Material Extrusion Additive Manufacturing of Ceramics: A Review on Filament-Based Process.

Additive manufacturing is very important due to its potential to build components and products using high-performance materials. The filament-based 3D printing of ceramics is investigated, revealing significant developments and advancements in ceramic material extrusion technology in recent years. Researchers employ several typologies of ceramics and binders to achieve fully dense products. The design of the filament and the necessary technological adaptations for 3D printing are fully investigated. From a material perspective, this paper reviews and analyzes the recent developments in additive manufacturing of material-extruded ceramics products, pointing out the performance and properties achieved with different material-binder combinations. The main gaps to be filled and recommendations for future developments in this field are reported.

Homogenization simulation of material extruded lattice structures.

The paper investigates the mechanical behavior of structural elements of a material extruded component using a multiscale analysis based on a homogenization method. The development and validation of a homogenization model start with designing a tailor-made lattice structure. The material model is described using elastoplastic properties and Hill's yield criterion. The numerical validation of the homogenized model and its comparison with the full detail is also described.

Early-onset post-cardiotomy severe constrictive pericarditis: a case report.

Background: Constrictive pericarditis (CP) can be one of the most challenging conditions to diagnose within cardiovascular medicine. Iatrogenic causes of CP are increasingly recognized in higher income countries. This case provides insight into the need for clinical suspicion when diagnosing this relatively under recognized clinical entity as well as the need for multimodality imaging combined with invasive haemodynamic assessment. Case summary: A 68-year-old man presented with decompensated heart failure 4 weeks after open-heart surgery. A diagnosis of early-onset post-cardiotomy CP was made using multimodality imaging and invasive haemodynamic assessment, which demonstrated the cardinal features of constrictive physiology. Surgical intervention with two pericardiectomy procedures was pursued given the aggressive and recalcitrant nature of his presentation. Our patient died shortly after his second surgery due to progressive multi-organ dysfunction. Conclusion: Constrictive pericarditis is a challenging but important clinical entity to diagnose. Differentiating CP from restrictive cardiomyopathy is important as there are key differences in management and prognosis. Our case supports the clinical utility of multimodality imaging combined with invasive haemodynamic assessment in patients with suspected CP.

Technological scouting of bi-material face masks: experimental analysis on real faces.

The need for personal protective equipment rapidly grew during the COVID-19. Companies had to face problems related to their products' sustainability, adherence, and comfortability. Designing a face mask with proper adherence and comfortability in wearing and breathing became a matter of great importance. In this work, the adherence of an innovative face mask and its comfortability were experimentally tested with real faces, considering the deformation of the mask and the soft facial tissues. A stereophotogrammetric acquisition was made of the face with the face mask during these tests. A comparison between the geometries of the face and the mask, undeformed and deformed, gave the respective deformations. The force applied by the mask to the face was calculated, measuring the elastic strain of the mask bands during wearing and the deformation.

Technological scouting of bi-material face masks: simulation of adherence using 3D Facial Norms.

During the COVID-19 pandemic started in March 2020, the need for personal protective equipment rapidly grew as it became mandatory. The availability of a set of faces can be of great utility in designing a face mask with proper adherence and comfortability in wearing and breathing. A 3D geometry of a face with user-defined anthropometric measures was generated with Blender, a powerful development tool for creating 3D images. Using 3D Facial Norms, a free online database, it was possible to compute the mean anthropometric measures for the age groups of 17-20, 20-30, and 30-40 years old and then generate the respective faces for both genders. The adherence of an innovative face mask was then simulated with the reverse engineering software considering both the face mask and the faces rigid.

Prophylactic paclitaxel-eluting stent placement does not improve covered femoropopliteal stent patency.

OBJECTIVE: Covered stents are an important tool in managing femoropopliteal peripheral arterial disease. However, their performance is impaired by edge neointimal hyperplasia and restenosis. We examined the effectiveness of prophylactic deployment of paclitaxel-eluting stents to prevent edge restenosis. METHODS: A retrospective case-control study was performed. Patients with femoropopliteal peripheral arterial disease who were treated with Viabahn stent placement were compared to patients treated with Viabahn stents deployed in conjunction with paclitaxel-eluting stents (PTX). The primary outcome was time to loss of stent primary patency. The Kaplan-Meier method was used. RESULTS: A total of 36 Viabahn and 25 Viabahn + paclitaxel-eluting stent procedures were evaluated, with mean follow-up periods of 27 and 18 months, respectively. The Viabahn + paclitaxel-eluting stent group had a longer length of vessel stented (P = .0023). Twelve-month primary patency was 74% in the Viabahn group and 75% in the Viabahn + paclitaxel-eluting stent group. Pre-existing dyslipidemia correlated with earlier loss of primary patency across the combined cohort (P = .0193). CONCLUSION: Viabahn stent primary patency is unaffected by the addition of paclitaxel-eluting stents.

