Multiscale structural and crystallographic characterisation of pigeon eggshells and membranes as an evolutionary...

We present the first comprehensive multiscale characterization of domestic pigeon Columba livia eggshells. It is a sustainable by-product of low-input poultry farming, which is important for rural communities in India. It reveals a hierarchically structured organic-inorganic composite optimized for biological function. Through integrated XRD, SEM-EDX, and FTIR analyses, we identify: (1) a dominant calcite phase (R3-C rhombohedral, a ~ 4.99 Å, c ~ 17.06 Å) with average nanocrystalline domains 24.7 ± 2.1 nm, moderate crystallinity (62%), and unique microstructural features (1.01 ± 0.009% Microstrain), ((1.64 ± 0.2) × 10¹⁵ m⁻² dislocation density); (2) proteinaceous components (amide I/II bands) and hydrated interfaces coexisting with the mineral matrix; and (3) a gas-exchange-optimized architecture featuring calcium-rich eggshell (42.39 weight% Ca), carbon-dominated membranes (54.18 weight% C), nanofibrous textures (1.07-1.89 μm), and precisely tuned pore geometries (566.3 ± 166.5 nm diameter, 0.026% pore-to-thickness ratio). Surface roughness was quantitatively assessed using a multi-line grayscale extraction approach from SEM micrographs. It yields nanoscale-correlated roughness values (Ra ≈ 23.9 ± 0.3, Rq ≈ 28.7 ± 0.4 intensity units), indicative of localized microtopographic features that may contribute to passive antimicrobial function. These structural and compositional traits surpass chicken egg models in their balanced porosity-crystallinity relationship. Our work establishes pigeon eggshells as a model system for evolutionary biomaterials science while providing quantitative design principles for potential sustainable, nature-inspired composites.