Protrusive growth and periodic contractile motion in surface-adhered vesicles induced by Ca2+-gradients

Local signaling, cell polarization, and protrusive growth are key steps in directed migration of biological cells guided by chemical gradients. Here we present a minimal system which captures several key features of cellular migration from signaling-to-motion. The model system consists of flat, negatively charged phospholipid vesicles, a negatively charged surface, and a local, and controllable point-source supply of calcium ions. In the presence of a Ca2+ gradient, the surface-adhered vesicles form protrusions in the direction of the gradient. We also observe membrane shape oscillations between expanded (flattened), and spherical states as a function of the Ca2+-concentration. The observed phenomena can be of importance in explaining motile action in prebiotic, primitive, and biomimetic systems, as well as in development of novel soft-matter nano- and microscale mechanical devices.