Origins of Microfluidics
Microfluidics is the study and manipulation of fluids in very small channels with dimensions on the order of tens to hundreds of micrometers. George M. Whitesides, often regarded as the “father of microfluidics,” suggests that the field has its origins in four key areas: molecular analysis, biodefense, molecular biology, and microelectronics1.
Microfluidics is an interdisciplinary domain encompassing knowledge from physics, chemistry, engineering, and biology to conceive, manufacture, and manipulate microscale systems for various applications. The origins of microfluidics date back to the 1950s and 1960s, when researchers began to explore the behavior of fluids in small capillaries.
One of the early applications of microfluidics was in inkjet printers, where minuscule nozzles were employed to deposit small ink droplets onto paper. During the 1980s, advancements in microfabrication techniques such as photolithography and soft lithography facilitated the production of more intricate microfluidic devices that allowed for accurate control of fluid flow and mixing.
This opened new opportunities for applications in areas such as chemical analysis, medical diagnostics, and drug discovery.
Today, microfluidics is a rapidly growing field with applications in diverse areas such as point-of-care diagnostics, environmental monitoring, and microscale chemical synthesis.
Figure 1 Different application filed of Microfluidics2–4
High-Throughput Microfluidics: Mimicking Nature for Innovative Applications
Microfluidic technology is typically associated with the handling of small volumes of liquids, typically in microliters and nanoliters. However, Eden Tech is taking it to the next level by designing microfluidic networks that can handle large volumes of water, up to several cubic meters.
Eden Tech’s design approach takes inspiration from nature’s most efficient and innovative systems. For instance, the micro-architecture of blood vessels in the human body enables the heart to pump 7 liters of blood per minute, using only an average of 1.3 W of energy.
Eden Tech has replicated this biomimetic design in its microfluidic networks, allowing for the transportation and processing of fluids at low energy, while achieving high performance. Thin microchannels pose a major obstacle due to their elevated fluidic resistance, which leads to a notable decline in pressure when large volumes of fluid are circulated. The art of handling large volumes of fluid in microfluidic networks in laminar flow is achieved by connecting the circuits in parallel.
This can be explained by drawing an analogy with Kirchhoff’s Law. Kirchhoff’s current law is a fundamental principle in electrical circuit analysis that states that the sum of currents entering and exiting any node in a circuit is zero. This principle can be applied to microfluidic circuits as well, as the laws of fluid dynamics and electrical circuit theory share similarities. In microfluidics, the application of Kirchhoff’s Law involves interconnecting the microchannels in a highly parallelized manner to reduce fluidic resistance.
This is achieved by arranging the microchannels in a network configuration such that the flow rate of fluid is divided equally between them. By doing so, the overall resistance of the microfluidic circuit is reduced, and the pressure drop is minimized, allowing for the circulation of larger volumes of fluid without the need for high-pressure pumps.
The parallel arrangement of microchannels also ensures that the laminar flow regime is maintained, which is essential for the efficient execution of chemical reactions. This is because the laminar flow regime is characterized by a low rate of mixing, resulting in efficient heat and mass transfer and uniform reaction conditions throughout the microfluidic circuit. However, it is also crucial to achieve uniform flow distribution in all the parallel connected channels which could be achieved by adjusting the channel dimensions and inlet design to minimize the pressure drop and promote uniform flow.
Figure 2 The physical similarities between the flow of a fluid and the flow of electricity: (a) Poiseuille flow in a circular channel, (b) the hydraulic resistance of the circular channel (Cgeometry 1⁄4 8p for the circular channel), (c) equivalent circuit symbol of a fluidic resistor for the hydraulic resistance and Hagen– Poiseuille’s law analogous to a resistor for the electric resistance and Ohm’s law, (d) a partially exposed Tesla TR-212 1 kU carbon film resistor, (e) the electric resistance of a conductive wire, and (f) circuit symbol of the resistor for the electric resistance and Ohm’s law.5
Eden Tech has perfected this parallelized microfluidic network design. These innovative designs have been successfully integrated into two of Eden Tech’s products, namely AKVO for wastewater treatment and ASCANDRA for microplastic removal.
