Towards ultra-responsive biodegradable polysaccharide humidity sensors

Sodium alginate is a biodegradable natural polymer that is derived from algae and is water soluble. Upon immersion in a CaCl₂ solution, a sodium alginate water solution is cross-linked to form water-insoluble calcium alginate. When the sodium alginate water solution is immersed in the CaCl₂ bath via a syringe pump, calcium alginate fibers are produced. By changing the CaCl₂ concentration, calcium alginate fibers with different degrees of cross-linking can be produced. Such fibers were found to differ in mechanical and morphological properties, and more interestingly, were found to possess humidity sensing and conductive properties. Interestingly, the higher the CaCl₂ concentration, the lower the degree of cross-linking, which produced softer fibers with better humidity sensing and conductive properties. The fibers were able to trap water in their structures, and a higher water content increased the conductivity due to the presence of an electrolyte salt in the fiber and due to the polyelectrolyte nature of the fiber itself. The cross-linking and percent shrinking degree, morphology and mechanical properties of the fibers were found to create significant changes in the conductivity and humidity sensing properties of the fibers. High humidity environments led to an increase in the conductivity of the fibers, whereas dry environments led to a decrease in the conductivity. The fibers, especially those with the highest CaCl₂ concentration, were determined to be ultra-responsive to humidity changes and exhibited very good repetition in humidity cycles. These tailored fibers are proposed as novel biodegradable conductive materials for various humidity sensing, robotic and bio-robotic applications.     

Wettability increase by "corona" ionization

Experiments showing an increase in the wettability of a hydrophobic surface when using corona air ionization are shown. Photoluminiscence observations support the predictions of charge accumulation at the triple line and confirm previous experiments. In all of the experiments, the contact angle was in the saturation regime at a value smaller than that predicted by the condition of a zero value for the solid-liquid surface tension. The PDMS did not show any deterioration due to the corona exposure under the experimental conditions used. The contact angle is shown to increase with humidity.     

A computational analysis of the binding mode of closantel as inhibitor of the <Emphasis Type="Italic">Onchocerca volvulus</Emphasis> chitinase: insights on macrofilaricidal drug design

Onchocerciasis is a leading cause of blindness with at least 37 million people infected and more than 120 million people at risk of contracting the disease; most (99%) of this population, threatened by infection, live in Africa. The drug of choice for mass treatment is the microfilaricidal Mectizan^® (ivermectin); it does not kill the adult stages of the parasite at the standard dose which is a single annual dose aimed at disease control. However, multiple treatments a year with ivermectin have effects on adult worms. The discovery of new therapeutic targets and drugs directed towards the killing of the adult parasites are thus urgently needed. The chitinase of filarial nematodes is a new drug target due to its essential function in the metabolism and molting of the parasite. Closantel is a potent and specific inhibitor of chitinase of Onchocerca volvulus (OvCHT1) and other filarial chitinases. However, the binding mode and specificity of closantel towards OvCHT1 remain unknown. In the absence of a crystallographic structure of OvCHT1, we developed a homology model of OvCHT1 using the currently available X-ray structures of human chitinases as templates. Energy minimization and molecular dynamics (MD) simulation of the model led to a high quality of 3D structure of OvCHIT1. A flexible docking study using closantel as the ligand on the binding site of OvCHIT1 and human chitinases was performed and demonstrated the differences in the closantel binding mode between OvCHIT1 and human chitinase. Furthermore, molecular dynamics simulations and free-energy calculation were employed to determine and compare the detailed binding mode of closantel with OvCHT1 and the structure of human chitinase. This comparative study allowed identification of structural features and properties responsible for differences in the computationally predicted closantel binding modes. The homology model and the closantel binding mode reported herein might help guide the rational development of novel drugs against the adult parasite of O. volvulus and such findings could be extrapolated to other filarial neglected diseases.     

