2) Biofilms – What can we learn from other disciplines?

Biofilms are the result of adhesion and growth of microorganisms at interfaces. They consist mainly of water, held by the extracellular polymers (EPS) in which the microorganisms are embedded. They are found in several environments, and play both beneficial and detrimental roles depending on whether their formation is controlled or naturally occurring.
In drinking water distribution systems, biofilms formation poses a significant problem to the distribution network conditions, constituting a risk for microbial contamination and a major-health threat when pathogens are present.
For decades, the fight against “undesired biofilms” was a masterpiece in a wide range of fields, from medicine to industry. For this reason, it’s time for water technology to look at the state of the art and the know-how on biofilm prevention from other disciplines, which might lead to a new exciting interdisciplinary field of science and technology and to new successful strategies against biofilm development.


Henny C. van der Mei, University Medical Center Groningen:
Biomaterial implants and devices are indispensable in modern medicine for the restoration or temporary support of function. Biomaterial-associated-infection (BAI) remains the number one cause of prosthetic implant failure, despite development of various state-of-the-art strategies to control BAI after implantation. The main problem is that a unified theory for adhesion of bacteria to surfaces does not exist due to the myriad of mechanisms bacteria have available to adhere. Microbial adhesion is considered to be the onset of BAI and leads to formation of a biofilm in which microorganisms are embedded in a complex extracellular-polymeric-matrix which make them resistant against antibiotic treatment and host immune system. Surface modifications can significantly reduce microbial adhesion to biomaterial surfaces. However, an anti-adhesive coating may be a sufficient functionality when applied on a surface in an environment with flow as urinary catheters, but not sufficient for an environment without flow as on hip prostheses. Drinking water distribution systems have similar environmental problems as water flow or no flow and biofilm formation on unwanted places, which are difficult to treat.

Patrick van Rijn, University of Groningen & University Medical Center Groningen:
Polymers have been used on many occasions to prevent fouling. Particularly hydrogel coatings are of major interst as these function in aqueous environment, are chemically easy to vary, and provice the possibillity to respond external stimuli making the system “smart”. Among these stimuli are temperature, ionic strenght, pH, and light all relevant stimuli for biological environments. In addition to chemical diversity, also mechanical properties and internal polymer structural arrangement play a tremendous role as this will dictate compressibility but also stability and mode of formation of the coating. Many novel coating systems rely on controlled radical polymerizations, which provide so-called polymer brushes when the polymers are grown from the surface directly. This is generally a challenging approach and conventional free radical polymerization is regarded as an easier alternative but also provides less control over internal structure. Coating function, stability, easy of formation are put to discussion in terms of their anti-fouling capabilities.

Emanuel Dinis, Wetsus & University of Twente:
Extracellular Polymeric Substances (EPS) are a mixed group of biopolymeric compounds, produced by microorganisms as secondary metabolites. Different microbial species produce different types of EPS with different functions (stress response, environmental protection, energy storage, communication). In fields like medicine, food packaging or water treatment, EPS production from microbial communities can cause problems. Indeed, EPS enhances attachment and growth of microorganisms on different surfaces, leading to changes in surface functionality or even to the destruction of the surface. In freshwater and wastewater treatment by membrane filtration, EPS molecules can become an issue when retained on the membrane surface, resulting in deteriorating filtration properties and a need of frequent membrane cleaning/replacement. However, we want to look at such EPS layers from a more positive point of view. The layer, by itself, can also be used as a cheap membrane when attached to a cheap carrier material, and with filtration properties similar to commercial microfiltration membranes. Study of EPS layer formation and its characteristics is not straightforward due to the complexity of the EPS and its behavior. Initially, therefore, model compounds have been used to better understand such complex systems.


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