Elastic Properties of Nematic Liquid Crystals Formed by Living and Migrating Cells

In culture migrating and interacting amoeboid cells can form nematic liquid crystal phases. A polar nematic liquid crystal is formed if the interaction has a polar symmetry. One type of white blood cells (granulocytes) form clusters where the cells are oriented towards the center. The core of such an orientational defect (disclination) is either a granulocyte forced to be in an isotropic state or another cell type like a monocyte. An apolar nematic liquid crystal is formed if the interaction has an apolar symmetry. Different cell types like human melanocytes (=pigment cells of the skin), human fibroblasts (=connective tissue cells), human osteoblasts (=bone cells), human adipocytes (= fat cells) etc., form an apolar nematic liquid crystal. The orientational elastic energy is derived and the orientational defects (disclination) of nematic liquid crystals are investigated. The existence of half-numbered disclinations show that the nematic phase has an apolar symmetry. The densityand order parameter dependence of the orientational elastic constants and their absolute values are estimated. From the defect structure, one finds that the splay elastic constant is smaller than the bend elastic constant (melanocytes). The core of a disclination is either a cell free space or occupied by non oriented cells (isotropic phase) or occupied by a cell with a different symmetry or occupied by another cell type.