Super-stretchy jelly can take a hit

Suo’s hydrogel is made from a mixture of two polymers — alginate and polyacrylamide. Each polymer forms networks using different types of chemical bond: alginate molecules are linked together by ionic bonds, and polyacrylamide molecules by stronger covalent bonds. When the gel is stretched, hit or torn, the ionic bonds can break and reform throughout the material, dissipating energy over a wide area and causing fewer of the covalent bonds to be irreversibly ruptured. The covalent bonds hold the material together, allowing it to spring back to its original shape.