Nanobubbles provide pathway to build better medical devices

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A new way to reduce drag in small-scale devices has been discovered by researchers from the University of Sydney.

Liquid drag within micro devices can cause internal fouling or damage to biological samples due to high pressure. The discovery could lead to the development of lab-on-a-chip devices that can be used to detect disease pathogens.

The wrinkled coating developed by the team reduces drag by up to 38 percent compared to smooth surfaces. The slippery coating is resistant to biofouling.

The team discovered that the fluids were able to slip through the channels with lower friction because of the formation of tiny bubbles.

The results are in Nature Communications.

There is a potential medical application.

Many medical diagnostic tools rely on small-scale analysis of tiny amounts of biological and other materials in liquid form. Microchannels and microreactors are used in these'microfluidic devices' to conduct reactions at a small scale.

Analyzing smaller volumes of material allows faster and more efficient diagnostics. The problem with microfluidic devices is that the fluid flow is slowed down by the solid walls of the channels, creating a large drag. The devices apply high pressures to drive the flow.

The high pressure inside these devices can damage delicate samples in the device, such as cells and other soft materials. The solid walls can easily be biofouled by biologicalmolecules orbacteria.

A solution to both of these problems is to use surfaces in which small amounts of a lubricant can be trapped, forming a slippery liquid interface, which reduces drag and prevents surface biofouling.

Liquid- infused surfaces replace the solid wall with a liquid wall, allowing the flow of a second liquid with lower pressure. The mechanism by which these liquid- infused surfaces work has not been understood, as the reduction of friction that these surfaces offer has been reported to be 50 times larger than would be expected based on theory.

Is there a way to save the bubbles?

Professor Neto and her team have described how they created liquid- infused walls on their devices by developing wrinkled coating that reduces drag by up to 38 percent. The team includes an expert in atomic force microscopy and a student who works on microfluidics.

The new slippery surfaces reduced drag relative to solid surfaces to a degree that would be expected only if the surface was infused with air. The team worked to demonstrate the mechanism by which the surfaces slip after the successful drag reduction.

They used atomic-force microscopy to image the bubbles on the surface. Their presence explains the huge slip in the flow.

The facilities of the Australian Centre for Microscopy & Microanalysis at the University of Sydney were used for part of the work.

Professor Neto said that they want to understand the fundamental mechanism by which these surfaces work and push the boundaries of their application. Now that we know why these surfaces are slippery and drag-reducing, we can design them to reduce the energy required to drive flow in confined geometries.

Christopher Vega-Snchez and his team explain the large slip observed on lubricant- infused surfaces. There is a DOI of 10.1038/s41467-022-28016-1.

Nature Communications is a journal.

There is a pathway to build better medical devices with the help ofnanobubbles.

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