Glass Engineering For Sponges

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Glass engineering for sponges described in an article in Science, vol 309, p253, 8 July 2005. A team of scientists led by Joanna Aizenberg of Bell Laboratories/Lucent Technologies, Murray Hill, New Jersey has studied the skeleton of the glass sponge, Euplectella, to see how it constructs a strong stable structure from spicules of glass. Glass is a brittle, inflexible substance that cracks easily but sponges need resilience and tensile strength, as well as rigidity in their skeletons in order to cope with ocean currents. Aizenberg's team found the combination of rigidity and resilience in the sponge skeleton came from the precise organisation of component parts in the way they were built up, starting from microscopic glass spicules to the overall shape of the skeleton.

The researchers identified seven levels of organisation, some involving combining the glass with organic materials. The first, most microscopic level consisted of nanometre sized glass spheres arranged around a filament of protein. These clusters are arranged into alternating layers of silica and organic materials to form larger (but still microscopic) spicules, which were bundled into rod shaped spicules. The rods are arranged into a grid structure with struts running lengthways, crossways and diagonally. The resulting square meshwork is cemented together with a layer of silica and is very good at resisting shearing forces. This grid structure is rolled into a curved cylinder, and this is reinforced with surface ridges running in helical pattern along the cylinder, which enable the structure to resist twisting forces. Finally the whole structure is anchored to the sea floor by flexible struts that enable the whole sponge to bend freely with ocean currents and not break.

The researchers also comment the glass itself has optical properties similar to manufactures optical fibres. In their conclusion the researchers write: "The resultant structure might be regarded as a textbook example in mechanical engineering, because the seven hierarchical levels in the sponge skeleton represent major fundamental construction strategies such as laminated structures, fibre-reinforced composites, bundled beams, and diagonally reinforced square-grid cells, to name a few. We conclude that the Euplectella sp. skeletal system is designed to provide structural stability at minimum cost, a common theme in biological systems where critical resources are often limited. We believe that the study of the structural complexity of unique biological materials and the underlying mechanisms of their synthesis will help us understand how organisms evolved their sophisticated structures for survival and adaptation and ultimately will offer new materials concepts and design solutions."

Editorial Comment: The paragraph quoted above indicates that the scientists who carried out the study of the Euplectella skeleton can recognise engineering design when they find it. The American Association for the Advancement of Science (AAAS) which publishes the journal Science is also obviously pleased to have engineering design presented in their journal. However, in the recent political and legal debate about the teaching of "intelligent design" in science classes, the AAAS has been amongst the loudest in proclaiming it is unscientific to claim living organisms have been designed if that design comes from an outside intelligence. This is in spite of the fact that it is easy to show the probability of seven levels of mutually dependant design occurring naturally is zero. This inconsistency points to the real problem evolutionary scientists have with design. It is not that there is no evidence for design. Rather, they do not want to be confronted with a personal Designer, Who is more powerful than them, and Who will call them to account for how they responded to the overwhelming evidence He built into the world they study. (Ref. biotechnology, education, design)

 

 

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