Prediction of mechanical hemolysis in medical devices via a Lagrangian strain-based multiscale model

Hemocompatibility studies in nanotoxicology: Hemolysis or eryptosis? (A review)

Hemocompatibility evaluation is an important step in nanotoxicological studies. It is generally accepted that nanomaterials promote lysis of erythrocytes, blood clotting, alter phagocytosis, and upregulate pro-inflammatory cytokines. However, there are no standardized guidelines for testing nanomaterials hemocompatibility despite the fact that nanomaterials enter the bloodstream and interact with blood cells. In this review, the current knowledge on the ability of nanomaterials to induce distinct cell death modalities of erythrocytes is highlighted primarily focusing on hemolysis and eryptosis. This review aims to summarize the molecular mechanisms underlying erythrotoxicity of nanomaterials and critically compare the sensitivity and efficiency of hemolysis or eryptosis assays for nanomaterials blood compatibility testing. The list of eryptosis-inducing nanomaterials is growing, but it is still difficult to generalize how physico-chemical properties of nanoparticles affect eryptosis degree and molecular mechanisms involved. Thus, another aim of this review is to raise the awareness of eryptosis as a nanotoxicological tool to encourage the corresponding studies. It is worthwhile to consider adding eryptosis to in vitro nanomaterials hemocompatibility testing protocols and guidelines.

A computational study of cell membrane damage and intracellular delivery in a cross-slot microchannel

We propose a three-dimensional computational framework to simulate the flow-induced cell membrane damage and the resulting enhanced intracellular mass transport in a cross-slot microchannel. We model the cell as a liquid droplet enclosed by a viscoelastic membrane and solve the cell deformation using a well-tested immersed-boundary lattice-Boltzmann method. The cell membrane damage, which is directly related to the membrane permeability, is considered using continuum damage mechanics. The transport of the diffusive solute into the cell is solved by a lattice-Boltzmann model. After validating the computational framework against several benchmark cases, we consider a cell flowing through a cross-slot microchannel, focusing on the effects of the flow strength, channel fluid viscosity and cell membrane viscosity on the membrane damage and enhanced intracellular transport. Interestingly, we find that under a comparable pressure drop across the device, for cells with low membrane viscosity, the inertial flow regime, which can be achieved by driving a low-viscosity liquid at a high speed, often leads to much larger membrane damage, compared with the high-viscosity low-speed viscous flow regime. However, the enhancement can be significantly reduced or even reversed by an increase of the cell membrane viscosity, which limits cell deformation, particularly in the inertial flow regime. Our computational framework and simulation results may guide the design and optimisation of microfluidic devices, which use cross-slot geometry to disrupt cell membranes to enhance intracellular delivery of solutes.

Numerical methods for hemolysis and thrombus evaluation in the percutaneous ventricular assist device

BACKGROUND

A percutaneous ventricular assist device (pVAD) is an effective method to treat heart failure, but its complications, mainly hemolysis and thrombus formation, cannot be ignored. Accurate evaluation of hemolysis and thrombus formation in pVAD is essential to guide the development of pVAD and reduce the incidence of complications.

METHODS

This study optimized the numerical model to predict hemolysis and thrombus formation in pVAD. The hemolysis model is based on the power law function, and the multi-component thrombus prediction model is improved by introducing the von Willebrand factor.

RESULTS

The error between the numerical simulation and the hydraulic performance experiment is within 5%. The numerical results of hemolysis are in good agreement with those of in vitro experiments. Meanwhile, the thrombus location predicted by the numerical model is the same as that found in the in vivo experiment.

CONCLUSION

The numerical model suggested in this study may therefore accurately assess the possible hemolytic and thrombotic dangers in pVAD, making it an effective tool to support the development of pVAD.

