Influence of Polyols on the In Vitro Biodegradation and Bioactivity of 58S Bioactive Sol-Gel Coatings on AZ31B Magnesium Alloys.

The mechanical qualities of AZ31B magnesium alloys make them a promising material for biodegradable metallic implants. However, rapid degradation limits the application of these alloys. In the present study, 58S bioactive glasses were synthesized using the sol-gel method and several polyols such as glycerol, ethylene glycol, and polyethylene glycol, were used to improve the sol stability and to control the degradation of AZ31B. The synthesized bioactive sols were dip-coated onto AZ31B substrates and then, characterized by various techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical techniques (potentiodynamic and electrochemical impedance spectroscopy), among them. FTIR analysis confirmed the formation of a silica, calcium, and phosphate system and the XRD the amorphous nature of the 58S bioactive coatings obtained by sol-gel. The contact angle measurements confirmed that all the coatings were hydrophilic. The biodegradability response under physiological conditions (Hank's solution) was investigated for all the 58S bioactive glass coatings, observing a different behaviour depending on the polyols incorporated. Thus, for 58S PEG coating, an efficient control of the release of H2 gas was observed, and showing a pH control between 7.6 and 7.8 during all the tests. A marked apatite precipitation was also observed on the surface of the 58S PEG coating after the immersion test. Thus, the 58S PEG sol-gel coating is considered a promising alternative for biodegradable magnesium alloy-based medical implants.

Synthesis and Characterization of Fluorite-Type La2Ce2O7 Plasma Sprayable Powder for TBCs Application.

This work focuses on the fabrication of lanthanum cerate (La2Ce2O7, LC) powders via two chemical routes: modified Pechini sol-gel method and solid-state synthesis. The synthesized LC powders were heat treated in the temperature range of 1000-1400 °C for 6 h and investigated as a material for thermal barrier coating (TBC) applications. For this purpose, the powder morphology, chemical composition, crystal structure and thermal stability were studied. Scanning electron microscopy (SEM) of the synthesized powders revealed an agglomerated structure consisting of fine and uniformly distributed grains. Energy-dispersive X-ray spectroscopy (EDXS) indicated that the chemical compositions of the LC powders were similar to the stoichiometric ratio of La2Ce2O7. A cubic fluorite structure was observed by X-ray diffraction analysis (XRD) after calcining the LC powder prepared by solid-state synthesis at 1300 °C. In contrast, there was always a fluorite structure in the LC powder synthesized by the Pechini sol-gel method after heat treatment over the entire temperature range. The thermal behavior of the LC powders was analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) in the temperature range of 25-1300 °C. Neither an obvious mass change nor a visible energy change was observed within the tested temperature range, indicating high phase stability of the LC powder and its suitability for TBC applications. Spheroidization on the prepared LC powders was also investigated, revealing that powder size and morphology had a significant impact on the spheroidization efficiency.

Electrochemical Characterization of Polymeric Coatings for Corrosion Protection: A Review of Advances and Perspectives.

The development of anti-corrosion polymeric coatings has grown exponentially in the fields of material science, chemistry, engineering, and nanotechnology during the last century and has prompted the evolution of efficient characterization techniques. Nowadays, polymeric coatings represent a well-established protection system that provides a barrier between a metallic substrate and the environment. However, the increase in complexity and functionality of these coatings requires high-precision techniques capable of predicting failures and providing smart protection. This review summarizes the state of the art for the main electrochemical techniques, emphasizing devices that track the anti-corrosion properties of polymeric coatings from the macroscale to the nanoscale. An overview of the advances in accelerated corrosion testing and the electrochemical characterization of coatings is explored, including insights into their advantages and limitations. In addition, the challenges and potential applications of the theoretical approaches are summarized based on current knowledge. Finally, this work provides the reader with the trends and challenges of designing future technologies and models capable of tracking corrosion and predicting failures.

Recent Advancements in Materials and Coatings for Biomedical Implants.

