Materials Science

Tough Gels

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Science  22 Aug 2003:
Vol. 301, Issue 5636, pp. 1019
DOI: 10.1126/science.301.5636.1019a

Hydrogels are made of swollen, cross-linked polymer networks and can contain in excess of 90% water by volume. When functionalized with free chains on their surfaces, these gels exhibit low surface friction and thus have been attractive candidates as artificial replacements for damaged cartilage. Unfortunately, many hydrogels aren't very strong.

Using a variety of cross-linkable hydrophilic polymers, Gong et al. have overcome this problem by synthesizing hydrogels with a double network structure. They found that the resistance to stress could be improved considerably by controlling two key parameters. The first was the molar ratio of the two polymers, and the second was the cross-linking density of the two polymers. The highest strength gels were obtained when the first network was highly cross-linked, and the second only lightly so. The highly cross-linked network has a high Young's modulus but is quite brittle on its own, and the authors speculate that the fluidity of the second network provides for the efficient transfer and dissipation of applied stress that enhances strength overall. — MSL

Adv. Mater. 15, 1155 (2003).

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