Specific Ion Effects and pH Dependence on the Interaction Forces between Polystyrene Particles.

Colloidal interactions have been extensively studied due to the wide number of applications where colloids are present. In general, the electric double layer force and the van der Waals interaction dominate the net force acting between two colloids at large separation distances. However, it is well accepted that some other phenomena, especially those acting at short separation distances, might be relevant and induce substantial changes in the force profiles. Within these phenomena, those related to the surface contact angle, the hydration degree of the ions, or the pH, may dominate the force profiles features, not only at short distances. In this paper, we analyzed the effect of the pH and counterion type on the long-range as well as short-range forces between polystyrene colloidal particles by using the colloidal probe technique based on AFM. Our results confirm that the features of the force profiles between polystyrene surfaces are strongly affected by the pH and hydration degree of the counterions in solution. Additionally, we performed a study of the role of the pH on the wettability properties of hydrated and nonhydrated polystyrene sheets to scan the wettability properties of this material with pH. Contact angle measurements confirmed that the polystyrene surface is hydrophobic in aqueous solutions over the entire range of pHs investigated. These results are in good agreement with the features observed in the force profiles at low pH. At high pH, a short-range repulsion similar to the one observed for hydrophilic materials is observed. This repulsion scales with the pH, and it also depends on the hydration degree of the ions in solution. This way, the short-range forces between polystyrene surfaces may be tunable with the pH, and its origin does not seem to be related to the hydrophobicity of the material.

Long-ranged and soft interactions between charged colloidal particles induced by multivalent coions.

Forces between charged particles in aqueous solutions containing multivalent coions and monovalent counterions are studied by the colloidal probe technique. Here, the multivalent ions have the same charge as the particles, which must be contrasted to the frequently studied case where multivalent ions have the opposite sign as the substrate. In the present case, the forces remain repulsive and are dominated by the interactions of the double layers. The valence of the multivalent coion is found to have a profound influence on the shape of the force curve. While for monovalent coions the force profile is exponential down to separations of a few nanometers, the interaction is much softer and longer-ranged in the presence of multivalent coions. The force profiles in the presence of multivalent coions and in the mixtures of monovalent and multivalent coions can be accurately described by Poisson-Boltzmann theory. These results are accurate for different surfaces and even in the case of highly charged particles. This behavior can be explained by the fact that the force profile follows the near-field limit to much larger distances for multivalent coions than for monovalent ones. This limit corresponds to the conditions with no salt, where the coions are expelled between the two surfaces.

Accurate predictions of forces in the presence of multivalent ions by Poisson-Boltzmann theory.

Forces between positively and negatively charged colloidal particles across aqueous salt solutions containing multivalent ions are measured directly with the atomic force microscope (AFM). The measurements are interpreted quantitatively with Poisson-Boltzmann (PB) theory. Thereby, the surface potentials and regulation properties of the particle surfaces are extracted from symmetric measurements between the same types of particles. This information is used to predict force profiles in the asymmetric situations involving different types of particles without any adjustable parameters. These predictions turn out to be very accurate, which demonstrates that the mean-field PB theory is reliable down to distances of about 5 nm. While various reports in the literature indicate that this theory should fail due to neglect of ion correlations, such effects seem important only at higher concentrations and smaller distances.

Measurements of dispersion forces between colloidal latex particles with the atomic force microscope and comparison with Lifshitz theory.

Interaction forces between carboxylate colloidal latex particles of about 2 µm in diameter immersed in aqueous solutions of monovalent salts were measured with the colloidal probe technique, which is based on the atomic force microscope. We have systematically varied the ionic strength, the type of salt, and also the surface charge densities of the particles through changes in the solution pH. Based on these measurements, we have accurately measured the dispersion forces acting between the particles and estimated the apparent Hamaker constant to be (2.0 ± 0.5) × 10(-21) J at a separation distance of about 10 nm. This value is basically independent of the salt concentration and the type of salt. Good agreement with Lifshitz theory is found when roughness effects are taken into account. The combination of retardation and roughness effects reduces the value of the apparent Hamaker constant and its ionic strength dependence with respect to the case of ideally smooth surfaces.

Direct measurements of forces between different charged colloidal particles and their prediction by the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO).

