INTELLECTUAL MERIT: The complex structures of mollusk shells will be analyzed with unprecedented resolution, and on a large scale, using new spectromicroscopy methods developed with the previous NSF grant and which are now available to many other synchrotron users around the world. The mollusks produce a variety of mineralized shells that are presumably adapted to specific functions. The PI will study the processes leading to the formation of complex shell structures, and correlate these observations with the physical parameters (e.g. depth, pressure, temperature) of the environments in which the mollusks live. This will provide insights into the evolution of mollusk shells, how they adapted to different environments, and possibly provide new tools to for measurement of environmental parameters. Beyond this, a full understanding of how mollusk shells are constructed can serve as a guide for biomimetic manufacture of strong, tough composites.
BROADER IMPACTS: The methods developed with the previous NSF grant have now been established, and are available to hundreds of other spectromicroscopy users around the world. The PI has also developed software to process the spectromicroscopy data, which is distributed free-of charge to the community on http://home.physics.wisc.edu/gilbert/. The experiments proposed here will yield detailed microcrystal and nanocrystal architectures and the formation mechanisms of tough biominerals, and may therefore inspire the engineering of new synthetic materials with improved performances for medical implants or micro-mechanical machines. One graduate and one undergraduate student per year will be involved in the proposed experiments. Women and underrepresented minority students will be actively recruited. Four major outreach activities will be performed, including: (1) Development of instructional modules on biomineralization within the framework of the Wisconsin Center for the Integration of Research, Teaching, and Learning (CIRTL). These will be actively disseminated through CIRTL for use by high school teachers and college educators for their own classes. (2) Presentations to about 3000 people/year from the general public at the UW-Madison Physics Fair. (3) The PI and her students will continue to provide lectures and lab experiments to African American students within the PEOPLE program every summer. (4) The PI has given and will continue to give invited talks at the American Association of Physics Teachers (AAPT) annual meeting, during which she has and will disseminate teaching tools, modules, and slides to the teachers, to teach the fascination of biominerals to high school and college students.
We studies seashells and imaged their microscopic structure, that is, we looked at how micro-and nano-crystals are arranged in various parts of seashells. We used PIC-mapping, an imaging method developed by the PI to show the orientation of tiny crystals, down to 20 nanometers, or 20 billionths of a meter. PIC-mapping made us discover new aspects of inner and outer sides of 15 different seashell species. The inner layer is also called mother-of-pearl or nacre, the outer is called the prismatic layer. In nacre from all species the order of nacre tablet orientation increases with growth in shell thickness, but the rates of this gradual ordering differ. The tablet thickness and average width are also characteristic of each species, as is the way co-oriented tablets are stacked on top of one another in vertical columns staggered diagonally In the prismatic layer we found that all species differ in prism size and orientation. We observed for the first time that the crystal orientation tilts gradually, as if forming a curved crystal. This is highly unusual for a crystal, which usually grows straight, at the atomic scale but also macroscopically, with flat faces and straight edges. If the atomic structure of the crystal tilts the crystal grows curved, not straight. Most interestingly, we found the crystals that curved only in the Pinctada species, these are pearl oysters from Japan and French Polynesia. After measuring the hardness of all prismatic layers in all shells, we found that the pearl oysters have the hardest. Therefore, we conclude that it is possible that the observed crystal curving is a hardening mechanism. As far as we know this is the first structure-property relation thus far observed in the prismatic layer of seashells.
