Manipulating surfaces to prevent microbial biofilms
In our previous article we established that biofilms were simply defined as microbes attached to surfaces and investigated the potential of plant-based compounds to control biofilms. One of the key components of the biofilm interaction is, of course, the surface to which they attach. Depending on the type of biofilm and environment the surface microbes attach to can be living, inorganic, organic and even the interface between two liquids. Traditionally biofilms have been controlled by removing them from these surfaces using chemical and physical treatments. With advances in material science and driven largely by the medical device and implant sector, there is strong interest in manipulating surfaces to prevent or decrease microbial attachment or enhance the ease with which they can be removed. Key to this is understanding of how microbes interact with surfaces. Although they are based on common principles, these interactions can be very complex and vary from one microbe to another and one surface to another, making a one-size-fits -all approach exceedingly difficult.
Attachment of microbes to a surface is the first stage in biofilm formation. As microbes approach a surface a wide range of chemical and physical interactions occur which determine if they will attach or not. These interactions include features such as the charge and hydrophobicity of both the microbe and surface. These interactions change as the microbe approaches the surface and the distance changes from a micro to nano scale. The type of material the surface is made of, and surface appendages and proteins on the microbe, such as flagella, all play a role in this process. The roughness of the surface, at different scales, can also play a role both in the initial attachment (at a nano-scale) but also during biofilm growth (at a micro-scale) by providing cracks and fissures which allow microbes to avoid being removed. All these interactions mean that in some cases, for example, a highly charged surface will reduce attachment of some microbes but, at the same time, encourage the attachment of others. In addition, some interactions will have a “sweet spot” for control in terms of surface hydrophobicity or roughness, with microbial attachment increasing as values both increase and decrease from the optimal control value. If it seems complicated it is and it is definitely difficult (if necessary) to explain in a paragraph! Of greater interest is how we can use this knowledge to control biofilms in a practical way.
A number of approaches have been applied to control biofilms by manipulation of surfaces with a varying degree of success. The development of highly hydrophobic surfaces (1), nano-brushes on surfaces to prevent strong microbial interactions (2) and nano-spikes which “impale” microbes and are based on the structure of dragonfly wings (3) are exciting examples. While some of these innovations have been carried through to prototypes and trials, costs for the wider use of these solutions can be prohibitive. The high margin medical implant industry may be able to implement these innovations but the lower margin food industry, for example, is unlikely to find these solutions affordable or practical. In these other cases alternative selection of existing surface materials and minor manipulations may be more sensible. In addition, a much more targeted approach to reducing microbes of particular concern may be possible. We have developed a statistical model, for example, which could be used to predict the surface parameters most likely to reduce attachment of particular microbes of interest (4). This could allow, with some empirical testing, the selection of alternative materials to use in particular problem areas in food processing to prevent attachment of pathogens of concern.
As material science advances a range of new and innovative solutions to prevent biofilm formation will emerge. Hopefully, this will be accompanied by a reduction in costs of these materials so that they can be more widely applied in a range of industries.
If you are interested in further information on any of this content, please contact us here.
