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Scratch Resistance of Proteinaceous layers: Applications to the Study of Salivary Films

Scratch Resistance of Proteinaceous layers: Applications to the Study of Salivary Films. Javier Sotres 1 , Alejandro Barrantes 1 , Olof Svensson 1 , Liselott Lindh 2 , Thomas Arnebrant 1 1 Biomedical Science, Faculty of Health and Society, Malmö University

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Scratch Resistance of Proteinaceous layers: Applications to the Study of Salivary Films

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  1. Scratch Resistance of Proteinaceous layers: Applications to the Study of Salivary Films Javier Sotres1, Alejandro Barrantes1, Olof Svensson1, Liselott Lindh2, Thomas Arnebrant1 1 Biomedical Science, Faculty of Health and Society, Malmö University 2 Prosthetic Dentistry, Faculty of Odontology, Malmö University Nano Update 2012, Helsinborg

  2. The method: AFM-based Friction Force Spectroscopy (Scratching the layers) • AFM allows monitoring the evolution of the topography of the sample during the scratching. Topography images: Scan area: 2μm x 2μm Roughness vs Load Plot:

  3. The method: AFM-based Friction Force Spectroscopy (Scratching the layers) • AFM allows monitoring the evolution of the topography of the sample during the scratching. ii) AFM allows exerting and monitoring both normal and frictional forces with sub-nN precision.

  4. The method: AFM-based Friction Force Spectroscopy (Scratching the layers) • 2D-Scans of the sample, each of them applying a constant load force. • The topography and the average friction force are registered for each scan. • The load is modified between the scans. • The scratching process is then characterized through the evolution of the topography and the friction signals.

  5. Application to protein monolayers Systems: monolayers of model proteins formed on hydrophobic surfaces in liquid medium (PBS buffer) Substrate: methylated silica θc ~ 100° BSA monolayers (soft globular protein) β-casein (disordered amphiphilic protein)

  6. Application to protein monolayers BSA on a hydrophobic surface (PBS buffer) Representative Scans of the Scratching Process Scan Size= 2µm Height Scale=5nm Topo after the scratch “Sweeping Scan” and forces needed for this complete removal of the layer “Rupture Scan” and forces needed for this rupture Sotres et al., 2011.  Langmuir. 27: 9439-48.

  7. Application to protein monolayers β-casein on a hydrophobic surface (PBS buffer) Scan Size= 2µm Height Scale=3nm Higher forces are needed to break and to remove β-casein than BSA layers Sweeping Scan Rupture Scan Sotres et al., 2011.  Langmuir. 27: 9439-48.

  8. Application to protein monolayers β-casein on a hydrophobic surface (PBS buffer) Scan Size= 2µm Height Scale=3nm Topo after the scratch Lateral diffusion of the molecules onto the underlying substrate Profile Length (µm) Sotres et al., 2011.  Langmuir. 27: 9439-48.

  9. Application to salivary films (substrata: methylated silica θc ~ 100° ) Water with pH adjusted to ~5 (similar results for pH7) Topo after the scratch Scan area: 2μm x 2μm Lateral Diffusion Process Roughness (nm) Roughness (nm) The film is different at the beginning and at the end of the experiment Sotres et al., 2011.  Langmuir. 27: 13692-13700.

  10. Application to salivary films (substrata: methylated silica θc ~ 100° ) Water with pH adjusted to ~5 (similar results for pH7) Topo after the scratch Scan area: 2μm x 2μm Lateral Diffusion Process Roughness (nm) Roughness (nm) The film is different at the beginning and at the end of the experiment Salivary films are composed of at least two different fractions, only one of them diffusing laterally onto hydrophobic substrates. Sotres et al., 2011.  Langmuir. 27: 13692-13700.

  11. Application to salivary films Effect of soft (acidic) drinks Films formed at pH ~5 were rinsed with water with the pH adjusted to ~3.3 On hydrophobic surfaces On hydrophilic surfaces Topo after the scratch Topo after the scratch At low pHs, saliva does no longer form a homogeneous film on clean silica surfaces. Instead, it forms big aggregates (typical size of tens of nanometers) separated by zones of clean substratum. Rinsing with acidic water removes the fraction which does not diffuse on the hydrophobic surfaces Sotres et al., 2011.  Langmuir. 27: 13692-13700.

  12. Conclusions • Development of a methodology (FFS) to study in liquid medium the strength of protein films, the diffusion of the proteins within these films, and even the structure of these films. • Specifically, in the study of salivary films : - The methodology is sensitive to the strength needed to break and remove salivary films. Also, it provided with structural information (different fractions with different lateral diffusion properties). - Different mechanisms leading to a lost of the pellicle protective function when lowering the pH.

  13. Welcome to ECIS 2012 in Malmö!co-organized by Malmö and Lund Universitieswww.ecis2012.org Thanks to: Alejandro Barrantes Olof Svensson Liselott Lindh Thomas Arnebrant Malmö-Lund 2-7 September 2012 Thanks to all of you for your attention! javier.sotres@mah.se

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