J.M. Bruque

Thermodynamic Analysis of Growth Temperature Dependence in the Adhesion of Candida parapsilosis to Polystyrene

ABSTRACT The purpose of this work was to study the adhesion to polystyrene of two Candida parapsilosis strains, grown at 22 and 37°C, in terms of hydrophobicity, surface charge, and interaction free energy. Growth temperature changed the surface properties of microorganisms, yielding a good correlation between thermodynamic predictions and adhesion behavior.

Bactericidal behaviour of Ti6Al4V surfaces after exposure to UV-C light.

TiO(2)-coated biomaterials that have been excited with UV irradiation have demonstrated biocidal properties in environmental applications, including drinking water decontamination. However, this procedure has not been successfully applied towards the killing of pathogens on medical titanium-based implants, mainly because of practical concerns related to irradiating the inserted biomaterial in situ. Previous researchers assumed that the photocatalysis on the TiO(2) surface during UV application causes the bactericidal effects. However, we show that a residual post-irradiation bactericidal effect exists on the surface of Ti6Al4V, not related with photocatalysis. Using a combination of staining, serial dilutions, and a biofilm assay, we show a significant and time-dependent loss in viability of different bacterial strains of Staphylococcus epidermidis and Staphylococcus aureus on the post-irradiated surface. Although the duration of this antimicrobial effect depends on the strains selected, our experiments suggest that the effect lasts at least 60 min after surface irradiation. The origin of such phenomena is discussed in terms of the physical properties of the irradiated surfaces, which include the emission of energy and changes in surfaces charge occurring during electron-hole recombination processes. The method here proposed for the preparation of antimicrobial titanium surfaces could become especially useful in total implant surgery for which the antimicrobial challenge is mainly during or shortly after surgery.

Serum as a Factor Influencing Adhesion of Enterococcus faecalis to Glass and Silicone

ABSTRACT The purpose of this work was to analyze the effect of serum on the physicochemical surface properties and adhesion to glass and silicone of Enterococcus faecalis ATCC 29212 at 37°C. As is presented using thermodynamics analysis, serum minimizes the interaction of cells with water, which correlates well with the increase in hydrophobicity and in bacterial adhesion to glass and silicone.

Wettability and surface free energy of zirconia ceramics and their constituents

Measurements of contact angle for water, glycerol, formamide and diiodomethane on surfaces of zirconia ceramic stabilized with 4% magnesia, zirconia ceramic stabilized with 3% yttria, zirconia ceramic stabilized with 5% yttria, tetragonal-Y-zirconia ceramic, cubic-Y-zirconia ceramic, zirconium (IV) oxide, aluminum oxide, magnesium oxide and yttrium oxide were conducted. Using the values of contact angle, the total surface free energy of these solids, and its components resulting from different kinds of intermolecular interactions were calculated. It was found that the Lifshitz-van der Waals component of the surface free energy of zirconia ceramics only slightly depends on the amount and kind of metal oxides present in the ceramics. The acid-base component of all the studied solids is lower than 13 mJ/m2, showing a small dependence on the kind of metal oxide. For all samples studied the electron-donor parameter of the acid-base components of the surface free energy is many times higher that electron-acceptor one. It was stated that the acid-base component probably depends on the density of OH groups on the surface of the solids studied.

Analysis of the adsorption isotherms of a non-ionic surfactant from aqueous solution onto activated carbons

Abstract The adsorption isotherms at 20°C onto four activated carbons of the non-ionic surfactant Triton X-100 from aqueous solution have been studied over a wide concentration range. The adsorption was explained using one or a combination of two Langmuir equations, depending on the equilibrium concentration range studied. A description of the adsorbed layer was constructed on the basis of the information obtained from the isotherms and assuming the model of van Oss et al. for the interfacial interaction between adsorbent and adsorbate. The results indicate that there are at least two kinds of interactions, the first related to a direct interaction between the activated carbon surface and adsorbate molecules, and the second mainly due to the interaction between surfactant molecules at the adsorbent–solution interface leading to the formation of interfacial aggregates.

