Comparison of cross-linking types

Ionic Crosslinking

Advantage

• simple and mild procedure
• no need for potentially toxic catalysts
• biocompatible
• reversible
• rapid dissolution for recovery and analysis

Disadvantage

• pH-sensitive swelling
• weak mechanical properties
• risk of dissolution of the system

Other characteristic

• gel strength can be tuned based on type of ions and concentration

Photo/ radical Crosslinking

Advantage

• low activation energy
• rapid reaction rate
• high conversion of the polymer precursors
• controllable grafting on polymeric surface without affecting bulk properties

Disadvantage

= limited penetration of the light can limit the overall thickness of the hydrogel = optimization of irradiation time and selection of photoinitiator and its concentration is required

Other characteristic

• potential irritant in in vivo applications
• radicals can attack other macromolecules in the hydrogel

Enzymatic Crosslinking

Advantage

• mild reaction conditions
• enzyme selectivity and specificity
• better control of macromolecular structure without protection/ deprotection steps

Disadvantage

• expensive

Other characteristic

• in certain cases, initiation needs the enzyme to form free radicals
• can be coupled with other polymerization methods

Michael addition

Advantage

• mild reaction conditions
• high number of possibple functional groups (with different donors and acceptors)
• high conversions and favorable reaction rates

Disadvantage

• hydrolytic instability that was attributed to hydrolysis of the ester linkages in the presence of the base catalyst.

Other characteristic

• easily achieved reaction between nucleophiles and activated olefins and alkynes
• base-catalyzed