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Significance: Imaging biofluid flow under physiologic conditions aids in understanding disease processes and health complications. We present a method employing a microparallel plate strain induction chamber (MPPSIC) amenable to optical coherence tomography to track depth-resolved lateral displacement in fluids in real time while under constant and sinusoidal shear. Aim: Our objective is to track biofluid motion under shearing conditions found in the respiratory epithelium, first validating methods in Newtonian fluids and subsequently assessing the capability of motion-tracking in bronchial mucus. Approach: The motion of polystyrene microspheres in aqueous glycerol is tracked under constant and sinusoidal applied shear rates in the MPPSIC and is compared with theory. Then 1.5 wt. % bronchial mucus samples considered to be in a normal hydrated state are studied under sinusoidal shear rates of amplitudes 0.7 to 3.2 s−1. Results: Newtonian fluids under low Reynolds conditions (Re∼10−4) exhibit velocity decreases directly proportional to the distance from the plate driven at both constant and oscillating velocities, consistent with Navier–Stokes’s first and second problems at finite depths. A 1.5 wt. % mucus sample also exhibits a uniform shear strain profile. Conclusions: The MPPSIC provides a new capability for studying biofluids, such as mucus, to assess potentially non-linear or strain-rate-dependent properties in a regime that is relevant to the mucus layer in the lung epithelium.

Significance: The onset of several diseases is frequently marked with anomalous mechanical alteration of the affected tissue at the intersection of cells and their microenvironment. Therefore, mapping the micromechanical attributes of the tissues could enhance our understanding of the etiology of human disease, improve the diagnosis, and help stratify therapies that target these mechanical aberrations. Aim: We review the tremendous opportunities offered through using optics for imaging the micromechanical properties, at length scales inaccessible to other modalities, in both basic research and clinical medicine. We specifically focus on laser speckle rheology (LSR), a technology that quantifies the mechanical properties of tissues in a rapid, noncontact manner. Approach: In LSR, the shear viscoelastic modulus is measured from the time-variant speckle intensity fluctuations reflected off the tissue. The LSR technology is engineered and configured into several embodiments, including bench-top optical systems, endoscopes for minimally invasive procedures, portable point-of-care devices, and microscopes. Results: These technological nuances have primed the LSR for widespread applications in diagnosis and therapeutic monitoring, as demonstrated here, in cardiovascular disease, coagulation disorders, and tumor malignancies. Conclusion: The fast-paced technological advancements, elaborated here, position the LSR as a competent candidate for many more exciting opportunities in basic research and medicine.

Hypothesis Due to their highly retentive properties, innovative recently developed, semi-interpenetrated hydrogels made up of poly(vinyl pyrrolidone) (PVP) chains embedded in a poly(2-hydroxyethyl methacrylate) (p(HEMA)) network should be efficiently used as cleaning material for fragile and degraded paper artworks. In restoration practice, indeed the wet cleaning of these artworks is usually performed by immersion of paper in water, a procedure which may lead to several drawbacks, including paper fibers swelling and dissolution of water-soluble original components. Experiments This class of gels were yet presented in literature, but their interactions with paper materials and ability to be spiked with active enzymes (as cleaning agents), have not been analyzed. To establish the suitability of these hydrogels as paper cleaning materials, first, a rheological and microstructural characterization of the gels was performed. Moreover, diffusion of macromolecules inside gels was studied using fluorescence microscopy, to check if these innovative hydrogels can be used as carriers for hydrolytic enzymes. Indeed, pastes and glues are usually found in old paper artworks, and their removal is a very delicate operation that requires a selective action, which is granted by specific hydrolytic enzymes. At the same time, spectroscopic analyses on paper samples under investigation before and after cleaning treatment has been performed, thus assessing the capabilty of these gels as cleaning materials. Findings With the aim of demonstrating the versatility of these hydrogels, several case studies, i.e., the removal of grime and water-soluble cellulose degradation byproducts, the removal of animal glue and the removal of starch paste from real samples, are presented. Results obtained with these gels have been compared to those obtained by using another gel used for paper artworks cleaning, i.e., Gellan gel.

