Table 2.

Summary on hydrogels applied in IVD tissue engineering research

Material		Advantages	Disadvantages	References
Natural Origin Hydrogels	Alginate	• Polymerization under mild conditions; • Injectable in situ; • NP similar mechanical properties; • Cell adherent.	• Lack of long-term mechanical stability; • Impurities make it unpredictable; • Difficult to sterilize and to handle.	[54–56]
	Hyaluronan	• Non-immunogenic; • Easy control over the polymer chain sizes; • Bioactive; • Low manufacturing cost.	• Osteogenic; • Cytotoxic in high concentration.	[48, 49, 51, 66]
	Chitosan	• Bioactive; • Cell adherent • Antibacterial activity; • Non-immunogenic.	• Bad mechanical properties; • Cytotoxic cross-linkers; • Impurities make it unpredictable.	[48, 49, 51, 57, 58, 67]
	Collagen	• Non-immunogenic; • Piezoelectric properties; • Bioactive.	• Bad mechanical properties; • High degradation rate; • Some level of toxicity (cross-linking agents).	[48, 49, 51, 59, 60]
	Gellan Gum	• Non-angiogenic; • Able to polymerize until 1% (w/v); • Non-immunogenic; • Very low manufacturing cost; • Good mechanical properties.	• Weak in physiological conditions due to the exchange of divalent cations by monovalent ones.	[48, 49, 61–65]
Synthetic Hydrogels	Polyethylene glycol	• pH-switchable electronic properties; • Photo-polymerizable; • Adjustable mechanical properties; • Easy control over architecture and chemical composition.	• Bioinert; • No cell adherence; • Expensive to manufacture.	[48, 74, 138, 139]
	Polyvinyl Alcohol	• Catalytic activity; • Increases viscosity when added to other hydrogels; • Controllable crystallinity.	• Bad mechanical properties; • Regular chain structure; • Non-degradable; • Expensive to manufacture.	[48, 67, 138]
	Polyvinyl-pyrrolidone	• Good mechanical properties; • Biocompatible.	• Non-degradable; • Expensive to manufacture.	[51, 72, 74]