Biomedicine: An adhesive secreted by a marine worm inspires a promising new treatment for compound fractures of human bones
TORN flesh is easy to put back together with stitches, but when bone breaks, repairs are nowhere near as simple. Bones with fractures that run in a straight line can often be placed back in their proper alignment and set in a cast to heal. Compound fractures, however—those that involve bones shattered into fragments—pose more of a challenge. Large fragments can, with the aid of metal screws and pins, be reattached and set in place for healing. Small fragments cannot be treated in the same way, as they are often too tiny to be connected with metal hardware. Medics have long sought a glue to do this work, and now Russell Stewart of the University of Utah may have found one in the secretions of a marine worm.
The sandcastle worm, as the creature is known, lives in a mineral shell. It does not, however, secrete this shell directly in the way that, for example, a mollusc does. Instead it secretes a glue and uses this to stick bits of sand together to form its casing. The glue does not dissolve in water. Indeed, it is able to displace water and thus adhere to surfaces even underwater. And it solidifies soon after being secreted. It, or something like it, therefore sounds ideal for repairing bones.
Dr Stewart and his team began by analysing sandcastle-worm glue to see how it works. What they found was a mixture of proteins, some positively charged and some negatively charged, and a lot of calcium and magnesium ions. The combination produces a material that can, when circumstances are right, bind the protein molecules so tightly together that any water molecules between them are expelled. The trigger for this to happen is a change in acidity. The gland in which the glue is generated is mildly acidic. In these circumstances the glue remains liquid. Seawater, however, is alkaline. This alkalinity causes the glue to set. It solidifies into a foam within 30 seconds and becomes a flexible, leathery substance over the course of several hours.
Having understood how the sandcastle worm performs its trick, Dr Stewart was in a position to replicate it. Instead of proteins, he and his team used two synthetic polymers. These, however, had the same crucial chemical groups as their natural counterparts and similar electric charges. The result, as the team reported to a recent meeting of the American Chemical Society, was a substance even better, from a medical point of view, than the natural glue. Not only did it solidify in response to changes in acidity, it also did so in response to changes in temperature, being liquid at room temperature and solid at body temperature.
The resulting glue not only sticks bits of bone together in watery environments, but also does so with twice the strength of the glue used by the worm. And, although it is still early days, preliminary tests suggest it is both non-toxic and biodegradable. If further testing confirms this, it means that, as the broken bone heals, the glue will disappear naturally. Compound fractures will thus heal more easily.
This article appeared in the Technology Quarterly section of the print edition under the headline "Glue bones"
From the December 12th 2009 edition
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