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We numerically investigate the hydrodynamics of a spherical swimmer carrying a rigid cargo in a Newtonian fluid. This swimmer model, a ‘squirmer’, which is self-propelled by generating tangential surface waves, is simulated by a direct-forcing fictitious domain method (DF-FDM). We consider the effects of swimming Reynolds numbers (Re) (based on the radius and the swimming speed of the squirmers), the assembly models (related to the cargo shapes, the relative distances (ds) and positions between the squirmer and the cargo) on the assembly's locomotion. We find that the ‘pusher-cargo’ (pusher behind the cargo) model swims significantly faster than the remaining three models at the finite Re adopted in this study; the term ‘pusher’ indicates that the object is propelled from the rear, as opposed to ‘puller’, from the front. Both the ‘pusher-cargo’ and ‘cargo-pusher’ (pusher in front of the cargo) assemblies with an oblate cargo swim faster than the corresponding assemblies with a spherical or prolate cargo. In addition, the pusher-cargo model is significantly more efficient than the other models, and a larger ds yields a smaller carrying hydrodynamic efficiency η for the pusher-cargo model, but a greater η for the cargo-pusher model. We also illustrate the assembly swimming stability, finding that the ‘puller-cargo’ (puller behind the cargo) model is stable more than the ‘cargo-puller’ (puller in front of the cargo) model, and the assembly with a larger ds yields more unstable swimming.

Immiscible contaminants are commonly involved in naturally occurring suspensions. The resulting variations in their flow behavior have rarely been evaluated. Here, we investigate the variation in the viscosity of an oil-based two-phase suspension over a period of 2 years, which is exposed to the ambient air at the production stage. We find that the absolute humidity of air, which strongly varies with seasons, causes exchanges of water droplets with the suspension, substantially altering its shear-thinning behavior. Only in winter, when the humidity is low, is the latter close to that of the ideal two-phase suspensions. Our measurements suggest that when the surface roughness of the suspended solid particles is sufficiently low, immersed droplets remain in a free state, effectively increasing repulsion between particles, weakening shear thinning. In contrast, when the roughness is sufficiently high, immersed droplets become trapped on the particle surfaces, inducing an attractive particle interaction via water bridging, enhancing shear thinning.

Material mismatch between the welding bead and its surrounding matrix has been known to cause stress concentration due to incompatible deformation, and/or even crack regeneration, thus greatly affecting the performance of a welding repaired material. In this paper, a semi-analytical method (SAM) is developed to tackle problems for material mismatch in a welding repaired material with free surface under remote tensile loading. The heterogeneous welding bead is modeled by a homogeneous base material containing unknown eigenstrains through the equivalent inclusion method; after which a numerical discretization is adopted and the eigenstrains within each computational element are determined by iteratively solving a set of linear equations with the assistance of conjugate gradient method. Stress field arising from the eigenstrains can be obtained by employing previously derived influence coefficients. The SAM is then examined by a simple finite element model and utilized to analyze influences of material properties, aspect ratio, angle of differently shaped welding bead and interactions among multiple welding beads on the stress distribution. The SAM may have potential applications in dealing with problems related to residual stress in welded material due to eigenstrains.

