Fidget spinners are hand-held toys based on a roller bearing and three weighted lobes, which can spin freely, creating centrifugal force when activated manually.

Generating centrifugal force with a fidget spinner takes neither electricity nor trained staff. And that has suggested to several researchers that such spinners, under the right circumstances, could be used for centrifugation under circumstances where reliably operating a centrifuge, for whatever reason, is a challenge.

Korean scientists at Ulsan National Institute of Science and Technology (UNIST) have engineered a diagnostic device based on a fidget spinner child’s toy, which was designed specifically to meet all of the requirements for managing urinary tract infections (UTI) using point-of-care-testing (POCT) in resource-limited settings.

In field trials, the diagnostic fidget spinner (Dx-FS) was shown to fulfill all WHO criteria for an ideal POCT device, being affordable, sensitive, specific, user-friendly, rapid, robust, and being equipment-free and accessible, the engineers reported in a study published the May 18, 2020, edition of Nature Biomedical Engineering.

Earlier in 2020, researchers at National Taiwan University’s Institute of Applied Mechanics had reported the use of a fidget spinner to separate plasma from whole blood.

In resource-limited settings, the use of conventional modern medical laboratory equipment is restricted by factors including unreliable power supplies, shortage of trained staff, adverse environmental conditions and the absence of rapid data connectivity.

In such circumstances, clinical decisions are of necessity based on patients’ symptoms, rather than diagnostic tests, leading to clinical complications.

Although several POCT devices have been developed for diagnosing infections, most cannot be used in resource-limited settings, hence the need for more suitable devices, especially for common infections such as UTIs.

UTIs

UTIs are associated with a significant health care burden and are common in pregnancy, when they can be dangerous without adequate screening and treatment.

For patients with clinical UTI symptoms, the gold standard for diagnosis is urine culture and urinalysis, which is expensive, time-consuming and may be unavailable in many areas.

Clinicians must therefore use symptom-based diagnosis, resulting in prescription of broad-spectrum antimicrobials, which can lead to resistance, as can the use of UTI dipstick tests, which are less reliable than urine cultures.

Fidget spinners

“Based on this idea of a device spinning like a centrifuge, we designed a centrifugal microfluidic device by adapting the working principles of a fidget spinner,” said Yoon-Kyoung Cho, a professor in the Department of Biomedical Engineering at UNIST and the senior author of the Nature Biomedical Engineering paper describing the UTI fidget spinner.

“Inexpensive, palm-sized, simple in design, robust and easy to operate, the fidget spinner could be a good platform for a fully integrated ‘sample-in-and-answer-out’ sensitive diagnostic detection with the naked eye, which is important in limited-resource settings,” said Cho.

Consequently, she and her team at UNIST designed and engineered a custom-made Dx-FS to function as an easily used, instrument-free lab-on-a-disc platform to provide a low-cost, electricity-free UTI diagnosis.

However, because it is hand-powered, the Dx-FS generates limited available centrifugal force, which is highly variable depending on the operator. “We overcame this problem by using a pressure equalization technique,” said Cho.

The device was then shown to rapidly concentrate pathogens in 1 ml samples of undiluted urine by more than 100-fold for the colorimetric detection of bacterial load and pathogen identification.

A field test of the Dx-FS was then performed in India, where a large proportion of patients diagnosed with a UTI worldwide are located.

On-site testing

In on-site validation testing, which included input from doctors in local hospitals, urine samples from 39 patients with clinical UTI symptoms were analyzed using a Dx-FS and the results compared with conventional culture.

This demonstrated that the Dx-FS could detect the presence of viable bacteria in urine with the naked eye within just 50 minutes, compared to several days with conventional culture.

“Our Dx-FS can be used to perform a UTI diagnosis in 50 minutes with no additional device or electricity requirements, while the material costs for a Dx-FS kit is an estimated US$0.48,” said Cho.

Clinically, this rapid and inexpensive test would help to identify patients requiring antimicrobials from among those who are suspected symptomatically.

To expand the scope of the clinical usefulness of the Dx-FS, the researchers performed a simplified antimicrobial susceptibility test (Fidget-AST) in clinical samples of UTIs from 30 patients.

This was shown to allow antimicrobial susceptibility testing for the antibiotics, ciprofloxacin and cefazolin, within approximately 120 minutes.

“This confirms that in resource-limited settings, a Fidget-AST could be a viable alternative to conventional ASTs methods, unlike which a Fidget-AST can be performed instrument-free by someone with minimal training,” said Cho.

Taken together, these findings indicate that the Dx-FS could be used in low-resource settings as an inexpensive handheld point-of-care device for the rapid concentration and detection of UTI pathogens.

However, noted Cho, “our proof-of-concept study involved only Escherichia coli, which causes an estimated 80% of UTIs, so in future, further tests should be performed for other bacterial species such as Klebsiella pneumoniae or Proteus mirabilis.”

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