SKIN TRAUMA

Background

The protective role of the skin is paramount, providing a barrier between our organs and tissues and the inherent dangers of the external environment. Skin also plays a vital role in fluid balance and the regulation of temperature. Each year more than 2 million burn injuries demand medical care. This number compounded with the 750,000 people who suffer every year from diabetic leg ulcers creates a large market for replacement skin grafts. [1]

In the past, allograft transplantation was the most prominent option for deep wounds that required a skin graft. These grafts are woefully insufficient as they offer only temporary cover and are quickly rejected by a patient's immune system. The development of a bio-engineered skin graft was the ultimate goal of research that began in the early 1970's.

Anatomy of the Skin

The most difficult challenge to researchers trying to grow engineered skin is the replication of natural skin's unique anatomy. [2] The dermal and epidermal layers are derived from different stem cells, with the former being formed by fibroblasts and the latter a product of the differentiation of keratinocytes. In natural skin, fibroblast produce collagen and elastin that serve as a foundation upon which keratinocytes differentiate into the epidermal layers.

Culturing Technology and the Development of Skin Grafts

This process offers limited assistance in the treatment of the third degree burns and deep ulcers, for which skin grafts are most needed. In these cases the dermal layer is destroyed and must be replaced before epidermal tissue can be grafted. The replacement of the dermal layer can be accomplished using Integra, a tissue engineered product that was introduced in the mid 1995 from the bio-tech sector.

Integra contains no living cells, but is a protective covering and scaffold that promotes the growth of the dermal layer. The product consists of two distinct parts, a bottom layer which is a matrix of bovine collagen and sugars, and a temporary flexible silicon upper layer. The sugar (glycosaminoglycan) serves to facilitate the growth of any remaining dermal cells into the matrix. [4] Over time the matrix degrades and a sheet of cultured epithelium can be applied over the newly established dermal layer.

The approval of Apilgraf by the FDA in 1998 marked a clear advance in the technology of cultured skin grafts. The profile of the bi-layered product is unique in that it is composed of both living fibroblasts and keratinocytes structurally organized like natural skin. [5] The keratinocytes and fibroblast used to manufacture Apilgraf are derived from donor tissue that is thoroughly screened for pathogens. Apilgraf is currently approved for treatment of diabetic foot ulcers and is undergoing further study for burn treatment applications. The cost per Apilgraf treatment is listed at $3 to $4 thousand dollars and it is hopeful that the bioengineered tissue will become the standard of care for foot ulcers. [6]