Spatial inhomogeneity in poly(acrylic acid) hydrogels

“…It may be concluded that the addition of calcium affects the surface properties of the gels in the dry state, and has thus also affected the molecular structure. It seems plausible that the spherical elevations are derived from microgelation during synthesis, which has been reported for other gel systems [7,21]. In the literature it has been described that intramolecular crosslinking or cyclization during the initial stages of polymerization may result in compact particles or microgel formation [19].…”

Section: Surface Characterisationmentioning

confidence: 76%

“…These properties are strongly affected by the degree of crosslinking. It has been shown that for PAA the equilibrium degree of swelling decreases [5,6] and the elastic modulus increases with an increasing degree of crosslinking [7]. In order to achieve a high swelling capacity PAA is commonly neutralized with sodium, which increases the swelling pressure of the gel [8].…”

Section: Introductionmentioning

confidence: 99%

“…Polymer networks synthesized by free radical polymerization are inherently inhomogeneous due to non ideal effects such as different and conversion dependent reactivities of the functional groups [7,18,19,20], resulting in fluctuations in the polymer network structure in space. Furthermore, the phase behaviour of the polymerization mixture may change as the reaction propagates, giving rise to phase separated domains or heterogeneities.…”

Section: Introductionmentioning

confidence: 99%

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Effect of calcium neutralization on elastic and swelling properties of crosslinked poly(acrylic acid) - correlation to inhomogeneities and phase behaviour

et al. 2009

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Abstract:Crosslinked hydrogels of poly(acrylic acid) neutralized with calcium hydroxide were synthesized using free radical co-polymerization. The effects of the amount added calcium on the elastic modulus and swelling properties of the gels and the correlation to phase behaviour and structural changes within the gels were studied using texture analysis, gravimetric analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and atomic force microscopy (AFM). It was found that the elastic modulus decreased nonlinearly with increasing amount of added calcium and that the swelling's dependence on the amount of added calcium was complicated. The maximum swelling increased with increasing amount of added calcium until a critical calcium content was reached, upon which the gels phase separated, with a strong decrease in swelling as a result. The changes in properties are explained by the fact that calcium affects the structure of the polymer network during synthesis and by the phase behaviour of the gels. Changes in the gel structure with the addition of calcium were detected with AFM. Furthermore, AFM revealed different phases on the nanometre scale for the sample with a calcium content around which phase separation is macroscopically observed. Finally, it was shown that the sulphur from the initiator potassium persulfate formed crystal like regions with high sulphur and calcium content upon drying of the hydrogels.

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“…[23] In our PEG-CaM-PEG networks, changes in the conformation of CaM from an extended conformation to a collapsed conformation would effectively increase the network's crosslinking density, and previous studies have demonstrated that increases in the cross-linking density can be accompanied by decreased homogeneity in cross-linking density. [24,25] Taken together, these results suggest that a dynamic change in cross-link density distribution in CaM-based hydrogel networks may lead to increased light scattering in the network and, in turn, changes in optical transparency.…”

Section: Discussionmentioning

confidence: 94%

Protein‐Based Hydrogels with Tunable Dynamic Responses

Sui

King

Murphy

2008

Adv Funct Materials

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Development of hydrogel materials that respond to specific stimuli has been of significant interest in the design of modern functional materials. A variety of previous studies have used the ligand‐binding capability of proteins to design hydrogels that change their crosslinking density in response to stimuli. However, these materials generally undergo relatively small dynamic response, with limited control over response characteristics. This manuscript describes an alternative approach that exploits the ability of proteins to undergo nanometer‐scale conformational changes in response to stimuli. We report a class of novel protein‐based hydrogel materials that undergo tunable, reversible dynamic responses with a wide dynamic range (volume decreases to ∼25–90% of initial volume). These materials also undergo tunable, reversible changes in optical transparency (optical transparency decreases to ∼35–100% of initial optical transparency), and this phenomenon is used as a mechanism for label‐free biosensing. The materials are generated by photo‐crosslinking of an engineered version of the protein calmodulin flanked on each end with poly(ethylene glycol)‐diacrylate (PEGDA) moieties. The mechanism for dynamic changes derives from calmodulin's well‐characterized “hinge motion”‐upon‐ligand binding. Variations in network parameters in these hydrogels, including the molecular weight between cross‐links and the cross‐linking density, result in systematic tuning of material responsiveness. The influence of network parameters on hydrogel dynamics reported here may serve as a guide for the design of other protein‐based, responsive materials assembled using similar principles, and these materials may be a useful platform for design of biosensors, actuators, and drug delivery systems.

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Spatial inhomogeneity in poly(acrylic acid) hydrogels

Cited by 54 publications

References 37 publications

Effective parameters in surface cross-linking of acrylic-based water absorbent polymer particles using bisphenol A diethylene glycidyl ether and cycloaliphatic diepoxide

Effective parameters in surface cross-linking of acrylic-based water absorbent polymer particles using bisphenol A diethylene glycidyl ether and cycloaliphatic diepoxide

Effect of calcium neutralization on elastic and swelling properties of crosslinked poly(acrylic acid) - correlation to inhomogeneities and phase behaviour

Protein‐Based Hydrogels with Tunable Dynamic Responses

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