A. Méndez-Vilas

Atomic force microscopy of mechanically trapped bacterial cells.

This article presents a study on the influence of the protocol used for immobilization of bacterial cells onto surfaces by mechanically trapping them into a filter. In this sense, the surface and structure of trapped cells are analyzed. Bacteria can be present solely or with extracellular polymeric substances (EPS). To test the behavior of the EPS layer duing the filtering process, different strains of a well-known EPS-producer bacteria (Staphylococcus epidermidis), which produce an extracellular matrix clearly visible in AFM images, have been used. Results show that this immobilization method can cause severe structural and mechanical deformation to the cell membrane. This altered mechanical state may possibly influence the parameters derived from AFM force curves (which are micro/nano-mechanical tests). Also, our results suggest that the EPS layer might move during the filtering process and could accumulate at the upper part of the cell, thus favoring distorted data of adhesion/pull-off forces as measured by an AFM tip, especially in the case of submicron-sized microbial cells such as bacteria.

Effect of UV irradiation on the surface Gibbs energy of Ti6Al4V and thermally oxidized Ti6Al4V

Thermal oxidation of Ti6Al4V increases the thickness, modifies the structure, and changes the amount of alloying elements of the surface titanium dioxide layer with respect to the spontaneous passive layer of Ti6Al4V. The effects on the surface properties of Ti6Al4V and thermally oxidized Ti6Al4V after different periods of UV irradiation have been studied by measurement of water, formamide, and diiodomethane contact angles. The rate of modification of the water contact angle with the irradiation time is dependent on the surface treatment, but the water adhesion work, after an initial energetic step, follows a similar trend for both. Application of the Young equation together with the van Oss approach allowed evaluation of the surface Gibbs energy of the alloys. Similar to the water adhesion work, the surface Gibbs energy dependence on the irradiation time follows a similar trend for both samples and it is due to the change of the electron-donor parameter of the acid-base component. Also, a linear relationship common for both samples has been obtained between the cosines of the water contact angle and the formamide or diiodomethane contact angle. These facts indicate that the surface modification continuously produced by the UV irradiation is similar all along the process and similar for both samples after an energetic threshold for the thermally oxidized sample. It has been also tested that the hydrophilic-hydrophobic conversion is reversible for Ti6Al4V and Ti6Al4V thermally treated.

Experimental analysis of the influence of surface topography on the adhesion force as measured by an AFM

Force curves have been acquired using an atomic force microscope (AFM) on homogeneous microspheres of three different materials (latex, glass and yttria), in order to study the possible influence of the surface topography/geometry on the adhesion force as measured by an AFM. Forces were measured in regions at the top of the spheres ( ≈ 90°), at half-heights ( ≈ 0°) and in an intermediate region between these two ( ≈ 45°), where the angle is measured from the equatorial plane of the sphere to its polar axis. A very irregular and non-reproducible behaviour was found at ≈ 0°, so only the other two regions were quantitatively analysed. For all the three materials, a much smaller adhesion force was obtained in the region corresponding to ≈ 45° as compared to ≈ 90°. Moreover, a quite similar adhesion decrease ratio of about 1.60 ± 0.5 was obtained for all the three materials, which may suggest that the observed behavior might be due to geometrical factors. This observed influence could, in part, explain the observed heterogeneity in adhesion maps of microbial cells reported in the literature. The influence of the surface roughness is also discussed and it seems to result in a poor reproducibility of force curves.

Optical interference artifacts in contact atomic force microscopy images.

Atomic force microscopy images are usually affected by different kinds of artifacts due to either the microscope design and operation mode or external environmental factors. Optical interferences between the laser light reflected off the top of the cantilever and the light scattered by the surface in the same direction is one of the most frequent sources of height artifact in contact (and occasionally non-contact) images. They are present when imaging highly reflective surfaces, or even when imaging non-reflective materials deposited onto reflective ones. In this study interference patterns have been obtained with a highly polished stainless steel planchet. The influence of these artifacts in surface roughness measurements is discussed, and a semi-quantitative method based on the fast Fourier transform technique is proposed to remove the artifacts from the images. This method improves the results obtained by applying the usual flattening routines.

Ionic Liquid Microdroplets as Versatile Lithographic Molds for Sculpting Curved Topographies on Soft Materials Surfaces

Soft lithography comprises a set of approaches for shaping the surface of soft materials such as PDMS on the microscopic scales. These procedures usually begin with the development of templates/masters normally generated by electron or photolithography techniques. However, the richness in available shapes is limited, usually producing shapes containing sharp parts. Innovation is called for to develop reliable approaches capable of imparting well-defined 3D curved shapes to these solids, a topology that is somehow unnatural for solid surfaces. Here we report on the use of tiny drops of room-temperature ionic liquid, organic liquids that have attracted increasing amounts of attention in recent years because of their unique chemical properties) as a versatile platform for imprinting PDMS with tunable 3D curved geometry, which is out of reach of conventional lithographic techniques and ranges from almost flat depressions to almost closed cavities on the millimeter to micrometer scale. The concept exploits a peculiar combination of physical properties displayed by ionic liquids as their null volatility and their polarity, together with some unique properties of liquid surfaces as their virtually null surface roughness. Proof-of-concept experiments show their application as chemical microreactors and ultrasmooth optical lenses. This all-liquid method is simple, low-cost, versatile, maskless, tension-free, and easily scalable, so we envision a community-wide application in numerous modern physical, chemical, biological, and engineering settings.

Interdisciplinary applied microbiology: an introduction

This special issue of Antonie van Leeuwenhoek contains selected papers related to contributions presented in short during the 1st International Conference on Environmental, Industrial and Applied Microbiology (BioMicroWorld-2005), held on March 15 –18th, 2005 in Badajoz (Spain). http://www.formatex.org/biomicroworld2005. While microbiology is about the study of microorganisms (bacteria, viruses, algae, fungi, and protozoa) and related topics such as microbe interactions, the immune response and molecular genetics, applied microbiology is quite interdisciplinary, overlapping aspects of several other academic branches, some of them traditionally close, such as cell biology, molecular and cell biophysics, physiology, parasitology, biochemistry, genetics, medicine, pharmacology, and medical technology, and others not so near, such as physics, physical (bio)chemistry, materials science, nanotechnology, computer science, information technology, instrumentation. But collaboration with these is resulting in extraordinary advances in this post-genomic world. Thus, cross-disciplinary cooperation in microbiology has enabled microbiologists to study not only traditionalmicroorganisms, but also aspects of molecular genetics, biosensors, cancer, aging, inmunodeficiency diseases, animal and plant cell cultures, and microscopy, among others. Modern microbiology includes a broad variety of scholarly approaches which lead to a better understanding of all living things at the micrometer/cellular and nanometer-scale/molecular level, which produce beneficial applications in medicine, agriculture, industry, and ecology. In this context, the Conference called for papers reporting interdisciplinary research, relating microbiology with other sciences, such as physico/ chemistry, environmental science, genetics, pharmacology, nanoscience, microscopy/imaging science, etc. In other words, we are specially (but not exclusively) interested in reports applying the techniques, the training, and the culture of microbiology to research areas usually associated with other scientific and engineering disciplines. Over 750 participants from more than 60 countries attended the Conference, 15% of whom participated with a grant from the conference organization. Over 1100 works were presented during the different oral and posters sessions. Good examples of modern interdisciplinary applied microbiology were the works represented by the three Plenary Speakers.