Microstructural Breakdown Research Articles

Cellulose nanocrystal and Pluronic L121-based thermo-responsive composite hydrogels

Cellulose nanocrystal (CNC) is a promising sustainable material with its biocompatibility, high aspect ratio, and mechanical strength. CNC-based systems have potential applications in various fields including biosensors, packaging, coating, energy storage, and pharmaceuticals. However, turning CNC into smart systems remains a challenge due to the lack of stimuli-responsiveness, limitation in compatibility with hydrophobic matrices, and their agglomeration tendency. In this work, a thermo-responsive nanocomposite system is constructed with CNCs and polymersome forming Pluronic L121 (L121), and its phase behavior and mechanical properties are investigated in detail. Two different CNC concentration (4 % and 5 %) is studied by changing the L121 concentration (1–20 %) to understand the effect of unimers and polymersomes on the CNC network. At dilute L121 concentrations (1–5 %), the composite system becomes softer but more fragile below the transition temperature. However, it becomes much stronger at higher L121 concentrations (10–20 %), and a gel network is obtained above the transition temperature. Interestingly, the elastically reinforced CNC gels exhibit greater resistance to microstructural breakdown at large strains due to the soft and deformable nature of the large polymersomes. It is also found that the gelation temperature for hydrogels is tunable with increasing L121 concentration, and the nanocomposite hydrogels displayed thermo-reversible rheological behavior.

Real-time monitoring of casein gel microstructure during simulated gastric digestion monitored by small-angle neutron scattering

The evolving structure of protein-based foods during the digestion process is critical to the release of nutrients. However, traditional in vitro monitoring of the gel micro- and nano-structure during digestion involves analysing sample aliquots taken at different digestion time periods. This can pose issues for some gels, such as casein-based gels, as they are sensitive to sample manipulation and environmental changes. Herein, a newly developed flow setup was utilised to monitor (at the micro- and nano-length scales) the gel protein network of rennet-induced (RG) and transglutaminase-induced acid gels (TG) in situ and in real-time during simulated gastric digestion using ultra-small and small-angle neutron scattering (USANS and SANS). The proteolysis kinetics of the gels were investigated at two different pepsin enzyme concentrations (2000 and 8000 U mL-1) and in two different solvent environments (H2O and D2O). Results indicate that the flowing in situ system had a greater effect on the microstructural breakdown of TG relative to the acid-sensitive RG, compared to the traditional static method. This is the first in situ digestion study observing the structural changes of large protein gel particles with USANS or SANS in real-time. Our findings advance the understanding of the kinetics of casein gel disintegration under simulated conditions of gastric digestion relating to pepsin enzyme concentration and solvent environment, and critically, the utilisation of a new in situ and real-time setup for neutron studies.

Relationship between cathepsin K and total oxidative state in diabetes mellitus female patients with osteoporosis in Iraq

Introduction and Aim: Diabetes mellitus patients almost always struggle with a metabolic condition known as chronic hyperglycemia. According to the World Health Organization, osteoporosis is a progressive systemic skeletal disorder that is characterized by decreasing bone mass and microstructural breakdown of bone tissue that increases susceptibility to fracture and increased risk of breaking a bone. Here, we aimed to compare the levels of CatK and total oxidative state in patients with diabetes and osteoporosis among the female Iraqi population and study the possible relationship between them. Materials and Methods: This study included 40 females with diabetes (Group G1), 40 with diabetes and osteoporosis (Group G2) and 40 normal healthy females (Group G3) as controls. All participants were checked for their height, weight and BMI. Blood drawn from everyone was analyzed for fasting blood sugar, HbA1c, Cathepsin K, TOS, TAC and MDA. Data obtained was subjected to statistical analysis. Results: According to the findings, the levels of cathepsin K increased significantly (P 0.001) from Group 1 to Groups 2 and 3, as measured by their mean and standard deviation values. The results of total oxidant status, expressed as means and standard deviations (Mean SD), demonstrated a high significant (P 0.001) decline from group G1 to groups G2 and G3. Conclusion: Cathepsin K was observed to be linked to both type 2 diabetes and bone loss. In postmenopausal Iraqi women with type 2 diabetes, Cathepsin K may serve as a biomarker for both diabetes and osteoporosis.

