Table 1.

Characteristics and applications of common polymers in skin bioprinting

Category	Polymers	Gelation mechanism	Biodegradability	Cell binding domains	Disadvantages	Applications
						Common usage	Target structure	Cells	Bioprinting strategy	Ref.
Natural polymers	Gelatin	Thermal Chemical	Yes	Yes	Low viscosity Mechanical instability	GelMA Alginate/Gelatin	Dermis Epidermis/dermis	Fbs AECs/MSCs	Extrusion Extrusion	[19] [20]
	Collagen	Thermal	Yes	Yes	Low viscosity Mechanical instability Slow gelation rate Fast degradation rate	Collagen Collagen Collagen/GelMA	Epidermis/Dermis Epidermis/dermis Epidermis/dermis	KCs/Fbs/MCs KCs/Fbs KCs/Fbs/MCs	Droplet Droplet Extrusion	[21] [22] [23]
	Alginate	Ionic	No	No	Low biodegradability Lack cell adhesion site	Alginate/Gelatin Alginate/PLGA Alginate/NFC/CMC	Sweat gland Epidermis/dermis Dermis	EPs KCs/Fbs Fbs	Extrusion Extrusion Extrusion	[24] [25] [26]
	Chitosan	pH	Yes	Yes	Mechanical instability Poor solubility Slow gelation rate	Chitosan Chitosan/gelatin	Epidermis/dermis Dermis	KCs/Fbs Fbs	Extrusion Extrusion	[27] [28]
	Fibrin	Thrombin	Yes	Yes	Mechanical instability High viscosity Low shear thinning	Fibrin	Epidermis/dermis	KCs/Fbs	Extrusion	[29]
Synthetic polymers	PEG	Thermoplastic	NO	NO	Hydrophobicity Long degradation time Lack cell adhesion site	PEG/chitosan/genipin Silk fibroin/PEG	Epidermis/dermis Epidermis/dermis	KCs/Fbs KCs/Fbs	Extrusion Droplet	[30] [31]
	PLA	Thermoplastic	Yes	No	Hydrophobicity Long degradation time Lack cell adhesion site	PLA/chitosan/HA	Dermis	Fbs	Extrusion	[32]
	PCL	Thermoplastic	Yes	No	Hydrophobicity Long degradation time Lack cell adhesion site	PCL/collagen	Epidermis/dermis	KCs/Fbs	Inkjet	[33]

AECs, amniotic epithelial cells; CMC, carboxymethyl cellulose; Eps, epidermal progenitors; Fbs, fibroblasts; GelMA, gelatin methacryloyl; HA, hyaluronic acid; KCs, keratinocytes; MCs, melanocytes; MSCs, mesenchymal stem cells; NFC, nano-fibrillated cellulose; PCL, poly(ε-caprolactone); PEG, polyethylene glycol; PLA, poly(lactic acid); PLGA, poly(lactic-co-glycolic acid).