Table 2.

Advantages and limitations of different biomaterials for hydrogels used in AC TET.

No.	Name (Abbreviation)	Advantages	Limitations	Refs.
1	Polyethylene glycol (PEG)	1. Biocompatible	Biologically inert	Wei et al.96
		2. Easy to be functionalized		Roberts and Bryant107
2	Poly (2-methacryloyloxyethyl phosphorylcholine) (PMPC)	1. Monomer and polymer biocompatible	NO cell adhesion molecules	Wei et al.96
		2. Lubricant
		3. Mechanical strength
3	Polyvinyl alcohol (PVA)	1. MSCs chondrogenic differentiation	1. Mechanical strength	Wei et al.96
			2. Biologically inert	Shi et al.108
			3. Low cell adhesion	Maher et al.109
			4. Low bioactivity	Bichara et al.110
			5. Non-degradable
			6. Low equilibrium water content
4	Poly(N-vinylcaprolactam) (PVCL)	1. Thermosensitive	1. Wettability	Wei et al.96
		2. Biocompatibility	2. Mechanical properties	Whittaker et al.111
		3. Water uptake capacity	3. Antibiofouling
5	Poly(N-isopropylacrylamide) (PNIPAm)	1. Thermosensitive	1. Low viscosity	Lima et al.112
		2. Biocompatibility	2. Fast adhesive polymerized properties	Guo et al.113
		3. Mechanical properties
		4. Reversible cell adhesion
6	Polyacrylic acid (PAA)	pH-responsive	1. Ionized at high pH	Jiang et al.97
			2. Lower coefficient of friction	Bichara et al.110
7	Polyaniline	1. Electric-responsive	Limited hydrophilicity	Jiang et al.97
		2. Rigid backbone
8	Poly(N,Ndiethylaminoethyl meth acrylate) (PDEAEM)	pH-responsive	Ionized at low pH	Jiang et al.97
9	Poly(lactic-co-glycolic acid) (PLGA)	1. Thermosensitive	1. Mechanical strength	Sadat Tabatabaei Mirakabad et al.114
		2. Approved by the US FDA and European Medicine Agency to use in drug delivery systems	2. Poor loading	Qu et al.115
		3. Biodegradation	3. High burst release
		4. Improved cartilage regeneration	4. Production of acids
		5. Biocompatibility
10	Poloxamer 407 (PX)	1. Thermosensitive	Induced hyperlipidemia	Goo et al.116
		2. Mechanical properties		Wang et al.117
		3. Supersaturating
11	Azobenzene and its derivatives	1. Thermosensitive	1. Stability of the switch in vivo	Jiang et al.97
		2. Light-responsive	2. Rapid spatiotemporal control
		3. Hypoxia-response	3. Absorption wavelengths compatible with biological tissue optical windows
			4. UV phototoxic damage
12	Lithium phenyl (2,4,6-trimethylbenzoyl) phosphinate (LAP)	1. UV photoinitiator	1. Cytotoxic	Qin et al.94
		2. Water-soluble	2. Mutagenic
13	Cellulose	1. Can be sulfated	1. Mechanical properties	Wei et al.96
		2. Nanofibrils similar to collagen fibrils of tissue ECM	2. Limited 3D nano-scale pore structure	Li et al.118
			3. Lack of biological function
14	Chondroitin sulfate (CS)	1. Component of natural cartilage	Rapid degradation	Wei et al.96
		2. Regulate hypertrophy during MSCs chondrogenesis		Chen et al.119
		3. Promote cartilage ECM production
		4. Inhibiting inflammation
15	Hyaluronic acid (HA)	1. pH-responsive	NO cell adhesion molecules	Wei et al.96
		2. Component of natural cartilage		Jiang et al.97
		3. Increase the synthesis of ECM and chondrogenesis
		4. Easy to be functionalized
16	Chitosan, chitin and their derivatives	1. Thermosensitive	1. Low solubility	Wei et al.96
		2. Ions-responsive	2. High viscosity	Jiang et al.97
		3. Electric-responsive
		4. pH-responsive
		5. Drug delivery
		6. Easy to be functionalized
17	Alginate	1. Thermosensitive	1. Lack of biodegradability	Wei et al.96
		2. pH-responsive	2. Immunological responses for its endotoxin contents	Liu et al.120
		3. 3D bioprinting	3. The rapid gelling process
		4. Mechanical strength	4. Limited capacity to retain GAGs
		5. Gene carriers	5. Insufficiently cell adhesion
		6. Biocompatible component with a high water content, good porosity and tunable viscosity
		7. Powerful capacity to retain collagen
18	Collagen	1. Natural ECM protein	1. Limited number of functional groups for crosslinking	Wei et al.96
		2. Immunomodulation	2. Fast degradation	Long et al.121
			3. Poor mechanical properties
			4. Excessive cell-mediated shrinkage
19	Gelatin	1. Promote cell adhesion	1. Weakly mechanical properties and brittleness	Shi et al.122
		2. UV photoinitiator	2. Low thermal stability	Vassallo et al.123
		3. 3D bioprinting	3. High sensitivity to enzymatic degradation
		4. Highly biocompatible, biodegradable, and cost-effective
20	Silk fibroin (SF)	1. Mimicking the collagen structure of native cartilage with biocompatibility, biodegradability, high tensile strength, and various cells adherence	1. Limited options for anchoring growth factor	Cheng et al.124
		2. Immunocompatible	2. Large brittleness	Qi et al.125
		3. The diverse ability to crosslink or solution-to-gel	3. Low stability in aqueous solution
		4. Natural photoluminescence	4. Difficult to be crosslinked
21	Fibrin	Easy to be functionalized	No chondro-permissive	Thorpe et al.126
22	Agarose (AG)	1. Thermosensitive	1. Low mechanical properties	Bahcecioglu et al.127
		2. Biocompatibility	2. Low cell adhesion
		3. Promote expression of GAGs
		4. Non-immunogenic properties
23	Methacrylic anhydride (MA)	Photo-crosslinkable	Low mechanical properties	Xia et al.95
24	Peptides	Promote MSCs chondrogenesis	Need proper peptide design, synthesis, and purification	Jiang et al.97