microvalve

Introduction to Microvalves

Microvalves are one of the most important microfluidic components. Along with pumps and flow sensors, active microvalves are key components for controlling fluid flow in microfluidic systems. Especially in various chemical, analytical and biological assays, microvalves are considered as important components for on-chip flow operations.

Today, the various industries of microfluidic systems continue to force valve design development and reform due to new developments in microscale.

Smaller device sizes, higher pressures, high reliability, manufacturing costs, biocompatibility, responsiveness, and most importantly microtechnology required for high-density integration of microvalves on a chip are contributing to the development of microscale valve design. Based on their structure, microvalves can be categorized into active and passive microvalves.

Active microvalves require an actuator to control the microfluid, whereas passive microvalves can generally control the microfluid through back pressure.

In conventional design, an active micro-valve is a pressure-containing mechanical device used to shut off or otherwise alter the flow of fluid through it. The valve's operating condition is determined by the closing element (seat), which is actuated by an actuator.

A valve is a very simple device that has only a body that holds a fluid and its pressure, a seat that manipulates the fluid, and an actuator that controls the position of the seat.

There are many ways to categorize active microvalves. Based on their initial operating state, microvalves can be categorized into three types: normally open, normally closed, and bistable. Bistable microvalves can actively open and close the valve seat; no closed state is defined.

Valves control flow in a similar way to electronic transistors: analog and digital. In analog or proportional mode, with a constant inlet pressure, the valve actuator changes the gap between the valve seat and the valve opening to change the fluid resistance and thus the flow rate.

In digital mode, there are only two valve states: fully open and fully closed. However, digital active micro-valves can be driven in pulse width modulation (PWM) mode or as an array of digitally weighted valves for proportional flow control.

In PWM mode, the turn-on time can be controlled so that the net flow is proportional to the turn-on time. In an array, a number of digital valves are used to control the flow rate. If the flow rate of each valve is equal, the net flow rate is proportional to the number of valves opened.

It may be a better control method to weight the flow rate of each valve with a binary system. In this way, the array could represent a fluid digital/analog converter.

Active microvalves are categorized by their actuation principle:

Pneumatic Micro Valves	Thermo-pneumatic micro-valves	Thermo-mechanical micro-valves	Piezoelectric Micro Valves
Electrostatic microvalves	Solenoid Micro Valve	Electrochemical and chemical microvalves	Capillary force miniature valves

The main parameters of micro valves are leakage, valve capacity, power consumption, closing force (pressure range), temperature range, response time, reliability, biocompatibility and chemical compatibility. An ideal active micro valve should have zero leakage in the closed position.

Valve capacity indicates the maximum flow rate the valve can handle.

The power consumption is the total input power of the valve in its operating, power-consuming state. Depending on the principle of actuation, the power consumption may vary by several orders of magnitude, from very small (electrochemical) to very large (thermo-pneumatic).

The closing force depends on the pressure generated by the actuator.

The temperature range of a valve depends to a large extent on its material and actuation concept. Pneumatically actuated valves are usually used in high temperature applications, since the temperature range depends only on their material. The response time of a valve is actually the response time of the actuator used.

Actuators and operating conditions determine the reliability of miniature valves. In miniature valves, operational failures are usually caused by particulate contamination rather than actuator reliability.

Microvalve Applications

With the rapid development of microfluidic technology, microvalves are getting more and more attention. In order to improve the performance of microvalves, a large number of new structures and new materials have been proposed for application in microvalves.

The new working mechanism significantly reduces the manufacturing cost, leakage rate, power loss and size of the useless area of the microvalve, and improves the response speed and biocompatibility.

The use of microvalves is rapidly expanding from their initial use in laboratory biochemical analysis to many other areas. Increasingly, microvalves are being used in the human body, such as the brain, eyes and blood vessels, to treat diseases.

Biomedical: Microvalves can be used to control the mixing and flow of tiny volumes of liquids, enabling high-throughput biological experiments.

Chemical analysis: Micro valves can be used in micro liquid chromatograph, capillary electrophoresis and other chemical analysis instruments for sample separation and mixing.

Biomanufacturing: In biomanufacturing processes, microvalves can be used to control the flow of cell culture solution, media and nutrients for precise cell culture and production.

Drug Delivery: Micro-valves can be used in drug delivery systems to control the rate of release and dosage of a drug, for example, to deliver a drug to a patient via a wearable or implantable medical device.

Laboratory Automation: Microvalves can be used in laboratory automation systems to control the movement and dispensing of liquid samples and reagents, increasing experimental efficiency and reducing manual handling.

Microvalve development and outlook

Although the performance of microvalves has improved in recent years, they still suffer from many drawbacks, including high energy consumption, high cost, complexity, and leakage throughout the microfluidic system. Since microvalves require micromechanical system fabrication techniques, their manufacturing costs are usually high, which may limit their wide application in certain fields.

Conventional mechanically actuated microvalves suffer from leakage problems due to their complex structure and many components that cannot be fully integrated with the microfluidic system. Active microvalves utilize external actuators, and power consumption and portability remain a major problem.

Heat dissipation problems with external actuators can also affect the performance and accuracy of microvalves. Current microvalves can often only meet a specific requirement and cannot meet multiple requirements simultaneously. If progress can be made in the following areas, there should be a major improvement in the performance of microvalves, while also promoting the development of microfluidic technology:

1. Development of new materials: The use of lightweight materials can reduce the weight of micro-valves and improve their portability. The current trend is to move from metal to polymer materials. the emergence of PDMS with nanomaterials could be a new development opportunity.
2. Integrated processing: the development of micromachining technology is conducive to the development of integrated processing technology for microvalves, such as laser etching, rapid prototyping, etc. 3D printing technology may also be a good choice for manufacturing micro valves. The development of integrated processing technology has a great impact on the leakage problem of micro-valves.
3. Improve control performance: Controlling fluid flow is one of the most important functions of microvalves, so the control performance of microvalves should be improved by optimizing the actuation mechanism.
4. Study of flow characteristics: Combining numerical simulation methods with experiments to study the internal flow mechanism of micro-valves is conducive to the manufacture of micro-valves, reducing costs and improving efficiency. External and internal factors are equally important, and a two-pronged approach is not a new idea.

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DingXu (Suzhou) Microfluidics Technology Co., Ltd. is a high-tech enterprise dedicated to the field of microfluidics. We are committed to providing customers with comprehensive microfluidic solutions, including customized microfluidic chip development, surface modification, microfluidic chip processing equipment, and microfluidic instruments. Our team boasts extensive experience and technical expertise, continuously combining professional knowledge with innovative thinking to deliver high-quality solutions. We consistently prioritize customer-centric values, embrace self-challenges, and pursue excellence. Through professionalism, innovation, and collaboration, we aim to create greater value for our customers and contribute to a brighter future in the field of microfluidics.