Large-Scale Robot-Based Polymer and Composite Additive Manufacturing: Failure Modes and Thermal Simulation.

Additive manufacturing (AM) of large-scale polymer and composite parts using robotic arms integrated with extruders has received significant attention in recent years. Despite the contributions of great technical progress and material development towards optimizing this manufacturing method, different failure modes observed in the final printed products have hindered its application in producing large engineering structures used in aerospace and automotive industries. We report failure modes in a variety of printed polymer and composite parts, including fuel tanks and car bumpers. Delamination and warpage observed in these parts originate mostly from thermal gradients and residual stresses accumulated during material deposition and cooling. Because printing large structures requires expensive resources, process simulation to recognize the possible failure modes can significantly lower the manufacturing cost. In this regard, accurate prediction of temperature distribution using thermal simulations is the first step. Finite element analysis (FEA) was used for process simulation of large-scale robotic AM. The important steps of the simulation are presented, and the challenges related to the modeling are recognized and discussed in detail. The numerical results showed reasonable agreement with the temperature data measured by an infrared camera. While in small-scale extrusion AM, the cooling time to the glassy state is less than 1 s, in large-scale AM, the cooling time is around two orders of magnitudes longer.

Identification and Characterization of the miRNAs and Cytokines in Response to Leishmania infantum Infection with Different Response to Treatment.

PURPOSE: Due to the complexity of cytokine and microRNA function in progression and/or suppression of an infection, in this study, we examined miR-3473f, miR-2128, miR-6994-5p, miR-7093-3p, miR-5128, miR-574-5p, miR-7235, IL-2, IL-4, IL-5, IL-10 and IL-13 in patients with VL caused by Leishmania infantum in an in vivo study. METHODS: Sampling was carried out from patient with leishmaniasis and with different responses to treatment during March 2016-January 2020. DNA was extracted and purified using QIAamp Kit. The L. infantum were cultured in DMEM medium and protein content was determined by the Micro BCA Protein Assay Kit. Cytokines were evaluated using a MILLIPLEX MAP Mouse Cytokine/Chemokine Panel I kit. The relative expression of miRNAs was measured in duplicate using automatic thermocycler ABI Prism 7500 sequence detection system (Applied Bio-systems) using the TaqMan MicroRNA Assay kit. RESULTS: The real-time PCR assay revealed that miR-2128, miR-6994-5p, miR-7093-3p, miR-5128, miR-574-5p and miR-7235 were down-regulated and miR-3473 were up-regulated in patients with semi-resistance and resistance parasite strain (P < 0.05). In the current work, cytokine patterns in patients who were slow-to-clear or unable-to-clear L. infantum infection during drug treatment were seen to have decreased protective Th1 cytokines (IL-2, IL-12, TNF-α, and IFN-ɤ, P < 0.001) and increased Th2 cytokines (IL-5, IL-10, and IL-13, P < 0.001). No association was seen with IL-4 in patients with different treatment outcomes. CONCLUSION: Overall, the results of a recent study have shown that cytokines and microRNAs can play a key role in response to treatment, and more comprehensive studies are needed to support this hypothesis.

Does the addition of a heteropoly acid change the water percolation threshold of PFSA membranes?

A large system containing heteropoly acids (HPAs) and Nafion® 117 was simulated and studied to verify whether the additive particles affect the formation of the water percolating network or not. Two structures of HPA particles were considered as dopants, i.e. H9AlW6O24 and H3PW12O40. The SAXS simulation revealed that HPA particle addition to the membrane matrix leads to an increased order in the abundance and size of the hydrophilic region beside an expansion of the distance between the ionic domains. The morphological assessment shows that the hydrophilic phase domains in the HPA-doped Nafion® were spaced further apart than in the undoped membrane. These results show that adding HPA particles to the PFSA membrane reduces the so-called dead-pockets and makes the water channels more interconnected. For undoped Nafion®, the so-called percolating hydration level (λp) was 5.63. In other words, according to these results, approximately 8 wt% of water molecules are required to establish a spanning water network. The H9AlW6O24 and H3PW12O40 particles directly influence the morphology of water clusters and reduce by 10.12% and 17.41% the required hydration level to reach the percolation threshold, respectively.

An Experimental Study on Hydrodynamic Retention of Low and High Molecular Weight Sulfonated Polyacrylamide Polymer.

