Engineering Curved Strontium Sulfate Crystals through Biomimetic Crystallization

Nanoscale molecular interactions between growing crystals and charged polyelectrolytes are crucial to understand the self-assembly of hierarchical organic-inorganic superstructures. Little is known about earth alkaline sulfate biominerals. Yet, a detailed understanding of bioinspired crystallization is crucial for developing general descriptors for bottom-up syntheses of complex ceramics. This study investigates biomimetic strontium sulfate (SrSO₄) crystallization in the presence of poly(α-glutamic acid) using multiscale microscopy and vibrational spectroscopy. Using scanning electron microscopy, we observed doughnut-shaped spherulites with granular surface texture. Biomolecule inclusion led to pronounced peak broadening in synchrotron X-ray powder diffraction, wide-angle X-ray scattering, and Raman spectroscopy, commensurate with nanoscale domain sizes and pronounced lattice strain. Texture-like wide-angle X-ray scattering patterns and nanosized domains in transmission electron microscopy support the notion of mesocrystalline organization. Based on <i>Z</i>-contrast STEM imaging, intercalated organics are organized as elongated nanoclusters. Diffracting planes radiate outward from the crystal center, indicating a centrosymmetric strain field. The three-dimensional (3D) chemistry was investigated using atom probe tomography, which revealed a helical distribution of organic inclusions. This approach exemplifies how organic-inorganic templating can guide the evolution of intricate biomorphic crystal shapes. Round strontium sulfate crystals bear technological potential in the field of optoelectronics, such as IR-vis conversion materials or curved waveguides.