Computational modeling and simulation of cellular blood ow is highly desirable for understanding blood microcirculation and blood-related diseases, such as anemia, thrombosis and tumor, but it remains a challenge because the blood requires to be described as a dense suspension of di_erent types of cells and the microvessels continually bifurcate or merge into a complex network. A smoothed dissipative particle dynamics-immersed boundary method (SDPD-IBM) has been developed, integrating the uid ow and cell behavior to simulate physiological and pathological phenomena involved in blood ow. The SDPD is used to model the uid ow, the IBM is used to model the interactions between the uid and cells, and three phenomena are taken into account, cell deformation, aggregation and adhesion. The simulations consist of two parts: validation studies for the _delity of the SDPD-IBM, and case studies for its potential Computational modeling and simulation of cellular blood ow is highly desirable for understanding blood microcirculation and blood-related diseases, such as anemia, thrombosis and tumor, but it remains a challenge because the blood requires to be described as a dense suspension of di_erent types of cells and the microvessels continually bifurcate or merge into a complex network. A smoothed dissipative particle dynamics-immersed boundary method (SDPD-IBM) has been developed, integrating the uid ow and cell behavior to simulate physiological and pathological phenomena involved in blood ow. The SDPD is used to model the uid ow, the IBM is used to model the interactions between the uid and cells, and three phenomena are taken into account, cell deformation, aggregation and adhesion. The simulations consist of two parts: validation studies for the _delity of the SDPD-IBM, and case studies for its potential and usefulness. The validation studies consider the ow of pure uid, the mechanical behavior of cells, and the multi-outlet cellular ow, while the case studies include cells passing through simple vessels, successive bifurcations, and even a complex microvascular network. These studies concern the formation of a thrombus, the partitioning of red blood cells, and the metastasis of tumor cells. The SDPD-IBM has special advantages in modeling uid ows in complex domains and with uid-structure interactions, because the SDPD is convenient to model a complex domain by discrete particles, while the IBM is exible to model the interactions between the uid and structures.and usefulness. The validation studies consider the ow of pure uid, the mechanical behavior of cells, and the multi-outlet cellular ow, while the case studies include cells passing through simple vessels, successive bifurcations, and even a complex microvascular network. These studies concern the formation of a thrombus, the partitioning of red blood cells, and the metastasis of tumor cells. The SDPD-IBM has special advantages in modeling uid ows in complex domains and with uid-structure interactions, because the SDPD is convenient to model a complex domain by discrete particles, while the IBM is exible to model the interactions between the uid and structures.

Over 60 million tons of aluminium are produced annually, requiring sustainable and eco-friendly recycling methods of aluminium waste. In this work, aluminium metal waste is utilized in the fabrication of aluminium hydroxide aerogels using a cost-effective and environmental-friendly process. The developed aerogels with varying contents of aluminium and poly(vinyl alcohol) as a binder exhibit a low density (0.060–0.108 g/cm3), a high porosity (92.3–95.5%) and a low electrical conductivity ([1.8–5.2] × 10–8 S/m). The results indicated that aluminium hydroxide aerogels have an ultra-low thermal conductivity of 0.028–0.032 W/m K and are able to withstand high temperature of 800 °C with less than 50% decomposition. It is suggested that the synthesized aerogels can be a promising candidate for high-value engineering applications such as thermal insulation of pipes and buildings to expand the usage of recycled aluminium.

We study the hydrodynamics of a spherical and dumbbell-shaped microswimmer in a tube. Combined with a squirmer model generating tangential surface waves for self-propulsion, a direct-forcing fictitious domain method is employed to simulate the swimming of the microswimmers. We perform the simulations by considering the variations of the swimming Reynolds numbers (Re), the blockage ratios (κ) and the relative distances (ds) between the squirmers of the dumbbell. The results show that the squirmer dumbbell weakens the inertia effects of the fluid more than an individual squirmer. The constrained tube can speed up an inertial pusher (propelled from the rear) and an inertia pusher dumbbell; a greater distance ds results in a slower speed of an inertial pusher dumbbell but a faster speed of an inertial puller (propelled from the front) dumbbell. We also illustrate the swimming stability of a puller (stable) and pusher (unstable) swimming in the tube at Re = 0. At a finite Re, we find that the inertia and the tube constraint competitively affect the swimming stability of the squirmers and squirmer dumbbells. The puller and puller dumbbells swimming in the tube become unstable with increasing Re, whereas an unstable–stable–unstable evolution is found for the pusher and pusher dumbbells. With increasing κ, the puller and puller dumbbells become stable while the pusher and pusher dumbbells become unstable. In addition, we find that a greater ds yields a higher hydrodynamic efficiency η of the inertial squirmer dumbbell.

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The perturbation technique based on the retardation-motion expansion is a simple method to obtain flow solutions at low Weissenberg number. In this context, this perturbation analysis is used to develop simple expressions for the motion of fibers suspended in viscoelastic fluids. In particular, the suspending fluid is characterized by a second-order fluid, Giesekus and PPT (Phan–Thien–Tanner) models, and their derivatives, such as the upper and lower convected Maxwell models. The first-order perturbation results in a similar effective velocity gradient that is exploited to express the translation and rotational motion of a single fiber and the associated extra stress tensor. In terms of a parameter related to the various viscoelastic fluid models, it is found that a fiber aligns along the vorticity direction when subjected to a shear flow. However, when a lower convected Maxwell model is considered, the elongated particle orients in the flow direction, as basically predicted by the Jeffery solution for a Newtonian suspending fluid. Furthermore, the conservation equation for particle concentration leads to particle migration in a pressure-driven flow channel and good agreement is observed with experimental data.

