Biomimetic generation of the strongest known biomaterial found in limpet tooth

A Functionally Conserved yet Dynamically Evolving Toolkit Underpinning Molluscan Biomineralization: Insights From Shell and Radula

The molluscan shell and radula constitute pivotal molluscan innovations, each characterized by distinct functions and diverse forms, regulated by the highly specific biomineralization regulatory networks. Despite their paramount importance, the conserved components and adaptive evolutionary processes governing these regulatory networks remain unresolved. To address this knowledge gap, we advocate for the integration of data from less-explored lineages, such as Scaphopoda, as an essential step. This study presents the inaugural comprehensive transcriptome analysis of Pictodentalium vernedei, a representative species of Scaphopoda distinguished by a unique and evolutionarily conserved shell morphology and radula structure. Furthermore, comparative transcriptome/genome analyses are employed to unravel the conservatism and evolutionary innovation of the involved biomineralization regulatory elements. Our findings underscore the central role of secretomes in governing biomineralization processes, and we identified a fundamental set of 26 domains within molluscan secretomes, forming an essential functional protein domain repertoire necessary for the transformation of inorganic ions into biomineralized structures. This core biomineralization toolkit has undergone independent expansion and lineage-specific recruitment, giving rise to novel, modular domain architectures. This may be essential for the functional specialization and morphological diversification of shell and radula structures. These evolutionary processes are driven by the independent co-option of ancient genes and the emergence of novel de novo genes. This comprehensive investigation not only contributes insights into the evolution of molluscan biomineralization structures but also establishes avenues for further scholarly exploration.

Multiscale Mechanical Characterization of Mineral-Reinforced Wood Cell Walls

Studying the multiscale mechanics of bio-based composites offers unique perspectives on underlying structure-property relations. Cellular materials, such as wood, are highly organized, hierarchical assemblies of load-bearing structural elements that respond to mechanical stimuli at the microscopic, mesoscopic and macroscopic scale. In this study, we modified oak wood with nanocrystalline ferrihydrite, a widespread ferric oxyhydroxide mineral, and characterized the resulting mechanical properties of the composite at various levels of organization. Ferrihydrite nanoparticles were deposited inside the wood cell wall by an in situ chemical reaction, resulting in increased stiffness and hardness of the functionalized secondary cell wall, as evidenced by region-specific nanoindentation tests under an electron microscope. Chemically modified and pristine wood samples were characterized by using atomic force microscopy in the bimodal frequency modulation mode, which produced topographical images from the cellular ultrastructure with high lateral resolution and localized nanomechanical information across distinct cell wall layers. Despite mineral reinforcement at the cell wall level, the macroscopic fracture behavior examined through three-point flexural testing remained unchanged upon modification, as cell-cell adhesion could be impaired by harsh chemical conditions.

Anisotropy-dependent chirality transfer from cellulose nanocrystals to β-FeOOH nanowhiskers

Chiral iron oxides and hydroxides have garnered considerable interest owing to the unique combination of chirality and magnetism. However, improving their g-factor, which is critical for optimizing the chiral magneto-optical response, remains elusive. We demonstrated that the g-factor of β-FeOOH could be boosted by enhancing the anisotropy of nanostructures during a biomimetic mineralization process. Cellulose nanocrystals were used as both mineralization templates and chiral ligands, driving oriented attachment of β-FeOOH nanoparticles and inducing the formation of highly aligned chiral nanowhiskers. Circular dichroism spectra and time-dependent density-functional theory proved that chirality transfer was induced from cellulose nanocrystals to β-FeOOH through ligand-metal charge transfer. Interestingly, chirality transfer was significantly enhanced during the elongation of nanowhiskers. A nearly 34-fold increase in the g-factor was observed when the aspect ratio of nanowhiskers increased from 2.6 to 4.4, reaching a g-factor of 5.7 × 10-3, superior to existing dispersions of chiral iron oxides and hydroxides. Semi-empirical quantum calculations revealed that such a remarkable improvement in the g-factor could be attributed to enhanced dipolar interactions. Cellulose nanocrystals exert vicinal actions on highly anisotropic β-FeOOH with a large dipole moment, increasing structural distortions in the coordination geometry. This mechanism aligns with the static coupling principle of one-electron theory, highlighting the strong interaction potential of supramolecular templates. Furthermore, paramagnetic β-FeOOH nanowhiskers alter the magnetic anisotropy of cellulose nanocrystals, leading to a reversed response of helical photonic films to magnetic fields, promising for real-time optical modulation.

Chiton-Inspired Composites Synergizing Strength and Toughness Through Sinusoidal Interlocking Interfaces for Protective Applications

Introducing biological structures into materials design is expected to develop strong and tough structural materials. However, multiple interfaces are introduced simultaneously. They are always the weakest part of load transfer, becoming a critical vulnerability and failure-prone area. Here, it is the first found that the chiton achieves superior mechanical properties just by incorporating a unique sinusoidal interlocking interface into cross-lamellar architecture. These special interlocking interfaces make the chiton shell achieve damage delocalization and increase the resistance to crack initiation and propagation. Meanwhile, this "pre-engineered" path significantly increases the travel path of the cracks and balances the strength and toughness under quasi-static and impact loading. Inspired by this, a novel chiton-inspired composite is proposed. Through coupling the cross-lamellar structures and sinusoidal interlocking interfaces, its strength and toughness are increased by 88% and 107% under quasi-static loading, as well as by 17.8% and 52.4% under impact loading, respectively. These unusual interfaces make up the weak point of cross-lamellar structures and provide insights into the longer evolution of structural materials.

