Living organisms make use of incredibly creative, efficient solutions to engineering problems. Having had several hundreds of millions of years of evolution to get things right, they got a bit of a head start as far product development is concerned. In my group at Northwestern Engineering, we try to understand biological engineering solutions so that one day we can apply this understanding and make better, more energy-efficient, sustainable materials, materials that fight disease or support your body in healing itself. We essentially think of our work at the Materials Science and Engineering Department as reverse-engineering biological engineering solutions.

Consider for example your bones - they grow with you, get stronger when you work out, and mend themselves when you do happen to break them. In a different example, sea urchins have used fiber-reinforced graded ceramic materials to build self-sharpening teeth. This may be astonishing; it is, however, by no means unique. Organisms from all domains make use of the materials properties of crystalline and amorphous solids (e.g. inorganic minerals) to provide structure and physical integrity, to feed, to sense gravity and acceleration, to guide light and even perceive the earth's magnetic field.

Evolutionary optimization of these so-called biominerals has led to organic-inorganic composite structures of amazing complexity, ordered across many levels of hierarchy and on length scales between the nano- and the macro scale. We have recently made a breakthrough in the way we can analyze and visualize the three-dimensional chemical structure at the (sub)nano-meter scale using atom probe tomography (read more ...). The progression of dental caries (tooth decay) in tooth enamel is another area in which atom probe tomography is helping us elucidate structural and compositional characteristics at the nano-meter scale. Using this powerful tool will help deepen our understanding into how caries infiltrates and demineralizes tooth enamel, informing potential new treatments for one of the most ubiquitous human diseases (read more ...).

One particularly impressive feature of biominerals is that the organisms freely sculpt single-crystalline material into smoothly and continuously curving shapes, seemingly overriding the thermodynamic control of crystal morphology. We are working with sea urchin embryo-derived cells capable of this amazing feature and try to control the biosynthesis of single crystals by providing external and internal guidance cues (read more ...).

Biomineralization, like nearly all biological processes, is inherently non-equilibrium. The formation of hard tissues like bones and teeth does not conform to our current theories of equilibrium phase transitions. Therefore, new mechanisms to convert mineral nutrients like calcium into solid materials must be envisioned. Using in vitro model systems to precipitate minerals in cell-like environments, we study the nanoscale processes that govern biomineral phase transitions. Our goal is to use these observations to expand current theories to biologically relevant conditions (read more ...).

As man-made materials become more similar to the biological structures that inspire them, they increasingly combine nano-sized hard and soft, synthetic and biological components. This creates new challenges for characterization, especially in those materials where water is an integral part of the structure. Sample preparation of hydrated composite systems, for example the sea urchin embryo with its endoskeleton, is further complicated by the large hardness contrast between the organic and the biomineral phase. We are developing a new cryogenic sample preparation technique, called cryo triple ion gun milling (CryoTIGMâ„¢), that preserves the water in biological specimens via rapid cryo-fixation, thus allowing the samples to be studied in a near-native-state. Furthermore, CryoTIGMâ„¢ can generate large and smooth cross-sections of the sea urchin embryo endoskeleton to allow ultrastructural studies at the mineral-organics interfaces (read more ...).

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Northwestern University
Materials Science and Engineering Department
2220 Campus Drive, Evanston, IL 60208-3108