In the DPD simulation of particulate suspensions, the viscosity of the solvent phase is typically estimated by a non-equilibrium approach, where the fluid is subjected to a flow process (a shear flow), and the local stress and shear rate tensors are calculated; the obtained values (shear stress/shear rate) are then used in calculating the particulate fluid rheology, for example the ratio of the suspension to the matrix viscosity (reduced/relative viscosity) for a given volume fraction of the suspended phase. However, when suspended particles are added, an additional length scale is introduced into the solvent system and this may affect the solvent’s macroscopic properties. In this study, a particulate suspension is simulated using a spring model, and the solvent’s viscosity is estimated taking into account the finite-size effect (i.e., in the generalised hydrodynamic regime, as hydrodynamics of an integrable system) to produce improved results. Furthermore, it is observed that the simulation results are also affected by the repulsion strength and an appropriate high value of this coefficient, where the actual solvent viscosity in the hydrodynamic limit is still kept close to the input viscosity, can lead to a further improvement. New results are presented and compared with existing data.

The change of the rheological behavior of a bentonite suspension with the gap of the parallel-plate geometry in a rotational rheometer is investigated. An obvious gap-dependent behavior is found in both the gel and flowing states, based on which it is found that slip at the boundary plays an important role in the viscometric measurement at low shear rates, as well as in the small amplitude oscillatory shear experiment; shear banding is considered to take place at the vicinity of the yielding point, as well as in flows at low shear rates if the boundary slip is suppressed by using rough plates. Furthermore, relaxation behavior, similar to that of a polymeric system, is observed. The motion of the gel structure is slower with increasing gap, indicating a larger size of the networking structure. This is also the origin for the decrease of the yield stress observed with increasing gap.The change of the rheological behavior of a bentonite suspension with the gap of the parallel-plate geometry in a rotational rheometer is investigated. An obvious gap-dependent behavior is found in both the gel and flowing states, based on which it is found that slip at the boundary plays an important role in the viscometric measurement at low shear rates, as well as in the small amplitude oscillatory shear experiment; shear banding is considered to take place at the vicinity of the yielding point, as well as in flows at low shear rates if the boundary slip is suppressed by using rough plates. Furthermore, relaxation behavior, similar to that of a polymeric system, is observed. The motion of the gel structure is slower with increasing gap, indicating a larger size of the networking structure. This is also the origin for the decrease of the yield stress observed with increasing gap.

Congenital heart malformations occur to substantial number of pregnancies. Studies showed that abnormal flow biomechanical environments could lead to malformations, making it important to understand the biomechanical environment of the developing heart. We performed 4D high-frequency ultrasound scans of chick embryonic hearts at HH25 to study the biomechanics of the whole heart (atria and ventricle). A novel and high-fidelity motion estimation technique, based on temporal motion model and non-rigid image registration algorithm, allowed automatic tracking of fluid-structure boundaries from scan images, and supported flow simulations. Results demonstrated that atrial appendages were the most contractile portion of the atria, having disproportionately high contribution to atrial blood pumping for its volume in the atria. However, the atria played a small role in blood pumping compared to the ventricle, as it had much lower ejection energy expenditure, and as the ventricle appeared to be able to draw inflow from the veins directly during late diastole. Spatially and temporally averaged wall shear stresses (WSS) for various cardiac structures were 0.062–0.068 Pa, but spatial-averaged WSS could be as high as 0.54 Pa in the RV. WSS was especially elevated at the atrial inlet, atrioventricular junction, regions near to the outflow tract, and at dividing lines between the left and right atrium and left and right side of the ventricle, where septation had begun and the lumen had narrowed. Elevated WSS could serve as biomechanics stimulation for proper growth and development.

