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“Nonswellable” Hydrogel Without Mechanical Hysteresis

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Science  21 Feb 2014:
Vol. 343, Issue 6173, pp. 873-875
DOI: 10.1126/science.1247811

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Optimizing Injectable Hydrogels

Injectable hydrogels are showing promise as scaffolds in regenerative medicine because they can be injected in liquid form and transform in situ into the gel state. However, when exposed to ionic solutions, such as those found in the body, hydrogels can increase in volume by a factor of 2, which can weaken the material. Kamata et al. (p. 873) added a thermoresponsive component to a hydrogel so that the thermoresponsive component would tend to collapse in shape when heated and counteract the hydrogel's tendency to swell. Indeed, the resulting gel retained its unswollen volume following immersion in a physiological solution and retained its mechanical strength during repeated stretching or compression.

Abstract

Hydrogels are three-dimensional polymer networks that contain a large amount of water inside. Certain hydrogels can be injected in solution and transformed into the gel state with the required shape. Despite their potential biomedical applications, the use of hydrogels has been severely limited because all the conventional hydrogels inevitably “swell” under physiological conditions, which drastically degrades their mechanical properties. We report the synthesis of injectable “nonswellable” hydrogels from hydrophilic and thermoresponsive polymers, in which two independently occurring effects (swelling and shrinking) oppose each other. The hydrogels can endure a compressive stress up to 60 megapascals and can be stretched more than sevenfold without hysteresis. Our results demonstrate that the suppression of swelling helps retain the mechanical properties of hydrogels under physiological conditions.

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