Chemo-sensitivity and reliability of flagellar rotary motor in a MEMS microfluidic actuation system

This paper presents a new MEMS microfluidic actuation mechanism using tethered, rotating bacterial flagella. In nature, bacteria swim with flagellar filaments driven by rotary motors embedded in the cell envelope. When a flagellum tethers down to a surface, the entire cell body counter-rotates around that flagellum. This distinctive rotary motion can be utilized to perform various mechanical functions in microfluidic systems, such as pumping, mixing, and/or valving. Most bacterial flagellar motors respond to changes in the acidity of their surroundings in a stochastic fashion. Our study shows that this sensitivity can be predicted through a probabilistic mathematical model and can be used to control their rotational behavior as actuators. Our model incorporates nanoscale physics into continuum level simulations using the Fokker–Planck Equation (FPE). The predictions of the model show a good agreement with experiments. Non-pathogenic, unidirectional Escherichia coli motors were utilized to experimentally validate the predictions of this model. In addition, their long-term performance as well as survivability was evaluated. The reliability of the flagellar motors, which can be influenced by time and environmental conditions, is critical for their practical application as actuators. The average rotational speed of bacterial motors was shown to decay over time with a half-life of 55 h in a closed system without additional nutrient feeding. The average lifetime of the entire population in the system was 34 h while a small percentage of cells lived for 168 h.