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The Science of Fat Transfer

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Plastic surgery is famously innovative. It takes theoretical techniques and refines them until they work. It is the specialty that stands at the very forefront of surgical knowledge and provides the skills, tools and science behind every great advance in surgery

This started 6000BC with the engineering of pedicled tissue flaps for nasal reconstruction, through to modern day microsurgery that benefits every aspect of transplant surgery to the now with the advancement and understanding of autologous fat transfer (AFG).

Rozina often describes fat as ‘liquid gold’ or the ‘elixir of youth’ since it is the richest adult tissue source of stem cells. It is the ultimate example of surgical ‘upcycling’. The technologies and expertise in fat transfer continue to develop rapidly and in the right hands, it is a very useful aesthetic tool in most breast reconstruction, breast aesthetics and facial and body rejuvenation procedures,

AFG is useful for both cosmetic and reconstructive indications because there is no scarring at the injection site, no foreign material implanted, a low rate of serious complications, and a typically desirable donor site. Fat transfer is a deceptively simple technique with myriad benefits in soft-tissue augmentation and its regenerative effects on local tissue such as reversal of hyperpigmentation, softening of hypertrophic scars, increased local vascularity, and improvement of radiated tissue.

The diverse applications of fat grafting include facial rejuvenation, hand rejuvenation, breast reconstruction and volume enhancement, treatment of skin photoaging, correction of contour deformities, and improvement of senile and diabetic plantar fat pad atrophy..

Unfortunately fat transfer is often misunderstood as a procedure with no limitiations, no scars and no downside. This is not the case and outcome is dependent on the limited fat sources available and  fat survival rates. The most troublesome and persistent issue in fat grafting is the unpredictable  volume retention of fat grafts after fat transplantation (fat tranfer)

The original theory of fat cell survival is the corollary of that of skin graft survival:-

The fat cells (adipocytes) are thought to be reliant on picking up an oxygenated blood supply and cellular hypoxia is the major factor adversely affecting the engraftment process and thus long-term volume retention. Studies demonstrate that mature adipocytes can tolerate low oxygen tensions (hypoxia) for only 24 hours at normal core body temperature due to the relatively active metabolic demand of the cell types.

Fat grafting involves placement of 1–4 mm diameter adipose tissue fragments, each consisting of thousands of individual cells, into a profoundly ischemic adipose tissue recipient site microenvironment. Ideally, the graft fragment is initially nourished by diffusion of oxygen and glucose from the surrounding tissue and quickly revascularized through microvascular inosculation and neovascularization.

A significant proportion of injected fat, however, fails to successfully engraft due to a lack of oxygen causing cell death before new vessels can develop. Passive diffusion of oxygen and glucose is not sufficient to sustain adipocytes located at a depth of more than about 10 cells from the surface and thus the cells die due to a lack of sufficient oxygen.

An alternative, or additional factor in successful fat engraftment is the presence of adipose-derived stem cells (ASCs). These cells are pluripotent mesenchymal stem cells that reside in large numbers in adult adipose tissue. It is estimated that 1–3 million of these small stellate-shaped cells typically reside in proximity to small vessels of adipose tissue. Adipose stem cells are known to tolerate the conditions associated with harvest and graft injection more successfully than mature adipocytes, participate in the tissue response to these stresses, and direct adipose tissue regeneration.

Adipose-derived stem cells have many characteristics which aid in the retention of fat grafts. First, ASCs are able to differentiate into new fat cells to replace mature fat cells that could not withstand the transfer process.

Second, ASCs have been shown to actively promote new blood vessels. By promoting the development of new vasculature in the grafted tissue, ASCs are able to speed the recovery and reduce the number of cells succumbing to hypoxic stress, thereby improving graft volume retention.

How to transfer across enough adipocytes and ASCs into a sufficiently well vascularized recipient bed is the ongoing work of fat transfer. The future is to continue developing gentle tissue handling techniques, fat purification without sacrificing ASCs and post-injection supportive measures to optimize fat survival.

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