Recent Progresses in Eco-Friendly Fabrication and Applications of Sustainable Aerogels from Various Waste Materials.

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.

A novel aerogel from thermal power plant waste for thermal and acoustic insulation applications.

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.

Thermoresponsive Hydrogel Induced by Dual Supramolecular Assemblies and Its Controlled Release Property for Enhanced Anticancer Drug Delivery.

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 ß-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 ß-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.

The key events of thrombus formation: platelet adhesion and aggregation.

Thrombus formation is a complex, dynamic and multistep process, involving biochemical reactions, mechanical stimulation, hemodynamics, and so on. In this study, we concentrate on its two crucial steps: (i) platelets adhered to a vessel wall, or simply platelet adhesion, and (ii) platelets clumping and arrested to the adherent platelets, named platelet aggregation. We report the first direct simulation of three modes of platelet adhesion, detachment, rolling adhesion and firm adhesion, as well as the formation, disintegration, arrestment and consolidation of platelet plugs. The results show that the bond dissociation in the detachment mode is mainly attributed to a high probability of rupturing bonds, such that any existing bond can be quickly ruptured and all bonds would be completely broken. In the rolling adhesion, however, it is mainly attributed to the strong traction from the shear flow or erythrocytes, causing that the bonds are ruptured at the trailing edge of the platelet. The erythrocytes play an important role in platelet activities, such as the formation, disintegration, arrestment and consolidation of platelet plugs. They exert an aggregate force on platelets, a repulsion at a near distance but an attraction at a far distance to the platelets. This aggregate force can promote platelets to form a plug and/or bring along a part of a platelet plug causing its disintegration. It also greatly influences the arrestment and consolidation of platelet plugs, together with the adhesive force from the thrombus.

Cellulose-based aerogels from sugarcane bagasse for oil spill-cleaning and heat insulation applications.

A promising and economic material for various applications, such as thermal insulation in construction building and oil clean-up in marine ecosystems, is successfully developed from the by-product of the sugarcane industry. Biodegradable sugarcane bagasse aerogels are produced using polyvinyl alcohol (PVA) binder, followed by a freeze-drying method. This environmental-friendly recycled aerogel has an ultra-low density ([0.016-0.112] g/cm3), a high porosity ([91.9-98.9]%), and a very low thermal conductivity ([0.031-0.042] W/mK). Its superhydrophobicity properties and its maximum oil absorption capacity (up to 25 g/g) are measured after coating aerogel samples with methyltrimethoxysilane (MTMS). The biodegradable aerogel has a Young's modulus of 88 K Pa and can be bent without breaking, demonstrating its high flexibility.

Organ Dynamics and Hemodynamic of the Whole HH25 Avian Embryonic Heart, Revealed by Ultrasound Biomicroscopy, Boundary Tracking, and Flow Simulations.

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.

Applications of functionalized polyethylene terephthalate aerogels from plastic bottle waste.

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.

Fluid dynamics and forces in the HH25 avian embryonic outflow tract.

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.

Numerical design of a microfluidic chip for probing mechanical properties of cells.

Microfluidic chips have been widely used to probe the mechanical properties of cells, which are recognized as a promising label-free biomarker for some diseases. In our previous work (Ye et al., 2018), we have studied the relationships between the transit time and the mechanical properties of a cell flowing through a microchannel with a single constriction, which potentially forms a basis for a microfluidic chip to measure cell's mechanical properties. Here, we investigate this microfluidic chip design and examine its potential in performances. We first develop the simultaneous dependence of the transit time on both the shear and bending moduli of a cell, and then examine the chip sensitivity with respect to the cell mechanical properties while serializing a single constriction along the flow direction. After that, we study the effect of the flow velocity on the transit time, and also test the chip's ability to identify heterogeneous cells with different mechanical properties. The results show that the microfluidic chip designed is capable of identifying heterogeneous cells, even when only one unhealthy cell is included. The serialization of chip can greatly increase the chip sensitivity with respect to the mechanical properties of cells. The flow with a higher velocity helps in not only promoting the chip throughput, but also in providing more accurate transit time measurements, because the cell prefers a symmetric deformation under a high velocity.

Quantifying Vascular Distribution and Adhesion of Nanoparticles with Protein Corona in Microflow.

