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1. Red blood cell hitchhiking enhances the accumulation of nano- and micro-particles in the constriction of a stenosed microvessel

   https://doi.org/10.1039/D0SM01637C  

   Ye, Huilin; Shen, Zhiqiang; Wei, Mei; Li, Ying (January 2021, Soft Matter)

   null (Ed.)

   We investigate the circulation of nano- and micro-particles, including spherical particles and filamentous nanoworms, with red blood cells (RBCs) suspension in a constricted channel that mimics a stenosed microvessel. Through three-dimensional simulations using the immersed boundary-based Lattice Boltzmann method, the influence of channel geometries, such as the length and ratio of the constriction, on the accumulation of particles is systematically studied. Firstly, we find that the accumulation of spherical particles with 1 μm diameter in the constriction increases with the increases of both the length and ratio of the constriction. This is attributed to the interaction between spheres and RBCs. The RBCs “carry” the spheres and they accumulate inside the constriction together, due to the altered local hydrodynamics induced by the existence of the constriction. Secondly, nanoworms demonstrate higher accumulation than that of spheres inside the constriction, which is associated with the escape of nanoworms from RBC clusters and their accumulation near the wall of main channel. The accumulated near-wall nanoworms will eventually enter the constriction, thus enhancing their concentration inside the constriction. However, an exceptional case occurs in the case of constrictions with large ratio and long length. In such circumstances, the RBCs aggregate together tightly and concentrate at the center of the channel, which makes the nanoworms hardly able to escape from RBC clusters, leading to a similar accumulation of nanoworms and spheres inside the constriction. This study may provide theoretical guidance for the design of nano- and micro-particles for biomedical engineering applications, such as drug delivery systems for patients with stenosed microvessels. 

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2. The effect of rigid cells on blood viscosity: linking rheology and sickle cell anemia

   https://doi.org/10.1039/d1sm01299a  

   Perazzo, Antonio; Peng, Zhangli; Young, Y.-N.; Feng, Zhe; Wood, David K.; Higgins, John M.; Stone, Howard A. (January 2022, Soft Matter)

   Sickle cell anemia (SCA) is a disease that affects red blood cells (RBCs). Healthy RBCs are highly deformable objects that under flow can penetrate blood capillaries smaller than their typical size. In SCA there is an impaired deformability of some cells, which are much stiffer and with a different shape than healthy cells, and thereby affect regular blood flow. It is known that blood from patients with SCA has a higher viscosity than normal blood. However, it is unclear how the rigidity of cells is related to the viscosity of blood, in part because SCA patients are often treated with transfusions of variable amounts of normal RBCs and only a fraction of cells will be stiff. Here, we report systematic experimental measurements of the viscosity of a suspension varying the fraction of rigid particles within a suspension of healthy cells. We also perform systematic numerical simulations of a similar mixed suspension of soft RBCs, rigid particles, and their hydrodynamic interactions. Our results show that there is a rheological signature within blood viscosity to clearly identify the fraction of rigidified cells among healthy deformable cells down to a 5% volume fraction of rigidified cells. Although aggregation of RBCs is known to affect blood rheology at low shear rates, and our simulations mimic this effect via an adhesion potential, we show that such adhesion, or aggregation, is unlikely to provide a physical rationalization for the viscosity increase observed in the experiments at moderate shear rates due to rigidified cells. Through numerical simulations, we also highlight that most of the viscosity increase of the suspension is due to the rigidity of the particles rather than their sickled or spherical shape. Our results are relevant to better characterize SCA, provide useful insights relevant to rheological consequences of blood transfusions, and, more generally, extend to the rheology of mixed suspensions having particles with different rigidities, as well as offering possibilities for developments in the field of soft material composites. 