The production processes of the pulp and paper industry often run in campaigns, leading to large variations in the composition of wastewaters and waste sludges. During anaerobic digestion (AD) of these wastes, the viscosity or the production of extracellular polymeric substances (EPS) and soluble microbial products (SMP) may be affected, with the risk of foam formation, inefficient digester mixing or poor sludge dewaterability. The aim of this study was to investigate how viscosity and production of EPS and SMP during long-term AD of pulp and paper mill sludge is affected by changes in organic loading rate (OLR) and hydraulic retention time (HRT). Two mesophilic lab-scale continuous stirred tank reactors (CSTRs) were operated for 800 days (R1 and R2), initially digesting only fibre sludge, then co-digesting fibre sludge and activated sludge. The HRT was lowered, followed by an increase in the OLR. Reactor fluids were sampled once a month for rheological characterization and analysis of EPS and SMP. The production of the protein fraction of SMP was positively correlated to the OLR, implicating reduced effluent qualities at high OLR. EPS formation correlated with the magnesium content, and during sulphate deficiency, the production of EPS and SMP increased. At high levels of EPS and SMP, there was an increase in viscosity of the anaerobic sludges, and dewatering efficiency was reduced. In addition, increased viscosity and/or the production of EPS and SMP were important factors in sludge bulking and foam formation in the CSTRs. Sludge bulking was avoided by more frequent stirring. Electronic supplementary material The online version of this article (10.1007/s00449-019-02224-4) contains supplementary material, which is available to authorized users.

Significance: Noninvasive in vivo fast pulsatile blood flow measurement in deep tissue is important because the blood flow waveform is correlated with physiological parameters, such as blood pressure and elasticity of blood vessels. Compromised blood flow may cause diseases, such as stroke, foot ulcer, and myocardial ischemia. There is great clinical demand for a portable and cost-effective device for noninvasive pulsatile blood flow measurement. Aim: A diffuse-optics-based method, diffuse speckle pulsatile flowmetry (DSPF), was developed for fast measurement (∼300 Hz) of deep tissue blood flow noninvasively. To validate its performance, both a phantom experiment and in vivo demonstration were conducted. Approach: Over the past two decades, single-mode fibers have been used as detection fibers in most diffuse-optics-based deep tissue blood flow measurement modalities. We used a multimode (MM) detection fiber with a core size of 200 μm for diffused speckle pattern detection. A background intensity correction algorithm was implemented for speckle contrast calculation. The MM detection fiber helped to achieve a level of deep tissue blood flow measurement similar to that of conventional modalities, such as diffuse correlation spectroscopy and diffuse speckle contrast analysis, but it increases the measurement rate of blood flow to 300 Hz. Results: The design and implementation of the DSPF system were introduced. The theory of the background intensity correction for the diffused speckle pattern detected by the MM fiber was explained. A flow phantom was built for validation of the performance of the DSPF system. An in vivo cuff-induced occlusion experiment was performed to demonstrate the capability of the proposed DSPF system. Conclusions: An MM detection fiber can help to achieve fast (∼300 Hz) pulsatile blood flow measurement in the proposed DSPF method. The cost-effective device and the fiber-based flexible probe increase the usability of the DSPF system significantly.

Coating of antibacterial layer on the surface of cellulosic paper has numerous potential applications. In the present work, sodium alginate (SA) served as a binder to disperse Zn 2+ and the prepared zinc oxide (ZnO) particles were used as antibacterial agents. The rheology test revealed that there were cross-linking between Zn 2+ and SA molecular chains in the aqueous solution, resulting in the viscosity of ZnO/SA composite coating increased in the low shear rate region and decreased in the high shear rate region as compared with pure SA. SEM and EDS mapping images showed that the ZnO particles were prepared successfully at 120 °C and dispersed homogeneously on the surface of cellulose fibers and the pores of cellulosic papers. The thermal stabilities of the coated papers decreased as compared to the original blank cellulosic paper, which was ascribed to the low thermal stability of SA and the catalytic effect of ZnO on SA. The tensile stress and Young’s modulus of ZnO/SA composite coated paper increased up 39.5% and 30.7%, respectively, as compared with those of blank cellulosic paper. The antibacterial activity tests indicated that the ZnO/SA composite coating endowed the cellulosic paper with effectively growth inhibition of both Gram-negative bacteria E. coli and Gram-positive bacteria S. aureu .

