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This review focuses on the physicochemical characterization of polyion complex (PIC) micelles, particularly addressing the critical molecular factors to determine the self-assembly scheme of double-hydrophilic block copolymers composed of charged and non-charged segments into micelle structures. The process of PIC micelle formation provides new insights on the block copolymer self-assembly in thermodynamically equilibrium condition in aqueous medium, such as chain length recognition and transition from uPIC, which is the PIC of smallest neutralizing unit, to PIC micelle structures.

Polyion complex (PIC) formation is one of the most powerful techniques for obtaining molecular self-assemblies in aqueous media, and useful for material syntheses particularly in the biomedical field. In this review article, recent progress on PIC vesicles (PICsomes) is summarized. PICsomes are characterized by their simple preparation, semipermeability and environment-sensitivity. Very recently, the methods to control structural uniformity and size of the vesicles have been established, and the potential utility of PICsomes has been expanded by crosslinking their PIC layers. In addition, the unique dynamic nature of PICs is also described.

Acidic pH is identified for various types of tumors, whereby it can be employed for crafting tumor-targeted nanomaterials. Cationic net charge of the nanomaterials at tumorous pH achieves selective interaction with anionic tissue constituents at tumor sites, for the effective tumor accumulation. However, tumorous pH is ca. 6.5, whereas pH of normal tissues is 7.4, and therefore responsiveness to the small pH window is the key toward the success for tumor delivery. The present manuscript highlights the polymer designs that recognize tumorous pH to make tumor-targeted nanomaterials.

DNA undergoes large volume transition to organize several higher-order structures, including globular, rod-shaped, and ring-shaped (toroid) structures by polyion complexation with block copolymer comprising hydrophilic segment and polycations. This review discusses the origin of this versatile higher-order structure formation. The knowledge of underlying physical mechanisms might ultimately improve our understanding of the formation of hierarchically ordered structures in the nucleosomes and the operating principles governing how DNA functionality emerges, and also provide a solid strategy to prepare structured nonviral gene vectors.