Force measurements between three types of latex particles of diameters down to 1 µm with sulfate and carboxyl surface functionalities were carried out with the multi-particle colloidal probe technique. The experiments were performed in monovalent electrolyte up to concentrations of about 5 mM. The force profiles could be quantified with the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO) by invoking non-retarded van der Waals forces and the Poisson-Boltzmann description of double layer forces within the constant regulation approximation. The forces measured in the symmetric systems were used to extract particle and surface properties, namely, the Hamaker constant, surface potentials, and regulation parameters. The regulation parameter is found to be independent of solution composition. With these values at hand, the DLVO theory is capable to accurately predict the measured forces in the asymmetric systems down to distances of 2-3 nm without adjustable parameters. This success indicates that DLVO theory is highly reliable to quantify interaction forces in such systems. However, charge regulation effects are found to be important, and they must be considered to obtain correct description of the forces. The use of the classical constant charge or constant potential boundary conditions may lead to erroneous results. To make reliable predictions of the force profiles, the surface potentials must be extracted from direct force measurements too. For highly charged surfaces, the commonly used electrophoresis techniques are found to yield incorrect estimates of this quantity.

Ice adhesion of PDMS surfaces with balanced elastic and water-repellent properties.

HYPOTHESIS: Ice adhesion to rigid materials is reduced with low energy surfaces of high receding contact angles. However, their adhesion strength values are above the threshold value to be considered as icephobic materials. Surface deformability is a promising route to further reduce ice adhesion. EXPERIMENTS: In this work, we prepared elastomer surfaces with a wide range of elastic moduli and hydrophobicity degree and we measured their ice adhesion strength. Moreover, we also explored the deicing performance of oil-infused elastomeric surfaces. The ice adhesion was characterized by two detachment modes: tensile and shear. FINDINGS: The variety of elastomeric surfaces allowed us to simultaneously analyze the ice adhesion dependence with deformability and contact angle hysteresis. We found that the impact of these properties depends on the detachment mode, being deformability more important in shear mode and hydrophobicity more relevant in tensile mode. In addition, oil infusion further reduces ice adhesion due to the interfacial slippage. From an optimal balance between deformability and hydrophobicity, we were able to identify surfaces with super-low ice adhesion.

Comparison of the relaxation of sessile drops driven by harmonic and stochastic mechanical excitations.

Currently, there is no conclusive evidence regarding the global equilibrium condition of vibrated drops. However, it is well-known that vibration of sessile drops effectively reduces the contact angle hysteresis. In this work, applying a recent methodology for evaluating the most-stable contact angle, we examined the impact of the type of excitation signal (random signal versus periodical signal) on the values of the most-stable contact angle for polymer surfaces. Using harmonic signals, the oscillation frequency affected the postvibration contact angle. Instead, the white noise signal enabled sessile drops to relax regardless of their initial configuration. In spite of that, the values of most-stable contact angle obtained with different signals mostly agreed. We concluded that not only the amount of relaxation can be important for relaxing a sessile drop but also the rate of relaxation. Together with receding contact angle, most-stable contact angle, measured with the proposed methodology, was able to capture the thermodynamic changes of "wetted" polymer surfaces.

Comparison of sessile drop and captive bubble methods on rough homogeneous surfaces: a numerical study.

Quasi-static experiments using sessile drops and captive bubbles are the most employed methods for measuring advancing and receding contact angles on real surfaces. These observable contact angles are the most easily accessible and reproducible. However, some properties of practical surfaces induce certain phenomena that cause a built-in uncertainty in the estimation of advancing and receding contact angles. These phenomena are well known in surface thermodynamics as stick-slip phenomena. Following the work of Marmur (Marmur, A. Colloids Surf., A 1998, 136, 209-215), where the stick-slip effects were studied with regard to sessile drops and captive bubbles on heterogeneous surfaces, we developed a novel extension of this study by adding the effects of roughness to both methods for contact angle measurement. We found that the symmetry between the surface roughness problem and the chemical heterogeneity problem breaks down for drops and bubbles subjected to stick-slip effects.

Higher HLA class I expression in renal cell carcinoma than in autologous normal tissue.

A total of 93 frozen primary renal cell carcinoma (RCC) samples and 31 frozen samples of corresponding normal renal tissue were analyzed for human leukocyte antigen (HLA) class I and HLA-DR expression. Unexpectedly, HLA class I expression was much higher on RCC cells than on normal renal tubular cells. Immunohistochemistry analysis of frozen and paraffin-embedded tissue samples, applying an extended panel of specific anti-HLA monoclonal antibodies, showed elevated HLA class I antigen expression in 95.6% of the tumors vs only 12.9% of normal renal tissues. These findings were confirmed by molecular analysis of HLA heavy chain and beta2-microglobulin (beta2m) transcription levels using quantitative real-time polymerase chain reaction (PCR) on microdissected tissue samples (isolated tumor nests and autologous normal renal tubules) from four patients. These results might help to explain the relatively high success rate of immunotherapy in patients with RCC. The molecular mechanism underlying the increased HLA class I expression in RCC has yet to be elucidated.