Fully-resolved simulations of a sphere settling in an initially unstructured thixo-viscoplastic fluid

This paper investigates the settling of a single spherical particle immersed in an initially unstructured thixo-viscoplastic fluid. The phenomenon was numerically solved using the lattice Boltzmann method (LBM) for the mass and momentum transport equations, the immersed boundary method (IBM) for the particle dynamics, and the advection-diffusion LBM for the structural parameter transport equation. We utilized a simplified version of the Houska model to represent the rheological behavior of an inelastic thixo-viscoplastic material. The model evaluates the yield stress effects, which change based on a structural parameter, in the particle settling of an aging fluid. We fixed the particle properties (diameter, density) and varied the fluid rheological properties, such as the static and dynamic Bingham numbers and the build-up and breakdown numbers. Detailed fields of velocity, rate-of-strain, and structural parameters are presented to enrich the flow interpretation. The numerical results reveal that, for a thixotropic fluid, the classical viscoplastic critical yield number criterion does not correctly predict the condition for which the particle will become stationary. Although a higher dynamic yield stress will help the particle's stoppage, the microstructural breakdown has a powerful effect in facilitating its settling.

Influence of mechanical alloying on the particle size, microstructure and soft magnetic properties of coarse Fe-based amorphous powders prepared by gas atomization

The aim of this work is to refine the particle size of the coarse Fe-based amorphous powders by ball milling process without destroying the amorphous characteristics, thermal stability and soft magnetic properties. The gas atomized Fe-based amorphous powders were sieved, and the powders larger than 75 μm were selected as the raw materials. The effects of ball milling on the particle size, morphology, amorphous rate, thermal stability and soft magnetic properties of the Fe-based amorphous powders were systematically investigated. The results showed that the particle size of the Fe-based amorphous powders decreased as the ball milling time increased, and the mass median diameter (D50) of the powders was reduced by almost 80% after ball milling of 9 h compared with that of the initial powders (D50 reduced from 138.4 μm to 24.22 μm). The nanocrystallization and amorphization induced by the microstructural breakdown and intensified inter-diffusion of elements during the ball milling improved the amorphous rate of Fe-based powders. The ball milling reduced the saturation magnetization of the Fe-based amorphous powders, and had little effect on the coercivity. As a result, ball milling not only refined the particle size, but also improved the amorphous phase content of the Fe-based amorphous powders without changing the thermal stability and soft magnetic properties.

Shear-deformation based continuum-damage constitutive modeling of brain tissue

Traumatic brain injury (TBI) is a leading cause of death in the United States. Depending on the severity of injury, complications such as memory loss and emotional changes are common. While the exact mechanisms are still unclear, these cognitive deficiencies are thought to arise from microstructural damages to the brain tissue, such as in diffuse-axonal injury where neuron fibers are sheared. Constitutive models can predict such damage at a microstructural level and allow for insight into the mechanisms of injury initiating at lower length scales. In this study, we developed a continuum damage model of brain tissue that is validated by experimental quasi-static stress-strain tests in tension, compression, and shear. The present work shows that damage is most present in the shear stress state, making the tissue suitable for damage modeling via shear interaction terms. Using this model, new insights into microstructural breakdown due to shear stresses and strains can be gained by application to simulations.

Measuring cortical mean diffusivity to assess early microstructural cortical change in presymptomatic familial Alzheimer\u2019s disease

