During each heartbeat, the aorta’s walls expand to hold the pulse of blood, then rebound elastically to propel the blood downstream. At rest, a healthy human heart has a systolic blood pressure of about 16 kilopascals. But for strenuous, impulsive effort, like dashing upstairs or hoisting a sack of mulch, the systolic pressure can double, even triple.
If the aorta’s walls responded linearly to such increases, they’d balloon and most likely burst. Fortunately, Nature has endowed the aorta with a nonlinear property called strain stiffening. As stress increases so too does the ratio of stress to strain, the elastic modulus.
The aorta’s strain stiffening arises from its structure, a complex set of concentric, alternating layers of rubbery and stiff tissues. It’s surprising, therefore, to find strain stiffening in the far simpler gels that form the support structures within and between cells (see figure 1).
Those gels consist of weblike...
