Known as the polychaete worm, it uses the tip of its jaw to inject lethal venom. The design of the jaw, with a gradient of hard materials at the tip connected to softer tissues, dissipates force and prevents serious damage to the jaw. The gradient in mechanical properties is correlated to the number of metal ions available for bonding. This mechanism inspired a novel approach to generate stiffness gradients in human-made polymers. Through a simple process, scientists controlled the density of the metal ions along a sample. The gradient in metal ion interactions created a continuous gradient in mechanical properties that spanned over a 200-fold change in stiffness, approaching that of biology.