Significance Understanding how protein scaffolds direct mineral morphogenesis is crucial for engineering bone and tooth and would open new vistas in materials design. In the case of tooth enamel, which is the hardest tissue in the body and consists of organized bundles of coaligned apatite crystals, amyloid-like amelogenin nanoribbons are hypothesized to provide the scaffold. We show that these nanoribbons are far more potent calcium phosphate nucleators than other amelogenin motifs or collagen, which provides the scaffold for bone. This potency stems from a periodic array of charged sites that provide a template for calcium phosphate ion binding on a low-energy interface. The ubiquity of β-sheet protein structures suggests that this mechanism can be adopted for the design of synthetic mineralization-directing scaffolds.

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Liquid emulsion droplet evaporation is of importance for various sensing and imaging applications. The liquid-to-gas phase transformation is typically triggered thermally or acoustically by low–boiling point liquids, or by inclusion of solid structures that pin the vapor/liquid contact line to facilitate heterogeneous nucleation. However, these approaches lack precise tunability in vaporization behavior. Here, we describe a previously unused approach to control vaporization behavior through an endoskeleton that can melt and blend into the liquid core to either enhance or disrupt cohesive intermolecular forces. This effect is demonstrated using perfluoropentane (C5F12) droplets encapsulating a fluorocarbon (FC) or hydrocarbon (HC) endoskeleton. FC skeletons inhibit vaporization, whereas HC skeletons trigger vaporization near the rotator melting transition. Our findings highlight the importance of skeletal interfacial mixing for initiating droplet vaporization. Tuning molecular interactions between the endoskeleton and droplet phase is generalizable for achieving emulsion or other secondary phase transitions, in emulsions.

Zinc and stannous ions are commonly used in oral care to reduce tooth enamel degradation. However, mechanistic understanding of the role of the ions in the protection of enamel against acid insults remains inadequate due to limitations of experimental techniques to validate interfacial interactions at the atomic scale. We overcome this problem by the examination of adsorption and subsurface exchange of the ions on common hydroxyapatite (001) and (010) surfaces in contact with electrolytes at pH values of 5 and 7 using molecular dynamics simulations in unprecedented accuracy. The surface chemistry under these conditions is characterized by the presence of dihydrogenphosphate ions and a 70/30 mixture of dihydrogenphosphate ions and monohydrogenphosphate ions. Zn­(II) and Sn­(II) ions favorably adsorb and coat the surfaces under all conditions, with stronger attraction at pH 5 than at pH 7 and a preference for the prismatic (010) surface over the basal (001) surface. Subsurface substitution is only significant for Zn­(II) ions at pH 7 in small concentrations up to 6 mol % with free energies between 0 and −20 kcal/mol on both surfaces and largely unfavorable for Sn­(II) ions. Zn­(II) and Sn­(II) ions can therefore coat the enamel surface and it is likely that Zn2+ ions incorporate below the surface and play a role to stabilize apatite surfaces from dissolution. Computed substitution free energies, lattice strains up to 1.5%, and changes in X-ray data agree very well with available experimental data for bulk apatites. The results provide first quantitative insights into enamel surface stabilization, and the methods can be applied to other mineral phases.