Yukari Oda

Block versus Random Amphiphilic Copolymers as Antibacterial Agents

We examined the antibacterial and hemolytic activities in a series of amphiphilic block and random copolymers of poly(vinyl ether) derivatives prepared by base-assisting living cationic polymerization. Block and random amphiphilic copolymers with similar monomer compositions showed the same level of activity against Escherichia coli . However, the block copolymers are much less hemolytic compared to the highly hemolytic random copolymers. These results indicate that the amphiphilic copolymer structure is a key determinant of activity. Furthermore, the block copolymers induced dye leakage from lipid vesicles consisting of E. coli -type lipids, but not mammalian lipids, while the random copolymers disrupted both types of vesicles. In addition, both copolymers displayed bactericidal and hemolytic activities at concentrations 1 or 2 orders of magnitude lower than their critical (intermolecular) aggregation concentrations (CACs), as determined by light scattering measurements. This suggests that polymer aggregation or macromolecular assembly is not a requisite for the antibacterial activity and selectivity against bacteria over human red blood cells (RBCs). We speculate that different single-chain conformations between the block and random copolymers play an important role in the antibacterial action and underlying antibacterial mechanisms.

Effect of Side-Chain Carbonyl Groups on the Interface of Vinyl Polymers with Water

The nature of the polymer-water interface in the poly(methyl 2-propenyl ether) (PMPE)-water model system is investigated by sum-frequency generation spectroscopy, which at the moment gives the best depth resolution among available techniques. PMPE, synthesized via living cationic polymerization, is structurally similar to poly(methyl methacrylate) (PMMA) except for lacking a carbonyl group. We here probe the polymer local conformation as well as the aggregation states of water at the interface. Comparing the results of our measurements to the PMMA-water system, the effect of a carbonyl group on the water structure at the interface is discussed. This knowledge should be crucial to the design and construction of highly functionalized polymer interfaces for bioapplications.

Surface segregation of a branched polymer with hydrophilic poly[2-(2-ethoxy)ethoxyethyl vinyl ether] side chains

A poly[2-(2-ethoxy)ethoxyethyl vinyl ether] macromonomer with a terminal vinyl group synthesized by living cationic polymerization was successively copolymerized with methyl methacrylate by atom transfer radical polymerization. The branched polymer mixed into poly(methyl methacrylate) was preferentially segregated at the film surface, leading to an anti-biofouling polymer surface.

Surface Characterization and Platelet Adhesion on Thin Hydrogel Films of Poly(vinyl ether)

Poly(vinyl ether), with short oxyethylene side chains which possess a simple and relatively polar structure, should be a unique candidate for a bioinert material thanks to its solubility in water. On the basis of living cationic copolymerization and subsequent ultraviolet light irradiation, thin films of poly(2-methoxyethyl vinyl ether) with different cross-linking densities were prepared on solid substrates. The films were thickened in water, and the extent was dependent on the cross-linking density. Although the surface chemistry and aggregation states were almost identical to one another, the stiffness, or the softness, of the outermost region in the film was strongly dependent on the cross-linking density. That is, the interface between polymer and water became thicker, or more diffused, with decreasing cross-linking density. The blood compatibility based on the platelet adhesion on to the hydrogel films was better for a more diffused interface.

Control of Surface Structure and Dynamics of Polymers Based on Precision Synthesis

Aggregation states and dynamics of polymers at the surface are generally different from those in the corresponding bulk state. To what extent they differ from that of the bulk strongly depends on the polymer primary structure. Therefore, fine-tuning the surface properties of polymers can be achieved by exhibiting control over their structure using precision polymer synthesis. We here show how the polymer design effectively impacts the structure and dynamics at the surfaces.