This review is focused on current state-of-the-art research on electroactive-based materials and their synthesis, as well as their physicochemical and biological properties. Special attention is paid to pristine intrinsically conducting polymers (ICPs) and their composites with other organic and inorganic components, well-defined micro- and nanostructures, and enhanced surface areas compared with those of conventionally prepared ICPs. Hydrogels, due to their defined porous structures and being filled with aqueous solution, offer the ability to increase the amount of immobilized chemical, biological or biochemical molecules. When other components are incorporated into ICPs, the materials form composites; in this particular case, they form conductive composites. The design and synthesis of conductive composites result in the inheritance of the advantages of each component and offer new features because of the synergistic effects between the components. The resulting structures of ICPs, conducting polymer hydrogels and their composites, as well as the unusual physicochemical properties, biocompatibility and multi-functionality of these materials, facilitate their bioapplications. The synergistic effects between constituents have made these materials particularly attractive as sensing elements for biological agents, and they also enable the immobilization of bioreceptors such as enzymes, antigen-antibodies, and nucleic acids onto their surfaces for the detection of an array of biological agents. Currently, these materials have unlimited applicability in biomedicine. In this review, we have limited discussion to three areas in which it seems that the use of ICPs and materials, including their different forms, are particularly interesting, namely, biosensors, delivery of drugs and tissue engineering.

This critical review covers the use of carbon nano-onion (CNO) based materials for electrochemical capacitor (EC) electrodes. The performance of CNO capacitors is reviewed in detail and compared to the results obtained using different carbon nanostructures. The physico-chemical vs. electrochemical properties of CNOs are discussed. Their advantages, challenges and applications, especially in EC electrodes, are discussed in detail through an extensive analysis of the literature. Exohedral carbon nano-onions are much less limited by mass transfer kinetics; they show low resistance and can operate over a wide voltage and temperature window, at very high charge–discharge rates with almost unlimited cyclabilities. Although carbon nano-onions make excellent supercapacitor electrode materials, many challenges still remain, particularly to characterize and understand the physical, chemical, and electrochemical interactions within multicomponent systems that contain CNOs. The full potential of carbon nano-onions as electrochemical power sources has not been realized yet, but as outlined in this review, the future looks very promising.

This review is an extensive evaluation and essential analysis of the design and formation of hydrogels (HGs) for drug delivery. We review the fundamental principles of HGs (their chemical structures, physicochemical properties, synthesis routes, different types, etc.) that influence their biological properties and medical and pharmaceutical applications. Strategies for fabricating HGs with different diameters (macro, micro, and nano) are also presented. The size of biocompatible HG materials determines their potential uses in medicine as drug carriers. Additionally, novel drug delivery methods for enhancing treatment are discussed. A critical review is performed based on the latest literature reports.