Molecular dynamics simulation of the flow mechanism of shear-thinning fluids in a microchannel

Shear-thinning fluids have been widely used in microfluidic systems,but their internal flow mechanism is still unclear.Therefore,in this paper,molecular dynamics simulations are used to study the laminar flow of shear-thinning fluid in a microchannel.We validated the feasibility of our simulation method by evaluating the mean square displacement and Reynolds number of the solution layers.The results show that the change rule of the fluid system's velocity profile and interaction energy can reflect the shear-thinning characteristics of the fluids.The velocity profile resembles a top-hat shape,intensifying as the fluid's power law index decreases.The interaction energy between the wall and the fluid decreases gradually with increasing velocity,and a high concentration of non-Newtonian fluid reaches a plateau sooner.Moreover,the velocity profile of the fluid is related to the molecule number density distribution and their values are inversely proportional.By analyzing the radial distribution function,we found that the hydrogen bonds between solute and water molecules weaken with the increase in velocity.This observation offers an explanation for the shear-thinning phenomenon of the non-Newtonian flow from a micro perspective.

Mixing of miscible shear-thinning fluids in a lid-driven cavity

The concentration and velocity fields of two refractive index matched miscible shear-thinning fluids in a lid-driven cavity were investigated by using planar laser-induced fluorescence and particle image velocimetry,as well by computational fluid dynamics.Quantitative analyses show that the results obtained by flow simulations with the species transport model are in good agreement with the experimental results.The effects of different parameters were studied by using the intensity of segregation.For two fluids with the same rheological parameters,the relative amounts of liquids H_(1)/H and the power-law index n dominate the mixing process while the Reynolds number Re plays a marginal role.As for two fluids with density difference,buoyancy has significant influence on the mixing process.The dimensionless group Ar/Re(redefined such as to include shear thinning behavior)is proposed for assessing the effect of buoyancy and rheological properties on the mixing of miscible shear-thinning fluids.

Nanoengineered Shear-Thinning Hydrogel Barrier for Preventing Postoperative Abdominal Adhesions

More than 90%of surgical patients develop postoper-ative adhesions,and the incidence of hospital re-admissions can be as high as 20%.Current adhesion barriers present limited efficacy due to difficulties in application and incompatibility with minimally invasive interventions.To solve thisclinical limitation,we developed an injectable and sprayable shear-thinning hydrogel barrier(STHB)composed of silicate nanoplatelets and poly(ethylene oxide).We optimized this technology to recover mechanical integrity after stress,enabling its delivery though inject-able and sprayable methods.We also demonstrated limited cell adhesion and cytotoxicity to STHB compositions in vitro.The STHB was then tested in a rodent model of peritoneal injury to determine its e cacy preventing the formation of postoperative adhesions.After two weeks,the peritoneal adhesion index was used as a scoring method to determine the formation of postoperative adhesions,and STHB formulations presented superior e cacy compared to a commercially available adhesion barrier.Histological and immunohistochemical examination showed reduced adhesion formation and minimal immune infiltration in STHB formulations.Our technology demonstrated increased e cacy,ease of use in complex anatomies,and compatibility with di erent delivery methods,providing a robust universal platform to prevent postoperative adhesions in a wide range of surgical interventions.

Shear-thinning behavior of the CaO–SiO2–CaF2–Si3N4 system mold flux and its practical application

Satisfying the mold-flux performance requirements for high-speed continuous casting necessitates the development of a new non-Newtonian-fluid mold flux with shear-thinning behavior, i.e., a mold flux whose viscosity is relatively high under lower shear rates and relatively low under higher shear rates. In this work, a mold flux that exhibits shear-thinning behavior was developed by adding different amounts of Si_3N_4 to the CaO–SiO_2–CaF_2 mold flux. The shear-thinning behavior was investigated using a rotational viscometer. In addition, the microstructure of the newly prepared slags was studied by high-temperature Raman spectroscopy and X-ray photoelectron spectroscopy. The results showed that the mechanism of shear-thinning was attributable to a temporary viscosity loss caused by the one-way shear stress, whereas the corresponding magnitude of shear-thinning was closely related to the degree of polymerization(DP). Finally, the non-Newtonian fluid mold flux was used for laboratory casting tests, which revealed that the mold flux could reduce slag entrapment and positively affect the continuous casting optimization.

