delivery of insulin, IGF-1, and bFGF on fat-graft weight maintenance and the graft cell/stromal composition. We demonstrate that the long-term delivery of insulin, IGF-1, and bFGF successfully increases the weight maintenance of subdermally implanted autologous fat grafts. Furthermore, we demonstrate that the type of growth factor delivered may affect the ultimate graft cell/stromal composition.