Droplet Impact on Surfaces with Asymmetric Microscopic Features.

The impact of liquid drops on a rigid surface is central in cleaning, cooling, and coating processes in both nature and industrial applications. However, it is not clear how details of pores, roughness, and texture on the solid surface influence the initial stages of the impact dynamics. Here, we experimentally study drops impacting at low velocities onto surfaces textured with asymmetric (tilted) ridges.

Hypoxia triggers collective aerotactic migration in .

Using a self-generated hypoxic assay, we show that the amoeba displays a remarkable collective aerotactic behavior. When a cell colony is covered, cells quickly consume the available oxygen (O) and form a dense ring moving outwards at constant speed and density. To decipher this collective process, we combined two technological developments: porphyrin-based O -sensing films and microfluidic O gradient generators.