Discovery of New Phenomena in Biomineral Formation

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Non-technical: This award by the Biomaterials program in the Division of Materials Research to University of Wisconsin Madison is to investigate the mechanisms for the formation of natural biominerals. These biominerals are crystalline composite materials formed by living organisms. Despite being crystalline, they do not frequently exhibit the flat faces and sharp edges characteristic of geologic crystals, but have rounded surfaces, and shapes highly adapted to their functions. They grow by attachment of amorphous particles, as was first discovered in sea urchin biominerals, and later in eggshells and others, but never directly in the formation of seashells. This proposal will analyze these biominerals to study how they are formed. Using crystal orientation measurements, this award will study crystal growth in egg shells in a quantitative manner. The discoveries coming out of this study will greatly advance knowledge of biomineral formation mechanisms, and the results will be helpful for future biomimetic 3D printing of these biominerals, with potential use in bone repair and replacement, and other useful devices. The discoveries in these biominerals will be broadly disseminated in peer-reviewed publications, at conferences where the researcher gives frequent invited lectures, in popular science magazines, at the Conference for Undergraduate Women in Physics, to under-represented minority high-school students attending the "Pre-college Enrichment Opportunity Program for Learning Excellence" program, to grade school women attending the Expanding Your Horizon yearly events, and in public lectures. Technical: The researcher and the team members will study new phenomena in forming biominerals, selected to maximize the likelihood of new, unexpected results because they have never been studied with the same objectives as planned here: Objective 1 is to identify amorphous precursor phases in fresh, forming mussel nacre and prismatic layers, and eggshells using x-ray absorption near-edge structure spectroscopy at the calcium L-edge, and localization in component-mapping with 20 nm spatial resolution, and 3 nm probing depth. Calcite, aragonite, and their amorphous precursors have distinct XANES spectral lineshape and are therefore identifiable. If there are amorphous precursor phases in forming eggshell, nacre and prisms, we will identify them as proto-aragonite or proto-calcite. These "polyamorphs" have the short-range order of aragonite and calcite, respectively, and are expected to transform into the corresponding crystalline phases. Objective 2 is to obtain a quantitative definition of spherulite from synthetic aragonite using polarization-dependent imaging contrast (PIC)-mapping at the oxygen K-edge. This definition will then be used to determine if nacre and eggshells do or do not grow spherulitically. Both component- and PIC-mapping are state-of-the-art synchrotron methods, which this researcher introduced and continues to improve.