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Extremely stretchable thermosensitive hydrogels by introducing slide-ring polyrotaxane cross-linkers and ionic groups into the polymer network.

Bin Imran A, Esaki K, Gotoh H, Seki T, Ito K, Sakai Y, Takeoka Y - Nat Commun (2014)

Bottom Line: One of the most significant problems is that conventional stimuli-sensitive hydrogels are usually brittle.The resulting hydrogels are surprisingly stretchable and tough because the cross-linked α-cyclodextrin molecules can move along the polyethylene glycol chains.In addition, the polyrotaxane cross-linkers can be used with a variety of vinyl monomers; the mechanical properties of the wide variety of polymer gels can be improved by using these cross-linkers.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.

ABSTRACT
Stimuli-sensitive hydrogels changing their volumes and shapes in response to various stimulations have potential applications in multiple fields. However, these hydrogels have not yet been commercialized due to some problems that need to be overcome. One of the most significant problems is that conventional stimuli-sensitive hydrogels are usually brittle. Here we prepare extremely stretchable thermosensitive hydrogels with good toughness by using polyrotaxane derivatives composed of α-cyclodextrin and polyethylene glycol as cross-linkers and introducing ionic groups into the polymer network. The ionic groups help the polyrotaxane cross-linkers to become well extended in the polymer network. The resulting hydrogels are surprisingly stretchable and tough because the cross-linked α-cyclodextrin molecules can move along the polyethylene glycol chains. In addition, the polyrotaxane cross-linkers can be used with a variety of vinyl monomers; the mechanical properties of the wide variety of polymer gels can be improved by using these cross-linkers.

No MeSH data available.


Related in: MedlinePlus

Swelling behaviours of the polyelectrolyte hydrogels using nonionic PR cross-linker and the hydrogels using ionic PR cross-linker.The degree of swelling D/D0 for the (a) NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C during both heating (red) and cooling (blue) processes, and (b) NIPA–iPR-C hydrogel with 0.80 wt% of iPR-C during heating process in aqueous solutions with different pHs as a function of temperature. D and D0 denote the gel diameters at equilibrium and on synthesis, respectively.
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f5: Swelling behaviours of the polyelectrolyte hydrogels using nonionic PR cross-linker and the hydrogels using ionic PR cross-linker.The degree of swelling D/D0 for the (a) NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C during both heating (red) and cooling (blue) processes, and (b) NIPA–iPR-C hydrogel with 0.80 wt% of iPR-C during heating process in aqueous solutions with different pHs as a function of temperature. D and D0 denote the gel diameters at equilibrium and on synthesis, respectively.

Mentions: On the basis of the graft copolymer hydrogel properties, we successfully prepared pure poly(NIPA) hydrogels without ions that exhibit both mechanical toughness and thermo-responsiveness utilizing an ionic PR derivative as a cross-linker (Fig. 4a). This PR cross-linker (iPR-C) has carboxyl groups on the α-CD molecules, making it highly water soluble. It was expected that iPR-C can be well extended in a neutral poly(NIPA) network (Fig. 4b), as observed for HPR-C in the polyelectrolyte network (Fig. 2g). The most distinctive feature of the iPR-C gels is that the ionic groups are localized only on the PR cross-linker. The spatial distribution of the ionic groups on the polymer network is therefore remarkably different from that in the randomly copolymerized NIPA–AAcNa gels. As expected, the iPR-C hydrogels are as transparent, stretchable and tough in pure water (Fig. 4d; Supplementary Table 3; Supplementary Movie 3) as the NIPA–AAcNa–HPR-C hydrogels. The degree of dissociation of the carboxylic acid groups in the NIPA–AAcNa–HPR-C hydrogels changes with pH, and the osmotic pressure in the hydrogels therefore changes with pH because the ionic AAcNa monomer is distributed throughout the polymer network. As a result, the swelling behaviour of the NIPA–AAcNa–HPR-C hydrogels is highly dependent on the solvent pH (Fig. 5a). However, the swelling behaviour of the NIPA–iPR-C hydrogels shows little dependence on the solvent pH when the amount of iPR-C is lower than 3 wt% (Supplementary Figs 5 and 6). Although the carboxyl groups of iPR-C can also dissociate in water in response to changes in the pH, the dissociated ion does not affect the transition temperature significantly because the amount of iPR-C is very small and the ionic groups are localized only on the iPR-C cross-linker. Thus, the pH dependence of the temperature response is successfully regulated by controlling the spatial distribution of the ionic groups in the hydrogels via simple chemical modifications of the PR.


