Fibrous anisotropy and mineral gradients within the radula stylus of chiton: Controlled stiffness and damage tolerance in a flexible biological composite

Abstract

Over hundreds of millions of years, organisms have evolved architected structures via precise control over hierarchically assembled components, including the integration of dissimilar materials. One such example is found in the radula system of chitons, intertidal mollusks that feed on algae growing on the rock. Their radula consists of multiple rows of ultrahard teeth, each integrated with a foldable belt-like substrate via a stiff, yet flexible stylus, which is essential for efficient rasping during the feeding process. Here, we investigate the nano and micro-scale components and architectures as well as regional mechanical properties of the stylus, and their subsequent role during the rasping of Cryptochiton stelleri. Three important factors were determined to contribute to the regio-specific stiffness of the stylus: the presence of mineral components, highly oriented chitinous fibers, and a chemically cross-linked protein matrix. All these factors are varied throughout the stylus. There is a high mineral content on the trailing edge close to the tooth and a cross-linked matrix on the leading edge, both with orientational specific oriented chitin fibers that provide force transduction to the tooth. Conversely, there is a significant lack of mineral or cross-linked matrix in the proximal end as well as a low degree of fiber orientation, resulting in a flexible region that can accommodate torsion and flexure during rasping. Understanding the graded composite structure of the stylus and applying this unique design to various engineering fields such as soft robotics, biotechnology, and the medical industry, can inspire the production of high-performance materials.

Three‐dimensional visualization of predatory gastropod feeding teeth with synchrotron scanning

“…Testing these hypotheses rigorously would require advances over previous work, which have tended to focus on how radular teeth deform and distribute stresses and strain in isolation during feeding (Krings et al, 2020; Lee et al, 2023; Van der Wal et al, 2000). While studying tooth performance in isolation can give valuable insight into the structural performance of tooth morphology, interactions between adjacent tooth bases must be factored in in studies of the muricid radula.…”

Tunable Oxidized-Chitin Hydrogels with Customizable Mechanical Properties by Metal or Hydrogen Ion Exposure

“…Chitin exists in nature as three polymorphs, α-chitin, β-chitin, and G-chitin, which differ in their arrangements of polymeric chains: anti-parallel, parallel, and alternating, respectively [10]. The α-chitin is the most abundant polymorph and can be found in arthropods cuticles, fungi cell walls, or the cysts of Entamoeba [11,12]. The β-chitin is still abundant in nature and can be found in mollusks, or other biomineralizing organisms, as Foraminifera [13,14].…”