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• Drive and Control of Microfluid in Microfluidic Analysis System

Microfluidic driving and controlling technique is one of the essential techniques in the microfluidic analytical system. The driving and controlling technologies of microfluidic are very different from that of macrofluidic, which is mainly due to the change of fluid flow characteristics due to the decrease of the scale. The driving and controlling technology of microfluidic is more complex and diversified. According to the different technical principles, the micro-fluid driving and controlling techniques can be divided into two types:

Mechanical Micropumps

Mechanical micropumps are characterized by the presence of a moving mechanical component, such as a vibrating diaphragm or rotor, that exerts pressure on the working fluid for pumping. Mechanical micropumps have been integrated into microfluidic devices to accurately drive and control micro-fluid movement in microfluidic systems. Currently, commercialized mechanical micropumps are well established. Classified by physical principles, they can be divided into the following three types.

• Piston micropumps
• Diaphragm micropumps
• Rotary micropumps

Fig. 1 Integrated microfluidic chip with thermal bubble micropump.¹

Non-mechanical micropumps

Non-mechanical micropumps are characterized by converting non-mechanical energy into kinetic energy for pumping fluids. Due to their simple structure, they are widely used in the development of microfluidic systems. According to the different technical principles and forms, non-mechanical micropumps can be divided into electric drive, thermal drive, surface tension drive, centrifugal force drive, magnetically-driven pumps, etc. Below introduce two common types of non-mechanical micropumps.

• Electrokinetic pumps

Electrokinetic pumps are the most important type of non-mechanical micro-avalanches. They are designed using the principle of electrohydrodynamic pumps and mainly include electrophoretic pumps and electroosmotic pumps. The electrophoretic pumps mainly rely on the electrophoretic migration and/or electroosmotic flow of the medium in the microchannel under an electric field. They belong to direct flow drive technologies without valves and mechanical parts, which can drive the flow rate of nl/min to several μ/min in micron-level channels. They have the advantages of moderate flow, no pulsation of liquid flow, and easy integration and are widely used in the separation and analysis of capillary electrophoresis. Although various fluid drive technologies such as pressure, gravity, centrifugal force and shear force have appeared in the field of microfluidic chips, the electrophoresis pump is still the most important liquid drive method at present.

The electroosmotic pump is designed based on electroosmotic flow. It was first reported around 2000. It is now very well-established and has developed a variety of forms, such as packed bed, parallel multi-channel, monolithic housing, and microporous membrane. Although ectrokinetic pumps can achieve high-efficiency drive and control of microfluid in the microfluidic chip, it is not suitable for channel size in the range of 1-50um. Especially in nano-scale channels, the limitations of electrophoretic pumps will be even greater. Therefore, it is necessary to develop more efficient microfluid driving technologies in this area, such as optical drive or magnetic drive, to solve these limitations.

• Optically driven pumps

Optical fluid control refers to the microfluidic control technology that integrates microfluidics, optical technology and sensor technology. Compared with miniature pumps such as piezoelectric pumps, it has the characteristics of simple structure, small size and large-scale integration. Compared with electrokinetic pumps, it is not limited with the limitation of the properties of the driving fluid medium. Therefore it has a broad application prospect. In 1992, scientists proposed the principle of driving droplets with a spatial gradient of surface free energy. They believed that light, heat, chemistry, or electrochemistry could be used to drive droplets’ movement due to the imbalance of the relative surface tensions on both sides of the droplets.

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Reference

1. Xu, Wang, et al. " Single-Cell Isolation Microfluidic Chip Based on Thermal Bubble Micropump Technology." Sensors 23.7 (2023): 3623.

For Research Use Only. Not For Clinical Use.