A test for kidneys stones that gives a result within half an hour rather than the usual week would be a boon for patients suffering the discomfort, pain and bleeding that often accompany this common condition. Hui L of Pennsylvania State University and colleagues there and at Stanford University have developed the improved urine-testing system with a biomimetic approach they refer to as slippery liquid-infused porous surface (SLIPS)-LAB.

Kidney stones occur due when calcium salts and other materials accumulate in crystalline form in either of these organs. The solid masses can move into the urinary tract and are often passed without the person necessarily knowing. However, larger stones can cause bleeding, considerable pain and sometimes very hazardous blockages.

The standard test usually involves the patient collecting their urine in a large vessel over the course of a day and night. The fluid is then analysed for metabolic markers indicative of kidney stones being present. However, this testing process normally provides results after seven to ten days, which leaves the patient in doubt as to the cause of their pain and ongoing suffering for a week or more.

"The lengthy process, cumbersome collection procedure and delay in obtaining the results render 24-hour urine testing to be underutilized in clinical practice despite guideline recommendations," explains principal investigator Pak Kin Wong. Writing in the journal Science Advances, the team provides details of a much slicker approach. SLIPS, they explain, is a dynamic, extremely low-friction smooth surface which the team creates by locking lubricating liquids in micro/nanostructured substrates. They took inspiration from nepenthes carnivorous pitcher plants which have an extremely slippery surface that unwitting insects caught in the pitcher cannot cling to and end up falling into the insect-digesting juices within the "pitcher".

In the lab, the SLIPS-LAB allows a droplet or urine to move very readily without wetting the surface or otherwise being impeded. The droplet is moved by a Laplace pressure difference, due to surface tension which is down to the geometry of the device. Reagents can then very readily combine with the urine sample for the test to proceed quickly and easily. "We demonstrated that SLIPS-LAB enables the reagent and sample to move themselves and perform the reactions for us," Wong said. "It means the technology doesn't require a technician to run any test machinery, so it is possible to do the test in non-traditional settings, like a physician's office or even the patient's home." The doctor might then use a scanner or even a mobile phone to acquire an image of the reaction, which is then interpreted by a computer algorithm to give a diagnosis. [Li, H. et al., Sci.Adv. (2020) Vol. 6, no. 21, eaba8535; DOI: 10.1126/sciadv.aba8535]

"This should improve the management of patients with urinary stone disease and open new possibilities for stone patients to test their urine samples in mobile health settings," Wong adds.

David Bradley also writes at Sciencebase Science Blog and tweets @sciencebase. His popular science book Deceived Wisdom is now available.