The protein corona has emerged as an important determinant of biological response in nanoparticle (NP) drug delivery. However, there is presently no reported study on how the protein corona affects the behavior of NPs in microflow and its subsequent interactions with the vascular endothelium, which could affect their delivery to the target tumor site regardless of its targeting mechanism. Furthermore, a consensus on the role of physical and surface characteristics of NPs in affecting the margination of NPs is lacking due to different methods of quantifying margination. In this study, we examine how the particle adhesion (PA) method and particle distribution (PD) method quantify the margination of 20, 40, 100, and 200 nm polystyrene NPs (pNPs) differently in fibronectin or pluronic F-127-coated microfluidic straight channels. We found that PA reduced with increasing pNP size, whereas the PD was similar across all pNP sizes regardless of channel coating. We then formed a protein corona on all pNPs (pNPs-PC) and found that the protein corona increased the adhesion of 40-200 nm pNPs in fibronectin-coated channels, with no size dependence between them except for 40 nm, which had significantly higher particle adhesion. The PA method was also dependent on channel coating, whereas the PD method was independent of channel coating. These results suggested that the PA method was more amenable to surface interactions between the pNPs and the channel wall while providing a measure of the amount of NPs that interacted with the channel walls, whereas the PD method provided a representation of their distribution across the channel due to margination. The two methods complement each other to elucidate a more holistic understanding of how different factors might affect a NP's margination in future studies.

Relationship between transit time and mechanical properties of a cell through a stenosed microchannel.

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.

Advanced Recycled Polyethylene Terephthalate Aerogels from Plastic Waste for Acoustic and Thermal Insulation Applications.

This work presents for the first time, a simple, practical and scalable approach to fabricating recycled polyethylene terephthalate (rPET) aerogels for thermal and acoustic insulation applications. The rPET aerogels were successfully developed from recycled PET fibers and polyvinyl alcohol (PVA) and glutaraldehyde (GA) cross-linkers using a freeze-drying process. The effects of various PET fiber concentrations (0.5, 1.0 and 2.0 by wt.%), fiber deniers (3D, 7D and 15D) and fiber lengths (32 mm and 64 mm) on the rPET aerogel structures and multi-properties were comprehensively investigated. The developed rPET aerogels showed a highly porous network structure (98.3⁻99.5%), ultra-low densities (0.007⁻0.026 g/cm³), hydrophobicity with water contact angles of 120.7⁻149.8°, and high elasticity with low compressive Young's modulus (1.16⁻2.87 kPa). They exhibited superior thermal insulation capability with low thermal conductivities of 0.035⁻0.038 W/m.K, which are highly competitive with recycled cellulose and silica-cellulose aerogels and better than mineral wool and polystyrene. The acoustic absorption results were also found to outperform a commercial acoustic foam absorber across a range of frequencies.

Red blood cell motion and deformation in a curved microvessel.

The flow of cells through curved vessels is often encountered in various biomedical and bioengineering applications, such as red blood cells (RBCs) passing through the curved arteries in circulation, and cells sorting through a shear-induced migration in a curved channels. Most of past numerical studies focused on the cell deformation in small straight microvessels, or on the flow pattern in large curved vessels without considering the cell deformation. However, there have been few attempts to study the cell deformation and the associated flow pattern in a curved microvessel. In this work, a particle-based method, smoothed dissipative particle dynamics (SDPD), is used to simulate the motion and deformation of a RBC in a curved microvessel of diameter comparable to the RBC diameter. The emphasis is on the effects of the curvature, the type and the size of the curved microvessel on the RBC deformation and the flow pattern. The simulation results show that a small curved shape of the microvessel has negligible effect on the RBC behavior and the flow pattern which are similar to those in a straight microvessel. When the microvessel is high in curvature, the secondary flow comes into being with a pair of Dean vortices, and the velocity profile of the primary flow is skewed toward the inner wall of the microvessel. The RBC also loses the axisymmetric deformation, and it is stretched first and then shrinks when passing through the curved part of the microvessel with the large curvature. It is also found that a pair of Dean vortices arise only under the condition of De>1 (De is the Dean number, a ratio of centrifugal to viscous competition). The Dean vortices are more easily observed in the larger or more curved microvessels. Finally, it is observed that the velocity profile of primary flow is skewed toward the inner wall of curved microvessel, i.e., the fluid close to the inner wall flows faster than that close to the outer wall. This is contrary to the common sense in large curved vessels. This velocity skewness was found to depend on the curvature of the microvessel, as well as the viscous and inertial forces.

Organ Dynamics and Fluid Dynamics of the HH25 Chick Embryonic Cardiac Ventricle as Revealed by a Novel 4D High-Frequency Ultrasound Imaging Technique and Computational Flow Simulations.

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.

Hybrid smoothed dissipative particle dynamics and immersed boundary method for simulation of red blood cells in flows.

