Fundamental Aspects Of Skin Substitutes

The most commonly used technique to cover a skin defect is skin autografting. However, in certain situations and body regions, it is necessary to achieve stable skin coverage and good skin quality.

The dermis is the layer of the skin that gives it elasticity, foldability, texture, and consistency. Unfortunately, the remaining dermis is one of the major culprits of subsequent evolution in damaged skin because the dermis does not regenerate. This is the main reason why the development of “skin substitutes” is so important.

In the face of a full-thickness burn in particular areas or with exposure of noble tissues, the use of partial skin autografts can allow stable coverage, but often with a significant functional and aesthetic deficit—all due to the lack of sufficient dermis. In small lesions, the gold standard for covering defects in functional or esthetic areas is the total skin autograft. However, this has the limitation of size.

Dermal substitutes or dermal regeneration matrices are traditional skin coverings that replace the function of the dermis and must be covered with the epidermis to complete the coverage.

Dermal substitutes are suitable for skin-destroying processes such as burns involving 60% or more of the total body surface, trauma, and genetic diseases affecting chronic wounds. The method of choice for skin coverage of these injuries is partial skin grafting; however, its results are not adequate in some cases. Dermal substitutes are an alternative for skin coverage, which are currently available and allow better functional and aesthetic results. In addition, skin substitutes, also referred to as bioengineered alternative tissues (BATs), are increasingly being used to help facilitate wound closure.

Using skin grafts is a traditional technique to promote the healing of acute and chronic wounds. Unlike autografting, which relies on the availability of healthy tissue in the patient, substitute grafts can be acquired from other humans, animals, or produced in the laboratory. There are biological and synthetic skin substitutes. The former is cheaper and more abundant. The latter have no basement membrane and, despite their lack of organic elements, have proven to have more specific qualities in the treatment of patients. As you can see, there are different types of skin grafts.

Depending on the origin:

  • Autograft or autologous graft: skin obtained from a donor area of the patient himself.
  • Allograft or heterologous graft: skin obtained from another person.
  • Xenograft or hetero-graft: skin from other species, such as pigs.
  • Synthetic skin substitutes: manufactured in a laboratory or industry. They can be epidermal (keratinocyte cultures), dermal, or dermo-epidermal (artificial skin).

Only autografts are considered permanent. The rest, either because of their composition (degradable by the host) or their origin (rejected by the host’s immune response), only provide temporary coverage for a few weeks.

Although the ideal dermal substitute does not exist, the “ideal” principles or characteristics for an adequate function of dermal substitutes are:

  • Protection of the wound from infection and avoidance of fluid loss. The dermal regeneration matrix will hardly be able to fulfill this characteristic. It must therefore be covered by epidermis or a “pseudoepidermis.” This can be achieved by providing an almost impermeable cover to the wound. There are two strategies to accomplish this goal:
  • Provide temporary coverage by applying a covering that is usually a silicone sheet exchanged for a thin autograft after the dermal matrix is vascularized. The time is variable but does not exceed 28 days. This procedure is known as a two-stage surgical procedure.

In a single surgical procedure, the dermal substitute is applied and covered with a thin autograft. This alternative provides faster closure of the defect. However, the integration of the autograft may be hindered by the lack of vascularization of the dermal substitute. Therefore, the dermal substitutes that work best in this way are thinner. But they will, in turn, have less benefit than thicker ones because they have less new dermis.

Biological properties of the dermal substitute that allow the neodermis to develop. Stability, biodegradation, and immuno-compatibility are critical issues for the design and function of a dermal substitute.