Tatiana N. Popyrina

This review provides a comprehensive analysis of the current state of electroadhesion research and the development of electroadhesive systems. Over one hundred scientific references were analyzed, covering the theoretical frameworks and modeling of electroadhesion, electroadhesive manufacturing technologies, factors influencing electroadhesive interactions, and the development prospects and applications of electroadhesion. The necessity for a detailed molecular-level investigation into polymer structures is substantiated to improve the accuracy of engineering forecasting and the integration of this technology in robotics, medicine, and autonomous systems based on triboelectric nanogenerators.

Surface‐selective laser sintering (SSLS) allows fabrication of 3D structures with a well‐defined architecture via sintering of polymeric microparticles. In this work, polylactide microparticles stabilized with alkylated chitosan were prepared via an oil‐in‐water emulsion solvent evaporation method and used as starting material to produce 3D structures via SSLS. A Box–Behnken experimental design was employed to optimize three microparticle fabrication parameters– stirring speed (300–900 rpm), alkylated chitosan concentration (0.5–1.5 wt.%), and stirrer type (two‐, three‐, or four‐blade)—aiming to maximize the yield of the target fraction (0–200 μm). Only the alkylated chitosan concentration exhibited a statistically significant effect on the target fraction yield ( p = 0.0023), while stirring speed and stirrer type showed a nonsignificant tendency but did not reach the significance level ( p > 0.05). Under optimal conditions, the target fraction yield reached 32.58 ± 0.49 wt.%, representing a 1.8‐fold increase compared to the non‐optimized conditions (18 wt.%). The optimized microparticles exhibited a regular spherical shape, smooth nonporous surface morphology, and a narrow monomodal size distribution with a mean diameter of 63 ± 24 μm and a Span of 0.95. The particles possessed a bulk density of 213.7 ± 1.2 kg/m ³ , a theoretical specific surface area of 0.0904 ± 0.0451 m ² /g, and a water adsorption capacity of 0.0375 ± 0.0037 g/m ² . The prepared microparticles were successfully utilized in SSLS to fabricate 3D structures, confirming their suitability as raw material for this process.

By complexation of chitosan obtained by a mechanochemical method in a twin-screw extruder with dextran sulfate in different ratios (1 : 1, 1 : 2, and 2 : 1), nanoparticles were formed and studied by dynamic laser light scattering to evaluate their hydrodynamic radius and zeta potential. The obtained nanoparticles were used as a filler for chitosan-based films, and the effect of their concentration (from 0 to 5%) on the physical and mechanical characteristics of the films, as well as on their antimicrobial activity against the gram-positive bacterium Bacillus subtilis, the gram-negative bacterium Escherichia coli, and the filamentous fungus Aspergillus niger, was evaluated. It was found that the properties of the films depended on the concentration of the nanoscale filler, and the best values of deformation and strength characteristics, opacity, and antibacterial activity were achieved with the highest content of nanoparticles. To summarize, the study employed the properties of chitosan, such as the capacities of film formation and complexation, to demonstrate its potential for production of packaging materials with improved functional characteristics with minimal resource costs.

Modification of the chitosan chemical structure by grafting hydrophobic fragments makes it possible to synthesize derivatives with amphiphilic properties. These derivatives were used as emulsifiers in the aqueous phase during the production of polylactide microparticles via the oil/water solvent evaporation technique. The application of the derivatives allows to achieve a high yield of the microparticles and to provide a hydrophilic coating on the surface of polylactide microparticle. The chitosan‐coated polylactide microparticles were analyzed in terms of mean size, size distribution, surface, and internal morphology. The ability of the obtained microparticles to be used as a starting component for the fabrication of 3D materials through the surface‐selective laser sintering was evaluated, and the optimal parameters for the process have been determined.

