Novel evaluation technology for the demand characteristics of 3D food printing materials: a review.

As a recently developed way of food manufacturing - 3D printing - is bringing about a revolution in the food industry. Rheological and mechanical properties of food material being printed are the determinants of their printability. Therefore, it is important to analyze the requirements of different 3D printing technologies on material properties and to evaluate the performance of the printed materials. In this review, the printing characteristics and classification of food materials are discussed. The four commonly used 3D printing techniques e.g. extrusion-based printing, selective sintering printing (SLS), binder jetting, and inkjet printing, are outlined along with suitable material characteristics required for each printing technique. Finally, recent technologies for evaluation of 3D printed products including low field nuclear magnetic resonance (LF-NMR), computer numerical simulation, applied reference material, morphological identification, and some novel instrumental analysis techniques are highlighted.

Suitability of Polymers for 3D-Printing Laboratory Models for Shaking Table Experiments: Discussion and Indications.

This paper presents a comprehensive assessment of the suitability of seven commercially available polymers for crafting laboratory models designed for dynamic shaking-table tests using 3D-printing technology. The objective was to determine whether 3D-printed polymer models are effective for dynamic assessments of structures. The polymers underwent experimental investigations to assess their material properties, i.e., the elastic modulus, the mass density, and the limit of linear-elastic behaviour. The following methodology was applied to obtain the correct values of elasticity moduli and yield points of the polymers: (1) the uniaxial tensile test, (2) the compression test, and (3) the three-point loading test. The filament density was determined as the ratio of sample mass to its volume. The results indicate substantial variations in stiffness, density, and elasticity limits among them. For the similarity analysis, an existing reinforced concrete chimney 120 m high was chosen as a prototype. A geometric similarity scale of 1:120 for a laboratory mock-up was adopted, and a numerical model of the mock-up was created. The similarity scales were calculated for mock-ups made of each filament. Based on these scales, numerical calculations of natural frequencies and dynamic performance under a strong earthquake were carried out for models made of different polymers. Assessment of the polymers' suitability for laboratory models revealed positive outcomes. The agreement between field experiments, shaking-table tests, and numerical predictions in terms of natural frequencies was observed. Maximum stresses resulting from the earthquake indicated the satisfactory performance of the model below the linear-elastic limit. Despite differences in material properties, the selected polymers were deemed suitable for 3D-printing models for shaking-table tests. However, the discussion raised some important considerations. The upper frequency limit of the shaking-table imposes restrictions on the number of natural frequencies that can be determined. Numerical assessments of natural frequencies are recommended to prevent underestimation and to assess the feasibility of their determination. Additionally, resonance during natural frequency determination may lead to exceeding the linear-elastic limit, affecting filament properties, and making the similarity criteria invalid. Practically, this research contributes insights for planning shaking-table tests, aiding in selecting the most suitable filament and highlighting crucial considerations to ensure reliable and accurate dynamic assessments.

Mechanical characterization and torsional buckling of pediatric cardiovascular materials.

