Effect of bioprosthetic leaflet anisotropy on stent dynamics of Transcatheter Aortic Valve Replacement devices.

The assessment of stent fatigue in Transcatheter Aortic Valve Replacement (TAVR) systems is critical for the design of next-generation devices, both in vitro and in vivo. The mechanical properties of the bioprosthetic heart valves (BHVs) have a significant impact on the fatigue life of the metallic stent and thus must be taken into consideration when evaluating new TAVR device designs. This study aims to investigate the relationship between BHV anisotropic behaviour and the asymmetric deflections of the stent frame observed during in vitro testing. An explicit dynamics finite element model of the nitinol stent with attached bioprosthetic valve leaflets was developed to evaluate the deflections of the TAVR device under haemodynamic loading. Our results demonstrate that pericardium behaviour plays a dominant role in determining stent frame deflection. The anisotropic behaviour of the leaflets, resulting from collagen fibre orientation, affects the extent of deflection encountered by each commissure of the frame. This leads to asymmetric variation in frame deflection that can influence the overall fatigue life of the nitinol stent. This study highlights the importance of considering both the flexible nature of the metallic stent as well as the leaflet anisotropic behaviour in the design and fatigue assessment of TAVR systems.

Optimising Mg-Ca/PLA Composite Filaments for Additive Manufacturing: An Analysis of Particle Content, Size, and Morphology.

Low-temperature additive manufacturing of magnesium (Mg) alloy implants is considered a promising technique for biomedical applications due to Mg's inherent biocompatibility and 3D printing's capability for patient-specific design. This study explores the influence of powder volume content, size, and morphology on the mechanical properties and viscosity of polylactic acid (PLA) matrix composite filaments containing in-house-produced magnesium-calcium (Mg-Ca) particles, with a focus on their application towards low-temperature additive manufacturing. We investigated the effects of varying the Mg-Ca particle content in a PLA matrix, revealing a direct correlation between volume content and bending strength. Particle size analysis demonstrated that smaller particles (D50: 57 µm) achieved a bending strength of 63.7 MPa, whereas larger particles (D50: 105 µm) exhibited 49.6 MPa at 20 vol.%. Morphologically, the filament containing spherical particles at 20 vol.% showed a bending strength that was 11.5 MPa higher than that of the filament with irregular particles. These findings highlight the critical role of particle content, size, and shape in determining the mechanical and rheological properties of Mg-Ca/PLA composite filaments for use in material extrusion additive manufacturing.

The role of dislocation-solute interactions on the creep behaviour of binary Mg-RE alloys.

The effect of dislocation-RE atoms interactions on the creep behaviour has been studied via creep testing and HAADF-STEM analysis of two extruded alloys; Mg-0.5Ce and Mg-2Gd (wt%). Almost no Ce atoms are detected in the Mg matrix due to the low solid solubility and faster diffusion rate in as-extruded condition. However, Gd solute segregations are observed along dislocations and hexagonal dislocation patterns. Such segregations can not only pin the dislocation motion and enhance the creep strengthening via dislocation patterns, but also lead to dynamic precipitation. Thus, combing with the stress exponent values, the transition of creep mechanism between Mg-0.5Ce alloys and Mg-2Gd alloys has been found and dislocation-Gd atoms interactions are determined to be the main factor for superior creep resistance of Mg-2Gd alloys.

A Numerical Model for Experimental Designs of Vibration-Based Leak Detection and Monitoring of Water Pipes Using Piezoelectric Patches.

While the potential use of energy harvesters as structural health monitors show promise, numerical models related to the design, deployment and performance of such monitors often present significant challenges. One such challenge lies in the problem of leak detection in fluid-carrying pipes. Recent advances in experimental studies on energy harvesters for such monitoring has been promising but there is a paucity in existing literature in linking relevant fluid-structure interaction models around such applications. This paper addresses the abovementioned issue by developing a numerical model with Computational Fluid Dynamics (CFD) and Finite Element (FE) tools and carries out extensive analyses to compare it with existing experiments under controlled laboratory conditions. Conventional Polyvinylidene Fluoride (PVDF) films for leak detection and monitoring of water pipes were considered in this regard. The work provides guidelines on parameter selection and modeling for experimental design and repeatability of results for these types of experiments in future, around the demands of leak monitoring. The usefulness of such models is also demonstrated through the ability to estimate the optimum distribution frequency of these sensors that will enable the detection of the smallest leak of consequence under a known or established flow condition.

Development of regenerated fiber Bragg grating sensors with long-term stability.

The effect of annealing cycle on regeneration efficiency was investigated through isothermal treatments between 700 and 1000°C. We determined an inverse relationship between the recovery rate of the peak reflectivity and temperature. A regeneration efficiency of 85.2% and long-term stability at 1000°C for 500 hours were achieved via a slow regeneration process. Thermal sensors developed by isothermal regeneration were determined to be reliable up to 1000°C (±2 °C). Experimental findings suggest the involvement of both diffusion related phenomena and stress variation through densification of the fiber core in type-I FBG during the thermal regeneration process.

Modulating Exciton Dynamics in Composite Nanocrystals for Excitonic Solar Cells.

Quantum dots (QDs) represent one of the most promising materials for third-generation solar cells due to their potential to boost the photoconversion efficiency beyond the Shockley-Queisser limit. Composite nanocrystals can challenge the current scenario by combining broad spectral response and tailored energy levels to favor charge extraction and reduce energy and charge recombination. We synthesized PbS/CdS QDs with different compositions at the surface of TiO2 nanoparticles assembled in a mesoporous film. The ultrafast photoinduced dynamics and the charge injection processes were investigated by pump-probe spectroscopy. We demonstrated good injection of photogenerated electrons from QDs to TiO2 in the PbS/CdS blend and used the QDs to fabricate solar cells. The fine-tuning of chemical composition and size of lead and cadmium chalcogenide QDs led to highly efficient PV devices (3% maximum photoconversion efficiency). This combined study paves the way to the full exploitation of QDs in next-generation photovoltaic (PV) devices.