Figure 14.4 — Directed growth of neurons Figure 14.4 — Directed growth of neurons. Two counter-rotating optically trapped vaterite particles (rotation direction shown by curved arrows, rotation rate about 1 Hz) are positioned so that the induced microfluidic flow pattern directs the growth of an axon between the spheres.Reprinted by permission from Macmillan Publishers Ltd: Wu et al., Nature Photon. 6, 62–7, copyright 2012.