Designing microcapsule arrays that propagate chemical signals
Using analysis and simulation, we show how ordered arrays of microcapsules in solution can be harnessed to propagate chemical signals in directed and controllable ways, allowing the signals to be transmitted over macroscopic distances. The system encompasses two types of capsules that are localized on an adhesive surface. The "signaling" capsules release inducer molecules, which trigger "targets" to release nanoparticles. The released nanoparticles can bind to the underlying surface and thus, create adhesion gradients, which then propel the signaling capsules to shuttle between neighboring targets. This arrangement acts like a relay, so that triggering target capsules at a particular location in the array also triggers target capsules in adjacent locations. For an array containing two target columns, our simulations and analysis show that steady input signal leads to a sustained periodic output. For an array containing multiple target columns, we show that by introducing a prescribed ratio of nanoparticle release rates between successive target columns, a chemical signal can be propagated along the array without dissipation. We also demonstrate that similar signal transmission cannot be performed via diffusion alone.
Characterizing particle transport due to actuated cilia with adhesive tips
Biological tissues and organisms commonly utilize arrays of cilia to manipulate microparticles of different sizes. Motivated by biology, we use numerical simulations to study the interaction of microparticles with an array of actuated cilia, immersed in fluidic microchannel. For each cilium in the array, one end is tethered to the wall, while the other end is actuated by an external periodic force. Also, an adhesive force is introduced between the cilia tip and the microparticle. The simulations are performed using the Lattice Boltzmann Method for the flow, with a chain of point-forces, connected by springs, used to represent each cilium. We observe that a combination of hydrodynamic and adhesive forces can lead to size-specific control of microparticle transport. For instance, for certain adhesion strength and particle sizes, it is possible to trap and release particles by varying the actuation frequency. Also, for a given actuation frequency, the average particle speed is maximized at a particular adhesion strength. We will present the parameter range where we can observe the above behavior.
Updated: Aug, 2011