Nanobubbles provide a pathway to build better medical devices

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Researchers from the University of Sydney’s Nano Institute and School of Chemistry have revealed that tiny gas bubbles – nanobubbles 100 billionths of a meter high – form on surfaces in unexpected situations, providing a new way to reduce drag in small-scale devices.

The withdrawal of fluid within the microdevices can lead to internal contamination (accumulation of unwanted biological material) or damage to biological samples such as cells, due to the high pressure. Therefore, this discovery could pave the way for the development of better medical diagnostic tools, such as lab-on-chip devices that analyze DNA or are used in biomedical detection of pathogens.

The team, led by Professor Chiara Netto, has developed nano-engineered curly coatings that reduce drag by up to 38 percent compared to nominally “smooth” solid surfaces. Slippery coatings, once lubricated, are also highly resistant to biofouling.

Using atomic force microscopy—a high-resolution scanning microscope—the team discovered that fluids passing through microchannels with these surfaces were able to glide with less friction due to the spontaneous formation of nanobubbles, a phenomenon not previously described.

The results were published this week in Nature Communications.

Potential medical application

Many medical diagnostic tools rely on small-scale analysis of trace amounts of biological and other materials in liquid form. These “microfluidic devices” use microchannels and micro-reactors in which reactions are usually carried out on a large scale in a micro-scale chemistry or pathology lab.

Analysis of much smaller volumes of material enables faster and more efficient diagnostics. However, the problem with microfluidic devices is that the fluid flow is greatly slowed down by the fluid’s friction with the solid walls of the channels, resulting in significant hydrodynamic drag. To overcome this, devices apply high pressures to drive the flow.

In turn, the high pressure inside these devices is not only ineffective, but can also damage minute samples in the device, such as cells and other soft materials. Moreover, solid walls are easily contaminated with biological particles or bacteria, which leads to rapid deterioration through biofouling.

The solution to these two problems is to use surfaces in which nanopores trap small amounts of lubricant, forming a slippery-liquid interface, which reduces hydrodynamic drag and prevents biofouling on the surface.

In fact, the fluid-filled surfaces replace the solid wall with a fluid wall, allowing the second fluid to flow with less friction, requiring less pressure. However, the mechanism by which these liquid-filled surfaces operate is not understood, as the friction reduction provided by these surfaces has been reported to be 50 times greater than what would be expected based on theory.

Nanobubbles to the rescue?

Professor Netto and her team describe how they have molded fluid-filled walls on their microfluidic devices, by developing nano-engineered wrinkle coatings that reduce drag by up to 38 percent compared to solid walls. The team includes: student Chris Vega Sanchez, whose work over the past three years has focused on microfluidics; Dr. Sam Bebo Chapman, expert in liquid-impregnated surfaces; and Dr. Liwen Zhu, an expert in atomic force microscopy, which gives scientists the ability to see down to a billionth of a meter.

After performing microfluidic measurements, the team revealed that the new slippery surfaces reduced drag relative to solid surfaces to a degree that could only be expected if the surface was immersed in air rather than a viscous lubricant. Not satisfied with the successful drag reduction, the team worked to clarify the mechanism by which the surfaces caused slippage.

They did this by scanning underwater surfaces with an atomic force microscope, which enabled them to image the spontaneous formation of nanobubbles, just 100 nanometers high at the surface. Their presence quantitatively explains the huge slip observed in the microfluidic flow.

Part of the microscopy work was conducted using the facilities of the Australian Center for Microscopy and Microanalysis at the University of Sydney.

Professor Neto said: “We want to understand the basic mechanism by which these surfaces operate and push the boundaries of their application, particularly for energy efficiency. Now that we know why these surfaces slip and reduce drag, we can specifically design them to reduce the energy required to drive the flow in Confined geometric shapes and reduced pollution.”


The slippery liquid-filled surface performs better than the highly waterproof surface in long-term wear resistance


more information:
Christopher Vega-Sánchez et al., Nanobubbles explain the significant slip observed on oily surfaces, Nature Communications (2022). DOI: 10.1038 / s41467-022-28016-1

Presented by the University of Sydney

the quote: Nanobubbles Provides A Pathway to Building Better Medical Devices (2022, Jan 18) Retrieved Jan 18, 2022 from https://phys.org/news/2022-01-nanobubbles-pathway-medical-devices.html

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