In complex cardiovascular surgical reconstructions, conduit materials that avoid possible large-scale structural deformations should be considered. A fundamental mode of mechanical complication is torsional buckling which occurs at the anastomosis site due to the mechanical instability, leading surgical conduit/patch surface deformation. The objective of this study is to investigate the torsional buckling behavior of commonly used materials and to develop a practical method for estimating the critical buckling rotation angle under physiological intramural vessel pressures. For this task, mechanical tests of four clinically approved materials, expanded polytetrafluoroethylene (ePTFE), Dacron, porcine and bovine pericardia, commonly used in pediatric cardiovascular surgeries, are conducted (n = 6). Torsional buckling initiation tests with n = 4 for the baseline case (L = 7.5 cm) and n = 3 for the validation of ePTFE (L = 15 cm) and Dacron (L = 15 cm and L = 25 cm) for each are also conducted at low venous pressures. A practical predictive formulation for the buckling potential is proposed using experimental observations and available theory. The relationship between the critical buckling rotation angle and the lumen pressure is determined by balancing the circumferential component of the compressive principal stress with the shear stress generated by the modified critical buckling torque, where the modified critical buckling torque depends linearly on the lumen pressure. While the proposed technique successfully predicted the critical rotation angle values lying within two standard deviations of the mean in the baseline case for all four materials at all lumen pressures, it could reliably predict the critical buckling rotation angles for ePTFE and Dacron samples of length 15 cm with maximum relative errors of 31% and 38%, respectively, in the validation phase. However, the validation of the performance of the technique demonstrated lower accuracy for Dacron samples of length 25 cm at higher pressure levels of 12 mmHg and 15 mmHg. Applicable to all surgical materials, this formulation enables surgeons to assess the torsional buckling potential of vascular conduits noninvasively. Bovine pericardium has been found to exhibit the highest stability, while Dacron (the lowest) and porcine pericardium have been identified as the least stable with the (unitless) torsional buckling resistance constants, 43,800, 12,300 and 14,000, respectively. There was no significant difference between ePTFE and Dacron, and between porcine and bovine pericardia. However, both porcine and bovine pericardia were found to be statistically different from ePTFE and Dacron individually (p < 0.0001). ePTFE exhibited highly nonlinear behavior across the entire strain range [0, 0.1] (or 10% elongation). The significant differences among the surgical materials reported here require special care in conduit construction and anastomosis design.

Development and material characteristics of glaucoma surgical implants.

Background: Glaucoma is the leading cause of irreversible blindness worldwide. The reduction of intraocular pressure has proved to be the only factor which can be modified in the treatment, and surgical management is one of the important methods for the treatment of glaucoma patients. Main text: In order to increase aqueous humor outflow and further reduce intraocular pressure, various drainage implants have been designed and applied in clinical practice. From initial Molteno, Baerveldt and Ahmed glaucoma implants to the Ahmed ClearPath device, Paul glaucoma implant, EX-PRESS and the eyeWatch implant, to iStent, Hydrus, XEN, PreserFlo, Cypass, SOLX Gold Shunt, etc., glaucoma surgical implants are currently undergoing a massive transformation on their structures and performances. Multitudinous materials have been used to produce these implants, from original silicone and porous polyethylene, to gelatin, stainless steel, SIBS, titanium, nitinol and even 24-carat gold. Moreover, the material geometry, size, rigidity, biocompatibility and mechanism (valved versus nonvalved) among these implants are markedly different. In this review, we discussed the development and material characteristics of both conventional glaucoma drainage devices and more recent implants, such as the eyeWatch and the new minimally invasive glaucoma surgery (MIGS) devices. Conclusions: Although different in design and materials, these delicate glaucoma surgical implants have widely expanded the glaucoma surgical methods, and improved the success rate and safety of glaucoma surgery significantly. However, all of these glaucoma surgical implants have various limitations and should be used for different glaucoma patients at different conditions.

Hydrothermal carbon microspheres and their iron salt modification for enhancing biohydrogen production.

Dark fermentation (DF) for hydrogen (H2) evolution is often limited to industrial application due to its low H2 yield. In this work, hydrothermal carbon microspheres (HCM) and iron modified HCM (Fe-HCM) were prepared by hydrothermal process using waste corn cob. Subsequently, HCM and Fe-HCM were used in DF for more H2. The highest H2 yields amended with HCM and Fe-HCM at 600 mg/L were achieved to be 119 and 154 mL/g glucose (0.87 and 1.2 mol H2/mol glucose), respectively, being 24% and 59% higher than that of control yield. Soluble metabolites revealed HCM and Fe-HCM promoted butyric acid-based DF. Microbial composition depicted that HCM and Fe-HCM improved the abundance level of Firmicutes from 35% to 41% and 56%, while the abundance level of Clostridium_sensu_stricto_1 rose from 25% to 38% and 51%, respectively. This provides valuable guidance for hydrothermal carbon used in biofuel production.

Analysis of Material-Characterization Properties of Post-Production Waste-The Case of Apple Pomace.