Forces and Specific Energy of Polyamide Grinding.

This work investigated the grinding process of reinforced and nonreinforced polyamide materials using an Al2O3 grinding wheel. Samples were ground using a custom-made setup of sensors to evaluate in-line temperature, forces, and power. The surface roughness and images were acquired to assess the quality of the final products. The novelty of the work is to correlate the energy evaluation with the process efficiency during processing. Grinding at high cutting depths achieves good surface quality indicators, such as Ra < 5 µm and Rz < 5 µm. Results also reveal that special attention should be given to the infeed speed when cutting unfilled materials to produce good results. With high values of energy partition, the specific grinding energy stabilizes around 60 J/mm³. Strains must be applied quickly because, to ensure the unfilled materials respond better at this cutting depth, the reinforced materials suffer a slight degradation of quality.

Hygromechanical Performance of Polyamide Specimens Made with Fused Filament Fabrication.

The material performance of polyamide (PA) samples made with fused filament fabrication (FFF) was analyzed. The authors implemented a well-structured framework to identify the filaments main properties before processing them and characterizing the printed samples. Unfilled and glass-fiber reinforced PA were investigated, focusing on moisture absorption and its effects on dimensional stability and mechanical performance. The properties were collected using differential scanning calorimetry and Fourier-transform infrared spectroscopy, whereas the specimens were characterized by employing compression tests. This framework allowed for the moisture determination, as well as the influence of the moisture absorption. A significant impact was detected for the glass-fiber reinforced PA, with a decrease in the dimensional and mechanical performance. The novelty of this study was to define a well-structured framework for testing the moisture influence of FFF components.

Evaluation of Grinding of Unfilled and Glass Fiber Reinforced Polyamide 6,6.

This paper investigates the grinding process on unreinforced (PA66) and reinforced glass-fiber polyamide 6,6 (PA66 GF30) with Al2O3 and SiC abrasive wheels. Both materials were ground by varying rotations, workpiece infeed speed, depth of cuts for sequential roughing/finishing steps. Dry and liquid coolant conditions were also considered during the grinding process to evaluate the effects on part quality. The surface roughness was used to assess the quality of the final products with several parameter combinations, identifying the induced process trends. The results show that at the end of the finishing step, the surface roughness Rz was lower than 4 µm, attaining the lowest value of 1.34 µm for PA66 specimens. The analysis also suggested the choice of the Al2O3 grinding wheel to reach the lowest Rz values for both materials.

Deferred Intravascular Lithotripsy-Facilitated Stenting in ACS: Novel Approach to Improve PCI Outcomes in Severe Calcification?

Moderate/severe calcification, present in approximately one-third of culprit lesions in acute coronary syndromes (ACS), portends unfavorable procedural and post-primary percutaneous coronary intervention outcomes. Intravascular lithotripsy is a novel technique using shockwaves to fracture calcific plaques. Presenting a clinical case, we enumerate efficacy and safety parameters in using intravascular lithotripsy in ACS. (Level of Difficulty: Advanced.).

Performance Analysis of Colored PLA Products with a Fused Filament Fabrication Process.

The objective of the present work is to study the influence of color additives used for the polylactic acid (PLA) filament on the final quality of fused filament fabrication (FFF) parts. The main processing parameters of FFF parts were evaluated, identifying the significant correlations between PLA properties and part performance, using a commercial FFF machine. The quality of the products was evaluated in terms of thermo-mechanical properties such as mechanical strength, principal material temperatures, and viscosity. These last properties were characterized using differential scanning calorimetry (DSC) for the thermal measurements and a rotational rheometry (RHEO) for viscosity measurements. Cylindrical specimens were then produced for the compression test. The experimental activity and related testing of products are fully described, pointing out a significant difference in performance between parts made of different colored filaments.

Urgent transcatheter aortic valve replacement for severe acute aortic regurgitation following open mitral valve surgery.

