The increase in accessibility of fused filament fabrication (FFF) machines has inspired the scientific community to work towards the understanding of the structural performance of components fabricated with this technology. Numerous attempts to characterize and to estimate the mechanical properties of structures fabricated with FFF have been reported in the literature. Experimental characterization of printed components has been reported extensively. However, few attempts have been made to predict properties of printed structures with computational models, and a lot less work with analytical approximations. As a result, a thorough review of reported experimental characterization and predictive models is presented with the aim of summarizing applicability and limitations of those approaches. Finally, recommendations on practices for characterizing printed materials are given and areas that deserve further research are proposed.

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Hard roller burnishing is a cost-effective finishing and surface enhancement process where a ceramic ball rolls on the machined surface to flatten the roughness peaks. The ball is supported and lubricated by hydrostatic fluid in a special tool holder. The process not only improves surface finish but also imposes favorable compressive residual stresses in functional surfaces, which can lead to long fatigue life. Most research in the past focused on experimental studies. There is still a special need for a reliable finite element method (FEM) model that provides a fundamental understanding of the process mechanics. In this study, two-dimensional (2D) and three-dimensional FEM models for hard roller burnishing were established. The developed 2D FEM model was used to study the effects of process parameters (i.e., burnishing pressure, feed rate) on surface finish and residual stresses. The simulation results were evaluated and compared to the experimental data. Results show that the established FEM model could predict the residual stresses and provided useful information for the effect of process parameters. Both FEM and experiments show that burnishing pressure is the most influence, where high burnishing pressure produces less roughness and more compressive residual stress at the surface.

The circular economy (CE) model has become highly relevant in recent years, with the electronics industry being one of the sectors that has considered its application. Despite only a limited amount of literature being available on waste electric and electronic equipment (e-waste) in Mexico, the Mexican Government, academic institutions, and electronics industry have coordinated efforts to implement the CE in the country. This study evaluates the current technical and economic situation of cellphone e-waste generated in Mexico by surveying and analyzing the main actors that influence the management of this waste and using a material flow analysis. Extensive fieldwork was conducted in order to quantify the extent of cellphone e-waste processing in both formal and informal channels. The study of printed circuit boards in cellphones shows that the total value of cellphone e-waste materials ranges between $11.277 and $12.444 million USD per year in Mexico. However, a value of only $0.677 million USD is recycled through formal channels. After characterizing the remanufacturing and recycling CE loops, we conclude that the potential for improvement and advancing towards a CE model is significant

We used continuous flow micro-devices as bioreactors for the production of a glycosylated pharmaceutical product (a monoclonal antibody). We cultured CHO cells on the surface of PMMA/PDMS micro-channels that had been textured by micromachining and coated with fibronectin. Three different micro-channel geometries (a wavy channel, a zigzag channel, and a series of donut-shape reservoirs) were tested in a continuous flow regime in the range of 3 to 6 μL min(-1). Both the geometry of the micro-device and the flow rate had a significant effect on cell adhesion, cell proliferation, and monoclonal antibody production. The most efficient configuration was a series of donut-shaped reservoirs, which yielded mAb concentrations of 7.2 mg L(-1) at residence times lower than one minute and steady-state productivities above 9 mg mL(-1) min(-1). These rates are at about 3 orders of magnitude higher than those observed in suspended-cell stirred tank fed-batch bioreactors.

Stress shielding is a well-known failure factor in hip implants. This work proposes a design concept for hip implants, using a combination of metallic stem with a polymer coating (polyether ether ketone (PEEK)). The proposed design concept is simulated using titanium alloy stems and PEEK coatings with thicknesses varying from 100 to 400 μm. The Finite Element analysis of the cancellous bone surrounding the implant shows promising results. The effective von Mises stress increases between 81 and 92% for the complete volume of cancellous bone. When focusing on the proximal zone of the implant, the increased stress transmission to the cancellous bone reaches between 47 and 60%. This increment in load transferred to the bone can influence mineral bone loss due to stress shielding, minimizing such effect, and thus prolonging implant lifespan.

A B S T R A C TThe small punch test (SPT) is very useful in those situations where it is necessary to use small volumes of material. The aim of this paper is to create and validate a methodology for the determination of the mechanical and damage properties of steels from the loaddisplacement curve obtained by means of SPTs. This methodology is based on the inverse method, the design of experiments, the polynomial curve adjustment and the evolutionary multi-objective optimization, and also allows simulating the SPTs. In order to validate the proposed methodology, the numerical results have been compared with experimental results obtained by means of normalized tests. Two dimensional axisymmetric and threedimensional simulations have been performed in order to allow the analysis of isotropic and anisotropic materials, respectively.Keywords design of experiments; evolutionary multi-objective optimization; material characterization; small punch test (SPT). N O M E N C L A T U R EA = strain controlled nucleation rate a, b, c = fitting factors for the exponential adjustment of zones I and II (partially) of the load-displacement curve of the SPT a obj , b obj , c obj = objective values for the fitting factors a, b, c b i j = coefficients for the second-order model b i jk = coefficients for the third-order model E = Young's modulus f = current void volume fraction f * = modified void volume fraction f 0 = initial void volume fraction f c = critical void volume fraction f F = void volume fraction at final failure f n = void volume fraction of nucleating particles in the Gaussian distribution of the nucleation rate f * u = ultimate void volume fractioṅ f growth = void volume fraction growth ratė f nucleation = void volume fraction nucleation rate FE = finite element K = strength coefficient of the Hollomon's law K * = modified Hollomon's factor m 1 , m 2 = slope factors for the linear adjustment of zones I and II (partially) of the load-displacement curve of the SPT Correspondence: I. Peñuelas.

We report a proof-of-principle for the use of micro-devices as continuous bioreactors for the production of monoclonal antibodies. We culture CHO cells on the surface of PMMA "zigzag" channels textured with semi-spherical cavities coated with fibronectin, observing steady-state productivities 100 times higher than those observed in full scale systems.