Histological Findings from Controlled Application of a Thermal Plasma to Human Skin

Ionised gas or plasma is often described as the fourth state of matter since it can be produced from an electrically neutral gas which has been fully or partially ionised. The resulting mixture of free electrons, positively charged ions and un-ionized gas possess a rich chemistry and may be used to transport thermal energy. Plasma has thus found applications in such diverse fields as spacecraft propulsion, magnetic confinement fusion, silicon etching, and surface treatment and of course biomedicine. We have developed a plasma generating device that can deliver a controlled depth epidermal and dermal burn injury as a function of energy delivery over a unit area and time of exposure. This is important as a therapeutic tool for treating skin lesions; a device to create burn wound healing models, for medicolegal understanding of burn depth and for the development of new wound care products. In our study plasma is delivered onto a human skin model in an experiment approved by the local ethics committee. Fresh abdominoplasty skin was marked according to protocol and treated with a controlled energy dose per unit area using the new plasma delivery system developed at the Surrey Space Centre at Surrey University. Skin samples are biopsied and immediately placed in formal saline before sectioning and staining. The immediate histological changes of superficial burn injury in human skin can then be determined. The findings in this study show a reproducible depth of thermal injury as a function of energy delivery. Each 25 J/cm2 increment up to 100 J/cm2 causes a 0.5 mm depth of cutaneous thermal injury. In the 25 and 50 J/cm2 injury the epidermis remains intact and appears as a ‘first degree or superficial burn injury’. Histologically the basal epidermal cells show characteristic oedematous morphology which we have called ‘Frame Cells’ because the morphology after superficial injury has not been previously recognized. There is a clear line of demarcation within the superficial dermis where the zone of coagulation meets the zone of stasis. In the 75 and 100 J/cm2 the epidermis appears coagulated and has histologically separated from the dermis burn at the dermo-epidermoid junction. The line of dermal coagulative necrosis is clearly defined. Melanocytes are absent immediately after even the most superficial injury. Fibroblasts, vascular endothelial cells, epithelial cells, pigment cells, collagen and elastin are all examined using immunohistochemical stains.