Macroscopic Biaxial Order in Multilayer Films of Bent-Core Liquid Crystals Deposited by Combined Langmuir-Blodgett/Langmuir-Schaefer Technique.

Bent-core liquid crystals, a class of mesogenic compounds with non-linear molecular structures, are well known for their unconventional mesophases, characterized by complex molecular (and supramolecular) ordering and often featuring biaxial and polar properties. In the nematic phase, their unique behavior is manifested in the formation of nano-sized biaxial clusters of layered molecules (cybotactic groups). While this prompted their consideration in the quest for nematic biaxiality, experimental evidence indicates that the cybotactic order is only short-ranged and that the nematic phase is macroscopically uniaxial. By combining atomic force microscopy, neutron reflectivity and wide-angle grazing-incidence X-ray scattering, here, we demonstrate that multilayer films of a bent-core nematic, deposited on silicon by a combined Langmuir-Blodgett and Langmuir-Schaefer approach, exhibit macroscopic in-plane ordering, with the long molecular axis tilted with respect to the sample surface and the short molecular axis (i.e., the apex bisector) aligned along the film compression direction. We thus propose the use of Langmuir films as an effective way to study and control the complex anchoring properties of bent-core liquid crystals.

Sunset Yellow Confined in Curved Geometry: A Microfluidic Approach.

The behavior of lyotropic chromonic liquid crystals (LCLCs) in confined environments is an interesting research field that still awaits exploration, with multiple key variables to be uncovered and understood. Microfluidics is a highly versatile technique that allows us to confine LCLCs in micrometric spheres. As microscale networks offer distinct interplays between the surface effects, geometric confinement, and viscosity parameters, rich and unique interactions emerging at the LCLC-microfluidic channel interfaces are expected. Here, we report on the behavior of pure and chiral doped nematic Sunset Yellow (SSY) chromonic microdroplets produced through a microfluidic flow-focusing device. The continuous production of SSY microdroplets with controllable size gives the possibility to systematically study their topological textures as the function of their diameters. Indeed, doped SSY microdroplets produced via microfluidics, show topologies that are typical of common chiral thermotropic liquid crystals. Furthermore, few droplets exhibit a peculiar texture never observed for chiral chromonic liquid crystals. Finally, the achieved precise control of the produced LCLC microdroplets is a crucial step for technological applications in biosensing and anticounterfeiting.

Nanoscale Structure of Langmuir-Blodgett Film of Bent-Core Molecules.

Bent-core mesogens (BCMs) are a class of thermotropic liquid crystals featuring several unconventional properties. However, the interpretation and technological exploitation of their unique behavior have been hampered by the difficulty of controlling their anchoring at surfaces. To tackle this issue, we report the nanoscale structural characterization of BCM films prepared using the Langmuir-Blodgett technique. Even though BCMs are quite different from typical amphiphilic molecules, we demonstrate that stable molecular films form over water, which can then be transferred onto silicon substrates. The combination of Brewster angle microscopy, atomic force microscopy, and X-ray reflectivity measurements shows that the molecules, once transferred onto a solid substrate, form a bilayer structure with a bottom layer of flat molecules and an upper layer of upright molecules. These results suggest that Langmuir-Blodgett films of BCMs can provide a useful means to control the alignment of this class of liquid crystals.

Spherical Confinement of Chromonics: Effects of a Chiral Aminoacid.

Induced or spontaneous chirality in natural systems is an intriguing issue. In recent years, a lot of attention has been focused on chirality of chromonic liquid crystals, a class of materials that is able to self-assemble in columnar structures. However, the mechanism involved in the arising of chirality in these materials, that starts at the molecular level and controls the supramolecular structure, is poorly understood; however, it is certainly affected by ionic strength. In this work we present the results obtained doping Cromolyn, a chromonic material, with a strong helical-twisting-power peptide, and confining it in a spherical geometry. We demonstrate, by means of optical polarized microscopy and structural analysis, that both the geometrical constraint and the presence of the chiral dopant enhance the chiral effect; we also demonstrate that they favor the rise of a highly ordered helical superstructure, that may be optimized upon adding an ionic dye to the system. Finally, we report a procedure for the preparation of free-standing polymeric films, embedding and preserving the microspheres, and paving the way for the creation of biocompatible and eco-friendly optical devices to be used in the sensor and anticounterfeiting fields.

