Video Explainer about Microfluidic Flow Control

Microfluidic flow control is a key functionality for complex labs-on-chips. It is crucial in managing all the different on-chip assay steps to take place in the right manner, at the right moment. On-chip flow control enables the design of compact, autonomous microfluidic platforms, features that are especially vital in the growing market of Point-of-Care (POC) applications.

Steps that are made possible by microfluidic flow control:

• Accurate volume sampling
• Spatial and temporal control over fluid flows
• Mixing of specific volumes
• Multiple washing steps
• Incubation and heating

We distinguish two types of microfluidic flow control: active flow control and capillary flow control.

This is the mechanically driven type of microfluidic flow control, that relies on an external input for actuation. This type of flow control offers dynamic flow actuation.

The active flow control systems Micronit provides, are based on fully integrated membrane valves and pumps. These are actuated through pneumatic control systems. We make use of visibly clear materials and provide reliable on-chip valve and pump systems in a selection of materials and hybrid combinations. 

In capillary driven microfluidic flow control, actuation of the flow is determined by intricate properties of the microfluidic channel structure itself, like the geometry of the channels and the surface properties of the channels. These two key points provide the scope for us to make adjustments. In order to meet specific requirements, we can:

• Tune channel surfaces to reach the required flow conduct and assure capillary filling. See also surface modification.
• Adjust the geometry of the channels in order to control the flow and make streams stop and (re)commence at the right point and the right moment.

Burst valves are commonly used to regulate flow in a capillary driven system. These valves rely on an abrupt increase in the cross-section of a microfluidic channel, which causes the capillary filling to stop at the transition. The flow recommences as a result of a certain trigger, for example when a different fluidic stream passes the junction.

When a time component is of the essence in a multi-step assay, this can be induced by electrostatic triggering. When the flow has stopped at a capillary burst valve, applying a short voltage will retrigger the flow. The operation principle lies in applying a voltage between two electrodes which are placed in front of and behind the valve. Applying the voltage attracts the meniscus towards the second electrode and triggers the valve. Using electrostatic triggering, we can produce autonomous devices that require little operational power and are suitable for use in handheld instruments.

Microfluidic flow control is especially of the essence for Point-of-Care devices. These devices rely on a complete on-chip assay that can perform a test without the help of medically skilled personnel. Point-of-Care tests usually make use of disposable microfluidic chips that are made of cost-efficient and easily accessible materials. At Micronit, we focus on developing our polymer substrate technology and are capable of integrating functional elements, capillary valves, and metal electrodes into a polymer-based microfluidic chip.

We have experience in adding microfluidic flow control elements to different materials and various hybrid combinations:

• COC devices with elastomeric COC membranes
• Glass devices with PDMS membranes
• Full glass devices
• Polystyrene / SEBS membranes
• Tell us your application-specific needs and we will make a design that meets your requirements.