Migrating Cells: Living Liquid Crystals

Abstract Two conditions are necessary to built up a condensated state out of elementary units: (i) interaction between the elementary units and (ii) motion of the elementary units. A new type of liquid crystal is found by using migrating cells (human granulocytes) as elementary units. These cells show no interaction or a weak repulsion at high calcium concentration (2.5 mM). But at low calcium concentration (< nM) the cells attract each other and form a polar nematic liquid crystal. First, the machine for the directed movement is investigated phenomenologically. The direction of migration is guided by a cellular automatic controller. It can be characterized by two machine coefficients: (i) the response of the automatic controller is proportional to the strength of the extracellular guiding field times a cellular machine coefficient, and (ii) the random movement is induced by stochastic processes in the cellular machinery. These cellular stochastic processes are equivalent to the thermal motion of inert pa...