Shattering illusions about glass

Boxers susceptible to broken jaws are said to have "glass jaws," glass being a material that's commonly viewed as easily shattered. So, irony upon irony, researchers at the University of Missouri-Rolla are experimenting with special glasses that could be used to repair broken or diseased bones. They are mixing finely crushed, bioactive glasses with a polymer that could be injected into damaged bone. As the mixture hardens, it fills the cracks and acts as a super paste, adhering the reconnected bones to one another. Delbert Day, Curators' Professor Emeritus of ceramic engineering at Missouri, says these oxide glasses are not "foreign" to the body, like metals or pure polymers, because their ionic bonding is similar to natural bone. The glasses react with bodily fluids to form hydroxyapatite, a mineral component of living bone. "This is probably one reason why the family of bioactive glasses is not rejected by bone;' Day says. Glass gives the mixture increased mechanical strength and keeps the polymer composite from shrinking. Its reaction with bodily fluids also spurs the growth of new bone-so, in short, the glass acts as a template where bone cells can attach and multiply.

Day, a holder of 42 patents, was co-inventor of TheraSphere, a radioactive glass microsphere that's used to treat liver cancer patients. He is now developing radioactive glass spheres that could be injected into arthritic joints. The biodegradable orbs, each no more than one-fifth the diameter of a human hair, would safely deliver the radiation treatment, then dissolve. Tests on animals are promising, he says, but no human tests are in the offing any time soon. Injecting arthritic joins with radioactive particles is widely accepted in Europe as a treatment, but is not approved for humans in the United States. Thus, he suggests, it could be up to 10 years before the microspheres are commercially available. "It took over 15 years for TheraSphere to reach commercial use in humans. The wheels turn slowly," Day notes. He has also worked on hollow, biodegradable microspheres filled with drugs, which gradually deliver therapies as they dissolve to precisely targeted areas of the body.