In this paper, we describe mechanochemical approach as an environmentally friendly method to obtain chitosan and gallic acid derivatives. Covalent cross-linking with a polysaccharide is one way to stabilize antioxidants and improve their bioavailability. Since gallic acid is a solid compound with limited solubility and a high melting point (220-240 °C), it was of interest to conduct its interaction with chitosan using solid-state synthesis technique under shear deformations. The experimental conditions were selected using a pilot twin-screw extruder designed for processing solid dispersions. The insertion of gallate groups onto the polymeric backbones was confirmed by 1H NMR, FTIR and UV–vis analyses. Dynamometry was used for study of rheological properties. Depending on the synthesis conditions, the amount of bound gallic acid was more than 600 mg per 1 g of chitosan. It was found that gallate groups are predominantly linked to chitosan via salt bonds. Carrying out the process at a moderate temperature (100-120 °C) led to the formation of amide bonds between chitosan and gallic acid. In contrast to the physical mixing of components, the resulting products swelled well and partially dissolved in water, and tended to form aggregates with an average size of 206±36 µm in aqueous media.

Получение и исследование твердых дисперсий ацикловира с крахмалом и карбоксиметилцеллюлозой Получение и исследование твердых дисперсий ацикловира с крахмалом и карбоксиметилцеллюлозой

The introduction of hydrophilic fillers in the matrix of hydrophobic thermoplastic polymers is a complicated issue, due to thermodynamic incompatibility of the components and poor adhesion properties. These complications are the most pronounced in the case of a hydrophilic polymer which cannot melt without decomposition (as polysaccharides) used as the filler. In this study, we have taken advantage of the solvent-free extrusion method both to modify the chitosan chemical structure in order to impart amphiphilic properties and to mix the obtained derivatives with polyethylene. The influence of the processes parameters, the presence of plasticizer, and the filler content on the thermal and mechanical properties of the composite film materials as well as their morphology has been investigated. It has been found that the introduction of hydrophobic fragments in the structure of chitosan insignificantly improved the mechanical properties of the materials in comparison with the pristine polysaccharide. A more significant effect has been caused by simultaneous introduction of the plasticizer, affording the materials with uniform morphology and improved plasticity.

Solid dispersions based on acyclovir and polysaccharides (starch and sodium carboxymethylcellulose) have been prepared by means of mechanochemistry. Mechanical co-processing of the drug and the polymers in a ball mill, an extruder, and a pulse mechanical action cell has led to amorphization of acyclovir, followed by its uniform distribution in the polymer matrix. A set of the IR and UV spectroscopy, DSC, and X-ray diffraction analysis data has revealed the presence of intermolecular interactions between the polysaccharide matrix and the drug. The obtained materials can be considered as potential system for further investigation as solid formulations of acyclovir with improved bioavailability.

In the current study, novel matrices based on chitosan-g-oligo (L,L-/L,D-lactide) copolymers were fabricated. In particular, 2D films were prepared by solvent casting, while 3D macroporous hydrogels were obtained by lyophilization of copolymer solutions. Copolymers of chitosan (Chit) with semi-crystalline oligo (L,L-lactide) (Chit-LL) or amorphous oligo (L,D-lactide) (Chit-LD) were obtained by solid-state mechanochemical synthesis. The structure of the hydrogels was found to be a system of interconnected macropores with an average size of 150 μm. In vitro degradation of these copolymer-based matrices was shown to increase in the case of the Chit-LL-based hydrogel by 34% and decrease for the Chit-LD-based hydrogel by 23% compared to the parameter of the Chit sample. Localization and distribution of mouse fibroblast L929 cells and adipose tissue-derived mesenchymal stromal cells (MSCs) within the hydrogels was studied by confocal laser scanning microscopy (CLSM). Moreover, cellular response, namely cell adhesion, spreading, growth, proliferation, as well as cell differentiation in vitro were also evaluated in the hydrogels for 10–14 days. Both the Chit-LL and Chit-LD matrices were shown to support cell growth and proliferation, while they had improved swelling compared to the Chit matrix. Osteogenic MSCs differentiation on the copolymer-based films was studied by quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR). Maximal expression levels of osteogenesis markers (alkaline phosphatase (ALPL), bone transcription factor (Runx2), and osteopontin (SPP1) were revealed for the Chit-LD films. Thus, osteodifferentiation was demonstrated to depend on the film composition. Both Chit-LL and Chit-LD copolymer-based matrices are promising for tissue engineering.