Multiscale structural and crystallographic characterisation of pigeon eggshells and membranes as an evolutionary model for biomimetic applications

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.