Biocompatible hydrogels based on chitosan,cellulose/starch,PVA and PEDOT:PSS with high flexibility and high mechanical strength

Fabricating mechanically strong hydrogels that can withstand the conditions in internal tissues is a challenging task. We have designed hydrogels based on multicomponent systems by combining chitosan, starch/cellulose, PVA, and PEDOT:PSS via one-pot synthesis. The starch-based hydrogels were homogeneous, while the cellulose-based hydrogels showed the presence of cellulose micro- and nanofibers. The cellulose-based hydrogels demonstrated a swelling ratio between 121 and 156%, while the starch-based hydrogels showed higher values, from 234 to 280%. Tensile tests indicated that the presence of starch in the hydrogels provided high flexibility (strain at break?>?300%), while combination with cellulose led to the formation of stiffer hydrogels (elastic moduli 3.9–6.6 MPa). The ultimate tensile strength for both types of hydrogels was similar (2.8–3.9 MPa). The adhesion and growth of human osteoblast-like SAOS-2 cells was higher on hydrogels with cellulose than on hydrogels with starch, and was higher on hydrogels with PEDOT:PSS than on hydrogels without this polymer. The metabolic activity of cells cultivated for 3 days in the hydrogel infusions indicated that no acutely toxic compounds were released. This is promising for further possible applications of these hydrogels in tissue engineering or in wound dressings.

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A computational investigation of the electronic properties of Octahedral Al n N n and Al n P n cages (n = 12, 16, 28, 36, and 48)

Density functionla theory (DFT) calculations are performed to characterize geometric and electronic features of the octahedral Al _n N _n and Al _n P _n cages (n = 12, 16, 28, 32, and 48). Toward this aim, ¹⁵N, ²⁷Al, and ³¹P chemical shielding (CS) tensors as well as natural charge analyses are calculated for the optimized structures. CS parameters detect three distinct electronic environments for atoms within the Al _n N _n and Al _n P _n cages. The chemical shifts of N2 sites belonging to a hexagon and surrounded by three hexagons and a square obtained are different from those of N3 sites belonging to a hexagon that is surrounded only by hexagons—due to different curvatures exerted at the sites with different local structures. In addition, there is an increasing tendency in the Δσ values of the three local structures, Δσ (N1) > Δσ (N2) > Δσ (N3), N1 sites belonging to four-membered rings. The chemical shieldings of those Al and P sites belonging to a hexagon that is surrounded only by hexagons in the cages (360.7–366.7 and 496.5–514.7 ppm) are close to those previously reported for AlP nanotubes. Three distinct electrostatic environments around the N, Al, and P nuclei are also confirmed by the calculated natural charges. It should be noted that the positively charged Al atoms on the cages turn out to be the available sites for adsorption of H2 molecules.     

Preparation and Characterization of Functionalized Polyaniline-Based Nanocomposite as an Antibacterial Agent

Polyaniline-co-phenylenediamine (PAn/PDA) nanocomposite has been prepared in the aqueous medium using sodium dodecyl benzene sulfonate (DBSNa) and hydroxypropylcellulose (HPC) as a surfactant. The tests used in this research to characterize the products were SEM, TEM, FTIR, UV–Visible and TGA for morphology, particle size, chemical structure and stability. The results confirm that the spherical nanocomposites (40–90 nm) were formed with high thermal stability. It is shown in the results that the physicochemical properties of poly(alkyl substituted anilines) are depended on the substituent groups that are bonded to N-position. The prepared nanocomposites were then tested for the antibacterial properties against three pathogenic strains. The antibacterial properties of nanocomposites were investigated by disk diffusion, minimum inhibitory concentration (MIC), minimum bactericidal concentrations (MBC), and bactericidal kinetic methods. The disk diffusion result indicated that the diameter of the inhibition zones of PAn/PDA–HPC nanocomposite was 9, 11, and 10 mm against E. coli, P. aeruginosa, and S. aureus respectively. It was found that the value of MIC of PAn/PDA–HPC nanocomposite against E. coli, P. aeruginosa and S. aureus were 2.5, 1.25 and 2.5 mg/mL respectively. The evaluation results revealed the PAn/PDA–HPC nanocomposite exhibited excellent inhibitory activity against both gram-negative and gram-positive bacteria.     

