PDMS for Microfluidics: Limitations and Alternatives
Introduction
As a trusted partner in the world of microfluidic devices, we understand the significance of selecting the right materials for successful product development. When it comes to microfluidics, one material that frequently dominates academic conversations is polydimethylsiloxane (PDMS). It has gained significant popularity and recognition among researchers and academics for its extensive utilization in microfluidic experiments. However, as pioneers in the field of microfluidic-based products, we have made a deliberate choice to deviate from the prevalent use of PDMS. In this blog post, we aim to shed light on the limitations of PDMS and provide valuable insights into alternative materials and fabrication methods that we recommend for the creation of cutting-edge microfluidic products.
Challenges of Using PDMS in microfluidics
PDMS is a commonly used material in academic microfluidic labs due to advantageous properties such as transparency, biocompatibility, and relative ease of replication. It’s also a popular material that remained attached to the microfluidic community as a first choice since it was introduced more than 20 years ago as a direct child of conventional silicon processing technologies. However, working with this elastomer is by definition a highly manual and poorly scalable method, hence product manufacturing beyond a couple of devices is typically quite challenging or not possible.
Despite its popularity in academic labs, PDMS has limitations that must be taken into account when developing microfluidic systems. Below, we present a list with the most common disadvantages of PDMS for microfluidic applications.
Adsorption of small molecules and surface contamination
PDMS is known to adsorb hydrophobic molecules onto its surface, which can lead to irreversible binding and potentially alter experimental results. Furthermore, PDMS can easily pick up contaminants from the environment due to its hydrophobic nature. Both can lead to inconsistent experimental results. To overcome this issue, various surface treatment methods such as plasma treatment or coating with biocompatible materials are commonly employed. However, applying liquid or gas-driven coatings to devices with intricate microstructures can present challenges. Another consideration is that most treatment methods cause PDMS to quickly return to its native form.
Limited chemical compatibility
PDMS has limited chemical compatibility with some solvents, acids, and bases. Exposure to these chemicals can cause PDMS to swell or even dissolve, compromising the integrity of the microfluidic device and potentially affecting experimental conditions.
Poor mechanical strength
PDMS is a soft and flexible material that can deform under pressure, especially at high flow rates or when dealing with very small/thin microstructures. This deformation can cause leakage and failure of the microfluidic device. To overcome this issue, hybrid microfluidic devices that incorporate PDMS with other materials such as glass or thermoplastics are often developed. This brings challenges associated to more complex manufacturing and assembly methods. Further, the exposed surface of the channels becomes multi-material, creating potential challenges around surface interaction with the samples.
Unsuitable for upscaling
PDMS is unsuitable for scaling up to larger manufacturing volumes due to its highly manual processing, long curing times, limited mechanical strength and the difficulty in creating large, monolithic structures Additionally, the assembly of PDMS layers can be quite challenging and time-consuming.
Alternative materials and associated fabrication methods
Nowadays, there is a panel of alternative materials for prototyping that offer similarly or better-suited surface, mechanical and optical properties over PDMS. Their associated fabrication methods are typically directly translatable to mass manufacturing, allowing us to streamline the development process and reduce costs associated with multiple iterations and scaling up of production. If you are looking for a custom-made solution that suits your needs, you can ask Micronit for the prototyping service. We have established manufacturing processes with tight tolerances and quality control tooling to ensure our manufactured devices meet your requirements.
Glass
Glass is a widely used material in microfluidics due to its excellent optical properties, chemical resistance, and mechanical strength. Glass microfluidic devices can be fabricated using a variety of techniques such as wet etching, laser ablation or laser induced etching. Glass microfluidic devices are particularly useful for applications that require optical transparency over a wide wavelength spectrum, high pressure resistance and chemical compatibility with harsh solvents and acids.
Thermoplastics
Thermoplastics such as polymethyl methacrylate (PMMA), polystyrene (PS) and cyclic olefin copolymer (COC) are popular in microfluidic devices due to their low cost, optical transparency, biocompatibility, ease of fabrication, and excellent mechanical properties. Thermoplastics can be molded into various shapes and sizes using techniques from rapid prototyping (CNC micro milling, laser ablation, hot embossing) to mass manufacturing (injection molding, thermoforming, roll-to-roll extrusion coating). This flexibility enables a straightforward transition of your product from the initial phase of development until mass manufacturing.
Thermoplastic Elastomers (TPE's)
TPEs are a unique type of polymers that take advantage of elastomeric and thermoplastic properties at the same time. They typically exhibit rubber-like (soft) mechanical properties yet they can be easily molded into complex shapes by using some of the same fabrication methods as used for thermoplastics.
Other features of TPEs include transparency, excellent tear strength, good chemical resistance and biocompatibility. These materials typically exhibit reduced gas permeability when compared to PDMS, making them a good option to reduce evaporation and prevent bubble formation within the microfluidic network. The mechanical and bulk properties of the material can also be adjusted by the polymer blend choice and ratios between them. At Micronit, we can develop your product utilizing TPEs for your microfluidic products.
Silicon
Silicon is probably the first material to be used in microfluidics due to a direct translation of traditional silicon processing from the electronics/MEMS industry. Silicon is a very hard and durable material that has excellent mechanical properties and is resistant to high temperatures and pressure. It is also biocompatible and chemically inert, making it suitable for use in biomedical applications. However, silicon is processed using advanced lithographic techniques, which makes it harder to design and fabricate.
Need help with your microfluidic products?
While PDMS is a popular material for microfluidic applications amongst academic users, it also has several limitations that must be considered carefully, depending on the application. As presented in this brief document, there are several alternatives available that can be better-suited for your application.
If you are not sure about the right choice for your project, our team of experts is always available to support you on the optimal material combination.
If you are not sure about the right choice for your project, our team of experts is always available to support you on the optimal material combination.