Blood Particulate Analogue Fluids: A Review

The Relationship Between Nitrate-Induced Headache and -Blood Viscosity: An Observational Prospective Study

ABSTRACT

Nitrates are one of the most prescribed medications in the treatment of angina pectoris today. Headache is the most common side effect of nitrates, and there is limited prospective data on the determinants of this effect. Our aim in this study is to open a foresight window for clinicians in clinical practice by explaining the possible relationship between nitrate-induced headache and whole-blood viscosity (WBV). After coronary revascularization treatment, 869 patients with angina who were prescribed nitrate preparations were divided into groups according to the development of headache or not and categorized according to the 4-grade scale level. Those who had no headache during nitrate use were graded as grade 0, those who felt mild headache were grade 1, those who felt moderate headache were grade 2, and those who described severe headache were graded as grade 3. The groups were compared according to WBV values. A total of 869 participants were included in the study. Most patients (82.1%) experienced some level of headache. Headache severity correlated with both WBV at high shear rate (r = 0.657; P < 0.001) and WBV at low shear rate (r = 0.687; P < 0.001). In multivariate analysis, WBV was determined as an independent predictor of headache experience. WBV predicted nitrate-induced headache with 75% sensitivity and 75% specificity at high shear rate and 77% sensitivity and 77% specificity at low shear rate. WBV seems to be one of the major determinants for nitrate-induced headache. WBV may be a guide for initiating alternative antianginal drugs without prescribing nitrates to the patient to increase patient compliance.

Effect of Particle Migration on the Stress Field in Microfluidic Flows of Blood Analog Fluids at High Reynolds Numbers

In the present paper, we investigate how the reductions in shear stresses and pressure losses in microfluidic gaps are directly linked to the local characteristics of cell-free layers (CFLs) at channel Reynolds numbers relevant to ventricular assist device (VAD) applications. For this, detailed studies of local particle distributions of a particulate blood analog fluid are combined with wall shear stress and pressure loss measurements in two complementary set-ups with identical flow geometry, bulk Reynolds numbers and particle Reynolds numbers. For all investigated particle volume fractions of up to 5%, reductions in the stress and pressure loss were measured in comparison to a flow of an equivalent homogeneous fluid (without particles). We could explain this due to the formation of a CFL ranging from 10 to 20 μm. Variations in the channel Reynolds number between Re = 50 and 150 did not lead to measurable changes in CFL heights or stress reductions for all investigated particle volume fractions. These measurements were used to describe the complete chain of how CFL formation leads to a stress reduction, which reduces the apparent viscosity of the suspension and results in the Fåhræus-Lindqvist effect. This chain of causes was investigated for the first time for flows with high Reynolds numbers (Re∼100), representing a flow regime which can be found in the narrow gaps of a VAD.

Recent advances in micro-sized oxygen carriers inspired by red blood cells

Supplementing sufficient oxygen to cells is always challenging in biomedical engineering fields such as tissue engineering. Originating from the concept of a 'blood substitute', nano-sized artificial oxygen carriers (AOCs) have been studied for a long time for the optimization of the oxygen supplementation and improvement of hypoxia environments in vitro and in vivo. When circulating in our bodies, micro-sized human red blood cells (hRBCs) feature a high oxygen capacity, a unique biconcave shape, biomechanical and rheological properties, and low frictional surfaces, making them efficient natural oxygen carriers. Inspired by hRBCs, recent studies have focused on evolving different AOCs into microparticles more feasibly able to achieve desired architectures and morphologies and to obtain the corresponding advantages. Recent micro-sized AOCs have been developed into additional categories based on their principal oxygen-carrying or oxygen-releasing materials. Various biomaterials such as lipids, proteins, and polymers have also been used to prepare oxygen carriers owing to their rapid oxygen transfer, high oxygen capacity, excellent colloidal stability, biocompatibility, suitable biodegradability, and long storage. In this review, we concentrated on the fabrication techniques, applied biomaterials, and design considerations of micro-sized AOCs to illustrate the advances in their performances. We also compared certain recent micro-sized AOCs with hRBCs where applicable and appropriate. Furthermore, we discussed existing and potential applications of different types of micro-sized AOCs.

