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 PDMS microfluidic devices, Polydimethylsiloxane is mixed with a cross-linking agent, poured into a microstructured mold and heated to obtain an elastomeric replica of the mold (cross-linked).
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 monomers repetitions.
Depending on the size of 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 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. 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.
You can proceed to plasma treatment using a handheld plasma bonding pen for example.
PDMS is one of the most employed materials to mold microfluidic devices, along with paper [1]. It involves a master mold which is a negative of the design of the microfluidic chip on a substrate. This master mold can be obtained using for example the soft lithography technique. Once the mold is ready, it can be re-used and allows mass-production of microfluidic chips from a single mold.
Here are the main steps of the fabrication of PDMS microfluidic devices:
(1) The first step consists in mixing the PDMS with the curing agent and degassing the mixture.
(2) The mixture of polydimethylsiloxane (liquid) and crosslinking agent is poured onto the mold. Creation of air bubbles during pouring needs to be avoided to ensure the best possible quality of the chip.
(3) It is heated at high temperature. During this curing process, the PDMS block hardens.
(4) Once it has hardened, it can be taken off the mold. We obtain a replica of the micro-channels on the PDMS block. To allow the injection of fluids for future experiments, the inputs and outputs of the microfluidic device are punched with a PDMS puncher. The diameter of the puncher must be slightly smaller than the size of the future connection tubes to avoid leakages.
(5) Finally, the face of the block of PDMS with micro-channels and the glass slide are treated with plasma. The plasma treatment allows PDMS and glass bonding to seal the microfluidic chip.
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 not sure which tubing to choose 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:
Metal and dielectric deposition on PDMS is difficult, limiting the direct integration of electrodes and resistors. However, this can be overcome by spin-coating a thin layer of uncured PDMS onto a metalized surface, which then bonds well with the main PDMS layer after curing. While plasma bonding to glass is common, this method offers a simple workaround for bonding PDMS to metal.
You will find below an immersion study of microstructured PDMS (h: 11µm, L: 45 µm) in a variety of chemicals [6], this study was performed with PDMS Sylgard 184. Find more information about chemical resistance of different materials for microfluidics.
Table: Chemical and PDMS2 substrate characterization after immersion
(Legend: No: no effect on microstructures, Total: complete destruction of microstructures)
Polydimethylsiloxane (PDMS) is a go-to material in microfluidics for various reasons. Its flexibility, transparency, accessibility and biocompatibility make it the best material for fabricating microfluidic devices like single layer, bilayer and micro-imprint stamps. Researchers mainly use two types of PDMS: PDMS RTV-615 and PDMS Sylgard 184. The exact composition of these two products is kept secret. Both have their own particularities and uses, depending on the objective being pursued. This allows researchers to choose the most suitable PDMS for a specific application [6]:
This PDMS is popular for its robust nature and ability to bond bilayer microfluidic devices. This is even favored by the co-inventor of the microfluidic valve, S.Quake.
Despite all these factors, it has the reputation of being dirty (filled with impurities). It is known to vary from batch to batch in plasma bond strength. It is then 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 fabrications.
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-clean, self-heal, and self-report. 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 regular PDMS because of instability over time. To overcome this, researchers are developing modified PDMS surfaces that aim to enhance their performance by integrating antifouling properties and pH sensitivity.
A common method consists of chemically grafting 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% [7].
Another big innovation 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. It results in hierarchical structures with excellent self-cleaning properties. These MNDS PDMS films are especially promising for micro/nanofluidic applications and advanced light-absorbing coatings [8].
PDMS often undergoes complex stresses that can lead to gradual or sudden failure, impacting device performance. Preventing and managing such damage is key to ensuring long-term stability. Following are some of the popular approaches used to implement this.
One of the exciting breakthroughs is the work around 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 [9].
