Table 2.

A summary of transparent hydrogels derived from natural polymers.

Polymer	Resource	Gelation	Hydrogel	Applications	Reference
Silk	Silkworm cocoon, spider silk	Binary solvent-exchange-induced self-assembly		Light waveguide for photodynamic therapy, lenses for light emitting diode (LED), birefringence	[62]
		Gel with horseradish peroxidase and hydrogen peroxide			[63]
					[64]
Chitosan	Crusteacean shells, Mushrooms	Crosslink with glutaraldehyde prepared in HEPES buffer	–	Biosensors, leaky waveguides	[65]
Cellulose	Trees, plants	Crosslink with Al3+ ions		biosensor and signal transmission	[66]
Agarose	Brown seaweed	Gel upon cooling	–	in vivo imaging, light delivery, biosensor	[15]
Alginate	Green seaweed	Crosslink with calcium sulphate dihydrate solution		tamponading agent for vitreous substitute	[67]