Superhydrophobic and Self-Healing Mg-Al Layered Double Hydroxide/Silane Composite Coatings on the Mg Alloy Surface with a Long-Term Anti-corrosion Lifetime

Layered Double Hydroxides: Recent Progress and Promising Perspectives Toward Biomedical Applications

Layered double hydroxides (LDHs) have been widely studied for biomedical applications due to their excellent properties, such as good biocompatibility, degradability, interlayer ion exchangeability, high loading capacity, pH-responsive release, and large specific surface area. Furthermore, the flexibility in the structural composition and ease of surface modification of LDHs makes it possible to develop specifically functionalized LDHs to meet the needs of different applications. In this review, the recent advances of LDHs for biomedical applications, which include LDH-based drug delivery systems, LDHs for cancer diagnosis and therapy, tissue engineering, coatings, functional membranes, and biosensors, are comprehensively discussed. From these various biomedical research fields, it can be seen that there is great potential and possibility for the use of LDHs in biomedical applications. However, at the same time, it must be recognized that the actual clinical translation of LDHs is still very limited. Therefore, the current limitations of related research on LDHs are discussed by combining limited examples of actual clinical translation with requirements for clinical translation of biomaterials. Finally, an outlook on future research related to LDHs is provided.

Diatomite@MoS2 Nanocomposite Layers as Composite Coating Targeting for Mg Alloys Endowed with Properties of Anticorrosion and Antiwear

Molybdenum disulfide (MoS2) demonstrates promising applications in enhancing the corrosion and wear resistance of metals, but the susceptibility of this nanomaterial to agglomeration hinders its overall performance. In this study, the externally assisted corrosion inhibitor sodium molybdate (SM) was successfully constructed in diatomaceous earth (DE) and molybdenum disulfide (MoS2). This not only served as a molybdenum source for MoS2 but also enabled the preparation of DE@MoS2-SM microcapsules, achieving a corrosion inhibitor loading of up to 23.23%. The corrosion testing reveals that the composite coating, when compared to the pure epoxy coating, exhibits an impedance modulus 2 orders of magnitude higher (1.80 × 109 Ω·cm2), offering prolonged protection for magnesium alloys over a 40 day period. Furthermore, a filler content of 3% sustains a coefficient of friction (COF) at 0.55 for an extended duration, indicating commendable stability and wear resistance. The protective performance is ascribed to the synergistic enhancement of corrosion and wear resistance in the coatings, facilitated by the pore structure of DE, the high hardness of MoS2, and the obstructive influence of Na2MoO4. This approach offers a straightforward and efficient means of designing microcapsules for use in corrosive environments, whose application can be extended in industrial fields. In particular, we promote the application of nautical instruments, underwater weapons, and seawater batteries in the shipbuilding industry and marine engineering.

Eco-Friendly Superhydrophobic Coupling Conversion Coating with Corrosion Resistance on Magnesium Alloy

An eco-friendly superhydrophobic conversion coating is fabricated to enhance the corrosion resistance of the AZ31B Mg alloy by combining the deep eutectic solvent pretreatment and electrodeposition. The coral-like micro-nano structure formed by reacting deep eutectic solvent and Mg alloy provides a structural basis for constructing a superhydrophobic coating. Cerium stearate with low surface energy is deposited on the structure, providing the coating's superhydrophobicity and the corrosion inhibition effect. Electrochemical test results demonstrate that the as-prepared superhydrophobic conversion coating (water contact angle at 154.7°) with a 99.68% protection effect significantly improves anticorrosion properties for the AZ31B Mg alloy. The corrosion current density decreases from 1.79 × 10^-4 A·cm^-2 of Mg substrate to 5.57 × 10^-7 A·cm^-2 of the coated sample. Besides, the electrochemical impedance modulus reaches the value of 1.69 × 10³ Ω·cm² and increases approximately 23 times in magnitude compared with the Mg substrate. Furthermore, the corrosion protection mechanism is attributed to the coupling effect of water-repellency barrier protection and corrosion inhibition, resulting in excellent corrosion resistance. Results demonstrate a promising strategy for the corrosion protection of Mg alloys by replacing the chromate conversion coating with the superhydrophobic coupling conversion coating.

