AVS 52nd International Symposium
    Biomaterial Interfaces Wednesday Sessions
       Session BI2-WeM

Paper BI2-WeM4
Phospholipid Bilayers Nanomechanics

Wednesday, November 2, 2005, 9:20 am, Room 312

Session: Biomembranes and Spectroscopy
Presenter: F. Sanz, University of Barcelona, Spain
Authors: G. Oncins, University of Barcelona, Spain
S. Garcia-Manyes, University of Barcelona, Spain
F. Sanz, University of Barcelona, Spain
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Mechanical properties of several phosphocholine supported planar bilayers deposited on mica have been tested in liquid environment by lateral force microscopy (LFM) and force spectroscopy. The presence of these bilayers has been detected topographically using atomic force microscopy (AFM). To test how the presence of NaCl affects the frictional properties of phospholipid bilayers, samples in saline media ranging from 0 M to 0.1 M NaCl were prepared. Changes in the lateral force vs. vertical force curves were recorded as a function of NaCl concentration and related with structural changes induced in the phosphatidylcholine bilayers by the presence of electrolyte ions. Three friction regimes are observed as the vertical force exerted by the tip on the bilayer increases. In order to relate the friction response with the structure of the bilayer, topographic images were recorded simultaneously to friction data. Ions in solution have proved to be able to screen charges present in phosphatidylcholine polar heads, leading to more compact bilayers.@footnote 1@ As a consequence, the vertical force at which the bilayer breaks while performing friction experiments increases with NaCl concentration.@footnote 2@ In addition, images show that low NaCl concentration bilayers recover more easily due to the low cohesion between phospholipid molecules. The vertical mechanical resistance of phosphatidylcholine bilayers has been tested with force curves,@footnote 3@ showing a discontinuity when the bilayer breaks under the pressure exerted by the tip. As expected, the force at which this breakthrough takes place increases with NaCl concentration, pointing out an increase of vertical and lateral mechanical stability induced by ions. @FootnoteText@ @footnote 1@Pandit,S.A.; Bostick, D.; Berkowitz, M. L. Biophys. J., 2003, 84, 3743.@footnote 2@Oncins,G.; Garcia-Manyes, S.; Sanz,F.; (sent 1st revision to Langmuir)@footnote 3@Garcia-Manyes,S.; Oncins,G.; Sanz,F.; (sent 1st revision to Biophys.J.).