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3. Turbulent channel flow of suspensions of neutrally buoyant particles over porous media

   https://doi.org/10.1017/jfm.2022.982  

   Mirbod, Parisa; Abtahi, Seyedmehdi; Moradi Bilondi, Abbas; Rosti, Marco Edoardo; Brandt, Luca (January 2023, Journal of Fluid Mechanics)

   This study discusses turbulent suspension flows of non-Brownian, non-colloidal, neutrally buoyant and rigid spherical particles in a Newtonian fluid over porous media with particles too large to penetrate and move through the porous layer. We consider suspension flows with the solid volume fraction $${{\varPhi _b}}$$ ranging from 0 to 0.2, and different wall permeabilities, while porosity is constant at 0.6. Direct numerical simulations with an immersed boundary method are employed to resolve the particles and flow phase, with the volume-averaged Navier–Stokes equations modelling the flow within the porous layer. The results show that in the presence of particles in the free-flow region, the mean velocity and the concentration profiles are altered with increasing porous layer permeability because of the variations in the slip velocity and wall-normal fluctuations at the suspension-porous interface. Furthermore, we show that variations in the stress condition at the interface significantly affect the particle near-wall dynamics and migration toward the channel core, thereby inducing large modulations of the overall flow drag. At the highest volume fraction investigated here, $${{\varPhi _b}}= 0.2$$ , the velocity fluctuations and the Reynolds shear stress are found to decrease, and the overall drag increases due to the increase in the particle-induced stresses. 

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4. Assessing Micro-Void Formation at the Tips of Fibers within the Microstructure of Additively Manufactured Polymer Composite Bead

   Awenlimobor, Aigbe; Sayah, Neshat; Smith, Douglas E (October 2024, American Composites Society)

   Micro-voids within the bead microstructure of additively manufactured short carbon fiber- reinforced polymer composites are known to compromise the material performance. Unfortunately, a comprehensive understanding of the formation mechanisms of micro-voids during polymer processing is currently lacking. The present study considers micro-void nucleation at fiber inter-faces, particularly those occurring at the end of suspended fibers. Micro-computed tomography (μCT) image acquisition techniques are used to characterize microstructural features of a 13wt% carbon fiber reinforced ABS compo-site bead manufactured via Large Area Additive Manufacturing (LAAM). The results reveal a significant collection of micro-voids at the tips of fibers approaching 80% of the total micro-void volume fraction. In addition, fiber tip micro-voids are relatively larger and less spherical than micro-voids isolated within the ABS matrix. Theoretical formulations of several known mechanisms for micro-void nucleation during LAAM material processing indicate that local-ized fluid pressure likely plays a pivotal role in micro-void formation. To better expose this mechanism, we simulate the hydrostatic flow-field pressure distri-bution surrounding a single rigid fiber suspended in simple shear flow using fi-nite element analysis (FEA). Computed results demonstrate that the polymer matrix pressure decreases significantly at the fiber ends where micro-void nucleation is experimentally observed to occur. Our approach provides the fiber surface pressure distribution in simple shear flow that typifies nozzle regions with extreme flow conditions, enhancing our understanding of micro-void development mechanisms as the polymer melt flows through the nozzle. 

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5. Strength and its variability in 3D printing of polymer composites with continuous fibers

   https://doi.org/10.1016/j.matdes.2022.111505  

   Parker, Mallory; Ezeokeke, Ngozi; Matsuzaki, Ryosuke; Arola, Dwayne (January 2023, Materials design)

   Additive manufacturing (AM) of polymer composites with continuous fibers could play a major role in the future of aerospace and beyond but will require printed materials to achieve new levels of reliability. This study characterized the strength distribution of selected thermoplastic matrix composites as a func- tion of printing via fused filament fabrication (FFF). Experimental and commercial composite filaments of continuous carbon or Kevlar fibers were printed with volume fraction (Vf) ranging from approximately 28 to 56 %. The strength was evaluated under uniaxial tension after specific stages of printing and Weibull statistics were applied to characterize the strength distribution. There was a significant reduction in strength of the printed material with respect to the unprinted condition, regardless of reinforcement type, fiber volume fraction or printer used. Damage introduced by feed extrusion of the filament, and fiber failures induced at material deposition were most detrimental. For carbon fiber filaments, the reduc- tion ranged from approximately 10 % for an experimental material to over 60 % for a commercial filament. There was no correlation in the strength degradation or variability with Vf. The prevention of process-related fiber damage is key to advancing AM for continuous fiber composite and application to designs intended for stress-critical applications. 

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