Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

The brittleness of aging bones -- more than a loss of bone mass

30.08.2011
Berkeley Lab researchers show how loss of bone quality also a major factor

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.

"In characterizing age-related structural changes in human cortical bone at the micrometer and sub micrometer scales, we found that these changes degrade both the intrinsic and extrinsic toughness of bone," says Berkeley Lab materials scientist Robert Ritchie. "Based on multiscale structural and mechanical tests, we attribute this degradation to a hierarchical series of coupled mechanisms that start at the molecular level."

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!
Further information:
http://www.lbl.gov

More articles from Studies and Analyses:

nachricht The Great Unknown: Risk-Taking Behavior in Adolescents
19.01.2017 | Max-Planck-Institut für Bildungsforschung

nachricht A sudden drop in outdoor temperature increases the risk of respiratory infections
11.01.2017 | University of Gothenburg

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>