Mechanically Reinforced Artificial Enamel by Mg2+-Induced Amorphous Intergranular Phases.

Amorphous intergranular phases in mature natural tooth enamel are found to provide better adhesion and could dramatically affect their mechanical performance as a structure reinforcing phase. This study successfully synthesized an amorphous intergranular phase enhanced fluorapatite array controlled by Mg2+ (FAP-M) at room temperature. Furthermore, atom probe tomography (APT) observation presents that Mg2+ is enriched at grain boundaries during the assembly of enamel-like fluorapatite arrays, leading to the formation of intergranular phases of Mg-rich amorphous calcium phosphate (Mg-ACP). APT results also demonstrated that the segregation of Mg2+ caused the chemical gradient in nanocrystalline attachment and realignment under the drive of inherent surface stress. These results indicate that the amorphous intergranular phases served like glue to connect each nanorod to reinforce the enamel-like arrays. Therefore, the as-received FAP-M artificial enamel exhibits excellent mechanical properties, with hardness and Young's modulus of 2.90 ± 0.13 GPa and 67.9 ± 3.4 GPa, which were ∼8.3 and 2.2 times higher than those of FAP arrays without controlled by Mg2+, respectively.

Room-temperature growth of fluorapatite/CaCO3 heterogeneous structured composites inspired by human tooth.

Organisms can synthesize heterogeneous structures with excellent mechanical properties through mineralization, the most typical of which are teeth. The tooth is an extraordinarily resilient bi-layered material that is composed of external enamel perpendicular to the tooth surface and internal dentin parallel to the tooth surface. The synthesis of enamel-like heterostructures with good mechanical properties remains an elusive challenge. In this study, we applied a biomimetic mineralization method to grow fluorapatite/CaCO3 (FAP/CaCO3) heterogeneous structured thin films that mimic their biogenic counterparts found in teeth through a three-step pathway: coating a polymer substrate, growing a layered calcite film, and mineralization of a fluorapatite columnar array on the calcite layer. The synthetic heterostructure composites combine well and exhibit good mechanical properties comparable to their biogenic counterparts. The FAP/CaCO3 heterogeneous structured composite exhibits excellent mechanical properties, with a hardness and Young's modulus of 1.99 ± 0.02 GPa and 47.5 ± 0.6 GPa, respectively. This study provides a reasonable new idea for unique heterogeneous structured materials designed at room temperature.

Bioinspired 3D Printable, Self-Healable, and Stretchable Hydrogels with Multiple Conductivities for Skin-like Wearable Strain Sensors.

Bioinspired hydrogels have promising prospects in applications such as wearable devices, human health monitoring equipment, and soft robots due to their multifunctional sensing properties resembling natural skin. However, the preparation of intelligent hydrogels that provide feedback on multiple electronic signals simultaneously, such as human skin receptors, when stimulated by external contact pressure remains a substantial challenge. In this study, we designed a bioinspired hydrogel with multiple conductive capabilities by incorporating carbon nanotubes into a chelate of calcium ions with polyacrylic acid and sodium alginate. The bioinspired hydrogel consolidates self-healing ability, stretchability, 3D printability, and multiple conductivities. It can be fabricated as an integrated strain sensor with simultaneous piezoresistive and piezocapacitive performances, exhibiting sensitive (gauge factor of 6.29 in resistance mode and 1.25 kPa-1 in capacitance mode) responses to subtle pressure changes in the human body, such as finger flexion, knee flexion, and respiration. Furthermore, the bioinspired strain sensor sensitively and discriminatively recognizes the signatures written on it. Hence, we expect our ideas to provide inspiration for studies exploring the use of advanced hydrogels in multifunctional skin-like smart wearable devices.

Mineralization of calcium phosphate induced by a silk fibroin film under different biological conditions.