A novel phage display based platform for exosome diversity characterization.

We present an innovative approach allowing the identification, isolation, and molecular characterization of disease-related exosomes based on their different antigenic reactivities. The designed strategy could be immediately translated into any disease in which exosomes are involved. The identification of specific markers and their subsequent association with exosome subtypes, together with the possibility to engineer target-guided exosome-like particles, could represent the key for the effective adoption of exosomes in clinical practice.

Nano- and Micro-Porous Chitosan Membranes for Human Epidermal Stratification and Differentiation.

The creation of partial or complete human epidermis represents a critical aspect and the major challenge of skin tissue engineering. This work was aimed at investigating the effect of nano- and micro-structured CHT membranes on human keratinocyte stratification and differentiation. To this end, nanoporous and microporous membranes of chitosan (CHT) were prepared by phase inversion technique tailoring the operational parameters in order to obtain nano- and micro-structured flat membranes with specific surface properties. Microporous structures with different mean pore diameters were created by adding and dissolving, in the polymeric solution, polyethylene glycol (PEG Mw 10,000 Da) as porogen, with a different CHT/PEG ratio. The developed membranes were characterized and assessed for epidermal construction by culturing human keratinocytes on them for up to 21 days. The overall results demonstrated that the membrane surface properties strongly affect the stratification and terminal differentiation of human keratinocytes. In particular, human keratinocytes adhered on nanoporous CHT membranes, developing the structure of the corneum epidermal top layer, characterized by low thickness and low cell proliferation. On the microporous CHT membrane, keratinocytes formed an epidermal basal lamina, with high proliferating cells that stratified and differentiated over time, migrating along the z axis and forming a multilayered epidermis. This strategy represents an attractive tissue engineering approach for the creation of specific human epidermal strata for testing the effects and toxicity of drugs, cosmetics and pollutants.

Spicy Bitumen: Curcumin Effects on the Rheological and Adhesion Properties of Asphalt.

Over the years, the need for the synthesis of biodegradable materials has facilitated the drift of the asphalt industry towards eco-sustainable and cost-effective production of road pavements. The principal additives in the asphalt industry to improve the performance of road pavements and increase its lifespan are majorly rheological modifiers, adhesion promoters and anti-oxidant agents. Rheological modifiers increase physico-chemical properties such as transition temperature of asphalt binder (bitumen), adhesion promoters increase the affinity between binder and stone aggregates while anti-oxidant agents reduce the effects of oxidation caused by exposure to air, water and other natural elements during the production of asphalt pavements. In this study, we tested the effectiveness of a food grade bio-additive on these three aforementioned properties. We also sought to hypothesize the mechanisms by which the additive confers these desired features on bitumen. We present this study to evaluate the effects of turmeric, a food-based additive, on bitumen. The study was conducted through dynamic shear rheology (DSR), atomic force microscopy, scanning electron microscopy (SEM) and boiling test analysis.

Preparation and Characterization of Silver(I) Ethylcellulose Thin Films as Potential Food Packaging Materials.

Ag(I)-containing ethylcellulose (EC) films suitable as antbacterial packaging materials have been prepared and fully characterized. Different preparation methods, including the use of green casting solvents, are proposed. The Ag(I) acylpyrazolonato complexes, [Ag(Qpy,CF3 )(L)], L=benzylimidazole (Bzim) and L=ethylimidazole (EtimH), used as active additives, display different modes of interactions with EC, depending on their structural features. A thorough investigation of the EC liquid-crystalline lyotropic phase and its changes with the introduction of silver additives, has been conducted, revealing either the inclusion of complex molecules into the inner structure of the EC matrix or their dispersion on its surface. Moreover, the bactericidal activity of the prepared Ag(I) films seems to be related to the interaction between silver additives and the polymeric EC matrix. Indeed, the EC-2b films show a particularly good performance even with a low silver content, with a relative bacterial killing of about 100 %. Tests for Ag(I) migration have been performed by using three food stimulants under two assay conditions. Low values of silver release are recorded, particularly at low concentration of silver content, in the case of all new prepared Ag(I) films.

