Polarization Behaviors of Biofilms on Metallic Materials By E.coli and S.Epidermidis, and the Applicability of Results

Abstract

Biofilms are formed on materials by bacterial activities and bring about detrimental problems as well as beneficial ones in industrial fields and our daily lives. It is very important to establish effective countermeasures, to control biofilms properly and also to monitor the formation and growth. For any of those purposes, we have to know how the biofilms are constructed, what kind of components they have and also what is going on inside biofilms. Generally, we already know that biofilms are composed of dominated water, bacteria themselves and external polymeric substance (EPS) at the initial stages. From the academic viewpoints, the initial structures are illustrated very clearly and precisely and already well known. However, biofilms changes with time significantly. Inorganic and organic substances are introduced into biofilms from environments or substrates outside biofilms. They interact each other to form many new compounds or to decompose into new ones. And they break down due to many reasons. Since those interactions would be very complicated, lots of information about biofilms growth have been still missing. And the lack of information might bottleneck the development of countermeasure. Therefore, we need more effective investigations using various approaches. There is no doubt that electrochemical methods are very promising methods. In this experiment, we chose two kinds of bacteria, E.coli and S.epidermidis. Each is representative gram-negative bacteria and gram-positive ones, respectively. Using those bacteria, biofilms formed on some metallic materials, such as copper and titanium. During the formation and growth of biofilms, the natural immersion potential (open circuit potentials) changed with time. However, the behaviors differed from substrate material to substrate material and also from bacteria to bacteria. And at some specific growth stages, the polarization curves were measured. The cyclic polarization curves depended also on the growth stage of biofilms.The following results were obtained.1. On the metallic materials forming biofilms easily such as copper, the natural immersion potentials shifted in the less noble direction with biofilm formation and growth significantly.2. On the metallic materials with few biofilm formation/growth such as titanium, the natural immersion potentials did not change so much.3. The polarization curves showed typical current peaks around 0.1-0.2V (versus Ag/AgCl in 3.3N KCl solution), when biofilms formed on metallic substrates.4. In the case of few biofilm titanium specimens, polarization curves did not show any specific current peaks.5. All of those electrochemical behaviors could be applied to monitor biofilms growth stages.