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Chiton are marine mollusks who use heavily mineralized and ultrahard teeth to feed on epilithic and endolithic algae on intertidal rocks. To fulfill this function, chiton teeth must be tough and wear‐resistant. Impressive mechanical properties are achieved in the chiton tooth through a hierarchically arranged composite structure consisting of a hard shell of organic‐encased and highly oriented nanostructured magnetite rods that surround a soft core of organic‐rich iron phosphate. Microscopic and spectroscopic analyses combined with finite element simulations are used to probe the ultrastructural features and uncover structure–mechanical property relationships in the fully mineralized teeth of the gumboot chiton Cryptochiton stelleri. By understanding the effects of the nanostructured architecture within the chiton tooth, abrasion‐resistant materials can be developed for tooling and machining applications, as well as coatings for equipment and medical implants.

Four fluorinated derivatives of 9-anthracene carboxylic acid (9AC), a molecule that shows a reversible photomechanical response in its crystal form, have been synthesized and characterized. The spectroscopic properties and crystal structures of 4-fluoro-9-anthracene carboxylic acid (4F-9AC), 2-fluoro-9-anthracene carboxylic acid (2F-9AC), 10-fluoro-9-anthracene carboxylic acid (10F-9AC), and 2,6-difluoro-9-anthracene carboxylic acid (2,6DF-9AC) are all very similar to those of 9AC. However, their photomechanical properties vary widely. 405 nm light was used to induce [4 + 4] photodimerization and a mechanical response in crystalline microneedles and ribbons. Both the photodimer dissociation rate and the mechanical recovery varied by more than an order of magnitude, with 4F-9AC exhibiting the most rapid recovery time, on the order of 30 s. Nanoindentation measurements show that this crystal has a slightly reduced elastic modulus and a significantly reduced hardness, making it less brittle than the 9AC crystal. Large 4F-9AC crystals remain intact after irradiation, without fragmenting, while microneedles can undergo more than 100 mechanical bending cycles. Given the similarity of the crystal packing in all five molecules, the improved photomechanical properties must arise from subtle changes in intermolecular interactions or possibly differences in disorder. These results demonstrate that it is possible to significantly improve the properties of photomechanical materials through small modifications of the molecular structure.

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