Gi Protein Modulation of the Potassium Channel TASK-2 Mediates Vesicle Osmotic Swelling to Facilitate the Fusion of Aquaporin-2 Water Channel Containing Vesicles.

Vesicle fusion is a fundamental cell biological process similar from yeasts to humans. For secretory vesicles, swelling is considered a step required for the expulsion of intravesicular content. Here this concept is revisited providing evidence that it may instead represent a general mechanism. We report the first example that non-secretory vesicles, committed to insert the Aquaporin-2 water channel into the plasma membrane, swell and this phenomenon is required for fusion to plasma membrane. Through an interdisciplinary approach, using atomic force microscope (AFM), a fluorescence-based assay of vesicle volume changes and NMR spectroscopy to measure water self-diffusion coefficient, we provide evidence that Gi protein modulation of potassium channel TASK-2 localized in AQP2 vesicles, is required for vesicle swelling. Estimated intravesicular K⁺ concentration in AQP2 vesicles, as measured by inductively coupled plasma mass spectrometry, was 5.3 mM, demonstrating the existence of an inwardly K⁺ chemical gradient likely generating an osmotic gradient causing vesicle swelling upon TASK-2 gating. Of note, abrogation of K⁺ gradient significantly impaired fusion between vesicles and plasma membrane. We conclude that vesicle swelling is a potentially important prerequisite for vesicle fusion to the plasma membrane and may be required also for other non-secretory vesicles, depicting a general mechanism for vesicle fusion.

Temperature-tunable lasing from dye-doped chiral microdroplets encapsulated in a thin polymeric film.

In the last decade, much interest has grown around the possibility to use liquid-crystal droplets as optical microcavities and lasers. In particular, 3D laser emission from dye-doped cholesteric liquid crystals confined inside microdroplets paves the way for many applications in the field of sensors or tunable photonics. Several techniques can be used to obtain small microresonators as, for example, dispersing a liquid crystal inside an immiscible isotropic fluid to create an emulsion. Recently, the possibility to obtain a thin free-standing film starting from an emulsion having a mixture of water and polyvinyl alcohol as isotropic matrix has been reported. After the water evaporation, a polymeric film in which the microdroplets are encapsulated has been obtained. Bragg-type laser emission has been recorded from the emulsion as well as from the thin film. Here, we report on the possibility to tune the laser emission as a function of temperature. Using a chiral dopant with temperature dependent solubility, the emitted laser wavelength can be tuned in a range of 40 nm by a temperature variation of 18 °C. The proposed device can have applications in the field of sensors and for the development of anti-counterfeiting labels.

Mixed emulsion of liquid crystal microresonators: towards white laser systems.

Microdroplet systems have attracted great interest because of their wide range of applications, easiness in processing and handling, feasibility in developing miniaturized devices with high performances and large flexibility. In this study, a stable emulsion based on different dye-doped chiral liquid crystal droplets has been engineered in order to achieve simultaneous omnidirectional lasing at different wavelengths. To obtain the mixed emulsion of dye doped Bragg onion-type microresonators the twofold action, as a surfactant and a droplet stabilizer, of the polyvinyl alcohol dissolved in water has been exploited. Multiple wavelengths lasing in all directions around the mixed emulsion is demonstrated. By water evaporation, a plastic sheet including different types of chiral droplets is also obtained, retaining all the emission characteristic of the precursor emulsion. A relevant feature is the large flexibility of the preparation method that enables an easy and full control of the lasing spectrum addressing white laser systems. However, the simplicity of the procedure based on a single-step process as well as the high stability of the mixed emulsion is a relevant result, envisaging strong potentiality for developing easy and friendly technologies useful in the field of identification, sensing, imaging, coating and lab-on-a-chip architectures.

Biomechanical Strengthening of the Human Cornea Induced by Nanoplatform-Based Transepithelial Riboflavin/UV-A Corneal Cross-Linking.

