Light hardens bone-like polymer

Science News, March 13, 1999 by C.W.

Severe bone fractures sometimes need more help than a simple plaster cast can provide. Now, a new polymer that can act as a temporary bone replacement might offer doctors another tool to repair orthopedic defects. The material is not only hard and strong, but it also gradually breaks down in the body, allowing natural bone to regrow in its place.

The polymer starts out as a putty and hardens when exposed to blue light. In this way, the material can be spread into an area of missing bone and then triggered to solidify in the needed shape.

This polymer is one of the first systems that combines biodegradability with a light-triggered setting mechanism, says Robert Langer of the Massachusetts Institute of Technology. He, his MIT colleague Venkatram R. Shastri, and Kristi S. Anseth of the University of Colorado at Boulder report their findings in the February Nature Biotechnology.

The researchers demonstrated the utility of the light-hardening process in the laboratory by molding the polymer into bone screws, which are often used to hold together fractures. Shining light on just the head of a 4-centimeter-long screw caused the entire piece to solidify.

They also tested the polymer by surgically creating a hole 2 millimeters in diameter in a leg bone of a rat and filling it with the putty. After exposure to light, the restoration bonded to the existing bone without causing inflammation in the surrounding tissue.