Miguel A. Cabrerizo-Vílchez

Axisymmetric drop shape analysis as penetration Langmuir balance

A new Langmuir-type pendant-drop penetration film balance has been developed combining a Langmuir-type pendant-drop film balance with a new rapid-subphase-exchange technique. In addition to the determination of surface pressure—molecular area isotherms of insoluble monolayers deposited on the surface of a pendant drop, it allows the study of reactions with some surfactant added to the subphase. The monolayer is spread on the surface of a drop suspended from a capillary, which is the outer one of an arrangement of two coaxial capillaries connected to the different branches of a microinjector. Once the film is brought to the desired state of compression by varying the drop volume with the microinjector, the subphase liquid in the drop can be exchanged quantitatively by means of the coaxial capillaries. This exchange is complete for a through-flow of at least three times the drop volume, and the monolayers endure it at all tested film pressures. The determination of surface tension as a function of surface a...

Effect of acid etching and collagen removal on dentin wettability and roughness

It was recently reported that removal of the collagen network from etched dentin does not affect dentin bond strengths. The aim of this study was to determine if the removal of the collagen fibers results in changes in dentin roughness and wettability. Twenty cary-free extracted human third molars were sectioned parallel to the occlusal surface to expose either superficial or deep dentin. Dentin was ground flat through 600-grit SiC abrasive paper under water to provide uniform surfaces. Observed contact angle measurements were performed to assess wettability by using the axisymmetric drop shape analysis technique using water and a water-based primer. Average roughness was determined with a profilometer. The specimens were analyzed just after being ground, after etching with 35% H(3)PO(4) gel for 15 s, and after etching and deproteinization with 5% NaOCl for 2 min. Data were analyzed with two-way ANOVA and Newman-Keuls multiple comparison t test procedure. Etching resulted in an increase in surface roughness and dentin wettability. For deep dentin, collagen removal did not influence the average roughness, but it resulted in a significantly greater degree of wettability. The degree of wettability for deep dentin was greater than for superficial dentin.

Dentin wetting by four adhesive systems

OBJECTIVES To evaluate the dentin wetting by four adhesive systems and to relate the wetting properties with the adhesive efficiency. METHODS Scotch Bond Multipurpose Plus (3M), Syntac Single-Component (Vivadent), One-Step (Bisco) and Heliobond (Vivadent) were used. The substrate was superficial and deep human dentin. Roughness and water contact angle were measured before and after acid etching. Dentin wetting by resins was studied by contact angle measurements as a function of time to evaluate the spreading time. The shear bond strength was evaluated following a single plane method, and the microleakage was evaluated in Class V cavities. RESULTS Acid etching increased dentin roughness and wettability and no differences were found between acids tested. Dentin wetting and roughness was higher on deep dentin. Dentin wetting and shear bond strength of resins was similar except for Heliobond that displayed the lowest value. Microleakage was higher on the gingival wall, and the leaking was lowest for Scotch Bond Multipurpose Plus, and maximum for Heliobond. The spreading time exceeded 30s with water-based and hydrophobic adhesives, and was lower with an acetone-based adhesive. Dentin depth had some influence on contact angle and shear bond strength: contact angles obtained with SBMP and One-Step were higher on superficial dentin, and shear bond strength for One-Step was higher on superficial dentin. Dentin wetting by resins could be correlated to shear bond strength and microleakage. SIGNIFICANCE Dentin acid etching with different conditioners promotes similar roughness and wetting changes. On a similar substrate, the adhesion depends on the chemical and wetting characteristics of resins.