Iterated Joining of Rooted Trees

For a given pair of trees T ₁, T ₂, two vertices ${v_1\in T_1}$ and ${v_2\in T_2}$ are said to be path-congruent if, for any integer k ≥ 1, the number p _k (v ₁) of paths contained in T ₁, of length k and passing through v ₁, equals the number p _k (v ₂) of paths contained in T ₂, of length k and passing through v ₂. We first provide polynomial constructions, and related examples, of pairs of non-isomorphic rooted trees ${T_{v_1}, T_{v_2}}$ with path-congruent roots v ₁, v ₂. Then we employ a joining operation between ${T_{v_1}, T_{v_2}}$ to get a tree J ₂ where v ₁, v ₂ do not necessarily belong to a maximal path. For any integer number m, the joining can be made such that the set {v ₁, v ₂} has distance m from the center Z(J ₂) of J ₂. By iterating the idea, an s-fold joining J _s can be considered, where the roots v ₁, . . . , v _s , s ≥ 2, are consecutive vertices of J _s . For s = 3 we give an explicit general construction where ${\{v_1, v_2, v_3\} \cap Z(J_3)=\emptyset}$ . On the other hand we prove that ${\{v_1,v_2,\ldots,v_s\} \cap Z(J_s)\neq\emptyset}$ for all s > 2, if ${T_{v_1}}$ and ${T_{v_s}}$ are isomorphic.     

Luminescence Spectra of Alkali Feldspars: Influence of Crushing on the Ultraviolet Emission Band

Grinding and milling processes lower the intensity of the ultraviolet emission band of alkali feldspars. The luminescence spectra of aliquots of natural transparent adularia from Saint Gothard, Switzerland, that were crushed at different energies, show the irreversible collapse of the UV 290 nm peak. Simultaneously, the 390 nm blue emission increases in accordance with the milling treatment, which reduces the presence of ionic charge compensators (Na⁺) and sensitizes the structure (producing [AlO₄]° centers).

The annihilation of the 290 nm UV peak by crushing could be linked with cracks-strain-exsolution features of the lattice of adularia. For this reason, the use of this 290 nm peak and energetic milling treatments in dating and dosimetric routines, should be rejected.     

Hybrid nanostructured materials with tunable magnetic characteristics

Novel titanium oxide (TiO₂) nanoparticles were fabricated via a modified propanol drying step. These nanoparticles were loaded with anti-cancer drug paclitaxel (PTX) to yield PTX-TiO₂ nanocomposites. The nanocomposites were characterized for their size and surface morphology employing nanoparticle tracking analysis (NTA) and scanning electron microscopy (SEM). The SEM images showed spherical particles with smooth surface and narrow size distribution of ~30–40 nm, which was also supported by NTA analysis data. The drug loading efficiency of the air-dried nanoparticles was observed to be ~63.61 % while those prepared through propanol-induced drying step showed ~69.70 %, thereby demonstrating higher efficiency of the latter. In vitro pH-dependent release of the loaded PTX was observed with higher release at acidic pH compared with physiological pH. Cell uptake studies suggested of time-dependent internalization of nanocomposites with significant improvement in uptake by increasing incubation time from 2 to 24 h, as evidenced by flow cytometry. Further, the cell viability as a measure of anti-cancer activity revealed that cell viability upon exposure to PTX only was 40.5 % while that of PTX-TiO₂ nanocomposite showed 21.6 % viability after 24 h, suggesting better anti-cancer efficacy of nanocomposites. Apoptosis studies revealed that cells treated with PTX-TiO₂ nanocomposites possessed more amount of apoptotic bodies as compared to those treated with PTX only.     

Microcavity-controlled single-molecule fluorescence.

We present for the first time cavity-controlled fluorescence spectra and decay curves of single dipole emitters interacting at room temperature with the first longitudinal mode of a Fabry-Perot microcavity offering a lambda/2-spacing between its silver mirrors. The spontaneous emission rate of individual dye molecules was found to be enhanced by the Purcell effect by up to three times compared to the rate in free space, in agreement with theoretical predictions. Moreover, our new microcavity design was found to provide long-term stability and single-molecule sensitivity under ambient conditions for several months without noticeable reduction of the cavity-Q value. We consider this as a significant advance for single-photon sources operating at room temperature.