Polydimethylsiloxane, called PDMS or dimethicone, is a polymer widely used for the fabrication and prototyping of microfluidic chips.
It is a mineral-organic polymer (a structure containing carbon and silicon) of the siloxane family (word derived from silicon, oxygen and alkane). Apart from microfluidics, it is used as a food additive (E900), in shampoos, and as an anti-foaming agent in beverages or in lubricating oils.
For the fabrication of microfluidic devices, PDMS (liquid) mixed with a cross-linking agent is poured into a microstructured mold and heated to obtain an elastomeric replica of the mold.
The chemical structure will help us better understand the advantages and drawbacks of PDMS for microfluidic applications.
The Polydimethylsiloxane empirical formula is (C2H6OSi)n and its fragmented formula is CH3[Si(CH3)2O]nSi(CH3)3, n being the number of monomer repetitions.
Depending on the size of the the monomer chain, the non-cross-linked PDMS may be almost liquid (low n) or semi-solid (high n). The siloxane bonds result in a flexible polymer chain with a high level of viscoelasticity.
PDMS, once cured, becomes a hydrophobic elastomer. Due to its low surface energy polar solvents, such as water, struggle to wet the PDMS causing droplets to bead rather than spread and this leads to the adsorption of hydrophobic components from water on the material’s surface.
PDMS oxidation using plasma changes the surface chemistry, and produces silanol terminations (SiOH) on its surface. This helps make the material hydrophilic for it takes a few hours to one day to go back to normal hydrophobicity. This process also makes the surface resistant to the adsorption of hydrophobic and negatively-charged molecules. In addition, its plasma oxidation is used to functionalize the surface with trichlorosilane for example or to covalently bond polydimethylsiloxane (at the atomic scale) on an oxidized glass surface by the creation of Si-O-Si bonds.
PDMS is one of the most employed materials to mold microfluidic devices.
We describe here the fabrication of a microfluidic chip by soft-lithography methods with the following steps[1].
The chip is now ready to be connected to microfluidic reservoirs and pumps using microfluidic tubing. Tygon tubing and Teflon tubing are the most commonly used tubings on microfluidic setups.
If you are unsure about choosing the appropriate tubing for your setup, see our dedicated tutorial pages: Basics About Microfluidic Tubings & Sleeves and How to choose microfluidic Tubing
PDMS was chosen to make microfluidic chips primarily for those reasons:
Human alveolar epithelial and pulmonary microvascular endothelial cells were cultivated in a PDMS chip to mimic lung functions. It is transparent at optical frequencies (240 nM – 1100 nM), which facilitates the observation of contents in micro-channels visually or through a microscope.[2] It is considered bio-compatible (with some restrictions).
The PDMS bonds tightly to glass or another PDMS layer with a simple plasma treatment. This allows the production of multilayer PDMS devices to take advantage of the technological possibilities offered by glass substrates, such as the use of metal deposition, oxide deposition or surface functionalization.
PDMS, during cross-linking, can be coated with a controlled thickness on a substrate using a simple spincoat. This allows the fabrication of multilayer devices and the integration of micro valves.
It is deformable, which allows the integration of microfluidic valves using the deformation of PDMS micro-channels, the easy connection of leak-proof fluidic connections and its use to detect very low forces like biomechanics interactions from cells. It is also inexpensive compared to previously used materials (e.g., silicon).
The PDMS is also easy to mold because, even when mixed with the cross-linking agent, it remains liquid at room temperature for many hours. The PDMS can mold structures at high resolutions. With some optimization, it is possible to mold structures of a few nanometers [3].
It is gas permeable. It enables cell culture by controlling the amount of gas through PDMS or dead-end channels filling (residual air bubbles under liquid pressure may escape through PDMS to balance atmospheric pressure).
You will find below an immersion study of microstructured PDMS (h: 11µm, L: 45µm) in a variety of chemicals [5], this study was performed with PDMS Sylgard 184.
(Legend: No: no effect on microstructures, Total: complete destruction of microstructures)
For more tutorials about microfluidics, please visit our other tutorials here: «Microfluidics tutorials». The photos in this article come from the Elveflow® data bank, Wikipedia or elsewhere if specified. Article written by Guilhem Velvé Casquillas and Timothée Houssin.