Contact angle measurements on two (wood and stone) non-ideal surfaces

Abstract Surface properties of wood and stones are very important in influencing the bonding and finishing of wood and for road construction. Two important surface properties are wettability and surface free energy. Contact angle measurement is a simple, useful and sensitive tool for quantifying the wettability and the surface energy of different materials in contact with pure water and/or aqueous surfactant solutions. Nevertheless, a sessile drop on a real surface shows different contact angle values due to its lack of symmetry or to the loss of volume by capillary action. For this reason alternative techniques which supply an average contact angle value are required. In view of this fact, we applied axisymmetric drop shape analysis-diameter (ADSA-D) using a top view of a sessile drop and axisymmetric drop shape analysis-profile (ADSA-P) with a side view of a captive bubble. Both techniques calculate the contact angle by solving the Young–Laplace equation although with different algorithms, the former needs the maximum drop diameter while the last makes use of the complete bubble profile. ADSA-D was applied to study two wood species (eucalyptus and pine) and ADSA-P with polished rocks of two different compositions (silicate and calcite). The maximum contour of the drop was fitted to an ellipse after being detected and extracted by means of a semi-automatic procedure of image processing. Thus, two different contact angles were found out. The captive bubble method in conjunction with the current ADSA-P technique allows to obtain comfortable, automatic and reproducible measurements of contact angle on porous stones.

Dynamic contact angle and spreading rate measurements for the characterization of the effect of dentin surface treatments

A new methodology capable of providing reliable and reproducible contact angle (theta) data has been employed to study the effect of clinical treatments grinding, acid etching, and deproteinization on medial dentin tissue. It is based on the application of the ADSA-CD algorithm to the determination of low-rate dynamic contact angles, obtained from slowly growing drops, and on contact angle measurement, as well as spreading behavior analysis, during the relaxation of the system (water on treated dentin) after initial drop growth. The theta data obtained were substantially more reproducible than those obtained with classical methods. A net effect of the treatment on theta was found, increasing dentin wettability: theta (polished) >theta (etched) >theta (deproteinized). The spreading rates correlate with the angles and are adequate for the dentin surface characterization. ANOVA and SNK tests show that for advancing contact angles the means corresponding to all treatments are significantly different. In the relaxing phase, mean angle and spreading rates on polished dentin differ significantly from those on etched and deproteinized dentin, but the latter do not differ significantly from each other.

Measurement of surface tension and contact angle using entropic edge detection

This paper presents a new method to measure the surface tension and the contact angle of a liquid. The measurement procedure comprises three steps: acquisition of the liquid drop image, image segmentation to obtain the contour of the drop and surface-tension and contact-angle calculation by the ADSA method. In the second step a new segmentation method is used based on the Jensen-Shannon divergence, an entropic measurement of coherence among distribution probabilities. The advantages of using this entropic edge-detection method are shown; it is especially suitable when the source image of the drop is affected by any kind of noise, blur or low-contrast effect. Results reveal a better performance than other methods used in this field.

Wettability and bonding of self-etching dental adhesives. Influence of the smear layer.

OBJECTIVES To evaluate dentin wettability and bonding of self-etching and total-etch adhesives on smear layer-covered and smear layer-free dentin. METHODS Three self-etching adhesives (Clearfil SE Bond, AdheSE and Xeno III) and one total-etch adhesive (SingleBond) were evaluated. The substrates were mid coronal smear layer-covered and smear layer-free dentin. Dentin wettability by resins was studied from contact angle measurement using sessile drop method and Axisymmetric Drop Shape Analysis (ADSA). Shear-bond strength was evaluated using a push-out technique (ad hoc design). Data were analysed with two-way ANOVA and Tukeys test. RESULTS Similar values of dentin wettability were obtained for all adhesives tested regardless the presence of smear layer. Even though, Xeno III and AdheSE exhibited slightly lower wettability (higher contact angles values) on smear layer-free dentin. Likewise, the presence of smear layer did not affect the shear-bond strength. Total-etch adhesive obtained higher shear-bond strength than self-etching adhesives, which obtained similar values. SIGNIFICANCE Wettability is similar between self-etching and total-etch adhesives. The smear layer affects slightly the wettability of self-etching adhesives. Shear-bond strength is not sensitive to the smear layer presence. Total-etch adhesion is stronger than self-etching adhesion. There is no clear relationship between wettability and bond strength.

