Crystal growth kinetics as an architectural constraint on the evolution of molluscan shells  

Vanessa Schoeppler,a Robert Lemanis,a Elke Reich,a Tamás Pusztai,b László Gránásy,b,c Igor Zlotnikov a

In an article that appeared in the prestigious journal Proceeding of the National Academy of Sciences (US), scientists from the Wigner Research Centre for Physics (Hungary) and the Technical University Dresden (Germany) investigated a possible link between microstructures observed during directional solidification, well known in materials science, and rather similar structures that form during biomineralization, a process that yields hierarchically structured organic-inorganic composite structures in living organisms. In this study, ultrastructural morphogenesis of shells from three major molluscan classes, a bivalve Unio pictorum, a cephalopod Nautilus pompilius, and a gastropod Haliotis asinine, is compared to phase-field simulations based on the concept of directional solidification. It was demonstrated that by regulating only the chemical and physical boundary conditions during directional solidification, phase-field modelling can capture the generic features of the molluscan ultrastuctures. Based on this finding, an architectural constraint is proposed for the evolution of molluscan shells: the morphospace of possible shell ultrastructures is bounded by the thermodynamic and kinetic limitations of directional crystal growth.

The experiments were performed at the Technical University of Dresden, whereas the computer simulations were done at the Wigner Research Centre for Physics. 

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Fig. 1: Cross-sectional change of the shell microstructure (left) in the electron microscope image of the shell of Nautilus pompilius, and (right) the simulated microstructure predicted by the phase-field theory (different colours indicate different crystallographic orientations). 
 

a B CUBE–Center for Molecular Bioengineering, Technische Universität Dresden, 01307 Dresden, Germany 
b Wigner Research Centre for Physics, P.O. Box 49, H-1525 Budapest, Hungary
c Brunel Centre of Advanced Solidification Technology, Brunel University, Uxbridge, Middlesex UB8 3PH, UK 
 


Link to the paper: https://www.pnas.org/content/116/41/20388.full

Press release of the Technical University Dresden: https://www.eurekalert.org/pub_releases/2019-09/tud-cgk092319.php