Shape-changing element holds key to anti-bacterial coating

February 20, 2019, University of Canterbury
Pictured left to right: University of Canterbury PhD students Rukmini Gorthy and Johann Land and research lead Mechanical and Materials Engineering Professor Susan Krumdieck are co-authors on a paper about a new anti-microbial coating breakthrough. Credit: University of Canterbury

A University of Canterbury research team is another step closer to developing germ-proof surface coatings for environments such as hospitals, after an unexpected development in the lab.

Once commercially available, an anti-microbial applied to high-traffic surfaces, such as door handles, will help minimise infections that spread within hospitals.

Research lead UC Professor Susan Krumdieck had been working with titanium oxide (TiO2), a well known ceramic compound, for over a decade when the element suddenly changed form.

"TiO2 is famously bright white or transparent, but one day the coating came out all black," she says.

"We set it aside because we really didn't know what had happened. But then some undergraduate project students tested it for the self-cleaning performance, and it was so photocatalytically active without any UV radiation that we knew we had discovered something new."

TiO2 is used in sunscreens because it has the ability to absorb radiation. This action creates energy, which is expressed as oxygen ions and oxygen ions are deadly to bacteria. TiO2 is therefore ideal for use on surfaces such as door handles in environments where sterility is a priority, such as hospitals.

Professor Krumdieck pioneered the innovative coating technology during her Ph.D. at the University of Colorado in Boulder, United States, and continued her research in New Zealand at UC, winning a Marsden Fund grant to explore pulsed-pressure vacuum processing, which had not been used before in research or in industry. This was followed by a competitive funding grant with colleague Professor Mark Jermy to collaborate with a top university in Taiwan.

However, Professor Krumdieck and her team of 14 interdisciplinary UC researchers still had two challenges to overcome – how to fix a TiO2 coating onto something like a door handle, and how to activate it without UV radiation. The new black TiO2 held the key to both.

Shape-changing element holds key to anti-bacterial coating
Researchers at the SiMAP Institute were intrigued that the material could be the same as white TiO2 according to analysis, but instead of the typical smooth pyramid crystals of TiO2, the French team, led by Professor Raphaël Boichot, found that the crystals were nanostructured in ways previously only possible by hydrothermal growth of individual nanoparticles. Credit: University of Canterbury

Research collaborator Tim Kimmett at Callaghan Innovation helped to solve the puzzle.

"We spent a fun science day playing with the Scanning Electron Microscope and X-ray diffractometer and really marvelling at how different this material was. We knew had had a new material due to the strange nanostructures we were seeing, and of course the striking black colour," Professor Krumdieck says.

A few months later Professor Krumdieck was awarded a visiting researcher fellowship at Université Grenoble Alpes in France and took a few of the black coating samples with her. Researchers at the SiMAP Institute were intrigued that the material could be the same as white TiO2 according to analysis, but instead of the typical smooth pyramid crystals of TiO2, the French team, led by Professor Raphaël Boichot, found that the crystals were nanostructured in ways previously only possible by hydrothermal growth of individual nanoparticles.

"Professor Boichot suggested that the material could have visible light antimicrobial activity. When I got back to UC, I was lucky to run into Professor Jack Heinemann who is an expert in microbiology, and he worked with his students to set up a testing system," Professor says.

"Sure enough, the bacteria did not stand a chance – even after a short time in visible light."

With no need for radiation to energise the new form of TiO2 and an altered nanostructure that enables the compound to be fixed in coatings, the conditions are right for the multi-disciplinary team to move ahead to developing commercial applications.

The UC researchers have successfully deposited the black coating onto a door handle, and are now working with several companies to complete the engineering development science needed for designing and upscaling for advanced manufacture. Interested international companies are watching progress and hoping the black TiO2 will soon be warding off germs on hospital bed rails and door handles around the world.

Explore further: Attacking bacteria with shark skin-inspired surfaces

More information: Susan P. Krumdieck et al. Nanostructured TiO2 anatase-rutile-carbon solid coating with visible light antimicrobial activity, Scientific Reports (2019). DOI: 10.1038/s41598-018-38291-y

Related Stories

Attacking bacteria with shark skin-inspired surfaces

June 13, 2018

Sharks are often the subject of TV specials or news stories focusing on their attacks on humans. But scientists are finding that sharks could inspire a new type of surface that would attack bacteria, helping humans instead ...

Cicada wings inspire antireflective surfaces

October 11, 2016

A team of Shanghai Jiao Tong University researchers has used the shape of cicada wings as a template to create antireflective structures fabricated with one of the most intriguing semiconductor materials, titanium dioxide ...

Recommended for you

How fluid viscosity affects earthquake intensity

March 21, 2019

Fault zones play a key role in shaping the deformation of the Earth's crust. All of these zones contain fluids, which heavily influence how earthquakes propagate. In an article published today in Nature Communications, Chiara ...

Sustainable fisheries and conservation policy

March 21, 2019

There are roughly five times as many recreational fishers as commercial fishers throughout the world. And yet, the needs and peculiarities of these 220 million recreational fishers have largely been ignored in international ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.