The contribution of double layers to the free energy of interactions in the cassiterite-SDS solution system

Abstract From the values of contact angles for water, glycerol and diiodomethane taken from the literature. the Lifshitzvan der Waals, electron-acceptor and electron-donor parameters corresponding to the polar head of the surface free energy of sodium dodecyl sulphate (SDS[pwere determined and compared with those found in the literature. From these values, the Lifshitz-van der Waals and acid-base components of the free energy of interaction between SDS molecules through water were evaluated. The electrostatic component of the free energy was estimated from the ψ value for SDS found in the literature. These calculations allow the estimation of the total free energy of interaction between the SDS apolar and polar moieties through water on the basis of two models for interactions: plane-plane and cylinder cylinder. The results were compared with data from the literature, showing good agreement (for electrolyte of 0.1 M ionic strength) for both models, and with the value obtained from CMC data. However, for other ionic strengths some differences are observed. The free energy of interaction between SDS and cassiterite through water was evaluated from the components of the surface free energy for both the apolar and the polar moieties of SDS and its ψ value, and from the Lifshitz-van der Waals and acid-base components of the surface free energy of cassiterite with different surface treatments, taken from the literature. On the basis of these calculations, it was possible to infer the main influence of pH on the SDS-cassiterite interactions: they are predominantly electrostatic forces at low pH, and acid base forces at a pH corresponding to the ZPC. Also, at high pH, when negative charges are present at the cassiterite-water interface, SDS adsorption onto cassiterite is possible only by acid-base interactions between the apolar chain of SDS and the cassiterite surface.

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.

Components of the surface free energy of low rank coals in the presence of n-alkanes

Abstract Measurements of contact angles for water, glycerol, formamide and diiodomethane on the surfaces of four low rank coals (31.1, 31.2, 32.1 and 32.2) covered with n-alkanes (n-hexane, n-undecane and n-hexadecane) were made. Using the approaches of van Oss et al., the geometric mean of the interfacial free energy, and Youngs equation, the components of the surface free energy of coals and coal precovered with n-alkane films were calculated. Also the total surface free energy was determined from the so-called equation of state. Using the values of the components of surface free energy or total free energy of the coal, the spreading of the n-alkanes at the coal/water interface and the free energy of interaction between coal particles in the water phase were determined. On the basis of these results we have stated that, on the coal surface in air, a very stable, n-alkane film, resulting from a wetting process by spreading is formed, which first of all reduces the apolar component of the surface free energy of the coal and can partially block the polar component. However, it was found that n-alkanes cannot completely spread over a coal surface immersed in water, and the contact angle depends on the type of n-alkane. It was also found that the presence of an n-alkane film on a coal surface decreased the attractive interactions between the coal particles in the water phase, owing to Lifshitz-van der Waals forces and increased interactions resulting from acid-base forces in comparison to ‘pure’ coal.

Insights into bacterial contact angles: difficulties in defining hydrophobicity and surface Gibbs energy.

One of the principal techniques for evaluating the surface hydrophobicity of biological samples is contact angle. This method, applied readily to flat-smooth-inert surfaces, gives rise to an important debate when implemented with microbial lawns. After its initial description, in 1984, several authors have carried out modifications of the technique but the results obtained have not been previously judged. This work focuses on the particularities of contact angle measurements on bacterial lawns and enhances the idea of the impossibility of using water contact angle as a universal measurement of bacterial hydrophobicity. Contact angles can only be used as relative indicators of hydrophobicity, in a similar way to tests based on microbial adhesion to solvents. The strong dependence of contact angles on dried bacterial lawns with measuring time and environmental conditions (e.g. pH of the media) preclude the estimation of their absolute values, and so, of the cells surface Gibbs energy. Yet, for a given measuring time, it is found that the hydrophobicity and the apparent bacterial surface Gibbs energy components are qualitatively related to the bacterial surface electrical potential. In particular, a hydrophobic increase is always accompanied by an increase of the cells Lifshitz-Van der Waals component and a decrease of their acid-base component and absolute zeta potential. Therefore, the present study shows that the physico-chemical surface properties that characterize bacteria are not independent, and one of them can be qualitatively described in terms of the others when measuring contact angles at a fixed time after the drying of the microbial beds.

On the evaluation of the surface free energy of porous and powdered solids from imbibition experiments: equivalence between height-time and weight-time techniques

A study of the equivalence between the height-time and weight-time experimental techniques, based on the imbibition of liquids into porous or powdered solids, has been carried out, determining under what conditions the deductions about the surface free energy of these solids made from the analysis of the experimental results obtained as weight versus time are similar to those deduced from the analysis of height versus time. Concretely, we have proved that only if the particular values of the porosity of the solid determined from the proper technique of imbibition, named the effective porosity, are taken into account, the analysis of both type of experimental measurements leads to the same conclusions about the surface free energy of the porous and powdered solids. In order to exemplify this, capillary rise measurements have been carried out by means of these two techniques with different liquids on silica gel layers.