Nobody wants harmful bacteria colonizing the surfaces of objects such as medical implants, yet we also don't want them building up a resistance to antibiotics. Well, help may be on the way, in the form of tiny metal structures that kill the microbes by poking holes in them.
Metal-organic frameworks (MOFs) are a relatively new class of nanostructure, officially defined as "hybrid inorganic–organic microporous crystalline materials formed from metal ions and organic linkers through coordination bonds." And while they have been used to kill bacteria before, they've typically done so by releasing antimicrobial agents or heavy metal ions.
Scientists at Sweden's Chalmers University, however, have now taken a different approach.
They created a microscopic coating made up of two layers of MOFs grown one on top of the other. By precisely controlling the crystalline growth of the material, the researchers were able to tweak the spacing of sharp "nanotips" that protruded from the two layers of MOFs.
The spacing is such that when an individual bacterium lands on the coating, the nanotips pierce its protective outer membrane. This results in the death of the microbe, without promoting the development of antibiotic-resistant bacteria.
"If the distance between the nanotips is too large, bacteria can slip through and attach to the [underlying] surface," says Dr. Zhejian Cao, lead author of the study. "If the distance is too small, however, the mechanical stress exerted by the nanotips on the bacterial cell capsule may be reduced so that the bacteria survive – the same principle that allows you to lie on a bed of nails without getting hurt."
It is hoped that the MOF coating could ultimately be utilized not only on objects like implants and catheters, but even in non-medical applications such as ship hulls and the inner walls of pipes, where it would prevent biofouling by keeping bacterial biofilms from forming.
A paper on the research was recently published in the journal Advanced Science.
And just for the record, layered MOFs aren't the only things capable of killing bacteria by shredding their outer membranes. Scientists have also had success with spiky coatings inspired by the wings of cicadas and dragonflies, and that are made out of copper-coated stainless steel.
Source: Chalmers University