BackgroundThere is increasing interest in improving understanding of the timing and nature of early neurodegeneration in Alzheimer’s disease (AD) and developing methods to measure this in vivo. Autosomal dominant familial Alzheimer’s disease (FAD) provides the opportunity for investigation of presymptomatic change. We assessed early microstructural breakdown of cortical grey matter in FAD with diffusion-weighted MRI.MethodsDiffusion-weighted and T1-weighed MRI were acquired in 38 FAD mutation carriers (17 symptomatic, 21 presymptomatic) and 39 controls. Mean diffusivity (MD) was calculated for six cortical regions previously identified as being particularly vulnerable to FAD-related neurodegeneration. Linear regression compared MD between symptomatic and presymptomatic carriers and controls, adjusting for age and sex. Spearman coefficients assessed associations between cortical MD and cortical thickness. Spearman coefficients also assessed associations between cortical MD and estimated years to/from onset (EYO). Across mutation carriers, linear regression assessed associations between MD and EYO, adjusting for cortical thickness.ResultsCompared with controls, cortical MD was higher in symptomatic mutation carriers (mean ± SD CDR = 0.88 ± 0.39) for all six regions (p < 0.001). In late presymptomatic carriers (within 8.1 years of predicted symptom onset), MD was higher in the precuneus (p = 0.04) and inferior parietal cortex (p = 0.003) compared with controls. Across all presymptomatic carriers, MD in the precuneus correlated with EYO (p = 0.04). Across all mutation carriers, there was strong evidence (p < 0.001) of association between MD and cortical thickness in all regions except entorhinal cortex. After adjusting for cortical thickness, there remained an association (p < 0.05) in mutation carriers between MD and EYO in all regions except entorhinal cortex.ConclusionsCortical MD measurement detects microstructural breakdown in presymptomatic FAD and correlates with proximity to symptom onset independently of cortical thickness. Cortical MD may thus be a feasible biomarker of early AD-related neurodegeneration, offering additional/complementary information to conventional MRI measures.

The effect of heating rate on the microstructural breakdown required for thixoformability

AbstractThixoforming processes depend upon three basic features of the semisolid slurry: the thermodynamics of the liquid-to-solid transition; the morphology of the microstructure; and the slurry's rheological properties. By studying the thermodynamics of the solid-to-liquid transition of a specific alloy, one can determine whether the entire thixoforming process can be controlled when the alloy is used as the raw material. The rheology of the semisolid material is determined not only by the morphology of the microstructure of the primary solid phase immersed in the liquid, but also by the relative amounts of liquid and solid. In thixoforming operations the raw material is heated up to the semisolid state and injected into the die. Hence, the heating procedure has a significant impact on the morphology of the remaining solid and, consequently, its viscous behaviour, as shown in this paper. A heating rate close to 50 K min−1 was found to produce the most suitable morphology for semisolid processing as the mechanisms involved (Ostwald ripening and coalescence) were present to an equal extent.

Comparative viscoelasticity studies: Corn fiber gum versus commercial polysaccharide emulsifiers in bulk and at air/liquid interfaces

A comparative study of both the bulk and air/liquid interfacial rheological responses was carried out by using four kinds of representative high molecular weight and highly branched polysaccharide emulsifiers, (a) corn fiber gum (CFG), (b) octenyl succinate anhydride-modified starch (OSA-s), (c) gum arabic (GA) and (d) soybean soluble polysaccharides (SSPS), spanning the concentration range of 1–15 wt%. We found that the bulk and interfacial rheological properties of their aqueous solutions were significantly different. While both CFG and OSA-s showed Newtonian flow behavior at higher concentrations, both GA and SSPS exhibited obviously shear thinning behavior or thixotropy even at a low concentration of 1 wt%. The time-dependent flow behavior for CFG, GA and SSPS reflected microstructural breakdown and rebuilding in solutions under shear, indicated that their proteinaceous portion was strongly bound to their polysaccharide part. This phenomenon was not observed for the almost protein-free OSA-s. The interfacial rheology responses showed that the layers formed by CFG and OSA-s were viscously predominant with faster formation kinetics while they were elastically predominant for GA and SSPS with slower formation kinetics. Interfacial viscoelastic responses of CFG and OSA-s were weaker than those of GA and SSPS. By comparison, the interfacial layer for OSA-s showed pure viscous responses whereas SSPS showed the highest elastic responses. These significant disparities in bulk and interfacial viscoelasticity of the four polysaccharide emulsifiers reflect the influence of different fine chain structures on the dissimilarity in the intermolecular associations and the architectures of the interfacial layers.

