From Nanostructure to Function: Hierarchical functional structures in chitin and keratin

Abstract

Nature has long served as a master engineer, designing materials with optimized performance through hierarchical structures that span from the molecular to the macroscopic scale. Two of the most fascinating examples of such natural materials are chitin and keratin—structural biopolymers that exhibit a wide range of functionalities derived from their intricate architectures. The lecture presents an in-depth exploration of the hierarchical structuring in chitin and keratin and their emerging role in sustainable nanotechnology and biomimetics. Chitin, a polysaccharide composed of N-acetylglucosamine, is widely found in arthropod exoskeletons, fungal cell walls, and marine organisms. It can be extracted from waste sources such as shrimp shells, providing a sustainable and biodegradable feedstock for advanced materials. Its mechanical properties— arising from strong hydrogen bonding and crystalline polymorphs (α-, β-, and γ-chitin)—enable applications in protective structures and load-bearing composites. Moreover, chitin can be processed into nanocrystals and nanofibers with tuneable surface chemistries, making it ideal for nanocomposites, sensors, and drug delivery systems [1]. Keratin, a sulfur-rich fibrous protein found in hair, wool, feathers, and horns, is another abundant biomaterial. It is characterized by disulfide bonds between cysteine residues, contributing to its toughness and elasticity. Keratin waste, particularly from poultry feathers and sheep wool, represents an underutilized yet high-value resource. Its hierarchical structure— from α-helices and β-sheets to intermediate filaments—supports diverse bioinspired applications, including thermally insulating fibres, structural coloration, and advanced composites [2]. Both chitin and keratin exhibit remarkable functionalities such as structural colour, self-cleaning, thermal regulation, and reversible adhesion, which are observed in certain butterfly wings, bird feathers, and insect cuticles. Such structural colour effects are not pigment-based but result from light interacting with nanostructures, offering non-fading, environmentally friendly coloration for textiles and coatings [3]. The biomimetic implementation of these materials focuses on retaining their intrinsic hierarchical architecture while leveraging their sustainability. Innovations in extraction techniques, including environmentally friendly enzymatic and microbial methods, further enhance their viability in green chemistry. Their roles in passive radiative cooling, filtration, biocompatible implants, and packaging materials position them at the intersection of environmental sustainability and technological advancement. Moreover, chitin and keratin support the development of circular bioeconomies by valorising waste streams. Projects involving shrimp shell waste and feather recycling demonstrate the feasibility of turning environmental liabilities into functional, biodegradable materials with added economic and ecological value. These efforts contribute to solving pressing global challenges—such as plastic pollution, energy consumption, and toxic dye usage—by substituting synthetic inputs with naturally occurring, renewable materials. Future work shall focus on optimizing structure–property relationships and scaling up biomimetic production methods. Interdisciplinary collaboration between physicists, chemists, engineers, and biologists is essential to advance these materials from research labs to real-world applications. The lecture will highlight recent advances in the field, with particular emphasis on the nanostructure- function relationship, hierarchical organization, and integration of chitin and keratin in advanced material systems. Case studies include natural photonic structures, self-cleaning gecko setae, and radiative cooling in biological systems. These examples underscore the vast untapped potential of bioinspired materials derived from chitin and keratin in shaping a more sustainable technological future.