Layers of ice of few nanometres thick can remain frozen at human body temperature when grown on top of diamond sheets with a surface layer of sodium, detailed calculations suggest.
The icy coatings could help make diamond-toughened medical implants more biocompatible, according to the Harvard University team who carried out the work.
Thin diamond coatings are found in a growing number of wear-resistant medical implants, such as prosthetics, artificial heart valves and joint replacements. However, diamond can causes clotting by attracting coagulating proteins. Also, its hardness often results in more tissue abrasion than with other implant materials. Ice could lessen these effects by offering a biocompatible interface of water molecules.
This sodium layer would sustain a layer of ice around 2 nanometres thick at 37°C (human body temperature), thus providing a biologically compatible “barrier” to the diamond itself.
The researchers arrived at their result by using a computer simulation based on “molecular dynamics”. In particular, they simulated the motion of water atoms sitting on top of a sodium-diamond surface at different temperatures over long time periods. The calculations show that the ice layer can remain frozen at elevated temperatures thanks to dipole interactions between the water molecules and the film surface.
In 2001 researchers produced tiny tubes of ice inside carbon nanotubes; last year another group created nanoscale ice at room temperature, and showed that this could act like unwanted “glue” in extremely small devices of the future. But the new theoretical result is the first to suggest a practical application for nano-ice.
“We think our discovery will prove crucial for making scratch-resistant diamond coatings for medical implants – such as prosthetic joints – more bio-friendly,” Wissner-Gross told New Scientist. “The warm ice layer stabilised by the diamond could protect tissue from abrasion, as well as prevent blood clotting on the diamond’s surface,” he adds.
“This is an interesting result,” says David Martin, a professor of biomedical engineering at the University of Michigan and chief scientific officer at Biotectix, a company that makes soft, polymer coatings for biomedical devices. “The ability to create a hydrophilic layer on a hard diamond or diamond-like substrate may well prove to be an important advance.”
However, Martin warns that the new method may not solve the main problem with such devices – that the mechanical properties of implants are incompatible with those of soft, biological tissue. “The ice coating will be extremely thin and flat, and the difference in mechanics, as seen by a cell, will not be much different than the uncoated object,” he says.
Wissner-Gross has produced a short film about the research, which can be viewed on his website.
Journal reference: Physical Review E (DOI: 10.1103/PhysRevLett.97.036107)