Factors affecting the toxicity and oxidative stress of layered double hydroxide-based nanomaterials in freshwater algae

Layered double hydroxide (LDH) nanomaterials are utilized extensively in numerous fields because of their distinctive structural properties. It is critical to understand the environmental behavior and toxicological effects of LDHs to address potential concerns caused by their release into the environment. In this work, the toxicological effects of two typical LDHs (Mg-Al-LDH and Zn-Al-LDH) on freshwater green algae (Scenedesmus obliquus) and the main affecting factors were examined. The Zn-Al-LDH exhibited a stronger growth inhibition toxicity than the Mg-Al-LDH in terms of median effect concentration. This toxicity difference was connected to the stability of particle dispersion in water and the metallic composition of LDHs. The contribution of the dissolved metal ions to the overall toxicity of the LDHs was lower than that of their particulate forms. Moreover, the joint toxic action of different dissolved metal ions in each LDH belonged to additive effects. The Mg-Al-LDH induced a stronger oxidative stress effect in algal cells than the Zn-Al-LDH, and mitochondrion was the main site of LDH-induced production of reactive oxygen species. Scanning electron microscope observation indicated that both LDHs caused severe damage to the algal cell surface. At environmentally relevant concentrations, the LDHs exhibited joint toxic actions with two co-occurring contaminants (oxytetracycline and nano-titanium dioxide) on S. obliquus in an additive manner mainly. These findings emphasize the impacts of the intrinsic nature of LDHs, the aqueous stability of LDHs, and other environmental contaminants on their ecotoxicological effects.

Progress in self-healing hydrogels and their applications in bone tissue engineering

Bone tissue engineering (BTE) is constantly seeking novel treatments to address bone injuries in all their varieties. It is necessary to find new ways to create structures that perfectly emulate the native tissue. Self-healing hydrogels have been a breakthrough in this regard, as they are able to reconstitute their links after they have been partially broken. Among the most outstanding biomaterials when it comes to developing these hydrogels for BTE, those polymers of natural origin (e.g., gelatin, alginate) stand out, although synthetics such as PEG or nanomaterials like laponite are also key for this purpose. Self-healing hydrogels have proven to be efficient in healing bone, but have also played a key role as delivery-platforms for drugs or other biological agents. Moreover, some researchers have identified novel uses for these gels as bone fixators or implant coatings. Here, we review the progress of self-healing hydrogels, which hold great promise in the field of tissue engineering.

Progress in bioactive surface coatings on biodegradable Mg alloys: A critical review towards clinical translation

Mg and its alloys evince strong candidature for biodegradable bone implants, cardiovascular stents, and wound closing devices. However, their rapid degradation rate causes premature implant failure, constraining clinical applications. Bio-functional surface coatings have emerged as the most competent strategy to fulfill the diverse clinical requirements, besides yielding effective corrosion resistance. This article reviews the progress of biodegradable and advanced surface coatings on Mg alloys investigated in recent years, aiming to build up a comprehensive knowledge framework of coating techniques, processing parameters, performance measures in terms of corrosion resistance, adhesion strength, and biocompatibility. Recently developed conversion and deposition type surface coatings are thoroughly discussed by reporting their essential therapeutic responses like osteogenesis, angiogenesis, cytocompatibility, hemocompatibility, anti-bacterial, and controlled drug release towards in-vitro and in-vivo study models. The challenges associated with metallic, ceramic and polymeric coatings along with merits and demerits of various coatings have been illustrated. The use of multilayered hybrid coating comprising a unique combination of organic and inorganic components has been emphasized with future perspectives to obtain diverse bio-functionalities in a facile single coating system for orthopedic implant applications.

