Shape determination of attached fluctuating phospholipid vesicles

A method to determine the shapes of a thermally fluctuating phospholipid vesicle is described. The vesicle that was attached at one point to a glass plate was submitted to a flow. It was observed by an inverted optical microscope using phase contrast technique. A large number of consecutive video images were digitised at different flow velocities and stored on computer disk. They were off-line binarised using the global average value as a threshold. The vesicle outlines were determined by a contour following procedure based on the maze walking algorithm. They were described in terms of Fourier coefficients, which were calculated by the least square fitting of the contour points using normal equations and LU matrix decomposition. This method, which was the basis for the determination of the membrane bending modulus, was thoroughly tested and it proved to be robust and efficient.