Measurement of cortical mean diffusivity detects early microstructural breakdown of the cerebral cortex in presymptomatic familial Alzheimer’s disease

Measurement of cortical mean diffusivity detects early microstructural breakdown of the cerebral cortex in presymptomatic familial Alzheimer’s disease

Measurement of cortical mean diffusivity detects early microstructural breakdown of the cerebral cortex in presymptomatic familial Alzheimer’s disease

Measurement of cortical mean diffusivity detects early microstructural breakdown of the cerebral cortex in presymptomatic familial Alzheimer’s disease

Combined confocal microscopy and large deformation analysis of emulsion filled gels and stirred acid milk gels

Abstract The microstructural breakdown properties of heat-induced whey protein (WP) gels prepared at pH 7.0 or 5.4 and containing emulsified sunflower oil (7%, w/w) were studied using notch propagation tensile testing in combination with dynamic confocal laser scanning microscopy (CLSM). In addition, the microstructural breakdown properties of stirred acid milk gels containing added emulsified oil (0–15%, w/w) or Konjac glucomannan (0.05%, w/w) were studied using compressive rheological deformation in combination with dynamic CLSM imaging. The structural breakdown properties (Young's modulus and stress/strain at fracture), the microstuctural behaviour of the protein phase, the emulsified oil phase and the pattern of notch propagation during large deformation tensile testing of the WP emulsion filled gel prepared at pH 7.0 (fine stranded gel) differed from that of the WP emulsion filled gel prepared at pH 5.4 (particulate gel). The protein aggregates, emulsified oil droplets and the Konjac phase in the stirred acid milk gels flowed on compression; however, the flow pattern changed from “frictional” flow with no emulsified oil or Konjac to “slip” flow in the presence of emulsified oil or Konjac. Also, compression of stirred acid milk gels below a certain critical height led to disintegration of the aggregated protein structure, serum release and reduced stability of the oil droplets in the stirred gels. The critical compression height was influenced by emulsified oil level and the presence of added Konjac.

Effect of gamma irradiation on the physico-chemical and visual properties of mango (Mangifera indica L.), cv. ‘Dushehri’ and ‘Fazli’ stored at 20 °C

The effect of γ-irradiation doses (0.3, 0.5, 0.7, 1.0, 6.0, 10.0kGy) on different physico-chemical and visual properties of two Indian cultivars of mango, cv. ‘Dushehri’ and ‘Fazli’ was observed during storage at 20°C for the evaluation of delayed ripening and extension of shelf-life. Visually all the irradiated fruit showed greener peel and lighter pulp throughout the storage, however, radiation injuries were present in ‘Dushehri’ treated with 6–10kGy and in ‘Fazli’ with 1–10kGy. Loss of fruit due to rotting was less in the irradiated samples, treated up to 1kGy of both the cultivars. Irradiated fruit of both the cultivars at high doses (6–10kGy) showed increased sugar content from 0d, however, all the treated fruit registered a slower rate of increase of sugars with storage compared to the respective controls and those treated with the lower doses of 0.5 and 0.7kGy attained peak sugar concentration later. Significant (p≤0.05) textural deterioration could be detected immediately after irradiation, in ‘Dushehri’ at doses ≥1kGy and in ‘Fazli’ at doses ≥0.7kGy. However, low dose treated fruit (0.3–1kGy) of both the cultivars softened at a considerably slower rate during storage and registered significantly greater fruit firmness (compression strength) throughout the storage period. Similarly, ‘Dushehri’ treated with 0.3–0.7kGy and Fazli treated with 0.7kGy registered significantly greater flesh firmness (shear strength). ‘Dushehri’ treated with 0.3–1kGy and ‘Fazli’ with 0.5–1kGy also registered significantly harder and tougher peel, as determined by puncture test, throughout the storage. Scanning electron microscopy (SEM) performed on 3rd and 2nd d of storage of ‘Dushehri’ and ‘Fazli’ respectively, revealed microstructural breakdown at and above 1kGy in both cultivars. Cell separation could be observed in ‘Fazli’ even at 0.7kGy. SEM also revealed that the control fruit were in a more advanced stage of ripening than the low dose treated fruit. The study showed the feasibility of low dose γ-irradiation on ‘Dushehri’ (0.3–0.7kGy) and ‘Fazli’ (0.5 and 0.7kGy) that induced useful delay in ripening and extension of shelf-life by a minimum of 3 and 4d, respectively.

