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Axxicon highlights the bonding process considerations for microfluidic products

Axxicon offers a microfluidic bonding technology guide and webinar to ease the decision of choosing the suitable microfluidic bonding for a high-quality consumable product.

Figuring out the key criteria to consider and how several technical choices, at different stages of the process impact each other can be stressful when choosing the right microfluidic bonding technique. As an engineer, you must address design and process issues early to produce a high-quality consumable product.

Requirements for the selection of your bonding process

Each microfluidic product and application has unique requirements, and the bonding process you choose must meet those criteria as well. Common requirements are:

  • Optical properties In some applications, it is essential to compromise the optical properties of the consumable like transparency, prevent autofluorescence

  • Chemical and biological compatibility Biocompatibility, contact of reagents or samples with glues, VOCs

  • Pressure stability For some applications pressures within the consumable can increase.

  • Channel dimensions integrity The dimensions of structures like channels or cavities should stay within tolerance after bonding

  • Design limitations Not all bonding processes might be compatible with all designs. Distance of features, available surface for bonding, this all can be relevant

  • Reagent storage on-chip (before bonding) For example coatings or bio-reagents can be stored on-chip, but can they also survive the bonding process?

  • Material compatibility Not all bonding processes work with all materials

  • Shelf life How will the consumable be stored? Will there be reagents in the consumable during storage?

  • Scalability and cost In product development scalability and cost is always relevant. In the end, the bonded product has to be produced in volumes and for a certain target price.

It can be challenging to put these requirements together and choose a suitable process as there is no black and white answer. Luckily, we have outlined methods for selecting the best process for your specific application requirements in the remainder of this article. Also, our webinar on-demand will give you additional insight.

Common bonding technologies

There are a variety of bonding techniques available, some of which are more advanced than others. Let's look at the more mature ones that are commonly utilized in microfluidic consumables currently.

Solvent Bonding

With this technique, a solvent is used to form a strong, long-lasting bond between two polymer layers. This method is extremely adaptable and can be used with virtually any microfluidic design.

However, if you add bio-reagents before bonding, this will not be a suitable option. The time required to bond a product is relatively long (10s of seconds), which will have an impact on the final price of the polymer consumable.

Thermal Bonding

Because no additives are used, this method provides a very pure and very strong material bond. As this process involves heat, no biochemicals or bio-materials should be present on the chip prior to bonding. The used heat can also cause some deformation of the microfluidic structures.

The time it takes to bond layers together with this technique is longer, making it a costly operation with limited scaling possibilities.

Adhesive Bonding

This bonding process is extremely versatile due to the numerous options for application techniques, adhesive types, and curing parameters when necessary. Almost any structure can be bonded, and the process is simple to optimize. It is easy to scale up the process and offers a low-cost solution for producing microfluidic consumables in small to large quantities.

However, it might not be compatible with all assays and in some cases might affect the dimensions of the microfluidic structures. Not all microfluidic designs might be compatible with the application methods. Shelf life varies per adhesive.

Tape assisted bonding

There is a wide range of tapes available that are suitable for a broad variety of products and assays. It is a low-cost process that is ideal for rapid testing and development. Tape surface properties can be customized.

However, high hydrophilic tapes are hard to come by. Thinner tapes are difficult to process and can present difficulties, such as tape folding, and trapping bubbles.

Laser welding

Using this process the bond is formed by melting layers together with a laser. It creates a very pure and strong bond. The time required to form this type of bond is short, and it provides in-line capabilities for a production line.

However, as the processing time increases with the complexity of the microfluidic structures it might not be a low-cost process for some consumables. Also most laser welding processes available need a non-transparent part for bonding.

Ultrasonic welding

In this technique, energy directors use ultrasonic vibrations to create a pure bond between the layers. It is a fast process using a well-established technology with a low development effort.

This process, however, has an impact on your microfluidic design because energy directors must be implemented. Also if your product has very small and intricate features, this may not be the most accurate bonding method for your product.

But how to decide?

With all of this information, how do you choose the bonding process that is best for your unique polymer consumables, assay, and set up?

Returning to the requirements for microfluidic bonding mentioned earlier, we can examine the various bonding technologies that can meet those requirements. The image below depicts the most appropriate microfluidic bonding technologies for the aforementioned requirements.


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