Table 1 Some of the main features of various crosslinking types of hydrogels. PBS phosphate buffer saline
From: Recent advances of on-demand dissolution of hydrogel dressings
| Â | Classification | Exogenous dissolution agents | In situ formation or not | Expected dissolution time | Potential for wound treatment | Advantages | Disadvantages |
|---|---|---|---|---|---|---|---|
Chemically cross-linked hydrogels | Stimuli-sensitive hydrogels | Nothing | Yes | Immediately | Better application in vivo | Hydrogel are pure and less toxic | Low mechanical strength, less crosslinking species, less selectivity of polymer, long gelation time |
Supramolecular self-assembly hydrogels | Mild chemical irrigant | Yes | Within 2 min | Better application in vivo | Hydrogels have better mechanical properties and less toxic effects | Self-assembly process is difficult to control | |
Physically cross-linked hydrogels | Thiol-thioester exchange | Thiolate | Yes | Within 25 min | Better application in vivo | A cheaper way for hydrogel dissolution | Dissolution times of hydrogel are too long, and toxicity of thiolate is unknown |
Thiol-disulfide exchange | Thiol-containing reducing agent | Yes | Within 10 min | Better application in vivo | Built-in redox-sensitivity as living cells | Cytotoxicity of hydrogels or dissolution agents are uncertainty | |
Retro-Michael reaction | Glutamate, PBS (pH 7.4), or light | Yes | 2 days (glutamate); 4 days (PBS) 4.5 min (light) | Further research is needed | Increased stability for sustained release under highly reducing conditions | Michael acceptors for retro Michael Reaction have been less studied, and the effect of hydrogel dissolution is poor with side reaction | |
Retro-Diels-Alder reaction | Dimethy formamide | No | 0.4 h (100 °C) | Further research is needed | Hydrogels are formed need no catalysts or initiators | The dissolution temperatures of hydrogel are too high |