Temperature dependent electrophysical characteristics of GaAs-polymer composite varistors

A composition of GaAs-polymer tiny particles was pressed at a temperature of 130 °C and a pressure of 60 MPa and its current–voltage characteristic was studied. The result shows that the prepared disk has varistor behavior and can therefore be used to protect circuits from low overvoltage transients higher than 62 V. Temperature dependence of current-voltage characteristic and the electrical conductivity of the sample were investigated in the temperature range of 25–100 °C. It has been found that increase in temperature results in lower breakdown voltage and nonlinearity coefficient. At high temperatures, nonlinearity in the I–V characteristic of sample disappears and the conductivity becomes Ohmic in nature. The sample has hysteresis which decreases through increase in temperature. Annealing effect on leakage current and breakdown voltage was both investigated and analyzed using SEM micrographs. Finally, the electrical bandgap of the sample was measured.     

Chirp reduction in three-cavity semiconductor laser diodes

The oscillation frequency shift ratio (OFSR) of a three-cavity coupled laser diode, which is caused by refractive index changes due to current modulation and temperature variation, has been investigated. It is found that the OFSR is significantly reduced by using a laser with an AR coated facet and a high external-mirror reflectivity, in addition to large external cavity lengths. Also, compared with an external cavity laser, the three-cavity laser has a smaller OFSR provided that the external cavities' reflectivities r₀ and r₃, are not identical (that is, r₃ > r₀). The analysis indicates that the structural parameters affect the OFSR of the three-cavity laser, which was shown to have a high longitudinal mode discrimination¹.     

Electrode modification and the response of the acoustic shear wave device operating in liquids

The effect of electrode polarity, geometry, and stray capacitance on the performance of the thickness-shear mode acoustic wave sensor operating in electrolytes and solutions of biomolecules has been studied. In contrast to the well-known mass-based response of the device operating in the gas phase, the response in a liquid is governed by several factors including acoustoelectric and fringing field effects, which are known to be active at the edges of the electrodes. In order to investigate and utilize these effects, we modified the electrode geometry to increase the edge length, which, in turn, raises the sensitivity of the device. These changes which constituted either complete coverage of the back of the device with electrode material, or the removal of disks and lines from the electrode surface, resulted in a two to three times enhancement of sensor response. Such modifications that extend device sensitivity beyond the electrode area to the quartz region of the sensing structure also provide a better surface for the immobilization of various probes. We verified the enhancing ability of the modified electrodes for the case of adsorption of the protein avidin and neutravidin, followed by their affinity reactions with biotinylated biomolecules. It was found that the active electrode in contact with electrolyte exhibits a sensitivity of about twice that of the grounded electrode. The existence of stray capacitance around the cell was confirmed by shielding the cell assembly with a bath of concentrated KCl solution. This shielding effect was measured to be about 25-60 Hz in series resonant frequency and -1000 Hz in parallel resonant frequency.     

(SiH)48X12 Heterofullerenes with the Group III and V Dopants: A DFT Prediction of Geometry,Stability, and Electronic Structure

We have applied DFT calculations to devise some (SiH)₄₈X₁₂ heterofullerenes with replacing of 12 Si–H units with a series of the group III and V dopants, P, N, As, B, Al and Ga, with the configuration of one dopant per pentagonal ring. Our results indicate that binding energies of heterofullerenes with group III dopants are smaller than those of heterfullerenes with group V dopants. Density of state obtained for the systems indicate a distinct change near the valence level compared to that of Si₆₀H₆₀, and a local energy level appears after the doping. (SiH)₄₈X₁₂ heterofullerenes with the group III and V dopants are composed of positively and negatively charged dopant atoms, each of which is surrounded by opposite charged Si atoms. The electrophilicity values of (SiH)₄₈X₁₂ heterofullerenes, except for (SiH)₄₈N₁₂, are greater than that of their parent. Because of the higher electronegativity of group V elements and electron transfer from the cages to the group V dopants, electrophilicity values for the (SiH)₄₈X₁₂ heterofullerenes with the group V dopants are always smaller than those of heterofullerenes with the group III dopants.     

