Evaluation of Mechanical and Electrical Performance of Aging Resistance ZTA Composites Reinforced with Graphene Oxide Consolidated by SPS

This paper presents a study of Al₂O₃–ZrO₂ (ZTA) nanocomposites with different contents of reduced graphene oxide (rGO). The influence of the rGO content on the physico-mechanical properties of the oxide composite was revealed. Graphene oxide was obtained using a modified Hummers method. Well-dispersed ZTA-GO nanopowders were produced using the colloidal processing method. Using spark plasma sintering technology (SPS), theoretically dense composites were obtained, which also reduced GO during SPS. The microstructure, phase composition, and physico-mechanical properties of the sintered composites were studied. The sintered ZTA composite with an in situ reduced graphene content of 0.28 wt.% after the characterization showed improved mechanical properties: bending strength was 876 ± 43 MPa, fracture toughness—6.8 ± 0.3 MPa·m^1/2 and hardness—17.6 ± 0.3 GPa. Microstructure studies showed a uniform zirconia distribution in the ZTA ceramics. The study of the electrical conductivity of reduced graphene oxide-containing composites showed electrical conductivity above the percolation threshold with a small content of graphene oxide (0.28 wt.%). This electrical conductivity makes it possible to produce sintered ceramics by electrical discharge machining (EDM), which significantly reduces the cost of manufacturing complex-shaped products. Besides improved mechanical properties and EDM machinability, 0.28 wt.% rGO composites demonstrated high resistance to hydrothermal degradation.     

Correction: The structural and luminescence properties of plexcitonic structures based on Ag2S/l-Cys quantum dots and Au nanorods

Correction for ‘The structural and luminescence properties of plexcitonic structures based on Ag₂S/l-Cys quantum dots and Au nanorods’ by Irina G. Grevtseva et al., RSC Adv., 2022, 12, 6525–6532, DOI: 10.1039/D1RA08806H.

The authors regret the omission of a funding acknowledgement in the original article. This acknowledgement is given below.This study was supported by the Ministry of Science and Higher Education of the Russian Federation under Agreement N 075-15-2021-1351 as part of the structural analysis of colloidal Ag₂S/l-Cys QDs and Au NRs.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Degradation kinetic study of ZIF-8 microcrystals with and without the presence of lactic acid

The zeolitic imidazolate framework ZIF-8 (Zn(mim)₂, mim = 2-methylimidazolate) has recently been proposed as a drug delivery platform for anticancer therapy based on its capability of decomposing in acidic media. The concept presumes a targeted release of encapsulated drug molecules in the vicinity of tumor tissues that typically produce secretions with elevated acidity. Due to challenges of in vivo and in vitro examination, many studies have addressed the kinetics of ZIF-8 decomposition and subsequent drug release in phosphate buffered saline (PBS) with adjusted acidity. However, the presence of hydrogen phosphate anions [HPO₄]²⁻ in PBS may also affect the stability of ZIF-8. As yet, no separate analysis has been performed comparing the dissolving capabilities of PBS and various acidification agents used for regulating pH. Here, we provide a systematic study addressing the effects of phosphate anions with and without lactic acid on the degradation rate of ZIF-8 microcrystals. Lactic acid has been chosen as an experimental acidification agent, since it is particularly secreted by tumor cells. Interestingly, the effect of a lactic acid solution with pH 5.0 on ZIF-8 degradation is shown to be weaker compared to a PBS solution with pH 7.4. However, as an additive, lactic acid is able to enhance the decomposition efficacy of other solutions by 10 to 40 percent at the initial stage, depending on the presence of other ions. Additionally, we report mild toxicity of ZIF-8 and its decomposition products, as examined on HDF and A549 cell lines.

ZIF-8 microcrystals demonstrate different degradation kinetics in water, PBS (pH 7.4), and PBS with lactic acid (pH 5.0).     

