ADVANCED MATERIALS & PROCESSES | JANUARY/FEBRUARY 2024 25 gradually spreads the biofilm over the material’s surface. When a biofilm forms on the surface of a metal, for example, the metal of the substrate dissolves into the biofilm as ions. These ions react with polymer components in the biofilm, leading to corrosion and scale formation. Likewise, polymers and ceramics experience other problems, such as material degradation, deterioration of hygiene, and serving as a breeding ground for infectious diseases (Table 1). BIOFILM EVALUATION Destroying the biofilms that lead to material degradation is essential for materials science and engineering progress. However, effective countermeasures can only be achieved by developing new materials. To this end, creating a technology to quantitatively evaluate biofilms from an engineering perspective is necessary. Until now, evaluation methods for biofilms have relied on basic qualitative techniques. Biofilms may be observed by the naked eye as well as touching a surface where they exist. However, their exact identity cannot be determined until various components such as water, bacteria, and extracellular polymeric substances (EPS) are known. Of these, moisture is insufficient to determine whether a suspected biofilm is indeed a true biofilm, and the presence of bacteria needs to be verified. Even if bacteria are present, they may not form biofilms. Biofilm formation cannot be confirmed until the local concentration of bacteria increases to some extent, and it becomes clear that the water is fully hydrated due to the discharge of polysaccharides. Therefore, confirmation of EPS is the most important indicator of a true biofilm. Confocal laser microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR) are the most commonly used instrumental analysis methods to confirm the presence of EPS. From a materials science viewpoint, microorganisms are systems in which organic substances are formed on the surface of the substrate material. Over the course of numerous research studies, biofilms have been examined using various material analyzers and expensive biological instruments. Genetic analysis and mass spectrometry are examples of biological characterization techniques. From a materials science perspective, confocal laser microscopy is a typical analysis method, as are optical microscopy, SEM-EDX, AFM, FIB-SEM, Raman spectroscopy, FTIRATR, and other instruments. These methods are very effective as they can confirm the biofilm components and may provide new insights. For this reason, these techniques are still valid and necessary. However, from a practical standpoint there is still a need for more intuitive, inexpensive, and quantitative evaluation methods. MOVING TOWARD STANDARDIZATION The lead author of this article, Hideyuki Kanematsu, FASM, and his colleagues at the National Institute of Technology (KOSEN) in Japan began studying biofilms to address microbial corrosion around 2007. Kanematsu was part of a small research group working on microbial corrosion issues and anti- microbial research. Around 2012, executives from The Society of International Sustaining Growth for Antimicrobial Articles (SIAA) visited Kanematsu’s laboratory at Suzuka National College of Technology to discuss biofilms. During the meeting, it was agreed that a unified standard was needed with regard to this research. Several standards related to biofilm evaluation already exist in the United States (ASTM E2196, E2562, E2647, E2871, E2799, E3151, E3161) and also in the EU (BS EN 1276, EN 1040, EN 1275, EN 13717, EN 13697, EN 1500). However, these generally address an evaluation standard for biocides and are not standards for materials or products. In contrast, SIAA has focused on TABLE 1 — PROBLEMS CAUSED BY BIOFILMS Phenomena/ Environment Examples/Results Materials Corrosion Atmospheric corrosion Marine corrosion Corrosion in oil environments Corrosion of building materials Metallic materials (iron, steel, copper), concrete Scale and slime Buildup of scale and slime on cooling towers and pipes Copper and copper alloys, hot dip galvanized steels, iron and steel, cast iron, PVC Ships and marine structures Biofouling (such as attachment of oysters and barnacles) Carbon steels, polymers, stainless steels Food processing Decline in public health/hygiene Stainless steels Medical field Infection, chronic diseases, nosocomial infection Titanium alloys, stainless steels, hydroxyapatite Material degradation in soil Deterioration of soil pipes Concrete, cast iron Fishing Seagrass beds and fish reefs Concrete, metallic materials, slags Heat exchangers Air conditioners, washing machines, humidifiers Various polymers Kitchen and bathroom Dirt around water edge, clogged sinks Metallic materials, ceramics, polymers
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