[Progress in the analysis of hemolysis and coagulation models for interventional micro-axial flow blood pumps]

Interventional micro-axial flow blood pump is widely used as an effective treatment for patients with cardiogenic shock. Hemolysis and coagulation are vital concerns in the clinical application of interventional micro-axial flow pumps. This paper reviewed hemolysis and coagulation models for micro-axial flow blood pumps. Firstly, the structural characteristics of commercial interventional micro-axial flow blood pumps and issues related to clinical applications were introduced. Then the basic mechanisms of hemolysis and coagulation were used to study the factors affecting erythrocyte damage and platelet activation in interventional micro-axial flow blood pumps, focusing on the current models of hemolysis and coagulation on different scales (macroscopic, mesoscopic, and microscopic). Since models at different scales have different perspectives on the study of hemolysis and coagulation, a comprehensive analysis combined with multi-scale models is required to fully consider the influence of complex factors of interventional pumps on hemolysis and coagulation.

A mathematical model for assessing shear induced bleeding risk

PURPOSE

The objective of this study is to develop a bleeding risk model for assessing device-induced bleeding risk in patients supported with blood contact medical devices (BCMDs).

METHODS

The mathematical model for evaluating bleeding risk considers the effects of shear stress on von Willebrand factor (vWF) unfolding, high molecular weight multimers-vWF (HMWM-vWF) degradation, platelet activation and receptor shedding and platelet-vWF binding ability. Functions of the effect of shear stress on the above factors are fitted/employed and solved by the Eulerian transport equation. An axial flow-through Couette device and two clinical VADs which are HeartWare Ventricular Assist Device (HVAD) and HeartMate II (HM II) blood pump were employed to perform the simulation to evaluate platelet receptor shedding (GPIbα and GPIIb/IIIa), loss of HWMW-vWF, platelet-vWF binding ability and bleeding risk for validating the accuracy of our model.

RESULTS

The platelet-vWF binding ability after being subjected to high shear region in the axial flow-through Couette device predicted by our bleeding model was highly consistent with reported experimental data. As indicated by our CFD simulation results in the axial flow-through Couette device, it can find that an increase in shear stress led to a decrease in the adhesion ability of platelets on vWF, while the binding ability of vWF with platelets first increase and then decrease as shear stress elevates gradually beyond a threshold. The factor of exposure time can enhance the effect of shear stress. Additionally, the shear-induced bleeding risk predicted by our model increases with increasing shear stress and exposure time in an axial flow-through Couette device. As indicated by our numerical model, the bleeding risk in HVAD was higher than HMII, which is highly consistent with the meta-analysis based on clinical statistics. Our simulation investigations in these two clinical VADs also found that HVAD caused a higher rate of platelet receptor shedding and lower damage to HWMW-vWF than HeartMate II. The high shear stress generated in the narrow and turbulent regions of both VADs was the underlying cause of device-induced bleeding.

CONCLUSION

In this study, the shear-induced bleeding risk predicted by our bleeding model in axial flow-through Couette device and two clinical VADs is consistent or highly correlated with experimental and clinical findings, which proves the accuracy of our bleeding model. Our bleeding model can be used to aid the development of new BCMDs with improved functional characteristics and biocompatibility, and help to reduce risk of device-induced adverse events in patients.

Hemolysis prediction in bio-microfluidic applications using resolved CFD-DEM simulations

BACKGROUND AND OBJECTIVE

Hemolysis, namely hemoglobin leakage from red blood cells (RBCs), is one of the major sources of incorrect results in clinical tests, especially when passive microfluidics is involved. This is due to small characteristic dimensions which could cause strong RBCs deformation. Prediction of hemolysis is essential in the design and optimization of lab-on-a-chip devices for cell sorting and plasma separation. The aim of this work is to provide a numerical simulation tool this purpose applicable to real-scale bio-microfluidic devices with affordable computational cost.

METHODS

Blood is modelled as a suspension of biological cells, mainly RBCs, in liquid plasma assumed as a Newtonian, incompressible carrier fluid. Therefore, the physics of cells and carrier fluid is coupled by means of an immersed boundary concept known as resolved CFD-DEM. In this approach, the Navier-Stokes equations are numerically solved through a finite volume method with an additional penalty term to account for the presence of RBCs. RBCs' positions and velocities are updated by solving Newton and Euler equations for conservation of linear and angular momentum. To model the RBCs deformation, a reduced-order model is employed, where each RBC is represented by a clump of overlapping rigid spheres connected by fictional numerical bonds, whose properties are tuned to reproduce the ones of RBCs viscoelastic membrane. This coupled approach allows access to cell-level information and facilitates the usage of strain-based hemolysis models.

