Table 3.

The three most used materials (alginate, gelatin, GelMA, and its combinations in pairs) with its different cross-linking methods.

Material	Chemical	Physical	Thermal	References
Alginate	C1			Campbell et al., 2015; Markstedt et al., 2015; Narayanan et al., 2016; Freeman and Kelly, 2017; Naghieh et al., 2018; Wu Y. et al., 2018
	C1/C2			Khalil and Sun, 2009
	C1/C5			Kundu et al., 2015
	C2			Jia et al., 2014; Izadifar et al., 2016; Apelgren et al., 2017; Kosik-Kozioł et al., 2017; Nguyen et al., 2017; Polley et al., 2017; Schütz et al., 2017; Ahlfeld et al., 2018; Habib et al., 2018; He et al., 2018; Maiullari et al., 2018; Yu et al., 2018; Gonzalez-Fernandez et al., 2019
		P4		Jeon et al., 2019
	C3			Yang et al., 2017; Datta et al., 2018; Gao et al., 2018; Raddatz et al., 2018
	C4			Bakarich et al., 2014; Gao et al., 2015, 2017; Li et al., 2017
	C5			Hafeez et al., 2018; Aydogdu et al., 2019; Wei et al., 2019
	C6			Yoon et al., 2019
	C7	P1		Ji et al., 2019
		P2		Ooi et al., 2018
Gelatin	C1			Yan et al., 2018
	C5			Irvine et al., 2015; Choi et al., 2018
			T1	Tijore et al., 2018b
	C6			Shin et al., 2018
	C7	P3		AnilKumar et al., 2019
			T1	Tijore et al., 2018a
			T4	Xu X. et al., 2018
GelMA	C7	P1		Ersumo et al., 2016
		P2		Schuurman et al., 2013; Mouser et al., 2016; Levato et al., 2017; Celikkin et al., 2018; Zhou et al., 2019
		P3		Bertassoni et al., 2014
		P4		Billiet et al., 2014; Du et al., 2015; Suntornnond et al., 2017; Gu et al., 2018; Li et al., 2018cb; Pepelanova et al., 2018
Alginate Gelatin	C2			Wang et al., 2016; Ding et al., 2017, 2018
			T4	Giuseppe et al., 2017; Bandyopadhyay et al., 2018
	C2/C1		T2	Berg et al., 2018
	C3			Li et al., 2018c
	C3/C5			Akkineni et al., 2016
	C4			Chung et al., 2013
			T3	He et al., 2016
	C6			Aljohani et al., 2018
Alginate GelMA	C1	P2		Daly et al., 2016b
		P4		Daly et al., 2016a; Liu et al., 2018
	C2	P3		Zhang X. et al., 2018
		P4		Kosik-Kozioł et al., 2019; Krishnamoorthy et al., 2019
	C4	P4		Costantini et al., 2016
	C7	P2		Kang et al., 2017
		P4		García-Lizarribar et al., 2018
Gelatin GelMA	C5	P2		Haring et al., 2019
	C8	P2		McBeth et al., 2017

Codification is at follows: C for Chemical crosslinking: C1: <100 mM Ca²⁺ solution, C2: [100–500] mM Ca²⁺ solution, C3: ≥500 mM Ca²⁺ solution, C4: Not given concentration of Ca²⁺ solution, C5: Other solute solution, C6: No available details for chemical crosslinking, and C7: No chemical crosslinking. P for Physical crosslinking: P1: 405 nm UV light, P2: 365 nm UV light, P3: UV light (special wavelength), P4: UV light (no data of wavelength). T for Thermal Crosslinking: T1: 37 °C, T2: Room temperature, T3: Special temperature, T4: no available details of thermal crosslinking.