By mimicking tiny features of insect wings and shark skin, a team from Bengaluru’s Indian Institute of Science (IISc) has found a way to prevent bacterial infection on orthopaedic implants without using chemicals.
The team led by Kaushik Chatterjee from the Department of Materials Engineering at IISc relied purely on surface nanostructure to give the titanium metal used in implants the ability to kill bacteria.
Encouraging results were achieved in laboratory studies by making the shiny surface of implants rough through etching. The etched titanium surface is marked by randomly spaced nanopillars of 1 micrometre height and this makes it capable of killing infection-causing bacteria that adhere to the surface. The results were published in the journal Scientific Reports.
The rough surface of titanium was able to mechanically kill, within four hours of contact, nearly 95% of E. coli, 98% of Pseudomonas aeruginosa, and 92% of Mycobacterium smegmatis. Though only 22% of Staphylococcus aureus attached to the surface were killed within four hours, the efficiency shot up to 76% at the end of 24 hours.
Research on mechanism
Hospital-based bacterial infections from orthopaedic implants can lead to medical complications.
“We don’t know the precise mechanism by which the bacteria get killed. But we think the nanopillar architecture formed by dry etching mechanically ruptures the bacterial cells. Like in the case of the wing surface of cicadas, the bacterial cell membrane might be getting stretched by the nanopillars,” says Jafar Hasan from the Department of Materials Engineering at IISc and the first author of the paper.
Bacteria have high motion capability and adhere to the surface to form a biofilm. Since titanium surface is marked by sharp tips, the cell membrane gets mechanically damaged when in contact.
While the disease-causing bacteria get killed, stem cells of the kind that form bone were unaffected by the etched surface.
Unlike bacteria that have rigid membranes, the stem cells are bigger, softer and better able to conform and attach themselves to the rough surface.
“We want to etch actual implants and carry out trials on rats and rabbits to test for bactericidal activity and to understand how the rough implant behaves inside the body and study how the bone attaches itself to the implant and grows,” says Dr. Chatterjee, the corresponding author of the paper.