High strength and damage-tolerance in echinoderm stereom as a natural bicontinuous ceramic cellular solid

Evaluating the single crystallinity of sea urchin calcite

Recent advancements in electron backscatter diffraction (EBSD) data evaluation enable the determination of misorientation between crystals below 0.1°, while with conventional EBSD data evaluation, the smallest misorientation precision between crystals scatters between 0.5°-1°. Sea urchin tests and spines are lightweight biomaterials with a serrated microstructure comprising interlinked calcite crystals. We investigated the microstructure and crystallographic texture of Cidaris cidaris and Paracentrotus lividus test and spine calcite with advanced EBSD measurement and data evaluation. In particular, we re-evaluated the widely accepted single-crystallinity of sea urchin calcite. We found that the test and the spines comprise calcite crystals with different fabrics and a significant variation in crystal co-orientation strength. Even the highly co-oriented calcite of C. cidaris and P. lividus is not perfectly single-crystalline. We found test and spine portions that feature significant internal misorientations (1-3°). Test c-axis orientation in C. cidaris is tangential to the outer test surface, while in the spines, it is parallel to the morphological axis of the spine. Primary and secondary spines feature a bimodal crystal texture comprising co-oriented calcite surrounded by a cortex of misoriented crystals. Crystal misorientation in the spine cortex seems to result mainly from competitive growth determinants. Deciphering the degree of crystallinity and mode of crystal organisation of biological hard tissues is vital for understanding their exceptional control of structure, material architecture and material properties. STATEMENT OF SIGNIFICANCE: Echinoids form lightweight biomineralised skeletal elements with outstanding material properties and a complex microstructure formed of interlinked calcite crystals. The degree of crystallinity and the crystallographic organisation of the calcitic tests and spines are still under debate. We investigate and discuss the crystallinity, microstructure, and texture of Cidaris cidaris and Paracentrotus lividus test and spine crystals. Unprecedented and not yet used for biomineralised carbonate tissues, we apply electron backscatter diffraction pattern matching data evaluation, enabling detection of misorientation precision below 0.1°, relative to 0.5°-1° misorientation precision obtained from conventional EBSD data evaluation. We demonstrate that sea urchin test plates and spines are not single crystals. They feature internal small-angle misorientations and poorly co-oriented, polycrystalline regions with intricate microstructures.

Well-Ordered Nanonetwork Invar from Templated Electrochemical Deposition as Mechanical Metamaterials

This work presents a novel bottom-up approach using a template from a self-assembled block copolymer followed by selective etching for templated electrochemical deposition to fabricate well-ordered nanonetwork Invar (Fe64Ni36) thin film, giving exceptional mechanical properties as mechanical metamaterials. By utilizing pulse-current electrochemical deposition, it is feasible to achieve complete pore-filling for the template, giving diamond-structured Invar with a strut size of ≈20 nm that is one-order magnitude less than the smallest diameter from a top-down approach. The nanoindentation test reveals that the reduced modulus of the diamond-structured Invar exceeds the upper bound of the Gibson-Ashby scaling law due to its deliberate structuring. Following the same reasoning, as evidenced by the micro-compression test, the diamond-structured Invar exhibits an extensive plastic plateau region under loading, different from the catastrophic failure for intrinsic Invar. These findings also demonstrate that the specific strength and energy absorption per volume of the diamond-structured Invar surpasses that of nickel microlattices, in agreement with the "smaller is stronger and tougher" phenomenon. This work highlights the feasibility of fabricating lightweight Invar without sacrificing the inherent properties of Invar, offering a significant improvement over metallic micro-/nanolattices derived from a top-down approach.

Nature's Load-Bearing Design Principles and Their Application in Engineering: A Review

Biological structures optimized through natural selection provide valuable insights for engineering load-bearing components. This paper reviews six key strategies evolved in nature for efficient mechanical load handling: hierarchically structured composites, cellular structures, functional gradients, hard shell-soft core architectures, form follows function, and robust geometric shapes. The paper also discusses recent research that applies these strategies to engineering design, demonstrating their effectiveness in advancing technical solutions. The challenges of translating nature's designs into engineering applications are addressed, with a focus on how advancements in computational methods, particularly artificial intelligence, are accelerating this process. The need for further development in innovative material characterization techniques, efficient modeling approaches for heterogeneous media, multi-criteria structural optimization methods, and advanced manufacturing techniques capable of achieving enhanced control across multiple scales is underscored. By highlighting nature's holistic approach to designing functional components, this paper advocates for adopting a similarly comprehensive methodology in engineering practices to shape the next generation of load-bearing technical components.

A new extraction method of underglaze brown decorative pattern based on the coupling of single scale gamma correction and gray sharpening

In order to solve the problem of image quality and morphological characteristics of primary underglaze brown decorative pattern extraction, this paper proposes a method of primary underglaze brown decorative pattern extraction based on the coupling of single scale gamma correction and gray sharpening. The single-scale gamma correction is combined with the gray sharpening method. The single-scale gamma correction improves the contrast and brightness of the image by nonlinear transformation, but may lead to the loss of image detail. Gray sharpening can enhance the high frequency component and improve the clarity of the image, but it will introduce noise. Combining these two technologies can compensate for their shortcomings. The experimental results show that this method can improve the efficiency of last element underglaze brown decorative pattern extraction by enhancing the image retention detail and reducing the influence of noise. The experimental results showed that F1Score, Miou(%), Recall, Precision and Accuracy(%) were 0.92745, 0.82253, 0.97942, 0.92458 and 0.92745, respectively.

