It is a well-established fact that as we grow older, our bones become more brittle and prone to fracturing. It is also well established that loss of mass is a major reason for older bones fracturing more readily than younger bones, hence medical treatments have focused on slowing down this loss.
However, new research from scientists at the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) shows that at microscopic dimensions, the age-related loss of bone quality can be every bit as important as the loss of quantity in the susceptibility of bone to fracturing.Using a combination of x-ray and electron based analytical techniques as well as macroscopic fracture testing, the researchers showed that the advancement of age ushers in a degradation of the mechanical properties of human cortical bone over a range of different size scales. As a result, the bone's ability to resist fracture becomes increasingly compromised. This age-related loss of bone quality is independent of age-related bone mass loss.
Ritchie, who holds joint appointments with Berkeley Lab's Materials Sciences Division and the University of California (UC) Berkeley's Materials Science and Engineering Department, is the senior author of a paper published in the Proceedings of the National Academy of Science (PNAS) that describes this work. The paper is titled "Age-related changes in the plasticity and toughness of human cortical bone at multiple length scales."
Co-authoring the PNAS paper with Ritchie were Elizabeth Zimmermann, Eric Schaible, Hrishikesh Bale, Holly Barth, Simon Tang, Peter Reichert, Björn Busse, Tamara Alliston and Joel Ager.
Human cortical or compact bone is a composite of collagen molecules and nanocrystals of a mineralized form of calcium called hydroxyapatite (HA). Mechanical properties of stiffness, strength and toughness arise from both the characteristic structure at the nanoscale, and at multiple length scales through the hierarchical architecture of the bone. These length scales extend from the molecular level to the osteonal structures at near-millimeter levels. An osteon is the basic structural unit of compact bone, comprised of a central canal surrounded by concentric rings of lamellae plates, through which bone remodels.
"Mechanisms that strengthen and toughen bone can be identified at most of these structural length scales and can be usefully classified, as in many materials, in terms of intrinsic toughening mechanisms at small length scales, promoting non-brittle behavior, and extrinsic toughening mechanisms at larger length scales acting to limit the growth of cracks," Ritchie says. "These features are present in healthy, young human bone and are responsible for its unique mechanical properties. However, with biological aging, the ability of these mechanisms to resist fracture deteriorates leading to a reduction in bone strength and fracture toughness."
Working with the exceptionally bright beams of x-rays at Berkeley Lab's Advanced Light Source (ALS), Ritchie and his colleagues analyzed bone samples that ranged in age between 34 and 99 years. In situ small-angle x-ray scattering and wide-angle x-ray diffraction were used to characterize the mechanical response of the collagen and mineral at the sub micrometer level. A combination of x-ray computed tomography and in situ fracture-toughness measurements with a scanning electron microscope were used to characterize effects at micrometer levels.
"We found that biological aging increases non-enzymatic cross-linking between the collagen molecules, which suppresses plasticity at nanoscale dimensions, meaning that collagen fibrils can no longer slide with respect to one another as a way to absorb energy from an impact," Ritchie says. "We also found that biological aging increases osteonal density, which limits the potency of crack-bridging mechanisms at micrometer scales."
These two mechanisms that act to reduce bone toughness are coupled, Ritchie says, in that the increased stiffness of the cross-linked collagen requires energy to be absorbed by "plastic" deformation at higher structural levels, which occurs by the process of micro cracking.
"With age, remodeling of the bone can lead the osteons to triple in number, which means the channels become more closely packed and less effective at deflecting the growth of cracks," he says. "This growing ineffectiveness must be accommodated at higher structural levels by increased micro cracking. In turn, the increased micro cracking compromises the formation of crack bridges, which provide one of the main sources of extrinsic toughening in bone at length scales in the range of tens to hundreds of micrometers. Thus, age-related changes occur across many levels of the structure to increase the risk of fracture with age."
This research was supported by a grant from the the National Institutes of Health. The Advanced Light Source is a national user facility supported by the DOE Office of Science.
Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 12 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit www.lbl.gov.
Lynn Yarris | EurekAlert!
Drone vs. truck deliveries: Which create less carbon pollution?
31.05.2017 | University of Washington
New study: How does Europe become a leading player for software and IT services?
03.04.2017 | Fraunhofer-Institut für System- und Innovationsforschung (ISI)
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
28.06.2017 | Physics and Astronomy
28.06.2017 | Physics and Astronomy
28.06.2017 | Health and Medicine