A hybrid polymer gel with controlled rates of cross-link rupture and self-repair

Kersey, Farrell R.; Loveless, David M.; Craig, Stephen L.

doi:10.1098/rsif.2006.0187

Cited by 131 publications

(87 citation statements)

References 41 publications

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“…(iii) While the metalligand-complex theme can also be utilized to cross-link polymers in organic solvents (28) its incorporation into polymers in aqueous solvents under ambient conditions by simply increasing pH as presented here, provides a unique promising platform for environmental and physiological applications. (iv) Finally, in our initial polymer system, the pH-tunable cross-link kinetics offer easy control of viscoelastic properties over four orders of magnitude in modulus, from a low viscosity fluid to a stable self-healing gel.…”

Section: Discussionmentioning

confidence: 99%

pH-induced metal-ligand cross-links inspired by mussel yield self-healing polymer networks with near-covalent elastic moduli

Holten‐Andersen

Harrington

Birkedal

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

1,389

1,326

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Growing evidence supports a critical role of metal-ligand coordination in many attributes of biological materials including adhesion, self-assembly, toughness, and hardness without mineralization [Rubin DJ, Miserez A, Waite JH (2010) Advances in Insect Physiology: Insect Integument and Color, eds Jérôme C, Stephen JS (Academic Press, London), pp . Coordination between Fe and catechol ligands has recently been correlated to the hardness and high extensibility of the cuticle of mussel byssal threads and proposed to endow self-healing properties [Harrington MJ, Masic A, HoltenAndersen N, Waite JH, Fratzl P (2010) Science 328:216-220]. Inspired by the pH jump experienced by proteins during maturation of a mussel byssus secretion, we have developed a simple method to control catechol-Fe 3þ interpolymer cross-linking via pH. The resonance Raman signature of catechol-Fe 3þ cross-linked polymer gels at high pH was similar to that from native mussel thread cuticle and the gels displayed elastic moduli (G′) that approach covalently cross-linked gels as well as self-healing properties.biomaterials | catecholate polymer | metal coordination | reversible cross-links | physical gels M ussel byssal threads are protected against wear by a cuticle, an outer proteinaceous coating, that despite a hardness of ∼0.1 GPa, accommodates large cyclic strains in the turbulent intertidal zone (1, 2). During strain, the cuticle suppresses macroscale failure by limiting crack propagation to the microscale (1, 3). It was recently demonstrated that a small amount of Fe (<1 wt%) plays an important role in this mechanism; bonding with the catechol-like amino acid dihydroxy-phenylalanine (dopa) in the cuticle protein, mfp-1 (4-6). Tris-and bis-catecholFe 3þ complexes possess some of the highest known stability constants of metal-ligand chelates (log K S ≈ 37-40, where K S is the equilibrium constant for the complex formation) (7-10) and single molecule tensile tests have demonstrated that the breaking of a metal-dopa bond requires a force only modestly lower than the force required to rupture a covalent bond under identical loading conditions (∼0.8 nN vs. ∼2 nN, respectively) (11). Harrington et al. proposed a model where the catecholFe 3þ complexes in the cuticle function as sacrificial load-bearing cross-links facilitating extensibility of the material (4). In contrast to covalent bonds, metal-dopa bonds can spontaneously reform after breaking (11) and the model predicts that the damage accumulated in the cuticle could self-heal via reformation of broken catechol-Fe 3þ complexes (4). Here we describe a strategy for introducing bis-and/or tris-catechol-Fe 3þ cross-links into a synthetic polymer network and demonstrate that such a network indeed displays high elastic moduli and self-healing properties. ResultsThe stoichiometry of catechol-Fe 3þ complexes (mono-, bis-, or tris-) is controlled by pH via the deprotonation of the catechol hydroxyls (Fig. 1A). The pH required to establish the bis-and tris-complexes is typically reported to be above pH...

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Section: Discussionmentioning

confidence: 99%

pH-induced metal-ligand cross-links inspired by mussel yield self-healing polymer networks with near-covalent elastic moduli

Holten‐Andersen

Harrington

Birkedal

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

1,389

1,326

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“…Thus, gels with reversible disulfide cross-links have been studied [109][110][111]. Reversible metal-ligand cross-links with a self-repairing function have also been described [112]. Suitable modification of these systems could also be used to form chemically driven actuators.…”

Section: Chemically Driven Gel Actuatorsmentioning

confidence: 99%

Polymer Gel Actuators: Fundamentals

Calvert

2009

Biomedical Applications of Electroactive Polymer Actuators

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One view of materials development is to search for what materials correspond to empty spaces on a hypothetical multi-dimensional map of the properties of available materials. Following a biomimetic philosophy, for instance, it can be seen that tough ceramics and moldable short fiber composites with high moduli are possible but absent from the list of available synthetic materials. Likewise artificial muscle is missing, where the properties are defined as a developed stress of over 300 kPa, a linear contraction of 25 % and a response time of below one second. Currently dielectric elastomers come closest but have disadvantages [1,2].The actin-myosin muscle system provides the performance target for electroactive polymer actuators [3,4]. The process is driven chemically by the energy change from hydrolysis of the polyphosphate bond as ATP (adenosine triphosphate) binds to myosin and is converted to ADP (adenosine diphosphate) and phosphate. A simple chemical analogy suggests that muscle-like gels should be feasible but it is now clear that the task is much harder than it seems.Early work on gel actuation by Katchalsky-Katzir demonstrated that engines could be built using the chemical energy in diluting a lithium bromide solution to drive contraction and expansion of a collagen belt [5]. In essence, the collagen expands to take up the salt solution or contract to exclude the water. This change is both a molecular conformation change and a volume change. Other chemically driven gels, for instance polyacrylic acid fibers [6] which respond to a pH change, also rely on a solubility change giving rise to a volume change.

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“…The swelling properties and mechanical strength of the hydrogels are determined mainly by the cross-link density, which is the number of physical and chemical net points that connect polymer chains in a unit volume of gel [1,[6][7][8]. Although several theoretical models are available for the estimation of crosslinking density (e.g., Flory-Rehner swelling theory [9]), these models have several limitations and cannot distinguish chemical from physical net points.…”

Section: Introductionmentioning

confidence: 99%

A colourimetric method for the determination of the degree of chemical cross-linking in aspartic acid-based polymer gels

Hegyesi

Pukánszky

Szilágyi

2015

Express Polym. Lett.

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Abstract.A 2,4,6-trinitrobenzenesulphonic acid (TNBS)-based assay is developed to determine the degree of chemical cross-linking in aspartic acid-based polymer gels. The conventional colourimetric method for the quantitative determination of amine groups is difficult to use in polymer networks; thus, an improved method is developed to analyse polymer gels swollen in dimethyl sulfoxide (DMSO). Reaction products of the derivatizing reaction are examined by NMR. The chemical stability of the reagent is increased in DMSO, and the method shows satisfactory linearity and accuracy. The degree of chemical cross-linking in the investigated gels is close to its theoretical maximum, but the conversion of the pendant amine groups to cross-linking points is strongly dependent on the feed composition of the gels.

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A hybrid polymer gel with controlled rates of cross-link rupture and self-repair

Cited by 131 publications

References 41 publications

pH-induced metal-ligand cross-links inspired by mussel yield self-healing polymer networks with near-covalent elastic moduli

pH-induced metal-ligand cross-links inspired by mussel yield self-healing polymer networks with near-covalent elastic moduli

Polymer Gel Actuators: Fundamentals

A colourimetric method for the determination of the degree of chemical cross-linking in aspartic acid-based polymer gels

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