Advances in generation of three-dimensional skin equivalents: pre-clinical studies to clinical therapies

Abstract

The inability of two-dimensional cell culture systems to adequately map the structure and function of complex organs like skin necessitates the development of three-dimensional (3D) skin models. A diverse range of 3D skin equivalents have been developed over the last few decades for studying complex properties of skin as well as for drug discovery and clinical applications for skin regeneration in chronic wounds, such as diabetic foot ulcers, where the normal mechanism of wound healing is compromised. These 3D skin substitutes also serve as a suitable alternative to animal models in industrial applications and fundamental research. With the emergence of tissue engineering, new scaffolds and matrices have been integrated into 3D cell culture systems, along with gene therapy approaches, to increase the efficacy of transplanted cells in skin regeneration. This review summarizes recent approaches to the development of skin equivalents as well as different models for studying skin diseases and properties and current therapeutic applications of skin substitutes.

Chronic Diabetic Wounds and Their Treatment with Skin Substitutes

“…Given the extensive role that the ECM plays in wound healing, the examination of wound substitutes that mimic native dermis has been implicated as an effective ameliorative therapy, often in conjunction with supplementary cellular or molecular components [76,79,80]. Consequently, recent decades have seen innovation in 3D cell cultures and other substitutes which model human skin in vitro, allowing for the evaluation of skin substitutes more readily than with animal models alone [81]. Despite this, some skin substitutes (including dermal scaffolds) do not possess the ability to fully integrate with host fibroblast-derived ECM components, often leading to future complications in their extraction or inability to undergo desirable ECM/collagen deposition during the remodeling phase of wound healing.…”

Recent advances in the induced pluripotent stem cell‐based skin regeneration

“…Keratinocytes constitute the major cell types in the skin epidermis and play a key role in maintaining the physical and immunological barrier function of the skin. 72 Mutations in keratin encoding genes result in impaired keratin filament formation or hyper-proliferation of keratinocytes which can disrupt the structure and function of the skin as observed in genodermatoses like epidermolysis bullosa and hyperkeratosis. 77 Psoriasis, a chronic inflammatory disorder of the skin, also results in hyper-proliferation and impaired differentiation of epidermal keratinocytes.…”

“…114 Skin equivalents have also been used in drug discovery, clinical trials, and to model skin diseases in vitro. 72 Recent studies have shown successful incorporation of iPSC-derived skin cells including keratinocytes, fibroblasts, and epithelial stem cells for the construction of artificial skin substitutes that could effectively heal skin lesions. 115,116 iPSC-derived ECs were incorporated into artificial skin constructs to enable vascularization which is necessary for ensuring long-term survival and improved functionality of the skin constructs.…”

“…The epidermal layer is composed of keratinocytes, melanocytes, Langerhans cells, and Merkel cells. The dermal layer beneath the epidermis contains major fibroblasts as well as other cell types including endothelial cells (EC), smooth muscle cells, and immune cells 72 . iPSCs have been widely used to generate various types of skin cells with increased wound healing potential for skin regeneration and the construction of bioengineered skin equivalents for disease modeling and drug discovery (Figure 1).…”

“…Over the years, 3‐D skin equivalents have been used to study the properties of skin including epithelialization, permeability barrier formation, 112 aging, 113 and hair follicle formation 114 . Skin equivalents have also been used in drug discovery, clinical trials, and to model skin diseases in vitro 72 . Recent studies have shown successful incorporation of iPSC‐derived skin cells including keratinocytes, fibroblasts, and epithelial stem cells for the construction of artificial skin substitutes that could effectively heal skin lesions 115,116 .…”