Nonlinear elasticity in biological gels

Unlike most synthetic materials, biological materials often stiffen as they are strained. This property, critical for the physiological function of tissues such as blood vessels, lung parenchyma and blood clots, has been documented since the nineteenth century, but the molecular structures and design principles responsible for it are unknown. Storm et al. now show that a much simpler theory can account for strain stiffening in a wide range of...