Efficient recovery of HLA class I expression in human tumor cells after beta2-microglobulin gene transfer using adenoviral vector: implications for cancer immunotherapy.

Here we report a successful use of a non-replicating adenovirus expressing the wild-type human beta2m gene in recovery of normal human leucocyte antigen (HLA) class I expression in beta2m-null cancer cells. Total loss of HLA class I expression in these cell lines is caused by a mutation in beta2m gene and a loss of heterozygosity in chromosome 15 carrying another copy of that gene. Normal HLA class I expression on the tumour cell surface is critical for the successful outcome of cancer immunotherapy as T cells can only recognize tumour-derived peptides in a complex with self-HLA class I molecules. In this report we characterize the newly generated adenoviral vector AdCMVbeta2m and demonstrate an efficient beta2m gene transfer in tumour cell lines of different histological origin, including melanoma, prostate and colorectal carcinoma. The beta2m re-expression lasted for an extended period of time both in vitro and in vivo in human tumour xenograft transplants. We propose that in a subset of cancer patients with structural defect in beta2m gene or chromosome 15, the adenoviral-mediated recovery (or even increase) of HLA class I expression on tumour cells in combination with vaccination or adoptive T-cell therapy can provide a complementary approach to improve the clinical efficacy of cancer immunotherapy.

Wetting transitions on rough surfaces revealed with captive bubble experiments. The role of surface energy.

HYPOTHESIS: Wettability of solid surfaces is mostly probed with sessile drops rather than bubbles because this method is readily followed out. This recurrent use may lead to a misleading connection of certain phenomena to the hydrophobicity/hydrophilicity of materials. For instance, the Cassie-Baxter regime and the wicking effect are generally associated only to hydrophobic and hydrophilic surfaces, respectively. However, the same phenomenology should be observed when air bubbles (underwater conditions) in contact with solid surfaces are used instead. In particular, one might expect that rough-hydrophilic surfaces become superaerophobic due to the appearance of a hybrid dewetting regime, like the Cassie-Baxter regime described for rough-hydrophobic surfaces. Otherwise, rough-hydrophobic surfaces might become superaerophilic due to air-wicking. EXPERIMENTS: To elucidate this issue, in this work, we analyzed the wettability of surfaces with very different intrinsic contact angle and roughness degree. The analysis was performed with both Sessile Drop and Captive Bubble methods. FINDINGS: Our results with captive bubbles for rough-hydrophilic surfaces revealed phenomena only explained by the occurrence of a transition from the Wenzel regime to an "inverse" Cassie-Baxter regime. In addition, our results with captive bubbles for rough-hydrophobic surfaces showed evidences of air percolation through the interconnected asperities. This effect reminds the wicking effect reproduced on rough-hydrophilic surfaces, responsible for superhydrophilicity.

Wetting on axially-patterned heterogeneous surfaces.

Contact angle variability, leading to errors in interpretation, arises from various sources. Contact angle hysteresis (history-dependent wetting) and contact angle multiplicity (corrugation of three-phase contact line) are irrespectively the most frequent causes of this uncertainty. Secondary effects also derived from the distribution of chemical defects on solid surfaces, and so due to the existence of boundaries, are the known "stick/jump-slip" phenomena. Currently, the underlying mechanisms in contact angle hysteresis and their connection to "stick/jump-slip" effects and the prediction of thermodynamic contact angle are not fully understood. In this study, axial models of smooth heterogeneous surface were chosen in order to mitigate contact angle multiplicity. For each axial pattern, advancing, receding and equilibrium contact angles were predicted from the local minima location of the system free energy. A heuristic model, based on the local Young equation for spherical drops on patch-wise axial patterns, was fruitfully tested from the results of free-energy minimization. Despite the very simplistic surface model chosen in this study, it allowed clarifying concepts usually misleading in wetting phenomena.

Fabrication of Superhydrophobic Metal Surfaces for Anti-Icing Applications.

