Novel nanomaterial controls the race for the surface

With the increase in the demand for medical devices as a direct result of an ageing population, the prevention of infection resulting from medical biomaterials has become a global challenge.

Once a medical device is implanted into the human body, human and bacterial cells compete to colonise as much of the surface as possible. 

This means that despite strict sterilisation and aseptic procedures being applied, bacterial infection can become a major impediment to the use of medical devices.

An international team of researchers from RMIT, Swinburne University of Technology and Universitat Rovira I Virgili (Spain) collaborated to develop an excellent long-term antibacterial surface with integrated bactericidal capability, which represents a significant prospect for use in the design of antibacterial nanomaterials, especially in an era of increasing concern for antibiotic resistance.

According to Professor Russell Crawford, Executive Dean of the School of Science, the team exploited a unique surface “nanotopology” to physically rip apart attaching bacteria while leaving human cells unscathed.

“The study was extended to include the assessment of the bactericidal potential of dragonfly wings and black silicon; both of which are composed of bactericidal nanostructures,” he explained.

“Black silicon is a synthetic analogue of dragonfly wings, with similar bactericidal properties and its surface is made up of tiny spikes, reminiscent of a bed of nails.

“Because bacteria are small compared to these spikes, they place tremendous mechanical stress on them, causing them to rupture.

“But human (i.e. eukaryotic) cells are gigantic by comparison and by having stronger cell walls and distributing their weight over more points, they remain unharmed.”

To test this, the team used either black silicon or regular silicon and pre-infected their surfaces with human pathogens.

Then they added monkey kidney cells (called COS-7 cells) to determine how they fared in the presence of the bacterial pathogens on both silicon and black silicon.

The experiment revealed that the COS-7 cells could grow over the surface of black silicon, which killed the pathogenic bacterial cells. This was not the case for the smooth silicon surface, which did not kill the bacteria.

Microscopy revealed that the monkey cells’ membranes deformed around and engulfed the tiny spikes. In addition, black silicon implanted into mice did not trigger an inflammatory response.

The findings as published in the journal ACS Applied Materials and Interfaces demonstrated that human cells can grow over a surface that had previously been contaminated with deadly bacteria.

Lead investigator Professor Elena Ivanova from Swinburne University of Technology said it meant that the implant became protected from invading pathogens, ensuring that appropriate tissue integration took place, increasing the success rates of implants.

“Surfaces such as these represent an exciting opportunity for the development of a wide range of antibacterial biomaterials for industrial and biomedical applications,” she said.