Bacterial flagellar propulsion represents an extraordinary system in nature for generating motion at the micrometer scale due to their unique molecular polymeric structure adapting to different shapes, depending on the local chemical and flow conditions. Their motion induces a local flow that can be used to propel cells, as well as much larger structures through a fluid environment. This collaborative research team plans to understand, to model and to exploit the physics of flagellar propulsion for use in engineered microfluidic systems. The objective of the program is to understand the fundamental scientific principles that govern the assembly and operation of flagellar-propelled devices (both single swimmers and collectively-powered devices), as well as to demonstrate the enabling technologies necessary to harness polymeric protein nanostructures such as bacterial flagellar filaments on microstructures for use in micron-scale engineered propulsion systems. This collaborative proposal between Drexel University and Brown University is the first to focus on the specific characteristics associated with the polymorphic transformation of bacterial flagellar filaments to demonstrate the ability to move larger engineered elements through a microfluidic landscape in a controlled and directed manner. Fundamental scientific merits addressed by this proposal include using nanoscale flagellar filaments in engineered systems for micron-scale propulsion. Basic questions are to be answered regarding the mechanisms leading to self-coordination of flagellar filaments in responses to a variety of external stimuli. Possible coordination of flagellar filaments to transport microstructures in various microfluidic environments will be examined, thus enabling an entirely new class of swimming robotic systems with applications to bio-engineered actuators, drug delivery systems, and machines for micron-scale transport and assembly. Demonstration of the control of bacterial flagellar filaments at micro- and nanoscales and the ability to integration information technology with bio and nanotechnology will have great impact. The program will have an intensive outreach component, including active recruitment and training of women and underrepresented minorities engineers leveraging and expanding existing and proven programs already in place at Brown and Drexel and outreach to inner-city high school student and teacher populations in both Providence and Philadelphia through the BROWNOUT (Brown) and INSPIRE (Drexel) programs. These enable in-classroom training and teacher-in-residence programs at the university campuses.
During this award, we explored the physical basis for bacterial motility, and the requirements for making robotic swimmers that mimic bactertial motion at the microscale. There are many features of micron-scale swimming that are poorly understood including the motion of the helical flagella that push cells through the water, the interaction of the flexible flagella with the surrounding fluid,the interactions between multiple flagella and lastly, the role of non-Newtonian fluids on the motility of cells. We addressed all of these issues using a mixture of live cell experiments, experiments using model systems that mimic the key physical features, theoretical models and finally numerical experiments of the governing equations. Briefly, we have found a wealth of mechanisms that are now described for cell motility using helical flagella for propulsion, we have uncovered a model that can be used to predict the bending of fllexible flagella due to viscous stresses, we have developed theoretical models describing the synrhonization of adjacent flagella and finally we have demonstrated that cells can swim faster or slower in non-Newtonial viscoelastic media, depending on the geometry and operating parameters. the impact of the research program has been significant, including multiple papers published in the archival literature (including several that are already well-cited), the training of undergraduate, graduate and post doctoral scientists.