A quasi-zero-stiffness isolator with a shear-thinning viscous damper

Quasi-zero-stiffness(QZS)vibration isolators have been widely studied,because they show excellent high static and low dynamic stiffnesses and can effectively solve low-frequency and ultralow-frequency vibration.However,traditional QZS(T-QZS)vibration isolators usually adopt linear damping,owing to which achieving good isolation performance at both low and high frequencies is difficult.T-QZS isolators exhibit hardening stiffness characteristics,and their vibration isolation performance is even worse than that of linear vibration isolators under a large excitation amplitude.Therefore,this study proposes a QZS isolator with a shear-thinning viscous damper(SVD)to improve the vibration isolation performance of the T-QZS isolators.The force-velocity relation of the SVD is obtained,and a dynamic model is established for the isolator.The dynamic responses of the system are solved using the harmonic balance method(HBM)and the Runge-Kutta method.The vibration isolation performance of the system is evaluated using force transmissibility,and the isolator parameters are analyzed.The results show that compared with the T-QZS isolators,the proposed QZS-SVD isolator achieves the lower initial vibration isolation frequency and peak value,and exhibits better vibration isolation performance at medium and high frequencies.Moreover,the proposed isolator can withstand a large excitation amplitude in the effective vibration isolation range.

A shear-thinning,ROS-scavenging hydrogel combined with dental pulp stem cells promotes spinal cord repair by inhibiting ferroptosis

Spinal cord injury(SCI)is a serious clinical disease.Due to the deformability and fragility of the spinal cord,overly rigid hydrogels cannot be used to treat SCI.Hence,we used TPA and Laponite to develop a hydrogel with shear-thinning ability.This hydrogel exhibits good deformation,allowing it to match the physical properties of the spinal cord;additionally,this hydrogel scavenges ROS well,allowing it to inhibit the lipid peroxidation caused by ferroptosis.According to the in vivo studies,the TPA@Laponite hydrogel could synergistically inhibit ferroptosis by improving vascular function and regulating iron metabolism.In addition,dental pulp stem cells(DPSCs)were introduced into the TPA@Laponite hydrogel to regulate the ratios of excitatory and inhibitory synapses.It was shown that this combination biomaterial effectively reduced muscle spasms and promoted recovery from SCI.

Unsteady Flow of Shear-Thinning non-Newtonian Incompressible Fluid Through a Twin-Screw Extruder

The unsteady flow of viscous incompressible shear-thinning non-Newtonian fluid with mixed bound- ary is investigated. The boundary condition on the outflow is the modified natural boundary condition, it con- tains the additional nonlinear term, which enables us to control the kinetic energy of the backward flow. The global existence of weak solution is proved. The fictitious domain method which consists in filling the moving rigid screws with the surrounding fluid and taking into account the boundary conditions on these bodies by introducing a well-chosen distribution of boundary forces is used.

Easily-injectable shear-thinning hydrogel provides long-lasting submucosal barrier for gastrointestinal endoscopic surgery

Submucosal injection material has shown protective effect against gastrointestinal injury during endoscopic surgery in clinic.However,the protective ability of existing submucosal injection material is strictly limited by their difficult injectability and short barrier time.Herein,we report a shear-thinning gellan gum hydrogel that simultaneously has easy injectability and long-lasting barrier function,together with good hemostatic property and biocompatibility.Shear-thinning property endows our gellan gum hydrogel with excellent endoscopic injection performance,and the injection pressure of our gellan gum hydrogel is much lower than that of the small molecule solution(50 wt%dextrose)when injected through the endoscopic needle.More importantly,our gellan gum hydrogel shows much stronger barrier retention ability than normal saline and sodium hyaluronate solution in the ex vivo and in vivo models.Furthermore,our epinephrine-containing gellan gum hydrogel has a satisfactory hemostatic effect in the mucosal lesion resection model of pig.These results indicate an appealing application prospect for gellan gum hydrogel utilizing as a submucosal injection material in endoscopic surgery.

On the Motion of Shear-Thinning Heat-Conducting Incompressible Fluid-Rigid System

The full Navier-Stokes-Fourier system with mixed boundary condition that describes the motion of shear-thinning and incompressible viscous fluid in a rotating multi-screw extruder is investigated. The viscosity is assumed to depend on the shear rate and the temperature. The global existence of suitable weak solutions is established. The fictitious domain method which consists in filling the moving rigid screws with the surrounding fluid and taking into account the boundary conditions on these bodies by introducing a well-chosen distribution of boundary forces is used.

Partial Regularity of Suitable Weak Solutions to the System of the Incompressible Shear-thinning Flow

This paper is devoted to the partial regularity of suitable weak solutions to the system of the incompressible shear-thinning flow in a bounded domainΩ■R^(n),n≥2.It is proved that there exists a suitable weak solution of the shear-thinning fluid in the n-D smooth bounded domain(for n≥2).For 3 D model,it is proved that the singular points are concentrated on a closed set whose 1 dimensional Hausdorff measure is zero.

