Table 2.

Summary of drug loading technique of EVs.

Classification	Loading method	Type of cargo	Characteristic	Loading efficiency
Pre-loading method	Transfection	miRNA (Ohno et al., 2013), siRNA (Steinman, 2012), protein (Limoni et al., 2019)	Widely used but uncontrollable in quantity of cargo loading	Low loading efficiency
	Co-incubation	Paclitaxel (Merchant et al., 2017) carboplatin and etoposide (Akao et al., 2011)	Easy to operate but drugs may be cytotoxic to cells	Low loading efficiency
	Activities	miRNA (Pascucci et al., 2014)	Easy to operate but only applicable to specific cells	Low loading efficient
Post-loading method	Co-incubation	Curcumin (Street et al., 2017) hsiRNA (Seo et al., 2018), porphyrins (Lee et al., 2015), catalase (Li et al., 2019c)	A simplest way but uncontrollable in quantity of cargo loading	Low loading efficiency
	Electroporation	SiRNA (Steinman, 2012), TMP (Lee et al., 2015), DOX (Kantoff et al., 2010)	Superior loading of siRNA over chemical transfection but disrupting integrity of exosomes	Medium loading efficiency
	Sonication	PTX (Cheng et al., 2017), catalase (Li et al., 2019c), small RNAs (Sun et al., 2010)	High loading efficiency but not efficient for hydrophobic drugs	High loading efficiency
	Extrusion	Porphyrins (Lee et al., 2015), catalase (Li et al., 2019c)	High drug loading efficiency but potential deformation of membrane	High loading efficiency
	Freeze/thaw cycle	Catalase (Li et al., 2019c), prepare hybrid exosomes (Li et al., 2019d)	Exosomes may aggregate and the drugs loading efficiency is low	Low loading efficiency
	Saponin-assisted loading	Catalase (Li et al., 2019c), hydrophilic molecules (Lee et al., 2015)	High drug loading efficiency but generates pores in exosomes hemolysis/toxicity concerns	High loading efficiency