Designing Mechanical Properties of 3D Printed Cookies through Computer Aided Engineering

Additive manufacturing or 3D printing can be applied in the food sector to create food products with personalized properties such as shape, texture, and composition. In this article, we introduce a computer aided engineering (CAE) methodology to design 3D printed food products with tunable mechanical properties. The focus was on the Young modulus as a proxy of texture. Finite element modelling was used to establish the relationship between the Young modulus of 3D printed cookies with a honeycomb structure and their structure parameters. Wall thickness, cell size, and overall porosity were found to influence the Young modulus of the cookies and were, therefore, identified as tunable design parameters. Next, in experimental tests, it was observed that geometry deformations arose during and after 3D printing, affecting cookie structure and texture. The 3D printed cookie porosity was found to be lower than the designed one, strongly influencing the Young modulus. After identifying the changes in porosity through X-ray micro-computed tomography, a good match was observed between computational and experimental Young’s modulus values. These results showed that changes in the geometry have to be quantified and considered to obtain a reliable prediction of the Young modulus of the 3D printed cookies

Pore network modelling of single phase flow in 3D printed porous materials: permeability prediction and validation

status: publishe

Pore network model for permeability characterization of 3D printed porous materials for passive microfluidics

Stand-alone and portable lab-on-chips (LOC) can be obtained by exploiting capillary flow in porous media. Polymethylmethacrylate (PMMA) platforms obtained through powder-based three-dimensional (3D) printing are appropriate for capillarity-driven LOCs. However, fluid flow in such platforms needs to be characterized well. For this purpose, a 3D pore network (PN) was extracted from high-resolution μCT images of printed PMMA through a watershed algorithm and a PN model was developed with the final goal of characterizing material permeability. The effect of all parameters involved in the PN extraction and modeling was investigated. The study focused in particular on the effect of the number of seeds for the watershed segmentation, pore sphericity, and pore-to-pore channel shape that was modeled as a bicylindrical or biconical object. The results proved that all PN extraction and modeling parameters influenced the permeability, which was found to be lower the higher the number of seeds and when using sphericity and biconical channels. Eventually, the Calinski-Harabasz index value was used to identify the optimal number of watershed seeds.status: Published onlin

Computational and experimental fatigue analysis of contoured spinal rods.

Posterior fixation with contoured rods is an estabilished methodology for the treatment of spinal deformities. Both uniform industrial preforming and intraoperative contouring introduce tensile and compressive plastic deformations, respectively, at the concave and at the convex sides of the rod. The purpose of this study is to develop a validated numerical framework capable of predicting how the fatigue behavior of contoured spinal rods is affected by residual stresses when loaded in lordotic and kyphotic configurations. Established finite-element models describing static contouring were implemented as preliminary simulation steps and were followed by subsequent cyclical loading steps. The equivalent Sines stress distribution predicted in each configuration was compared to that in straight rods and related to the corresponding experimental number of cycles to failure. In the straight configuration, the maximum equivalent stress (441 MPa) exceeds the limit curve, as confirmed by experimental rod breakage after 10^5 loading cycles. The stresses further increased in the lordotic configuration, where failure was reached at at 10^4 cycles. The maximum equivalent stress was below the limit curve for the kyphotic configuration (640 MPa), for which a run-out of 106 cycles was reached. Microscopy inspection confirmed agreement between numerical predictions and experimental fatigue crack location. The contouring technique (uniform contouring or French Bender) was not related to statistically significant differences. Our study demonstrates the key role of residual stresses in altering the mean stress component, superposing to tensile cyclic load, potentially explaining the higher failure rate of lordotic rods compared to kyphotic ones.status: Published onlin

Spinal rods contouring: an experimental and finite element study to control fatigue

French bender is the clinical gold standard for spinal rod contouring. Despite it allows the surgeon in achieving any desired shape, it is believed to weaken the implants, finally promoting fatigue failure. The current study proposes a new method combining non-linear FE models and experimental tests to better understand the role of residual stresses resulting from contouring. Learning how to control this phenomenon may contribute in reducing the high failure rate met during clinical use, as well as improving the usage of current implants.status: accepte

3D pore network quantification of apples using X-ray CT of the microstructure of intact fruit

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Dynamic synchrotron microtomography for direct in-situ capillary flow visualization in functionalized porous material for passive microfluidics

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Phase angle and metabolic equivalents as predictors of frailty transitions in advanced age

The aim of this prospective study was to investigate whether two cellular and metabolic health indices, phase angle (PhA)and metabolic equivalents (METs), can predict changes in frailty states in fit community-dwelling older people. A sample of 118 individuals aged ≥65 years who attended a twice-weekly mild fitness program of aerobic and/or resistance exercises was enrolled in the study. At baseline and after three years, individuals underwent a clinical examination, biochemical determinations, bioelectrical impedance analysis, body composition assessment with dual energy X-ray absorptiometry, physical performance tests, and frailty and sarcopenia assessment. In 78 participants was executed indirect calorimetry, too. Based on frailty transitions during the follow-up between non-frailty, pre-frailty and frailty, participants were categorized as improved, stable (non-frail or pre-frail), and worsened or remaining frail. The chances to experience different frailty changes by baseline PhA and METs were explored through multinomial regression analysis and expressed as odds ratios (OR)and 95% Confidence intervals (95%CI). During the follow-up, 8 participants improved in frailty status, 84 were stable and 26 worsened or remained frail. For each one-unit increase in PhA, the odds of improving in frailty increased by 4.53 times (95%CI:1.18–17.46); while for each one-unit increase in METs, the odds of worsening in frailty decreased by 65% (95%CI:0.16–0.79). PhA and METs may be indirect measures of functional reserve, with lower values being potential biomarkers of evolving frailty