The paper presents the material-characterization properties of apple pomace-the post-production waste of juice pressing. Tests were carried out on the basic physical properties of apple pomace: color, specific-density, and energy properties. Extensive material-composition analyses based on DSC (differential scanning calorimetry) and TGA (thermogravimetry) methods were also performed. It has been shown that pomace, due to its energy value, can be a good fuel. The obtained thermal data confirm the presence of cellulose, hemicelluloses, lignins and pectins in the analyzed pomace. The results confirm that dried apple pomace is microbiologically stable with good health-promoting properties.

Statistical Modelling of the Fatigue Bending Strength of Norway Spruce Wood.

When wood is used as a structural material, the fact that it is a highly inhomogeneous material, which significantly affects its static and fatigue properties, presents a major challenge to engineers. In this paper, a novel approach to modelling the fatigue-life properties of wood is presented. In the model, the common inverse-power-law relationship between the structural amplitude loads and the corresponding number of load cycles to failure is augmented with the influence of the wood's mass density, the loading direction and the processing lot. The model is based on the two-parametric conditional Weibull's probability density function with a constant shape parameter and a scale parameter that is a function of the previously mentioned parameters. The proposed approach was validated using the example of experimental static and fatigue-strength data from spruce beams. It turned out that the newly presented model is capable of adequately replicating the spruce's S-N curves with a scatter, despite the relatively scarce amount of experimental data, which came from different production lots that were loaded in different directions and had a significant variation in density. Based on the experimental data, the statistical model predicts that the lower density wood has better fatigue strength.

Force transmission analysis of surface coating materials for multi-fingered robotic grippers.

Robotic systems are generally used for grasping, carrying, holding, and many similar operations, typically in industrial applications. One of the most important components of robotic systems is robot grippers for the aforementioned operations, which are not only mission-critical but also represent a significant operational cost due to the time and expense associated with replacement. Grasping operations require sensitive and dexterous manipulation ability. As a consequence, tactile materials and sensors are an essential element in effective robot grippers; however, to date, little effort has been invested in the optimization of these systems. This study has set out to develop inexpensive, easily replaced pads, testing two different chemical compositions that are used to produce a tactile material for robot grippers, with the objective of generating cost, time, and environmental savings. Each tactile material produced has its specific individual dimension and weight. First, each of the materials under construction was tested under different constant pressures, and its characteristics were analyzed. Second, each tactile material was mounted on a two-fingered robot gripper and its characteristics. Material characteristics were tested and analyzed as regards their ability to grasp different sizes and types of objects using the two-fingered robot gripper. Based on the analysis of the results the most sensitive and cost-effective material for industrial type multi-fingered grippers was identified.

An Overview on the Rheology, Mechanical Properties, Durability, 3D Printing, and Microstructural Performance of Nanomaterials in Cementitious Composites.

The most active research area is nanotechnology in cementitious composites, which has a wide range of applications and has achieved popularity over the last three decades. Nanoparticles (NPs) have emerged as possible materials to be used in the field of civil engineering. Previous research has concentrated on evaluating the effect of different NPs in cementitious materials to alter material characteristics. In order to provide a broad understanding of how nanomaterials (NMs) can be used, this paper critically evaluates previous research on the influence of rheology, mechanical properties, durability, 3D printing, and microstructural performance on cementitious materials. The flow properties of fresh cementitious composites can be measured using rheology and slump. Mechanical properties such as compressive, flexural, and split tensile strength reveal hardened properties. The necessary tests for determining a NM's durability in concrete are shrinkage, pore structure and porosity, and permeability. The advent of modern 3D printing technologies is suitable for structural printing, such as contour crafting and binder jetting. Three-dimensional (3D) printing has opened up new avenues for the building and construction industry to become more digital. Regardless of the material science, a range of problems must be tackled, including developing smart cementitious composites suitable for 3D structural printing. According to the scanning electron microscopy results, the addition of NMs to cementitious materials results in a denser and improved microstructure with more hydration products. This paper provides valuable information and details about the rheology, mechanical properties, durability, 3D printing, and microstructural performance of cementitious materials with NMs and encourages further research.

