Physical and chemical investigation into the internal fine structure of Ensis siliqua shells

Escalator Funds 2012An exciting new project has received funding, involving two Swansea University scientists, Dr. DJ Johnson from the College of Engineering and Dr N Yonow from the Department of Biosciences in the College of Science, with Dr DJ Scurr from the School of Pharmacy, University of Nottingham.  The project will involve some hi-tech microscopy and the common razor shell, found on lower sandy shores such as Oxwich and Rhossili.  The shell of the bivalve mollusc Ensis has been shown to be able to withstand much greater forces than expected before failure due to an unusual mechanism of crack propagation.  The intention of this research is to use the complementary imaging techniques of atomic force microscopy and time-of-flight secondary ion mass-spectrometry to examine the cross-sectional structure of the shells of this mollusc to provide insight into how they may be mimicked for future production of novel materials.  This work will be carried out in the context of understanding how these structures fulfil their biological function in the natural environment and how such structures could be recreated in a laboratory environment. 

It has been previously shown that the particular “prismatic” structure of calcium carbonate crystals in the shells of razor shells allows cracks to be deflected between laminate layers in the shell structure.  This delamination of the shell dissipates the energy applied to the shell by several orders of magnitude, meaning that much greater pressure is needed to cause a catastrophic failure of the shell.  Ensis shells will be cross-sectioned to allow access to their internal structure.  Atomic force microscopy will be used to image these cross-sections to provide high-resolution three-dimensional images of the shell internal structure and will also be used to study the mechanical properties of the different substructures of the shell.  Cross-sectioned samples from the same shells will also be examined at the University of Nottingham, with a technique which can chemically map the fine structure of surfaces - time-of-flight secondary ion mass-spectrometry.  This technique will not only be able to clearly distinguish between the calcium carbonate crystals which make up the bulk of the shell material and the surrounding organic matrix, but will give insight into the composition and structure of the surrounding matrix itself.