Wettability, Self-Cleaning Property, and Mechanical Durability of A390 Aluminum Alloy with the Major Effect of Si Phases

Si phases with specific shapes, including primary and eutectic Si phases, were etched on the surface of A390 Al alloy by chemical etching. Meanwhile, their effects on the wettability, self-cleaning properties, and mechanical durability of etched A390 aluminum alloy surfaces were investigated. The results showed that the surface etched for 5 min and modified by 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FAS-17) demonstrated a contact angle of 153.2 ± 1.4° and a sliding angle of 11.2 ± 1.6°. The theoretical contact angle calculated by constructing a wetting model of Si phases approximates the actual contact angle. Further experiments indicated that the etched surface acquired excellent self-cleaning properties. In addition, the exposed Si phases formed a strong support skeleton, which greatly improved the wear resistance of the hydrophobic surface.

Long-Term Static and Dynamic Corrosion Stability of Nonwetting Surfaces

Superhydrophobic surfaces (SHSs) and lubricant-infused surfaces (LISs) are two classes of nonwetting surfaces that have drawn attention due to their advanced functional properties including corrosion inhibition. Yet there is a conspicuous lack of corrosion study of SHSs and LISs with respect to their fabrication and material parameters, especially at high temperatures and under dynamic flow conditions over long durations, which is sought to be addressed in this article. Considering copper SHSs and LISs, a full factorial combinatorial study of two facile texturing processes, electrodeposition and etching, two different functionalization agents, stearic acid and mercaptan, and two types of infused lubricants, Krytox 104 and DOWSIL 510, is presented, encompassing over 650 measurements on 90 tested surfaces. All fabricated surfaces demonstrated water repellency with a contact angle above 150° and a sliding angle below 7°. For the first time, the study examines high-temperature corrosion stability and long-term corrosion durability of the nonwetting surfaces in both static fluid and dynamic turbulent flow conditions over a period of 30 days. LISs and SHSs are shown to provide excellent corrosion inhibition over all tested corrosion conditions, with negligible presence of corrosion species on the surfaces and no deterioration of the texturing. The surfaces are also shown to rejuvenate easily to the initial wettability and corrosion resistance values. This study provides valuable insights into the selection of materials and processing parameters for the fabrication of nonwetting surfaces for the application of interest.

The Potential of the Superhydrophobic State to Protect Magnesium Alloy against Corrosion

We describe the technologically simple route for the fabrication of the superhydrophobic coatings on top of wrought magnesium alloy MA8 based on nanosecond laser processing followed by the chemical vapor deposition of fluorosilane. The chemical and phase composition, surface morphologies, and variation of the coating wettability during prolonged contact with 0.5 NaCl solution or with salt aerosol were characterized using X-ray diffraction, FT-IR spectroscopy, scanning electron microscopy measurements, and the wettability analysis. The as-prepared coatings demonstrate corrosion current of more than eight orders of magnitude lower, while after 30 days of sample immersion into corrosive solution, the current was four orders of magnitude lower than that obtained for a polished sample which was for only 2 h in contact with electrolyte. The mechanisms of the protective activity of fabricated coatings were discussed.

Corrosion Resistance of Electrochemically Synthesized Modified Zaccagnaite LDH-Type Films on Steel Substrates

Modified zaccagnaite layered double hydroxide (LDH) type films were synthesized on steel substrates by pulsed electrochemical deposition from aqueous solutions. The resulting films were characterized by X-ray diffraction, scanning electron microscopy/X-ray dispersive spectroscopy, and Fourier transform infrared spectroscopy. Structural characterization indicated a pure layered double hydroxide phase; however, elemental analysis revealed that the surface of the films contained Zn:Al ratios outside the typical ranges of layered double hydroxides. Layer thickness for the deposited films ranged from approximately 0.4 to 3.0 μm. The corrosion resistance of the film was determined using potentiodynamic polarization experiments in 3.5 wt.% NaCl solution. The corrosion current density for the coatings was reduced by 82% and the corrosion potential was shifted 126 mV more positive when 5 layers of modified LDH coatings were deposited onto the steel substrates. A mechanism was proposed for the corroding reactions at the coating.