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Scanning force microscopy has been used to probe the surface of the emerging pathogenic yeast Candida parapsilosis, in order to get insight into its surface structure and properties at submicrometer scales. AFM friction images eventually show patches with a very strong contrast, showing high lateral interaction with the tip. Adhesion force measurement also reveals a high normal interaction with the tip, and patches show extraordinarily high pull off values. The tip eventually sticks completely at the center of the patches. While an extraordinarily high interaction is measured by the tip at those zones, topographic images show extraordinarily flat topography over those zones, both of which characteristics are consistent with a liquid-like area. High resolution friction images show those zones to be surrounded by microfibrillar structures, concentrically oriented, of a mean width of about 25 nm, structures that become progressively less defined as we move away from the center of the patches. No structure can be appreciated inside the zones of maximum contrast. Also some helical or ribbon-like structure can be resolved from friction images. There is not only an ordered disposition of the microfibrillar structures, but also the adhesion force increases radially in the direction towards the center of the patches. These structures responsible for the high adhesion are thought to be incipient-emerging budding zones. Microfibrillar structures are thought to represent the first steps of chitin biosynthesis and cell wall digestion, with chitin polymers being biosynthesized, associated with other macromolecules of the yeast cell wall. They can be also beta glucan helical structures, made visible in the zone of yeast division due to the action of autolysins. The observed gradient in surface adhesion and elastic properties correlates well with that expected from a biochemical point of view. The higher adhesion force measured could be either due to the different macromolecular nature of the patches, or to a mechanical adhesion effect due to the different plasticity of that zone. This work reveals the importance of taking into account the dynamic nature of the cell wall physico-chemical properties. Processes related to the normal cell-cycle, as division, can strongly alter the surface morphology and physico-chemical properties and cause important heterogeneities that might have a profound impact on the adhesion behavior of a single cell, which could not be detected by more macroscopic methods.

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La alúmina es uno de los materiales cerámicos de mayor relevancia en usos biomédicos. Así, este trabajo hace una completa caracterización de su superficie a través de propiedades que son de especial importancia en aquellos procesos de interacción con superficies biológicas como son células y microorganismos. Tensión superficial, potencial zeta y rugosidad superficial se analizan utilizando métodos diversos. La tensión superficial se muestra en torno a 35 mJ m-2 aunque los valores dependen en muchos casos de la aproximación escogida y de los grupos de líquidos prueba necesarios para su determinación. El punto isoeléctrico aparece a pH = 4,6 lo que indica una carga superficial negativa cuando la alúmina se encuentre inmersa en líquidos fisiológicos (pH = 7). Los accidentes topográficos responsables de la macrorugosidad pueden considerarse de periodicidad en torno a 25um presentando alta variabilidad a escalas inferiores, por ello, es importante determinar la rugosidad a escalas próximas al tamaño de las células que intervienen en el proceso de adhesión.