Transcatheter aortic valve replacement (TAVR) is not currently approved for pure native valve aortic incompetence, and is typically performed on a compassionate basis in selected patients who are at high risk for conventional surgery. We describe the first use of TAVR to treat iatrogenic severe acute pure aortic incompetence following mitral valve surgery. A 71-year-old gentleman developed life-threatening acute aortic regurgitation (AR) within hours of a very challenging fifth open heart mitral valve replacement. Careful inspection of echocardiographic and computed tomographic imaging identified the cause as a disrupted left coronary cusp at the commissure caused by the surgical mitral annular reconstruction. Medical management with afterload reduction failed with recurrent pulmonary edema, and a sixth open heart surgery was deemed prohibitively high risk. The lack of aortic annular calcium onto which anchors a transcatheter valve was a concern for TAVR. However, we postulated that the struts of the mitral valve bioprosthesis would offer some support to the TAVR valve. We opted for a self-expanding system because of concerns about potential unfavorable interaction between the balloon onto which balloon-expandable bioprosthesis is mounted and the struts of the mitral bioprosthesis, and because the Evolut R system has additional anchoring points at the crown which might enhance transcatheter valve stability in the non-calcified annulus, compared with the Edwards Sapien system. Transfemoral TAVR, performed with a Medtronic Evolut R 34 mm system under general anesthesia and using moderately rapid ventricular pacing, was successful with minimal residual AR. On follow-up 1 month later the patient was asymptomatic, and the aortic and mitral bioprostheses were functioning normally on echocardiogram.

Early Single-Site Experience With Transcatheter Tricuspid Valve Replacement.

OBJECTIVES: This study presents a single-site experience of 5 patients with severe tricuspid regurgitation (TR) who underwent implantation of a novel transcatheter tricuspid valve replacement device. BACKGROUND: Functional TR is the most common etiology of severe TR in the developed world and is associated with unfavorable clinical outcomes. Although numerous transcatheter repair devices are currently in early clinical trials, most result in incomplete degrees of TR reduction and functional improvement. METHODS: Transcatheter tricuspid valve replacement was performed in 5 patients with compassionate use of the novel GATE System. All patients had symptomatic, massive and/or torrential TR at baseline. All patients had computed tomography, transthoracic and transesophageal echocardiographic assessment of the tricuspid valve and right heart anatomy. All patients had a surgical transatrial approach performed with valve implantation guided by fluoroscopy and intraprocedural transesophageal echocardiography. RESULTS: Baseline characteristics of the patients showed a substantial burden of comorbidities. All patients had successful implantation of the transcatheter valve, with significant reduction of TR to ≤2+. Baseline poor right ventricular (RV) function measured by global longitudinal strain and RV change in pressure divided by change in time were associated with post-implantation RV failure and poor clinical outcomes in this small group. Four of the 5 patients were followed for 3 to 6 months following the initial implantation and showed evidence of RV remodeling, increased cardiac output, and reduction in New York Heart Association functional class. CONCLUSIONS: Implantation of a first-generation TTVR device was technically feasible in patients with more than severe TR. Transcatheter tricuspid valve replacement was associated with RV remodeling, increased cardiac output, and improvement in New York Heart Association functional class in most patients. Further studies are needed to refine patient population selection for this device and to determine long-term outcomes.

56-year-old lady with transaortic gradient.

CLINICAL INTRODUCTION: A 56-year-old lady with a background of hypertension was admitted to our institution with acute pulmonary oedema. She reported gradual and increasingly severe dyspnoea on exertion over the preceding 12 months and, prior to presentation, her exercise tolerance was restricted to one flight of stairs. On transthoracic echocardiography during the index admission, left ventricular size and systolic function were normal, and peak and mean transaortic gradients were 67 mm Hg and 33 mm Hg, respectively, with a peak velocity of 3.9 m/s. No aortic incompetence or other significant valvular abnormality was noted. A transoesophageal echocardiogram was performed. Figure 1 depicts the mid-oesophageal parasternal long-axis view. What is the explanation behind the significant transaortic gradient?heartjnl;104/12/1036/F1F1F1Figure 1Transoesophageal echocardiogram, mid-oesophageal long-axis view at 135 degrees. QUESTION: What is the explanation behind the significant transaortic gradient?Ventricular septal defect Supravalvular aortic stenosisAortic valvular stenosisSubaortic membraneHypertrophic obstructive cardiomyopathy.

Takotsubo cardiomyopathy following unintentionally large subcutaneous adrenaline injection: a case report.

