Alginate Hydrogels: Methods of Preparation and Application in Tissue Engineering and Targeted Drug Delivery

Widespread interest and broad application of alginic acid and its salts in tissue engineering, regenerative medicine, biotechnology, and pharmaceutical industry is due to the several unique properties: biomechanical compatibility with living tissue, lack of toxicity, and bioabsorption capacity. This literature review analyzes effects of the anionic structure of the binary alginate copolymer on physicochemical properties of the resulting solutions and gels, as well as characteristics and conditions of their processing to obtain functional products for medical and biological applications. Dependence of functionality of the products on the ratio of M(β-D-mannuronate)/G(α-L-guluronate) blocks in the chain and on the source of alginate are also considered. Influence of the quantitative content of guluronic (G) acid blocks in the chain of linear alginate on its susceptibility to H⁺-induced gelation is described. A review of the mechanisms of gelling in the alginate solutions caused by formation of ionic, hydrogen, and covalent bonds is provided. In particular, attention is paid to the rate of dissolution of alginate salts, viscosity properties of the solutions based on them, and their dependence on ionic strength and pH. The mechanisms of interaction between both native and chemically modified alginates with various biologically active substances, drugs, and surfactants are considered. A detailed study of these processes opens new possibilities not only for obtaining dimensionally stable gels for tissue engineering structures, but also for obtaining systems designed for the controlled release of drugs.