Extremely stretchable thermosensitive hydrogels by introducing slide-ring polyrotaxane cross-linkers and ionic groups into the polymer network.

Bin Imran A, Esaki K, Gotoh H, Seki T, Ito K, Sakai Y, Takeoka Y - Nat Commun (2014)

Swelling behaviours of the polyelectrolyte hydrogels using nonionic PR cross-linker and the hydrogels using ionic PR cross-linker.The degree of swelling D/D0 for the (a) NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C during both heating (red) and cooling (blue) processes, and (b) NIPA–iPR-C hydrogel with 0.80 wt% of iPR-C during heating process in aqueous solutions with different pHs as a function of temperature. D and D0 denote the gel diameters at equilibrium and on synthesis, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4214411&req=5

f5: Swelling behaviours of the polyelectrolyte hydrogels using nonionic PR cross-linker and the hydrogels using ionic PR cross-linker.The degree of swelling D/D0 for the (a) NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C during both heating (red) and cooling (blue) processes, and (b) NIPA–iPR-C hydrogel with 0.80 wt% of iPR-C during heating process in aqueous solutions with different pHs as a function of temperature. D and D0 denote the gel diameters at equilibrium and on synthesis, respectively.
Mentions: On the basis of the graft copolymer hydrogel properties, we successfully prepared pure poly(NIPA) hydrogels without ions that exhibit both mechanical toughness and thermo-responsiveness utilizing an ionic PR derivative as a cross-linker (Fig. 4a). This PR cross-linker (iPR-C) has carboxyl groups on the α-CD molecules, making it highly water soluble. It was expected that iPR-C can be well extended in a neutral poly(NIPA) network (Fig. 4b), as observed for HPR-C in the polyelectrolyte network (Fig. 2g). The most distinctive feature of the iPR-C gels is that the ionic groups are localized only on the PR cross-linker. The spatial distribution of the ionic groups on the polymer network is therefore remarkably different from that in the randomly copolymerized NIPA–AAcNa gels. As expected, the iPR-C hydrogels are as transparent, stretchable and tough in pure water (Fig. 4d; Supplementary Table 3; Supplementary Movie 3) as the NIPA–AAcNa–HPR-C hydrogels. The degree of dissociation of the carboxylic acid groups in the NIPA–AAcNa–HPR-C hydrogels changes with pH, and the osmotic pressure in the hydrogels therefore changes with pH because the ionic AAcNa monomer is distributed throughout the polymer network. As a result, the swelling behaviour of the NIPA–AAcNa–HPR-C hydrogels is highly dependent on the solvent pH (Fig. 5a). However, the swelling behaviour of the NIPA–iPR-C hydrogels shows little dependence on the solvent pH when the amount of iPR-C is lower than 3 wt% (Supplementary Figs 5 and 6). Although the carboxyl groups of iPR-C can also dissociate in water in response to changes in the pH, the dissociated ion does not affect the transition temperature significantly because the amount of iPR-C is very small and the ionic groups are localized only on the iPR-C cross-linker. Thus, the pH dependence of the temperature response is successfully regulated by controlling the spatial distribution of the ionic groups in the hydrogels via simple chemical modifications of the PR.

Bottom Line: One of the most significant problems is that conventional stimuli-sensitive hydrogels are usually brittle.The resulting hydrogels are surprisingly stretchable and tough because the cross-linked α-cyclodextrin molecules can move along the polyethylene glycol chains.In addition, the polyrotaxane cross-linkers can be used with a variety of vinyl monomers; the mechanical properties of the wide variety of polymer gels can be improved by using these cross-linkers.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.

ABSTRACT
Stimuli-sensitive hydrogels changing their volumes and shapes in response to various stimulations have potential applications in multiple fields. However, these hydrogels have not yet been commercialized due to some problems that need to be overcome. One of the most significant problems is that conventional stimuli-sensitive hydrogels are usually brittle. Here we prepare extremely stretchable thermosensitive hydrogels with good toughness by using polyrotaxane derivatives composed of α-cyclodextrin and polyethylene glycol as cross-linkers and introducing ionic groups into the polymer network. The ionic groups help the polyrotaxane cross-linkers to become well extended in the polymer network. The resulting hydrogels are surprisingly stretchable and tough because the cross-linked α-cyclodextrin molecules can move along the polyethylene glycol chains. In addition, the polyrotaxane cross-linkers can be used with a variety of vinyl monomers; the mechanical properties of the wide variety of polymer gels can be improved by using these cross-linkers.

No MeSH data available.


Related in: MedlinePlus