By Gail Gallessich

	A close look at a bone’s interior reveals shock-absorbing “glue” mechanisms (arrows).

UC Santa Barbara scientists have described a sort of “glue” in human bone that helps healthy bone resist fracture and heals bone fractures at the molecular level. It is being hailed as a major new discovery with implications for treatment of fractures.

Their research, and that of a Brazilian collaborator, made the cover of a recent issue of the international journal Nature Materials. Included with the article are the highest resolution images of bone ever published, which reveal the location of the adhesive or “glue” that holds together mineralized collagen fibrils (protein fibers) of bone.

The glue appears to contain “springs” that uncoil when the bone is stressed, helping the bone to absorb shock. The springs return to their original structures when the stressed bone relaxes.

The possible implications for human health are important, explained Georg E. Fantner, a UCSB physics doctoral student and first author of the report. “The findings may lead to therapy for bone fracture, or even to prevention,” he said.

Working in the laboratory of physicist Paul K. Hansma, in collaboration with the UCSB labs of molecular geneticist Daniel E. Morse, and biochemist Galen D. Stucky, the interdisciplinary group of scientists spent years tracking where the glue was located in bone and how it worked.

“Before this research, it was well known that the mechanical properties of bone depended on mineral particles and on collagen fibrils,” said Hansma. “What we found is that there is a glue in bone that holds these mineralized collagen fibrils together. This glue involves sacrificial bonds (of hidden length) that uncoil when the bone is stressed.”

This is “a fundamental and new discovery in an old and well-studied field,” Hansma added.

Said co-author Morse, director of UCSB’s Institute for Collaborative Biotechnologies: “It’s especially exciting for us to find the profound medical significance of our discoveries for human bone.” Six years ago, he described finding “molecular shock absorbers” that provided a self-healing glue holding together biological mineralized structures in the shells of abalone.

“It’s truly remarkable to find the same fundamental mechanisms operating in bone,” said Morse.

He noted that these mechanisms give young, healthy bone tremendous resiliency and resistance to fracture, and help heal small microcracks soon after they’ve formed. “We’re especially interested in learning how these molecules change and become depleted with age as well as in certain diseases,” said Morse.

Hansma explained, “The thing that’s exciting about this research is that we’ve identified a mechanically important component of bone.” When the exact molecules are identified, these can become therapeutic targets, for example, of diet or drug therapy.

Bone fracture is one of the leading factors in a decreased quality of life for the elderly. “Less than one-third of elderly women who have a hip fracture return to previous function,” Hansma said. “More women die within a year of hip fracture than die after a heart attack.”

And although bone is extensively studied, little is known about how bone works at the molecular level. “Our paper is the beginning research on this,” added Hansma.

In addition to Fantner, Hansma, Stucky and Morse, co-authors from UCSB include Tue Hassenkam, Johannesh H. Kindt, Leonid Pechenik, Jacqueline A. Cutroni, James C. Weaver, and Henrik Birkedal. Geraldo A. G. Cidade of the Biophysics Institute Carlos Chagas Filho at the Federal University of Rio de Janeiro also contributed.