AKVO has a treatment capacity of 200 cubic meters per day at 0.2 bar, while ASCANDRA can process 1 cubic meter of water per minute at 1-2 bars. To the best of our knowledge, Eden Tech is a pioneer in the development of biomimetic designs for high-volume microfluidics that offer energy-efficient solutions for environmental applications.
These designs have been modified and adapted for use in the MACGHYVER microfluidic electrolyzer, which aims to produce green hydrogen efficiently. Thus, Eden Tech is at the forefront of utilizing high-throughput microfluidics in the energy sector as well.
Figure 3 The ASCANDRA system developed by Eden Tech. It is a microplastic removal system that can collect microplastics while treating wastewater at a rate of 1 cubic meter per minute.6
Microfluidics: The future of green hydrogen?
Microfluidics presents a disruptive concept for the generation of green hydrogen that offers numerous advantages. Through the ‘miniaturization’ of electrolyzers and bringing the electrochemical conversion into a microscale regime, microfluidics offers a promising approach with immense potential for green hydrogen production. Microfluidic networks create a highly efficient environment for chemical processing by confining reactions to microscale dimensions.
This enables process intensification arising from a high surface-to-volume ratio thereby enhancing the speed and efficiency of chemical reactions. Moreover, the use of continuous flow ensures fast replenishment of reactants, which further contributes to the reaction kinetics and enhances the overall efficiency.
Figure 4
Reactant’s concentration from high (red) to low (blue) along the microchannel,
intensified chemical reactions take place rapidly thanks to the large surface
area to volume ratio in a scale of nanoliter
The use of microfluidic electrolyzers enables efficient hydrogen production without the need for membranes, which can be thick and prone to high maintenance. Instead, flow is utilized to separate gaseous products, reducing the equipment size and maintenance requirements. The absence of the membrane in microfluidic electrolyzers enables the placement of electrodes within close proximity, at distances of less than 1 mm.
This design significantly minimizes ohmic losses and reduces energy loss resulting from membrane material resistance, leading to greater energy efficiency. Although the inter-electrode gap width of 0.5 mm is comparable to that of a typical alkaline water electrolyzer separator, the ohmic drop is an order of magnitude smaller, allowing for significantly higher current densities.
Moreover, the scalability of the microfluidic electrolyzer is facilitated by Eden Tech’s stackable microfluidic disc design, where thousands of microchannels connected in parallel are engraved on each disc. These discs can be stacked together to form a cartridge, and as more discs are added, the volume of fluid processed increases.
With the massive integration of these discs, it creates a miniaturized factory capable of producing large-scale green hydrogen with minimal pumping losses. The modular design of the microfluidic electrolyzer permits simple scalability, allowing for hydrogen production on demand and in a distributed manner.
MACGHYVER’s microfluidic electrolyzer is a promising technology to produce green hydrogen, as it offers several advantages. The use of microchannels and the elimination of membrane separators allow for a more compact design with reduced ohmic losses and improved reaction kinetics. Furthermore, the stackable disc design enables easy scalability and mass production of green hydrogen which could propel the EU to the forefront of green hydrogen production.
References
1. Whitesides, G. M. The origins and the future of microfluidics. Nature 2006 442:7101 442, 368–373 (2006).
2. Guo, Q., Duffy, S. P., Matthews, K., Islamzada, E. & Ma, H. Deformability based Cell Sorting using Microfluidic Ratchets Enabling Phenotypic Separation of Leukocytes Directly from Whole Blood. Scientific Reports 2017 7:1 7, 1–11 (2017).
3. Matuła, K., Rivello, F. & Huck, W. T. S. Single-Cell Analysis Using Droplet Microfluidics. Adv Biosyst 4, 1900188 (2020).
4. Rebordão, G., Palma, S. I. C. J. & Roque, A. C. A. Microfluidics in Gas Sensing and Artificial Olfaction. Sensors 2020, Vol. 20, Page 5742 20, 5742 (2020).
5. Oh, K. W., Lee, K., Ahn, B. & Furlani, E. P. Design of pressure-driven microfluidic networks using electric circuit analogy. Lab Chip 12, 515–545 (2012).
6. ASCANDRA – Eden Tech. https://eden-microfluidics.com/ascandra/.