Using nuclear magnetic resonance (NMR) spectroscopy, Ames Laboratory scientist and Iowa State University chemistry professor Klaus Schmidt-Rohr and his colleagues studied bone, an organic-inorganic nanocomposite whose stiffness is provided by thin nanocrystals of carbonated apatite, a calcium phosphate, imbedded in an organic matrix of mostly collagen, a fibrous protein.
By understanding the nanostructure of naturally occurring materials, researchers may be able to develop new light-weight, high-strength materials that will require less energy to manufacture and that could make the products in which they are used more energy efficient.
"The organic, collagen matrix is what makes bones tough," Schmidt-Rohr said, "while the inorganic apatite nanocrystals provide the stiffness. And the small thickness – about 3 nanometers – of these nanocrystals appears to provide favorable mechanical properties, primarily in prevention of crack propagation."
While bone structure has been studied extensively, how these apatite nanocrystals form and what prevents them from growing thicker was a mystery. Some research pointed to sugars being involved, but that didn't match with the NMR spectra that Schmidt-Rohr was seeing.
"We can see all the peaks clearly," he says of a spectral graph which shows the points at which specific components in bone samples resonate; these specific signatures are the key to NMR technology, "even those at the organic-inorganic interface, where the organic material's signal strength is relatively weak."
After studying bone structure over a five-year period, it was actually serendipitous that Schmidt-Rohr came across a signature that appeared to match what he was seeing.
"We had gotten some crystalline collagen samples to study," he said, "and it turned out that the supplier, Sigma-Aldrich, had used citrate to dissolve the collagen. And the citrate signature in the collagen samples matched the signature we were seeing in bone."
According to Schmidt-Rohr, the role of citrate in bone had been studied up until about 1975, but since that time, no mention was made in any of the newer literature on bone. So in essence, his research team had to rediscover it.
The case for citrate was made most convincingly when graduate research assistant Yanyan Hu was able to extract citrate from cow bone and replace it with carbon 13 (C13) -enriched citrate, resulting in a 30-fold enhancement of the NMR signals of the bone sample. The peaks matched exactly, confirming the presence of citrate on the surface where the apatite nanocrystals had formed.
Schmidt-Rohr further hypothesized that, since citrate is too large to be incorporated into the apatite crystal lattice, it must be bound to the nanocrystals' surface where it stabilizes the nanocrystals' size by preventing their further growth. The findings were published in the Dec. 28, 2010 issue of the Proceedings of the National Academy of Sciences.
"Based on the old literature, we looked at the citrate levels in a variety of types of bone and found that herring spine had the highest citrate concentration – about 13 percent by weight," Schmidt-Rohr said. "So it should hold that the citrate signal for herring spine should be three times higher than for cow bone, and indeed it was."
In further studies, the group found that higher concentration of citrate, the thinner the apatite nanocrystals in bone. This was further confirmed on bone-mimetic nanocomposites in a collaboration with Ames Lab faculty scientists Surya Mallapragada and Muffit Akinc, using a polymer template with various concentrations of citrate to synthesize apatite nanocrystals. At higher concentrations, the nanocrystals that formed were thinner and should therefore be more resistant to crack propagation. This work was published in the April 12 issue of Chemistry of Materials.
"At this point, we feel that citrate probably also has a role in the biomineralization of the apatite," Schmidt-Rohr said. "It's also been noted in the literature that as an organism ages, the nanocrystal thickness increases and the citrate concentration goes down," Schmidt-Rohr said, "and there's also support from clinical studies that citrate is good for bones," adding that one of the leading supplements for bone strength contains calcium citrate.
"While calcium loss is a major symptom in osteoporosis, the decline of citrate concentration may also contribute to bone brittleness," he said.
The work was supported by DOE's Office of Science. The Ames Laboratory is a U.S. Department of Energy Office of Science national laboratory operated by Iowa State University. The Ames Laboratory creates innovative materials, technologies and energy solutions. We use our expertise, unique capabilities and interdisciplinary collaborations to solve global problems.
Kerry Gibson | EurekAlert!
Let the good tubes roll
19.01.2018 | DOE/Pacific Northwest National Laboratory
Method uses DNA, nanoparticles and lithography to make optically active structures
19.01.2018 | Northwestern University
On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.
We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
19.01.2018 | Materials Sciences
19.01.2018 | Health and Medicine
19.01.2018 | Physics and Astronomy