Robust Heterogeneous Hydrogels with Dynamic Nanocrystal–Polymer Interface

Huang, Heqin; Wang, Yonggui; Wang, Xiaojie; Rehfeldt, Florian; Zhang, Kai

doi:10.1002/marc.201600810

Cited by 8 publications

(7 citation statements)

References 37 publications

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“…This figure shows that (i) when elongation ratio k exceeds the maximum elongation ratio k max n at the previous cycle of deformation, the stress-strain diagram under reloading reaches rapidly that under tension of a virgin sample (the Mullins effect), (ii) when the maximum elongation ratios coincide for two deformation programs, the corresponding retraction paths coincide as well (fading memory of deformation history). These results are in accord with experimental data presented in [37,38,39].…”

Section: Accepted Manuscriptsupporting

confidence: 93%

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Mechanical response of double-network gels with dynamic bonds under multi-cycle deformation

Drozdov

Christiansen

2018

Polymer

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Mechanical behavior of double-network (DN) gels with covalent and non-covalent bonds under multi-cycle loading depends strongly on time, strain rate and deformation program. A model is developed for the viscoelastic and viscoplastic responses of a polymer network with permanent and temporary junctions. Viscoelasticity is modeled as breakage and reformation of temporary bonds driven by thermal fluctuations. Viscoplasticity is treated as sliding of permanent junctions with respect to their initial positions in the network. Slippage occurs when a junction becomes unbalanced due to transition of a chain linked by this junction from its active state into the dangling state. Analysis of observations in tensile tests with various strain rates, relaxation tests, loading-unloading tests, and multi-cycle tests with various deformation programs on a series of DN gels shows that the experimental stress-strain diagrams are described correctly by the governing equations, material parameters evolve consistently with experimental conditions, and predictions of the model are in quantitative (where sufficient data are provided) and qualitative agreement with experimental data. In particular, numerical simulation demonstrates the ability of the model to describe the Mullins effect in DN gels.

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Section: Accepted Manuscriptsupporting

confidence: 93%

“…the stress-strain diagram under reloading along the (n + 1)th cycle coincides with that under uniaxial tension, provided that the elongation ratio k exceeds sufficiently the maximum elongation ratio at the nth cycle (the Mullins effect) [37,38,39].…”

Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 85%

Mechanical response of double-network gels with dynamic bonds under multi-cycle deformation

Drozdov

Christiansen

2018

Polymer

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“…The flourishing development of versatile stimuli‐responsive polymers leads to the emergence of flexible polymer actuators . Hydrogels are highly hydrated 3D polymer networks, which showed excellent biodegradability, biocompatibility, and permeability . In recent years, hydrogel‐based actuators that can undergo precisely tunable motions enable transformative applications in diverse areas, such as biomedical fields, soft robotics, and soft electronics .…”

Section: Introductionmentioning

confidence: 99%

Multi‐Responsive Bilayer Hydrogel Actuators with Programmable and Precisely Tunable Motions

Wang

Huang

Liu

et al. 2019

Macro Chemistry & Physics

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Multi‐responsive hydrogel actuators show promising applications for soft robotics, biomedical engineering, and artificial muscles, but the uncontrollable nature of their motions poses a barrier to practical applications. Herein, a novel type of bilayer hydrogel actuators (BHAs) is presented comprising of a poly(N‐isopropylacrylamide) (PNIPAm) and a poly (N‐hydroxyethyl acrylamide) (PHEAm) hydrogel layer with various compositions, which demonstrate thermal‐responsive and novel solvent‐responsive actuation under water or within solvents. These BHAs exhibit a wide range of regulable bidirectional motions due to the simultaneous co‐nonsolvency property of PNIPAm and the shrinking behavior of PHEAm in ethanol/water mixtures with various ethanol contents. By adjusting the compositions of ethanol/water mixtures, the bending directions and amplitudes of BHAs are precisely regulable and the curvatures of actuators are tunable between −0.34 and 0.3. Because of the temperature‐responsive character of PNIPAm, BHAs fulfilled thermal‐driven motions to lift items. By reinforcing PHEAm layers with cellulose nanocrystals (CNCs) or CNCs bearing methacylamide moieties on the surface, the weight‐lifting capability of BHAs is highly improved to 18 times the weight of their own polymer weights. This design concept with bilayer structures provides a new strategy for the construction of precisely regulable hydrogel actuators, which allows using solvents to exactly control their motions.

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“…Thus, the nonuniform distribution of the static dicatechol bonds and dynamic PBA/catechol cross-links within the diverse regions in hydrogels in fact led to the heterogeneity in macrostructures. Another kind of heterogeneity can be constructed by establishing supramolecular interactions between nanoparticles and polymer chains. , The necking phenomenon was also observed in such nanocomposite hydrogels or polymers . To further investigate the necking behaviors in our heterogeneous hydrogels, we used anisotropic nanocellulose with two distinct surface functionalities: CNC (TEMPO-oxidized) with only carboxyl groups (1.52 ± 0.03 mmol/g) on the surface and CNC-PBA with surface-grafted phenylboronic acid groups (1.07 ± 0.05 mmol/g) in addition to the rest of the carboxyl groups (∼0.4 mmol/g) (Figures A and S8).…”

Section: Results and Discussionmentioning

confidence: 99%

Dually Heterogeneous Hydrogels via Dynamic and Supramolecular Cross-Links Tuning Discontinuous Spatial Ruptures

Huang

Wang

Rehfeldt

et al. 2018

ACS Sustainable Chem. Eng.

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Biological tissues are often highly and multiply heterogeneous in both structure and composition, but the integrity of multiheterogeneity in artificial materials is still a big challenge. Herein, dually heterogeneous hydrogels were constructed with two distinct strategies via dynamic bonds and supramolecular cross-links. The hydrogels showed discontinuous spatial ruptures, and the mechanical behaviors of hydrogels could be tuned. The primary heterogeneity resulted from a nonuniform distribution of dynamic and/or static cross-links. The presence of only primary heterogeneity within hydrogels led to uneven mechanical properties that were represented by discontinuous spatial ruptures during the stretching the hydrogel and therefore caused the necking deformation. Further introduction of the secondary heterogeneity by incorporating anisotropic cellulose nanocrystals (CNC) into the hydrogels allowed the adjustment of the necking phenomenon. Moreover, distinct CNC with diverse surface functionalities exhibited different effects: the "active" CNC with surface-attached dynamic bonds retarded the necking propagation, while the "neutral" CNC without further surface modification promoted the extension of necking points. Thus, the regulation of deformation and fracture mode of hydrogels was achieved by the synergy of dually heterogeneous structure.

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Robust Heterogeneous Hydrogels with Dynamic Nanocrystal–Polymer Interface

Cited by 8 publications

References 37 publications

Mechanical response of double-network gels with dynamic bonds under multi-cycle deformation

Mechanical response of double-network gels with dynamic bonds under multi-cycle deformation

Multi‐Responsive Bilayer Hydrogel Actuators with Programmable and Precisely Tunable Motions

Dually Heterogeneous Hydrogels via Dynamic and Supramolecular Cross-Links Tuning Discontinuous Spatial Ruptures

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