Activation Energies Control the Macroscopic Properties of Physically Cross‐Linked Materials

The self-assembly of nanoscale materials to form hierarchically ordered structures promises new opportunities in drug delivery, as well as magnetic materials and devices. Herein, we report a simple means to promote the self-assembly of two polymers with functional groups at a water-chloroform interface using microfluidic technology. Two polymeric layers can be assembled and disassembled at the droplet interface using the efficiency of cucurbit[8]uril (CB[8]) host-guest supramolecular chemistry. The microcapsules produced are extremely monodisperse in size and can encapsulate target molecules in a robust, well-defined manner. In addition, we exploit a dendritic copolymer architecture to trap a small hydrophilic molecule in the microcapsule skin as cargo. This demonstrates not only the ability to encapsulate small molecules but also the ability to orthogonally store both hydrophilic and hydrophobic cargos within a single microcapsule. The interfacially assembled supramolecular microcapsules can benefit from the diversity of polymeric materials, allowing for fine control over the microcapsule properties.

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“…liquid-liquid or soft matter interfaces, which is of great relevance in all biological systems 50,51 .…”

Section: Discussionmentioning

confidence: 99%

Interfacial assembly of dendritic microcapsules with host–guest chemistry

et al. 2014

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“…[15] NFC has been used for a wide range of emerging applications, such as high-strength nanomaterials and biomedical scaffolds. [16][17][18][19][20] NFC is extracted from plant cell walls and has high elastic moduli (26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36) and tensile strength in the GPa range. [21][22][23] Dispersed NFC forms stiff hydrogels that are thought to be mediated by fibril-fibril entanglement facilitated by hydrogen bonding.…”

Section: Recentlynaturalstructuralmaterialshaveinspiredsyntheticmentioning

confidence: 99%

“…[26,27] Specifically, the hostguest interactions of cucurbit [8]uril (CB [8]) display reversible complexation at rates approaching the diffusion limit. [28] CB [8] can form 1:1:1 heteroternary complexes with two guest motifs, still allowing very high binding constants in spite of the dynamic nature. In this study, first-guest methylviologen (MV) and second-guest naphthyl (Np) functional polymers were used.…”

Section: Recentlynaturalstructuralmaterialshaveinspiredsyntheticmentioning

confidence: 99%

Hybrid Supramolecular and Colloidal Hydrogels that Bridge Multiple Length Scales

et al. 2015

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Hybrid nanocomposites were constructed based on colloidal nanofibrillar hydrogels with interpenetrating supramolecular hydrogels, displaying enhanced rheological yield strain and a synergistic improvement in storage modulus. The supramolecular hydrogel consists of naphthyl-functionalized hydroxyethyl cellulose and a cationic polystyrene derivative decorated with methylviologen moieties, physically cross-linked with cucurbit[8]uril macrocyclic hosts. Fast exchange kinetics within the supramolecular system are enabled by reversible cross-linking through the binding of the naphthyl and viologen guests. The colloidal hydrogel consists of nanofibrillated cellulose that combines a mechanically strong nanofiber skeleton with a lateral fibrillar diameter of a few nanometers. The two networks interact through hydroxyethyl cellulose adsorption to the nanofibrillated cellulose surfaces. This work shows methods to bridge the length scales of molecular and colloidal hybrid hydrogels, resulting in synergy between reinforcement and dynamics.

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“…Analogous studies aimed at understanding the effect of crosslink kinetics on viscoelastic material responses have been performed for a number of synthetic polymeric materials. Besides investigating the effect of the crosslink properties themselves (Yount et al, 2005;Shen et al, 2007;Appel et al, 2014;Rossow et al, 2014;Grindy et al, 2015;Tunn et al, 2018), these studies have focused on the contributions of network defects such as dangling ends and loops (Annable et al, 1993;Rossow et al, 2014;Ciarella et al, 2018), crosslink functionality (Li et al, 2016;Gu et al, 2018;Tunn et al, 2019) and polymer length (Annable et al, 1993;Tan et al, 2017). Even though a direct comparison is difficult due to the different polymers used, it can generally be concluded that the number of elastically active chains and their ability to relax after crosslink dissociation are key parameters that determine the macroscopic relaxation time of a material.…”

Section: Introductionmentioning

confidence: 99%

Influence of Network Topology on the Viscoelastic Properties of Dynamically Crosslinked Hydrogels

Grad¹,

Tunn²,

Voerman³

et al. 2020

Preprint

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Biological materials combine stress relaxation and self-healing with non-linear stress-strain responses. These characteristic features are a direct result of hierarchical self-assembly, which often results in fiber-like architectures. Even though structural knowledge is rapidly increasing, it has remained a challenge to establish relationships between microscopic and macroscopic structure and function. Here, we focus on understanding how network topology determines the viscoelastic properties, i.e. stress relaxation, of biomimetic hydrogels. We have dynamically crosslinked two different synthetic polymers with one and the same crosslink. The first polymer, a polyisocyanopeptide (PIC), self-assembles into semi-flexible, fiber-like bundles and thus displays stress-stiffening, similar to many biopolymer networks. The second polymer, 4-arm poly(ethylene glycol) (starPEG), serves as a reference network with well-characterized structural and viscoelastic properties. Using one and the same coiled coil crosslink allows us to decouple the effects of crosslink kinetics and network topology on the stress relaxation behavior of the resulting hydrogel networks. We show that the fiber-containing PIC network displays a relaxation time approximately two orders of magnitude slower than the starPEG network. This reveals that crosslink kinetics is not the only determinant for stress relaxation. Instead, we propose that the different network topologies determine the ability of elastically active network chains to relax stress. In the starPEG network, each elastically active chain contains exactly one crosslink. In the absence of entanglements, crosslink dissociation thus relaxes the entire chain. In contrast, each polymer is crosslinked to the fiber bundle in multiple positions in the PIC hydrogel. The dissociation of a single crosslink is thus not sufficient for chain relaxation. This suggests that tuning the number of crosslinks per elastically active chain in combination with crosslink kinetics is a powerful design principle for tuning stress relaxation in polymeric materials. The presence of a higher number of crosslinks per elastically active chain thus yields materials with a slow macroscopic relaxation time but fast dynamics at the microscopic level. Using this principle for the design of synthetic cell culture matrices will yield materials with excellent long-term stability combined with the ability to locally reorganize, thus facilitating cell motility, spreading and growth.

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Activation Energies Control the Macroscopic Properties of Physically Cross‐Linked Materials

Cited by 30 publications

References 34 publications

Interfacial assembly of dendritic microcapsules with host–guest chemistry

Interfacial assembly of dendritic microcapsules with host–guest chemistry

Hybrid Supramolecular and Colloidal Hydrogels that Bridge Multiple Length Scales

Influence of Network Topology on the Viscoelastic Properties of Dynamically Crosslinked Hydrogels

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