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in industry. The wettability of the produced surface was analyzed by bouncing drop experiments and the topography was analyzed by confocal microscopy. In addition, we show various methodologies to measure its durability and anti-icing properties. Superhydrophobic surfaces hold a special texture that must be preserved to keep their water-repellency. To fabricate durable surfaces, we followed two strategies to incorporate a resistant texture. The first strategy is a direct incorporation of roughness to the metal substrate by acid etching. After this surface texturization, the surface energy was decreased by silanization or fluoropolymer deposition. The second strategy is the growth of a ceria layer (after surface texturization) that should enhance the surface hardness and corrosion resistance. The surface energy was decreased with a stearic acid film. The durability of the superhydrophobic surfaces was examined by a particle impact test, mechanical wear by lateral abrasion, and UV-ozone resistance. The anti-icing properties were explored by studying the ability to repeal subcooled water, freezing delay, and ice adhesion.

Genetic polymorphisms of CYP2C9 and CYP2C19 are not related to drug-induced idiosyncratic liver injury (DILI).

BACKGROUND AND PURPOSE: The general view on the pathogenesis of drug-induced idiosyncratic liver injury (DILI) is that parent compounds are rendered hepatotoxic by metabolism, mainly by cytochrome (CYP) 450, although other metabolic pathways can contribute. Anecdotal reports suggest a role of CYP 450 polymorphisms in DILI. We aimed to assess in a series of Spanish DILI patients the prevalence of important allelic variants of CYP2C9 and CYP2C19, known to be involved in the metabolism of several hepatotoxic drugs. EXPERIMENTAL APPROACH: Genotyping of CYP2C9 ((*)2, (*)3) and CYP2C19 ((*)2 and (*)3), was carried out in a total of 28 and 32 patients with a well established diagnosis of DILI. CYP2C9 and CYP2C19 variants were analysed in genomic DNA by means of PCR-FRET and compared with previous findings in other Caucasian populations. KEY RESULTS: CYP2C9 and CYP2C19 allele and genotype frequencies were in agreement with Hardy-Weinberg equilibrium. Fourteen patients (50%) were heterozygous and 1(4%) found to be compound heterozygous for the CYP2C9 allele. Seven (22%) were found to carry one and 1(3%) carried two CYP2C19 mutated alleles. No patients were homozygous for (*)3 allele. The distribution of both CYP2C9 and CYP2C19 allelic variants in DILI patients were similar to those in other Caucasian populations. Patients with variant and those with wild-type alleles did not differ in regard to clinical presentation of DILI, type of injury and outcome. CONCLUSIONS AND IMPLICATIONS: We find no evidence to support CYP2C9 and CYP2C19 genetic polymorphisms as predictable potential risk factors for DILI.

Forces between different latex particles in aqueous electrolyte solutions measured with the colloidal probe technique.

In this article, a compilation of results on direct force measurements between colloidal particles in monovalent salts carried out with the colloidal probe technique based on Atomic Force Microscopy was presented. The interaction forces between similar and dissimilar particles was studied and it was concluded that, in general, these force profiles may be satisfactorily quantified by the DLVO theory down to distances of few nanometers. However, in the specific case where the charge of one of the involved particle is close to neutral, it was found that the surface potential of this particle may change its sign depending on the sign of charge of the opposite particle. In this respect, the assumption that the surface potential of a particle is a property only related to the particle surface features and the bulk properties is called into question. Microsc. Res. Tech. 80:144-152, 2017. © 2016 Wiley Periodicals, Inc.

Testing the performance of superhydrophobic aluminum surfaces.

The analysis of wetting properties of superhydrophobic surfaces may be a difficult task due to the restless behavior of drops on this type of surfaces and the limitations of goniometry for high contact angles. A method to validate the performance of superhydrophobic surfaces, rather than standard goniometry, is required. In this work, we used bouncing drop dynamics as a useful tool to predict the water repellency of different superhydrophobic surfaces. From bouncing drop experiments conducted over a wide range of superhydrophobic surfaces, we found that those surfaces with a proper roughness degree and homogeneous chemical composition showed higher water-repellency. We also conducted a drop condensation study at saturating conditions aimed to determine whether there is direct correlation between water repellency and condensation delay. We found that the drop condensation process is strongly related to the surface topography, as well as the intrinsic wettability. The condensation is promoted on rough surfaces but it is delayed on intrinsically hydrophobic surfaces. However, the differences found in condensation delay between the superhydrophobic surfaces explored in this study cannot be justified by their chemical homogeneity nor their efficiency as water repellent surfaces, separately.

Comparison of the SYBR Green and the hybridization probe format for real-time PCR detection of HHV-6.

