Table 1.
The classification of hydrogels based on different standards.
| Classification standards | Kinds of hydrogels | References |
|---|---|---|
| Material | Natural hydrogels Synthetic hydrogels |
(28) |
| Crosslinking manner | Physically hydrogels Chemically hydrogels |
(29, 30) |
| Electrical charge | Anionic hydrogels Cationic hydrogels Neutral hydrogels |
(31, 32) |
| Polymeric composition | Homopolymer hydrogels Copolymer hydrogels Multipolymer hydrogels |
(33) |
| Type of stimuli responsive | Conventional hydrogels Intelligent hydrogels |
(34) |