Bottom-Up Assembling Hierarchical Enamel-Like Bulk Materials with Excellent Optical and Mechanical Properties for Tooth Restoration.

Enamel has good optical and mechanical properties because of its multiscale hierarchical structure. Biomimetic construction of enamel-like 3D bulk materials at nano-, micro-, mesh- and macro-levels is a challenge. A novel facile, cost-effective, and easy large-scale bottom-up assembly strategy to align 1D hydroxyapatite (HA) nanowires bundles to 3D hierarchical enamel structure with the nanowires bundles layer-by-layer interweaving orientation, is reported. In the strategy, the surface of oleate templated ultralong HA nanowires with a large aspect ratio is functionalized with amphiphilic 10-methacryloyloxydecyl dihydrogen phosphate (MDP). Furtherly, the MDP functionalized HA nanowire bundles are assembled layer-by-layer with oriented fibers in a single layer and cross-locked between layers at a certain angle at mesoscale and macroscale in the viscous bisphenol A-glycidyl methacrylate (Bis-GMA) ethanol solution by shear force induced by simple agitation and high-speed centrifugation. Finally, the excessive Bis-GMA and ethanol are removed, and (Bis-GMA)-(MDP-HA nanowire bundle) matrix is densely packed under hot pressing and polymerized to form bulk enamel-like materials. The composite has superior optical properties and comparable comprehensive mechanic performances through a combination of strength, hardness, toughness, and friction. This method may open new avenues for controlling the nanowires assembly to develop hierarchical nanomaterials with superior properties for many different applications.

Extrafibrillar demineralization: Yes or no?

OBJECTIVE: Extrafibrillar demineralization is considered to be an ideal solution for addressing the durability of resin-dentin bonding interfaces. However, its theoretical basis is contradictory to ionization equilibrium of hydroxyapatite dissolution. In this study, various calcium chelators were selected as dentin conditioners to explore the essence of dentin demineralization with chelators and its effect on resin-dentin adhesion. METHODS: Polyethyleneimine grafted with EDTA and polyacrylic acid sodium (PAAN450k) larger than 40 kDa, as well as PAAN (PAAN3k) and EDTA smaller than 6 kDa, were prepared as dentin conditioners. The dentin powder was designed to characterize whether it would demineralize without contact with PAAN450k. Dentin demineralization effect with four conditioners was evaluated with field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy and quantification of hydroxyproline concentration after enzymatic degradation. Micro-tensile bond strength (µTBS) test and failure mode analysis were employed to assess the bonding effect of the four chelators in both wet and dry bonding, with H3PO4 wet bonding serving as the control group. RESULTS: Demineralization occurs when PAAN450k was not in direct contact with the dentin powder. The extrafibrillar demineralization cannot be induced by any chelator regardless of its molecular weight. Complete demineralization including extrafibrillar and intrafibrillar demineralization would occur with sufficient interaction time. Moreover, chelators could not provide a reliable dentin bonding effect under a short interaction time. SIGNIFICANCE: From the perspective of theory and application, extrafibrillar demineralization is not a reliable strategy, which provides a reminder for exploring new strategies in the future.

Er:YAG Laser Physical Etching and Ultra-High-Molecular-Weight Cross-Linked Sodium Polyacrylate Chemical Etching for a Reliable Dentin Dry Bonding.

Dentin bond interface stability is the key issue of dental adhesion in present clinical dentistry. The concept of selective extrafibrillar demineralization has opened a new way to maintain intrafibrillar minerals to prevent interface degradation. Here, using ultra-high-molecular-weight sodium polyacrylate [Carbopol (Carbo) > 40 kDa] as a calcium chelator, we challenge this concept and propose a protocol for reliable dentin dry bonding. The results of high-resolution transmission electron microscopy revealed periodic bands of 67 nm dentin collagen fibrils after Carbo etching, and the hydroxyproline concentration increasing with prolonged chelating time denied the concept of extrafibrillar demineralization. The results that wet and dry bonding with Carbo-based demineralization produced a weaker bond strength than the traditional phosphoric acid wet adhesion suggested that the Carbo-based demineralization is an unreliable adhesion strategy. A novel protocol of Er:YAG laser physical etching followed by Carbo chemical etching for dentin adhesion revealed that a micro-/nano-level rough, rigid, and non-collagen exposed dentin surface was produced, the micro-tensile bond strength was maintained after aging under dry and wet bonding modes, and in situ zymography and nanoleakage within the hybrid layers presented lower signals after aging. Cell culture in vitro and a rabbit deep dentin adhesion model in vivo proved that this protocol is safe and biocompatible. Taken together, the concept of extrafibrillar demineralization is limited and insufficient to use in the clinic. The strategy of Er:YAG laser physical etching followed by Carbo chemical etching for dentin adhesion produces a bonding effect with reliability, durability, and safety.

Oxidized Dopamine Acrylamide Primer to Achieve Durable Resin-Dentin Bonding.