The synthesis of carboxymethylcellulose was investigated using effluents containing short cellulose fibers. Car-boxymethylcellulose was synthesized according to the slurry process using different amount of sodium hydroxideand different incubation times at 30◦C after the etherification reaction as variables. Characterization of the prod-uct was conducted by Fourier transformed infrared spectroscopy, X-ray diffraction, degree of substitution, averagedegree of polymerization, water imbibing capacity, color, rheological properties, apparent viscosity and trace ele-ments content. Incubation time slightly increased the yield of the reaction and the degree of substitution duringthe first 12 h. The reaction yield and degree of substitution both decreased when the initially concentration of NaOHwas increased from 7.0 g/mL to 10.5 g/mL. The carboxymethylcellulose obtained was darker and had lower hydrationproperties than commercial samples. Trace elements content suggests that the product could be only used in paintfactories or building materials industries., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Centro de Investigación y Desarrollo en Criotecnología de Alimentos, Facultad de Ciencias Exactas

The process of dried blood spot sampling involves simultaneous spreading and penetration of blood into a porous filter paper with subsequent evaporation and drying. Spreading of small drops of blood, which is a non-Newtonian liquid, over a dry porous layer is investigated from both theoretical and experimental points of view.A system of two differential equations is derived, which describes the time evolution of radii of both the drop base and the wetted region inside the porous medium. The system of equations does not include any fitting parameters. The predicted time evolutions of both radii are compared with experimental data published earlier.For a given power law dependency of viscosity of blood with different hematocrit level, radii of both drop base and wetted region, and contact angle fell on three universal curves if appropriate scales are used with a plot of the dimensionless radii of the drop base and the wetted region inside the porous layer and dynamic contact angle on dimensionless time. The predicted theoretical relationships are three universal curves accounting satisfactorily for the experimental data.

Flow monitoring in porous materials is critical for the engineering of paper-based microfluidic bioassays. Here, we present an electrochemical-sensor system that monitors the liquid flow in porous materials without affecting the real flow in paper-strip samples. The developed microfluidic sensor records an amperometric signal created by the solution movement mediated by paper wicking. This approach allows the in situ monitoring of the different hydrodynamic conditions of a specific paper geometry or composition. In addition, the method proposed in this work was employed to characterise the fluid flow of different nitrocellulose paper strips after oxygen-plasma treatment or dextran coating. The dextran fluid-flow modifiers were further used on the paper strip-based assays as means of signal enhancement. The proposed electrochemical-sensing method offers a valuable alternative to existing optical-based monitoring techniques for flow measurement in paper-based microfluidic systems.

The removal of old glue from paper artworks is of paramount importance for the preservation of its integrity during the restoration process. Wet cleaning is one of the traditional methods, although it may cause damages on artworks. In this work, an advantageous alternative method, based on the use of a rigid hydrogel, for a simple and localized removal of starch paste from paper supports is presented. The use of an appropriate hydrogel allows to overcome many of the problems faced by restorers minimizing damages, through a controlled release of water to the artwork, and a simple and not invasive application and removal. At the same time, the specific and targeted enzyme activity leads to a significant reduction in the application time of the cleaning procedure. In this context, experiments were carried out applying Gellan hydrogel carrying α-amylase enzyme on several paper samples soiled with starch paste. To assess the cleaning efficacy of the proposed hydrogel, we have used a multidisciplinary approach, by means of spectroscopic techniques, scanning electron microscopy, chromatographic analysis, and pH investigations.

