ACS Nano doi: 10.1021/nn901296y (2010)

Leukocytes, a type of white blood cell, carry a host of molecules that enable them to sense the location of wounds around the body so that they can respond to damage by rolling to and localizing in the affected area. Inspired by the role of leukocytes, researchers at the University of Pittsburgh have designed an artificial leukocyte that can repair a crack in a surface, by simulating the parameters required to roll spheres over a surface.

Anna Balazs and colleagues modelled the rolling motion of an amphiphilic (having both hydrophobic and hydrophilic character) microcapsule over a surface containing cracks. The compliant microcapsule has a thin wall and contains hydrophobic nanoparticles, which act as healing agents that get deposited when the capsule lodges in a crack. A range of shear rates and capsule–surface interaction parameters exist for arresting a capsule in a crack and depositing a maximum number of nanoparticles. Pulsatile shear-flow conditions that involve alternating high and low shear rates allows the capsule to localize and repair one site before continuing on to the next fissure in a 'repair and go' fashion.

Although the simulations involved the action of a single microcapsule, the parameters are expected to apply in actual systems because a high volume of capsules are available for repair. Such a fluid-driven repair system for surface defects may potentially be very attractive for precision materials.