Theoretical Investigation of Mono and Multiply Oxygenated C70 Fullerenes

We have applied DFT calculations to investigate atomic arrangements of fullerene oxides, C₇₀O _n with n = 1, 5, 15, 20, and 25. The oxidation reaction energies are generally exothermic. In the case of C₇₀O, the most stable configuration is the one in which the oxygen atom is chemisorbed on the C–C bond at the equatorial belt of fullerene with oxidoannulene like structure. In highly oxygenated fullerenes, the addition of oxygen atoms on the [6, 6] bonds near the pole area of the C₇₀ leads to lower values of reaction energies. Among these, C₇₀O₂₀ with three oxygen atoms adsorbed on a benzenoid ring yields the most energetically favorable configuration. Different positions of the oxygen atoms on the surface of the mono oxygenated fullerenes lead to significant differences in their ¹⁷O NQR parameters. Meanwhile, the ¹⁷O NQR parameters of the highly oxygenated fullerenes divide their oxygen nuclei into a few groups. For example, the electric field gradient tensor for oxygen atoms chemisorbed on the [6, 5] bonds with larger η values becomes considerably asymmetric in comparison to those chemisorbed on the [6, 6] bonds. These are also reflected in the calculated natural charges of oxygen atoms.     

Exploring the electronic and magnetic properties of zigzag and armchair BC2N nanotubes: a DFT study

A density functional study is performed to investigate the electronic and magnetic properties of zigzag and armchair BC₂N nanotubes based on the ¹³C, ¹⁵N, and ¹¹B NMR parameters and natural charge analysis. We considered three types of zigzag nanotubes, ZZ-1, ZZ-2, and ZZ-3 (n, 0) with n = 3, 4, and 5, as well as two types of armchair nanotubes: AC-1 and AC-2 (n, n) with n = 3 and 4. The obtained results indicate the divisions of the electrostatic environments around C nuclei into a few layers, consistent with the calculated natural charges on C atoms. A good correlation is seen between the layers of chemical shielding isotropy as well as anisotropy, σ _iso, and Δσ, and the five local structures around carbon atoms. Successive BN units lead to larger ¹⁵N σ _iso values (96.5–105.5 ppm) in comparison with the individual BN units (74.3–92.0 ppm in the ZZ-2(n, 0) and 47.4–61.7 ppm in the ZZ-3(n, 0)). Slight differences in the values of ¹¹B σ _iso clarify diminutive diversity in the electron densities of boron nuclei, while Δσ values indicate the more apparent range of changes.     

A comparative thermogravimetric study of polymers designed as dry-developing photoresists

We report a thermogravimetric study of the uncatalyzed and photo-acid-catalyzed decomposition of a series of polyformals and polycarbonates. Some of these polymers have previously been proposed as solventless photoresists. Such polymers should decompose at much lower temperatures when heated in the presence of strong acid than when heated in the absence of acid. In addition, decomposition should lead only to volatile break-down products. We found that most of these polymers underwent clean uncatalyzed thermal decomposition. When heated in the presence of acid, the onset of thermal decomposition occurred at much lower temperatures, as expected, but was accompanied by formation of significant amounts of non-volatile product. We also found that the extent of acid-catalyzed cross-linking (i.e., formation of non-volatile product) in the benzylic polyformals was greater than that for benzylic polycarbonates.