Preprocedural Planning of Left Atrial Appendage Occlusion: A Review of the Use of Additive Manufacturing.

Stroke is a significant public health problem, with non-valvular atrial fibrillation (NVAF) being one of its main causes. This cardiovascular arrhythmia predisposes to the production of intracardiac thrombi, mostly formed in the left atrial appendage (LAA). When there are contraindications to treatment with oral anticoagulants, another therapeutic option to reduce the possibility of thrombus formation in the LAA is the implantation of an occlusion device by cardiac catheterization. The effectiveness of LAA occlusion is dependent on accurate preprocedural device sizing and proper device positioning at the LAA ostium, to ensure sufficient device anchoring and avoid peri-device leaks. Additive manufacturing, commonly known as three-dimensional printing (3DP), of LAA models is beginning to emerge in the scientific literature to address these challenges through procedural simulation. This review aims at clarifying the impact of 3DP on preprocedural planning of LAA occlusion, specifically in the training of cardiac surgeons and in the assessment of the perfect adjustment between the LAA and the biomedical implant.

Optimization of Printing Parameters to Maximize the Mechanical Properties of 3D-Printed PETG-Based Parts.

Fused filament fabrication (FFF) is the most popular additive manufacturing method, which allows the production of highly complex three-dimensional parts with minimal material waste. On the other hand, polyethylene terephthalate glycol (PETG) has been used to replace traditional polymers for 3D printing due to its chemical resistance and mechanical performance, among other benefits. However, when fibres are added, these PETG-based composites can be suitable for many different applications. Nevertheless, to guarantee their good performance in-service in these applications, and even extend to new ones, it is necessary for their mechanical properties to be maximized. Therefore, this study intends to optimize the printing parameters (nozzle temperature, printing speed, layer height and filling) in order to maximize the mechanical properties of printed PETG, PETG+CF (carbon fibre-reinforced PETG composites) and PETG+KF (aramid fibre-reinforced PETG composites). The Taguchi method was used for the experimental procedure design, and the specimens were produced according to the L16 orthogonal array. Finally, an analysis of variance (ANOVA) was performed, with a 95% confidence interval, to analyse the effect of the printing parameters on the bending properties. It was possible to conclude that the best bending properties for PETG, PETG+CF and PETG+KF were obtained for extrusion temperatures of 265 °C, 195 °C and 265 °C, printing speeds of 20, 60 and 20 mm/s, layer heights of 0.4, 0.53 and 0.35 mm and an infill density of 100% for the three materials, respectively.

Hybridization Effects on Bending and Interlaminar Shear Strength of Composite Laminates.

Fiber-reinforced composites are gradually replacing the traditional materials in many engineering applications. However, for many applications these materials are still unsuitable, due to their lack of toughness. In this context, hybridization is a promising strategy in which two or more types of fiber are combined to obtain a better balance of mechanical properties compared to non-hybrid composites. Therefore, the main goal of this work is to study the hybridization effect on the static performance and interlaminar shear strength. For this purpose, carbon, glass, and Kevlar fibers were used and combined in different proportions. It was possible to conclude that there is an ideal value of fiber content to maximize both properties and, depending on the type of fiber, they should be placed specifically on the compression or tensile side. For example, for composites involving carbon and glass fibers the latter must be placed on the compression side, and for a value of 17% by weight the flexural strength decreases by only 2.8% and the bending modulus by around 19.8%. On the other hand, when Kevlar fibers are combined with glass or carbon fibers, the Kevlar ones must always be placed on the tensile side and with an ideal value of 13% by weight.

Effect of Hostile Solutions on the Residual Fatigue Life of Kevlar/Epoxy Composites after Impact Loading.

