Polymorphism in biophysics is the ability of
lipids to aggregate in a variety of ways, giving rise to structures of different shapes, known as "phases". This can be in the form of spheres of lipid molecules (
micelles), pairs of layers that face one another (lamellar phase, observed in biological system as a lipid
bilayer), a tubular arrangement (
hexagonal), or various
cubic phases (Fd3m, Im3m, Ia3m, Pn3m, and Pm3m being those discovered so far). More complicated aggregations have also been observed, such as
rhombohedral,
tetragonal and
orthorhombic phases.