Polymers are often added with water as a viscosifier to improve oil recovery from hydrocarbon reservoirs. Polymer might be lost wholly or partially from the injected polymer solution by adsorption on the grain surfaces, mechanical entrapment in pores, and hydrodynamic retention in stagnant zones. Therefore, having a clear picture of polymer losses (and retention) is very important for designing a technically and economically successful polymer flood project. The polymer adsorption and mechanical entrapment are discussed more in depth in the literature, though the effect of hydrodynamic retention can be just as significant. This research investigates the effect of the hydrodynamic retention for low and high molecular weight (AN 113 VLM and AN 113 VHM) sulfonated polyacrylamide polymer. Two high permeability Bentheimer core plugs from outcrops were used to perform polymer corefloods. Polymer retention was first determined by injecting 1 cm3/min, followed by polymer core floods at 3, 5, and 8 cm3/min to determine the hydrodynamic retention (incremental retention). A higher molecular weight polymer (AN 113 VHM) showed higher polymer retention. In contrast, hydrodynamic retention for lower molecular weight (AN 113 VLM) was significantly higher than that of the higher molecular weight polymer. Other important observations were the reversibility of the hydrodynamic retention, no permanent permeability reduction, the shear thinning behavior in a rheometer, and shear thickening behavior in core floods.

A New Empirical Model for Viscosity of Sulfonated Polyacrylamide Polymers.

Copolymers of acrylamide with the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid-known as sulfonated polyacrylamide polymers-had been shown to produce very promising results in the enhancement of oil recovery, particularly in polymer flooding. The aim of this work is to develop an empirical model through the use of a design of experiments (DOE) approach for bulk viscosity of these copolymers as a function of polymer characteristics (i.e., sulfonation degree and molecular weight), oil reservoir conditions (i.e., temperature, formation brine salinity and hardness) and field operational variables (i.e., polymer concentration, shear rate and aging time). The data required for the non-linear regression analysis were generated from 120 planned experimental runs, which had used the Box-Behnken construct from the typical Response Surface Methodology (RSM) design. The data were collected during rheological experiments and the model that was constructed had been proven to be acceptable with the Adjusted R-Squared value of 0.9624. Apart from showing the polymer concentration as being the most important factor in the determination of polymer solution viscosity, the evaluation of the model terms as well as the Sobol sensitivity analysis had also shown a considerable interaction between the process parameters. As such, the proposed viscosity model can be suitably applied to the optimization of the polymer solution properties for the polymer flooding process and the prediction of the rheological data required for polymer flood simulators.

Elucidating the morphological aspects and proton dynamics in a hybrid perfluorosulfonic acid membrane for medium-temperature fuel cell applications.

A perfluorosulfonic acid (PFSA) membrane, i.e. Nafion® 117, was doped with the heteropoly salts (HPS) Cs3PW12O40, Rb3PW12O40, and (NH4)3PW12O40. Also, composite membranes with CsxH3-xPW12O40 (x = 1, 2, and 3) as dopants were investigated, which were rendered insoluble by substituting protons with larger cations. Morphological assessment and a detailed analysis of the hopping events via SAXS measurement and analysis of the hydrogen bond networks were performed using classical and quantum hopping molecular dynamics simulation. The phase segregation decreased by increasing the extent proton substitution in HPA. HPS containing cations with a larger ionic radius induced smaller phase segregation in the membrane, as confirmed by the RDF plots. SAXS simulation revealed that the hydrophilic phase domains in the HPS-doped Nafion® membrane were spaced further apart than that in the HPA-doped membrane. Although there was a greater number of isolated clusters for the Cs3PW12O40-doped Nafion®, the average number of cluster decreased with an increase in the substitution cation/proton ratio and ionic radius of the cation. The analysis of the H-bond network stability revealed that the proton hops slower when the membrane contains HPS particles and the mean residence time of a proton on water molecules increases with an increase in the extent of proton substitution in H3PW12O40. Indeed, for the HPA-doped membrane, the diffusion of water molecules is lower than that in the HPS-doped system.

In vitro evaluation of decontamination effects on mechanical properties of fibrin membrane.

