A. A. Ol’khov

Structural-dynamic characteristics of matrices based on ultrathin poly(3-hydroxybutyrate) fibers prepared via electrospinning

Structural-dynamic analysis based on combined thermophysical and molecular mobility measurements via spin-probe ESR spectroscopy has been applied to films and fibrous matrixes based on poly(3-hydroxybutyrate). The dynamic behaviors of partially crystalline samples during deformation under conditions of electrospinning and cold rolling have been compared. The comparative results of the complex investigation of films and ultrathin fibers in the poly(3-hydroxybutyrate) matrix have shown that the electromechanical action leads to additional crystallization of the crystalline regions, spherulites, and lamellas in the polymer. The changes in the crystalline phase of the polymer are accompanied by an increase in the packing density of macromolecules in the intercrystalline space. With the use of the spin-probe ESR method, the effect of water and the oxidant ozone on the morphology of the amorphous phase of poly(3-hydroxybutyrate) ultrathin fibers has been determined. The measurements of the dynamics of spin-probe rotation in samples before and after cold rolling have shown that the additional orientation of poly(3-hydroxybutyrate) spherulites in a mechanical field results in stabilization of amorphous regions more resistant to the aggressive effects of ozone.

Nonwoven blend composites based on poly(3-hydroxybutyrate)–chitosan ultrathin fibers prepared via electrospinning

With the use of scanning electron microscopy, differential scanning calorimetry, and electron paramagnetic resonance, the structural–dynamic analysis of ultrathin fibrous matrixes based on poly(3-hydroxybutyrate) and blend composites of this polymer with chitosan is performed. It is shown that the addition of a small amount of chitosan causes change in the morphologies of the matrixes and leads to a marked increase in their melting enthalpies. It is found that the studied fibers contain amorphous regions with various morphologies. The dynamics of the spin probe TEMPO in these regions is investigated, and its change under the influence of increased temperature, an aqueous medium, and ozone is examined. The mechanism controlling the effects of chitosan, temperature, and an oxidative aggressive medium on the structuring of fibers is advanced.

Structure-Formation Features in Ultrathin Fibers of Poly(3-Hydroxybutyrate) Modified with Nanoparticles

Supramolecular structure formation of poly(3-hydroxybutyrate) ultrathin fibers prepared by electrospinning and the influence of low concentrations of silicon and TiO2 nanoparticles on the structure, physicomechanical and sorption properties, and resistance to thermal destruction and thermoand photo-oxidative destruction of non-woven fibrous material based on these fibers were studied. It was found that nanoparticles promoted the formation of thinner fibers with enhanced physicomechanical parameters and a structure that was more resistant to thermal and thermo- and photo-oxidative destruction and had a positive effect on the growth dynamics of mesenchymal stem cells.

Influence of drug on the structure and segmental mobility of poly(3-hydroxybutyrate) ultrafine fibers

Ultrafine fibers of biodegradable natural polyester such as poly(3-hydroxybutyrate) containing dipyridamole at various concentrations as a drug are prepared by the electrospinning method. It is shown by scanning electron microscopy that the absence of dipyridamole or its low concentrations (from 0 to 1%) provide the complex morphology of fibers composed of cylindrical regions 1–3 μm in diameter and thickened spindle-like ones 5–7 μm in average diameter. An increase in the concentration of dipyridamole in fibers leads to disappearance of the latter regions, with the morphology being cylindrical. The features of the crystalline and amorphous structures of poly(3-hydroxybutyrate) and its mixtures with dipyridamole are examined via DSC and EPR probe techniques. It is shown that the addition of dipyridamole to the poly(3- hydroxybutyrate) polymer matrix results in a sharp increase in the crystallinity and a slowdown of the molecular mobility in amorphous regions of ultrafine fibers. The heat treatment (annealing) of fibers leads to a sharp increase in the polymer crystallinity and a reduction of the segmental mobility in intercrystalline regions of the initial poly(3-hydroxybutyrate) fibers and those containing 1% of dipyridamole. All results including the influence of the drug concentration on the shape of fibers and their dynamic characteristics agree well with the thermal and physical parameters and should be used in the design of therapeutic systems for targeted and sustained delivery of bioactive compounds.

