Table 3.

Examples of bioprinted skin tissues.

Skin tissues	Cell sources	Materials	Printing method	Results	References
Dermis	Neonatal human foreskin Fbs NIH3T3 Fbs	Polyelectrolyte gelatin-chitosan hydrogel Matriderm®	DOD bioprinting Laser-assisted	The printed 3D constructs showed high shape fidelity and good biocompatibility with fibroblasts. The printed fibroblasts produced collagen, some blood vessels were found to grow in the direction of the printed cells.	Ozbolat and Hospodiuk 48 Maxson et al. 143
Full-layered skin	Primary human Fbs and KCs Primary human Fbs and KCs Human KCs and Fbs Allogeneic or autologous dermal Fbs and epidermal KCs	Collagen hydrogel Human plasma Fibrinogen/collagen hydrogels Fibrin/collagen hydrogel	Extrusion Extrusion Inkjet In situ bioprinting	The stratified layers of printed FB and KC within the multi-layered collagen scaffold were observed. The printed skin was very similar to normal human skin. After 8 weeks, wound healing and complete re-epithelialization were observed. In a murine full-thickness wound model, this in situ bioprinting system showed accelerated wound closure (<15% of original wound size at 2 weeks) with entire wound closure after 3 weeks post-surgery.	De Coppi et al. 145 Aasen et al. 147 Laato et al. 149 Gainza et al. 150
Blood vessel-containing skin	Newborn dermis Fbs, KCs, and HUVECs hMSCs and endothelial cells AFSCs and BMSCs Human endothelial cell, and hMSC	Type collagen I and fibrinogen Collagen hydrogel containing VEGF Fibrin-collagen gel Biodegradable PLA fibers and GelMA hydrogels.	Inkjet Laser-assisted A bioprinting device developed in-house FDM 3D bioprinting and SLA bioprinting	Neovascularization was observed in the skin grafts 2 weeks after surgery. Formation of capillary-like structures was dependent on a sufficient local density of endothelial cells. AFSCs and BMSCs can accelerate wound healing and increased microvessel density and capillary diameters. Highly organized vascular networks were generated in the construct.	Fielding et al. 65 Pal et al. 119 Zuo et al. 129 Duncan et al. 158
	HUVECs and Fbs	Pluronic F127 and GelMA	3D bioprinting	Reporting a new approach for creating vascularized, heterogeneous tissue constructs on demand based on 3D bioprinting.	Ng et al. 161
Melanocytes -containing skin	HUVECs, Fbs, KCs MCs, Fbs, and KCs (HaCaT) KCs, MCs, and Fbs from three different skin donors	Acellular fat matrix and fibrinogen as the subdermal layer; Gelatin and thrombin were used as vascular channels. ADM was used as a dermis layer Multiple layers of collagen hydrogel Hierarchical porous collagen-based structures	Extrusion and inkjet Extrusion A two-step DOD bioprinting	A novel printing platform is suggested for engineering a matured perfusable vascularized 3D human skin equivalent composed of epidermis, dermis, and hypodermis. MC-containing epidermal layer showed freckle-like pigmentations at the dermal-epidermal junction. Histological analysis indicated the presence of a well-developed epidermal region and uniform distribution of melanin granules in the epidermal region of the 3D-bioprinted pigmented skin constructs.	Cubo et al. 163 Wang et al. 164 Lee et al. 165 Ozbolat 166
Hair follicle Sweat glands	Dermal papilla cells (DPCs) Mouse dorsal epithelial progenitors, plantar dermis homogenate, and EGF MSCs Mouse mammary progenitor cells (MPCs)	Collagen gel containing dermal fibroblasts A cell-laden 3D extracellular matrix mimics (3D-ECM) with composite hydrogels based on gelatin and sodium alginate Alginate/gelatin hydrogel Gelatin-alginate hydrogels and components from mouse sweat gland extracellular matrix proteins	Extrusion Extrusion Extrusion Extrusion	DPCs in a physiologically relevant extracellular matrix and initiation of epidermal−mesenchymal interactions, which results in HF formation in human skin constructs in vitro. Bioprinted 3D-ECM could effectively create a restrictive niche for epidermal progenitors that ensures unilateral differentiation into sweat gland cells. Representing a novel strategy of directing MSC differentiation for functional SG regeneration by using 3D bioprinting. Differentiated mouse MPCs could regenerate SG cells by engineered SG microenvironment in vitro and Shh pathway was found to be correlated with the changes in the differentiation.	Kang et al. 173 Abaci et al. 136 Ng et al. 185 Feng 194