Finite element analysis of imposing femtonewton forces with micropipette aspiration.

A novel technique of imposing femtonewton forces with micropipette aspiration [i.e., the extended micropipette aspiration technique (EMAT)] is proposed, and an axisymmetric finite element analysis of this technique is provided. The EMAT is experimentally based upon a micropipette manipulation system and is theoretically based upon hydrodynamics. Any spherical object such as a human neutrophil or a latex bead can be employed as the force transducer, so cell-cell interactions can be directly studied. Our computational analysis shows that femtonewton forces can indeed be imposed. The force magnitude is sensitive to the radius of the micropipette and the micropipette-transducer distance, but it is much less sensitive to other parameters including the radius of the transducer, the substrate curvature, and the thickness of the micropipette wall. Combining the EMAT and the previously developed micropipette aspiration technique will allow us to impose an unprecedented range of forces, from a few femtonewtons to a few hundred piconewtons on single molecules or receptor-ligand bonds.