The durability of the resin-dentin bonding interface is a key issue in clinical esthetic dentistry. Inspired by the extraordinary bioadhesive properties of marine mussels in a wet environment, we designed and synthetized N-2-(3,4-dihydroxylphenyl) acrylamide (DAA) according to the functional domain of mussel adhesive proteins. DAA's properties of collagen cross-linking, collagenase inhibition, inducing collagen mineralization in vitro, and as a novel prime monomer for clinical dentin adhesion use, its optimal parameters, and effect on the adhesive longevity and the bonding interface's integrity and mineralization, were evaluated in vitro and in vivo. The results showed that oxide DAA can inhibit the activity of collagenase and cross collagen fibers to improve the anti-enzymatic hydrolysis of collagen fibers and induce intrafibrillar and interfibrillar collagen mineralization. As a primer used in the etch-rinse tooth adhesive system, oxide DAA can improve the durability and integrity of the bonding interface by anti-degradation and mineralization of the exposed collagen matrix. Oxidized DAA (OX-DAA) is a promising primer for improving dentin durability; using 5% OX-DAA ethanol solution and treating the etched dentin surface for 30 s is the optimal choice when used as a primer in the etch-rinse tooth adhesive system.

Improvement of Emulsion Stability and Plugging Performance of Nanopores Using Modified Polystyrene Nanoparticles in Invert Emulsion Drilling Fluids.

Drilling fluid invasion and pressure transmission caused by the development of micropores and fractures in shale oil and gas formations are the major factors contributing to wellbore instability during drilling using oil-based drilling fluids (OBFs). In this study, a modified polystyrene latex (MPL) material was synthesized through emulsion polymerization and was characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), particle size analysis, scanning electron microscopy (SEM) observations, and contact angle testing. The influence of the MPL on the stability of a water-in-oil emulsion was analyzed via sedimentation observations and electrical stability tests. The effects of the MPL on the plugging mechanism of white oil and water-in-oil emulsions were evaluated using 0.1-1.0 µm micro-porous filtration films. The experimental results revealed that the MPL has a favorable thermal stability, with an initial thermal decomposition temperature of 363°C, a median particle size (D50) of 233 nm, and a three-phase contact angle of 103.5°. The MPL can enhance the sedimentation stability of an emulsion to a considerable extent and can improve the electrical stability (ES) of the emulsion, which is conducive to the stability of OBFs. Due to the deformability of the MPL, it has a wide range of adaptations for micro-scale pores and fractures. In both the white oil and water-in-oil emulsions, the MPL can reduce the filtration loss through microporous membranes with pore sizes of 0.1-1.0 µm to within 10 ml. This paper details the methodology of the synthesis of nanomaterials that can effectively plug a formation's nanopores and fractures; thereby, stabilizing OBFs.

IGF2BP2 promotes gastric cancer progression by regulating the IGF1R-RhoA-ROCK signaling pathway.

BACKGROUND: Our study aimed to probe the intrinsic and concrete molecular mechanism of IGF2 mRNA-binding protein 2 (IGF2BP2) in gastric cancer (GC). METHODS: The mRNA and protein expressions were assessed using qRT-PCR and western blot, respectively. CCK-8 assay was employed to determine cell proliferation. Levels of TNFα and IL-1ß were analyzed using ELISA. Furthermore, cell apoptosis was evaluated using flow cytometry analysis. Cell migration and invasion were evaluated using Transwell assay. The experiment of tumor formation in nude mice was employed to analyze the effect of IGF2BP2 in regulating GC tumor growth and lung metastasis in vivo. Finally, the binding relationship between IGF1R and IGF2BP2 was verified using RIP and RNA pull down assays. RESULTS: IGF2BP2 was significantly elevated in both GC tissues and cells. Silencing of IGF2BP2 dramatically suppressed the inflammation, proliferation, migration and invasion, yet promoted cell apoptosis in vitro and in vivo. Furthermore, IGF2BP2, as a m6A reader, was proved to increase the expression of IGF1R by identifying m6A methylation modification sites in IGF1R mRNA, thus activating RhoA-ROCK pathway. Importantly, the anti-carcinogenic impacts of IGFBP2 silence were restrained by IGF1R overexpression, which was eliminated by the inactivation of RhoA-ROCK. CONCLUSION: We emphasized the oncogenic role of IGF2BP2 in gastric carcinogenesis and confirmed its activation is partly due to the activation of IGF1R-RhoA-ROCK signaling pathway. Our findings identified that IGF2BP2 might be a promising prognostic biomarker and provided clinical translational potential.

Synergistic effects of graphene quantum dots and carbodiimide in promoting resin-dentin bond durability.