Millions of tons of plastic are produced annually, but less than 10% are reported to be recycled. This work sets out to transform environmental plastic (polyethylene terephthalate – PET) waste into aerogels for high-value engineering applications, primarily to enhance the monetary incentive in recycling plastics. Coating techniques, using silicone ceramic (SCC) and (3-aminopropyl)triethoxysilane (APS, or APTES) solutions, are successfully devised to enhance the thermal stability and CO2 adsorption capability of rPET aerogel. The rPET/SCC aerogel exhibits improved thermal stability (up to 600 °C), enhanced thermal insulation (thermal conductivity Kavg = [31.8–34.9] mW/m·K), hydrophobic characteristics (up to 144.7° in contact angle) and enhanced rigidity (Young modulus Eavg = [4.5–124.8] kPa), while maintaining an ultra-low density (ρa = [14–62] g/cm3) and a high porosity (Φavg = [95.6–99.0]%). Moreover, the amine-functionalised rPET aerogel achieves a CO2 adsorption capacity of up to 0.44 mmol CO2/g, superior to several commercial physio-sorbents. These promising results obtained demonstrate that the rPET aerogel is a versatile material suitable for a wide variety of high-value engineering applications, including thermal insulation and direct CO2 capture applications.

Over twenty million tons of pineapples have been produced annually worldwide, but their waste is mostly discarded or burnt after harvesting. In this work, the high-value added aerogels from the pin...

The hydrodynamic loads and wake dynamics of the ducted propeller in oblique flow are investigated by detached eddy simulation (DES), with particular emphasis on the characteristics of wake fields a...

For the first time, recycled car tire fibers (RCTF) shredded from car tire waste are developed successfully into a novel material, a rubber aerogel, using polyvinyl alcohol (PVA) and glutaraldehyde (GA) as crosslinkers through a cost-effective freeze-drying method. Its structure and main physical properties are investigated comprehensively for high-value applications, such as heat and sound insulation of buildings and oil spill spilling clean up. The rubber aerogel has ultra-low density (ρa = 0.035 – 0.145 g/cm3) and high porosity (Φavg = 84.31–96.20 %). With a simple but effective coating method with methoxytrimethylsilane (MTMS), both the interior and exterior of the whole rubber aerogel surface can be well coated, and the coated aerogel exhibits a super-hydrophobicity with a water contact angle of up to 134.4°. The rubber aerogel exhibits excellent heat insulation properties (Kavg = 0.035 – 0.047 W/m.K), very good thermal stability up to 500 °C, and significantly-enhanced rigidity up to a Young modulus of Eavg = 458.12 kPa, much larger than that of commercial Styrofoam. The rubber aerogel shows very good durability as it springs back to its original shape after compression tests. The rubber aerogel has a noise reduction coefficient (NRC) of 0.41 and performs approximately 10% better than commercial sound foam absorber at 2000–3000 Hz. The maximum oil absorbtion capacity of the rubber aerogel in this work is 19.3 g/g, very competitive to commercial sorbents. The fabrication method can also be scaled up for several other industrial applications, not limited to sound, heat and sorbent applications.

Graphic Abstract Tons of waste from residential, commercial and manufacturing activities are generated due to the growing population, urbanization and economic development, prompting the need for sustainable measures. Numerous ways of converting waste to aerogels, a novel class of ultra-light and ultra-porous materials, have been researched to tackle the issues of waste. This review provides an overview of the status of aerogels made from agricultural waste, municipal solid, and industrial waste focusing on the fabrication, properties, and applications of such aerogels. The review first introduced common methods to synthesize the aerogels from waste, including dispersion and drying techniques. Following that, numerous works related to aerogels from waste are summarized and compared, mainly focusing on the sustainability aspect of the processes involved and their contributions for environmental applications such as thermal insulation and oil absorption. Next, advantages, and disadvantages of the current approaches are analyzed. Finally, some prospective waste aerogels and its applications are proposed.

The embryonic outflow tract (OFT) eventually undergoes aorticopulmonary septation to form the aorta and pulmonary artery, and it is hypothesized that blood flow mechanical forces guide this process. We performed detailed studies of the geometry, wall motions, and fluid dynamics of the HH25 chick embryonic OFT just before septation, using noninvasive 4D high-frequency ultrasound and computational flow simulations. The OFT exhibited expansion and contraction waves propagating from proximal to distal end, with periods of luminal collapse at locations of the two endocardial cushions. This, combined with periods of reversed flow, resulted in the OFT cushions experiencing wall shear stresses (WSS or flow drag forces) with elevated oscillatory characteristics, which could be important to signal for further development of cushions into valves and septum. Furthermore, the OFT exhibits interesting double-helical flow during systole, where a pair of helical flow structures twisted about each other from the proximal to distal end. This coincided with the location of the future aorticopulmonary septum, which also twisted from the proximal to distal end, suggesting that this flow pattern may be guiding OFT septation.