Alginate/xanthan gum hydrogels as forensic blood substitutes for bloodstain formation and analysis

Understanding the behaviour of human blood outside of the body has important implications in forensic research, especially related to bloodstain pattern analysis (BPA). The design of forensic blood substitutes (FBSs) can provide many advantages, including the incorporation of multiple physiological components for use as safe and reliable materials for forensic applications. In this work, we present the design of synthetic alginate and xanthan gum-based hydrogels that contain electrosprayed microparticles (MPs) with and without crosslinked DNA. In addition to the MPs, the alginate/xanthan gum FBS materials include fillers to alter the physical appearance and fluid properties of the material. The optimized FBS consisted of alginate (1% w/v) and xanthan gum (5.0 × 10^-3% w/v), 2 mM CaCl₂, ferric citrate (0.5% w/v), magnesium silicate (0.25% w/v), Allura Red dye (2% w/v), 0.025% v/v Tween 20 and 9.5% v/v MPs. The FBS was tested in passive dripping experiments relevant to BPA scenarios at various impact angles. The spreading ratio (D_s/D₀) was determined for 90° stains made on a paper surface and compared to bovine blood where the FBS was shown to simulate accurate and predictable spreading behaviour. In addition, we simulated other common BPA scenarios (e.g., impact patterns) and evidence processing potential. The FBS could be swabbed, and the DNA could be extracted, amplified, and genotyped analogous to human blood evidence. A stability test was also conducted which revealed a shelf-life of over 4 weeks where the material remains relevant to human blood at physiological temperature.

Experimental Characterization of a Microfluidic Device Based on Passive Crossflow Filters for Blood Fractionation

The separation of red blood cells (RBCs) from blood plasma and the analysis of individual RBCs are of great importance, as they provide valuable information regarding the health of their donor. Recent developments in microfluidics and microfabrication have contributed to the fabrication of microsystems with complex features to promote the separation and analysis of RBCs. In this work, the separation capacity of a multi-step crossflow microfluidic device was evaluated by using a blood analogue fluid made by Brij L4 micelles and human RBCs separated from whole blood, suspended in a solution with hematocrits (Ht) of 0.5 and 1%. All the samples collected at the outlets of the device were experimentally analyzed and compared. The absorbance spectrum was also measured for the prepared blood samples. The results indicate that the tested blood analogue fluid has exhibited a flow behavior similar to that of blood. In addition, the optical absorbance spectrophotometry revealed that it was possible to evaluate the separation efficiency of the microfluidic device, concluding that the concentration of cells was lower at the most lateral outside outlets of the microchannel due to the cumulative effect of the multiple cross-flow filters.

Red blood cell dynamics in extravascular biological tissues modelled as canonical disordered porous media

The dynamics of blood flow in the smallest vessels and passages of the human body, where the cellular character of blood becomes prominent, plays a dominant role in the transport and exchange of solutes. Recent studies have revealed that the microhaemodynamics of a vascular network is underpinned by its interconnected structure, and certain structural alterations such as capillary dilation and blockage can substantially change blood flow patterns. However, for extravascular media with disordered microstructure (e.g. the porous intervillous space in the placenta), it remains unclear how the medium’s structure affects the haemodynamics. Here, we simulate cellular blood flow in simple models of canonical porous media representative of extravascular biological tissue, with corroborative microfluidic experiments performed for validation purposes. For the media considered here, we observe three main effects: first, the relative apparent viscosity of blood increases with the structural disorder of the medium; second, the presence of red blood cells (RBCs) dynamically alters the flow distribution in the medium; third, symmetry breaking introduced by moderate structural disorder can promote more homogeneous distribution of RBCs. Our findings contribute to a better understanding of the cell-scale haemodynamics that mediates the relationship linking the function of certain biological tissues to their microstructure.

