The proposed toughening mechanism hypothesizes that the hydrogen bonds within
gel networks tend to preferentially break prior to the coordination bonds and the
survived coordination bonds with dynamic feature also serve as sacrificial bonds to
dissipate another amount of energy after the rupture of hydrogen bonds, which
collectively maximized the contribution of sacrificial bonds to energy dissipation
while affording elasticity. Additionally, the synergy of hydrogen bonds and coordination bonds act as dynamic but highly stable associations, leading to the effective
self-healing efficiency over 90% after damage. It is expected that this facile strategy
of incorporating the biocompatible and biodegradable CNFs may enrich the avenue
in exploration of dynamic and tunable cellulosic hydrogels to expand their potential
applications in the biomedical field.
Yang’s subsequent work [178] was based on dynamic coordination bonds that
mediated the tannic acid-coated cellulose nanocrystals (TA@CNCs) as building
blocks. This study was focused on addressing the inherent contradiction between
excellent self-healing and mechanical properties because of the dynamic cross-links
for healing and steady cross-links for mechanical strength. The hydrogel was
prepared by constructing synergistic interfacial dynamic coordination bonds
among tannic acid-coated CNCs (TA@CNCs), poly(acrylic acid) chains, and
metal ions in a covalent polymer network. The TA@CNC acting as a dynamic
connected bridge endows the ionic gels with hierarchically porous network crosslinked by multiple reversible coordination bonds (Fig. 11c), leading to the significant
mechanical reinforcement of ionic gels. Reversible nature of dynamic coordination
interactions contributes excellent recovery property as well as reliable mechanical
and electrical self-healing property without any assistance of external stimuli.
Intriguingly, the ionic gels display durable and repeatable adhesiveness ascribed to
the presence of catechol groups from the incorporated tannic acid, which can be
adhered directly on human skin and employed as flexible strain sensors to monitor
human motions, expanding the potential applications of dynamic cellulose-based
conductive hydrogels in wearable electronic sensors and healthcare monitoring.
By taking advantage of the strong and dynamic metal-ligand coordination,
Alizadehgiashi et al. [185] used a microfluidic approach to fabricate an
ion-scavenging nanocolloidal microgel material with the chemical cross-linking of
cellulose nanocrystals and graphene quantum dots. By immobilizing the
nanocolloidal building blocks through with imine formation, the hydrogels, with
tunable pore size and structure, sufficiently high mechanical strength, and good
permeability, were formed. Due to the large surface area and abundance of
ion-coordinating sites on the surface of nanoparticle building blocks, the microgels
exhibited a high ion-sequestration capacity. The microgels were recyclable and were
used in several ion-scavenging cycles.
In addition, Hai et al. [186] explored the application of invisible security probe for
the selective detection, protection, and storage of fingerprint information based on
the luminescent Tb
III -carboxymethyl cellulose (CMC) complex-binding aptamer
hydrogels with reversible responsive to ClO/SCN. The imaging information of the
fingerprint can be detected quickly under UV light, where ClO/SCN regulation
results in reversible on/off conversion of the luminescence signals for the encryption
Dynamics in Cellulose-Based Hydrogels with Reversible Cross-Links
345
gel networks tend to preferentially break prior to the coordination bonds and the
survived coordination bonds with dynamic feature also serve as sacrificial bonds to
dissipate another amount of energy after the rupture of hydrogen bonds, which
collectively maximized the contribution of sacrificial bonds to energy dissipation
while affording elasticity. Additionally, the synergy of hydrogen bonds and coordination bonds act as dynamic but highly stable associations, leading to the effective
self-healing efficiency over 90% after damage. It is expected that this facile strategy
of incorporating the biocompatible and biodegradable CNFs may enrich the avenue
in exploration of dynamic and tunable cellulosic hydrogels to expand their potential
applications in the biomedical field.
Yang’s subsequent work [178] was based on dynamic coordination bonds that
mediated the tannic acid-coated cellulose nanocrystals (TA@CNCs) as building
blocks. This study was focused on addressing the inherent contradiction between
excellent self-healing and mechanical properties because of the dynamic cross-links
for healing and steady cross-links for mechanical strength. The hydrogel was
prepared by constructing synergistic interfacial dynamic coordination bonds
among tannic acid-coated CNCs (TA@CNCs), poly(acrylic acid) chains, and
metal ions in a covalent polymer network. The TA@CNC acting as a dynamic
connected bridge endows the ionic gels with hierarchically porous network crosslinked by multiple reversible coordination bonds (Fig. 11c), leading to the significant
mechanical reinforcement of ionic gels. Reversible nature of dynamic coordination
interactions contributes excellent recovery property as well as reliable mechanical
and electrical self-healing property without any assistance of external stimuli.
Intriguingly, the ionic gels display durable and repeatable adhesiveness ascribed to
the presence of catechol groups from the incorporated tannic acid, which can be
adhered directly on human skin and employed as flexible strain sensors to monitor
human motions, expanding the potential applications of dynamic cellulose-based
conductive hydrogels in wearable electronic sensors and healthcare monitoring.
By taking advantage of the strong and dynamic metal-ligand coordination,
Alizadehgiashi et al. [185] used a microfluidic approach to fabricate an
ion-scavenging nanocolloidal microgel material with the chemical cross-linking of
cellulose nanocrystals and graphene quantum dots. By immobilizing the
nanocolloidal building blocks through with imine formation, the hydrogels, with
tunable pore size and structure, sufficiently high mechanical strength, and good
permeability, were formed. Due to the large surface area and abundance of
ion-coordinating sites on the surface of nanoparticle building blocks, the microgels
exhibited a high ion-sequestration capacity. The microgels were recyclable and were
used in several ion-scavenging cycles.
In addition, Hai et al. [186] explored the application of invisible security probe for
the selective detection, protection, and storage of fingerprint information based on
the luminescent Tb
III -carboxymethyl cellulose (CMC) complex-binding aptamer
hydrogels with reversible responsive to ClO/SCN. The imaging information of the
fingerprint can be detected quickly under UV light, where ClO/SCN regulation
results in reversible on/off conversion of the luminescence signals for the encryption
Dynamics in Cellulose-Based Hydrogels with Reversible Cross-Links
345