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This study aims to describe the effect of ironing process parameters on mixing efficiency and gradient generation in Y-micromixers and microfluidic gradient generators (MGGs), respectively.

Material extrusion (MEX) enables the production of miniaturized devices with the advantage of lower manufacturing costs and higher design freedom. However, surface finishing is the most important drawback when it comes to microfluidic applications where flow splitting is not required. First, the effect of ironing line spacing (LS) and speed (IS) on mixing efficiency in Y-micromixers was experimentally investigated. Then, the best ironing settings were chosen to further study the spatial stability of the normalized concentration gradient in MGGs.

Lower ironing LS and IS enhance the microchannel surface smoothness. The best combination of ironing parameters (lowest values of LS and IS) leads to an increase in mixing length of 191% at Q = 10 µL/min and 198% at Q = 20 µL/min, with respect to a similar Y-micromixer geometry where ironing was not performed. These findings were applied in the production of a MGG, showing that the normalized concentration gradient in the crosswise flow direction does not depend on the streamwise position when ironing is performed.

To the best of the authors’ knowledge, for the first time, the possibility of optimizing ironing parameters to enhance the surface roughness in MEX microfluidic devices has been investigated. Ironing of the channel bottom surface allows to reduce ridges-induced flow convection, thus delaying mixing in Y-micromixers and achieving stable concentration gradient in MGGs.

In this paper, the authors propose an experimental set-up to study the chemical vapour polishing technique confining pure dimethylketone atmosphere at a fixed temperature in a vacuum chamber. The purpose of this paper is to improve conventional vapour treatments lowering the amount of solvent, lowering time and temperature needed and improving the environmental impact of the technique.

A factorial design of experiments is adopted to understand the effect of the treatment on roughness and on the surface morphology of treated specimens.

The proposed method improves several aspects of well-known methods based on water–dimethylketone liquid solution such as: no interaction between water and workpiece and higher capability of process management. It also improves several aspects of well-known methods based on vapour, lowering the amount of solvent, time and temperature compared to conventional vapour treatments.

Chemical vapour polishing is a well-known technique for smoothing additive manufactured acrylonitrile butadiene styrene (ABS) parts. Several data and users' experiences are available on the Web about this topic. In recent scientific literature, a few papers are available about this topic, dealing with how process parameters affect the final surface roughness. In the present paper, the authors propose to improve the process performing the process using dimethylketone into a vacuum chamber. The main advantages are the significant reduction of the solvent needed to perform the process and lower time needed to obtain same results as atmospheric pressure treatments.

The purpose of this study is to introduce an alternative construction for microfluidic micromixers, where the effect of the extruded filaments in the fused deposition modeling (FDM) technique is used to enhance mixing performance identified as a challenge in microfluidic micromixers.

A simple Y-shaped micromixer was designed and printed using FDM technique. Experimental and numerical studies were conducted to investigate the effect of the extruded filaments on the flow behavior. The effects of the extruded width (LW), distance between adjacent filaments (b) and filament height (h₁) are investigated on the mixing performance and enhancing mixing in the fabricated devices. The performance of fabricated devices in mixing two solutions was tested at flow rates of 5, 10, 20, 40, 80 and 150 µL/min.

The experimental results showed that the presence of geometrical features on microchannels, because of the nature of the FDM process, can act as ridges and generate a lateral transform through the transverse movement of fluids along the groove. The results showed the effect of increasing ridge height on the transverse movement of the fluids and, therefore, chaotic mixing over the ridges. In contrast, in the shallow ridge, diffusion is the only mechanism for mixing, which confirms the numerical results.

The study presents an exciting aspect of FDM for fabrication of micromixers and enhance mixing process. In comparison to other methods, no complexity was added in fabrication process and the ridges are an inherent property of the FDM process.