One-Pot Hybridization of Microfibrillated Cellulose and Hydroxyapatite as a Versatile Route to Eco-Friendly Mechanical Materials

Hydroxyapatite was crystallized in an alkaline dispersion of mechanically fibrillated cellulose to prepare their composites with hydroxyapatite contents of 26-86 wt %. The composite powder was uniaxially pressed at 120 °C and 300 MPa to obtain the compacts. Three-point bending tests revealed that the bending strengths of the compacts were 40-100 MPa, and the elastic moduli were 4-9 GPa. The composite containing 43% hydroxyapatite showed the largest bending strength and the largest work of fracture, and the composite containing 62% hydroxyapatite showed the largest elastic modulus. The composites, derived from the bioderived eco-friendly materials, showed the mechanical properties comparable to those of engineering plastics such as polyamide-6. Scanning electron microscopic observation of the fracture surface showed that the organic phase was discontinuous when the hydroxyapatite weight fraction was increased from 43% to 62%, and the compacts with a discontinuous organic phase lost toughness.

Ion‐Specific Hydrogel Microcarriers with Biomimetic Niches for Bioartifical Liver System

Bioartificial livers have showcased significant value in the treatment of acute liver failure (ALF). Current efforts are directed toward overcoming challenges in the development of microcarriers, with a specific emphasis on integrating higher‐density liver cells to enhance detoxification capabilities. Here, inspired by the radial filtration model in hepatic lobules, ion‐specific silk fibroin microcarriers are proposed with biomimetic niches for cultivating functional liver cells at high density. These biomimetic microcarriers are generated by capillary microfluidic device with controllable adjustments of ion type or concentration within the aqueous phase. When cultivating human induced pluripotent stem cell ‐differentiated mature liver cells on these recrystallized microcarriers, notably enhanced cell proliferation activity, as well as increased metabolic and secretory functionality is observed. Based on these features, the microcarrier‐integrated bioreactor can effectively reduce hepatic transaminase levels and significantly improve urea, albumin production, and survival rate in rabbit ALF models is demonstrated. Thus, it is believed that the biomimetic microcarriers and their derived bioreactor may hold potential for clinical applications in managing ALF and other liver diseases.

Nonclassical crystallization of goethite nanorods in limpet teeth by self-assembly of silica-rich nanoparticles reveals structure-mechanical property relations

The intricate organization of goethite nanorods within a silica-rich matrix makes limpet teeth the strongest known natural material. However, the mineralization pathway of goethite in organisms under ambient conditions remains elusive. Here, by investigating the multi-level structure of limpet teeth at different growth stages, it is revealed that the growth of goethite crystals proceeds by the attachment of amorphous nanoparticles, a nonclassical crystallization pathway widely observed during the formation of calcium-based biominerals. Importantly, these nanoparticles contain a high amount of silica, which is gradually expelled during the growth of goethite. Moreover, in mature teeth of limpet, the content of silica correlates with the size of goethite crystals, where smaller goethite crystals are densely packed in the leading part with higher content of silica. Correspondingly, the leading part exhibits higher hardness and elastic modulus. Thus, this study not only reveals the nonclassical crystallization pathway of goethite nanorods in limpet teeth, but also highlights the critical roles of silica in controlling the hierarchical structure and the mechanical properties of limpet teeth, thus providing inspirations for fabricating biomimetic materials with excellent properties.

Fabricating biomimetic materials with ice-templating for biomedical applications

The proper organization of cells and tissues is essential for their functionalization in living organisms. To create materials that mimic natural structures, researchers have developed techniques such as patterning, templating, and printing. Although these techniques own several advantages, these processes still involve complexity, are time-consuming, and have high cost. To better simulate natural materials with micro/nanostructures that have evolved for millions of years, the use of ice templates has emerged as a promising method for producing biomimetic materials more efficiently. This article explores the historical approaches taken to produce traditional biomimetic structural biomaterials and delves into the principles underlying the ice-template method and their various applications in the creation of biomimetic materials. It also discusses the most recent biomedical uses of biomimetic materials created via ice templates, including porous microcarriers, tissue engineering scaffolds, and smart materials. Finally, the challenges and potential of current ice-template technology are analyzed.

High-resolution Raman spectroscopy reveals compositional differences between pigmented incisor enamel and unpigmented molar enamel in Rattus norvegicus

Dental enamel is a peculiar biological tissue devoid of any self-renewal capacity as opposed to bone. Thus, a thorough understanding of enamel composition is essential to develop novel strategies for dental enamel repair. While the mineral found in bone and dental enamel is generally viewed as the biologically-produced equivalent of hydroxy(l)apatite, the formation of these bioapatites is controlled by different organic matrix frameworks-mainly type-I collagen in bone and amelogenin in enamel. In lower vertebrates, such as rodents, two distinct types of enamel are produced. Iron-containing pigmented enamel protects the continuously growing incisor teeth while magnesium-rich unpigmented enamel covers the molar teeth. Using high-resolution Raman spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy, this work explores the differences in acid phosphate (HPO₄^2-), carbonate (CO₃^2-), hydroxyl (OH^-), iron, and magnesium content of pigmented incisor enamel and unpigmented molar enamel of Sprague Dawley rats. Bundles of hydroxy(l)apatite nanowires comprise the enamel prisms, where prisms in pigmented enamel are wider and longer than those in unpigmented molars. In contrast to magnesium-rich unpigmented enamel, higher mineral crystallinity, and higher HPO₄^2- and OH^- levels are hallmark features of iron-rich pigmented enamel. Furthermore, the apparent absence of iron oxides or oxy(hydroxides) indicates that iron is introduced into the apatite lattice at the expense of calcium, albeit in amounts that do not alter the Raman signatures of the PO₄^3- internal modes. Compositional idiosyncrasies of iron-rich pigmented and nominally iron-free unpigmented enamel offer new insights into enamel biomineralisation supporting the notion that, in rodents, ameloblast function differs significantly between the incisors and the molars.