An unusual interlocked biomineral interface in bivalve shells

Area of Science:

• Biomineralization research
• Materials science
• Marine biology

Background:

• Bivalve ligaments facilitate shell opening and are typically composed of organic lamellar and aragonitic fibrous layers (FL).
• The microstructure of the ligament-valve interface (LVI) remains understudied, despite its potential importance in shell mechanics.

Purpose of the Study:

• To investigate the microstructure and chemical composition of the LVI in the clam Cyclina sinensis.
• To understand the functional role of the LVI in preventing fibrous layer detachment from the shell valves.

Main Methods:

• Optical microscopy
• Field Emission Scanning Electron Microscopy (FE-SEM)
• Powder X-ray Diffraction (XRD)
• Fourier-Transform Infrared Spectroscopy (FTIR)

Main Results:

• The LVI comprises discrete bands of coarse aragonite fibers (0.4-7.6 μm) interspersed with fine aragonite fibers (106.5 ± 1.6 nm).
• These fine fibers are continuous with the FL fibers (116.8 ± 1.7 nm).
• The LVI exhibits a finger-joint-like microstructure where coarse fibers penetrate the FL, tapering and branching.

Conclusions:

• The LVI acts as a crucial transition zone between rigid valves and the flexible FL, preventing detachment due to modulus mismatch.
• This study presents a novel model for biomineral interfaces, with potential applications in advanced material design.