A particulate blood analogue based on artificial viscoelastic blood plasma and RBC-like microparticles at a concentration matching the human haematocrit

There has been enormous interest in the production of fluids with rheological properties similar to those of real blood over the last few years. Application fields range from biomicrofluidics (microscale) to forensic science (macroscale). The inclusion of flexible microparticles in blood analogue fluids has been demonstrated to be essential in order to reproduce the behaviour of blood flow in these fields. Here, we describe a protocol to produce a whole human blood analogue composed of a proposed plasma analogue and flexible spherical microparticles that mimic the key structural attributes of RBCs (size and mechanical properties), at a concentration matching the human haematocrit (∼42% by volume). Polydimethylsiloxane (PDMS) flexible microparticles were used to mimic RBCs, whose capability to deform is tunable by means of the mixing ratio of the PDMS precursor. Their flow through glass micronozzles allowed us to find the appropriate mixing ratio of PDMS to have approximately the same Young's modulus (E) as that exhibited by real RBCs. Shear and extensional rheology and microrheology techniques were used to match the properties exhibited by human plasma and whole blood at body temperature (37 °C). Finally, we study the flow of our proposed fluid through a microfluidic channel, showing the in vitro reproduction of the multiphase flow effects taking place in the human microcirculatory system, such as the cell-free layer (CFL) and the Fåhræus-Lindqvist effect. A macroscale application in the field of forensic science is also presented, concerning the impact of our blood analogue droplets on a solid surface for bloodstain pattern analysis.

Fire-Shaped Nozzles to Produce a Stress Peak for Deformability Studies

Fire-shaped nozzles can be used to study the deformability of microcapsules, particles, or cells traveling in a flow. Though their geometry depends on the dimensions of the original glass capillary and the heating conditions, they all produce a strain rate peak approximately at the section where the diameter is 1.5 times the minimum. The intensity of this peak and the time from its position to the neck can be easily estimated from the flow rate and three geometrical parameters, without the need for any simulation. In the convergent region of these nozzles, it is possible to observe the evolution of the deformation. It is necessary to use a sufficiently long nozzle to produce the maximum deformation before the neck.

Geometry effect in multi-step crossflow microfluidic devices for red blood cells separation and deformability assessment

The efficient separation of blood components using microfluidic systems can help to improve the detection and diagnosis of several diseases, such as malaria and diabetes. Therefore, a novel multi-step microfluidic device, based on passive crossflow filters was developed. Three different designs were proposed, fabricated and tested in order to evaluate the most suitable geometry to perform, simultaneously, blood cells separation and cell deformability measurements. All the proposed geometries include a main channel and three sequential separation steps, all comprised of symmetrical crossflow filters, with multiple rows of pillars, to reduce the amount of red blood cells (RBCs) flowing to the outlets of the microfluidic device (MD). Sets of hyperbolic constrictions located at the outlets allow the assessment of cells deformability. Based on the proposed geometries, the three correspondent MD were evaluated and compared, by measuring the RBCs velocities, the cell-free layer (CFL) effect through the microchannels and by quantifying the amount of RBCs at the outlets. The results suggest that the proposed MD 3 configuration was the most effective one for the desired application, due to the formation of a wider CFL. As a result, a minor amount of RBCs flow through the hyperbolic contraction at the third separation level of the device. Nevertheless, for all the proposed geometries, the existence of three separation levels shows that it is possible to achieve a highly efficient cell separation. If needed, such microdevices have the potential for further improvements by increasing the number of separation levels, aiming the total separation of blood cells from plasma.

Micro-particle entrapment dynamics in microfluidic pulmonary capillary networks

The journey of vascular targeted carriers (VTC) in the circulatory system is highly intricate and includes navigation through different vessel structures, such as the vast pulmonary capillary network (PCN) in the lungs where particles can get entrapped and lead to blockage. Here, we leverage microfluidic PCN models to explore, for the first time, micro-particle capillary entrapment, in a well-controlled biophysical environment mimicking human physiological hemodynamics at true scale. This in vitro strategy mimics the challenges of vascular carrier transport during their journey in the smallest capillaries of the body (∼5 µm). Specifically, we explore in the PCN model entrapment dynamics of spherical micro-particles of different diameters (i.e. 3, 4 and 4.5 µm) at different concentrations, comparing their motion in cell-free buffer to that in the presence of red blood cells (RBCs). Notably, while 3 µm particles exhibit undisturbed transport in all of the examined concentrations, both in cell-free buffer and in the presence of RBCs, particles of 4 and 4.5 µm exhibit a concentration-dependent transport where the presence of RBCs leads in fact to reduced entrapment. Our experiments suggest that collisions of micro-particles with RBCs can facilitate their navigability, allowing for carrier transport that would lead otherwise to rapid entrapment in a cell-free environment. Altogether, the proposed preclinical in vitro assays offer rapid screening opportunities for design optimization of VTC transport in capillary networks.

