Determination of the forces imposed by micro and nanopipettes during DOPC:DOPS liposome manipulation

Using micropipette-based probing methods and an image processing algorithm for measuring deformation, the bending energies of aspirated DOPC:DOPS liposomes were estimated both before and during manipulation with an injection pipette. We found that unlike cells, which are penetrable with pipettes as large as 2 μm in diameter and at speeds as slow as 4 μm/s, liposomes, without a cytoskeleton to resist deformation, are impenetrable with pipettes as small as 25 nm in diameter and at speeds as great as 4000 μm/s. Using energy calculations and the previously published mechanical properties of DOPC:DOPS liposomes, the forces that injection pipettes of various sizes can exert onto liposomes during probing were estimated. Forces ranged from ∼1 pN to 6 pN, and the forces exerted onto these liposomes increased as pipette size diminished. The quantification of the amount of force exerted on liposomes or cells during manipulation can assist in minimizing the damage during single-liposome, single-cell, or single-organelle injections and surgeries.