Thermodynamic Aspects of Molluscan Shell Ultrastructural Morphogenesis

Abstract

Over the years, molluscan shells have become an exemplar model system to study the process of mineral formation by living organisms, the process of biomineralization. Typically, the shells consist of a number of mineralized ultrastructural motifs, each exhibiting a specific mineral-organic composite architecture. These are made of calcium carbonate building blocks having a well-defined three-dimensional morphology that is significantly different from the shape of inorganically formed counterparts. Shell ultrastructures are known to form via a biologically controlled extracellular mineralization pathway in which the organism has no direct control over mineral formation. The cellular tissue, responsible for shell biomineralization, forms an organic framework and sets-up the physical conditions necessary for the deposition of a specific morphology, whereas the growth of the mineral part of the shell proceeds spontaneously via the process of self-assembly. In this feature article, the ability to employ thermodynamic models from classical materials science to describe the process of self-assembly and structural evolution of a variety of shell architectures is reviewed. Having the potential to offer an analytical framework to express ultrastructure formation in time and in space, these models not only provide a deeper insight into shell biomineralization, but also suggest tools for novel composite materials design.

Phase-Field Modeling of Biomineralization in Mollusks and Corals: Microstructure vs Formation Mechanism

“…14. This chiral structure closely resembles the screw dislocation-like defects reported in experiments [14,39]. Apparently, our dislocation pairs do not recombine even in a long simulation time, presumably because of the lack of mechanical stresses that are not incorporated into the phasefield models used in this study.…”

The Role of Confinement in Biomineralization

“…Despite their differences in appearance, these mollusk shell structures share common formation mechanisms. , Shell formation is initiated by the mantle, which secretes a thin organic layer termed the periostracum. This creates an isolated extracellular environment between the mantle and mineral growth surface called the extrapallial space and provides the surface on which new mineral deposits ( Figure b).…”

Deciphering mollusc shell production: the roles of genetic mechanisms through to ecology, aquaculture and biomimetics

“…Spontaneous chemical interaction then occurs between CaCO 3 , the organic precursors and physical properties within the extracellular pallial space. This mechanism is similar to mineral deposition processes from colloidal chemistry (Zlotnikov & Schoeppler, 2017). Whether any of these models operate in vivo is not resolved and will be difficult to demonstrate, however, they provide theoretical frameworks to describe shell structure and a basis for further experimental design.…”