ABSTRACT
The laser-based powder bed fusion of polymers (PBF-LB/P) process often utilizes a blend of powders with varying degrees of degradation. Specifically, for polyamide 12, the traditional reuse schema involves mixing post-processed powder with virgin powder at a predetermined ratio before reintroducing it to the process. Given that only about 15% of the powder is utilized in part production, and powders are refreshed in equal proportions, there arises a challenge with the incremental accumulation of material across build cycles. To mitigate the consumption of fresh powder relative to the actual material usage, this study introduces the incorporation of recycled material into the PBF-LB/P process. This new powder reuse schema is presented for the first time, focusing on the laser sintering process. The characteristics of the recycled powder were evaluated through scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, particle size distribution, and dynamic powder flowability assessments. The findings reveal that waste powders can be effectively reused in PBF-LB/P to produce components with satisfactory mechanical properties, porosity levels, dimensional accuracy, and surface quality.
ABSTRACT
Additive manufacturing (AM) is dynamically developing and finding applications in different industries. The quality of input material is a part of the process and of the final product quality. That is why understanding the influence of powder reuse on the properties of bulk specimens is crucial for ensuring the repeatable AM process chain. The presented study investigated the possibility of continuous reuse of AlSi7Mg0.6 powder in the laser powder bed fusion process (LPBF). To date, there is no study of AlSi7Mg0.6 powder reuse in the LPBF process to be found in the literature. This study aims to respond to this gap. The five batches of AlSi7Mg0.6 powder and five bulk LPBF samples series were characterised using different techniques. The following characteristics of powders were analysed: the powder size distribution (PSD), the morphology (scanning electron microscopy-SEM), the flowability (rotating drum analysis), and laser light absorption (spectrophotometry). Bulk samples were characterised for microstructure (SEM), chemical composition (X-ray fluorescence spectrometry-XRF), porosity (computed tomography-CT) and mechanical properties (tensile, hardness). The powder was reused in subsequent processes without adding (recycling/rejuvenation) virgin powder (collective ageing powder reuse strategy). All tested powders (powders P0-P4) and bulk samples (series S0-S3) show repeatable properties, with changes observed within error limits. Samples manufactured within the fifth reuse cycle (series S4) showed some mean value changes of measured characteristics indicating initial degradation. However, these changes also mostly fit within error limits. Therefore, the collective ageing powder reuse strategy is considered to give repeatable LPBF process results and is recommended for the AlSi7Mg0.6 alloy within at least five consecutive LPBF processes.
ABSTRACT
In the era of the coronavirus pandemic, one of the most demanding areas was the supply of healthcare systems in essential Personal Protection Equipment (PPE), including face-shields and hands-free door openers. This need, impossible to fill by traditional manufacturing methods, was met by implementing of such emerging technologies as additive manufacturing (AM/3D printing). In this article, Poly(lactic acid) (PLA) filaments for Fused filament fabrication (FFF) technology in the context of the antibacterial properties of finished products were analyzed. The methodology included 2D radiography and scanning electron microscopy (SEM) analysis to determine the presence of antimicrobial additives in the material and their impact on such hospital pathogens as Staphylococcus aureus, Pseudomonas aeruginosa, and Clostridium difficile. The results show that not all tested materials displayed the expected antimicrobial properties after processing in FFF technology. The results showed that in the case of specific species of bacteria, the FFF samples, produced using the declared antibacterial materials, may even stimulate the microbial growth. The novelty of the results relies on methodological approach exceeding scope of ISO 22196 standard and is based on tests with three different species of bacteria in two types of media simulating common body fluids that can be found on frequently touched, nosocomial surfaces. The data presented in this article is of pivotal meaning taking under consideration the increasing interest in application of such products in the clinical setting.
ABSTRACT
BACKGROUND: Balloon pulmonary angioplasty (BPA) is a novel treatment option for inoperable or persistent chronic thromboembolic pulmonary hypertension (CTEPH). Little is known about renal function in CTEPH patients undergoing BPA. OBJECTIVES: The aim of this study was to assess the frequency of contrast-induced acute kidney injury (CI-AKI) in patients with CTEPH undergoing BPA and to evaluate the relationship between hemodynamic and renal function. METHODS: A total of 41 CTEPH patients were included and 250 consecutive BPA sessions were analyzed for frequency of CI-AKI. The serum creatinine (SC) concentration was measured and the glomerular filtration rate (GFR) was estimated using the Modification of Diet in Renal Disease equation before and 72 h after each BPA procedure. CI-AKI was defined as an increase of 25% or 0.5 mg/dL in SC from the baseline value within 48-72 h of contrast administration. SC and GFR were assessed before and after 3-6 months of completing the BPA treatment and correlated with hemodynamic parameters. RESULTS: The SC concentration and GFR did not change significantly within 72 h after BPA (+1%, p = 0.921, and +4%, p = 0.112, respectively). CI-AKI was noted in 2 cases (0.8%). Significant improvement was noted in GFR (75.4 ± 21.2 vs. 80.9 ± 22.4 mL/min/1.73 m2; p = 0.012) in addition to improvement in right atrial pressure (RAP; 9.1 ± 4.1 to 5.0 ± 2.2 mm Hg; p < 0.001), mean pulmonary artery pressure (49.1 ± 10.7 to 29.8 ± 8.3 mm Hg; p < 0.001), cardiac index (CI; 2.42 ± 0.6 to 2.70 ± 0.6 L/min/m2; p = 0.004), and pulmonary vascular resistance (9.42 ± 3.6 to 4.4 ± 2.3 Wood units; p < 0.001). In a subpopulation of 12 patients with impaired renal function at baseline, the relative increase in GFR was significantly correlated with relative improvement in CI (r = 0.060; p = 0.037), RAP (r = -0.587; p = 0.044), and mixed venous saturation (r = 0.069; p = 0.012). CONCLUSIONS: Hemodynamically effective BPA procedures improve renal function in patients with CTEPH with a minimal risk of CI-AKI in the course of treatment.
