Shapes of red blood cells during micropipette aspiration.

The principle of minimum energy of deformation is used to determine the shapes of red cells during micropipette aspiration. Both bending and shear stresses are included in the analysis. The red cells shapes are described by equations with adjustable parameters. The parameters are then used to satisfy the geometrical and mechanical constraints. The geometrical constraints are that the surface area and volume have specific values. The mechanical constraint is that the red cell satisfy the equilibrium criterion that the total energy of deformation is a minimum. A numerical procedure is used to find a variety of shapes satisfying the geometrical constraints. The total energy of deformation, which is the sum of bending and shear energies, is calculated for each of these shapes. An optimization procedure is then used to determine the shape which has the least energy of deformation.