Purpose: The purpose of this study was to investigate the biomechanical stiffening effect induced by nanoplatform-based transepithelial riboflavin/UV-A cross-linking protocol using atomic force microscopy (AFM). Methods: Twelve eye bank donor human sclerocorneal tissues were investigated using a commercial atomic force microscope operated in force spectroscopy mode. Four specimens underwent transepithelial corneal cross-linking using a hypotonic solution of 0.1% riboflavin with biodegradable polymeric nanoparticles of 2-hydroxypropyl-ß-cyclodextrin plus enhancers (trometamol and ethylenediaminetetraacetic acid) and UV-A irradiation with a 10 mW/cm2 device for 9 minutes. After treatment, the corneal epithelium was removed using the Amoils brush, and the Young's modulus of the most anterior stroma was quantified as a function of scan rate by AFM. The results were compared with those collected from four specimens that underwent conventional riboflavin/UV-A corneal cross-linking and four untreated specimens. Results: The average Young's modulus of the most anterior stroma after the nanoplatform-based transepithelial and conventional riboflavin/UV-A corneal cross-linking treatments was 2.5 times (P < 0.001) and 1.7 times (P < 0.001) greater than untreated controls respectively. The anterior stromal stiffness was significantly different between the two corneal cross-linking procedures (P < 0.001). The indentation depth decreased after corneal cross-linking treatments, ranging from an average of 2.4 ± 0.3 µm in untreated samples to an average of 1.2 ± 0.1 µm and 1.8 ± 0.1 µm after nanoplatform-based transepithelial and conventional cross-linking, respectively. Conclusions: The present nanotechnology-based transepithelial riboflavin/UV-A corneal cross-linking was effective to improve the biomechanical strength of the most anterior stroma of the human cornea.

Near-IR Electrochromism in Electrodeposited Thin Films of Cyclometalated Complexes.

Homogeneous thin films of controlled thickness obtained from cyclometalated complexes of general formula [(C(∧)N)M(O(∧)N)], where M = Pd(II) or Pt(II), H(C(∧)N) = 2-phenylpyridine and, respectively, 2-thienylpyridine and H(O(∧)N) = a triphenylamine functionalized Schiff base, have been deposited by oxidative electropolymerization. The films have been electrochemically and morphologically characterized. The metallopolymeric thin films present stable reversible redox behavior and typical cauliflower-like textures in agreement with a nucleation-growth electropolymerization mechanism. However, the film growth is greatly influenced by the nature of the metal center, with a higher tendency of the Pt complexes to promote the 3D growth. Furthermore, a complete spectroelectrochemical study has been performed on electrodeposited films showing near-IR absorption in the oxidized state, high contrast ratios (up to 65%) and low response times.

Detection of Gold Nanoparticles Aggregation Growth Induced by Nucleic Acid through Laser Scanning Confocal Microscopy.

The gold nanoparticle (GNP) aggregation growth induced by deoxyribonucleic acid (DNA) is studied by laser scanning confocal and environmental scanning electron microscopies. As in the investigated case the direct light scattering analysis is not suitable, we observe the behavior of the fluorescence produced by a dye and we detect the aggregation by the shift and the broadening of the fluorescence peak. Results of laser scanning confocal microscopy images and the fluorescence emission spectra from lambda scan mode suggest, in fact, that the intruding of the hydrophobic moiety of the probe within the cationic surfactants bilayer film coating GNPs results in a Förster resonance energy transfer. The environmental scanning electron microscopy images show that DNA molecules act as template to assemble GNPs into three-dimensional structures which are reminiscent of the DNA helix. This study is useful to design better nanobiotechnological devices using GNPs and DNA.

Rewritable Optical Storage with a Spiropyran Doped Liquid Crystal Polymer Film.

Rewritable optical storage has been obtained in a spiropyran doped liquid crystal polymer films. Pictures can be recorded on films upon irradiation with UV light passing through a grayscale mask and they can be rapidly erased using visible light. Films present improved photosensitivity and optical contrast, good resistance to photofatigue, and high spatial resolution. These photochromic films work as a multifunctional, dynamic photosensitive material with a real-time image recording feature.

