A current overview of polyions and polyelectrolyte complexes for pharmaceutical applications with special emphasis to brain purposes

Abstract Background Polyelectrolyte complexes (PECs) are formed through the electrostatic interactions between oppositely charged polyions in aqueous solutions. These systems have garnered significant interest in both academic and industrial pharmaceutical research due to their potential applications in drug delivery. PECs present a promising drug delivery platform by enabling environmentally friendly preparation methods under mild conditions, which also facilitate large-scale production. Their ability to encapsulate and protect various therapeutic agents, including small synthetic drugs and biomacromolecules, makes them valuable in innovative pharmaceutical formulations. Although PECs are relatively simple formulations, their composition plays a critical role in determining their final physicochemical properties, such as size, surface charge, shape, entrapment efficiency, and drug release profile. These properties must be carefully tailored for specific applications. Area covered This review discusses the most commonly used polycations and polyanions for the preparation of PECs and their pharmaceutical applications, with special attention to brain-related purposes. Specifically, it focuses on PECs designed for brain delivery, brain tissue regeneration, and brain matrix in-vitro models. Expert opinion PECs represent a versatile and innovative approach to drug delivery; however, their full potential is still under investigation. A deeper understanding of how formulation parameters influence their performance is essential for optimizing their application in targeted drug delivery. In particular, PECs hold great promise for treating brain-related conditions, including therapies for neurological diseases, brain tissue regeneration, and the development of in-vitro brain matrix models. Continued research in this area will be crucial for unlocking new therapeutic possibilities and improving drug delivery strategies for neurological applications.