Silica nanoparticles help keep microbes at bay.

Silica nanoparticles help keep microbes at bay.

UK researchers have developed a ’non-stick’ coating that prevents bacteria and other living cells from attaching to surfaces and multiplying. The coating, based on silica nanoparticles, could have a wide range of applications from keeping clinical equipment free from pathogenic microbes to preventing unsightly mould growing on tiles around the shower.

The team at the University of Liverpool found that coating glass slides with silica particles a few nanometres in diameter prevented cells from sticking to the slides and proliferating. Many cell types appear to be affected, including bacteria, fungi and mammalian cells.

The surface is first treated with a cationic polymer or surfactant to give it a uniform positive charge. It is then exposed to an aqueous suspension of the silica particles. The negatively charged particles adhere to the surface in random arrays, with each particle in contact with its neighbour.

If a glass slide is coated on one half with the particles and then exposed to a culture of cells, the cells attach to the uncoated side and proliferate up to the boundary with the silica, but fail to encroach on it (see image).

’The cells just stop in their tracks when they meet the silica coating,’ says Mike Garvey, a colloid scientist in the University’s Department of Physics. ’It appears that the cells cannot get a grip on the silica. What we think is happening is that when the silica particles make lateral contact with each other on the surface they undergo condensation to form Si-O-Si bonds. Due to the thermodynamics of surfaces, the high radius of curvature of such small nanoparticles gives rise to dissolution of the curved surface and deposition on the particle-particle contact points. It is this transfer of material on the surface, which continues over several weeks, which we believe plays a significant part in preventing cellular adhesion,’ he explains. ’It is as if there is a brittle skin over the surface; it’s a bit like trying to grab thin sheets of ice from the top of a frozen pond. You can’t get a firm hold.’

The silica particles are widely available commercially and do not need to be manufactured specially. Garvey predicts that the coating system could be used in the clinic to prevent films of bacteria growing on equipment. The system could also have applications in wound dressings because it prevents adherence of mammalian cells and could thus stop healing tissue from sticking to dressings. It could even be used as a spray coating in bathrooms to prevent the growth of mould, he suggests. The university is now in the process of establishing a company to develop and market the technology.

Simon Hadlington