Table 2.

Light-sensitive polymer classifications.

Classification		Characteristics	Examples
Organic nano-drug carrier	Micelles and vesicles	Prepared from amphiphilic polymers; a photo-responsive amphiphilic polymer can be obtained by introducing light-sensitive groups onto the hydrophobic side. After self-assembly and encapsulation of drug micelles or vesicles, controlled drug release can be achieved.	Poly(ethylene oxide-b-methacrylic acid) (PEO-PMAA)
	Liposomes	Achieved by stem grafting light-sensitive groups into polymers to construct a liposomal or hydrophobic region in amphiphilic materials [34].	trans-liposomes and Bis-Azo-PC liposomes
	Hydrogels	A photo-responsive crosslinker breaks when exposed to light; then, the capsule structure disintegrates and the drug is released.	Chlorophyllin, dichromate, aromatic azide, diazo compounds, aromatic nitro compounds, organic halogen compounds
Inorganic nano-drug carrier		Inorganic nanoparticles have a well-controlled size and shape with large surface areas. Unique light-, electricity-, and magnetic-sensitive properties enable functions such as bioimaging, targeted delivery, and collaborative drug therapy with the potential for drug delivery inside cells [35].	Mesoporous silica, gold nanomaterials, iron oxide
Light-sensitive group	Spiropyran	Light treatment leads to reversible structural changes in light-sensitive groups, destroys the carrier structure to release drugs, and reassembles the carrier structure [36].	Benzo thiopyran compound of spiro monoaza crown ethers, benzo-crown ether spiropyran, benzo thiopyran compound of monazo sulfide crown ether [36]
	Azobenzene	In light stimulation, cis-trans isomerism can be reversed to elicit changes in material properties such as color, size, shape, polarity, refractive index, and solubility [37].	dendritic polyamide-amine (PAMAM)
	Nitrobenzene	Light induces irreversible fracture of light-sensitive groups and removes light-sensitive compounds to disassemble micelles.	O-nitrobenzyl alcohol, ortho-nitrobenzal
	Coumarin	Unsaturated double bonds in the structure of coumarin compounds form an extended conjugation system. Most compounds show blue or blue-green fluorescence under UV light [38].	Furocoumarins, psoralens, 5-methoxypsoralen (5-MOP),8-methoxypsoralen (8-MOP)