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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

SAXS results of the polyelectrolyte hydrogels using nonionic PR cross-linker.(a) SAXS isointensity patterns of the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C for different elongations in the vertical direction. (b) Sector-averaged I(q) of the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C for different elongations in the parallel (open circles) and perpendicular (filled circles) directions. The solid lines are the equation (1) fitting results. (c) Stretching ratio dependence of ξ and Ξ for the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C in parallel to the elongation direction, and (d) stretching ratio dependence of ξ and Ξ for the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C in perpendicular to the elongation direction.
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f3: SAXS results of the polyelectrolyte hydrogels using nonionic PR cross-linker.(a) SAXS isointensity patterns of the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C for different elongations in the vertical direction. (b) Sector-averaged I(q) of the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C for different elongations in the parallel (open circles) and perpendicular (filled circles) directions. The solid lines are the equation (1) fitting results. (c) Stretching ratio dependence of ξ and Ξ for the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C in parallel to the elongation direction, and (d) stretching ratio dependence of ξ and Ξ for the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C in perpendicular to the elongation direction.

Mentions: These excellent mechanical properties of this hydrogel are most likely achieved because of the homogeneous network structure afforded by the pulley effect. To confirm the structural homogeneity of the hydrogels, their structures were analysed under uniaxial elongation by small-angle X-ray scattering (SAXS). In general, the spatial inhomogeneity of cross-links is hidden by the fluctuation in the polymer chain concentration before the elongation. When the chemical gels are deformed, the inhomogeneous structure is exposed and the two-dimensional (2D) X-ray or neutron scattering patterns become elliptical26. Figure 3a shows 2D SAXS patterns of as-prepared (elongation ratio ε=1) and vertically stretched (ε>1) NIPA–AAcNa–HPR-C hydrogels cross-linked with 0.65 wt% HPR-C. These patterns are almost isotropic, which is consistent with the results for slide-ring gels in a good solvent27. This hydrogel contains water, which is a good solvent; therefore, it has no internal aggregation structure. The SAXS pattern of this hydrogel remains isotropic when the hydrogel is elongated by a factor of greater than four, which is in contrast to the elliptical pattern observed for a poly(acrylamide) gel when elongated by a factor of 1.5 (ref. 27)27. We quantitatively evaluated the SAXS patterns by calculating the sector average of the intensity in the directions of parallel and perpendicular to the elongation. The angle of the sector was 20° in each direction. Figure 3b shows the sector-averaged scattering profiles of the hydrogel at elongation ratios of ε=1–4 in each direction. The scattering function for polymer gels in a good solvent is given as follows2829:


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)

SAXS results of the polyelectrolyte hydrogels using nonionic PR cross-linker.(a) SAXS isointensity patterns of the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C for different elongations in the vertical direction. (b) Sector-averaged I(q) of the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C for different elongations in the parallel (open circles) and perpendicular (filled circles) directions. The solid lines are the equation (1) fitting results. (c) Stretching ratio dependence of ξ and Ξ for the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C in parallel to the elongation direction, and (d) stretching ratio dependence of ξ and Ξ for the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C in perpendicular to the elongation direction.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4214411&req=5

f3: SAXS results of the polyelectrolyte hydrogels using nonionic PR cross-linker.(a) SAXS isointensity patterns of the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C for different elongations in the vertical direction. (b) Sector-averaged I(q) of the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C for different elongations in the parallel (open circles) and perpendicular (filled circles) directions. The solid lines are the equation (1) fitting results. (c) Stretching ratio dependence of ξ and Ξ for the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C in parallel to the elongation direction, and (d) stretching ratio dependence of ξ and Ξ for the NIPA–AAcNa–HPR-C hydrogel with 0.65 wt% of HPR-C in perpendicular to the elongation direction.
Mentions: These excellent mechanical properties of this hydrogel are most likely achieved because of the homogeneous network structure afforded by the pulley effect. To confirm the structural homogeneity of the hydrogels, their structures were analysed under uniaxial elongation by small-angle X-ray scattering (SAXS). In general, the spatial inhomogeneity of cross-links is hidden by the fluctuation in the polymer chain concentration before the elongation. When the chemical gels are deformed, the inhomogeneous structure is exposed and the two-dimensional (2D) X-ray or neutron scattering patterns become elliptical26. Figure 3a shows 2D SAXS patterns of as-prepared (elongation ratio ε=1) and vertically stretched (ε>1) NIPA–AAcNa–HPR-C hydrogels cross-linked with 0.65 wt% HPR-C. These patterns are almost isotropic, which is consistent with the results for slide-ring gels in a good solvent27. This hydrogel contains water, which is a good solvent; therefore, it has no internal aggregation structure. The SAXS pattern of this hydrogel remains isotropic when the hydrogel is elongated by a factor of greater than four, which is in contrast to the elliptical pattern observed for a poly(acrylamide) gel when elongated by a factor of 1.5 (ref. 27)27. We quantitatively evaluated the SAXS patterns by calculating the sector average of the intensity in the directions of parallel and perpendicular to the elongation. The angle of the sector was 20° in each direction. Figure 3b shows the sector-averaged scattering profiles of the hydrogel at elongation ratios of ε=1–4 in each direction. The scattering function for polymer gels in a good solvent is given as follows2829:

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