Reported April 2006

BACKGROUND: When Virginia Tech's star running back fractured his ulna (an arm bone) three weeks before a big game, students in the engineering department worked with their professor to develop a better bracing system to provide better support for the athlete. They used a polypropylene/carbon fiber composite to mold a prototype, and found the prototype was stiffer and stronger than the current braces commercially available.

WHAT ARE COMPOSITES? A composite material combines two or more separate materials to build a single construct that combines the best properties of both, such as the silion-germanium-arsenide composites used to build ultra-fast semiconductor chips. More common materials, such as concrete, paper, cardboard, plywood, fiberglass and bricks are all composites. The first manmade composite was probably the adobe brick. Mud or clay can be shaped and dried into a hard block, but it has little load-bearing strength. Mixing in dried grass or straw makes the bricks tougher. Reinforced concrete has steel rods encased in a matrix to improve strength and load-bearing properties and is used in bridges and buildings. Tiny carbon nanotubes are beginning to serve the same purpose in building structures.

ABOUT FRACTURES: A fractured bone is the same thing as a broken bone. They occur because a bone area is unable to support the energy placed on it. That energy can be acute, like from a car crash or a two-story fall, or chronic and low-energy repetitive activity. The latter is responsible for stress fractures, an overuse injury commonly seen in athletes. The increased demand placed on the bone causes it to remodel and become stronger in areas of higher stress. If the repetitive demands become too great, however, a stress fracture can result.

HOW BONES HEAL: The 206 bones in the body renew themselves continually through a process known as remodeling, which is also how fractures heal. Complex chemical signals prompt osteoclast cells to break down and remove old bone through absorption, while osteoblast cells deposit new bone. When a bone breaks, inflammatory cells rush to destroy invaders and isolate injured tissue, causing pain, swelling and heat at the breakage site for a few days. Tiny new blood vessels, or capillaries, along with new cells begin growing into the site. New connective tissue bonds fractured bone ends and the remodeling process begins.

DON'T SMOKE! Research shows smoking cigarettes can significantly slow down healing time for bone fractures -- it can take more than two months longer. Bones are nourished by blood carrying nutrients, minerals and oxygen. Smoking elevates the levels of nicotine in the blood, causing the vessels to constrict by as much as 25 percent, decreasing blood flow and consequently the levels of nutrients supplied to the bones.

If you would like more information, please contact:

Lynn Nystrom
Public Information Officer, Virginia Polytechnic University
Blacksburg, VA
540-231-4371
tansy@vt.edu

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