In biofluid flow systems, often the flow problems of fluids of complex structures, such as the flow of red blood cells (RBCs) through complex capillary vessels, need to be considered. The smoothed dissipative particle dynamics (SDPD), a particle-based method, is one of the easy and flexible methods to model such complex structure fluids. It couples the best features of the smoothed particle hydrodynamics (SPH) and dissipative particle dynamics (DPD), with parameters having specific physical meaning (coming from SPH discretization of the Navier-Stokes equations), combined with thermal fluctuations in a mesoscale simulation, in a similar manner to the DPD. On the other hand, the immersed boundary method (IBM), a preferred method for handling fluid-structure interaction problems, has also been widely used to handle the fluid-RBC interaction in RBC simulations. In this paper, we aim to couple SDPD and IBM together to carry out the simulations of RBCs in complex flow problems. First, we develop the SDPD-IBM model in details, including the SDPD model for the evolving fluid flow, the RBC model for calculating RBC deformation force, the IBM for treating fluid-RBC interaction, and the solid boundary treatment model as well. We then conduct the verification and validation of the combined SDPD-IBM method. Finally, we demonstrate the capability of the SDPD-IBM method by simulating the flows of RBCs in rectangular, cylinder, curved, bifurcated, and constricted tubes, respectively.

Particle-based simulations of red blood cells-A review.

Particle-based methods have been increasingly attractive for solving biofluid flow problems, because of the ease and flexibility in modeling complex structure fluids afforded by the methods. In this review, we focus on popular particle-based methods widely used in red blood cell (RBC) simulations, including dissipative particle dynamics (DPD), smoothed particle hydrodynamics (SPH), and lattice Boltzmann method (LBM). We introduce their basic ideas and formulations, and present their applications in RBC simulations which are divided into three classes according to the number of RBCs in the simulation: a single RBC, two or multiple RBCs, and RBC suspension. Furthermore, we analyze their advantages and disadvantages. On weighing the pros and cons of the methods, a combination of the immersed boundary (IB) method and some forms of smoothed dissipative particle hydrodynamics (SDPD) methods may be required to deal effectively with RBC simulations.

Concentration dependence of yield stress and dynamic moduli of kaolinite suspensions.

The concentration dependence of yield stress and dynamic moduli of kaolinite suspensions is studied. Complex electrostatic interactions between kaolinite platelets promote a more liquid-like behavior, with clay particles changing from attractive interactions to a face-face repulsive interaction as the mass fraction of clay particles increases. A yield stress model is developed based on the repulsive interaction between disk-shaped particles, which yields a good prediction of experimental observations when repulsive face-face interaction is dominant. The critical concentration when attractive interaction changes completely to face-face repulsive interaction is estimated from the theory. Four regions are identified in the variation of yield stress as a function of the concentration.

Stretching and relaxation of malaria-infected red blood cells.

The invasion of red blood cells (RBCs) by malaria parasites is a complex dynamic process, in which the infected RBCs gradually lose their deformability and their ability to recover their original shape is greatly reduced with the maturation of the parasites. In this work, we developed two types of cell model, one with an included parasite, and the other without an included parasite. The former is a representation of real malaria-infected RBCs, in which the parasite is treated as a rigid body. In the latter, where the parasite is absent, the membrane modulus and viscosity are elevated so as to produce the same features present in the parasite model. In both cases, the cell membrane is modeled as a viscoelastic triangular network connected by wormlike chains. We studied the transient behaviors of stretching deformation and shape relaxation of malaria-infected RBCs based on these two models and found that both models can generate results in agreement with those of previously published studies. With the parasite maturation, the shape deformation becomes smaller and smaller due to increasing cell rigidity, whereas the shape relaxation time becomes longer and longer due to the cell's reduced ability to recover its original shape.

Rotation of a spheroid in a Couette flow at moderate Reynolds numbers.

The rotation of a single spheroid in a planar Couette flow as a model for simple shear flow is numerically simulated with the distributed Lagrangian multiplier based fictitious domain method. The study is focused on the effects of inertia on the orbital behavior of prolate and oblate spheroids. The numerical orbits are found to be well described by a simple empirical model, which states that the rate of the spheroid rotation about the vorticity axis is a sinusoidal function of the corresponding projection angle in the flow-gradient plane, and that the exponential growth rate of the orbit function is a constant. The following transitions in the steady state with increasing Reynolds number are identified: Jeffery orbit, tumbling, quasi-Jeffery orbit, log rolling, and inclined rolling for a prolate spheroid; and Jeffery orbit, log rolling, inclined rolling, and motionless state for an oblate spheroid. In addition, it is shown that the orbit behavior is sensitive to the initial orientation in the case of strong inertia and there exist different steady states for certain shear Reynolds number regimes.