Rheological properties of polymer micro-gel dispersions

The influence of swelling time, temperature, NaCl concentration and polymer micro-gel concentration on rheological properties of polymer micro-gel dispersions was studied by using a HAAKE rheometer. The results showed that with increasing swelling time and NaCl concentration, the polymer micro-gel dispersions changed from a shear-thickening fluid to a Newtonian fluid. The polymer micro-gel dispersion show shear-thinning in non-saline water. At higher swelling temperature, the time of the polymer micro-gel dispersion showing shear-thickening was shorter. With increasing polymer micro-gel concentration, the dispersion changed from shear-thickening to shear-thinning.

On the Study of Magneto-Hydrodynamic Non-Newtonian Fluid Flow throughout Curvilinear Channel with Corrugated Walls

This article aims to numerically investigate the flow pattern for Newtonian and power law non-Newtonian fluid in a semi-half circular channel with corrugated walls under the influence of a magnetic field. The results indicate that, presence of a magnetic field affects the flow field in several aspects, especially in the vortex creation and dissipation. In addition, the analysis is carried out for different Reynolds numbers to ascertain the influence of magnetic field on each flow regime. Eventually, the analysis is carried out for a range of power indices including pseudo plastic (shear-thinning) to dilatants (shear-thickening) fluids. The results show that by increasing the power-index, the vortices begin to form and grow gradually so that in the shear-thickening fluid an extra vortex is formed and created nearby the corrugated part of the channel.

THE UNIQUE PROPERTIES OF THE SOLID-LIKE CONFINED LIQUID FILMS:A LARGE SCALE MOLECULAR DYNAMICS SIMULATION APPROACH

The properties of the confined liquid are dramatically different from those of the bulk state, which were reviewed in the present work. We performed large-scale molecular dynamics simulations and full-atom nonequilibrium molecular dynamics simulations to investigate the shear response of the confined simple liquid as well as the n-hexadecane ultrathin films. The shear viscosity of the confined simple liquid increases with the decrease of the film thickness. Apart from the well-known ordered structure, the confined n-hexaxiecane exhibited a transition from 7 layers to 6 in our simulations while undergoing an increasing shear velocity. Various slip regimes of the confined n-hexadecane were obtained. Viscosity coefficients of individual layers were examined and the results revealed that the local viscosity＇coefficient varies with the distance from the wall. The individual n-hexadecane layers showed the shear-thinning behaviors which can be correlated with the occurrence of the slip. This study aimed at elucidating the detailed shear response of the confined liquid and may be used in the design and application of microand nano-devices.

Simulation of Power-Law Fluid Flows in Two-Dimensional Square Cavity Using Multi-Relaxation-Time Lattice Boltzmann Method

In this paper,the power-law fluid flows in a two-dimensional square cavity are investigated in detail with multi-relaxation-time lattice Boltzmann method(MRTLBM).The influence of the Reynolds number(Re)and the power-law index(n)on the vortex strength,vortex position and velocity distribution are extensively studied.In our numerical simulations,Re is varied from 100 to 10000,and n is ranged from 0.25 to 1.75,covering both cases of shear-thinning and shear-thickening.Compared with the Newtonian fluid,numerical results show that the flow structure and number of vortex of power-law fluid are not only dependent on the Reynolds number,but also related to power-law index.

Effect of Antibacterial Enoxacin on the Properties of Injectable Nano-hydroxyapatite/Polyurethane Cement for Bone Repairing

Biomaterial-associated infection(BAI)is a kind of serious post-operative complication in orthopaedic surgery.Antibiotic-loaded bone cement shines a light on BAI prevention for convenient manipulation and complex filling.To this aim,we designed an antibacterial bone cement based on Nano-hydroxyapatite/Polyurethane(PUHA)loading with antibiotic Enoxacin(EN).The distinct shear-thinning behavior of the prepolymers was observed,indicating a good injectability.The PUHA bone cement possessed a suitable curing speed,and the addition of EN might slightly expedite the curing process and enhance the mechanical properties.The EN release profile indicated that the EN-loaded bone cement could reach the minimum inhibitory concentration in 2 h,and sustainedly released EN for almost 8 days,exhibiting an antibacterial delivery potential.Antibacterial test further confirmed the antibacterial ability of EN-loaded bone cement is in a dose-dependent manner.However,the osteogenic performance of drug-loaded bone cement with high dosage is not as good as antibacterial activity.When the EN concentration of antibacterial cement was lower than 32μg·mL^(-1),the proliferation and osteogenic differentiation of rat mesenchymal stem cells could be significantly promoted.Overall,this study verified the potential of the EN-loaded PUHA bone cement in anti-infection and osteogenesis for bone repairing.