Polydimethylsiloxane (PDMS) is a go-to material in microfluidics for various reasons. Its flexibility, transparency and biocompatibility make it the best material for fabricating microfluidic devices like single-layer and bilayer micro-imprint stamps. Among them, the most commonly used types by researchers are PDMS RTV-615 and PDMS Sylgard 184. The exact composition of these two is kept a secret; they both have their quirks and best scenario use. This allows researchers with experience to choose the most suitable PDMS for an application [5]:
This is popular for its robust nature and seamless ability to bond bilayer microfluidic devices. This is even favoured by the co-inventor of the microfluidic valve, S.Quake.
Despite all these factors,it has the reputation of being dirty. For example, Fluidigm has discarded 90% of the RTV-615 they received. It is known to vary from batch to batch in plasma bond strength. This makes it necessary to adjust the bonding parameters with each purchase.
On the other hand, The PDMS Sylgard is known for being cleaner and is most commonly preferred for applications like mammalian cell culture. It’s less suited to multilayer chips, as bonding can be more difficult and less reliable, which can result in ineffective device fabrication.
The rapid advancement in materials science have not only expanded the use of PDMS in microfluidics but have also transformed it into a ‘smart’ material. With new functionalities like self-report, self-heal, and self-clean. Smart PDMS is now more effective, durable, and reliable in challenging environments, making it ideal for a variety of applications.
This feature is Ideal for biomedical applications, as these are restricted to little to no biofouling and hydrophobic recovery over a long period. This limits a normal PDMS because of its ineffectiveness and instability over time.To overcome this researchers are developing modified PDMS surfaces that aims to enhance their performance by integrating antifouling properties and pH sensitivity.
One common method is to chemically graft poly(GMA-co-SBMA-co-DMAEMA), a zwitterionic and pH-sensitive polymer, onto a PDMS surface after it has been activated by UV and ozone. By decreasing fibrinogen adsorption and blood cell attachment, this improves PDMS’s antifouling properties. When exposed to basic pH conditions, the amount of attached E. coli bacteria is remarkably reduced by 98%. [6].
One of the big innovations in PDMS is the development of superhydrophobic micro/nano dual-scale (MNDS) films using a streamlined, wafer-level fabrication process. This method involves direct replication from an ultralow-surface-energy silicon substrate at high temperatures, eliminating the need for surfactant coatings. An improved deep reactive ion etching (DRIE) technique enhances surface passivation, resulting in hierarchical structures that impart excellent self-cleaning properties. These MNDS PDMS films are especially promising for micro/nanofluidic applications and advanced light-absorbing coatings. [7].
Often PDMS undergoes complex stresses that can result in gradual or sudden failure, impacting device performance. Preventing and managing such damage is key to ensuring long-term stability. The following are some of the popular approaches used to implement this:
Development of Smart PDMS, one of the exciting breakthroughs, is working with high-modulus, self-healing elastomers. Researchers achieve this by incorporating acylsemicarbazide (ASC) groups with varying polarities, boosting both the stiffness and robustness of the material. The highlight of using this method is that the enhanced PDMS still retains its transparency. This opens up new possibilities in areas like reversible adhesives and rugged microfluidic systems. It’s a promising leap forward for applications where standard PDMS just isn’t enough. [8].
While PDMS remains a staple in microfluidic and lab-on-a-chip applications, its hydrophobic nature often leads to challenges, like unwanted protein and drug molecule adsorption. To overcome this, researchers have successfully modified PDMS with polyethylene glycol (PEG), which dramatically improves its hydrophilicity.
When the surface is treated with the contact angle down to 23.6° ± 1°, this decreases the wettability of the material. Even more impressively, this modification is effective for up to 20 months, ensuring long-term performance. Thanks to reduced unwanted adsorption and enhanced compatibility, PEG-PDMS is proving to be especially useful in sensitive biological models, like liver-on-a-chip systems and other advanced organ-on-chip platforms. [9].
This modification into polymeric materials like polydimethylsiloxane (PDMS) is accumulating significant attention. As this enables traditional polymer matrices to communicate the mechanical stress or damage, hence Self-Reporting. This is crucial for maintaining structural integrity. Following approaches can help reach this:
In this method incorporate microcapsules into PDMS matrices that allow the release of charge transfer precursors upon mechanical failure.In this method we use 1,2,4,5‐tetracyanobenzene as an electron acceptor and two types of electron donors, forming charge transfer complexes (CTCs). This would reveal any damage through visible color transformations. These microcapsules can be synthesized via in-situ polymerization of an oil-in-water emulsion. This could be also adopted for dual functionality, if enhanced by self-healing agents like hexamethylene‐diisocyanate. This would allow autonomous self-reporting and healing processes, making the matrix suitable for diverse applications [10].