Current role of laser angioplasty of restenotic coronary stents

Treatment of in-stent restenosis (ISR) with conventional percutaneous transluminal coronary angioplasty (PTCA) causes significant recurrent neointimal tissue growth in 30-85%. Therefore, laser ablation of intrastent neointimal hyperplasia before balloon dilation can be an attractive alternative. However, the long-term outcomes of such treatment have not been studied thoroughly enough. This prospective case-control study evaluated angiographic and clinical outcomes of PTCA alone and a combination of excimer laser coronary angioplasty (ELCA) and adjunct PTCA in 125 patients with ISR. ELCA was performed before balloon dilation in 67 patients, PTCA alone was performed in 58 patients. Basic demographic and clinical data were comparable in both groups. Lesions included in ELCA group were longer (17.1+/-9.9 vs 13.6+/-9.1 mm; p = 0.034), more complex (36.5% type C stenoses vs 14.3%; p = 0.006), and more frequently had reduced distal blood flow (TIMI <3: 18.9% vs 4.8%; p = 0.025) compared to lesions in the PTCA group. Immediate angiographic results of PTCA and ELCA + PTCA appeared to be comparable. PTCA alone was successful in 57 patients (98.3%), ELCA + PTCA, in 66 patients (98.5%). The rates of hospital complications were comparable (3.0% in ELCA group vs 8.6% in PTCA group). The 1-year follow-up showed that the rates of major adverse cardiac events (MACE) were comparable in the 2 groups (37.3% in ELCA group vs 46.6% in PTCA group). The rates of target vessel revascularization (TVR) within 1 year after the intervention were also similar in the 2 groups (32.8% vs 34.5%). The data mean that ELCA in patients with complex ISR is efficient and safe. Despite a higher complexity of lesions in the ELCA group, no increase in the rate of complications was registered.     

Evidence for Trapped Surface Bubbles as the Cause for the Twinkling Artifact in Ultrasound Imaging

The mechanism of the twinkling artifact (TA) that occurs during Doppler ultrasound imaging of kidney stones was investigated. The TA expresses itself in Doppler images as time-varying color. To define the TA quantitatively, beam-forming and Doppler processing were performed on raw per channel radio-frequency data collected when imaging human kidney stones in vitro. Suppression of twinkling by an ensemble of computer-generated replicas of a single radio frequency signal demonstrated that the TA arises from variability among the acoustic signals and not from electronic signal capture or processing. This variability was found to be random, and its suppression by elevated static pressure and return when the pressure was released suggest that the presence of bubbles on the stone surface is the mechanism that gives rise to the TA.     

Flecainide attenuates rate adaptation of ventricular repolarization in guinea-pig heart

Objectives: Flecainide is class Ic antiarrhythmic agent that was found to increase the risk of sudden cardiac death. Arrhythmic responses to flecainide could be precipitated by exercise, suggesting a role played by inappropriate rate adaptation of ventricular repolarization. This study therefore examined flecainide effect on adaptation of the QT interval and ventricular action potential duration (APD) to abrupt reductions of the cardiac cycle length. Design: ECG and ventricular epicardial and endocardial monophasic APD were recorded in isolated, perfused guinea-pig heart preparations upon a sustained cardiac acceleration (rapid pacing for 30 s), and following a single perturbation of the cycle length evoked by extrasystolic stimulation. Results: Sustained increase in heart rate was associated with progressive bi-exponential shortening of the QT interval and APD. Flecainide prolonged ventricular repolarization, delayed its rate adaptation, and decreased the amplitude of QT interval and APD shortening upon rapid cardiac pacing. During extrasystolic stimulation, flecainide attenuated APD shortening in premature ventricular beats, with effect being greater upon using a longer basic drive cycle length (S₁-S₁=550 ms versus S₁-S₁=300 ms). Conclusions: Flecainide-induced arrhythmia may be partly accounted for by attenuated adaptation of ventricular repolarization to sudden changes in cardiac cycle length provoked by transient tachycardia or ectopic beats.