Twist in a clogged tale

a springy plastic wire that changes shape at the flick of a switch can become an answer to the woes of stroke patients. Cerebral arteries clogged by blood clots cause most strokes. At present, surgeons remove these clots by using drugs that dissolve the clots. But the risk of these drugs far outweighs their potential benefits -- they can cause potentially fatal haemorrhages.

Now engineers at California-based Lawrence Livermore National Laboratory have devised a novel way for clot removal -- a plastic wire made from a shape-memory polymer. The wire can change shape because it is made from two types of synthetic plastics bundled into one. One type is harder than the other.

During their laboratory testing of the wire, the engineers fixed it to the end of an optical fibre and put both into a catheter. They then inserted the catheter into a pig's blood clot. After the fibre speared the clot, the catheter was withdrawn. The wire was then heated by shinning infrared light down the fibre. This transformed the wire into a coil. "The wire changed into a coil in a fraction of a second," said Duncan Maitland, one of the engineers. When the wire coiled up, it gripped the clot from behind. When it was withdrawn along with the optical fibre, the clot also came out ( New Scientist , Vol 173, No 2334, March 16, 2002, p20).

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