Table 1.

Overview of hydrogels with different polymer types for cartilage tissue engineering: chemical structure and features for cartilage engineering.

	Name (Abbreviation)	Chemical structure	Features for cartilage engineering	Limitations	Refs
Synthetic polymers	Polyethylene glycol (PEG)		1.Biocompatible	Biologically inert	[[47], [48], [49], [50], [51]]
			2.Easy to be functionalized
	Poly (N-vinylcaprolactam) (PVCL)		1.Thermosensitive	Moderate wettability, weak mechanical properties, low anti-biofouling	[42,157]
			2.Cytocompatible to chondrocytes and MSCs
	Polyvinyl alcohol (PVA)		1.Mechanical strong	Biologically inert	[19,37,38,158]
			2.MSCs chondrogenic differentiation
	Poly (2-methacryloyloxyethyl phosphorylcholine) (PMPC)		1.Monomer and polymer biocompatible	Do not support cell attachment	[[39], [40], [41],159]
			2.Lubricant
			3.Mechanical strong
Polysaccharides	Chondroitin sulfate (CS)		1.Component of natural cartilage	Rapid degradation	[11,34,[54], [55], [56]]
			2.Regulate hypertrophy during MSC chondrogenesis
			3.Promote cartilage ECM production
	Hyaluronic Acid (HA)		1.Component of natural cartilage and tissue	Do not support cell attachment	[62,64,68,160,161]
			2.Promote cartilage marker gene expression of chondrocytes
			3.Easy to be functionalized
	Chitosan		1.Drug delivery capacity	Low solubility and high viscosity	[[81], [82], [83],162]
	Alginate		1.Fast cross-linking and mechanical strong	Non-biodegradable and elicit immunological responses	[[86], [87], [88], [89],91]
			2.Able to 3D printing/bioprinting
			3.Can be used as gene carriers
	Cellulose		1.Can be sulfated	Lack of mechanical properties	[92,93,95]
			2.Nanofibrils similar to collagen fibrils found in tissue ECM
Proteins	Collagen		1.Natural extracellular matrix (ECM) protein	Limited number of functional groups for crosslinking	[30,99,100,103,163]
			2.Immunomodulation
	Gelatin		1.Promote cell adhesion	Poor mechanical properties and low thermal stability	[35,104,107,130]
			2.Easy to be modified for UV crosslinking
			3.Able to 3D printing/bioprinting
	Silk Fibroin (SF)		1.Mimicking the collagen structure of native cartilage	Limited options for anchoring growth factor	[111,113,114,164]
			2.Immunocompatible
			3.Multiple methods for crosslinking
			4.High mechanical strength
	Sericin		1.Low cost	Low stability in aqueous solution	[117,165]
			2.Nutrition-supplying
	Fibrin	–	1.Easy to be functionalized	Not chondro-permissive	[118,119]
Peptides	–	–	1.Promote MSC chondrogenesis	Need proper peptide design, synthesis, and purification	[125,128]