Paper BI+AS-TuA9
Combining Colloidal Probe Atomic Force and Reflection Interference Contrast Microscopy to Study the Mechanics of Biopolymer Films
Tuesday, October 30, 2012, 4:40 pm, Room 23
| Session: |
Characterization of Biointerfaces |
| Presenter: |
R.P. Richter, CIC biomaGUNE, Spain; Joseph Fourier University, France; Max Planck Institute for Intelligent Systems, Germany |
| Authors: |
R.P. Richter, CIC biomaGUNE, Spain; Joseph Fourier University, France; Max Planck Institute for Intelligent Systems, Germany
S. Attili, CIC biomaGUNE, Spain; Max Planck Institute for Intelligent Systems, Germany
V. Borisov, Institut Pluridisciplinaire de Recherche sur l’Environnement et les Materiaux, France
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| Correspondent: |
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Highly solvated polymer films have naturally evolved as multifunctional interfaces in biological systems, e.g. as mucosal films, cellular coats or bacterial biofilms. Surface-confined polymer films are also becoming increasingly popular as biomaterials and in various (bio)technological applications. The mechanical response of such polymer films is not only important for functional performance, but it can also provide valuable information about the film’s internal organization, interactions and dynamics.
Here, we present a method that combines colloidal probe atomic force microscopy (AFM) and reflection interference contrast microscopy (RICM) to measure the mechanical properties of thin and solvated polymer films. When analyzing such films, a fundamental problem in colloidal probe AFM experiments is to determine the distance at closest approach between the probe and the substrate on which the film is deposited. By combining AFM and RICM in situ, forces and absolute distances can be measured simultaneously, and experimental drifts that otherwise would pass unnoticed can be corrected (1).
We used the combined setup to quantify the compressive mechanics of films of end-grafted hyaluronan (HA brushes) (2). Hyaluronan is a polysaccharide that plays a vital role in the organization and function of pericellular coats and extracellular matrices in vertebrates, and that is also attractive for biomedical applications. We show that HA brushes can swell dramatically as a function of ionic strength or upon binding of the cartilage proteoglycan aggrecan. Detailed comparison of the experimental data with polymer theory reveals that hyaluronan is a prototype of a strongly charged, semiflexible polyelectrolyte with intrinsic excluded volume (3).
The novel combined AFM/RICM setup should be broadly applicable to quantify the mechanical properties of soft hydrated polymer films with precise control of probe-sample separation. The generated data on HA brushes represent a valuable reference for future quantitative studies of more complex HA-rich films and to refine theories of polyelectrolyte brushes of strongly charged and intrinsically stiff polyelectrolytes.
References:
(1) Attili and Richter Langmuir 2012, 28:3206;
(2) Richter et al. J. Am. Chem. Soc. 2007, 129:5306;
(3) Attili et al. Biomacromolecules 2012, in press.