1. PHB Based Amphiphilic Copolymers and Self-Assembly
Poly[(R)-3-hydroxybutyrate) (PHB) is a class of natural biopolyester, produced by some microorganisms as intracellular carbon and energy storage material. Being biodegradable and biocompatible, PHB is attractive for biomedical applications. Moreover, PHB is a non-petroleum natural polymer resource, and is environmentally friendly.
1-1. Amphiphilic Triblock Copolymers
A series of novel PEO-PHB-PEO triblock copolymers were synthesized. They were found to have strong tendency towards self-assembly in aqueous medium, forming stable micelles with very low critical micellization concentrations. The micelles can be used as stable drug carriers under a very dilute condition.
1-2. Thermogelling Amphiphilic Block Copolymers
With increase in temperature, the copolymer solutions turned from clear sol to gels, and further turned into turbid sol at even higher temperature. The critical gelation concentrations of the copolymers were between 2 – 5 wt %, which were much lower than Pluronic F127 (17 wt %).
2. Cyclodextrin Based Supramolecular Biomaterials and Hydrogels
We have been working on supramolecular self-assembly of cyclodextrins (CDs) and various synthetic polymers. CDs are a series of natural cyclic oligosaccharides composed of 6, 7, or 8 d(+)-glucose units, which have been interesting building blocks for construction of supramolecules.
2-1. Injectable Supramolecular Hydrogels
We developed injectable supramolecular hydrogels based on the self-assembly between cyclodextrin and PEO-PHB-PEO triblock copolymers, which showed relatively long-term sustained release of model macromolecular drugs for over one month.
2-2. Supramolecular Gene Delivery Systems
Novel cationic supramolecules composed of multiple oligoethylenimine-grafted b-cyclodextrins that were threaded and blocked on a PEO-PPO-PEO triblock copolymer chain were developed as new gene delivery vectors. In contrast to conventional polycations, the supramolecules contain many cationic cyclic units that are threaded upon a polymer chain to form an integrated entity to function as a macromolecular gene vector.