**2. Classification of skin substitutes**

Skin substitutes encompass a diverse group of materials and may be classified based on five main properties [5–7], as outlined with examples in **Table 1**.

Permanence: Temporary or permanent Material source: Biological (either natural biological or constructed biological dermal substitutes), synthetic or mixed (biosynthetic) dermal substitutes Layering: Single layer, bilayer, multilayer Replaced region: Epidermal component only, dermal component only, composite (dermal and epidermal components) Cellularity: Acellular or cellular

This classification system inspired by factorial design reported by Davison-Kotler et al. (**Figure 1**) [7]. borrows elements from four earlier classification systems which have been summarised in **Table 2** [8–11]. Classification systems can be helpful to both researchers in comparing outcomes of different skin substitutes and to clinicians who need to understand their composition in order to make an appropriate selection based on the clinical scenario faced.


#### **Table 1.**

*Classification of skin substitutes by various properties.*

#### **Figure 1.**

*Skin substitute classification adapted from Davison-Kotler et al. [7].*

Classifications have evolved over time in parallel with advancements in skin substitute design. A commonality to all classification systems was an emphasis placed on the tissue layer replaced by the skin substitute in question, be it epidermal, dermal or composite skin replacement. This concept marries well with standard categorisation of burns and other wounds by the depth of injury when planning reconstructive requirements. Earlier classification systems failed to differentiate between products based on permanence [8], material source [8] and cellularity [8–10]. The omission


#### **Table 2.** *Chronological development of skin substitute classification systems.*

of these integral features created classification systems that were non-intuitive and confusing, whereby some dissimilar products could be placed in the same category or qualify for multiple categories.

The system outlined by Davison-Kotler et al. [7] allows multiple key properties to be simultaneously incorporated, since all skin substitutes possess a variety of characteristics. This multifactorial classification system allows for clear and comprehensive descriptive categorisation of commercially available skin substitutes with potential to expand to include novel skin substitutes still under development. A glossary to further expand



#### **Table 3.**

*Glossary with description of skin substitutes in alphabetical order.*

on the examples skin substitutes provided in this chapter is found in **Table 3**. This list is not exhaustive and many additional commercially products are available but it serves to illustrate the classification systems outlined, with a particular focus on materials utilised commonly in contemporary management of burns and other extensive wounds.

#### **2.1 Skin substitute properties**

#### *2.1.1 Permanence*

Skin substitutes can be subdivided into two groups with distinct objectives and indications in burn care with regards to their permanence: namely temporary and permanent skin substitutes. Permanence may be defined by biodegradability as described in the classification reported by Davison-Kotler et al. [7]. However, many bilayered skin substitutes such as Integra and Biodegradable Temporising Matrix, (BTM), have a non-biodegradable outer component that requires removal before autografting of a slowly biodegradable scaffold following ingrowth of host cellular material (no polyurethane residues present by 18 months in the case of BTM) [12]. A more intuitive definition preferred by the authors of this chapter has been provided by Ferreira et al. [10] who describes the distinction as follows: Temporary skin substitutes 'refer to those

#### *Role of Skin Substitutes in Burn Wound Reconstruction DOI: http://dx.doi.org/10.5772/intechopen.105179*

that remain in the wound for the period of time necessary to modulate and improve the characteristics of the lesion and are replaced by autogenous grafts. Permanent materials are those that restore part or the total structure of the skin and remain on the wound bed even after a possible grafting of autogenous skin for complete coverage of the lesion.' Similarly, permanence is defined by the FDA as any material persisting more than 30 days in a wound, therefore permanence does not imply infinite presence in a wound.

Temporary skin substitutes do not generally achieve full integration with the wound bed. However, they may temporarily adhere while they promote healing by protecting, reducing water loss and accelerating epithelialisation.

The *objective* of temporary skin substitutes is to provide a moist environment, protect the wound from water loss and bacterial invasion while limiting the number of dressing changes.

*Indications* include definitive dressing of superficial or partial thickness burns until epithelialisation, temporary excised burn wound closure while awaiting autografting, protection of widely meshed autografts, 'test' graft in questionable wound beds while awaiting burn depth demarcation, donor site dressing to facilitate epithelialisation and pain control.

Examples: Cadaveric allograft, Amniotic membrane, Biobrane, Suprathel

Permanent skin substitutes are generally composed of constructs or scaffolds that become integrated with the wound architecture by hosting or allow ingrowth of dermal cells, before eventual scaffold reabsorption.

The *objective* of permanent skin substitutes is to provide a stable but biodegradable template for the synthesis of neo-dermis by enabling the influx of cells that produce dermal tissue rather than scar tissue [13, 14]. Epidermal constructs alone have proven to be problematic in the absence of viable dermis due to inadequate long term wound stability. Scar fragility with propensity to mechanical damage and shear demonstrated following cultured epithelial autografting [15] highlighted the challenge of dermal-epidermal junction regeneration. Dermal and dermal-epidermal constructs have been developed in response to these issues, to improve the quality of healing and reduce scarring.

*Indications* include excised deep partial or full thickness burn wounds. Examples: Biodegradable Temporising Matrix (BTM), Integra.
