Merk, Vivian

Living organisms synthesize and assemble complex bioinorganic composites with enhanced structure and properties to fulfill needs such as structural support and enhanced mechanical function. With the advent of advanced materials characterization techniques, these biomineral systems can be explored with high resolution to glean information on their composition, ultrastructure, assembly, and biomechanics. In this work, the endoskeletal features of two marine organisms are explored.
Acantharia are geographically widespread marine planktonic single-celled organisms. Their star-shaped SrSO4 endoskeleton consists of spicules emanating from a central junction, arranged to satisfy crystallochemical and spatial requirements of their orthorhombic crystal lattice. In this work, synchrotron X-ray nanotomography and deep-learning guided image segmentation methods were used to characterize the endoskeleton of 5 types of Acantharia and to extrapolate their growth mechanism. The results highlight the diverse morphology of the spicules and spicular junctions that Acantharia achieve whilst maintaining overall spatial arrangement. Fine structural features, such as interspicular interstices thought to play a role in the robustness of the overall endoskeleton, were resolved.

In this research, we use calcite and celestite inorganic model systems to better understand biological crystallization in the presence of organic biomolecules. Our goal is to understand what happens when biomolecules occlude into crystals and how that affects the structural organization. Specifically, we focus on the role the respective biomolecule chemistry plays in regulating the incorporation into a crystal. To visualize and characterize the biomolecule/mineral role in crystallization, a variety of techniques were used to image and analyze the respective model systems. The synthesized single crystals were characterized by light microscopy (LM). Scanning electron microscopy (SEM) and field-emission SEM (FE-SEM) were used to examine the morphology of the crystals. Structural and topographical analyses were carried out using atomic force microscopy (AFM). Fourier transform infrared spectroscopy (FTIR) and confocal Raman microscopy were both used to characterize functional groups, where Raman spectroscopic mappings provided the region-specific chemical composition of the crystal.

Water pollution can be detrimental to humans and the surrounding ecosystem. I tested whether iron oxide mineralization could be used to yield new biocomposite materials for the remediation of environmental pollutants, such as arsenic and crude oil. Both ferrihydrite and magnetite minerals were embedded within the cell wall and cell wall-lumen interface of balsa wood. Ferrihydrite was tested for degradation of crude oil, while magnetite was investigated for the absorption of arsenic from contaminated water. Research suggests that these hybrid biomaterials will prove successful in absorbing harmful pollutants by providing a porous scaffold holding the iron oxides. Methodology included a variety of spectroscopic and microscopic methods, such as Raman imaging and Scanning Electron Microscopy. A microscopic analysis of wood analysis suggested ferrihydrite was maintained and traces of oil were present in the wood cells. Preliminary data suggested a retention of the iron oxide with the wood cell structure and an uptake of arsenic from the water.