Technology and product reviews


performs a number of vital functions [Box 2]. The timely restoration of the protective and homeostatic functions of the skin is essential for successful clinical outcomes. Burn injuries, depending on depth, can be


divided into: n


n Superficial (also called epidermal)


Superficial dermal (also called superficial partial thickness)


n References


12. Boyce ST, Goretsky MJ, Greenhalgh DG, Kagan RJ, Rieman MT, Warden GD. Comparative assessment of cultured skin substitutes and


native skin autograft for treatment of full thickness burns. Ann Surg 1995; 222: 743–52.


13. Herndon DN, Parks DH.


Comparison of serial debridement and autografting and early


massive excision with cadaver skin overlay in the treatment of large burns in children. J Trauma 1986; 26: 149–52.


14. Enoch S, Roshan A, Shah M.


Emergency and early management of burns and scalds. Br Med J 2009; 338: b1037.


15. Halim AS, Teng LK, Mohd J. Biologic and synthetic skin


substitutes: An overview Indian J Plast Surg 2010; 43: 3; 23–8.


16. Montaño I, Schiestl C, Schneider J, et al. Formation of human


capillaries in vitro: The engineering of pre-vascularized matrices. Tissue Eng Part A 2010; 16(1): 269–82.


17. Horch RE, Kopp J, Kneser U, Beier J, Bach, AD. Tissue engineering of cultured skin substitutes, J Cell Mol Med 2005; 9: 592–608.


18. Sterodimas A, De Faria J, Correa


WE, Pitanguy I. Tissue engineering in plastic surgery: an up-to-date review of the current literature, Ann Plast Surg 2009; 62: 97–103.


19. Pampaloni F, Reynaud EG, Stelzer EH. The third dimension bridges the gap between cell culture and


live tissue. Nat Rev Mol Cell 2007; 8: 839–845.


20. Michel M, Torok N, Godbout MJ, et al. Keratin 19 as a biochemical


marker of skin stem cells in vivo and in vitro: keratin 19 expressing cells


are differentially localized in function of anatomic sites, and their number varies with donor age and culture stage. J Cell Sci 1996; 109: 1017–28.


FEATURES


Autograft: tissue grafted to a new position on the same individual


Allograft: graft of tissue transplanted between genetically non-identical individuals of the same species


Xenograft: graft of tissue harvested from one species to an unlike species (or genus or family)


n


Deep dermal (also called deep partial thickness)


Full thickness. Although this classification is mainly used


in burns, the principle nevertheless applies to any tissue defect, eg an abrasion or split skin graft donor site is equivalent to a superficial burn and a grade IV pressure ulcer is equivalent to a full thickness burn. Ulcers of varying aetiologies range from superficial to full thickness.


HEALING Superficial (epidermal) injuries heal by re- epithelialisation from existing keratinocytes or keratinocyte stem cells and scarring in such injuries is minimal. If the injury extends to the superficial layer of the dermis it is possible that regeneration of the epidermis will occur without surgical intervention, provided there are a sufficient number of keratinocyte stem cells. If epidermal keratinocytes are lost, redevelopment may be performed by epithelial stem cells derived from hair follicles and/or sweat glands that are present in the deep layers of the skin (dermis).


Technology and product reviews However, if the injury extends to the


deeper dermis (including the hypodermis, fat, muscle or bone), the injured surface is depleted of its keratinocytes, fibroblasts and any stem cells). Thus surgical excision of the involved tissue is frequently required along with reconstruction using STSG, which contains all the epidermis and superficial parts of the dermis, thereby transferring self-renewing keratinocyte stem cells to the recipient area. Deep dermal and full-thickness skin


injuries usually require surgical excision and will inevitably result in scarring due to the action of myofibroblasts, even after skin grafting[14]


.


SKIN SUBSTITUTES Skin substitutes are a heterogeneous group of products aimed at replacing, either temporarily or permanently, the form and function of lost skin. These products are alternatives to standard wound coverage in circumstances when established wound dressings are not appropriate[7] From a practical point of view, skin


.


substitutes are best classified as: n


n n


Synthetic, biosynthetic or biological Temporary or permanent


Epidermal, dermal or composite.


Synthetic skin substitutes are products of tissue engineering and consist of a microengineered biocompatible polymer matrix. If used in combination with cellular and/or extracellular elements such as collagen, they result in a biosynthetic product. Synthetic and biosynthetic constructs are made to be stable, biodegradable and aimed at providing an adequate environment for the regeneration of tissue. They are intended to maintain their three-dimensional structure for a minimum of three weeks to allow for a growth of blood vessels and fibroblasts and coverage by epithelial cells. Biodegradation takes place after this period[15]


. This process should


preferably occur without extensive foreign body reaction as this will lead to increased scarring. Biological skin substitutes (eg allografts


Box 3 – Definition of different types of grafts.


or xenografts) are similar to the skin, with an intact and native extracellular matrix allowing for restoration of a more natural new dermis. They also support re-epithelialisation due to the presence of a basement membrane. However, natural constructs can exhibit problems with slow vascularisation. The most


29 Wounds International Vol 2 | Issue 1 | ©Wounds International 2011


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