OBJECTIVE: Resin-based dental adhesion is mostly utilized in minimally invasive operative dentistry. However, improving the durability and stability of resin-dentin bond interfaces remain a challenge. Graphene quantum dots (GQDs) reinforced by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) were introduced to modify the resin-dentin bond interfaces, thereby promoting their durability and stability. METHODS: GQDs, EDC, and EDC+GQDs groups were designed to evaluate the effects of GQDs and EDC on collagenase activity, the interaction of GQDs with collagen, and the resin-dentin interface. First, the effects of GQDs and EDC on collagenase activity was evaluated by Collagenase (EC 3.4.24.3) reacting with its substrate. The interaction of GQDs and EDC with collagen were evaluated by cross-linking degree analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, attenuated total reflection Fourier transform infrared spectroscopy and enzymatic hydrolysis. Second, the acid-etched and rinse adhesive system was used to evaluate the resin-dentin bond on the basis of microtensile bond strength, in situ zymography and fluorescence confocal laser scanning microscopy. RESULTS: GQDs could inhibit collagenase activity. GQDs with the aid of EDC could cross-link collagen via covalent bonds and improve the anti-enzymatic hydrolysis of collagen. In the resin-dentin adhesion model, the µTBS of the EDC+GQDs group was significantly higher than the other control groups after thermocycling. The addition of EDC to GQDs could inhibit matrix metalloproteinase activity and promote the integrity of the bonding interfaces after thermocycling. SIGNIFICANCE: This study presents a novel strategy to modify the resin-dentin interface and provides a new application for GQDs. This strategy has the potential to improve the durability of resin-based restoration in dentistry.

A Dopamine Acrylamide Molecule for Promoting Collagen Biomimetic Mineralization and Regulating Crystal Growth Direction.

The reconstruction of the intra/interfibrillar mineralized collagen microstructure is extremely important in biomaterial science and regeneration medicine. However, certain problems, such as low efficiency and long period of mineralization, are apparent, and the mechanism of interfibrillar mineralization is often neglected in the present literature. Thus, we propose a novel model of biomimetic collagen mineralization that uses molecules with the dual function of cross-linking collagen and regulating collagen mineralization to construct the intrafibrillar and interfibrillar collagen mineralization of the structure of mineralized collagen hard tissues. In the present study completed in vitro, N-2-(3,4-dihydroxyphenyl) acrylamide (DAA) is used to bind and cross-link collagen molecules and further stabilize the self-assembled collagen fibers. The DAA-collagen complex provides more affinity with calcium and phosphate ions, which can reduce the calcium phosphate/collagen interfacial energy to promote hydroxyapatite (HA) nucleation and accelerate the rate of collagen fiber mineralization. Besides inducing intrafibrillar mineralization, the DAA-collagen complex mineralization template can realize interfibrillar mineralization with the c-axis of the HA crystal on the surface of collagen fibers and between fibers that are parallel to the long axis of collagen fibers. The DAA-collagen complex, as a new type of mineralization template, may provide a new collagen mineralization strategy to produce a mineralized scaffold material for tissue engineering or develop bone-like materials.

Rapid regeneration of enamel-like-oriented inorganic crystals by using rotary evaporation.

Enamel, the hardest tissue in the human body, has excellent mechanical properties, mainly due to its highly ordered spatial structure. Fabricating enamel-like structure is still a challenge today. In this work, a simple and highly efficient method was introduced, using the silk fibroin as a template to regulate calcium- and phosphate- supersaturated solution to regenerate enamel-like hydroxyapatite crystals on various substrates (enamel, dentin, titanium, and polyethylene) under rotary evaporation. The enamel-like zinc oxide nanorod array structure was also successfully synthesized using the aforementioned method. This strategy provides a new approach to design and fabricate mineral crystals with particular orientation coatings for materials.

Mechanism and Effects of Polyphenol Derivatives for Modifying Collagen.

This study is aimed to investigate the relationship of the mechanism and the effect of polyphenol derivatives cross-linking collagen with polyphenol molecular structural complexity and reaction conditions of polyphenols with collagen and to present a reference for cross-linker selection. Three kinds of polyphenols were selected to cross-link collagen under nonoxidized and oxidized conditions in vitro. These polyphenols included tannic acid, which represents the most complex stereo structure and the highest number of phenolic hydroxyl groups; epigallocatechin gallate, which represents a moderately complex structure and contains fewer phenolic hydroxyl groups than tannic acid; and N-2-(3,4-dihydroxylphenyl) ethyl acrylamide, which represents only one hydroxyl phenol group. Particle size analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, attenuated total reflection Fourier transform infrared spectroscopy, and cross-linking degree analysis were conducted. Mechanical properties, thermal stability, swelling properties, hydrophilicity, and antienzymolysis properties were also determined. Results showed that all polyphenol derivatives cross-linked collagen mainly by noncovalent bonding under acidic nonoxidized conditions and by covalent bonding under alkaline-oxidized conditions. In general, the modification effect of polyphenol on collagen was related to its molecular complexity and the number of its phenolic hydroxyls. Several phenolic hydroxyls in the polyphenol derivative caused a good modification effect on collagen, especially under acidic nonoxidized conditions. Under alkaline conditions, each polyphenol was oxidized, resulting in improved cross-linking strength by covalent bonding compared to that under acidic nonoxidized condition via noncovalent bonding. The selection of cross-linkers and cross-linking conditions should be based on the purpose of collagen modification consistent with the effect of cross-linking.