INTRODUCTION: Stress cardiomyopathy, also known as takotsubo syndrome, is characterized by transient left ventricular dysfunction not attributable to obstructive epicardial coronary artery disease. Several pathological mechanisms have been proposed, including multivessel coronary artery vasospasm, coronary microcirculatory dysfunction, and excess catecholamine secretion. CASE PRESENTATION: A 68-year-old male presented to our institution for elective surgical removal of a cutaneous basal cell carcinoma on the right side of his face. Within minutes following the administration of local anaesthesia, the patient developed severe hypertension, tachycardia, ST-segment elevation on the electrocardiogram, and non-sustained broad-complex tachycardia. Urgent cardiac catheterization revealed non-obstructive coronary artery disease and left ventriculography demonstrated apical hypokinesia and moderate systolic dysfunction consistent with the takotsubo syndrome. On review of the medications administered, it was noted that an unintentionally large dose of adrenaline (4mg) had been injected subcutaneously with lignocaine. He was monitored in the coronary care and recovered fully with supportive care only. Bisoprolol was initiated on day 1 post procedure. On follow-up one month later, his left ventricular function had normalized. DISCUSSION: Our case report provides direct evidence supporting the pathogenetic role of excess catecholamine secretion in the development of the takotsubo syndrome. A review of the literature reveals that both exogenous catecholamine administration (adrenaline injection in the context of anaphylaxis or infiltrative anaesthesia) and excess endogenous catecholamine (phaechromocytoma) secretion has been associated with the takotsubo syndrome. Local infiltrative anaesthesia with the addition of adrenaline is commonly used as a vasoconstrictor in a wide variety of surgical procedures. To reduce the risk of adverse events, the lowest effective concentration of adrenaline to provide pain control and vasoconstriction is recommended.

Acute left main stem coronary occlusion following transcatheter aortic valve replacement in a patient without recognized coronary obstruction risk factors: a case report.

BACKGROUND: Acute coronary obstruction following transcatheter aortic valve replacement (TAVR) is an uncommon but life-threatening event. CASE SUMMARY: A 78-year-old man developed acute left main obstruction following transfemoral TAVR with a balloon-expandable valve. Cardiac arrest ensued, requiring emergent peripheral cardiopulmonary bypass. Percutaneous coronary intervention (PCI) to the left main coronary artery was performed with one drug-eluting stent. Intravascular ultrasound (IVUS) demonstrated focal underexpansion of the stent in its proximal segment which was not responsive to high-pressure non-compliant balloon dilatation, suggesting stent compression from either valve strut or calcific native leaflet. Therefore, to increase radial strength of the scaffolding at the site of compression, we deployed a second stent within the first stent, and further expanded that segment with high-pressure balloon inflations. Final IVUS demonstrated better expansion of the focally compressed segment. Following PCI, left ventricular function normalized completely. The patient was discharged from hospital on Day 3 post-procedure. At 12 weeks follow-up, his dyspnoea had improved significantly, and follow-up transthoracic echocardiography demonstrated normal left ventricular systolic function and normal aortic valve function. DISCUSSION: Established risk factors for coronary ostial occlusion include a short distance between the aortic annulus and the coronary ostia (<10 mm) and a narrow aortic root (<28 mm at the sinuses of Valsalva). These two factors increase the likelihood that the native valve leaflets are displaced over and obstruct the coronary ostia when the aortic bioprosthesis is deployed. Perplexingly, our patient did not present with any of the recognized risk factors for acute coronary occlusion, suggesting other factors might be at play. We suggest that a leaflet length to coronary sinus height ratio greater than 1 might be an additional useful predictor of coronary occlusion during TAVR. In addition, we suggest that if residual focal stent compression from either valve strut or calcific leaflet exists after stent deployment and the latter is resistant to balloon dilatation, deploying a second concentric layer of stent might improve the radial strength of the scaffolding and improve overall stent expansion.

Primary percutaneous coronary intervention for inferior ST-segment elevation myocardial infarction in a patient supported by the HeartWare left ventricular assist device.

A 63-year-old man with an ischaemic cardiomyopathy, supported by the HeartWare left ventricular assist device (LVAD), presented with ventricular tachycardia and inferior ST-elevation myocardial infarction (STEMI) with associated acute right ventricular (RV) dysfunction. He underwent primary percutaneous coronary intervention with balloon angioplasty and placement of three drug-eluting stents in the proximal-to-mid right coronary artery. Post-procedure, ventricular arrhythmias abated, RV systolic dysfunction resolved and RV size normalised. Percutaneous coronary intervention (PCI) facilitated by the use of miniaturised percutaneous LVAD has become an increasingly available treatment option for high-risk patients. PCI in patients on established full mechanical circulatory support is not a common occurrence. Indeed, to our knowledge, this is the first case of primary percutaneous coronary intervention on an LVAD-supported heart reported in the medical literature. The case raises several specific issues that are of peculiar interest to clinicians involved in the care of patients supported by mechanical assist devices who experience an acute coronary syndrome requiring emergent revascularisation.