Application of AFM to determine friction between polyelectrolyte multilayer
films and colloidal probes
Tatyana Sherstova, Astrid Bjørkøy, Gjertrud Maurstad and Bjørn Torger Stokke
Biophysics and medical technology, Dept. of Physics, The Norwegian University of Science
and Technology, NTNU, Trondheim, Norway
Tribology, the science of friction, lubrication and wear of surfaces in relative motion,
is very important for mankind. Examples in biomedical applications include e.g. wear in
artificial joints, friction between eye and contact lenses1. Clear understanding of the
mechanics of sliding interfaces and friction parameters are critical to the solution of any
tribological problem. Friction properties of material depend directly on the properties of
immobilized molecules and on the dimension of immobilized structures. Frictional behaviour
can be modified by the attachment of polymer layers to the surface.2
In our work we’ve analysed friction properties of multilayers with different number
and type of biopolymer using atomic force microscope (AFM). In addition to the impact of
AFM in imaging biological samples and as force probe for biological interactions, we
implement here the measurement mode directed towards determination of friction properties,
with potentially unprecedented resolution. Mechanical interaction on the length scale of
micrometers (µm) to nanometers (nm) and the force scale of millinewtons (mN) to
nanonewtons (nN)3 are supported. The biopolymer multilayers were probed with respect
friction towards micrometer large colloidal probes (polystyrene beads4) glued to tipless
cantilevers. Polystyrene beads are a versatile tool for this study since the surface of a bead can
be easily modified with different molecules, and different bead diameters can be chosen,
depending on the substrate patterning. To calibrate AFM for quantitative lateral force
measurements the “pivot” method of calibration was used. In this method the tipless
cantilever are ramped across another tapping mode AFM tip glued to a glass coverslip. In this
procedure, the deflection and torsional signals were collected and used as basis for deflection
and torsional sensitivity, respectively. Torsional spring constant and torsional sensitivity were
calculated for each tip for further analysing of friction data.5 6
M.Scherge, S.Gorb, Biological Micro- and Nanotribology. Nature’s Solutions, Springer, 2001
Jacob Klein, Shear, friction, and lubrication forces between polymer-bearing surfaces, Ann. Rev. Mater. Sci.
1996. 26:581-612
3
David B. Assay and Seong H.Kim, Direct force balance method for atomic force microscopy lateral force
calibration, Rev. of scintific inst. 77, 043903, 2006
4
JPK instruments Technical report, Attaching microspheres to cantilever using the NanoWizard Life Science
stage and AFM head.
5
G.Bogdanovich, A. Meurk, M.W. Rutland, Tip friction- torsional spring constant determination, Colloids and
Surfaces B: Biointerfaces 19 (2000) 397-405
6
Koo-Hyun Chung and Mark G. Reitsma, Note: Lateral force microscope calibration using multiple location
pivot loading of rectangular cantilevers, Review of scientific instruments 81, 026104 (2010)
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