The science of fat transfer
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 techniques 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 current advancement and understanding of autologous fat transfer (AFG).
Rozina Ali 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. It has a vital role in breast reconstruction, breast aesthetics and many facial rejuvenation procedures.
Using your own fat, autologous fat transfer (AFT) is the ultimate in upcycling tissues from an area of excess (thighs, belly) to an area of deficit (face, breasts) and is useful for both cosmetic and reconstructive indications. There is no scarring at the injection site, no foreign material implanted, a very low rate of any serious complications, and a typically desirable donor site.
Fat transfer is a deceptively simple technique with myriad benefits in soft-tissue augmentation and regenerative effects on local tissue such as reversal of hyperpigmentation, softening of hypertrophic scars and improvement of irradiated tissue.
Diverse applications of fat grafting include facial rejuvenation, hand rejuvenation, breast reconstruction and volume enhancement, treatment of skin photoaging and correction of contour deformities (tear trough, scars, divots).
Unfortunately, fat transfer is often misunderstood as a procedure with no limitations, 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 transfer.
Studies on fat grafting
Rozina is currently supervising PhD research into fat transfer and how to accurately determine the volumes that survive.
The original theory of fat cell survival was mooted to be comparable to that of skin graft survival, however, it is now considered more complex and multifactorial since the outcome takes 9-12 months to become established and is thought to be dependent on both fat cell survival and stem cell differentiation.
The fat cells (adipocytes) are thought to rely on picking up an oxygenated blood supply and a lack of sufficient oxygen (cellular hypoxia) is the major obstacle to successful fat transfer and 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 high metabolic demand of the fat cells.
Fat grafting involves placing large (1–4 mm) fatty fragments, each consisting of thousands of individual cells, into a potentially ischemic (poor blood perfusion) tissue recipient site. Ideally, the graft fragment is initially nourished by diffusion of oxygen and glucose from the surrounding tissue and rapid revascularisation. This process can only function up to 10 cells deep, so all fat cells need to be placed close to a vascular bed microenvironment (dermis, fascia, muscle).
A significant proportion of injected fat, however, fails to engraft or ‘take’ due to a lack of oxygen; this results in cell death before new blood vessels can form. Thus there is no merit in injecting large boluses of fat into spaces far from skin or muscle blood supply.
A hitherto overlooked factor in successful fat transfer is the presence of high concentration of adipose-derived stem cells (ASCs). These cells are pluripotent mesenchymal stem cells that reside in large numbers in adult adipose tissue and they have the potential to become any type of cell. It is estimated that 1–3 million of these small cells reside close to the small vessels in fatty tissue. Adipose stem cells are known to tolerate the conditions associated with harvest and graft injection more successfully than mature fat cells and participate in the tissue response to these stresses with adipose tissue regeneration. In other words, the traumas of the transfer process and death of the mature fat cells, signals the ASC’s to develop into fat cells themselves.
The ASC’s are also known to actively promote new blood vessels. By promoting the development of new vasculature in the grafted tissue, ASCs are able to speed successful fat transfer and reduce the number of fat cells dying due to lack of oxygen, thereby improving volume retention.
How to safely transfer across enough fat cells and ASCs into a better vascularized recipient bed is the ongoing work of fat transfer that Rozina is involved in. Future strategies include continuing to develop precise tissue handling techniques, gentle fat purification without sacrificing ASCs and focused post-injection measures to optimize fat survival. Recipient site vascularity is key to a good outcome as much as surgical expertise and surgical techniques. Fat is very much the future.