A comparative study was conducted of a novel real-time quantitative PCR test (LightCycler System) with FastStart DNA Master(PLUS) SYBR Green I dye to detect DNA of human herpes virus 6 (HHV-6). Results were compared with those of a real-time quantitative PCR with hybridization probe (HP) formats using the fluorescence resonance energy transfer method, and with those of a single qualitative PCR test. The detection limit of the test with SYBR Green I dye was 20 copies of the virus, similar to that of the other two tests. The reproducibility was satisfactory. The new test has the same advantages as real-time PCR with HP formats and offers a greater versatility at lower cost.

Altered HLA class I expression in non-small cell lung cancer is independent of c-myc activation.

We studied the expression of major histocompatibility complex class I antigens in 59 bronchogenic carcinomas, as well as in pneumocytes and epithelial respiratory cells distant from the tumor. We observed in all cases that normal lung tissue expressed major histocompatibility complex class I antigens, while this expression was completely lost in 16 tumors (27%). The defect in HLA gene expression affected both heavy chain and beta 2-microglobulin, as demonstrated by the null reactivity with the monoclonal antibodies GRH1, W6/32, and HC10. Selective underexpression was detected in 1 tumor for HLA-A locus antigens and in 3 tumors for HLA-B locus antigens. Southern blot analyses of major histocompatibility complex class I genes were performed in 20 tumor tissue specimens and 6 cell lines. No class I gene rearrangements were detected using HLA coding and locus specific noncoding probes. We also used the Southern blot method to investigate the possible relationship between c-myc amplification and HLA class I antigens in non-small cell lung cancers and detected no apparent amplification in 20 tumor tissue specimens (5 negative for HLA class I antigens) and 6 cell lines (3 with decreased expression). Northern blot analysis revealed no relationship between c-myc mRNA levels and specific mRNA for HLA-A and HLA-B antigens in cell lines with imbalanced HLA-A or HLA-B expression.

Expression of HLA class I and II antigens in bronchogenic carcinomas: its relationship to cellular DNA content and clinical-pathological parameters.

We studied the presence of HLA class I antigens in 115 samples of bronchogenic carcinomas (66 frozen and 49 formalin-fixed and paraffin-embedded specimens) by the immunophosphatase alkaline and immunoperoxidase methods with antibodies against major histocompatibility complex antigens. We also studied HLA class II antigens on the 66 frozen tumor samples. Nonneoplastic lung tissue was also analyzed for purposes of comparison. Pneumocytes and epithelial respiratory cells expressed HLA class I and II antigens. The expression of class I antigens was totally lost in 29 tumors (25%). The defect in HLA gene expression affected both heavy chain and beta 2-microglobulin, as demonstrated by the null reactivity with specific antibodies. In 2 cases of 66 studied in cryostatic section, the selective loss of A locus was observed, and in three cases selective loss of B locus was detected. The expression of class I antigens was compared with clinical-pathological parameters such as histological type, degree of differentiation, and tumor stage, as well as tumoral ploidy. The absence of expression of HLA class I molecules was significantly associated with poorly differentiated and undifferentiated tumors (P less than 0.0001) and with aneuploid tumors (P less than 0.001), suggesting that some lung tumors may escape immune surveillance and become biologically more aggressive. Class II antigens were expressed in 13 cases of 66 studied (18%) in frozen specimens, and a clear relationship was observed with well-differentiated tumors (P less than 0.05).

Integration of high-risk human papillomavirus DNA is linked to the down-regulation of class I human leukocyte antigens by steroid hormones in cervical tumor cells.

A crucial event in the malignant progression of cervical intraepithelial neoplasia appears to be the up-regulation of high-risk human papillomavirus (HPV) early gene expression. Steroid hormones have been linked to the progression from premalignant to neoplastic status in HPV positive lesions. This report demonstrates that at physiological levels, the glucocorticoid hormone hydrocortisone consistently down-regulates class I human leukocyte antigen (HLA) surface expression in HPV-positive cervical tumor cells but can up-regulate expression in HPV-negative epithelial tumor lines. Suppression of HLA expression was also seen with progesterone, another steroid hormone. The hydrocortisone-mediated modulation of HLA expression is dependent on integration and transcription of the HPV genome and can be blocked by Ru38486, an antagonist of both glucocorticoid and progesterone receptors, indicating the role of these receptors in mediating HLA suppression. The data suggest that HPV integration events in cervical epithelia correlate with hormone-dependent HLA suppression, possibly contributing to the avoidance of tumor recognition by cytotoxic T cells. These studies imply that clinical use of steroids may be contraindicated in HPV-positive individuals who have early premalignant cervical disease or neoplasia but provide evidence that the antiprogestin Ru38486 may be useful in the management of early stage cervical disease.