Constitutive modeling of the rate-dependent resilient and dissipative large deformation behavior of a segmented copolymer polyurea

Phase-separated segmented copolymers comprised of hard and soft segments can be tailored to offer hybrid mechanical performance including a highly dissipative yet resilient large strain behavior. The phase-separated morphology provides multiple relaxation processes which lead to a rate-dependent stress–strain behavior with a transition in rate sensitivity. In addition to the viscoelastic–viscoplastic dissipation pathways, stretch-induced softening due to microstructural breakdown provides a significant source of dissipation as evident in the hysteresis observed during cyclic loading. Extensive shape recovery is observed upon unloading, showing a highly resilient behavior in tandem with extensive dissipation. Here a microstructurally informed three-dimensional constitutive model is developed to capture the remarkable features of the large strain behavior of the segmented copolymers. The model employs multiple micro-rheological mechanisms to capture the time-dependent nonlinear constitutive responses of both hard and soft domains as well as the stretch-induced softening of the hard domains. In direct comparison to experimental data, the model is found to successfully capture the behavior of an exemplar polyurea copolymer over least six orders of magnitude in strain rate (10−3 to 103 s−1) including a transition in rate sensitivity at 1 s−1. The model is also shown to be predictive of the highly dissipative yet resilient stress–strain behavior under a variety of cyclic loading conditions. The microstructurally informed nature of the model provides insights into tailoring copolymeric microstructures to provide tunable energy storage and dissipation mechanisms in this important class of material.

Thames

Human Immunodeficiency Virus (HIV) and current stimulant abuse have both been shown to damage basal ganglia and hippocampus. While the effects of current stimulant abuse on neurological functioning is well- documented, whether residual damage can be detected in patients with a distant history of past stimulant abuse/ dependence remains to be understood. Given that past stimulant abuse is common among HIV-infected individuals; this is a question of considerable clinical significance. The present study employed Diffusion Tensor Imaging (DTI) and structural MRI to examine brain integrity (as measured by FA and MD) and volume in the basal ganglia (BG) and hippocampus among older HIV-infected adults with histories of stimulant abuse. Lower fractional anisotropy and greater diffusivity (representative of microstructural breakdown) in basal ganglia and hippocampal structures were documented among former stimulant abusers compared to stimulant-naive individuals. Length of abstinence was also associated with BG integrity, such that those with shorter abstinence periods demonstrated greater MD of the BG. Our findings suggest that past stimulant abuse is associated with neurological dysfunction, though this improves with increasing abstinence.

Rheological study of gum arabic solutions: Interpretation based on molecular self-association

This study deals with the rheological properties of aqueous solutions of gum arabic, the complex arabinogalactan polysaccharide containing about 2% protein. The flow behavior of control gum and a matured gum (EM2), which have different molecular associations, was investigated at different concentrations in water and added urea (6M) by rheological and dynamic light scattering methods. The influence of molecular association on rheological behavior of gum arabic solutions was studied. It was found that though Newtonian behavior was observed across a wide range of concentrations and at high shear rates, gum arabic solutions showed a pronounced shear thinning in low shear rate ranges. The maximum difference in viscosity between shear rate increasing and decreasing processes was observed at 6% for both control gum and EM2 in water, and at 3% for control gum and 9% for EM2 in urea solutions. The results demonstrated macromolecular association of gum arabic occurring in the solutions, and the observed time-dependent flow behavior reflected microstructural breakdown and re-building in the systems. This phenomenon was understood in view of the relationship between rheological properties and microstructural characteristics. A model was presented to interpret the rheological behavior, which is attributed to the occurrence of shear-induced breakdown and re-formation of gum arabic aggregates.