Massive quantities of fly ash are produced worldwide from thermal power plants, posing a serious environmental threat due to their storage and disposal problems. In this study, for the first time, fly ash is converted into an advanced and novel aerogel through a green and eco-friendly process. The developed aerogel has a low density of 0.10–0.19 g cm−3, a high porosity of up to 90%, a low thermal conductivity of 0.042–0.050 W/mK, and a good sound absorption coefficient (noise reduction coefficient [NRC] value of 0.20–0.30). It also shows a high compressive Young’s modulus of up to 150 kPa. Therefore, the newly developed fly ash aerogel is a potential material for thermal and acoustic insulation applications, along with lightweight composites in automotive and aerospace applications.

Supramolecular hydrogels based on inclusion complexation between cyclodextrins (CDs) and polymers have attracted much interest because of their potential for biomedical applications. It is also attractive to incorporate stimuli-responsive properties into the system to create "smart" hydrogels. Herein, a poly(N-isopropylacrylamide) (PNIPAAm) star polymer with a β-CD core and an adamantyl-terminated poly(ethylene glycol) (Ad-PEG) polymer were synthesized. They self-assembled into a thermoresponsive pseudo-block copolymer through host-guest complexation and formed supramolecular micelles with the change in environment temperature. Subsequently, an injectable polypseudorotaxane-based supramolecular hydrogel was formed between α-CD and the PEG chains of the pseudo-block copolymer. The hydrogel had a unique network structure involving two types of supramolecular self-assemblies between cyclodextrins and polymers, that is, the host-guest complexation between β-CD units and adamantyl groups and the polypseudorotaxane formation between α-CD and PEG chains. We hypothesize that the dual supramolecular hydrogel formed at room temperature may be enhanced by increasing the temperature over the lower critical solution temperature of PNIPAAm because of the hydrophobic interactions of PNIPAAm segments. Furthermore, if the hydrogel is applied for sustained delivery of hydrophobic drugs, the copolymer dissolved from the hydrogel could micellize and continue to serve as micellar drug carriers with the drug encapsulated in the hydrophobic core. Rheological tests revealed that the hydrophobic interactions of the PNIPAAm segments could significantly enhance the strength of the hydrogel when the temperature increased from 25 to 37 °C. As compared to hydrogels formed by α-CD and PEG alone, the sustained release property of this thermoresponsive hydrogel for an anticancer drug, doxorubicin (DOX), improved at 37 °C. The hydrogel dissolved slowly and released the pseudo-block copolymer in the form of micelles that continued to serve as drug carriers with DOX encapsulated in the hydrophobic core, achieving a better cellular uptake and anticancer effect than free DOX controls, even in multidrug-resistant cancer cells. According to these findings, the dual supramolecular hydrogel developed in this work with remarkable thermoresponsive properties might have potential for sustained anticancer drug delivery with enhanced therapeutic effect in multidrug-resistant cancer cells.

An immersed boundary-lattice Boltzmann method is employed to simulate a squirmer (a classical self-propelled model) array swimming in a Newtonian fluid. The swimming Reynolds number Res is set in the range 0.05 ≤ Res ≤ 5 to study three typical arrays (i.e., the two-squirmer, triangular-squirmer, and quadrilateral-squirmer arrays) in their swimming speed, their power expenditure ( P), and their hydrodynamic efficiency ( η). Our results show that the two-pusher array with a smaller ds (the distance between the squirmers) yields a slower speed in contrast to the two-puller array, where a smaller ds yields a faster speed at Res ≥ 1 (“pusher” is propelled from the rear and “puller” from the front). The regular triangular-pusher (triangular-puller) array with θ = −60° (the included angle between the squirmers) swims faster (slower) than that with θ = 60°; the quadrilateral-pusher (quadrilateral-puller) array with model 2 swims faster (slower) than model 1 (the models are to be defined later). It is also found that a two-puller array with a larger ds is more likely to become unstable than that with a smaller ds. The triangular-puller array with θ = 60° is more likely to become unstable than that with θ = 60°; the quadrilateral-puller array with model 1 becomes unstable easier than that with model 2. In addition, a larger ds generally results in a less energy expenditure. A faster squirmer array yields a higher η, except for two extraordinarily puller arrays. A quantitative relation for η with ReU > 1 is obtained approximately, in that the increasing ratio of η is proportional to an exponent of the motion Reynolds number ReU.

