Table 3.

Internal gelation with water-insoluble or weakly soluble cross-linkers which are pH sensitive

References		Zhang et al., 2007 [61]	Akbari and Pirbodaghi, 2014 [3]	Yu et al., 2019 [56]	Utech et al., 2015 [49]
Droplet generation	Concentration of Na-alginate	2 wt%	1,5 wt%	2 w/v%	2 wt%
	Continuous fluid	Soybean oil	Fluorocarbon oil	Mineral oil	Fluorinated carbon oil
	Use of surfactant	Span 80	Fluorinated surfactant	Span 80	Biocompatible surfactant
	Geometry	Flow-focusing	Flow-focusing	Flow-focusing	Flow-focusing
	Microfluidic material	PDMS chip	PDMS chip	PDMS chip	PDMS chip
Internal gelation by mixing Na-alginate and water-insoluble or weakly soluble cross-linkers	Cross-linkers	CaCO3 (0,1 wt%)	CaCO3 (35 mM)	CaCO3 (200 mM)	Ca-EDTA (50 mM)
	Mixing	Off-line, before droplet generation	Before droplet generation	Off-line, before droplet generation	Off-line, before droplet generation
	Gelation by acid addition	In continuous fluid	In continuous fluid	In collecting fluid	In continuous fluid