Table 1.
The differences between the various types of stimulus-responsive hydrogels.
| Types | Principle of Change under Stimulus | Advantages | Examples | Ref. |
|---|---|---|---|---|
| Temperature-responsive | Change of hydrophobic interaction. |
Biocompatibility, easy to function with drug molecules, controlled degradation. | Poloxamer, Pluronic, HA, PPZ, PLGA; PEG. | [182,183,184,185,186,187,188,189] |
| Light-responsive | Destruction of seepage balance. |
Space–time control of drug release; | HPMC, IR820/methylcellulose hydrogels. | [143,190] |
| Enzyme-responsive | Can be formed or degraded under the catalysis of related enzymes. | Can realize molecular recognition, high affinity, mild stimulus. |
MMP-responsive Peptide-crosslinked PEG hydrogels. | [191,192,193,194] |
| pH-responsive | Change of hydrophobicity; increase of electrostatic repulsion. | Biocompatibility, Suitable for acidic tumor microenvironment, strong electrostatic interaction, strong stability. |
PEI, PAM, PAAm, PDMAEMA, PDEAEMA, PMAA, PVAm | [195,196,197,198] |
Abbreviation: Polyorganophosphazene (PPZ); poly (lactic acid-co-glycolic acid) (PLGA); Polyethyleneglycol-diacid (PEG); Polymers hydroxypropyl methylcellulose (HPMC); Poly(ethylene imine) (PEI); Poly(acrylamide) (PAAm); Poly(N,N’-dimethyl aminoethyl methacrylate) (PDMAEMA); Poly(N,N’-diethyl aminoethyl methacrylate) (PDEAEMA); Poly(2-aminoethyl methacrylate) (PMAA); Poly(vinylamine) (PVAm).