In this paper, we show that a Dissipative Particle Dynamics (DPD) model of a viscous Newtonian fluid may actually produce a linear viscoelastic fluid. We demonstrate that a single set of DPD particles can be used to model a linear viscoelastic fluid with its physical parameters, namely the dynamical viscosity and the relaxation time in its memory kernel, determined from the DPD system at equilibrium. The emphasis of this study is placed on (i) the estimation of the linear viscoelastic effect from the standard parameter choice; and (ii) the investigation of the dependence of the DPD transport properties on the length and time scales, which are introduced from the physical phenomenon under examination. Transverse-current auto-correlation functions (TCAF) in Fourier space are employed to study the effects of the length scale, while analytic expressions of the shear stress in a simple small amplitude oscillatory shear flow are utilised to study the effects of the time scale. A direct mechanism for imposing the particle diffusion time and fluid viscosity in the hydrodynamic limit on the DPD system is also proposed.

Recycled polyethylene tetraphalate (rPET) fiber–silica aerogels are successfully developed from rPET fibers obtained from PET plastic bottle waste and tetraethoxysilane (TEOS). The rPET – silica aerogels are prepared through a direct gelation of silica on PET. rPET fibers are treated with dichloromethane to partially dissolve the fibers. The fibers are then dipped and allow to swell in TEOS/ethanol mixture, with the pH controlled to 2.5 using HCl to promote hydrolysis. After the acid hydrolysis, the pH was controlled to 7 with an ammonium hydroxide solution (NH4OH) to promote condensation. The surface modification is carried out in a trimethylchlorosilane (TMCS)/n-hexane solution and washed with n-hexane to dry at room temperature to prevent shrinkage. The developed rPET – silica aerogels exhibit super-hydrophobicity with an average water contact angle of 149.9°. Their thermal conductivity is approximately 0.037 W/m K. They have a very low compressive Young’s Modulus (0.95–4.19 kPa) and hence very soft. By utilizing rPET fibers, this work provides an alternative method of recycling PET plastic wastes which ultimately helps in reducing its detrimental impact to the environment. The developed aerogels can be used in several industrial applications such as heat insulation, filtering, sound insulation and absorption.

The dynamics of Newtonian and pseudoplastic yield-stress fluid drops impacting on solid surfaces are studied numerically by the many body dissipative particle dynamics (MDPD) method. The pseudoplastic yield stress fluid is modelled by two groups of different MDPD particles, in which the parameters are tuned so that the overall fluid behaves in a similar manner to the Herschel–Bulkley pseudoplastic material in simple shear flow. The droplet characteristics are measured by its central drop diameter and its height, and an effective unyielded region is observed in the drop impacting process. The MDPD simulation results compare well with previous drop impact experiments and simplified theoretical studies on the slump test, serving to demonstrate the capability of the MDPD method to explore yield-stress fluid drop’s flow processes.

The Schmidt number effect on the rheology of finitely extensible nonlinear elastic chains (FENE) in many-body dissipative particle dynamics (MDPD) is investigated in this work. We find that the Schmidt number, ranging from (101) to (103), has limited influence on the polymer properties, such as its radius of gyration (Rg), diffusion coefficient (D) and relaxation time (τ). The simulation results follow Zimm model's predictions well. The hydrodynamic interaction strength parameter h* demonstrates that the full hydrodynamic interaction can be simulated for Schmidt number from (100-106) in MDPD. Next, the rheology of FENE polymers is studied using Lees-Edward boundary condition in shear flow. The shear-thinning and normal stress difference are measured and analysed with MDPD; meanwhile, the volume fraction, solvent quality and chain length are varied to explore their effects on the extent of the Newtonian region. Finally, the non-Newtonian droplet is firstly simulated in MDPD. Its maximum spreading d...