Background: Tissue engineering has been investigated as a potential method for healing traumatized tissues. Biomaterials are material devices or implants used to repair or replace native body tissues and organs. The present study was conducted to evaluate the effects of decontamination methods on biological/mechanical properties and degradation/adhesion test of the platelet-rich fibrin (PRF) membranes to compare these properties with intact membranes as a biological biomaterial. Methods: The in vitro degradation tests were conducted by placing the equal sizes of (i) intact PRF membrane, (ii) PRF membrane sterilized by autoclave (iii), ultraviolet (UV), and (iiii) gamma irradiation in phosphate buffer solution on a shaker. The degradation profiles were expressed. Adhesion test was performed by counting adhered mouse fibroblast and sterilized fibrin membrane was compared to normal fibrin membrane by different sterilization methods. Results: The preliminary findings of sterilized PRF membranes showed that UV exposure (p<0.05) and autoclaved fibrin membranes (p<0.01) have significantly lower degradability compared to normal fibrin membranes. Gamma irradiation is similar to normal membrane in degradability. Cell adherence in all groups of fibrin membrane was significantly lower than the group without membrane, but there was no significant difference between intact and sterilized groups of fibrin membranes. Conclusion: Sterilization of fibrin membrane with different protocols does not have any adverse effects on cell adhesion; however, cell adherence is naturally very weak even in normal membranes. Also, it seems that ultraviolet ray polymerizes fibrin filaments and merges them to each other and increases the ability of fibrin membrane against degradation. Autoclaved fibrin membrane content proteins are denatured because of pressure and heat and show an increase in hardness and stability against degradation.

Water Dynamics and Proton-Transport Mechanisms of Nafion 117/Phosphotungstic Acid Composite Membrane: A Molecular Dynamics Study.

The use of a Nafion/phosphotungstic acid composite membrane and the impact of varying concentration of heteropoly acid (HPA) on the well-known effective mechanisms of proton transport were investigated by using classical and quantum hopping molecular dynamics simulation. Our simulations demonstrated that the HPA particles have a favorable influence on the Grotthuss mechanism in proton transportation at low hydration levels. From radial distribution function examinations, it was found that HPA particles were solvated with water and also exhibited stronger affinity toward hydronium ions. It can be concluded that addition of hydrophilic particles such as HPA improved proton conductivity. To assess this effectiveness, lifetime and half-life of the hydrogen bond (H-bond) network in the formed water clusters were investigated at different HPA concentrations. The analysis of H-bond network stability revealed that the lifetime of H-bonds between water molecules and protons decreased with increasing HPA concentration. Moreover, we found that the H-bond network between water molecules was more stable, and the mismatch between simulated bulk water and those formed water clusters in the considered systems decreased upon HPA addition. Indeed, for HPA doped membrane, the activation energy of proton transfer process from a hydronium ion to a water molecule was lower than for the undoped system. The water diffusion coefficient decreased and that of the hydronium ion enhanced with an increase in HPA doping level.

Flexible shape-memory scaffold for minimally invasive delivery of functional tissues.

Despite great progress in engineering functional tissues for organ repair, including the heart, an invasive surgical approach is still required for their implantation. Here, we designed an elastic and microfabricated scaffold using a biodegradable polymer (poly(octamethylene maleate (anhydride) citrate)) for functional tissue delivery via injection. The scaffold's shape memory was due to the microfabricated lattice design. Scaffolds and cardiac patches (1 cm × 1 cm) were delivered through an orifice as small as 1 mm, recovering their initial shape following injection without affecting cardiomyocyte viability and function. In a subcutaneous syngeneic rat model, injection of cardiac patches was equivalent to open surgery when comparing vascularization, macrophage recruitment and cell survival. The patches significantly improved cardiac function following myocardial infarction in a rat, compared with the untreated controls. Successful minimally invasive delivery of human cell-derived patches to the epicardium, aorta and liver in a large-animal (porcine) model was achieved.

Effect of Aging, Antioxidant, and Mono- and Divalent Ions at High Temperature on the Rheology of New Polyacrylamide-Based Co-Polymers.

The viscosity of four new polymers was investigated for the effect of aging at high temperature, with varying degrees of salinity and hardness. The four sulfonated based polyacrylamide co-polymers were FLOCOMB C7035; AN132 VHM; SUPERPUSHER SAV55; and THERMOASSOCIATIF copolymers. All polymer samples were aged at 80 °C for varying times (from zero to at least 90 days) with and without isobutyl alcohol (IBA) as an antioxidant. To see the effect of divalent ions on the polymer solution viscosity, parallel experiments were performed in a mixture of CaCl2-NaCl of the same ionic strength as 5 wt % NaCl. The polymers without IBA showed severe viscosity reduction after aging for 90 days in both types of preparation (5 wt % NaCl or CaCl2-NaCl). In the presence of IBA, viscosity was increased when aging time was increased for 5 wt % NaCl. In CaCl2-NaCl, on the other hand, a viscosity reduction was observed as aging time was increased. This behavior was observed for all polymers except AN132 VHM.

Assessment of Polyacrylamide Based Co-Polymers Enhanced by Functional Group Modifications with Regards to Salinity and Hardness.

