How to choose the best chip material for microfluidic fabrication?

The selection of chip material for microfluidic fabrication depends on various properties, including optical clarity, mechanical strength, gas permeability, and surface wettability. Conventional materials like glass and silicon were initially used due to their precision and stability, but they have cost and fabrication limitations. This led to exploring alternative materials, including elastomers, thermoplastics, paper, and composites, to enhance manufacturability and functionality in various applications.

Chip material	Advantages	Limitations	Applications
Silicon	– High chemical and thermal stability – Precise microfabrication – Semiconducting properties	– Opaque, limiting optical applications – Fragile – Difficult to integrate active components like pumps and valves	– MEMS integration – Organ-on-chip devices
Glass	– Optical transparency – Chemically resistant – Biocompatible – Electrically insulating	– Complex and expensive fabrication – Requires high temperatures and pressures for bonding	– Capillary electrophoresis (CE) – Analytical chemistry
PDMS	– Low cost – Optical transparency – Biocompatible – Easy to mold for rapid prototyping	– High biomolecule adsorption – Poor surface treatment stability – Incompatible with organic solvents	– Rapid prototyping – Low-cost bioassays
Thermoplastics	– Low cost – Scalable production – Good optical properties – Biocompatible	– Some types have low chemical resistance – Surface modifications often required	– Disposable microfluidic chips – Point-of-care device
Paper-based microfluidic	– Low cost – Portable – No external power needed – Easy fabrication	– Low detection sensitivity – Fluid control challenges – Evaporation issues	– Point-of-care diagnostics – Simple bioassays

Silicon chip material

Silicon was one of the first materials used for microfluidic due to its semiconducting properties, availability, ease of fabrication, chemical resistance, and thermal stability. However, its opacity limits its use in optical applications, and its fragility makes it unsuitable for incorporating active components like pumps and valves. Despite these drawbacks, silicon-based microfluidic chip materials are still employed in high-precision applications such as point-of-care diagnostics and organ-on-a-chip devices.

Glass chip material

Glass is a transparent and electrically insulating material with excellent chemical resistance, biocompatibility, and thermal stability. However, glass chip fabrication is complex and expensive, requiring high temperatures, pressures, and stringent environmental conditions for bonding. These challenges have limited its widespread, leading to the search for alternative materials. One of its primary applications is capillary electrophoresis (CE).

Elastomer chip material

Polydimethylsiloxane (PDMS): PDMS has revolutionized microfluidic since its introduction in 1998 due to its low cost, optical transparency, biocompatibility, and ease of molding. It is particularly useful for rapid prototyping, as it allows for the quick fabrication of microfluidic devices through conventional machining or photolithography. However, PDMS has limitations, including poor surface treatment stability, high biomolecule adsorption, and chemical incompatibility with organic solvents, which restrict its use in biomedical applications. Despite these drawbacks, it remains a popular choice in academic research and rapid prototyping.

Perfluorinated polymers: Teflon-based materials provide an alternative to glass and silicon by offering high chemical inertness, non-stick properties, and optical transparency. These chip materials resist swelling, prevent biofouling, and are compatible with all solvents, making them attractive for advanced chemical and biological applications. However, their high cost and fabrication complexity limit their broad adoption.

Thermoplastic chip material

Various thermoplastics offer different advantages:

Poly(methyl methacrylate) (PMMA): One of the most widely used thermoplastics, PMMA chip material is valued for its optical clarity, low price, and compatibility with electrophoresis applications. However, it has limited stability against organic solvents and poor UV transmissivity, which may restrict its use in specific applications.
Polystyrene (PS): PS is commonly used in cell culture and biomedical assays due to its biocompatibility, optical transparency, and commercial availability. It is naturally hydrophobic but can be modified to improve cell adhesion and surface properties. Despite its advantages, expensive equipment is often needed for proper surface treatment.

Polycarbonate (PC): PC is a stronger and more heat-resistant alternative to PMMA, offering excellent optical transparency and biocompatibility. It is frequently used in DNA thermal cycling and pathogen detection applications. However, its low stability against organic solvents and high background fluorescence are challenging for imaging techniques.
Cyclic Olefin (co)polymers (COC/COP): These chip materials are known for high chemical resistance, superior optical properties, and compatibility with UV-based imaging techniques. COC/COP polymers have been used in hydrogel polymerization and grafting inside microfluidic channels, making them valuable for biomedical and analytical applications.

Paper chip material

Paper-based microfluidic gained significant popularity around 2007 due to its low-cost, ease of fabrication, portability, and capillary-driven flow transport without external power sources. However, challenges such as low detection sensitivity, difficulty guiding low-surface-tension fluids, and evaporation issues have limited its use. However, paper microfluidic remains a promising approach for point-of-care diagnostics and bioassay-based applications.

Composite materials

To overcome the limitations of individual materials, researchers have developed composite microfluidic devices that combine materials to optimize performance. For example, paper/polymer offers rapid immobilization of biomolecules and high performance in flow control. Another design uses polyvinyl chloride (PVC) layers and ceramic tapes to create microfluidic devices with high reliability, reproducibility, and flow control. These innovations offer a balance between cost, manufacturability, and functionality.

Want to know more on this subject? Check the extended review comparing the different chip materials and fabrication techniques.

Conclusion

Microfluidic chip fabrication has evolved from traditional chip materials like glass and silicon to more cost-effective and scalable alternatives such as polymers, thermoplastics, paper, and hybrid composites. While glass and silicon offer precision and chemical resistance, PDMS and thermoplastics have gained popularity due to their ease of manufacturing and biocompatibility. Paper-based microfluidic presents a promising low-cost alternative but faces challenges in fluid control and sensitivity. Meanwhile, composite materials offer a hybrid approach to overcoming individual material limitations. As research continues, developing new materials and fabrication techniques will further enhance the capabilities and accessibility of microfluidic technologies.

Funding and Support

This review was written under funding from the European Union’s Horizon research and innovation program HORIZON-CL4-2021-DIGITAL-EMERGING-01-27, grant agreement no. 101070120 (BIOPROS),

and the European Union’s Horizon research and innovation program Marie Skłodowska-Curie grant agreement no. 956387 (LasIonDef).