Tough and Self-Healing Hydrogels Formed via Hydrophobic Interactions

Tuncaboylu, Deniz Ceylan; Sarı, Murat; Oppermann, Wilhelm; Okay, Oğuz

doi:10.1021/ma200579v

Cited by 670 publications

(590 citation statements)

References 63 publications

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“…To increase hydrogel dissipative properties, modifications at the molecular level have been suggested including reversible interactions like hydrophobic bilayers in a hydrophilic polymer network (Haque et al, 2011), ionic cross-linking (Sun et al, 2012), and physical interactions instead of covalent cross-linking (Abdurrahmanoglu et al, 2009;Tuncaboylu et al, 2011). The obtained noncovalent cross-linked hydrogels usually present a high degree of toughness.…”

Section: Introductionmentioning

confidence: 99%

“…In conjunction with this covalently bonded structure, PHEMA chains are held together by noncovalent forces in a secondary structure stabilized by hydrophobic bonding (Refojo, 1967). It has been reported that hydrophobic interactions can increase energy dissipation in hydrogels' network under loading by the reversible disengagements of the hydrophobes from the hydrophobic associations (Abdurrahmanoglu et al, 2009;Tuncaboylu et al, 2011). With these special properties, PHEMA hydrogels offer then the possibility to simultaneously increase their stiffness and toughness properties.…”

Section: Introductionmentioning

confidence: 99%

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Improving hydrogels׳ toughness by increasing the dissipative properties of their network

Moghadam

Pioletti

2015

Journal of the Mechanical Behavior of Biomedical Materials

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a b s t r a c tThe weak mechanical performance and fragility of hydrogels limit their application as biomaterials for load bearing applications. The origin of this weakness has been explained by the low resistance to chains breakage composing the hydrogel and to the cracks propagation in the hydrogel submitted to loading conditions. These low resistance and crack propagation were in turn related to an insufficient energy dissipation mechanism in the hydrogel structure. The goal of this study is to evaluate the dissipation mechanism in covalently bonded hydrogels so that tougher hydrogels can be developed while keeping for the hydrogel a relatively high mechanical stiffness. By varying parameters such as crosslinker type or concentration as well as water ratio, the dissipative properties of HEMAbased hydrogels were investigated at large deformations. Different mechanisms such as special friction-like phenomena, nanoporosity, and hydrophobicity were proposed to explain the dissipative behavior of the tested hydrogels. Based on this analysis, it was possible to develop hydrogels with increased toughness properties.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Improving hydrogels׳ toughness by increasing the dissipative properties of their network

Moghadam

Pioletti

2015

Journal of the Mechanical Behavior of Biomedical Materials

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“…16 Formation of hydrophobic associations is limited by low solubility of the hydrophobes. 17 Hydrogen bonds have very low association strength in hydrogels due to competition of water for binding sites. 18 Ionic cross-links are particularly effective in toughening hydrogels -alginate-polyacrylamide hydrogels in which the alginate is cross-linked with calcium ions exhibit remarkably high toughness.…”

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confidence: 99%

Stiff, strong, and tough hydrogels with good chemical stability

2014

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Most hydrogels have poor mechanical properties, severely limiting their scope of applications.Here we report on a hybrid hydrogel that combines extremely high stiffness, strength, and toughness, while maintaining physical integrity in electrolyte solutions. The hydrogel consists of a hydrophilic polymer network that is covalently cross-linked and a second polymer network that can crystallize. We show that the crystallites serve as physical cross-links for the second network.The crystallites contribute to the high stiffness and strength of the hydrogel; they unzip and dissipate energy under deformation, and reform due to the incompatibility of the two polymers in the hydrogel. The crystallite-toughened hydrogel can achieve an elastic modulus of 5 MPa, a strength of 2.5 MPa, and a fracture energy of 14,000 Jm -2 . Unlike alginate-based hybrid hydrogels, this hydrogel preserves its mechanical properties in electrolyte solutions and could be considered for further development in a variety of engineering applications. 20 Unfortunately, hydrogels synthesized using this method are compliant and brittle. 22 It is possible to achieve higher stiffness and toughness using a dry-anneal method, but only at the expense of a much lower water content ( Supplementary Fig. S1). 23 Muratoglu and coworkers polymerized acrylamide monomers in the pores of a PVA hydrogel to form uncross-linked chains, and showed that the equilibrium water content of the resulting gels increased with acrylamide content, while the coefficient of friction, tear strength and creep resistance decreased. 21Here we propose that a hybrid network of a crystalline polymer and a covalently crosslinked hydrophilic polymer may form a hydrogel with robust mechanical properties and good chemical stability: the crystalline polymer can generate a large number of crystallites to serve as physical cross-links that are both stable and reversible; the covalently cross-linked hydrophilic polymer maintain the elasticity of the network during deformation and controls the swelling of the hydrogel. We describe one such hybrid hydrogel that combines extremely high stiffness, strength, and toughness. The hydrogel consists of a hydrophilic polyacrylamide (PAAm) polymer network that is covalently cross-linked and a PVA network that forms crystallites. We show that the PVA crystallites result in a high cross-link density, thus producing a gel of remarkable stiffness and strength. The crystallites unzip under deformation, dissipating energy in the process and yielding a hydrogel with exceptional toughness. After deformation, unzipped crystallites recover at room temperature due to the incompatibility of the two polymers in the gel. The 4 crystallite-toughened hydrogel can achieve an elastic modulus of 5 MPa, a strength of 2.5 MPa, and a fracture energy of 14,000 Jm -2 . Moreover, these properties are stable, even in concentrated electrolyte solutions. ResultsWe prepared the hybrid hydrogels in a simple three-step protocol. First, we form a cross- Supplementary Fig. S2); e...

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“…In general because hydrogels have poor mechanical properties and are very brittle, their use is limited for load-bearing applications. It has been shown that the poor mechanical performance and fragility of hydrogels mainly originate from their very low resistance to crack propagation due to the lack of an efficient energy dissipation mechanism in the gel network [32,33]. The high dissipation property of the developed The release of the Xylene Cyanole FF from hydrogels containing nanoparticles was quantified after 5 and 8 min of cyclic mechanical loading.…”

Section: Discussionmentioning

confidence: 99%

Controlled release from a mechanically-stimulated thermosensitive self-heating composite hydrogel

et al. 2014

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a b s t r a c tTemperature has been extensively explored as a trigger to control the delivery of a payload from environment-sensitive polymers. The need for an external heat source only allows limited spatiotemporal control over the delivery process. We propose a new approach by using the dissipative properties of a hydrogel matrix as an internal heat source when the material is mechanically loaded. The system is comprised of a highly dissipative hydrogel matrix and thermo-sensitive nanoparticles that shrink upon an increase in temperature. Exposing the hydrogel to a cyclic mechanical loading for a period of 5 min leads to an increase of temperature of the nanoparticles. The concomitant decrease in the volume of the nanoparticles increases the permeability of the hydrogel network facilitating the release of its payload. As a proof-of-concept, we showed that the payload of the hydrogel is released after 5e8 min following the initiation of the mechanical loading. This delivery method would be particularly suited for the release of growth factor as it has been shown that cell receptor to growth factor is activated 5e20 min following a mechanical loading.

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Tough and Self-Healing Hydrogels Formed via Hydrophobic Interactions

Cited by 670 publications

References 63 publications

Improving hydrogels׳ toughness by increasing the dissipative properties of their network

Improving hydrogels׳ toughness by increasing the dissipative properties of their network

Stiff, strong, and tough hydrogels with good chemical stability

Controlled release from a mechanically-stimulated thermosensitive self-heating composite hydrogel

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