A Concise Review on Tissue Engineered Artificial Skin Grafts for Chronic Wound Treatment: Can We Reconstruct Functional Skin Tissue In Vitro?

Abstract

Chronic wounds occur as a consequence of a prolonged inflammatory phase during the healing process, which precludes skin regeneration. Typical treatment for chronic wounds includes application of autografts, allografts collected from cadaver, and topical delivery of antioxidant, anti-inflammatory, and antibacterial agents. Nevertheless, the mentioned therapies are not sufficient for extensive or deep wounds. Moreover, application of allogeneic skin grafts carries high risk of rejection and treatment failure. Advanced therapies for chronic wounds involve application of bioengineered artificial skin substitutes to overcome graft rejection as well as topical delivery of mesenchymal stem cells to reduce inflammation and accelerate the healing process. This review focuses on the concept of skin tissue engineering, which is a modern approach to chronic wound treatment. The aim of the article is to summarize common therapies for chronic wounds and recent achievements in the development of bioengineered artificial skin constructs, including analysis of biomaterials and cells widely used for skin graft production. This review also presents attempts to reconstruct nerves, pigmentation, and skin appendages (hair follicles, sweat glands) using artificial skin grafts as well as recent trends in the engineering of biomaterials, aiming to produce nanocomposite skin substitutes (nanofilled polymer composites) with controlled antibacterial activity. Finally, the article describes the composition, advantages, and limitations of both newly developed and commercially available bioengineered skin substitutes.

Keywords: antibacterial skin grafts; biomaterials; dermal skin grafts; dermo-epidermal skin grafts; epidermal skin grafts; mesenchymal stem cells; nanocomposites; skin appendages; skin substitutes.

Figure 1

Graphical representation of the four phases of the normal wound healing process.

Figure 2

Main features of chronic wounds (ECM: extracellular matrix, MMPs: matrix metalloproteinases, ROS: reactive oxygen species).

Figure 3

Different variants of tissue-engineered artificial skin grafts.

Figure 4

Epidermal skin graft: (a) image presenting a thin chitosan/agarose membrane (produced according to Polish patent application no. P.430458 [52,53] for regenerative medicine application as epidermal skin substitute; (b) confocal laser scanning microscope (CLSM) image presenting human epidermal keratinocytes stained with AlexaFluor635-Phalloidin (red fluorescence of cytoskeleton) grown on the surface of the chitosan/agarose membrane that was visualized by application of Nomarski contrast.

Figure 5

Dermal skin graft: (a) image presenting 2-mm thick chitosan/curdlan film (Polish patent application no. P.430456 [59]) for regenerative medicine application as dermal skin substitute; (b) CLSM image presenting human skin fibroblasts stained with calcein-AM (green fluorescence of viable cells) and propidium iodide (red fluorescence of dead cells) grown on the surface of the chitosan/curdlan film that was visualized by application of Nomarski contrast; (c) CLSM image presenting human skin fibroblasts stained with AlexaFluor635-Phalloidin (red fluorescence of cytoskeleton) and DAPI (blue fluorescence of nuclei) grown on the surface of the chitosan-based thin membrane that was visualized by application of Nomarski contrast; (d) scanning electron microscope (SEM) image presenting well-attached human skin fibroblasts on the surface of the chitosan hydrogel; (e) SEM micrograph presenting porous foam-like chitosan-based wound dressing (Polish patent application no. P.430455 [60]) for regenerative medicine application.

Figure 6

Co-culture of human skin fibroblasts and keratinocytes: (a) CLSM image (fibroblasts show blue fluorescence of nuclei, red fluorescence of actin filaments, and green fluorescence of vimentin filaments, whereas keratinocytes show blue fluorescence of nuclei and red fluorescence of actin filaments); (b) phase-contrast image showing co-culture of skin cells (fibroblasts reveal spindle-shaped morphology, whereas keratinocytes are visible as round cells).

Figure 7

Graphical representation of the potentially ideal artificial skin graft.