micropump

Introduction to Micropumps

The microfluidic system with micro pump as the power source is the core component of the whole system, which plays a key role in the microfluidic transfer process and is widely used in Microfluidic Chip.

According to whether the micropump itself contains movable mechanical parts, micropumps can be divided into two categories: mechanical pumps and non-mechanical pumps.

Mechanical micropumps rely on mechanical components to transport and control microfluidic action, non-mechanical micropumps mainly rely on a variety of physical effects or will be certain non-mechanical energy into microfluidic kinetic energy to realize the microfluidic drive.

Mechanical pumps can be further categorized according to the principle of mechanical energy acting on the fluid. Under this system, mechanical pumps can be divided into two main categories: piston pumps and power pumps.

In a piston pump, energy is periodically increased by applying a force to one or more moveable boundaries of any desired number of closed fluid-containing volumes, thereby directly increasing the pressure to the force required to allow fluid to pass through a check valve or port into the discharge line.

In a power pump, mechanical energy is constantly being increased to increase the speed of the fluid within the machine.

Non-mechanical pumps add momentum to a fluid by converting another form of non-mechanical energy into kinetic energy. Mechanical pumps are mainly used in large and miniature pumps with relatively large dimensions and high flow rates, whereas non-mechanical pumps are advantageous in microscopic areas.

Since the viscous forces in the microchannels increase in a second-order manner with miniaturization, a mechanical pump cannot provide enough power to overcome the high viscous forces in the microchannels.

mechanical pump

electromagnetic pump

Solenoid pumps work by utilizing a magnetic field generated by an electromagnet to control the flow of liquid. Electromagnetic pumps are usually composed of electromagnets, valves and pipes. When current passes through the solenoid, the magnetic field generated will cause the valve to open and the liquid to be drawn into the pump; when the current stops, the valve closes and the liquid is pushed out.

Pros:

Since there are no mechanical moving parts, there is less wear and tear and low maintenance costs;

Electromagnetic force actuation makes it easy to change the direction of fluid flow;

The biggest advantage is that since there are no mechanical seals, there is no leakage in electromagnetic pumps.

Cons:

Compared to other types of micropumps electromagnetic pumps cost more;

The working efficiency is not considered outstanding, and it is difficult to realize large-scale industrialization and commercial application.

peristaltic pump

A peristaltic pump is a pump that works on the peristaltic principle, also known as a hose pump. Fluid is propelled by compressing a hose (also known as a peristaltic tube).

Peristaltic pumps work by applying pressure around a hose to move liquid through the tube. This is usually accomplished by one or more rotating rollers or pressure rollers that compress the hose and push the liquid forward.

Pros:

Easy to assemble, does not limit the volume of fluid to be delivered, and can be pumped in high volumes.

Cons:

Just the opposite of solenoid pumps, the most serious problem with peristaltic micropumps is leakage; the hose is a critical component of the peristaltic pump and needs to be replaced regularly to avoid wear and tear and leakage;

A small pressure difference between the outlet and inlet can then lead to backflow in the non-driven state.

pneumatic pump

Pneumatic pumps are pumps that utilize gas pressure to drive and are commonly used to transfer liquids, liquid mixtures, or suspended particles. Pneumatic pumps utilize the energy of compressed air or gas to propel liquids and typically consist of an air motor, a liquid inlet, outlet, and control valve.

When gas pressure is applied to the air motor, the resulting power causes the liquid to be pumped into the pump and piped to the desired location.

Pros:

Pneumatic pumps can provide high pressure, high output efficiency and low flow rate fluctuations.

Cons:

The most obvious disadvantage is the large noise generated during operation;

The compressed gas needs to be recharged once the energy is depleted, so continuous sampling is not possible.

centrifugal pumps

Centrifugal pumps work on a simple principle, using centrifugal force to suck liquid from the inlet into the center section of the pump and rotate it along the pump wheel, discharging it by the outlet.

Pros:

Small size, simple operation; can provide a stable force to drive the uniform flow of fluid; long service life.

Cons:

Requires external force drive, does not have self-priming capability; pump body and piping need to be filled with liquid before starting, otherwise air binding will occur; not applicable to high viscosity fluids.

syringe pump

A syringe pump is a device used to accurately control the flow of liquids, typically in the medical and laboratory fields. Syringe pumps use a motor to push (or pull) a moving piston in a syringe for fluid actuation.

Pros:

Easy to operate, you can set the injection rate and time;

Provides a more consistent flow rate with less flow pulsation than other pump types.

Cons:

The conveying volume is limited to meet the demand of large flow rate, and the application scenario is limited to the laboratory place.

Non-mechanical pumps

electroosmotic pump

Electroosmotic pumps are miniature pumps that utilize an electric field effect to propel the flow of liquids and are commonly used in microfluidic control and lab-on-a-chip. They move liquids through microchannels by applying an electric field without the need for mechanical parts.

Electro-osmotic pumps work by utilizing the phenomenon of charged liquids moving in an electric field, known as electro-osmotic flow, to drive the flow of liquids.

Pros:

No mechanical parts are required to propel the fluid, the processing is simple, and it is easy to miniaturize and integrate;

Electro-osmotic pumps are more reliable than conventional pumps as they do not suffer from head blockage.

Capillary driven pumps

Through chemical or physical methods to change the solid surface structure wettability, so that the microchannel on both sides of the substrate to form a hydrophilic or hydrophobic zone, the use of capillary tube in the capillary tube pipeline to achieve the transport of liquid.

Pros:

No external drive is required, utilizing its own structure to drive the fluid;

Simple structure, low process cost, easy to manufacture and integrate into miniature systems.

Cons:

There is no guarantee of pumping flow accuracy and drive with poor controllability.

Gravity Drive Pumps

Gravity-driven pumps are pumps that utilize gravity as the primary driving force to propel liquids, utilizing the difference in height between the inlet and outlet levels to create pressure, and this difference in height creates a hydrostatic pressure differential and pressure gradient within the microchannel resulting in fluid flow.

Pros:

No external drive required, simple operation, no complicated structure, low production cost;

Cons:

Restricted by the driving principle, applicable to specific scenarios and cannot be miniaturized;

The construction and usage scenarios make it impossible for gravity-driven pumps to produce a stable drive.

Thermal Bubble Micropumps

It usually consists of a miniature heating element and a miniature fluid channel. The heating element heats the fluid, creating hot air bubbles whose expansion pushes the fluid through the microchannel.

Pros:

No mechanical drive parts, simple structure, easy to produce, high reliability, can be integrated;

Cons:

Lack of stability, high pumping pulsations, and working with ambient temperatures.