More entanglements in the material help polymer chains slip without breaking
Read the research: https://www.science.org/doi/10.1126/science.abg6320
Hydrogels, water-absorbing materials similar to soft tissues, have been used in countless biomedical applications, from contact lenses to pill coatings. But it’s hard to create hydrogels that can hold up to repeated stresses—after enough uses, many reach a “breaking” point where they stretch out and cannot return to their original shape. Now, researchers at Harvard University have manipulated one material’s underlying structure to make a hydrogel that is both stretchy and tough.
Hydrogels are made of polymer strands that stick together in two ways: chemical bonds known as cross-links, and entanglements, in which one polymer chain weaves around another. Increasing the number of cross-links creates a more rigid, brittle hydrogel. But the researchers found that when they increased the number of entanglements along each chain—from just one or two along each chain to over a hundred—they made a material that was tough, but still stretchy enough to use as an artificial muscle or to coat the surface of an artificial joint. The dense entanglements allowed the chains to slip around and tug on each other without breaking. Watch the video to learn how they perfected this recipe.