Self-healing PDMS is emerging as a game-changer for applications requiring long-term material resilience, especially in space exploration. A recent study highlights the use of electrospinning to create PDMS thin films with tunable thickness, showing that thicker films (up to 201.2 µm) offer significantly enhanced self-repair capabilities, achieving 35% healing in just 3 hours and up to 60% over 95 hours at room temperature. This breakthrough demonstrates the potential of smart, self-healing materials to improve the reliability of spacecraft components and opens new possibilities for their use in both aerospace and medical technologies [10].
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.
When microcapsules are incorporated into PDMS matrices, it allows the release of charge transfer precursors upon mechanical failure. In this method, 1,2,4,5‐tetracyanobenzene are used 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 (like anti-corrosion performance or crack penetration depth visualization in PDMS chips) [11].
Another method concerns 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 for refined damage-sensing applications [12].
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 hinders fluorescence, essential for effective stress reporting. The resulting materials have increased MCL intensity and can provide a more sensitive diagnostic tool for mechanical integrity over both thermal and mechanical disruptions [13].
In conclusion, polydimethylsiloxane (PDMS) has been playing an essential role in advancing microfluidic research, due to its unique properties like flexibility, biocompatibility, and transparency. Today, it’s even more powerful, thanks to the significant advances that have been made. Functionalities such as self-reporting, self-healing and self-cleaning have been added to the PDMS with which we are all familiar. Each technique used represents cutting-edge techniques aimed at improving the performance and versatility of PDMS in a variety of applications [14].
Elveflow, with its full microfabrication stations and its microfluidic instruments, continues to be at the forefront in enabling researchers to explore new discoveries and applications in PDMS-based microfluidics. Elveflow is a trusted partner in scientific innovation with its range of instruments created by researchers for researchers. For additional insights on microfluidics, you can check out: Microfluidics Reviews.
The photos in this article come from the Elveflow® data bank or elsewhere if specified. Article written by Guilhem Velvé Casquillas and Timothée Houssin, revised by Louise Fournier.
[1] Y. Xia and G. M. Whitesides, “Soft lithography,” Angewandte Chemie International Edition, vol. 37, pp. 550–575, 1998.
[2] U. Marx, T. B. Andersson, A. Bahinski, M. Beilmann, S. Beken, F. R. Cassee, et al., “Biology-inspired microphysiological system approaches to solve the prediction dilemma of substance testing,” ALTEX – Alternatives to Animal Experimentation, vol. 33, no. 3, pp. 272–321, 2016, doi: 10.14573/altex.1603161.
[3] T. Eder, A. Mautner, Y. Xu, M. R. Reithofer, A. Bismarck, and J. M. Chin, “Transparent PDMS Surfaces with Covalently Attached Lubricants for Enhanced Anti-adhesion Performance,” ACS Applied Materials & Interfaces, vol. 16, no. 8, pp. 2024, doi: doi/10.1021/acsami.3c17110
[4] F. Hua et al., “Polymer imprint lithography with molecular-scale resolution,” Nano Letters, vol. 4, pp. 2467–2471, 2004.
[5] S. Bunthawin, J. Kongklaew, A. Tuantranont, K. Jaruwongrangsri, and T. Maturos, “Microchip electrode development for traveling wave dielectrophoresis of non-spherical cell suspensions,” Engineering, vol. 5, pp. 88–93, 2012.
[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] 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.
[8] 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.
[9] 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.
[10] F Madiyar, J Vu, M Ricciardella, F Dohner, J Shivakumar, E Rojas, “Electrospinning Thin Films of Stretchable and Self-Healing PDMS,” 2024 IEEE Aerospace Conference, 2024, doi: 10.1109/AERO58975.2024.10520941
[11] 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.
[12] 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.
[13] 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.
[14] J Nedoma, M Fajkus, J Cubik, S Kepak, R Martinek, J Vanus, R Jaros, “SMART medical polydimethylsiloxane for monitoring vital signs of the human body,” IEEE 20th International Conference on e-Health Networking, Applications and Services (Healthcom), 2018, doi: 10.1109/HealthCom.2018.8531190
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