Making glass structures usually involves the high-temperature melting of minerals. So, how do marine creatures produce glassy spicules in the relatively chilly realm of the world's oceans? Researchers at the Technische Universität Dresden, and colleagues at IMBE, CNRS, IRD, ESRF, the Julius Wolff Institute for Biomechanics and Musculoskeletal Regeneration and the Technion-Israel Institute of Technology think they have the answer and report details of their findings in the journal Science Advances. The work could lead to a new route to glassy structures for a wide range of technological applications. [Schoeppler et al., Sci Adv(2017), 3, eaao2047; DOI: 10.1126/sciadv.aao2047].
The researchers used X-ray methods, nanoscale tomography and focused X-ray diffraction, available at the European Synchrotron Radiation Facility in Grenoble, France, to investigate spicule morphogenesis in marine sponges. Marine sponges, such as Demospongiae and Hexactinellida, have an evolutionary heritage stretching back half a billion years. The organisms are capable of synthesizing mineralized silica-based skeletal elements, glass spicules, which endow the animals not only with structural support and mechanical strength but help protect them from their environment. The spicules just micrometers or sometimes millimeters long and come in many shapes and forms but almost always with highly symmetrical three-dimensional branched morphologies.
The organisms apparently use axial organic filament to template silica deposition. This organic component is mostly enzymatically active proteins, silicatein and its derivatives, which catalyzes the bio-fabrication of silica. The process is controlled genetically by specialist cells, known as sclerocytes.
The new study reveals that the protein components of the axial filaments have a crystal-like three-dimensional structure with hexagonal symmetry but the pores within the structure are filled with amorphous silica. The crystalline symmetry of the biological part somehow generates these shapely glassy structures from the amorphous feedstock.
"By using the crystalline axial filament, nature has mastered the fabrication of extremely complex glass structures at low temperatures that is far beyond the abilities of current human technology," explains Technion's Emil Zolotoyabko. "Further understanding of how the organisms regulate the branching events in the filaments has the potential to be adopted in the production of technologically relevant nano-crystalline materials of complicated shapes for nano-electronics. Mimicking natural recipes in the lab will allow us to develop novel glass technology working at room temperature."
The team adds that the process is analogous to the growth of synthetic inorganic nanocrystals with high spatial regularity. "We demonstrate that the branching of the filament follows specific crystallographic directions of the protein lattice," the team reports. "In correlation with the symmetry of the lattice, filament branching determines the highly regular morphology of the spicules on the macroscale."
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase.
This story was updated on 4th December 2017 to correct the citation of institutions involved.