Hall-Héroult cell stability is highly affected by anode changing operations. Upon the insertion of a cold anode in the cell, a layer of molten cryolite freezes under the anode. The thickness, microstructure, and chemical composition of this layer vary as a function of time and its location in the cell. To better understand the evolution of the frozen layer, mandatory for the validation of numerical models, a measurement campaign was conducted on the anodes having a few hours of operation in the cell. The macrostructure of the selected frozen bath samples has been investigated using computed tomography while scanning electron microscope (SEM) has been used to qualify its microstructure. An energy-dispersive X-ray spectroscope (EDS) coupled to the SEM has revealed the chemical content. The results showed not only very different macrostructures between samples, but also significantly heterogeneous structure within the same sample. Nevertheless, for all samples, there is a clear distinction between the frozen cryolite and alumina/dusting phases, with the latter surrounding the cryolite matrix.
Transcatheter aortic valve replacement (TAVR) is an alternative technique to surgical valve replacement for over 300,000 patients worldwide. The valve material used in the TAVR is made of biological tissues, whose durability remains unknown. The success of the TAVR favors the research toward synthetic valve leaflet materials as an alternative to biological tissues. In particular, polyethylene terephthalate (PET) textile valves have recently proven durability over a 6‐month period in animal sheep models. Excessive fibrotic tissue formation remains, however, a critical issue to be addressed. The aim of this work was therefore to investigate the potential of PET textiles covalently conjugated with polyethylene glycol (PEG), known for its antifouling properties, to modulate the fibrosis formation both in vitro and in vivo. For this purpose, the surfaces of heart valves made of PET textiles were functionalized with an atmospheric pressure plasma, leading to the formation of carboxylic acid (COOH) groups, further used for PEG‐NH2 conjugation. Surface modification efficiency was assessed by X‐ray photoelectron spectroscopy and water contact angle measurements. The biological behavior of the as‐modified surfaces was evaluated by in vitro assays, using rat cardiac fibroblast cells. The results show that PEG treated substrates restrained the fibroblasts adhesion and proliferation. The PEG treated valve, implanted in a juvenile sheep model, showed a significant fibrosis reduction. The explant also revealed calcification issues that need to be addressed.
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