The review concerns the results of studies on the synthesis of polyelectrolyte coatings on charged surfaces. These coatings represent nanostructured systems with clearly defined tendency to self-assembly and self-adjustment, which is of particular interest for materials science, biomedicine and pharmacology. A breakthrough in this area of knowledge is due to the development and introduction of a new technique, so-called layer-by-layer (LbL) deposition of nanofilms. The technique is very simple, viz., multilayers are formed as a result of alternating treatment of a charged substrate of arbitrary shape with water-salt solutions of differently charged polyelectrolytes. Nevertheless, efficient use of the LbL method to fabricate nanofilms requires meeting certain conditions and limitations that were revealed in the course of research on model systems. Prospects for applications of polyelectrolyte layers in various fields are discussed. The bibliography includes 58 references.

Advances in the development of water-soluble nonstoichiometric polyelectrolyte complexes, which are characterized by high stability and can be involved in competitive interpolyelectrolyte reactions, are summarized and analyzed. The complexes remain stable over a wide range of external conditions (pH, ionic strength, temperature), but show a rapid, reversible and highly sensitive response to environmental changes outside this range by changing the phase state. The review considers methods of preparation and properties of nonstoichiometric polyelectrolyte complexes formed by interactions between oppositely charged polyelectrolytes. These reagents can be used for controlled modification of various surfaces, the preparation of soluble complexes functionalized by different molecules, the suppression and prevention of protein aggregation. The review briefly summarizes new types of soluble polyelectrolytes and polyelectrolyte complexes of different nature and with different structures, including biopolymers and dendrimers, suitable for solving problems in medicine and agricultural biotechnology. In order to evaluate the results achieved, there is a need to integrate and analyze the data on interpolyelectrolyte reactions, which are of most interest for a wide range of researchers. The bibliography includes 118 references.

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Polymer cryogels are very promising for producing functional materials. Their porous structure makes them indispensable for some areas of medicine, catalysis, and biotechnology. In this review we focused on methods for producing cryogels based on biopolymers, interpolyelectrolyte complexes of biopolymers, and composite cryogels based on them. First, the properties of cryogels and brief theoretical information about the production of cryogels based on biopolymers were considered. The second section summarizes the latest advances in the production of cryogels based on complexes of biopolymers and composite cryogels. The features of the synthesis and the factors affecting the final properties of materials were considered. In the final part the fields of application of cryogels of the considered types in biotechnology, catalysis and medicine were studied in detail. In biotechnology cryogels are used to immobilize molecules and cells, as a basis for cell growth, and as chromatographic materials for cell separation. In catalysis cryogels are used as a matrix for the immobilization of metal nanoparticles, as well as for the immobilization of enzymes. Biocompatible cryogels and their composites are widely used in medicine for bone and cartilage tissue regeneration, drug delivery, providing a long-term profile of drug release in the body.

Soil degradation is an important problem on a global scale. Suitable materials for its solution are interpolyelectrolyte complexes (IPEC) of biodegradable polymers. IPEC based on the oppositely charged pairs of biodegradable polymers-chitosan and sodium alginate (Ch-SA), chitosan and sodium carboxymethylcellulose (Ch-SC), and chitosan-gellan gum (Ch-GG) were prepared and studied using different physicochemical techniques (FTIR-spectroscopy, dynamic light scattering, conductometric and turbidimetric titration, and rheoviscometric measurements). Thin films of IPECs were prepared by pouring polymer solutions on a flat surface and subsequent evaporation of water. These films were tested using mechanical analysis. Young modulus of IPEC films increases in the following order: Ch-SC < Ch-GG < Ch-SA. Urban soil samples were sequentially treated with Ch solution and negatively charged polymer solution (SC, SA, GG). This technique of soil treatment leads to formation of IPEC within the soil surface layer. The soil structures and also soil treated with pure water and individual polymer solutions were also tested using mechanical analysis. It was found that the most durable structures are formed by IPEC based on Ch and SC. All the applied systems can be arranged in the following sequence in ascending order of the Young's modulus: GG < Ch < SA < Water < SC < Ch-GG < Ch-SA < Сh-SC. The IPEC based on biodegradable and biocompatible polymers of polysaccharide nature can be successfully used for soil structuring. These polymers significantly increase the mechanical strength of the soil without harmful effects to the environment. Among the studied systems, the Ch-SC system has the greatest structuring ability. These soil structuring agents can be applied for improving of the quality of urban and agricultural soils.