Table 2 |.
Hydrogel cross-linking chemistries used to generate hydrogel microparticles
| Base hydrogel | Chemical modification | Cross-linking method | Fabrication technique |
|---|---|---|---|
| Alginate | Unmodified77 | Ionic cross-linking with CaCl2 | EHD spraying |
| Unmodified47,112 | Ionic cross-linking in the presence of CaCl2 | Microfluidic emulsion | |
| Methacrylate232 | Radical polymerization (UV) | Microfluidic emulsion | |
| Gelatin | Unmodified86 | Temperature | Mechanical fragmentation |
| Methacrylate35,233 | Radical polymerization (UV) | Microfluidic emulsion | |
| Methacrylate194 | Temperature (cooling to 4 °C then radical polymerization (UV)) | Microfluidic emulsion | |
| Methacrylate58 | Radical polymerization (UV) | Lithography | |
| Hyaluronic acid | Methacrylate234 | Radical polymerization (UV) | Batch emulsion |
| Methacrylate67 | Radical polymerization (UV) | Lithography | |
| Acrylate103 | Radical polymerization (UV) | Microfluidic emulsion | |
| Norbornene7 | Thiol-ene reaction | Microfluidic emulsion | |
| Tyramine235 | Sequential enzymatic and radical polymerization (UV) | Lithography (two-photon) | |
| Tyramine + furan236 | Enzymatic cross-linking and/or Diels–Alder click chemistry | Microfluidic emulsion | |
| Vinyl ester69 | Thiol-ene reaction | Lithography (two-photon) | |
| Aldehyde + hydrazide237 | Hydrazone covalent cross-linking | Batch emulsion | |
| Methacrylate + tetrazole238 | Tetrazole–alkene photoclick chemistry (UV) | Microfluidic emulsion | |
| PEG | Acrylate59,239,240 | Radical polymerization (UV) | Microfluidic emulsion and lithography |
| Methacrylate34 | Radical polymerization (UV) | Lithography | |
| Norbornene195 | Thiol-ene reaction (UV) | EHD spraying | |
| Vinyl sulfone8 | Michael addition | Microfluidic emulsion | |
| Vinyl sulfone and thiol39,125 | Michael addition | Microfluidic emulsion | |
| Maleimide29,33,38 | Michael addition | Microfluidic emulsion | |
| PVA | Thiol and ene68 | Thiol-ene reaction (UV) | Lithography |
| Chitosan | Unmodified82 | Electrostatic interactions | EHD spraying |
| Silk/fibroin | Norbornene241 | Thiol-ene photoclick chemistry and β-sheet formation | Batch emulsion |
| Agarose | Unmodified7,37,242 | Temperature | Microfluidic emulsion |
EDH, electrohydrodynamic; PEG, poly(ethylene glycol); PVA, poly(vinyl alcohol); UV, ultraviolet.