In vitro digestion of interfacial protein structures

It is important to understand how interfacial composition influences the digestion of coated interfaces in order to rationally design emulsion based food products with specific digestion profiles. This study has been designed to investigate the effects of gastrointestinal digestion on protein covered interfaces. In this work, we have used a new apparatus fully designed and assembled at the University of Granada: the OCTOPUS. This new device enables the design of a customised static sequential in vitro digestion process in a single droplet. Physiological conditions of each compartment/step of the digestion process are met through subphase exchange of artificial digestive media, hence mimicking the transit through the gastrointestinal tract. We can measure in situ the evolution of the interfacial tension throughout the whole simulated gastrointestinal transit and the mechanical properties of the interfacial layer (interfacial dilatational modulus) after each digestion stage (mouth, stomach, small intestines). The in vitro digestion model used here focuses on pepsinolysis and lipolysis of two dairy proteins: β-lactoglobulin (BLG) and β-casein (BCS) adsorbed at the olive oil–water interface. The results show different susceptibilities of interfacial layers of BLG and BCS to pepsinolysis; while pepsinolysis of adsorbed BLG weakens the interfacial network, pepsinolysis of adsorbed BCS strengthens it as measured by the dilatational moduli. These numbers provide an interfacial scenario for previous findings on emulsification of these proteins, which was found to improve BLG pepsinolysis but somehow protected BCS from pepsinolysis in the stomach. The desorption profiles provide quantification of the extent of lipid digestion in subsequent simulated intestinal fluid containing lipase. The extent of lipid hydrolysis was found to be similar in BLG and BCS covered interfaces and comparable to that in the absence of coverage (pure oil–water interface) indicating that proteins do not comprise a barrier to lipolysis. This similar susceptibility is attributed to the similar interfacial properties of the interfaces reaching the duodenum despite the structural differences between native BCS and BLG, thus demonstrating the impact of the transit through the gut on lipolysis. This research allows identification of the interfacial mechanisms affecting enzymatic hydrolysis of proteins and lipolysis. The results can be exploited in tailoring novel food matrices with improved functional properties such as decreased digestibility, controlled energy intake and low allergenicity.

Axisymmetric drop shape analysis as penetration film balance applied at liquid–liquid interfaces

Abstract A new application of the axisymmetric drop shape analysis (ADSA) has been developed, using the pendant-drop film balance technology for penetration studies of insoluble monolayers at the liquid–liquid interface. A monolayer is spread on the surface of a drop of a buffer solution suspended from a capillary, which is the outer one of an arrangement of two coaxial capillaries connected to the two different branches of a microinjector. Next the monolayer-coated buffer drop is immersed into the oil phase. The interfacial area is varied changing the drop volume with the microinjector, and the determination of surface tension as a function of the interfacial area or time is performed using ADSA. Once the monolayer is brought to the desired compression state, the aqueous phase is exchanged quantitatively by through-flow through the coaxial capillaries, permitting to study reactions with some surfactant added to the subphase. The complete set-up, i.e. the image capturing and microinjector system is fully computer controlled by a user-friendly, Windows-integrated program, including the ADSA surface tension calculus algorithm. Compared with ‘conventional’ oil–water interface film balances, the new device presents several advantages such as a more stringent control of the environmental conditions and therefore more uniform temperature, pressure and concentration along the interface, small amounts of material needed and a 20-times greater interface/volume ratio than in conventional Langmuir troughs.

CLUSTER-SIZE DISTRIBUTION IN COLLOIDAL AGGREGATION MONITORED BY SINGLE-CLUSTER LIGHT SCATTERING

The aggregation of polymer colloids is studied in processes induced at high ionic concentration. Cluster-size distributions are measured with a single-cluster light scattering instrument constructed by our team. A brief description of the instrument is given and its proper performance is checked. The results are interpreted with the framework of Smoluchowskis equation. The rate constant for dimer formation is measured and compared with the theoretical prediction. Viscous interaction is taken into account to explain the differences. The temporal evolution of the number-average mean cluster size and the time-independent scaling function are determined from the cluster-size distributions. Dynamic scaling is observed even for small clusters and short aggregation times. Parameters λ and μ from Van Dongen and Ernsts classification scheme for homogeneous kernels are estimated and the aggregation mechanism is identified.