Influence of the structure and morphology of ultrathin poly(3-hydroxybutyrate) fibers on the diffusion kinetics and transport of drugs

Ultrathin fibers of a biodegradable polymer poly(3-hydroxybutyrate) with an encapsulated drug (dipyridamole, 0–5% of poly(3-hydroxybutyrate) mass) are obtained by electrospinning. Introduction of the drug substantially affects the geometric shape and crystallinity of individual filaments as well as the total porosity of the fibrillar film on their basis. As follows from the SEM data, in the absence of the drug or at its low concentration (<3%), poly(3-hydroxybutyrate) fibers appear as ellipse-like fragments alternating with cylindrical ones. At a higher content of the drug (3–5%), the abnormal ellipse-like structures are practically absent and the fiber acquires the cylindrical shape. A set of morphological and crystallinity characteristics of the fibers determines the absorption of water and the rate of the diffusion transport of the drug as well as the corresponding profiles of its controlled release. A simplified model of drug desorption from the fibrillar film is advanced which considers two sequential stages of the process: (i) diffusion of the drug in the polymer fiber with coefficient D _f ~ 10^–12 cm²/s and dimeter φ_f ~ 2–4 μm and (ii) transport of the drug in the interfibrillar porous space filled by solvent with diffusion coefficient D _w = 5.5 × 10^–6 cm²/s. Using the characteristics of porosity, crystallinity, and geometry of the fibers and diffusion effective coefficients D _eff calculated from the profile of drug release, it is shown that the limiting stage of the transport of the drug is its diffusion in the volume of the cylindrical fiber. The model makes it possible to turn from the experimental values of D _eff to partial diffusion coefficients D _f and to calculate the kinetic profile of drug release with allowance made for the above-listed factors.     

Synthesis of New Substituted Thioglycolurils via a Tandem Hydrazone Formation‐ Ring Contraction Reaction

A series of new (E)‐1,3‐dialkyl‐4‐((hetarylmethylidene)amino)‐5‐thioxohexahydroimidazo[4,5‐d]imidazole‐2(1H)‐ones (thioglycolurils) was synthesized via tandem hydrazone formation—ring contraction reaction of 5,7‐dialkyl‐3‐thioxoperhydroimidazo[4,5‐e]‐1,2,4‐triazin‐6‐ones with heteroaromatic aldehydes.     

Elastic properties of a magnetic fluid with an air cavity retained by levitation forces

The paper describes the process of an air cavity rising in a magnetic fluid filling a tube with a bottom, transport, and retention of the cavity by magnetic levitation forces. The elastic and dissipative properties of a vibratory system with an inertial element that is a column of a magnetic fluid over an air cavity are considered. The possibility of using a transported air cavity as a movable reflector for a sound wave is evaluated.     

Synthesis and investigation of organosilicon dendrimers based on octavinylsilsesquioxane and sulfenyl chlorides of metal acetylacetonates

The addition of sulfenyl chlorides of metal acetylacetonates to octavinylsilsesquioxane was studied. The addition was shown to proceed at four of the eight vinyl groups of the octavinylsilsesquioxane, without the formation of cross-linked polymers. This allowed us to synthesize with high yields new non-functianalized and functianalized dendrimers based on octavinylsilsesquioxane and the sulfenyl chlorides of metal acetylacetonates.     

Investigation of physico-chemical properties and structural parameters of diene-vinyl aromatic thermoplastic elastomers as a polymeric base of adhesive compositions

Adhesion and mechanical properties of vinyl aromatic thermoplastic elastomers on the Russian market were studied. Significant differences between the materials were shown that are due to differences in the chemical natures and structural parameters of block copolymers.     

Elasticity of a magnetic fluid in a strong magnetic field

Complex measurements of the following elastic-magnetic parameters of a magnetic fluid suspended by magnetic levitation within a horizontal tube in a strong magnetic field were performed: the oscillation frequency and decay coefficient; the static, ponderomotive, and dynamic elasticity coefficients; the fluid displacement under hydrostatic pressure; magnetization curve; and the magnetic field strength and gradient. Calculations based on a model of ponderomotive elasticity with correction for the resistance of a viscous fluid in motion and on the fluid column displacement for two magnetic fluid samples agree well with the experimental magnetization curve. The discussed technique holds promise for research into magnetophoresis and nanoparticle aggregation in magnetic colloids.     

Influence of the Solvent on the Formation of CNR/BNR Polymer Blends

Structural dynamic analysis combining IR spectroscopy, DSC, and EPR spectroscopy is applied to studying films based on chlorinated natural rubber (CNR), butadiene nitrile rubber (BNR), and blends thereof. The influence of various solvents, such as methyl ethyl ketone (MEK), ethyl acetate (EA), methyl acetate (MA), and acetone (A), on the structure and molecular dynamics (τ) of CNR/BNR polymer films is examined. The strongest changes in the molecular mobility (τ) and the glass transition temperature (T_gt) relative to those of the starting materials are observed for the 50: 50% CNR/BNR blends prepared using all the solvents (except for acetone, the maximum values of τ for which is observed at a ratio of CNR: BNR = 80: 20%), which can be explained by the inversion of phases in the blends. Annealing at 140°С causes an increase in the correlation time of the probe, and, consequently, a decrease in the molecular mobility, which is due to the intermolecular crosslinking of the components.     

Surface Morphology and Structure of Plasma Coatings

Technical Physics - Specific features of the structure formation in rapidly quenched high-cobalt alloy coatings formed by plasma sputtering have been investigated. The structural state of the...