One of the methods is using mechanophores (MPs), embedded within elastomeric matrices such as spiropyran-functionalized PDMS. These mechanophores are molecular units that identify the mechanical force and exhibit fluorescent properties. With the help of confocal microscopy we can observe the fluorescence intensity that correlates with uniaxial strain. Researchers have found a linear relationship between mechanical stress and fluorescence output through finite element analysis. This method enhances the ability to quantitatively gauge local stresses, paving the way for refined damage-sensing applications [11].
This method is related to the advancements in mechanochemiluminescent (MCL) sensitivity. This can be achieved by synthesizing PDMS polymers that incorporate difluoroboron β-diketonate dye and 1,2-dioxetane as co-crosslinkers. The combination of these materials enhances the energy transfer within the polymer network. It also minimizes aggregation that impedes fluorescence, essential for effective stress reporting. The resulting materials have increased MCL intensity and can provide a more sensitive diagnostic tool mechanical integrity over both thermal and mechanical disruptions [12].
Polydimethylsiloxane (PDMS) has been playing an essential role in advancing microfluidic research, due to its unique properties like flexibility, biocompatibility, and transparency. Now even better with its notable advancements have emerged across various functionalities for ’Smart PDMS’, like self-reporting, self-healing, and self-cleaning. Each of these represents cutting-edge techniques aimed at enhancing PDMS’s performance and versatility in various applications
Elveflow, with its groundbreaking microfluidic instruments, continues to lead the way in enabling researchers to explore new discoveries and applications in PDMS-based microfluidics. Instruments created by researchers for researchers, a trusted partner in scientific innovation and progress. For additional insights on microfluidics, you can check out: Microfluidics Reviews.
[1] Y. Xia and G. M. Whitesides, “Soft lithography,” Angewandte Chemie International Edition, vol. 37, pp. 550–575, 1998.
[2] A. Piruska et al., “The autofluorescence of plastic materials and chips measured under laser irradiation,” Lab on a Chip, vol. 5, pp. 1348–1354, 2005.
[3] F. Hua et al., “Polymer imprint lithography with molecular-scale resolution,” Nano Letters, vol. 4, pp. 2467–2471, 2004.
[4] J. M. Spotts, Microfluidics Course, Institute for Systems Biology, Nov. 17, 2008.
[5] J. S. De Vera, A. Venault, Y. Chou, L. L. Tayo, H. Chiang, P. Aimar, and Y. Chang, “Self-cleaning interfaces of polydimethylsiloxane grafted with pH-responsive zwitterionic copolymers,” Langmuir, American Chemical Society, 2018, doi: 10.1021/acs.langmuir.8b01569.
[6] A. Mata, A. J. Fleischman, and S. Roy, “Characterization of polydimethylsiloxane (PDMS) properties for biomedical micro/nanosystems,” Biomedical Microdevices, vol. 7, pp. 281–293, 2005.
[7] X. Zhang, F. Zhu, M. Han, X. Sun, X. Peng, and H. Zhang, “Self-cleaning poly(dimethylsiloxane) film with functional micro/nano hierarchical structures,” Langmuir, American Chemical Society, 2013, doi: 10.1021/la4023745.
[8] W. Ma et al., “A self-healing polydimethylsiloxane elastomer with high strength and high modulus,” Polymer, Elsevier, 2023, doi: 10.1016/j.polymer.2023.126164.
[9] A. Gökaltun, Y. B. Kang, M. L. Yarmush, O. B. Usta, and A. Asatekin, “Simple surface modification of poly(dimethylsiloxane) via surface segregating smart polymers for biomicrofluidics,” Scientific Reports, Springer, 2019, doi: 10.1038/s41598-019-43625-5.
[10] Y. Chen, F. Li, H. Cang, S. Chen, and G. Zhang, “Early detection of polymer deformation via poly(urea‐formaldehyde) microcapsules encapsulated with charge transfer precursors,” Journal of Applied Polymer Science, Wiley, 2025, doi: 10.1002/app.57120.
[11] M. L. Rencheck, B. T. Mackey, Y. Hu, C. Chang, M. D. Sangid, and C. S. Davis, “Identifying internal stresses during mechanophore activation,” Advanced Engineering Materials, Wiley, 2021, doi: 10.1002/adem.202101080.
[12] Y. Yuan, B. Di, and Y. Chen, “Mechanically induced bright luminescence from 1,2‐dioxetane containing PDMS boosted by fluoroboron complex as an in‐chain fluorophore,” Macromolecular Rapid Communications, Wiley, 2020, doi: 10.1002/marc.202000575.
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