Skin Substitutes in Burns

Abstract

The natural history of burn injury has been substantially modi®ed over the past few decades. The ®rst recorded recognition of the exaggerated uid requirements of burn patients was probably that of Underhill in 1930 [1]. After this important clinical observation, investigations began to develop methods to manage burn shock. In the aftermath of the Coconut Grove ®re, Moore and colleagues [2] re®ned the concept of burn resuscitation and proposed a formula for intravenous volume repletion based on body weight [3], and in the 1950's the Evans formula was promulgated by the sta€ at the United States Army Institute of Surgical Research [4]. Subsequent re®nements in burn shock resuscitation have virtually eliminated this as a cause of death. In the 1970's, the advantage of early excision and closure of small burn wounds was recognized [5]. This excisional approach was subsequently taken to patients with large injuries by Burke and others [6±8] who documented truncated hospital stays and enhanced survival in burn patients who were routinely expected to die; a burn over more than a third of the body surface being almost universally lethal at that time. Re®nement of the surgical approaches to large wounds combined with the ongoing evolution of critical care techniques has extended our ability to support patients with increasingly severe injuries through the physiologic trial of staged wound closure. Burn physical and occupational therapy and burn reconstruction have developed in parallel, facilitating our ability to deliver increasingly satisfying long term outcomes. However, further progress is seriously impaired by our lack of a suitable skin substitute. In both the acutely injured and those requiring extensive post burn reconstruction, the absence of a durable skin substitute regularly hinders recovery. The successful development of a permanent skin substitute will have an enormous impact on the care of patients with serious burns. Skin is a complex organ. Functionally, it has two layers with a highly specialized and e€ective bonding mechanism. The epidermis, consisting of the strata basale, spinosum, granulosum and corneum, provides a vapor and bacterial barrier. The dermis provides strength and elasticity. The thin epidermal layer is constantly replacing itself from its basal layer, with new keratinocytes undergoing terminal di€erentiation over approximately 4 weeks to anuclear keratin ®lled cells that make up the stratum corneum, which provides much of the barrier function of the epidermis. The basal layer of the epidermis is ®rmly attached to the dermis by a complex bonding mechanism containing collagen types IV and VII. When this bond fails, serious morbidity results, as demonstrated by the disease processes of toxic epidermal necrolysis [9] and dystrophic epidermolysis bullosa [10]. At present, most full thickness burn wounds are best closed as quickly as possible with split thickness autograft. However, split thickness autograft is an imperfect replacement for full thickness skin, may be limited in quantity and is associated with donor site morbidity. The ideal skin substitute (Table 1): (1) is inexpensive, (2) has a long shelf life, (3) is used o€ the shelf, (4) is non-antigenic, (5) is durable, (6) is exible, (7) prevents water loss, (8) is a barrier to bacteria, (9) conforms to irregular wound surfaces, (10) is easy to secure, (11) grows with children, (12) is applied in one operation, (13) does not become hypertrophic and (14) does not exist at the present time [11, 12]. Conceptually, skin substitutes are temporary or permanent; epidermal, dermal or composite; and biologic or synthetic. Biologic components are xenogeneic, alloBurns 25 (1999) 97±103