Endothelial-like nitric oxide synthase immunolocalization by using gold nanoparticles and dyes.

Immunofluorescence is a biological technique that allows displaying the localization of the target molecule through a fluorescent microscope. We used a combination of gold nanoparticles and the fluorescein isothiocianate, FITC, as optical contrast agents for laser scanning confocal microscopy imaging to localize the endothelial-like nitric oxide synthase in skeletal muscle cells in a three-dimensional tissue phantom at the depth of 4µm. The FITC detected fluorescence intensity from gold-nanoparticles-labelled cells was brighter than the emission intensity from unlabelled cells.

Light-controllable linear dichroism in nematics.

We report a method to obtain a light-controllable dichroism. The main effect is achieved using spiropyran-doped (SP-doped) nematic liquid crystal mixtures. SP molecules exhibit a high solubility in the liquid crystal host, which can vary between 1% and 4% in weight, without destroying the liquid crystalline phase. Due to their elongated shape, SP molecules are oriented along the nematic liquid crystal director. The obtained linear dichroism was measured to be 1.08 with a dichroic ratio of 7.12. Further, a two-direction linear dichroism was obtained by adding a dichroic dye to the mixture. The angle between the two dichroic axes was found to be 11°. Two-direction linear dichroism is also light controllable and can be switched back to one-direction dichroism.

Understanding of the viscoelastic response of the human corneal stroma induced by riboflavin/UV-a cross-linking at the nano level.

PURPOSE: To investigate the viscoelastic changes of the human cornea induced by riboflavin/UV-A cross-linking using Atomic Force Microscopy (AFM) at the nano level. METHODS: Seven eye bank donor corneas were investigated, after gently removing the epithelium, using a commercial AFM in the force spectroscopy mode. Silicon cantilevers with tip radius of 10 nm and spring elastic constants between 26- and 86-N/m were used to probe the viscoelastic properties of the anterior stroma up to 3 µm indentation depth. Five specimens were tested before and after riboflavin/UV-A cross-linking; the other two specimens were chemically cross-linked using glutaraldehyde 2.5% solution and used as controls. The Young's modulus (E) and the hysteresis (H) of the corneal stroma were quantified as a function of the application load and scan rate. RESULTS: The Young's modulus increased by a mean of 1.1-1.5 times after riboflavin/UV-A cross-linking (P<0.05). A higher increase of E, by a mean of 1.5-2.6 times, was found in chemically cross-linked specimens using glutaraldehyde 2.5% (P<0.05). The hysteresis decreased, by a mean of 0.9-1.5 times, in all specimens after riboflavin/UV-A cross-linking (P<0.05). A substantial decrease of H, ranging between 2.6 and 3.5 times with respect to baseline values, was observed in glutaraldehyde-treated corneas (P<0.05). CONCLUSIONS: The present study provides the first evidence that riboflavin/UV-A cross-linking induces changes of the viscoelastic properties of the cornea at the scale of stromal molecular interactions.

Atomic force microscopy analysis of normal and photoablated porcine corneas.

We showed the capabilities and accuracy of atomic force microscopy (AFM) techniques for imaging and analyzing the corneal epithelium and the photoablated corneal stroma. Eight normal porcine corneas, half of which were ablated using a scanning-spot excimer laser, were examined. All the corneas were imaged in balanced salt solution after fixation in glutaraldehyde. In the normal untreated corneas we observed the epithelial surface showing the typical polygonal cells and presenting numerous microprojections. The superficial epithelial cells were classified in three types as a result of the anterior-surface roughness measurements. AFM images of the photoablated corneal specimens showed undulations and granule-like features on the ablated stromal surface, specific to 193-nm ArF laser irradiation. Nevertheless, the quantitative analysis confirmed the precision of excimer laser surgery in removing sub-micrometric amounts of tissue. AFM showed to be a high-resolved imaging tool for the scanning of both native as well as photoablated corneal specimens. Also, this technique permits precise topographic analysis of the corneal plane, in the nanometric scale, of which smoothness is an important physical characteristic and necessary to achieve an optimal optical quality of the eye.