Due to the enormous benefits inherent to composite materials, they have been widely used in the most diverse fields of engineering. Therefore, it is not surprising that in many of these applications they can be exposed to hostile environments, which can affect the mechanical performance of such materials. Therefore, the main goal of this work was to study the effect of immersion into different hostile solutions on the impact strength and, subsequently, to evaluate the residual fatigue life. For this purpose, the specimens were initially immersed into solutions of hydrochloric acid (HCl), sodium hydroxide (NaOH), sulphuric acid (H2SO4), diesel, distilled water, and seawater. Subsequently, the specimens were subjected to impact loads with an energy of 12 J and, finally, subjected to fatigue loads to assess the residual fatigue life. Seawater and NaOH solution provided the lowest impact strength. This was confirmed by the lower energy restored and impact bending stiffness (IBS), a parameter that allows evaluating the damage resistance of a composite. In terms of restored energy, for example, the seawater promoted a decrease around 30.4% in relation to the value obtained with non-immersed samples, while this value was 27.6% for the alkaline solution (NaOH). In terms of IBS, the lowest values were also obtained with these solutions (437.4 and 444.9 N/mm, respectively). Finally, the lowest residual fatigue life was also observed for these two solutions, and it was noticed that there was a direct relationship between the IBS and the residual fatigue life.

Fused Filament Fabrication-4D-Printed Shape Memory Polymers: A Review.

Additive manufacturing (AM) is the process through which components/structures are produced layer-by-layer. In this context, 4D printing combines 3D printing with time so that this combination results in additively manufactured components that respond to external stimuli and, consequently, change their shape/volume or modify their mechanical properties. Therefore, 4D printing uses shape-memory materials that react to external stimuli such as pH, humidity, and temperature. Among the possible materials with shape memory effect (SME), the most suitable for additive manufacturing are shape memory polymers (SMPs). However, due to their weaknesses, shape memory polymer compounds (SMPCs) prove to be an effective alternative. On the other hand, out of all the additive manufacturing techniques, the most widely used is fused filament fabrication (FFF). In this context, the present paper aims to critically review all studies related to the mechanical properties of 4D-FFF materials. The paper provides an update state of the art showing the potential of 4D-FFF printing for different engineering applications, maintaining the focus on the structural integrity of the final structure/component.

Olive Stones as Filler for Polymer-Based Composites: A Review.

Olives' consumption produces copious agricultural byproducts that have accompanied humanity for millennia, but the increasing worldwide production complicates its management. Most wastes are generated during olive oil production in form of olive stones and other lignocellulosic derivatives. Industrial processes of chemical or physical nature to recover economically compounds from biomass residues are costly, difficult, and non-environmentally friendly. Cellulose, hemicellulose, and lignin biopolymers are the principal components of olive stones, which present interesting qualities as lignocellulosic fillers in polymeric composites. This review will summarize examples of composites based on thermoplastic polymers, such as polystyrene (PS), polylactide (PLA), polyvinyl chloride (PVC), polypropylene (PP), and polycaprolactone (PCL); thermosetting resins (phenol-formaldehyde, unsaturated polyesters, and epoxy) and acrylonitrile butadiene rubber/devulcanized waste rubber (NBR/DWR) blends focusing on the fabrication procedures, characterization, and possible applications. Finally, thanks to the wide disparity in polymer matrix types, the variability in applications is important, from adsorption to mechanical enhancement, showing the easiness and benefit of olive stone integration in many materials.

Effect of Post-Cure on the Static and Viscoelastic Properties of a Polyester Resin.

This work intends to study the effect of the curing parameters on the mechanical properties of a polyester resin without a complete curing reaction process. For this purpose, cures at room temperature, 40 °C, and 60 °C, and post-cures at 40 °C and 60 °C, with different exposure times, were considered. Three-point bending tests were performed to assess the bending properties and both stress relaxation and creep behavior. The degree of crosslinking was estimated by evaluating the C = C ester bond, by Fourier infrared spectroscopy and complemented with the thermal characterization made by differential scanning calorimetry. The results showed that higher curing temperatures are preferable to methods involving curing and post-curing, which can be confirmed by the higher degree of conversion of unsaturated ester bonds at 60 °C. Compared to the resin cured at room temperature, the bending strength increased by 36.5% at 40 °C and 88.6% at 60 °C. A similar effect was observed for bending stiffness. In terms of stress relaxation and creep strain, the lowest values were obtained for samples cured at 60 °C.