Ashis Kumar Sen

We report the evaporation kinetics and the morphological deposition pattern of a bi-dispersed droplet over hydrophobic PDMS substrate. Unlike hydrophilic substrate, the droplet on hydrophobic substrate undergoes a distinct evaporation kinetics, which recedes at the very early phases of evaporation and the particles present inside the droplet are driven radially inward to form a centralized deposition pattern with no particles deposited at the edge. A portion of the smaller (fluorescent) particles are deposited at the outermost edge and rest of the particles are at the center as observed under the fluorescent microscopy.

This paper presents analytical modeling, 3-D electro-fluid-structural simulations, fabrication and test of a piezoelectrically actuated PDMS based planar valveless micropump. The analytical model considers force balance in the nozzle-diffuser elements and at the fluid-membrane interface to predict the natural frequency and flow rate performance of the proposed micropump. The numerical model employs two-way fluid-structure coupling to represent fluid-structure interaction (FSI) between the membrane and working fluid by mapping displacement data from the membrane to the fluid and force data from the fluid to the surface of the membrane. Also, electro-structure coupling between deformation of a piezoelectric disk due to an applied voltage and resulting displacement of the membrane is considered. Based on the simulations, the circular shape of the chamber used in conventional micropump designs is modified to include a taper at the outlet, which provides a significant improvement (∼28%) in the flow rate. Numerical simulations are performed to study the effects of the nozzle-diffuser angle and size, chamber diameter and height and membrane diameter and thickness on the flow rate. Using simulation results, a suitable design of the micropump is identified and the proposed micropump is fabricated. Experiments are performed to study the effect of frequency and voltage on the flow rate and pressure-flow characteristics. The predictions of the analytical model and numerical simulations in terms of flow rate versus frequency and voltage and pressure-flow characteristics compare well with the corresponding experimental data (within 20%). Using a peak-to-peak voltage of 30 V, the micropump delivers a maximum flow rate of 20 μL/min and back pressure of 220 Pa. The proposed micropump is polymer based and thus suitable for low-cost and disposable applications.

We report the fabrication and experimental study of a flexible bi-layer microfluidic device for blood oxygenation, mimicking the thin alveolar exchange barrier constituting a lung. A facile technique is employed to fabricate the device by sandwiching a thin polymeric membrane as the gas exchange layer between two flexible microchannels. A numerical model coupling the mass, momentum, and species transport equations, is used to simulate oxygen diffusion between the blood and oxygen channels across the gas exchange membrane. The oxygen saturation is experimentally measured at different locations in the blood channel along the flow direction and compared against the simulation results, which show a very good agreement. The effect of blood and oxygen flow rates, channel height, and membrane thickness on the variations in oxygen concentration in the blood and oxygen channels and the diffusion membrane are studied. The outcome of the present study may find relevance in the development of organ-on-chip devices for blood oxygenation.