Posted on 08/21/2003 11:18:43 AM PDT by bedolido
ENGINEERS often admire the ways in which living creatures solve problems. The difficulty with man-made fibre-optic cables, says Joanna Aizenberg of Lucent Technologies in Murray Hill, New Jersey, is that they often crack and break. For a solution, Dr Aizenberg and her colleagues have turned to the exquisitely structured siliceous skeleton of a deep-sea sponge known as the Venus flower basket. This sponge, they say, can do things better.
As they explain in a paper published in this week's issue of Nature, the sponge has a lattice of spiny outgrowths, or “spicules”, at its base, which provide structural support. These spicules behave remarkably like conventional fibre-optic cables. They are similar in size, and are even made of the same material. And as with commercial optical fibres, the spicules have three separate layers of material with different refractive index values which allow them to bend light waves that travel through their core.
According to Dr Aizenberg, these layers are glued together by organic films at their surface, which make them less likely to break. Furthermore, the spicules are formed under normal, low-temperature conditions. Commercial optical fibres, by contrast, must be manufactured under high temperatures, and often require additives such as sodium ions to improve their refractive index properties (and hence their ability to conduct light waves). Adding the sodium ions at high temperatures is problematic, says Dr Aizenberg, because these are lost during cooling. Again, though, the spicules of the sea sponge have the upper hand, because sodium ions are naturally present throughout their lengths.
The team is not sure just how these optical fibre spicules benefit the sponge. The job of anchoring the sponge to the sea bed seems unlikely to require the high-grade optical properties found in the spicules.
The researchers do suggest one intriguing possibility, however. This is that the sponge may be using the fibres to distribute light emitted by bioluminescent animals. The filter-feeding sponge lives in the inky depths of the ocean, at between 1,000 and 15,000 feet. If it is harbouring some of the light-emitting creatures that live at these depths, the spicules may serve as a fibre-optic network to attract other micro-organisms to serve as food for the sponge. Dr Aizenberg says “it is potentially an ‘illuminated glass house' of the deep”.
The research group hopes that, by modelling such natural processes, it can not only learn more about the lifestyle of the sea sponge but also exploit its chemical prowess to build better fibre-optical materials. The Venus flower basket derives its name partly from its delicate lattice-like skeleton, and partly from the fact that its interior typically houses a pair of shrimps that breed in it for life. As such, it is a symbol of a happy marriage in some cultures. In the world of fibre-optics, a marriage between conventional technology and biology may prove equally fruitful.
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