Actuated Post Arrays for Integrated Studies of Pumping, Mixing and Free Swimmers

An understanding of how flows are produced and controlled by microactuators is of significant interest for fundamental fluids physics, for microfluidics technologies and for microrobotics. Microscopic flows generated by cilia are central to biology; examples include muco-ciliary clearance in the lung, ciliary transport of the fertilized ovum along the fallopian tube to the uterus, and the propulsion of bacteria and protozoa.

Engineered mimics of these structures developed as microfluidic technologies offer unique solutions for transport at the microscale for mixers, pumps and as microfluidic rheological sensors in blood clotting diagnostics. In this project, photolithographically molded biomimetic ciliated surfaces will be used to investigate fundamental questions pumping and mixing.

The lessons learned will be used to design and control ciliated swimmers, i.e. biomimetic paramecia.

This project has three goals focused on pumping, mixing, and swimming in low Reynolds number fluid. Starting with pumping, the project will study the ways in which arrays of actuators can generate flows. Using designed arrays and actuation strategies, the project will use arrays of similar actuator geometry and compare the utility of different strategies for breaking time symmetry of motion.

Using the same arrays, the project will generate coordinated time-asymmetric beats between actuators (pairs, arrays, etc.), time asymmetric beats in single actuators, and metachronal waves where the time-asymmetry extends over tens of actuators. The nature of these flows will be studied to understand the length scale of long-range fluid motions and for mixing, which in part may occur on short length scales.

Next, the project will use the arrays to focus on mixing. In the low Reynolds number of microfluidics systems, fluids cannot support turbulence and therefore mixing is diffusion limited. The project will identify the parameters of beating actuators that provide high mixing.

Finally, the project will fabricate free swimmers that will be untethered. The design rules that govern the generation of directed flow for surface attached structures directly transfer to swimmer design. In this way, the project will completely close the loop between fluid pumping and swimmer propulsion.

In total, the research program will design actuating surfaces for better biomedical diagnostics and design micro-robotics for future implantable treatment strategies.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.