Performance Enhancement of Disposable Chamber Valveless Micropump through Annular Excitation for Biomedical Applications

Abstract

The precise manipulation of fluid with pumping systems has been a technological challenge in microfluidic applications. Micropumps play a significant role in the accurate delivery of fluids in microfluidic systems. Micropumps find extensive applications in different domains such as biomedical, automobile, electronic cooling systems, chemical and biological analysis. Over the past few years, researchers have emphasized different configurations of the micropump with different actuation principles, valves and chamber designs. Among different configurations of the micropump, piezo actuated mechanical micropumps find extensive application in microfluidic devices for precise delivery of the fluids. The precise and accurate delivery of fluid with piezo actuated micropump enables them to be extensively implemented in biomedical applications. Other advantages of piezo actuated micropump include reliability, miniaturization, the flexibility of integration with subsystems, and quick response. Considering the advantageous feature of the piezo actuated micropump, the present study proposes a novel disposable chamber valveless micropump actuated through an amplified piezoelectric actuator for biomedical applications. Piezoelectric mechanical micropumps are characterized by the oscillating diaphragm, which deforms under the action of force developed by the piezoelectric actuators inside the pump chamber. The deformation of the diaphragm leads to variation in pressure and volume inside the pump chamber, which in turn pumps the fluid. The performance of the piezo actuated micropump majorly depends on actuator configuration, diaphragm design/actuation principle and valve/chamber design. The proposed micropump is designed with the unique feature of a disposable chamber and employs an amplified piezoelectric actuator as the primary source of actuation. Integrating the disposable chamber as a separate entity with the reusable actuator allows disposal of the chamber after use, thus eliminating the risk of infection or contagion. The retrofit actuator can be reused to accommodate a new chamber for biomedical application. The micropump is made of polymeric materials like Polymethylmethacrylate (PMMA), Silicone rubber with different parts fabricated through CNC milling, laser cutting, and moulding operation. The micropump chamber, nozzle/diffusers, and the bossed diaphragm constituted the disposable part, and the amplified piezo actuator with structural support formed the reusable part of the micropump. The bossed diaphragm of the pump chamber consists of a central cylindrical protrusion which reduces the formation of wrinkles, allows uniform distribution of stress and transmits force required for micropump actuation. The valveless configuration of the micropump provides the advantage of the static geometric structure free from clogging, blockage, wear and fatigue failure. Since the deflection of the bossed diaphragm greatly influences the performance of the mechanical micropump, the present work is emphasized on the enhancement of the deflection of the bossed diaphragm, which in turn can enhance the volumetric performance of the micropump. Conventionally the bossed diaphragm is subjected to excitation force on the central bossed region. The application of excitation force on the central bossed region limits the deflection range of the bossed diaphragm. Therefore a novel annular excitation approach is proposed to enhance the deflection range where the diaphragm is subjected to excitation away from the central bossed region. A detailed study is carried out to compare the deflection behaviour of both central and annular excitation of the bossed diaphragm. The appropriate theoretical background is presented to analyze the amplified piezoelectric actuator, actuation mechanism and the bossed diaphragm. Finite element analysis is carried out to analyze the deflection behaviour of the amplified piezoelectric actuator, actuation mechanism and the bossed diaphragm under central and annular excitation. Experimental characterization is performed to validate the results obtained from finite element analysis of the centrally excited and annularly excited bossed diaphragm. The experimental characterization is carried out to determine the optimal performance parameters of the micropump with water, fluids mimicking blood plasma, and whole blood. Initial characterization considered micropump with the centrally excited bossed diaphragm. The effects of factor such as bossed ratio, diaphragm thickness, depth of the micropump chamber, and viscosity of the fluid is considered to optimize the performance of the micropump with central excitation. The second phase of the micropump characterization considered the novel approach of annular excitation of the bossed diaphragm. Characterization of the micropump with central excitation followed a similar approach to that of the micropump with central excitation. The maximum simulated deflection of the annularly excited bossed diaphragm with the actuation parameters of 150 V, 45.5 Hz is about 1998.4 μm which is far superior to the deflection value 725.91 μm achieved with the centrally excited bossed diaphragm at 150 V, 9.96 Hz. The corresponding maximum deflection measured with the experimental characterization of annularly excited and centrally excited bossed diaphragm is about 1953.4±8.00 μm at 150 V, 43.5 Hz and 717.99±4.00 μm at 150 V, 9.5 Hz. Thus, the annular excitation method for bossed diaphragm delivers a higher deflection range compared with the conventional method of central excitation. The proposed micropump with central excitation delivered the maximum water flow rate of about 7.192±0.147 ml/min and backpressure of 294 Pa at 150 V, 5 Hz. However, the enhancement of the deflection characteristics of the bossed diaphragm under annular excitation leads to performance enhancement of the micropump with the flow rate of 95.10±0.444 ml/min and backpressure of 1472 Pa at 150, 30 Hz.