Metallic materials such as stainless steel (SS), titanium (Ti), magnesium (Mg) alloys, and cobalt-chromium (Co-Cr) alloys are widely used as biomaterials for implant applications. Metallic implants sometimes fail in surgeries due to inadequate biocompatibility, faster degradation rate (Mg-based alloys), inflammatory response, infections, inertness (SS, Ti, and Co-Cr alloys), lower corrosion resistance, elastic modulus mismatch, excessive wear, and shielding stress. Therefore, to address this problem, it is necessary to develop a method to improve the biofunctionalization of metallic implant surfaces by changing the materials' surface and morphology without altering the mechanical properties of metallic implants. Among various methods, surface modification on metallic surfaces by applying coatings is an effective way to improve implant material performance. In this review, we discuss the recent developments in ceramics, polymers, and metallic materials used for implant applications. Their biocompatibility is also discussed. The recent trends in coatings for biomedical implants, applications, and their future directions were also discussed in detail.

Phase Evaluation, Mechanical Properties and Thermal Behavior of Hot-Pressed LC-YSZ Composites for TBC Applications.

In this work, La2Ce2O7-yttria-stabilized zirconia (LC-YSZ) composites with different weight fractions of YSZ (40−70 wt.%) were prepared by hot pressing at 1400 °C and investigated as a material for thermal barrier-coating (TBC) applications. For this purpose, the effect of YSZ addition on the phase composition, microstructure, mechanical performance and thermal behavior was studied. X-ray diffraction analysis showed that the LC-YSZ composites were mainly composed of a cubic ZrO2 and La2O3-CeO2-ZrO2 solid solution with a pyrochlore structure, indicating that the reaction between LC and YSZ took place during hot pressing. Scanning electron microscopy revealed the high microstructural stability of the prepared composites, as the pore formation was significantly controlled and a high relative density (>97%) was obtained. The microstructure of LC-YSZ bulk samples was relatively fine-grained, with an average grain size below or very close to 1 µm. YSZ doping improved the Vickers hardness of the LC-YSZ composites; the highest hardness, with value of 12 ± 0.62 GPa, was achieved for the composite containing 70 wt.% of YSZ. The fracture toughness of LC-YSZ composites was in the range from 2.13 to 2.5 MPa·m1/2. No statistically significant difference in heat capacity or thermal conductivity was found between the composites with different content of YSZ. The results showed that LC-YSZ composites have relatively low thermal conductivities from room temperature (1.5−1.8 W·m−1·K−1) up to 1000 °C (2.5−3.0 W·m−1·K−1). This indicates that the prepared LC-YSZ composite materials are promising candidates for TBC applications.

A HepG2 Cell-Based Biosensor That Uses Stainless Steel Electrodes for Hepatotoxin Detection.

Humans are frequently exposed to environmental hepatotoxins, which can lead to liver failure. Biosensors may be the best candidate for the detection of hepatotoxins because of their high sensitivity and specificity, convenience, time-saving, low cost, and extremely low detection limit. To investigate suitability of HepG2 cells for biosensor use, different methods of adhesion on stainless steel surfaces were investigated, with three groups of experiments performed in vitro. Cytotoxicity assays, which include the resazurin assay, the neutral red assay (NR), and the Coomassie Brilliant Blue (CBB) assay, were used to determine the viability of HepG2 cells exposed to various concentrations of aflatoxin B1 (AFB1) and isoniazid (INH) in parallel. The viability of the HepG2 cells on the stainless steel surface was quantitatively and qualitatively examined with different microscopy techniques. A simple cell-based electrochemical biosensor was developed by evaluating the viability of the HepG2 cells on the stainless steel surface when exposed to various concentrations of AFB1 and INH by using electrochemical impedance spectroscopy (EIS). The results showed that HepG2 cells can adhere to the metal surface and could be used as part of the biosensor to determine simple hepatotoxic samples.