Biomimicry of Reptile Eggshells Based on Keratin Nanofibrous Membranes

Eggs are multifunctional structures that enabled vertebrates to colonize the land millions of years ago. Life on Earth imposes a series of environmental challenges on eggs, often presenting conflicting or contradicting demands. For example, eggs must be crack-resistant yet allow breakage from the inside, be impermeable to bacteria yet breathable and in some cases allow water absorption. Eggshells also offer protection from harmful radiation while allowing some light transmission. As a result, they have evolved into multifunctional systems with extraordinary properties, including unique combinations of high flexibility and strength, strong water absorption and antimicrobial filtration. Biomimicking of these natural structures could lead to the development of new materials with advanced properties for filtration/separation technology, sensors and biomedical applications. Through chemical and physical analysis of sixty-two reptile eggshells (Debruyn et al., 2024), the key structural components - namely a proteinaceous layer (primarily keratin) and an inorganic calcium carbonate component - were identified and used to develop biomimicry models. The non-woven layer of proteinaceous fibers closely resembles randomly oriented nanofibrous membranes produced via solvent electrospinning. Hence, keratin, extracted through a sulphitolysis process, was electrospun from formic acid. A subsequent heat treatment ensured crosslinking of residual amine and carboxyl groups in the keratin chains, imparting hydrophobicity and improved water stability to the nanofibrous membranes. To further approximate the eggshell's inner proteinaceous layer, the keratin nanofibers were embedded in an egg white matrix using a dip-coating procedure. The mineral component, typically found in Testudines and Crocodylia eggshells, was mimicked by depositing calcium carbonate particles onto the keratin-based membranes. This biomimetic approach paves the way for the production of multifunctional, biocompatible keratin-based membranes tailored to the specific needs of various end-applications such as filtration membranes, wound dressings, smart textiles, etc. Debruyn, G., Geltmeyer, J., Schoolaert, E., Nicolaï, M. P. J., Xie, W., Wynant, M., Shawkey, M. D., De Clerck, K., & D'Alba, L. (2024). Hydric Environment and Chemical Composition Shape Non-avian Reptile Eggshell Absorption. Integrative and Comparative Biology, 64(1), 107–119. https://doi.org/10.1093/ICB/ICAE040