PEG
Poly(ethylene glycol)
PF
Paraformaldehyde
PNIPAAm
Poly(N-isopropylacrylamide)
PVA
Poly(vinyl alcohol)
QDs
Quantum dots
Q-TCNCs
Quaternized tunicate cellulose nanocrystals
SA
Succinic anhydride
TA@CNCs Tannic acid-coated cellulose nanocrystals
t-BAA
Tert-butyl acetoacetate
TBAF
Tetrabutylammonium fluoride
TEAC
Triethylammonium chloride
UPy
2-Ureido-4[1H]-pyrimidone pendant groups
1 Introduction
Hydrogels are a unique form of soft-and-wet functional material with a threedimensional (3D) cross-linked hydrophilic network entrapping with large amounts
of water (or biological fluids) without dissolving [1, 2]. Once immersed in water,
hydrogels can continue to absorb and swell to equilibrium state due to the presence
of hydrophilic groups including –NH 2 , –OH, –COOH, and –SO 3 H in their polymer
networks. The basic principle behind swelling in polymeric hydrogels is that the
mixed free energy causes the solvent to diffuse into the hydrogel driven by the form
of osmotic pressure. Retaining the 3D structure integrity under swelling is attributed
to either physical interactions (chain entanglements, van der Waals forces, hydrogen
bonds, crystallite associations, ionic interactions, etc.) or chemical cross-links (covalent bonding), which prevent hydrogels from dissolution in the solvent.
According to the polymer source, hydrogels are generally available from the
synthetic or biopolymer-based ones [3, 4]. The development of synthetic polymerbased hydrogels has been widely witnessed via cross-linking poly(ethylene glycol)
(PEG) [5], poly(acrylic acid) (PAA) [6], polyacrylamide (PAAm) [7], poly(vinyl
alcohol) (PVA) [8], and poly(N-isopropylacrylamide) (PNIPAAm) [9] and their
copolymers [10]. However, most synthetic polymer gels lack biocompatibility and
biodegradability, limiting their practical application in biomedical fields [11]. Contrastingly, owing to their essential biocompatibility and biodegradability, natural
polymer-based hydrogels featured with tissue-mimicking consistency characteristic
draw tremendous popularity in varied fields including biomedical materials (drug
carriers [12], pharmaceutical wound dressings [13], and tissue engineering scaffolds
[1]), hygiene (disposable diapers and feminine care products) [14], agriculture (water
retention [15] and pesticide delivery [16]), pollutant adsorbents (heavy metal ions
Dynamics in Cellulose-Based Hydrogels with Reversible Cross-Links
321
Poly(ethylene glycol)
PF
Paraformaldehyde
PNIPAAm
Poly(N-isopropylacrylamide)
PVA
Poly(vinyl alcohol)
QDs
Quantum dots
Q-TCNCs
Quaternized tunicate cellulose nanocrystals
SA
Succinic anhydride
TA@CNCs Tannic acid-coated cellulose nanocrystals
t-BAA
Tert-butyl acetoacetate
TBAF
Tetrabutylammonium fluoride
TEAC
Triethylammonium chloride
UPy
2-Ureido-4[1H]-pyrimidone pendant groups
1 Introduction
Hydrogels are a unique form of soft-and-wet functional material with a threedimensional (3D) cross-linked hydrophilic network entrapping with large amounts
of water (or biological fluids) without dissolving [1, 2]. Once immersed in water,
hydrogels can continue to absorb and swell to equilibrium state due to the presence
of hydrophilic groups including –NH 2 , –OH, –COOH, and –SO 3 H in their polymer
networks. The basic principle behind swelling in polymeric hydrogels is that the
mixed free energy causes the solvent to diffuse into the hydrogel driven by the form
of osmotic pressure. Retaining the 3D structure integrity under swelling is attributed
to either physical interactions (chain entanglements, van der Waals forces, hydrogen
bonds, crystallite associations, ionic interactions, etc.) or chemical cross-links (covalent bonding), which prevent hydrogels from dissolution in the solvent.
According to the polymer source, hydrogels are generally available from the
synthetic or biopolymer-based ones [3, 4]. The development of synthetic polymerbased hydrogels has been widely witnessed via cross-linking poly(ethylene glycol)
(PEG) [5], poly(acrylic acid) (PAA) [6], polyacrylamide (PAAm) [7], poly(vinyl
alcohol) (PVA) [8], and poly(N-isopropylacrylamide) (PNIPAAm) [9] and their
copolymers [10]. However, most synthetic polymer gels lack biocompatibility and
biodegradability, limiting their practical application in biomedical fields [11]. Contrastingly, owing to their essential biocompatibility and biodegradability, natural
polymer-based hydrogels featured with tissue-mimicking consistency characteristic
draw tremendous popularity in varied fields including biomedical materials (drug
carriers [12], pharmaceutical wound dressings [13], and tissue engineering scaffolds
[1]), hygiene (disposable diapers and feminine care products) [14], agriculture (water
retention [15] and pesticide delivery [16]), pollutant adsorbents (heavy metal ions
Dynamics in Cellulose-Based Hydrogels with Reversible Cross-Links
321