What gives seashells, corals, and bone their exceptional mechanical strength and resilience? These biominerals, which are produced by living organisms for protection and/or structural integrity, exhibit qualities we humans would like to replicate in our own engineering projects. However, to truly understand how biominerals grow at the molecular scale, we need a microscope capable of detecting both chemical and structural information with nanoscale precision.
A multidisciplinary team of scientists from UCLA, University of Colorado Boulder, University of Wisconsin Madison, UC Berkeley, and the Advanced Light Source (ALS) has now demonstrated this capability in a powerful microscope developed at ALS Beamline 7.0.1 (COSMIC). The work was performed under the umbrella of the STROBE Science and Technology Center, funded by the National Science Foundation to integrate different imaging modalities for the characterization of complex samples at multiple scales.
In this study, the team looked at the coral species Seriatopora aculeata. Specifically, they examined particles of the rigid, branch-like exoskeleton that supports the anemone-like coral organisms. “Understanding how coral skeletons are oriented at the nanoscale can allow us to engineer more resilient hard structures, and to explain how coral skeletons became so prevalent during the course of evolution,” said first author Yuan Hung (Mike) Lo, a UCLA Ph.D. student in Physics and Bioengineering at the time of the study.
The team’s visualization technique combines the high resolution of ptychography (a scanning coherent diffractive imaging method) with x-ray linear dichroism (a contrast mechanism used to reveal crystal orientations). The scientists discovered that crystals in the coral skeleton are much more diverse at the nanoscale than previously appreciated, with some growing outward at wide angles while others grow at narrower angles. This richness in growth pattern suggests that there is still much to learn about how coral skeletons grow.
“This was the first use of x-ray ptychography combined with linear dichroism to quantify crystal orientation,” said David Shapiro, lead scientist for COSMIC’s microscopy experiments and leader of the ALS Microscopy Program. “This previously unachievable spatial resolution and contrast, along with cross-compatibility with electron microscopes, will open up new lines of research for users of x-ray microscopy at the ALS.”
Y.H. Lo, J. Zhou, A. Rana, D. Morrill, C. Gentry, B. Enders, Y.-S. Yu, C.-Y. Sun, D. Shapiro, R. Falcone, H. Kapteyn, M. Murnane, P.U.P.A. Gilbert, and J. Miao, “X-ray linear dichroic ptychography,” PNAS 18, e2019068118 (2021), doi:10.1073/pnas.2019068118.
For more about ptychography at COSMIC, see the Berkeley Lab news release, “A COSMIC Approach to Nanoscale Science.”