Large Continuous Mechanical Gradient Formation via Metal-Ligand Interactions.

Mechanical gradients are often employed in nature to prevent biological materials from damage by creating a smooth transition from strong to weak that dissipates large forces. Synthetic mimics of these natural structures are highly desired to improve distribution of stresses at interfaces and reduce contact deformation in manmade materials. Current synthetic gradient materials commonly suffer from non-continuous transitions, relatively small gradients in mechanical properties, and difficult syntheses. Inspired by the polychaete worm jaw, we report a novel approach to generate stiffness gradients in polymeric materials via incorporation of dynamic monodentate metal-ligand crosslinks. Through spatial control of metal ion content, we created a continuous mechanical gradient that spans over a 200-fold difference in stiffness, approaching the mechanical contrast observed in biological gradient materials.