Silk fibroin is a promising biomaterial that has been used for tissue engineering applications. However, the influence of silk fibroin on the mineralization of calcium phosphate in different biological environments has not been discussed before. In this work, we fabricated organized silk fibroin film as the organic framework and amorphous calcium phosphate (ACP) deposited on the films as precursors. The transformation pathways and morphology of ACP was then studied in both enzyme and PBS (phosphate buffer saline) solutions. While only hydroxyapatite (HA) crystals formed in enzyme solution, a mixture of tricalcium phosphate (TCP) and HA crystals were obtained in PBS solution, which can be related to the variations of the content of silk fibroin and pH of the solution. Therefore, silk fibroin films can have an important effect on the mineralization process of calcium phosphate in different biological environments. In addition, cell cultivation experiments show that the silk films after mineralization promoted osteogenesis and exhibited good biocompatibility.

Escherichia coli templated iron oxide biomineralization under oscillation.

Motility is significant in organisms. Studying the influence of motility on biological processes provides a new angle in understanding the essence of life. Biomineralization is a representative process for organisms in forming functional materials. In the present study, we investigated the biomineralization of iron oxides templated by Escherichia coli (E. coli) cells under oscillation. The formation of iron oxide minerals with acicular and banded morphology was observed. The surface charge of E. coli cells contributed to the biomineralization process. The surface components of E. coli cells including lipids, carbohydrates and proteins also have roles in regulating the formation and morphology of iron oxide minerals. As-prepared mineralized iron oxide nanomaterials showed activity in photocatalytic degradation of methylene blue as well as in electrocatalytic hydrogen evolution reaction. This study is helpful not only in understanding motility in biological processes, but also in developing techniques for fabricating functional nanomaterials.

Sol-gel Autocombustion Synthesis of Nanocrystalline High-entropy Alloys.

A reduction in the particle size is expected to improve the properties and increase the application potential of high-entropy alloys. Therefore, in this study, a novel sol-gel autocombustion technique was first used to synthesize high-entropy alloys. The average grain size of the prepared nanocrystalline CoCrCuNiAl high-entropy alloys showed was 14 nm with an excellent and uniform dispersion, exhibiting a distinct magnetic behavior similar to the superparamagnetic behavior. We show that the metal nitrates first form (Co,Cu,Mg,Ni,Zn)O high-entropy oxides, and then in situ reduce to CoCrCuNiAl high-entropy alloys by the reducing gases, and the chelation between citric acid and the metal ions and the in situ chemical reactions are the dominant reaction mechanisms. We demonstrate that the sol-gel autocombustion process is an efficient way to synthesize solid solution alloys eluding the restriction of a high mixing entropy.

A novel enhanced visible-light-driven photocatalyst via hybridization of nanosized BiOCl and graphitic C3N4.

Nanosized C3N4/BiOCl composites were synthesized via a facile method in the presence of arabic gum. Arabic gum acts as the structure-directing agent and helps the formation of BiOCl nanoparticles. A significant enhanced photodegradation is observed and a possible mechanism is proposed by combining photosensitization and photocatalysis.

[Investigation on multiband attenuation compatibility of carbon nanotubes].

The present investigation was focused on how to realize the attenuating compatibility of the electromagnetic defilade material in UV-Vis-Infrared band. Optical spectra of CNTs was investigated on the basis of analytical technologies such as Fourier transform infrared spectroscopy, UV-Vis spectrophotometer, laser scattering, and electron microscopy. It was demonstrated that the multi-band attenuation characteristic of CNTs is effectively associated with additives, concentrations and configurations. The measured sample with a concentration of 0.04 g x L(-1), in which the radius of CNTs was 30-50 nm, bore the maximum value of the extinction coefficient of 7.825 m2 x g(-1) at the point of 265 nm. Meanwhile, this kind of CNTs presents outstanding unified attenuation properties in infrared wave band when the thickness of the CNTs film is 0.1 mm and the total mass of CNTs is 0.349 mg in optical path. Especially, the unified attenuation goes beyond 90% in 4.0-6.25 and 7.0-16.7 microm.