Synergistic Effect of PVDF-Coated PCL-TCP Scaffolds and Pulsed Electromagnetic Field on Osteogenesis

Bone exhibits piezoelectric properties. Thus, electrical stimulations such as pulsed electromagnetic fields (PEMFs) and stimuli-responsive piezoelectric properties of scaffolds have been investigated separately to evaluate their efficacy in supporting osteogenesis. However, current understanding of cells responding under the combined influence of PEMF and piezoelectric properties in scaffolds is still lacking. Therefore, in this study, we fabricated piezoelectric scaffolds by functionalization of polycaprolactone-tricalcium phosphate (PCL-TCP) films with a polyvinylidene fluoride (PVDF) coating that is self-polarized by a modified breath-figure technique. The osteoinductive properties of these PVDF-coated PCL-TCP films on MC3T3-E1 cells were studied under the stimulation of PEMF. Piezoelectric and ferroelectric characterization demonstrated that scaffolds with piezoelectric coefficient d₃₃ = −1.2 pC/N were obtained at a powder dissolution temperature of 100 °C and coating relative humidity (RH) of 56%. DNA quantification showed that cell proliferation was significantly enhanced by PEMF as low as 0.6 mT and 50 Hz. Hydroxyapatite staining showed that cell mineralization was significantly enhanced by incorporation of PVDF coating. Gene expression study showed that the combination of PEMF and PVDF coating promoted late osteogenic gene expression marker most significantly. Collectively, our results suggest that the synergistic effects of PEMF and piezoelectric scaffolds on osteogenesis provide a promising alternative strategy for electrically augmented osteoinduction. The piezoelectric response of PVDF by PEMF, which could provide mechanical strain, is particularly interesting as it could deliver local mechanical stimulation to osteogenic cells using PEMF.     

Optimization of A-TIG process parameters using response surface methodology

In the present work, the influence of process parameters such as welding current (I), welding speed (S), and flux coating density (F) on different aspects of weld bead geometry for example depth of penetration (DOP), bead width (BW), depth to width ratio (D/W), and weld fusion zone area (WA) were investigated by using the central composite design (CCD). 9–12% Cr ferritic stainless steel (FSS) plates were welded using A-TIG welding. It was observed that all input variables have a direct influence on the DOP, BW, and D/W. However, flux coating density has no significant effect on WA. Mathematical models were generated from the obtained responses to predict the weld bead geometry. An optimized DOP, BW, D/W, and WA of 6.95?mm, 8.76?mm, 0.80, and 41.99?mm², respectively, were predicted at the welding current of 213.78 A, the welding speed of 96.22?mm/min, and the flux coating density of 1.99?mg/cm². Conformity test was done to check the practicability of the developed models. The conformity test results were in good agreement with the predicted values. Arc constriction and reversal in Marangoni convection were considered as major mechanisms for the deep and narrow weld bead during A-TIG welding.     

Measurement sensitivity improvement in tapping-mode atomic force microscopy through bi-harmonic drive signal

This article presents a novel method to improve the measurement sensitivity and reduce impact forces in tapping-mode atomic force microscopy by reshaping the tip trajectory. A tapping drive signal composed of two harmonics is used to generate an oscillating trajectory with a broader valley compared to the typical sinusoidal trajectory. The wide broad valley reduces the velocity of the tip in the vicinity of the sample and allots a greater portion of each period in the vicinity of the sample. Numerical simulations show that this results in decreased impact force and increased sensitivity of the cantilever oscillation to changes in tip-sample offset. Experimental results demonstrate an increase in image sharpness and decrease in tip wear using the bi-harmonic driving signal.     

A subtle review on the challenges of photocatalytic fuel cell for sustainable power production

The revolution in the arena of functional materials for the development of well advanced engineered photocatalyst can efficiently harness photon energy from a wide spectrum of electromagnetic radiation. These next-generation smart materials would be a spectacular approach in designing devices such as photovoltaic cells, photoelectrochemical cells, and photocatalytic fuel cells. Photocatalytic oxidation of water or wastewater for concurrent production of hydrogen and electric current has turned out as a principal concept for the construction of modern photocatalytic fuel cells (PFCs). Such PFCs mimics reverse photosynthesis process where electrical energy is generated from organic pollutants. In recent years many reviews on focusing the design, fabrication, and theoretical efficiency of the PFCs have been published. Hence the present review is aimed to unveil the wall-to-wall information starting from fundamentals spanning to working principles, structural configuration, electrochemical degradation of pollutants and photoelectrochemical properties, electron transport, thermodynamic behavior and columbic efficiency of studied PFCs.     

Optimization of pulsed current GTAW process parameters for sintered hot forged AISI 4135 P/M steel welds by simulated annealing and genetic algorithm

Abundant improvements have occurred in materials handling, especially in metal joining. Pulsed current gas tungsten arc welding (PCGTAW) is one of the consequential fusion techniques. In this work, PCGTAW of AISI 4135 steel engendered through powder metallurgy (P/M) has been executed, and the process parameters have been highlighted applying Taguchi’s L9 orthogonal array. The results show that the peak current (Ip), gas flow rate (GFR), welding speed (WS) and base current (Ib) are the critical constraints in strong determinant of the Tensile strength (TS) as well as percentage of elongation (% Elong) of the joint. The practical impact of applying Genetic algorithm (GA) and Simulated annealing (SA) to PCGTAW process has been authenticated by means of calculating the deviation between predicted and experimental welding process parameters.     

Crystallographic,Structural and Band Gap Tailoring of Zn<Subscript>0.98</Subscript>Mn<Subscript>0.02</Subscript>S Quantum Dots Co-Doped with Cu by Co-Precipitation Method

Zn_0.98?xCu_xMn_0.02S (x = 0, 0.02, 0.04) quantum dots with different Cu concentrations have been successfully synthesized by co-precipitation method. Cubic phase exhibited in Zn_0.98Mn_0.02S turned to mixture of both cubic and hexagonal phases by Cu-doping which was confirmed by X-ray diffraction pattern. The shift of peak position along (111) plane and the diminishing of interplanar distance and lattice constant confirmed the proper substitution of Cu and Mn in ZnS. Cubic phase of ZnS was tuned towards hexagonal phase by Cu-doping i.e., morphology diminishes stability which was confirmed by microscopic images. Optical studies revealed the wide tuning of band gap between 3.3 and 3.93 eV by Mn-doping and Cu co-doping which is useful for opto-electronic device applications. Photoluminescence spectra illustrated two distinct emission bands, UV emission around 392–396 nm and defect related blue emission around 470–481 nm. The change in intensity and peak position of UV and blue emission was discussed based on crystallite size formation of defect states by Cu-doping.     

Low resistive silicon substrate as an etch-stop layer for drilling thick SiO2 by spark assisted chemical engraving (SACE)

Controlling precisely the depth in glass micro-drilling by spark assisted chemical engraving (SACE) remains challenging, particularly for low depths. The possibility of using an electrically conductive material as an etch-stop layer for SACE gravity-feed drilling is investigated in this paper. Micromachining with constant DC and pulsed DC of 30–35 μm thick SiO₂ deposited on low resistive silicon substrate demonstrated the etch-stop function of the conductive silicon. Measurements of etch rates and hole profiles along with scanning electron microscope imaging revealed the mechanism underlying the etch-stop process. Low resistive silicon is demonstrated to be a good etch-stop layer for SACE gravity-feed drilling. Demonstration of machining of SiO₂ layer on silicon as a substrate and an etch-stop layer opens up new possibilities to adapt SACE for developing devices on silicon platform.