Smart coatings monitor strain and kill bacteria on orthopaedic implants

The coatings are said to integrate flexible sensors with a nanostructured antibacterial surface inspired by the wings of dragonflies and cicadas.

In their study, a multidisciplinary team of researchers found the coatings prevented infection in live mice and mapped strain in commercial implants applied to sheep spines to warn of various implant or healing failures. The research is detailed in Science Advances.

“This is a combination of bio-inspired nanomaterial design with flexible electronics to battle a complicated, long-term biomedical problem,” said study leader Qing Cao, a U. of I. professor of materials science and engineering.

Infection and device failure are major problems with orthopaedic implants, each affecting up to 10 per cent of patients, Cao said. Several approaches to fighting infection have been attempted, but all have severe limitations, he said: Biofilms can form on water-repelling surfaces, and coatings laden with antibiotic chemicals or drugs run out in a span of months and have toxic effects on the surrounding tissue with little efficacy against drug-resistant strains of bacterial pathogens. 

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Taking inspiration from the antibacterial wings of cicadas and dragonflies, the Illinois team created a thin foil patterned with nanoscale pillars like those found on the insects’ wings. When a bacterial cell attempts to bind to the foil, the pillars puncture the cell wall, killing it. 

“Using a mechanical approach to killing bacteria allowed us to bypass a lot of the problems with chemical approaches, while still giving us the flexibility needed to apply the coating to implant surfaces,” said pathobiology professor Gee Lau, a co-author of the study.

On the rear of the nanostructured foil, the researchers integrated arrays of flexible electronic sensors to monitor strain. This could help physicians watch the healing progress of individual patients, guide their rehabilitation to shorten the recovery time and minimise risks, and repair or replace devices before they hit the point of failure, the researchers said.

The engineering group worked with veterinary clinical medicine professor Annette McCoy to test their prototype devices. They implanted the foils in live mice and monitored them for any sign of infection, even when bacteria were introduced. They also applied the coatings to commercially available spinal implants and monitored strain to the implants in sheep spines under normal load for device failure diagnosis. The coatings performed both functions well. 

The prototype electronics required wires, but the researchers are planning to develop wireless power and data communications interfaces for their coatings. They are working also to develop large-scale production of the nanopillar-textured bacteria-killing foil.