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Mimoza Naseska, PhD, and Assist. Prof. Matjaž Humar, PhD, from the Department of Solid State Physics F5, in collaboration with colleagues from CENN Nanocenter, Imperial College London, and the Faculty of Mathematics and Physics, University of Ljubljana, have published an article titled Non-contact Monitoring of Glucose Concentration and pH by Integration of Wearable and Implantable Hydrogel Sensors with Optical Coherence Tomography in the journal Optics Express.

Optical coherence tomography (OCT) is a noninvasive imaging technique with large penetration depth into the tissue, but limited chemical specificity. By incorporating functional co-monomers, hydrogels can be designed to respond to specific molecules and undergo reversible volume changes. In this study, we present implantable and wearable biocompatible hydrogel sensors combined with OCT to monitor their thickness change as a tool for continuous and real-time monitoring of glucose concentration and pH. The results demonstrate the potential of combining hydrogel biosensors with OCT for non-contact continuous in-vivo monitoring of physiological parameters.

Figure: pH-sensitive hydrogel film for wound monitoring. a) The graph shows the deswelling of the film as a response to increasing pH of the solution. b) OCT B-scan of the hydrogel film located below a finger patch (upper right) and of the surrounding area with no hydrogel film (lower right).… Read the rest “Article in Optics Express”

Prof Igor Serša, PhD from the Department of Solid State Physics F5 published an article in Journal of magnetic resonance with the title Comparison of driven equilibrium and standard spin-echo sequence in MR microscopy: Analysis of signal dependence on RF pulse imperfection and diffusion. Fast MR imaging of samples with long NMR relaxation times is often challenging. In this study, a solution to this problem is proposed, based on the use of a spin-echo (SE) sequence for MR imaging, upgraded with a driven equilibrium method. The proposed (DE-SE) sequence was first theoretically analyzed and later verified by experiments on test samples performed on a 9.4 T system for MR microscopy. Experiments on water have shown that the DE-SE sequence can produce about 10 times more signal than the SE sequence. The presented DE-SE sequence has proven to be effective for fast imaging of samples with long T1 relaxation times in MR microscopy and is therefore also suitable for fast proton density weighted imaging of materials.

Samo Kralj from the Department of Condensed Matter Physics F5 and colleagues from The Faculty of Electrical Engineering at the University of Ljubljana have published an article in the journal Nanomaterials. They numerically studied localized elastic distortions in curved, effectively two-dimensional nematic shells using a mesoscopic Helfrich-Landau-de Gennes-type approach. They limited our theoretical consideration to axially symmetric shapes. They determined conditions for which nonsingular line-like localized nematic distortions could appear enabled by order reconstruction mechanism.

Young researcher Maha Zid has with collaborators theoretically studied the generic mechanisms that could establish critical behavior in nematic liquid crystals (NLCs). The corresponding free energy density terms should exhibit linear coupling with the nematic order parameter and, via this coupling, enhance the nematic order. They consider both temperature- and pressure-driven, order–disorder phase transitions. They derive a scaled effective free energy expression that describes how qualitatively different mechanisms enforce critical behavior.  Main focus is devoted on the impact of nanoparticles (NPs) in homogeneous NP-NLC mixtures. They illustrate that in the case of pressure-driven phase changes, lower concentrations are needed to impose critical point conditions in comparison with pure temperature variations.

Researchers Gregor Pirnat, Matevž Marinčič, Miha Ravnik, and Matjaž Humar from the F5 department at the “J. Stefan” Institute and the Faculty of Mathematics and Physics at the University of Ljubljana have published a paper titled Quantifying Local Stiffness and Forces in Soft Biological Tissues Using Droplet Optical Microcavities in the journal PNAS. Researchers developed a method for quantitative measurements of mechanical properties of soft biological tissues and materials based on the measurements of »whispering gallery mode« spectra of optical resonances in droplet microresonators. They implanted the droplets in test samples (e.g. brain tissue) and determined the droplet’s deformation and shape with nanometer precision, by measuring small shifts of the optical resonances in spectra, measured at different positions in the droplet. The elastocapillary interaction couples the droplet to the deformation of the surrounding medium, enabling the determination of material properties of the medium. Because of the high sensitivity of optical resonances they could measure forces of only a few piconewtons at the droplet surface. The purpose of the method is elastography of soft biological tissues, ranging from mucus to muscle tissue.