Numerical modelling of uniaxial compressive failure of granite with and without saline porewater

It is important for rock engineering design to be able to validate numerical simulations, i.e. to check that they adequately represent the rock reality. In this paper, the capability and validity of four numerical models is assessed through the simulation of an apparently simple case: the complete process of microstructural breakdown during the uniaxial compressive failure of intact crystalline rock. In addition to comparing the capabilities of the four models, the results generated by each model were compared with the experimentally determined complete stress–strain curves for the Swedish Ävrö granite for different porewater conditions. In this way, it has been possible to audit the models’ adequacy for this particular simulation task. It was found that although the models had common features, they were each idiosyncratically different and required considerable expertise to match the actual stress–strain curves (which did not monotonically increase in axial strain)—indicating that, for more complex simulations, both adequate modelling and appropriate validation are not going to be an easy task. The work was conducted within the framework of the international 2004–2007 DEmonstration of COupled models and their VALidation against EXperiments with emphasis on Thermo Hydro Mechanic and Chemical aspects (DECOVALEX-THMC) phase on coupled modelling extended to include chemical effects and with application to the excavation damaged zone (EDZ) in crystalline rock.

The effect of SiC particle reinforcement on the creep behavior of 2080 aluminum

The influence of SiC particle reinforcement on the creep behavior of 2080 aluminum is investigated between 150 °C and 350 °C. The effect of particle size (F-280, F-600, and F-1000), volume fraction (10, 20, and 30 vol pct), and heat treatment (T6 and T8) on creep behavior is studied. In both the T6 and T8 conditions all composites are less creep resistant than similarly heat-treated monolithic materials when crept at 150 °C. These results contradict continuum mechanics predictions for steady-state creep rate, which predict composite strengthening. A high dislocation density is observed near SiC particles. It is proposed that strain localization near the reinforcements leads to microstructural breakdown and the subsequent reduction in creep resistance. When both materials are severely overaged or when they are tested at very high temperatures (350 °C), composite materials exhibit improved creep resistance relative to monolithic material. In these cases, the strengthening is consistent with continuum predictions for direct composite strengthening.

Some microrheological aspects of wood-pulp fibres subjected to fatigue loading

Wood-pulp fibres are recognized as concentrically-layered, laminated composite tubes of structural reinforcing material, the cellulose microfibrils, embedded in a cementing matrix of hemicellulose and lignin. When the single fibres are subjected to cyclic mechanical action, their morphological behaviour is characterized by the fatigue growth of micro-voids and surface damage which individually and collectively give rise to stress concentrations, and eventually crack development. The progressive damage phenomena, evinced by the surface imaging and optical sectioning techniques through utilizing confocal laser scanning microscopy, are understood to be consequences of the cumulative material micromechanical degradation and subsequent microstructural breakdown of the cellulose microfibrillar framework. This structural breakdown is believed to effect the fibrillation and flexibilization of the fibres

Rheological, Mass Transfer, and Mixing Characterization of Cellulase-Producing Trichoderma reesei Suspensions

Steady and dynamic shear measurements are utilized to characterize the rheological behavior of Trichoderma reesei RUT-C30 fungal suspensions during batch growth on xylose (soluble substrate) or cellulose (particulate solid substrate) at three different fermentor impeller speeds (250, 400, and 550 rpm). Biomass concentrations versus time were unimodal on xylose and bimodal on cellulose. This behavior is consistent with relatively rapid, early growth on easily metabolized growth medium components (yeast extract), followed by a second, slower growth phase due to hydrolysis of recalcitrant cellulose by increasing cellulase concentrations. Critical dissolved oxygen (DO) concentration for T. reesei growth on cellulose was found to be 0.073 mmol/L. The DO was kept above this level by supplementing the air feed with pure oxygen, implying that mass transfer limitations were not the cause of bimodal cell growth. Steady shear rheological data showed shear thinning behavior and a yield stress for all broth samples regardless of substrate. Casson and Herschel−Bulkley constitutive equations fit steady shear data well. Dynamic shear measurements on broth suspensions indicated “gel-like” behavior at low strains, with microstructural breakdown at larger displacements. Time variations of the Casson model parameters (yield stress and Casson viscosity) and dynamic moduli (elastic and viscous modulus) followed both cell mass and morphology: a single maximum in all rheological variables resulted when cells were grown on xylose or on cellulose at impeller speeds of 400 or 550 rpm, and dual maxima were observed for cellulose-grown cells at 250 rpm.