Dynamic modulation of fimbrial extension and FimH-mannose binding force on live bacteria under pH changes: a molecular atomic force microscopy analysis.

Mechanical and conformational properties of type 1 fimbriae were evaluated on live bacterial cells by Single Molecule Force Spectroscopy (SMFS) and Dynamic Force Spectroscopy (DFS) in buffered solutions whose pH varied from 3 to 9. We evidenced that both fimbrial extension and fimbrial binding force to mannosylated-surface are modulated with changing the externally applied shear force and the solution pH. In particular, intertwined FimA-FimA and FimH-mannose interactions lead to a 5 to 25-fold decrease of the fimbrial unwinding for pulling rates larger than 10 µm/s and for pH values outside the range 5 to 7. In this pH range, the FimH-mannose binding force is maximal with a magnitude of -150-200 pN and the fimbriae extension reaches 8 µm. The enhancement of the FimH-mannose binding force at neutral pH, as evidenced from molecular AFM analyses, strongly correlates with an optimum in yeast agglutination detected at pH 5 to 7. The results reported in this work suggest that "catch bond effect" was negligible over the range of pulling rates tested, and both FimA-FimA and FimH-mannose interactions under given pH and external shear force conditions modify the ability of the bacteria to efficiently colonize host surfaces.

Double entrapment of growth factors by nanoparticles loaded into polyelectrolyte multilayer films.

Delivery of growth factors and control of vascularization are prominent problems in regenerative medicine. Vascular endothelial growth factor (VEGF) has been used both in vitro and in vivo to promote angiogenesis but due to its short half-life its controlled delivery is a sought after method. In this study we present a new concept of degradable drug loaded nanoparticles entrapped into exponentially growing multilayer films. Through hydrolysis of the nanoparticles, the drug can be delivered over long periods in a controlled manner. Poly(ε-caprolactone) nanoparticles were loaded with VEGF and in turn the release of VEGF from a surface is controlled by a thick layer-by-layer polyelectrolyte film. Direct loading of VEGF inside the film was not efficient for long-term applications. When VEGF loaded nanoparticles were introduced into the film, the particles were equally distributed inside and were stable after several washes. Moreover, the presence of the film sustained the release of VEGF for 7 days. Addition of the nanoparticles to the film promoted endothelial cell proliferation, mainly due to the presence of VEGF. Mechanical properties of the film (Young's moduli) were also improved by the presence of nanoparticles. However, in the presence of the film loaded with nanoparticles and without any direct contact with this film, endothelial cell growth was also enhanced on polystyrene and on Transwell insert surfaces which demonstrates the effectiveness of the nanoparticles not only to improve the mechanical properties of the film but also to deliver active VEGF. An increase in nitric oxide levels as an indicator of endothelial cell activity was monitored and was correlated with the release of VEGF from the nanoparticle/film platform. Finally, such a system can be used as an auxiliary delivery body within implants to finely control the release of bioactive agent containing nanoparticles.

Functional analysis of aberrant behavior through measurement of separate response topographies.

Functional analysis results for multiple topographies of aberrant behavior were graphed in an aggregate fashion and then separately for 48 clients. The results indicated that multiple topographies of behavior may be maintained by different contingencies. These results indicate that graphing functional analysis data in an aggregate fashion and then separately may improve the accuracy of their interpretation.