Fluid Flow and Structural Numerical Analysis of a Cerebral Aneurysm Model

Intracranial aneurysms (IA) are dilations of the cerebral arteries and, in most cases, have no symptoms. However, it is a very serious pathology, with a high mortality rate after rupture. Several studies have been focused only on the hemodynamics of the flow within the IA. However, besides the effect of the flow, the development and rupture of the IA are also associated with a combination of other factors such as the wall mechanical behavior. Thus, the objective of this work was to analyze, in addition to the flow behavior, the biomechanical behavior of the aneurysm wall. For this, CFD simulations were performed for different Reynolds numbers (1, 100, 500 and 1000) and for two different rheological models (Newtonian and Carreau). Subsequently, the pressure values of the fluid simulations were exported to the structural simulations in order to qualitatively observe the deformations, strains, normal stresses and shear stress generated in the channel wall. For the structural simulations, a hyperelastic constitutive model (5-parameter Mooney–Rivlin) was used. The results show that with the increase in the Reynolds number (Re), the recirculation phenomenon is more pronounced, which is not seen for Re = 1. The higher the Re, the higher the strain, displacement, normal and shear stresses values.

Properties and Applications of PDMS for Biomedical Engineering: A Review

Polydimethylsiloxane (PDMS) is an elastomer with excellent optical, electrical and mechanical properties, which makes it well-suited for several engineering applications. Due to its biocompatibility, PDMS is widely used for biomedical purposes. This widespread use has also led to the massification of the soft-lithography technique, introduced for facilitating the rapid prototyping of micro and nanostructures using elastomeric materials, most notably PDMS. This technique has allowed advances in microfluidic, electronic and biomedical fields. In this review, an overview of the properties of PDMS and some of its commonly used treatments, aiming at the suitability to those fields' needs, are presented. Applications such as microchips in the biomedical field, replication of cardiovascular flow and medical implants are also reviewed.

Polydimethylsiloxane Composites Characterization and Its Applications: A Review

Polydimethylsiloxane (PDMS) is one of the most promising elastomers due its remarkable proprieties such as good thermal stability, biocompatibility, corrosion resistance, flexibility, low cost, ease of use, chemically inertia, hyperplastic characteristics, and gas permeability. Thus, it can be used in areas such as microfluidic systems, biomedical devices, electronic components, membranes for filtering and pervaporation, sensors, and coatings. Although pure PDMS has low mechanical properties, such as low modulus of elasticity and strength, it can be improved by mixing the PDMS with other polymers and by adding particles or reinforcements. Fiber-reinforced PDMS has proved to be a good alternative to manufacturing flexible displays, batteries, wearable devices, tactile sensors, and energy harvesting systems. PDMS and particulates are often used in the separation of liquids from wastewater by means of porosity followed by hydrophobicity. Waxes such as beeswax and paraffin have proved to be materials capable of improving properties such as the hydrophobic, corrosion-resistant, thermal, and optical properties of PDMS. Finally, when blended with polymers such as poly (vinyl chloride-co-vinyl acetate), PDMS becomes a highly efficient alternative for membrane separation applications. However, to the best of our knowledge there are few works dedicated to the review and comparison of different PDMS composites. Hence, this review will be focused on PDMS composites, their respective applications, and properties. Generally, the combination of elastomer with fibers, particles, waxes, polymers, and others it will be discussed, with the aim of producing a review that demonstrates the wide applications of this material and how tailored characteristics can be reached for custom applications.