Zwitterionic polymers are ionic polymers containing both positively and negatively charged groups in one monomer unit. These polymers exhibit excellent biocompatibility derived from high polarity and hydrophilicity. Recently, zwitterionic polymer hydrogels have attracted attention not only for applying bioinert biocompatibility for wound healing but also for biosensors and other applications combined with multifunctionality of high mechanical strength, self-healing properties, high ionic conductivity, etc. In this review, we describe recent research in the design of zwitterionic polymer hydrogels for biomedical applications.

Polymeric nanophase systems that undergo a phase transition in response to pressure changes are known as "baroplastic," a term coined following pioneering research by Professor Anne M. Mayes et al. at the Massachusetts Institute of Technology. More than a quarter of a century has passed since their theoretical and experimental elucidation of this phenomenon. Taniguchi and Mayes discovered that a block copolymer consisting of a poly(ε-caprolactone) derivative with a glass transition temperature below room temperature, and a polylactide with a higher transition point, undergoes a reversible phase transition from a phase-separated or solid state to a miscible or melt/solid state under pressure at ambient temperature. This polymeric material, owing to its pressure-induced plasticity, can be formed under pressure at low temperatures as low as room temperature, achieving both energy-saving molding with reduced CO₂ emissions and enhanced recyclability by suppressing thermal decomposition during processing. The low environmental impact of the degradable block copolymers draws attention as a novel high polymeric material. In this review, a series of research on the design, properties, and functions of degradable baroplastics are presented.

Coacervation is a liquid-liquid phase separation phenomenon observed in aqueous solutions of polymers into a concentrated polymer phase and a dilute phase. The concentrated phase is called coacervate. In our cells, coacervates compartmentalize proteins and play an important role in homeostasis. Inside the coacervate, the molecular interactions form dynamic network that determines the properties of the coacervate. Therefore, research has been conducted to fabricate coacervates with controlled properties using artificial polymers and to encapsulate proteins. In particular, the vulnerability to salt is a major issue in the application of ionic polymeric coacervates to protein delivery systems. Here, we will introduce the dynamics of coacervates made from artificial polymers and recent studies on the use of coacervates as a substrate for protein encapsulation to provide salt resistance.

Physically crosslinked nanogels, formed through the self-assembly of hydrophobically modified polysaccharides, exhibit macromolecular host functions such as protein incorporation in water. They have been explored for medical applications as innovative modalities, including vaccine carriers. This paper discusses the construction and functions of nanogel crosslinked macrogels, which are hybrid gels forming networks with nanogels. These macrogels result from reactions involving the reactive groups introduced into polysaccharide nanogels with water-soluble monomers or multibranched polyethylene glycol macromonomers. We design gel biomaterials with diverse structures and properties, utilizing nanogels as building blocks through a bottom-up approach (nanogel technonics). Furthermore, we investigate their functions as drug delivery systems (DDS) and as artificial extracellular matrices for regenerative medicine.

Boronic acids (BA) are able to reversibly interact with the diol groups, a commonly found chemical structural motif in biomolecules including sugars, ribose and catechols. In some aspects, they optimally enhance the environmental stability of ribose, supporting a rationale for the "RNA world hypothesis," one of the theories of the origin of life. For their carbohydrate-binding properties, they can be regarded as a synthetic mimic of lectins, often termed “borono-lectins”. Remarkably, the borono-lectins platform can be chemically tailored to manifest a broad profile of binding strength and specificity. Besides the structural versatility, a pronounced change in solubility accompanies some molecular-recognition events, enabling the "network polymers" to enjoy their complex and hierarchical functionalities. Here we provide a brief overview of our recent efforts on the related applications with special focuses on the intracellular environment-responsive nucleic acid drug delivery system, cancer diagnosis and targeted therapy by sialic acid recognition, and glucose-responsive insulin delivery system for the treatment of diabetes.