Inactivation effect and mechanisms of combined ultraviolet and metal-doped nano-TiO2 on treating Escherichia coli and Enterococci in ballast water.

The discharge of ship ballast water (containing large amounts of alien organisms) has caused severe ecological hazards to marine environments. In this study, three metal elements (Ag, Fe, and Gd) were doped to nano-TiO2 material respectively (content: 0.4%, 0.7%, and 1.0%) to improve inactivation effect of Escherichia coli and Enterococci in ballast water. Experimental results indicate that compared with the sole ultraviolet (UV) and the UV and original nano-TiO2, the UV and metal-doped nano-TiO2 increased the bacterial inactivation rate to different extents. For each metal element, high external metal content (1.0%) corresponded to high inactivation effort. The doping of Ag resulted in optimal inactivation effort, and the addition of Fe and Gd caused unobvious effort. At the end of the inactivation process (20 s), the UV and 1% Ag-doped nano-TiO2 reached the highest logarithmic sterilization rates (0.915 for Escherichia coli and 0.805 for Enterococcus). The doping of Ag, Fe, and Gd did not change the anatase phase TiO2 crystal form, and 1% Ag-doped nano-TiO2 had the smallest particle diameter and the evenest distribution of nanoparticles. Compared with the sole UV, the UV and Ag-doped nano-TiO2 treatment resulted in higher malondialdehyde contents (0.0646 µmol/L for Escherichia coli and 0.0529 µmol/L for Enterococci) and lower superoxide dismutase activities (0.672 U/mL for Escherichia coli and 0.792 U/mL for Enterococci), which were in accordance with high inactivation rates in these cases.

Understanding the Thermal Properties of Precursor-Ionomers to Optimize Fabrication Processes for Ionic Polymer-Metal Composites (IPMCs).

Ionic polymer-metal composites (IPMCs) are one of many smart materials and have ionomer bases with a noble metal plated on the surface. The ionomer is usually Nafion, but recently Aquivion has been shown to be a promising alternative. Ionomers are available in the form of precursor pellets. This is an un-activated form that is able to melt, unlike the activated form. However, there is little study on the thermal characteristics of these precursor ionomers. This lack of knowledge causes issues when trying to fabricate ionomer shapes using methods such as extrusion, hot-pressing, and more recently, injection molding and 3D printing. To understand the two precursor-ionomers, a set of tests were conducted to measure the thermal degradation temperature, viscosity, melting temperature, and glass transition. The results have shown that the precursor Aquivion has a higher melting temperature (240 °C) than precursor Nafion (200 °C) and a larger glass transition range (32⁻65°C compared with 21⁻45 °C). The two have the same thermal degradation temperature (~400 °C). Precursor Aquivion is more viscous than precursor Nafion as temperature increases. Based on the results gathered, it seems that the precursor Aquivion is more stable as temperature increases, facilitating the manufacturing processes. This paper presents the data collected to assist researchers in thermal-based fabrication processes.

Experimental and Theoretical Analysis of Sound Absorption Properties of Finely Perforated Wooden Panels.

Perforated wooden panels are typically utilized as a resonant sound absorbing material in indoor noise control. In this paper, the absorption properties of wooden panels perforated with tiny holes of 1-3 mm diameter were studied both experimentally and theoretically. The Maa-MPP (micro perforated panels) model and the Maa-Flex model were applied to predict the absorption regularities of finely perforated wooden panels. A relative impedance comparison and full-factorial experiments were carried out to verify the feasibility of the theoretical models. The results showed that the Maa-Flex model obtained good agreement with measured results. Control experiments and measurements of dynamic mechanical properties were carried out to investigate the influence of the wood characteristics. In this study, absorption properties were enhanced by sound-induced vibration. The relationship between the dynamic mechanical properties and the panel mass-spring vibration absorption was revealed. While the absorption effects of wood porous structure were not found, they were demonstrated theoretically by using acoustic wave propagation in a simplified circular pipe with a suddenly changed cross-section model. This work provides experimental and theoretical guidance for perforation parameter design.