Newly discovered properties of hydroxyapatite’s band structure open doors for medical applications

Hydroxyapatite (HAp), an important compound found in bones and teeth, has become widely used in medical implants, but its fundamental properties remain poorly constrained. New research on HAp’s optical and electronic properties, reported in The Journal of Chemical Physics, reveals a fresh look at the material, finding a highly directional and dispersive conduction band. The finding could pave the way for the development of biocompatible electronic-grade materials.

The study modeled HAp using hybrid density functional theory and state-of-the-art many-body perturbation methods. “The way that scientists have been describing the motion of electrons in this material is inaccurate,” said co-author José Coutinho. They found that previous conventional methods using a local or semilocal treatment to account for the many-body electronic interactions leads to severe errors in the description of HAp’s optoelectronic properties.

The authors modeled and calculated fundamental properties of HAp, including optical transitions, describing how light interacts with the material and how imperfections impact electron interactions and transitions. The new research found icelike wavefunctions in conduction band states, localized on linear OH-chains. Consequentially, replacing calcium cations with donor dopants — which would allow electron transfer along the OH-chain — would create a conductive HAp. This method could be used to fabricate a new electron-grade HAp, opening up a wide range of functionalities in medical implants.

The newly described properties will also allow scientists to understand the mechanisms behind HAp-based photocatalysis, a way to accelerate chemical reactions with vast applicability, including splitting water to produce hydrogen and the conversion of carbon dioxide into hydrocarbons.

Source: “Optoelectronics and defect levels in hydroxyapatite by first-principles,” by Leon A. Avakyan, Ekaterina V. Paramonova, José Coutinho, Sven Öberg, Vladimir S. Bystrov, and Lusegen A. Bugaev, Journal of Chemical Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5025329 .