This research aims to test four new polymers for their stability under high salinity/high hardness conditions for their possible use in polymer flooding to improve oil recovery from hydrocarbon reservoirs. The four sulfonated based polyacrylamide co-polymers were FLOCOMB C7035; SUPERPUSHER SAV55; THERMOASSOCIATIF; and AN132 VHM which are basically sulfonated polyacrylamide copolymers of AM (acrylamide) with AMPS (2-Acrylamido-2-Methylpropane Sulfonate). AN132 VHM has a molecular weight of 9⁻11 million Daltons with 32 mol % degree of sulfonation. SUPERPUSHER SAV55 mainly has about 35 mol % sulfonation degree and a molecular weight of 9⁻11 million Daltons. FLOCOMB C7035, in addition, has undergone post-hydrolysis step to increase polydispersity and molecular weight above 18 million Daltons but it has a sulfonation degree much lower than 32 mol %. THERMOASSOCIATIF has a molecular weight lower than 12 million Daltons and a medium sulfonation degree of around 32 mol %, and also contains LCST (lower critical solution temperature) type block, which is responsible for its thermoassociative characteristics. This paper discusses the rheological behavior of these polymers in aqueous solutions (100⁻4500 ppm) with NaCl (0.1⁻10 wt %) measured at 25 °C. The effect of hardness was investigated by preparing a CaCl2-NaCl solution of same ionic strength as the 5 wt % of NaCl. In summary, it can be concluded that the rheological behavior of the newly modified co-polymers was in general agreement to the existing polymers, except that THERMOASSOCIATIF polymers showed unique behavior, which could possibly make them a better candidate for enhanced oil recovery (EOR) application in high salinity conditions. The other three polymers, on the other hand, are better candidates for EOR applications in reservoirs containing high divalent ions. These results are expected to be helpful in selecting and screening the polymers for an EOR application.

Increase in intraocular pressure is less with propofol and remifentanil than isoflurane with remifentanil during cataract surgery: A randomized controlled trial.

BACKGROUND: This double-blinded, randomized clinical trial was designed to evaluate intraocular pressure (IOP) change in cataract surgery using the combination of propofol and remifentanil or the combination of isoflurane and remifentanil. MATERIALS AND METHODS: One hundred sixty patients were randomly allocated to a maintenance anesthetic consisting of remifentanil + isoflurane (group I), normal saline + isoflurane (group II), propofol + remifentanil (group III) or normal saline + propofol (group IV). IOP was measured at seven predefined time points, baseline (T0), 3 min after the start of continuous remifentanil infusion (T2), after induction of anesthesia (T3), immediately after laryngoscopy and intubation (T4), 5 min after laryngoscopy (T5), immediately after the block of continuous remifentanil infusion (T6) and 3 min after T6 (T7). Outcomes included IOP, systole blood pressure (SBP) and diastole blood pressure (DBP), mean arterial pressure (MAP) and heart rate (HR). RESULTS: The mean of IOP in Group III was lower than other groups and in group IV was higher than other groups. At time point T4 and T5 differences in the mean of IOP between groups III and IV was significantly different (P > 0.05). The trend in changes in the mean of IOP was statistically significant among groups (P value = 0.01). The trends in changes in the mean of SBP, DBP and MAP were not significantly different among groups (P value = 0.41). HR in group III was significantly lower than other groups. The trend in changes in the mean of HR was significantly different among groups (P value = 0.002). CONCLUSION: Propofol with remifentanil was more effective than placebo or adding remifentanil to isoflurane in management of IOP in cataract surgery.

Effects of leached components from silorane and methacrylate-based dental composites on the male mice reproductive system.

BACKGROUND: This study aimed to investigate the potential toxic effects of leached components from either a methacrylate-based composite (Filtek Z250) or a silorane-based composite (Filtek P90) on the male mice reproductive system. METHODS: Sixty adult Syrian male mice were divided into six groups. In test groups, leached components from composite specimens in artificial saliva or 75% aqueous ethanol solution were administered intragastrically daily for 28 days. The mice were then euthanized and the following reproductive parameters recorded: body weight changes; weight of paired testes; testis volume; Gonadosomatic Index (GSI); sperm motility; sperm viability; daily sperm production and epididymal sperm count. RESULTS: There were no significant differences in body weight changes, weight of paired testes, GSI, testis volume, epididymal sperm count, and daily sperm production between groups. Sperm motility and sperm viability were significantly lower in all the test groups in comparison to the control groups. In addition, they were significantly lower in the test groups in which composite samples were immersed in aqueous ethanol solution. CONCLUSIONS: Within the limitations of this study, the present data indicate that leached components from dental composites could affect sperm quality and therefore could potentially cause adverse effects on the male mice reproductive system.