Currently, technologies based on the use of electrode systems implanted in the head interacting with the human brain are under active development. Such systems are used both for stimulation of the brain in various diseases and as full-fledged neural interfaces. Electrodes in this case are one of the key elements, since they provide contact with the nervous tissue. Recently, considerable attention has been paid to polymer electrodes and, in particular, hydrogels due to the fact that they have mechanical properties close to body tissues and can carry various functional molecules. At the same time, the electrical conductivity of polymer electrodes is lower than that of metal or carbon materials. In this regard, this work provides an overview of publications in this area and notes the most promising trends. Also, based on the publications reviewed, it is noted that an important task for such electrodes remains their miniaturization. It is concluded that despite their shortcomings, electrodes based on polymer hydrogels are an extremely promising system for creating invasive neural interfaces.

The work presents the results of testing nonwoven fibrous matrices based on poly-L-lactide modified with biopolymers (chitosan and collagen) under in situ stretching in a scanning electron microscope (SEM) chamber operating in the environmental mode. Matrix stress-strain curves and SEM images are obtained simultaneously during uniaxial stretching of the matrices until rupture. The change in the mechanical characteristics of the matrices during degradation is studied depending on the time of their incubation in the culture medium.

The adhesion, proliferation, differentiation, and other types of interaction of a cell culture with synthetic biocompatible matrices completely depend on the type of cells, as well as on the structure, filling, and surface of the matrix itself. The results of studying the proliferation of HEK293T cells on polylactide matrices of various architectures are presented. An estimate of the rate of cell proliferation is obtained for oriented and nonoriented spongy and nonwoven fibrous matrices, as well as composite polylactide matrices with collagen and chitosan.

The architecture and mechanical properties of synthetic biocompatible scaffolds used in modern tissue engineering are the most important characteristics in the manufacture of medical implants, and the evolution of their mechanical properties during degradation is of particular interest. This paper presents the results of in situ mechanical tests in a scanning-electron-microscope chamber of spongy oriented and nonoriented polymer matrices of various compositions. The stress-strain curves for the matrices under uniaxial compression are obtained, and the mechanical properties of the materials are analyzed depending on their morphological features, modification with biopolymers, and degree of degradation. The results of mechanical tests are compared with images obtained in a scanning electron microscope at different stages of compression.

The adhesive properties of scaffolds, which primarily depend on the chemical and structural features of their surface, play an important role in the tissue engineering. The cell adhesion of dissociated primary neuronal culture to isotropic and anisotropic nonwoven and sponge polylactide scaffolds was studied by fluorescence and environmental scanning electron microscopy. Neurons extracted from neonatal mouse brain showed improved adhesion on all types of scaffolds after the plasma treatment. The most pronounced effect was observed for non-oriented scaffolds.

Microbial fuel cells are beginning to be widely used to solve various applied problems; in the last decade, considerable attention has been paid to photobiofuel cells (PBFCs), in particular, biofuel cells with a photocathode. Information on the current state of research in the field of PBFCs is presented. The application of these devices, namely, systems for treating various types of wastewater with electricity generation, power-supply systems for distributed sensors, and systems for urban and park illumination, is shown. Special attention is given to ways of PBFC integration into existing surface wastewater-treatment systems and urban systems such as rain gardens. The main materials used for PBFC electrodes and membranes are considered. It is shown that various types of carbon materials from graphene and carbon nanotubes to activated carbon are widely used, since they generally meet the requirements for PBFC electrodes. It is noted that it is necessary to develop methods for analyzing the efficiency of the immobilization of microorganisms over the entire electrode, but not for its individual sections. PBFCs are a promising technology that will be widely used in urban economy in the near future.

Today there are a lot of areas where the use of soft robotics is necessary. Nowadays the main task in this field is to find a device that sets a soft robot in motion. In this work we propose the prototype of a mechanism that works by stimulating muscle cells and can act as an actuator. The possibility of using low-power biofuel elements as a battery for the actuator is also investigated. A microbial biofuel cell is selected as the most suitable for this field of application. During assembly of the biofuel cell, the materials of the electrodes and biofilms are explored, and the voltages produced by the cell are measured. In addition, we develop and assemble a board that generates a pulse-width-modulation (PWM) signal to stimulate muscle cells with a pulse which has certain characteristics. The attained results make clear the fact that a low-power energy source such as a biofuel cell can be successfully used to stimulate muscle cells in the development of soft robots.

Адгезивные свойства матриксов, преимущественно зависящие от химических и структурных особенностей их поверхности, играют важнейшую роль в тканевой инженерии. С помощью флуоресцентной и растровой электронной микроскопии в режиме окружающей среды исследована адгезия клеток диссоциированной нейрональной культуры на изотропных и анизотропных нетканых и губчатых матриксах из полилактида. Нейроны, полученные из головного мозга новорожденных мышей, демонстрировали улучшенную адгезию на матриксах всех типов после обработки плазмой, при этом наиболее выраженный эффект наблюдался на неориентированных матриксах.

The structural and mechanical features of synthetic matrices are examined using the developed in situ mechanical testing setup in a scanning-electron-microscope chamber. The mechanical behavior is correlated with direct visualization of the structural changes occurring during the deformation of oriented and nonoriented sponges and nonwoven fiber polylactide-based materials, which allows a detailed characterization of the structural deformation processes in these materials.

A production technology for conductive materials with different morphologies is developed: flat (films) and porous (sponges) composites suitable for use as the anode of a biofuel cell. Chitosan is used as a polymer matrix, and carbon-black particles with an average size of aggregates of 17 μm act as a conductive component. The morphological, electrically conductive, and mechanical characteristics of the composites are studied. Based on the functional characteristics, the optimum concentration of the filler in the composite materials for their use as the electrode of a microbial biofuel cell is 5 wt %.

This paper highlights the idea of creating highly porous composite materials for osteogenesis purposes based on chitosan with various functional fillers: reduced graphene oxide (rGO) and tricalcium phosphate (TCP). RGO filler is a carbon based electrical conductor with a high aspect ratio, therefore it is preferred for growth of osteoblasts populations with concomitant electrical stimulation. TCP is the main building block of bone tissue; hence composites filled with it can be used to accelerate the process of osteosynthesis. This paper considers the aspects of the functional agents influence on the morphological, electrically conductive, and mechanical characteristics of composites based on chitosan.

The effects of plasma treatment on the surface roughness and hydrophility of polymer materials used as biodegradable scaffolds (polylactide films, sponges, and nonwoven fibrous sheets) have been studied. Two methods have been used for quantitative estimation of changes: three-dimensional reconstruction of the scaffold surfaces using scanning electron microscopy (SEM) and BET physical adsorption analysis. Proceeding from the experimental results, it is established that plasma treatment forms nano- and micropits on the sample surface and thus increases its hydrophility (moreover, the surface morphology can be varied by changing the treatment duration). It is shown that plasma treatment is an efficient method for controlled increase in the roughness of polymer materials, which can lead to enhancement of adhesion and proliferation of cells.