Thermal oxidation and degradation of poly-3-hydroxybutyrate nonwoven materials

Studies of the thermal degradation of poly-3-hydroxybutyrate samples in the presence and absence of oxygen demonstrate that, in the first case, the degradation begins sooner, but the decomposition temperature (maximum of degradation peak) changes only slightly for two different types of samples. It is shown that the activation energy for the thermal degradation of samples without access of oxygen is higher. According to the oxygen uptake curves at T = 150°C and an oxygen pressure of p = 600 Torr, the longest induction period is observed for film samples, whereas the maximum rate of oxidation, for fine nonwoven fiber samples. The kinetics of water uptake is investigated, which shows that the thermophysical characteristics of the samples alter after exposure to an aquatic environment.

Structural dynamic properties of nonwoven composite mixtures based on ultrafine tissues of poly(3-hydroxybutyrate) with chitosan

The structural dynamic parameters of ultrafine fibrous matrices of poly-3-hydroxybutyrate (PHB) and composite mixtures of PHB with chitosan were studied by differential scanning calorimetry, EPR spectroscopy, and scanning electron microscopy. The melting enthalpy of PHB fibers considerably increased when a small amount of chitosan was added. Amorphous regions with diverse morphology were found in the fibers under study. The dynamics of the TEMPO spin probe in these regions and its change in the fibers under the action of temperature, aqueous medium, and ozone was determined. The mechanism responsible for the effect of chitosan, temperature, and aggressive oxidating medium on the structure of ultrafine PHB fibers was suggested.

Electrospinning of biodegradable poly-3-hydroxybutyrate. Effect of the characteristics of the polymer solution

The effect of viscosity and electric conductivity of the polymer solution of poly-3-hydrobutyrate (PHB) on the formation of ultrafine fibers was studied. It was found that these parameters largely determine the geometrical parameters and morphology of the ultrafine fibers of PHB obtained by electrostatic forming. The increase in the viscosity of solutions at increased concentration and/or molecular mass of the polymer leads to an increase in the thickness uniformity of fibers and affects the diameter and diameter distribution width of the ultrathin fibers. Modification of the solutions with an ionogen electrolyte and hydrolytic agent (formic acid) decreases the initial molecular mass of the polymer and leads to increased viscosity of the system. The obtained fibers have found use in biomedicine, in particular, in the design of the elements of the locomotor system.

Effect of scaling factors on the kinetics of drug release from polyhydroxybutyrate-based film systems

The effect of various scale factors, such as the molecular weight of the polymer and the film thickness, on the kinetics of the release of drugs from polyhydroxybutyrate-based film systems is studied. Changes in the structure of the films undergoing hydrolytic degradation in biological environments are observed. It is found that, with increasing molecular weight and film thickness, the release of drugs from film matrices slows down.

Effect of the Concentration of the Spinning Solution on the Morphology and Properties of Nonwoven Poly-3-Hydroxybutyrate Fibers

The nonwoven fibrous materials of poly-3-hydroxybutyrate obtained by electrospinning were studied. The average diameter of the fibers was correlated with the polymer concentration in solution. As the concentration of poly-3-hydroxybutyrate in the spinning solution increased from 5 to 9 wt %, its crystallinity in the fibrous material increased by 4–5%, and the melting temperature changed insignificantly. A paramagnetic resonance study showed that the density of the amorphous phase of the fibers increased with the polymer concentration in solution. The resistance of the fibrous materials to aggressive environmental factors also increased.

Controlled-Release Matrixes for Drugs Based on Polyamide-Polyhydroxybutyrate Compositions

The transport properties of films based on poly(3-hydroxybutyrate) (PHB) and polyamide were studied. The factor responsible for the rate of controlled release of antiseptic from film compositions was the link between diffusion and PHB destruction. A model of this process and measurements of the coefficients of diffusion of an antiseptic are presented. The fundamental possibility of using these compositions as matrix systems for prolonged (more than one month) controlled delivery of a model pharmaceutical (the antiseptic furacillin) with constant and controllable release rates is discussed. The study matrixes could be used as wound coverings (dressings).