Attension® Seminar 2021 - Practical Applications for Surface Tension and Contact Angle

Iria studied Pharmacy at the University of Santiago de Compostela in Spain. She joined the Biopharmacy department of Sanofi Frankfurt in 2018 through a two years graduate program. Since January 2020 she is doing her PhD in the same group, in collaboration with University Greifswald. Her research focuses on the development of biorelevant media for predicting drug absorption. 

he surface activity plays a significant role in determining the ability of a molecule to stabilize the interface. Lignin adsorbs 

spontaneously at the air–water interface. Surface tension of lignin fraction produced by MetGen’s METNIN™ enzymatic lignin refining technology has been studied to understand the effect of refining on the surface activity of lignin. This has important consequence in stabilizing aqueous dispersions of lignin.  

Based on a survey among our tensiometer users I tried to get better knowledge about how people use the tensiometer, and what are the troubles and needs. 

The surface of the majority of biological materials is very complex and highly difficult to characterize. It is related to the chemical composition of the constitutive polymer matrix, porous nature of biomaterials, directional heterogeneities and also process-induced features such as roughness, local densification or thermal/chemical modification. Reliable estimation of the contact angle and/or surface free energy requires therefore a special approach for the correct sample presentation, optimal measurement configuration as well as appropriate interpretation of obtained results. The optimal solution would combine multi-directional drop observation, combined with a detailed mapping of the chemical surface heterogeneity and geometrical texture/topography. A prototype of such measurement protocol was developed and tested by authors including the Biolin Scientific Theta Flex optical tensiometer as a core component.

Various types of dairy powders are used as ingredients in food industry. Depending on powder composition, process and storage, their wetting and thus, reconstitution characteristics may differ. Traditionally, quality testing has been relying on practical methods indicating powder quality. As the variability in product compositions increases, more understanding and thus, methods relating characteristics to phenomena are needed. Contact angle method for dairy powders was developed and the effect of tableting, moisture equilibration and powder composition were studied. 

In material science, particularly focused on the design and formation of new separation materials, the assessment of wettability is an essential point. Based on the contact angle value, it is possible to select the best membrane materials for the process to ensure the highest effectiveness and performance. There are many requirements to the membrane samples depending on the process, e.g. stability, pore size, porosity as well as roughness and hydrophobic or hydrophilic character. To evaluate the latter ones, the goniometry method must be applied. Based on the mentioned approach, it is possible to determine not only the character by simple water contact angle measurement of the material but to calculate a variety of factors describing the physiochemistry of the membranes, e.g. surface free energy with its components, critical surface tension, and to plot so-called Kao and Zisman diagrams. Based on these parameters, it is possible to predict the interactions between the membrane material and separated system, to prepare suitable washing mixtures for membranes that will prevent wetting and subsequently maintain the membrane stability, to study membrane stability by detecting liquid tension of the feed solution and made the goniometric measurements under similar conditions with the experimental ones. Moreover, by the implementation of fringe projection phase shifting method, it is possible to measure the contact angle corrected by roughness. It should be stressed that roughness has a very important influence on the contact angle, where increasing amounts of roughness tend to boost up the existing properties of the material. To understand in the most precise way how the modification of membrane materials will influence materials features and, as a consequence, the transport and separation, it is must know the contact angle as well as roughness.  

In work, a broad range of applications of the goniometry technique in membrane science will be presented.  

Wettability in gluing and finishing processes of lignocellulosic materials"  

The specific of the wood and wood based material surfaces in the aspect of the formation of glue lines and lacquer coatings will be presented. Based on many years of experience of the Department Gluing and Finishing of Wood workers the problems of surface wettability in undertaken studies will be presented. The results of investigations using the THETA system will be showed.

Electrowetting uses an externally applied electric field to actuate or manipulate small volumes of liquid by altering its interfacial tension. First, a set of electrodes is positioned on the substrate and covered with a dielectric and hydrophobic layer. Then a droplet is positioned on the top layer. With the tensiometer, we can see, film, calculate, and compare the effect of the applied voltage, the shape of the electrodes, the different types of materials, and liquids on the contact angle, the shape, and the movement of the droplets. 

Superhydrophilic and superhydrophobic patterned surfaces are fabricated from silicon through plasma etching and a plasma coating. These surfaces are optimized for their wetting properties. The superhydrophobic surfaces consist mostly of air which also makes them extremely repellent toward adhesion of cells, at least in short term. The wettability patterned surfaces are utilized for single cell trapping of immune cells and in the future the aim is to apply them in single cell metabolomic and transcriptomic analysis.  

Monoclonal antibodies (mAbs) have become a leading candidate for oncological therapeutics due to their unparalleled selectivity.  The amphiphilic nature of mAbs drives them to adsorb to air/water interfaces, where they expose their hydrophobic residues to the gas phase, leading to irreversible adsorption, partial unfolding, interfacial aggregation, and recruitment of additional proteins from the solution phase.  In the therapeutic administration of mAbs, air/water interfaces are present in the air head space of IV bags and syringes, and the adsorption of mAbs depletes the solution of the therapeutically effective native form of the mAbs, resulting in inaccurate dosages and shortened shelf-lives. 

Surfactants added to the mAb solution are commonly used as excipients to compete with mAbs for available surface area at the air/water interface, and thereby limit the depletion of the mAbs.  A major issue is to determine the concentration of surfactant necessary to prevent significant mAb adsorption.  Our research has used a combination of pendant drop tensiometry  and X-ray reflectivity (XR) at Argonne National Laboratory to measure the molecular adsorption of both mAbs and surfactant to the interface. Additionally, the dynamic orientational change in the adsorbed mAb as a function of concentration at the air/water interface using XR coupled with homology modeling will be discussed. We believe this information about the complex phase space can be of value in designing methodologies for transferring and administrating the antibodies with maximal dosage. 

In this presentation we demonstrate how pendant drops can be used to measure surface pressure versus area isotherms and interfacial dilatational rheology of mixed lipid monolayers, including 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) mixed with cholesterol. We will show how those data can be further analyzed to gain deeper insight into the films, including quantifying intermolecular interactions and interpreting major rheological differences due to the change in headgroup between DPPE and DPPC. Practical considerations and limitations of the technique will be discussed. 

The talk will be about static and dynamic surface tension measurements, characterization of them to interpret hydrophobicity of different acetyl-TAG. Acetyl TAG (3-acetyl-1,2-diacyl-sn-glycerols) which is produced from transgenically engineered Camelina sativa plant. Acetyl TAG has useful functional properties to be used as plasticizers in biodegradable food packaging film formulations to improve their physical properties. Surface tension and contact angle measurements would be one of the methods to evaluate these functional properties of acetyl TAG. This approach may bring novel approach to use ace-TAG as a plasticizer to improve the physical, mechanical and thermal properties of renewable and eco-friendly food packaging films.