The changes in the mechanical properties of a cell are not only the cause of some diseases, but can also be a biomarker for some disease states. In recent times, microfluidic devices with built-in constrictions have been widely used to measure these changes. The transit time in such devices, defined as the time that a cell takes to pass through a constriction, has been found to be a crucial factor associated with the cell mechanical properties. Here, we use smoothed dissipative particle dynamics (SDPD), a particle-based numerical method, to explore the relationship between the transit time and mechanical properties of a cell. Three expressions of the transit time are developed from our simulation data, with respect to the stenosed size of constrictions, the shear modulus and bending modulus of cells, respectively. We show that a convergent constriction (the inlet is wider than the outlet), and a sharp-corner constriction (the constriction outlet is narrow) are better in identifying the differences in the transit time of cells. Moreover, the transit time increases and gradually approaches a constant as the shear modulus of cells increases, but increases first and then decreases as the bending modulus increases. These results suggest that the mechanical properties of cells can indeed be measured by analyzing their transit time, based on the recommended microfluidic device.

Haemostatic devices can exert internal pressure to promote blood clotting and reduce blood flow, potentially reducing mortality rates of gunshot wounds or other deeply penetrating wounds. For the first time, cotton aerogels have been successfully developed from commercial cotton fibers. The developed cotton aerogels can be compressed to form aerogel pallets which can be used for haemostatic devices. The effects of various cotton fiber concentrations, their morphology and chitosan concentrations on volume expansion ratio, expansion time and hydrostatic pressure of the hybrid cotton aerogels are investigated comprehensively. The chitosan-coated cellulose-cotton aerogel pallets having 0.7 wt% of the fibers, with cellulose-cotton ratio of 1:2 and 0.5 wt% of the coated chitosan showed excellent haemostatic performance. The volume expansion ratio of 16.0, expansion time of 4.5 s and hydrostatic pressure of 11.5 mmHg of each aerogel pallet are much better than those of commercial haemostatic sponges. The developed cotton-based aerogels have several potential applications such as haemostatic devices, stopping serious liquid leakage, oil-spill cleaning, personal care and heat and sound insulation applications.

A nanoporous rubber aerogel (NRA) is fabricated successfully using recycled textile fibers (RTFs) from car tire wastes, polyvinyl alcohol (PVA) via freeze-drying. The NRA exhibits a low density (down to 0.025 g/cm3), a high porosity (up to 98%), a robust mechanical property with the compressive resistance at 10% deformation above 20 kPa, a high oil-absorption capacity (up to 18 g/g), low thermal conductivity (down to 35 mW/m-K), and a high noise reduction coefficient (NRC value of up to 0.55). In our study, the production time is reduced significantly from 48 h to 17 h compared to previous works. More importantly, the central composite design and response surface methodology are applied to investigate the effect of the RTFs and PVA contents on the volume shrinkage, density, porosity, compressive resistance, oil absorption capacity, and thermal conductivity. As a result, it is found that the contents of RTFs and PVA should be in the range of high-level (4.0–5.0 wt%) and low-level (1.0–1.5 wt%), respectively. In addition, the effect of thicknesses and compositions on the sound absorption property of the NRA is further discussed using the analysis of variance (ANOVA). A higher noise reduction coefficient (NRC) is attained at a large thickness for compositions 1 (5.0 wt% RTFs, 1 wt% PVA). The sound absorption coefficient of the NRA in the high frequencies (1000–6000 Hz) is relatively high, and for the low- and medium frequencies (125–1000 Hz) relatively low. As a result, the NRA can be a potential candidate for oil-spill cleaning, heat-insulating and sound absorbing applications.

