Table 1.

Representative list of hydrophilic materials used to form hydrogel nanofibers with post-processing techniques.

Material	Example crosslinking method(s)	Modulation of biophysiochemical properties
Fully-Synthetic Materials
Polyacrylamide (PA)	Chemical:  • Glutaraldehyde crosslinker105	Biochemical:  • Likely adsorption-based modifications Biophysical:  • Degree (extent) of crosslinking105
Poly(vinyl alcohol) (PVA)	Chemical:  • Glutaraldehyde crosslinker106  • PVA composites for crosslinking107 Physical:  • Controlling hydrophobicity through PVA modifications108	Biochemical:  • Likely adsorption-based modifications Biophysical:  • Degree (extent) of crosslinking106 or PVA modification108  • Degree of hydrolysis (i.e. quantity of pendant reactive groups)107
Poly(ethylene glycol) (PEG)	Chemical:  • Pendant norbornenes (step-growth polymerization)85,136  • Pendant methacrylates (chain-growth polymerization)32	Biochemical  • Adsorption-based modifications32  • Pendant norbornenes provide sites for addition of biomolecules   ○ Light-mediated thiol-ene conjugation85 Biophysical:  • Stiffness controlled via irradiation and crosslinker– for example: norbornenes136 and methacrylates32
Naturally-Derived Materials
Collagen	Chemical:  • Glutaraldehyde crosslinker95,97,99  • Carbodiimide crosslinking (EDC/NHS)102	Biochemical:  • Collagen provides natural bioactive sites for cell adhesion and interaction95 Biophysical:  • Degree (extent) of chemical crosslinking97
Gelatin	Chemical:  • Glutaraldehyde98 and diisocyanate crosslinkers100  • Carbodiimide crosslinking (EDC/NHS)101,103  • Pendant methacrylates (chain-growth polymerization)115–117 Physical:  • Dehydrothermal crosslinking (generally weaker fibers)96	Biochemical:  • Gelatin provides natural bioactive sites for cell adhesion and interaction96 Biophysical:  • Degree (extent) of chemical crosslinking96  • Degree of chain-growth polymerization (e.g. with methacrylates)115,116
Hyaluronic Acid (HA)	Chemical:  • Pendant norbornenes (step-growth polymerization)86  • Pendant methacrylates (chain-growth polymerization)30,88,118,126,144  • Pendant maleimides (chain-growth polymerization)8  • Hydrazide/aldehyde proximity reactions to crosslink adjacent fibers145	Biochemical:  • Pendant molecules provide sites for addition of biomolecules   ○ Michael addition: thiolated biomolecules react with pendant alkenes in basic conditions8,118   ○ Light-mediated thiol-ene conjugation86 Biophysical:  • Stiffness also controlled via irradiation time – for example: methacrylates88,122  • Stiffness within norbornene modified systems can conceivably be controlled via crosslinker added, following from Gramlich et al.112
Dextran	Chemical:  • Pendant methacrylates (chain-growth polymerization)2,3,31  • Pendant vinyl sulfones (chain-growth polymerization)87,124,146	Biochemical:  • Pendant molecules provide sites for addition of biomolecules   ○ Methacrylated heparin conjugated to free methacrylates within methacrylated-dextran fibers87   ○ Michael addition: thiolated biomolecules react with pendant alkenes in basic conditions2,3,31,87,124,146 Biophysical:  • Stiffness also controlled via irradiation time – for example: chain-growth polymerization2