Making polymers for surgical implants.

Making polymers for surgical implants

Making artificial materials that the biologically complex human body can safety assimilate keeps a community of medically minded polymer chemists working.

Since the mid-1980s, chemical engineer Robert Langer of the Massachusetts Institute of Technology in Cambridge and his colleagues have been developing a family of degradable polymers called polyanhydrides. Sixteen medical centers now use one of these to treat certain brain cancer patients. When injected, powerful cancer-fighting drugs can kill healthy cells along with malignant ones. To minimize this systemic toxicity, doctors implant drug-laced polyanhydride capsules directly into the cancerous region of the brain without exposing other body parts to the drug. As the implant degrades "like a bar of soap," it slowly releases the drug, Langer explains.

Now, he and his co-workers aim for a new family of degradable polymers strong enough to use as temporary bone screws, plates and other load-bearing implants. The new polymers contain two types of building blocks. The researchers make the strength-giving component by reacting trimellitic anhydride with an amino acid such as glycine. This yields a product containing a tough imide bond--similar to the rigid linkage that makes the polymer Kevlar strong enough to serve in bulletproof vests. The other component contains a long, flexible carbohydrate chain and forms the easily degradable anhydride bond when it links to the imide-containing components. By varying the proportions of the two components as well as their constituent amino acids and carbohydrate chains, Langer expects to design polymers with specific degradation rates and strengths. The researchers outline the chemical procedures for making the materials in the May 23 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY.

"This should open up a whole new series of medical applications where one would want both degradability and strength," he told SCIENCE NEWS.