Actuating surface attached posts as sensors for microfluidic applications

Cilia are hair-like projections from cells that act as sensors and micro-actuators. They are around 250 nm in diameter and range in length from a few microns to hundreds of microns and beat in complex shapes to generate fluid flow. Cilia are found across the entire eukaryotic tree, essentially unchanged, suggesting that they are extremely efficient fluid flow generators and sensors. At this micro scale fluids behave differently, viscous forces and surface tension become dominant, and gravity and inertial forces become minor forces. Biomimetic actuators that mimic biological cilia have been developed to act as pumps, mixers, and potentially sensors at the micron scale for applications in microfluidics. This dissertation focuses on understanding how these micro-actuators operate. I begin with trying to understand how biological cilia function. I will show experimental results demonstrating that the structural elements of the cilium, microtubules, are highly curved when isolated from the axoneme and that this curvature is protein dependent. I will then propose a new model for cilia actuation that takes this curvature into account, and show that it could account for some of the missing force in the cilium. In the rest of the dissertation, I focus on developing a model for describing the motion of biomimetic nickel poly-dimethylsiloxane (PDMS) composite actuating surface attached post arrays (ASAP) that were developed previously in our lab. This model of the ASAP arrays takes into account the magnetics, the transmitted light by the array, and the post fluid structure interaction. In the last sections of the dissertation, I will demonstrate that the model can be used to describe the post motion in viscous fluids and blood clots, which allows the biomimetic ASAP arrays to be used as sensors. The results of this dissertation shows that ASAP arrays have the potential to be effective sensors along as well as pumps and mixers in micro-fluidic systems.