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Lessons from the Sea: Mimicking Marine Structures
by Lay Leng TAN

and, sea and surf - the words immediately conjure up the image of a lone figure combing the beach, picking up shells against a backdrop of rolling waves. Before putting that conch to the ear, however, the shell seeker should examine its form. Its curves flow smoothly to create a marvellous structure, delicate-looking yet strong in its protective role.

Understanding how nature confers strength and other intrinsic qualities on such marine structures is the task Daniel E Morse and his colleagues at the University of California at Santa Barbara (UCSB) have set for themselves. They hope that during the learning process they will discover things from these formations that they can apply to human bodies to repair broken bone and mend torn tissue as naturally as possible.

Nature makes materials with a precision that surpasses any present human-engineering capability, marvels Morse. This synthesis occurs under very mild conditions compatible with living systems - low temperature, ambient pressure, near neutral-pH - in large contrast to the harsh and sometimes violent artificial manufacturing conditions. Furthermore, the scope of the synthesis of these materials on a global scale boggles the mind - microorganisms churn out gigatonnes of silica per year, enough to cover all the beaches in the world.

As chair of the Biomolecular Science and Engineering Program and director of the Marine Biotechnology Center, UCSB, Morse elaborates: "We aim to understand the underlying mechanism of this biological synthesis and then with our colleagues in chemistry, chemical engineering and materials research, translate these mechanisms biomimetically. The idea here is not to imitate the structures that nature makes. However, if we can extract fundamental new principles not recognised before and translate these into synthetic materials, we can hope to develop a synthetic system - one based not on proteins but rather on less expensive and more thermally robust, stable polymeric materials that could achieve the same precision control of the synthesis of these materials."

The researcher has been focusing on the identification and characterisation of the proteins, genes and molecular mechanisms that control the nanofabrication and properties of biomineralised composite structures such as seashells, pearls, bone and silica. Via interdisciplinary collaboration with various departments at UCSB - engineering, science and molecular biology - he and his team have been able to apply the power of molecular genetics and advanced physical instrumentation, such as atomic force microscopy, to identify what is special about these materials' biological synthesis.

This interdisciplinary approach has become so successful in UCSB's research on nanobiomaterials that the university administration has asked Morse to help organise a graduate instruction programme along the same lines. Relying on his team's research experience, he set up a new graduate programme - the interdepartmental graduate programme in Bio-Molecular Science and Engineering (BMSE), which unites campus faculty and students.

The cross-disciplinary and collaborative approach is not restricted to the campus. UCSB and the University of California at Los Angeles have joined forces to form the research backbone of the US$100 million California Nano Systems Institute, initiated last year by the state of California. Morse has also extended his collaboration overseas, sharing experience and knowledge with the National University of Singapore and the Institute of Materials Research and Engineering (IMRE).

A joint project with Suresh Valiyaveettil of the Department of Chemistry, NUS, analyses the molecular mechanisms at work in controlling the synthesis of biomineral composites (see "The Fascinating World of Calcium-Rich Materials Synthesis in Organisms" on page 58). They have planned a workshop to be held at UCSB in April 2003 that will cover nanotechnology, bioengineering and materials science. Participants will include faculty, researchers and students from UCSB, NUS and IMRE.

The researchers in Santa Barbara and Singapore believe that biology and biotechnology actually afford some of the best ways to approach nanotechnology experimentally. Biology at the molecular level operates on the nanoscale, i.e. the dimension in which the biological interactions of molecular recognition and all the subsequent processes occur. The powerful techniques of molecular biology and molecular genetics now make it possible to help dissect and understand these mechanisms in conjunction with physical analyses.

Morse's laboratory has discovered enzymes that catalyse the formation of silica and the polymerisation of silicon-based polymers while controlling the structure of these materials on the nanoscale. The fact that these enzymes work under biological conditions such as low temperature and neutral pH without caustic chemicals or environmental remediation makes the discovery exciting. The totally unanticipated presence of a catalytic route and an informatic route to these materials has given rise to a new field the team dubbed "silicon biotechnology."

Dow Corning Inc, the largest United States manufacturer of silicon-based materials, and Genencor International Corp, an American biotechnology firm, have formed a US$40 million strategic alliance to commercialise products from this patented silicon biotechnology. Roll-outs are expected in a few years. By means of this revolutionary route, silicon-based materials can be made and simultaneously channelled into nanostructures. Other companies are involved in the exploration of further use of the technology.

Morse reveals: "We recently discovered that this process can be extended to the nanofabrication of other high-performance materials based on metals currently being used in semiconductors, photovoltaic converters, lasers and photodiodes. For all these applications, you need to control the nanostructures to achieve the highest functional performance." However, he cautions, these are still early days in terms of making devices that utilise materials made this way.

The scientist is both excited and impressed by the strength and diversity of the biological side of nanotechnology developments aimed at medical application in Singapore. UCSB, the NUS Nanoscience and Nanotechnology Initiative, and IMRE, either in collaboration or in parallel, are also making advances in the production of exciting new materials for possible application in electronics, microelectronics, optoelectronics, optics, information storage, aerospace, bioengineering and photonics medicine.

According to Morse, two trends are gaining recognition and support worldwide. The first is the move to understand biological approaches in nanotechnology. The second is the attempt to understand and harness the interaction of energy and materials structured on the nanoscale. In other words, nanoscale particles interact with light, electrons and magnetic energy in ways different from the interaction on today's bulk scale. Success will provide the key to new means of information-transfer storage and processing such as spintronics and quantum dots. (See articles in this issue.)

Alan Heeger, chemistry Nobel laureate 2000, is working with Morse on the photophysics of biological molecules with light, particularly optoelectronics or the conversion of electrical energy to light and vice versa. The latter says: "I am interested in polymers that combine silicon and carbon, or metals and carbon atoms. These polymers combine the flexibility and ductility of carbon with the energy-transducing property of silicon and metal."

In addition to inorganic materials, Morse's laboratory focuses on harnessing biological catalysts to make polymers that incorporate metals and silicon with carbon. This merging of the living world with the inorganic means that the mixed composition impregnated with nanocomposite polymers offers special high-performance capabilities.

High-performance capability has use in information transfer and sensing. Morse highlights biosensing, where carbon-based functionality will provide the interface with the living system for a new era of implanted, indwelling biosensors that continually monitor physiology and may, through feedback, regulate homoestatic control of physiology and disease.

For more information contact Daniel Morse at d_morse@lifesci.ucsb.edu

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