Recently, our direct numerical simulations [Yuan et al., “Hydrodynamic interaction and coalescence of two inline bubbles rising in a viscoelastic liquid,” Phys. Fluids 33, 083102 (2021)] indicated that a stable chain can be formed for a pair of bubbles rising in a viscoelastic liquid, consistent with experimental observations. Motivated by the fact that the flow in bubble chains is still poorly understood, this Letter extends the investigations to multiple small bubbles ascending in a vertical file in a viscoelastic medium with different configurations. With an increasing bubble number, it is found that the rising velocity of the bubble group increases and the vertical chain of bubbles becomes unstable due to the distinct oscillation of the uppermost bubble. The terminal separation distance between two adjacent bubbles decreases in the upward direction, diminished by the neighborhood rising bubbles due to increasing loading. By probing the polymeric stresses and deformation, our results demonstrated that the accumulation of viscoelastic normal stresses promotes the aggregation of rising bubbles, while the successive chain of bubbles is stable because of the near-field repulsion induced by the non-monotonic polymer stretching among the bubble chain. In addition, the large bubble deformation appears to enhance the accumulative polymeric normal stress effect, and the bubbles can form more stable vertical chains at increasing initial spacing. Our findings provide insights into the mechanism of bubbles clustering in viscoelastic fluids, as chaining of bubbles is believed to be more prevailing in highly elastic flows.

In the mesoscale simulations by the dissipative particle dynamics (DPD), the motion of a fluid is modelled by a set of particles interacting in a pairwise manner, and it has been shown to be governed by the Navier–Stokes equation, with its physical properties, such as viscosity, Schmidt number, isothermal compressibility, relaxation and inertia time scales, in fact its whole rheology resulted from the choice of the DPD model parameters. In this work, we will explore the response of a DPD fluid with respect to its parameter space, where the model input parameters can be chosen in advance so that (i) the ratio between the relaxation and inertia time scales is fixed; (ii) the isothermal compressibility of water at room temperature is enforced; and (iii) the viscosity and Schmidt number can be specified as inputs. These impositions are possible with some extra degrees of freedom in the weighting functions for the conservative and dissipative forces. Numerical experiments show an improvement in the solution quality over conventional DPD parameters/weighting functions, particularly for the number density distribution and computed stresses.

Viscometric properties of polymer are explored by the many-body dissipative particle dynamics (MDPD) using Lees–Edwards boundary conditions. The equation of state for the MDPD system is modified by...

Past literature has provided evidence that a normal mechanical force environment of blood flow may guide normal development while an abnormal environment can lead to congenital malformations, thus warranting further studies on embryonic cardiovascular flow dynamics. In the current study, we developed a non-invasive 4D high-frequency ultrasound technique, and use it to analyze cardiovascular organ dynamics and flow dynamics. Three chick embryos at stage HH25 were scanned with high frequency ultrasound in cine-B-mode at multiple planes spaced at 0.05 mm. 4D images of the heart and nearby arteries were generated via temporal and spatial correlation coupled with quadratic mean ensemble averaging. Dynamic mesh CFD was performed to understand the flow dynamics in the ventricle of the 2 hearts. Our imaging technique has sufficiently high resolution to enable organ dynamics quantification and CFD. Fine structures such as the aortic arches and details such as the cyclic distension of the carotid arteries were captured. The outflow tract completely collapsed during ventricular diastole, possible serving the function of a valve to prevent regurgitation. CFD showed that ventricular wall shear stress (WSS) were in the range of 0.1-0.5 Pa, and that the left side of the common ventricle experienced lower WSS than the right side. The pressure gradient from the inlet to the outlet of the ventricle was positive over most of the cardiac cycle, and minimal regurgitation flow was observed, despite the absence of heart valves. We developed a new image-based CFD method to elucidate cardiac organ dynamics and flow dynamics of embryonic hearts. The embryonic heart appeared to be optimized to generate net forward flow despite the absence of valves, and the WSS environment appeared to be side-specific.

Dissipative particle dynamics (DPD) and smoothed dissipative particle dynamics (sDPD) have become most popular numerical techniques for simulating mesoscopic flow phenomena in fluid systems. Several DPD/sDPD simulations in the literature indicate that the model fluids should be designed with their dynamic response, measured by the Schmidt number, in a relevant range in order to reach a good agreement with the experimental results. In this paper, we propose a new dissipative weighting function (or a new kernel) for the DPD (or the sDPD) formulation, which allows both the viscosity and the Schmidt number to be independently specified as input parameters. We also show that some existing dissipative functions/kernels are special cases of the proposed one, and the imposed viscosity of the present DPD/sDPD system has a lower and upper limit. Numerical verification of the proposed function/kernel is conducted in viscometric flows.