Conformal polymer coating leads to damage-tolerant architected ceramic structures with high strength and toughness.

Considerable effort has been devoted recently to replace platinum-based catalysts with their non-noble-metal counterparts in the oxygen reduction reaction (ORR) in fuel cells. Nitrogen-doped carbon structures emerged as possible candidates for this role, and their earth-abundant metal-decorated composites showed great promise. Here, we report on the simultaneous formation of nitrogen-doped graphene and iron nitride from the lyophilized mixture of graphene oxide and iron salt by high-temperature annealing in ammonia atmosphere. A mixture of FeN and Fe₂N particles was formed with average particle size increasing from 23.4 to 127.0 nm and iron content ranging from 5 to 50 wt %. The electrocatalytic oxygen reduction activity was investigated via the rotating disk electrode method in alkaline media. The highest current density of 3.65 mA cm^–2 at 1500 rpm rotation rate was achieved in the 20 wt % catalyst via the four-electrode reduction pathway, exceeding the activity of both the pristine iron nitride and the undecorated nitrogen-doped graphene. Since our catalysts showed improved methanol tolerance compared to the platinum-based ones, the formed non-noble-metal system offers a viable alternative to the platinum-decorated carbon black (Pt/CB) ORR catalysts in direct methanol fuel cells.

Human dental enamel is a uniquely hard and tough biological realization of the inherently brittle apatite crystal. In sound enamel both structure and chemistry are organically fine-tuned, while developmental disorders - such as hypomineralization - often lead to severe enamel alterations resulting in weaker mechanical performance and shorter lifetime as in case of molar-incisor hypomineralization (MIH) which has a global prevalence of 13.5%. However, causes of the development of hypomineralization disorder remain unclear up to date. In the present paper, a new form of dental hypomineralization is reported for the first time. Structural and chemical alterations of dental enamel exhibiting a special ribbon-like hypomineralization (RLH) are compared to the characteristics of sound and MIH-affected teeth. Microporosity, mineral density and characteristic 3D macroscopic shape of the RLH affected volumes were captured by micro-CT analysis. On the submicron-scale, nanoporosity, unusual morphologies and reduced size of apatite nanocrystals have been revealed. These RLH specific features are coupled with a particular chemical fingerprint in Raman spectroscopy, which allows its clear separation from MIH affected and sound enamel. Based on these nanostructural features we conclude different failure mechanisms in the biochemical control during crystallization of the RLH and MIH enamel. STATEMENT OF SIGNIFICANCE: Molar-incisor hypomineralization (MIH) is a developmental enamel disorder with up to 14% prevalence, characterized by reduced mineral content, hypersensitivity, and post-eruptive enamel breakdown. The causes of the development of this disorder remain unclear up to date. In this study, we examine molars with hypomineralization in a ribbon-like macroscopic morphology. These molars show increased porosity, organic content, and reduced mineral content, while carbonate levels remain unchanged in both affected and unaffected areas, unlike MIH-affected enamel. Ribbon-like hypomineralized (RLH) enamel also features unusual apatite nanocrystal morphologies, including isometric crystals in the prism boundary zone and bean-shaped crystals with a soft central zone. Nanoscale analysis reveals RLH as a developmental anomaly distinct from MIH, offering novel insights into the biochemical controls of hypomineralization.

Ornithopod dinosaurs evolved numerous craniodental innovations related to herbivory. Nonetheless, the relationship between occlusion, tooth wear rate, and tooth replacement rate has been neglected. Here, we reconstruct tooth wear rates by measuring tooth replacement rates and tooth wear volumes, and document their dental microwear. We demonstrate that total tooth volume and rates of tooth wear increased steadily during ornithopod evolution, with deeply-nested taxa wearing up to 3360 mm³ of tooth volume/day. Increased wear resulted in asymmetric tooth crown formation with uneven von Ebner line increment width by the Late Jurassic, and in faster tooth replacement rates in multiple lineages by the mid-Cretaceous. Microwear displays a contrasting pattern, with decreasing complexity and pit percentages in deeply-nested and later-occurring taxa. We hypothesize that early ornithopods were browsers and/or frugivores but deeply nested iguanodontians were bulk-feeders, eating tougher, less nutritious plants; these trends correlate with increasing body mass and longer gut passage times.