This work was motivated by medical device associated infections, a major challenge facing our society. For example, urinary catheters are colonized by microbes at an alarming rate of 15% per day, leading to catheter associated urinary tract infections (CAUTIs) and causing increase in hospital stay, healthcare cost and patient morbidity and mortality. Unlike common infections that can be eradicated by antibiotics, these infections persist even if the causative bacteria are not antibiotic resistant strains. This is because they form biofilms on the surfaces of medical devices, with bacterial cells protected by an extracellular matrix. Despite the extensive efforts in past decades, biofilm control is still challenging.

To find a possible solution, we wanted to learn from the nature. Humans encounter numerous bacterial cells on a daily basis but remain healthy thanks to the protection of our immune system. For example, cilia of the respiratory epithelium beat in a periciliary fluid layer under the mucus to remove trapped bacteria out of the lung. This inspired us to engineer antifouling surfaces with such active topographies. To achieve this goal, we engineered micron-sized pillars with superparamagnetic nanoparticles loaded at the tips of pillars. In this way, the pillars can bend and stand up with an external electromagnetic field turned on and off, resulting in the beating of micron-sized pillars with tunable frequency and force level. To load these nanoparticles in the small pillars was not trivial at the beginning. But by optimizing the vacuum and magnetic field, we found the right condition to achieve that.

Figure 1. Removal of UPEC biofilms by active topography. Representative fluorescence images of UPEC biofilms before (left) and after (right) pillar actuation for 3 minutes are shown. UPEC biofilms were formed in static LB medium for 48 h and gently washed before being labeled with STYO 9 (green fluorescence). These images are part of Supplementary Fig. 11 in the manuscript. 

We are intrigued by the results that active topographies have strong activities in both biofilm prevention and removal of established biofilms. We then engineered a prototype catheter based on this design with a coil embedded in the catheter wall to generate electromagnetic field. The prototype catheter was found to remain clean for at least 30 days, while the control catheters were blocked within 5 days by the biofilms of uropathogenic E. coli (UPEC), the leading cause of CAUTI.

With more antibiotic resistant infections emerging, it is helpful to consider bioinspired alternative approaches. The strategy developed in this study has several advantages as it is programmable, effective in both biofilm inhibition and biofilm removal, and has synergy with conventional antibiotics in biofilm control. This work was made possible with great teamwork. I want to specially thank Dr. Huan Gu for major contributions to the design and tests of active topographies, and Dr. Teng Zhang for the simulation work.