A numerical tool has been developed for particle-level simulations of fibre suspension flows, particularly forming of the fibre network structure of paper sheets in the paper machine. The model considers inert fibres of various equilibrium shapes, and finite stiffness, interacting with each other through normal, frictional, and lubrication forces, and with the surrounding fluid medium through hydrodynamic forces. Fibre–fluid interactions in the non-creeping flow regime are taken into account, and the two-way coupling between the solids and the fluid phases is included by enforcing momentum conservation between phases. The incompressible three-dimensional Navier–Stokes equations are employed tomodel themotion of the fluid medium. The validity of the model has been tested by comparing simulation results with experimental data from the literature. It was demonstrated that the model predicts well the motion of isolated fibres in shear flow over a wide range of fibre flexibilities. It was also shown that the model predicts details of the orientation distribution of multiple, straight, rigid fibres in a sheared suspension. Furthermore, model predictions of the shear viscosity and first normal stress difference were in fair agreement with experimental data found in the literature. Since the model is based solely on first principles physics, quantitative predictions could be made without any parameter fitting. Based on these validations, a series of simulations have been performed to investigate the basic mechanisms responsible for the development of the stress tensor components for monodispersed, non-Brownian fibres suspended in a Newtonian fluid in shear flow. The effects of fibre aspect ratio, concentration, and inter-particle friction, as well as the tendency of fibre agglomeration, were examined in the nonconcentrated regimes. For the case of well dispersed suspensions, semi-empirical relationships were found between the aforementioned fibre suspension properties, and the steady state apparent shear viscosity, and the first/second normal stress differences. Finally, simulations have been conducted for the development of paper structures in the forming section of the paper machine. The conditions used for the simulations were retrieved from pilot-scale forming trial data in the literature, and from real pulp fibre analyses. Dewatering was simulated by moving two forming fabrics toward each other through a fibre suspension. Effects of the jet-to-wire speed difference on the fibre orientation anisotropy, the mass density distribution, and three-dimensionality of the fibre network, were investigated. Simulation results showed that the model captures well the essential features of the forming effects on these paper structure parameters, and also posed newquestions on the conventional wisdom of the forming mechanics.

Most of the water fed into a paper machine is removedmechanically in the forming and press sections. One of thefactor which has an important influence on mechanicaldewatering, i.e. in both forming and pressing, is thestress-strain behaviour of the fibre network. The focus of this thesis is on the development of improvedmathematical descriptions of the stress-strain behaviourexhibited by fibre networks in the forming and press sections.The first part of the thesis presents a physically based modelof the forming and densification of fibre mats in twin-wireformers. The model can calculate the ecect of the applicationof a varied load through the forming section. It was developedfrom mass and momentum balances of the fibre and liquid phases,the fibre mat stress-porosity relation and an expression forthe permeability as a function of the porosity. The fibre-matstress-porosity relation used is rate-independent and presentshysteresis. Simulations have been conducted to study theeffects of roll pressure, blade pulses, wire tension andbeating. The effect of sequential blade pressure pulses afterthe forming roll on the dewatering and the concentrationgradients could be characterised. The simulations alsoexhibited rewetting by expansion when the fibre mats left theforming roll. Increasing wire tension resulted in increaseddewatering, but the rate of increase diminished rapidly withincreasing tension. The simulation results also indicated thatbeating has a large influence on dewatering. The second part of the thesis presents two models of therate-dependent stress-strain behaviour of the fibre networkthat is observed in wet pressing. The first model was based onthe approach pioneered by Perzyna (1966) for strain-ratedependent plasticity and was quite satisfactory for calculatingthe stress-strain behaviour of the fibre network in singlepress nips. It was successfully applied for studyingdensification and dewatering in both normal wet pressing andhigh temperature wet pressing. However, the first model onlyincludes rate dependence in the compression phase of thecompressionexpansion cycle; the expansion phase is treated asbeing rate independent The second model of the stress-strain behaviour of the fibrenetwork treats both compression and expansion as being ratedependent, according to experimental observations. It is basedon the idea that the wet fibre web may be conceived as alayered network of restricted swelling gels. A swollen fibre isa restricted gel, the inner swelling pressure in a swollenfibre wall being balanced by the stresses in the fibre wallstructure. The observed rate dependence of wet webs in bothcompression and expansion phases was attributed to the flow ofwater out of and into the fibre walls. The second model gavepredictions that are in good agreement with results fromuniaxial experiments using pressure pulses of arbitrary shapefor both a single pulse and a sequence of pulses. It maytherefore be used as a general model for the rheologicalbehaviour of the wet fibre network in wet pressing, providedthe model parameters are estimated from experimental data withsmall experimental error. KEYWORDS:Paper, modelling, dewatering, forming, wetpressing, fibre network stress, rheology, hysteresis,intra-fibre water, compressibility, structural stress,stress-strain, restricted gels, swelling. QC 20161026

