We study catalytic Janus swimmers and Escherichia coli bacteria swimming in a two-dimensional colloidal crystal. The Janus swimmers orbit individual colloids and hop between colloids stochastically, with a hopping rate that varies inversely with fuel (hydrogen peroxide) concentration. At high fuel concentration, these orbits are stable for 100s of revolutions, and the orbital speed oscillates periodically as a result of hydrodynamic, and possibly also phoretic, interactions between the swimmer and the six neighbouring colloids. Motile E.~coli bacteria behave very differently in the same colloidal crystal: their circular orbits on plain glass are rectified into long, straight runs, because the bacteria are unable to turn corners inside the crystal.
@article{arxiv.1411.6847,
title = {Swimming in a Crystal:},
author = {Aidan T. Brown and Ioana D. Vladescu and Angela Dawson and Teun Vissers and Jana Schwarz-Linek and Juho S. Lintuvuori and Wilson C. K. Poon},
journal= {arXiv preprint arXiv:1411.6847},
year = {2015}
}