Polymer Brush Made By Ionic Liquids and the Inhibition Effects for Biofilm Formation
Authors: Kanematsu Hideyuki , Oizumi Atsuya , Sato Takaya , Kamijo Toshio , Honma Saika , Barry Dana M. , Hirai Nobumitsu , Ogawa Akiko , Kogo Takeshi , Kuroda Daisuke , Tsunashima Katsuhiko 
Published: February 2020

The polymer brush generally has high water repellency, adhesion, durability and antifouling properties. As for the last characteristics, it often works well to clean materials’ surfaces. Since it displays the lotus effect, it repels water. This water (which rolls off of the surface) picks up and carries away contaminants. What about its effect for biofilm? In this study, we seek the answer by using a polymer brush formed on glass.

Biofilms are produced by bacterial activities. Usually, bacteria attach to tissues in human bodies, and also to solid materials, since organic compounds (which serve as their nutrition) exist there. When the number of bacteria attached to these interfaces increases and reaches the threshold value, then exopolymeric substances are excreted from their cells. Therefore bacteria on materials’ surfaces are surrounded by sticky water including various kinds of organic polymers (exopolymeric substances: EPS). At this point, biofilms form on materials. Generally speaking, bacteria in biofilms have a high tolerance against biocides and antibiotics. This means that biomaterials should have high anti-biofilm formation capabilities. The application of a polymer brush to the surface finishing of biomaterials may serve as a countermeasure to protect biomaterials against biofilm formation. In this study, a polymer brush was formed on glass specimens by living radical polymerization of ionic liquids (N,N-diethyl-N-(2-methacryloylethyl)-N-methylammonium bis imide(DEMM-TFSI). Also their inhibition effects against biofilm formation were investigated.

The biofilm evaluation system was mainly composed of artificial biofilm production and various evaluation processes. In this study, the artificial biofilm formation was carried out by two different processes. One was a static process where specimens were placed in plastic wells filled with liquid cultures (LB and HI cultures) with and without bacteria (E.coli and S. epidermidis, respectively). The other was the process using a flow type Laboratory Biofilm Reactor (LBR). The specimen was suspended in a reservoir and fixed by a jig. And the same culture liquids, including bacteria in the reservoir, flowed by using a rotating stirrer. After a certain amount of time (a couple of days), each sample was taken out of the system and the specimen’s surface was observed by Raman spectroscopy and stained by crystal violet (0.1%) to check the extent of biofilm formation. The results were analyzed, compared, and discussed qualitatively and quantitatively. We confirmed that the polymer brush tended to control biofilm formation. The mechanism was considered in the following two ways. One of them would be the Lotus effect where the surface profile of a polymer brush might work well (Lotus effect). The other one was the antibacterial and anti-biofilm effects by ionic liquids. In this case, ionic liquid as a raw material was almost completely fixed and insoluble. However, a very small amount might dissolve at the tip of polymer brush.