To achieve higher productivity in papermaking, the increasing of web speed is the most efficient way. However, velocity increase will also immediately cause greater demands according to the web strength. In normal papermaking process, the form of the web changes gradually through the forming and press sections from suspension to solid form. After the press section, the basic fiber structure of the paper has already been created, but its rheological properties are in the beginning state of their development. Due to the water removal method by pressing the wet fiber network against a press roll surface, an adhesion force is generated between the web and the surface. At the end of the press section, the strength of the web is still very low due to the web's great moisture content. At this point, the mechanical properties of the paper can be affected or even deteriorated by wrong web peeling methods. For this reason, the understanding and controlling of the adhesional behaviour of the web is essential especially in the cases of high velocity levels. This paper studies the adhesional behaviour of the open draw, which is usually the first time during the papermaking process when the wet web is stressed mechanically in the longitudinal direction. This behaviour is studied by a quasi-dynamic mathematical model, which includes force balance and continuity models and also a rheological model for the open draw and material properties of the web respectively. The model consists of steady-state and nonsteady-state portions. Time-dependency is applied through mass flow and rheological equations, force balance equation is in static form. The solving method for this coupled equation system is to first solve the ideal steady-state situation and, after this nonsteady-stale equations which can be solved by using the steady-state situation as an initial condition. The qualitative behaviour of this model is correct, for example the increase in peeling angle between the surface and the web can be observed in cases of both velocity increase and adhesion energy increase even if the relative speed difference of the open draw has remained constant. Limitations appear mainly in the correctness of web material, adhesion and external pressure parameters. However, by using this model, also the effects of such external disturbances as adhesion and pressure disturbances can be studied efficiently. One of the main results is also an exponential increase in the peeling angle as a function of velocity. In this paper, it is caused by the centripetal force affecting the web. As a conclusion, the peeling behaviour of the wet web in an open draw is a very sensitive system. The main advantage of this system is its capability to self-adjustment through changes of the mass flow rate and peeling angle. However, also the rheological properties of the web and the adhesion force itself play a significant role in the optimization and stabilization of the web transfer in an open draw.

The rheological nature of paper or board is usually treated either as elasto-plastic or as viscoelastic depending on the studied paper making process or behavior in converting and end use. In this paper we study several stress–strain curve models and the determination of material parameters from an elasto-plastic point of view. Finally, a suitable approach for all stress–strain curves measured from 180 strips is constructed using a linear function for an elastic region and a nonlinear function for a strain hardening region. This model determines a proportional limit (elastic limit) and gives fairly elegant dependencies between material/fitting parameters and two important factors of mechanical properties of paper: dry solids content and anisotropy. In this paper the dependency of a plastic strain on dry solids content and anisotropy is estimated using the introduced stress–strain curve model. Correspondingly, the model can be used to estimate many other mechanical behaviors, for example, the tension differences arising from non-uniform moisture content of the paper web profile. However, the main target of this study is to produce competent parameters based on modeled stress–strain curves for further construction of a material model. This elasto-plastic material model will be utilized in out-of-plane deformation and fracture models.