A team of researchers at Princeton University have devised an experimental set-up that closely mimics the flow of bacteria through working medical devices. Their findings show that bacteria clog medical devices extremely fast – much faster than previously thought – and warrant new strategies and designs in order to counter machine failure.
The researchers used time lapse cameras to monitor fluid flow in narrow tubes or pores similar to those used in water filters and medical devices. What’s important to note is that the scientists used pressure driven fluid and rough tube surface, instead of stationary liquid and smooth surface, in order to mirror as closely as possible natural occurring conditions.
A number of bacteria commonly found in clogged devices were introduced in the experiment, and were observed over a period of 40 hours. The researchers dyed the microbes green in order to better monitor them. What they found, however, took them by surprise. The microbes steadily attached themselves to the walls of the narrow tube and began to multiply, eventually forming a slimy layer of coating called a biofilm.
Additional microbes, this time dyed red, were introduced and, naturally, these too adhered to the walls surface, where they stuck to the biofilm. During this time, however, fluid flow wasn’t considerably disrupted. Some 55 hours in the experiment, the biofilm streamers tangled with each other and formed a sort of net-like structure that progressively trapped more and more bacteria as the snare became larger. Within an hour, the entire tube became blocked and the fluid flow stopped.
“For me the surprise was how quickly the biofilm streamers caused complete clogging,” said Howard Stone, Princeton’s Donald R. Dixon ’69 and Elizabeth W. Dixon Professor of Mechanical and Aerospace Engineering.. “There was no warning that something bad was about to happen.”
So in less than 60 hours of operation, their set-up had become clogged, much sooner and more devastating then anyone would have ever thought. The Princeton scientists’ work, published in the journal Proceedings of the National Academy of Sciences, shows how easily susceptible water and soil filter or, most importantly, medical devices are to clogging in the face of flowing bacteria.