Figuring out the key criteria to consider and how several technical choices, at different stages of the process impact each other can be stressful. Especially when it comes to the right microfluidic bonding technique. As an engineer, you must address design and process issues in an early stage to produce a high-quality consumable product.
But what are key criteria to consider? And how do several technical choices in different stages of the process impact each other? Finding the answers to these and more questions can be stressful with the amount of information around.
At the Flow Alliance, we have been working on several projects where bonding is an important part of the product’s functionality. This article summarizes some of the knowledge we gained. Continue reading to find out more.
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 the optical properties of the consumable like transparency, prevention of autofluorescence are essential.
Chemical and biological compatibility Think of biocompatibility, contact of reagents or samples with glues, volatile organic compounds (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 Some bonding processes are not compatible with all designs. For instance distance of features, available surface for bonding, all can be relevant to your choice.
Reagent storage on-chip before bonding For example coatings or bio-reagents can be stored on-chip, but will they also survive the bonding process?
Material compatibility The choice of raw materials excludes certain bonding processes because of their properties.
Shelf life The chosen bonding process affects shelf life, as well as the method of storage and the presence of reagents in the consumable during storage.
Scalability and cost In product development, scalability and costs are always relevant to your choice. 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 not 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. Keep on reading to learn more!
Common Bonding Technologies
There are a variety of bonding techniques available, some of which are more advanced than others. Let's have a look at the more mature ones that are commonly utilized in microfluidic consumables currently. We briefly summarized some of the bonding methods, as well as their advantages and disadvantages below.
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, 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. Additionally, this is not a suitable method if you have to add bio-reagents in advance.
Being additive free 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 before bonding.
The used heat can also cause some deformation of the microfluidic structures.
Finally, the time it takes to bond layers together is longer, making it a costly operation with limited scaling possibilities.
This bonding process is extremely versatile because of the numerous options for application techniques, adhesive types, and curing parameters. 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 sometimes might even affect the dimensions of the microfluidic structures. Also, it can occur that a microfluidic design might not be compatible with the application method, and 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 problems can arise, such as tape folding, and trapping bubbles.
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 become a costly process for some consumables. Also, most of the laser welding processes available do need a non-transparent part for bonding.
With 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 as 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 this information, how do you choose the bonding process that is best for your unique polymer consumable, 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.
As you can see, some of the processes mentioned appear several times in the table. These combinations could be significant to your process. Because each application, assay, and consumable has its own requirements, there might be solutions or (a combination of) processes that would surprise you. Our experts at the Flow Alliance will gladly discuss the best process for your specific microfluidic consumable. Get in touch with us here.
How to move forward? Read on.
Webinar Bonding Process Considerations
Do not miss our on-demand webinar on microfluidic bonding process considerations to learn more about the individual processes and decision criteria. The presentation will be followed by a question and answer session with our expert panel who will give valuable insights to pressing questions around this topic.