What does a microbial biofilm have in common with a memory foam pillow?

 

If you are one of those people who are using memory foam pillow, then you probably noticed that when you lift your head, the pillow does not bounce back completely, but rather transforms into a bit different shape than the shape of your head. This happens because your pillow is a viscoelastic material. 

 

Viscoelastic? What is that? The term is composed of two words: viscous and elastic. Viscous part is associated with liquid-like property (viscosity is defined as the resistance to flow). Whereas elastic is associated with solid-like property (elasticity is defined as the resistance to deformation). So, a viscoelastic material is a material exhibiting both liquid and solid-like behavior. When there is stress, for example due to the load of your head on the pillow, a viscoelastic material deforms instantly due to the elastic component but also deforms more with time due to the viscous component. When stress is removed, deformation due to the elastic component is instantly recovered whereas the viscous deformation either recovers slowly or is not recovered, or both.

 

What about microbial biofilms? First I want to remind you what a microbial biofilm is: It is a group of microorganisms attached to each other and/or surfaces embedded in an self-produced extracellular matrix. This polymer-rich matrix is also a living, evolving material with amazing mechanical properties. Luckily, some scientists have started to study mechanical characteristics of biofilms and found out that biofilms can also exhibit viscoelastic behavior. (The animation shows a viscoelastic biofilm under high water flow)

 

For me that is fascinating enough to study for its sake, but you may ask “why care about the mechanical properties of a biofilm ?”.

 

Well, from microbial perspective, viscoelasticity is found to increase resistance of biofilms against mechanical stressors. This can, for example, hinder cleaning efforts in hospitals or food processing facilities when highly pressurized water is used to remove biofilms because viscoelastic materials dissipates energy. 

 

Or, from material science and design perspective, considering the increased interests in biomaterials, producing materials with specific mechanical properties can be useful depending on the application, such as a new fabric for clothing or a wound dressing.

 

Whether we want to promote biofilm growth for beneficial applications or to prevent their growth in critical settings, knowing mechanical properties of biofilms offers many possibilities.