Bone discovery to aid medical implants

A team from UL provides important new data on one of the world's most popular bone and dental implant materials that could aid…

A team from UL provides important new data on one of the world's most popular bone and dental implant materials that could aid biocompatability, writes Dick Ahlstrom.

Scientists at the University of Limerick have published important new information about the structure of a widely used bone-implant material. Their work could lead to major improvements in the performance of the substance, hydroxyapatite.

The work was carried out at UL's Materials and Surface Science Institute (MSSI). The team provided a much better model of the substance's structure, and discovered that like real bone, hydroxyapatite can produce piezoelectricity when stressed.

"Hydroxyapatite has been used for a long time in dental fillings and artificial bone," says Seamus McMonagle, a senior lecturer in physical chemistry and a member of the MSSI group. What wasn't known until the team's publication earlier this month in the journal, Physical Review B, was that the existing structural models for the substance were wrong, and no one had recognised its piezoelectric potential.

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"We found that there were two commonly accepted structures for it but neither of them had any piezoelectric effect. We proposed an alterative structure for hydroxyapatite that fitted its properties much better," says McMonagle.

Hydroxyapatite is a pure compound in its own right, a calcium phosphate with other compounds associated with it, he explains. The group began looking at it when one of the team was trying to calculate quantum energy values related to it and saw that the existing models didn't fit their data.

Using facilities funded under the HEA's Programme for Research in Third Level Institutions, they carried out quantum mechanical simulations of the crystal structure and thermal stability of hydroxyapatite.

Existing X-ray diffraction patterns of the compound revealed weak peaks that had been ignored in existing structural models, says McMonagle.

"People had tried to explain away these signals but they were related to the hydroxyapatite structure. We also did energy calculations for these computer simulations."

The result was a much better structural model for hydroxyapatite, opening up as a consequence ways to better exploit the material.

"It helps us understand the bioactivity of the material," McMonagle says. The existing models did not predict piezoelectric effects, and this is the most exciting thing about the discovery, states Donnacha Haverty, MSSI quantum chemist and team member. "Piezoelectricity has been a known property of natural bone for many years, and it is considered one of the driving mechanisms by which bones grow and bond together," he says.

"This is of potentially huge significance in terms of developing new bone-implant structures that utilise this piezoelectric potential and are thus much more bioactive and biocompatible," he adds.

The team is now trying to measure the level of piezoelectricity the substance can produce, with expectations of a "reasonable level" that could aid biocompatibility, says McMonagle.

The work is of considerable importance given the value of hydroxyapatite in medical implants, adds the director of the MSSI, Dr Edmond Magner. "With an estimated €2.1 billion global market for bone and dental implants, this sector of the healthcare and biomedical industry is obviously important to the Irish economy," he says.

"This work is a good example of how government investment in basic scientific university research could translate into marketable products with a distinct competitive edge."