Highly Flexible, High-Performance, and Stretchable Piezoelectric Sensor Based on a Hierarchical Droplet-Shaped Ceramics with Enhanced Damage Tolerance

Stretchable self-powered sensors are of significant interest in next-generation wearable electronics. However, current strategies for creating stretchable piezoelectric sensors based on piezoelectric polymers or 0-3 piezoelectric composites face several challenges such as low piezoelectric activity, low sensitivity, and poor durability. In this paper, a biomimetic soft-rigid hybrid strategy is used to construct a new form of highly flexible, high-performance, and stretchable piezoelectric sensor. Inspired by the hinged bivalve Cristaria plicata, hierarchical droplet-shaped ceramics are manufactured and used as rigid components, where computational models indicate that the unique arched curved surface and rounded corners of this bionic structure can alleviate stress concentrations. To ensure electrical connectivity of the piezoelectric phase during stretching, a patterned liquid metal acts as a soft circuit and a silicone polymer with optimized wettability and stretchability serves as a soft component that forms a strong mechanical interlock with the hierarchical ceramics. The novel sensor design exhibits excellent sensitivity and durability, where the open circuit voltage remains stable after 5000 stretching cycles at 60% strain and 5000 twisting cycles at 180°. To demonstrate its potential in heathcare applications, this new stretchable sensor is successfully used for wireless gesture recognition and assessing the progression of knee osteoarthritis.

Composite material in the sea urchin Cidaris rugosa: ordered and disordered micrometre-scale bicontinuous geometries

The sponge-like biomineralized calcite materials found in echinoderm skeletons are of interest in terms of both structure formation and biological function. Despite their crystalline atomic structure, they exhibit curved interfaces that have been related to known triply periodic minimal surfaces. Here, we investigate the endoskeleton of the sea urchin Cidaris rugosa that has long been known to form a microstructure related to the Primitive surface. Using X-ray tomography, we find that the endoskeleton is organized as a composite material consisting of domains of bicontinuous microstructures with different structural properties. We describe, for the first time, the co-occurrence of ordered single Primitive and single Diamond structures and of a disordered structure within a single skeletal plate. We show that these structures can be distinguished by structural properties including solid volume fraction, trabeculae width and, to a lesser extent, interface area and mean curvature. In doing so, we present a robust method that extracts interface areas and curvature integrals from voxelized datasets using the Steiner polynomial for parallel body volumes. We discuss these very large-scale bicontinuous structures in the context of their function, formation and evolution.

Biomimetic Bouligand chiral fibers array enables strong and superelastic ceramic aerogels

Ceramic aerogels are often used when thermal insulation materials are desired; however, they are still plagued by poor mechanical stability under thermal shock. Here, inspired by the dactyl clubs of mantis shrimp found in nature, which form by directed assembly into hierarchical, chiral and Bouligand (twisted plywood) structure exhibiting superior mechanical properties, we present a compositional and structural engineering strategy to develop strong, superelastic and fatigue resistance ceramic aerogels with chiral fibers array resembling Bouligand architecture. Benefiting from the stress dissipation, crack torsion and mechanical reinforcement of micro-/nano-scale Bouligand array, the tensile strength of these aerogels (170.38 MPa) is between one and two orders of magnitude greater than that of state-of-the-art nanofibrous aerogels. In addition, the developed aerogels feature low density and thermal conductivity, good compressive properties with rapid recovery from 80 % strain, and thermal stability up to 1200 °C, making them ideal for thermal insulation applications.

Hierarchical structure design of sea urchin Shell-Based evaporator for efficient omnidirectional Solar-Driven steam generation

Solar-driven steam generation (SSG) is regarded as a feasible solution to the problem of fresh water scarcity. Although several attempts have been devoted to increase the efficiency of solar-to-steam conversion, it remains difficult to fabricate cost-effective, steady, and multi-angle sunlight-absorbing evaporators from readily available biomass materials. Herein, a novel hierarchical structured SSG evaporator (PDA@Shell-NaClO) is developed through a simple, low-cost, and scalable etching treatment on discarded sea urchin (SU) shells. Attributing to the dedicatedly designed microneedles array structure and porous skeleton structure of the SU shell, this PDA@Shell-NaClO evaporator shows an outstanding average light absorption performance (>90%) in a broad range of angles from 0° to 60° and exceedingly high evaporation rate of 2.81 kg m^-2 h^-1 under one sun condition. Furthermore, the prepared evaporator also maintains an overall stable evaporation performance and exhibits an excellent durability for a long time of up to two weeks in actual seawater. This full-ocean biomass-based SSG evaporator with plentiful raw material availability offers innovative opportunities for large-scale fresh water production.