RESULTS

Different micro-channel geometries and blood hematocrits are simulated, to explore the influence of these factors on RBCs damage. Statistical analysis is performed to extract relevant biophysical quantities from numerical simulations such as hemolysis index distribution at the channel exit. Finally, the effect of carrier fluid viscosity is studied in relation to cell-cell interactions.

CONCLUSIONS

Simulation results show that hemolysis occurrence is almost independent of the hematocrit values in the microchannel, implying the possibility to speed up calculation using low hematocrit values. Nevertheless, using whole blood viscosity for the carrier fluid overestimates the value of the hemolysis index by almost one order of magnitude.

Mechanical stress-induced hemolysis of bovine blood is donor-dependent

INTRODUCTION

In vitro hemolysis testing is an essential method for assessing the hemolytic potential of blood pumps, but has poor reproducibility. Further investigations are needed to determine the sources and extent of variability and to find a practical way to reduce the variation.

METHODS

A small volume blood circulating loop driven by a Centrimag pump was established to provide relatively higher hemolysis readouts within a short run time and to be able to sequentially perform multiple repeated hemolysis tests in a working day.

RESULTS

The repeatability with this system was demonstrated as the %RSD at 4.3% for the NIH or MIH from three repeated tests using the same blood. The bovine blood from different randomly selected donors was tested and gave more than a two-fold difference in NIH results (0.077 vs. 0.032 g/100 L) under the same testing conditions and same pump. This wide variation in hemolysis using bovine blood from different donors happened repeatedly. More importantly, it was observed that the difference in hemolysis test results using the blood drawn from the same donor on multiple days was narrow although the native hematocrits varied. The %RSD of NIH values obtained on five different days were 6.8%, 8.4%, 11.5%, and 7.8% for donor-specific blood from donors 1 to 4, respectively.

CONCLUSION

The study results indicate that the mechanical stress-induced hemolysis behavior is donor-dependent. It has been also demonstrated that the reproducibility of in vitro hemolysis testing can be improved when the blood drawn from same donor is used.

Flow simulation-based particle swarm optimization for developing improved hemolysis models

The improvement and development of blood-contacting devices, such as mechanical circulatory support systems, is a life saving endeavor. These devices must be designed in such a way that they ensure the highest hemocompatibility. Therefore, in-silico trials (flow simulations) offer a quick and cost-effective way to analyze and optimize the hemocompatibility and performance of medical devices. In that regard, the prediction of blood trauma, such as hemolysis, is the key element to ensure the hemocompatibility of a device. But, despite decades of research related to numerical hemolysis models, their accuracy and reliability leaves much to be desired. This study proposes a novel optimization path, which is capable of improving existing models and aid in the development of future hemolysis models. First, flow simulations of three, turbulent blood flow test cases (capillary tube, FDA nozzle, FDA pump) were performed and hemolysis was numerically predicted by the widely-applied stress-based hemolysis models. Afterward, a multiple-objective particles swarm optimization (MOPSO) was performed to tie the physiological stresses of the simulated flow field to the measured hemolysis using an equivalent of over one million numerically determined hemolysis predictions. The results show that our optimization is capable of improving upon existing hemolysis models. However, it also unveils some deficiencies and limits of hemolysis prediction with stress-based models, which will need to be addressed in order to improve its reliability.

A cell-resolved, Lagrangian solver for modeling red blood cell dynamics in macroscale flows

When red blood cells (RBCs) experience non-physiologically high stresses, e.g., in medical devices, they can rupture in a process called hemolysis. Directly simulating this process is computationally unaffordable given that the length scales of a medical device are several orders of magnitude larger than that of a RBC. To overcome this separation of scales, the present work introduces an affordable computational framework that accurately resolves the stress and deformation of a RBC in a spatially and temporally varying macroscale flow field such as those found in a typical medical device. The underlying idea of the present framework is to treat RBCs as one-way coupled tracers in the macroscale flow by capturing the effect of the flow on their dynamics but neglecting their effect on the flow at the macroscale. As a result, the RBC dynamics are simulated after those of the flow in a postprocessing step by receiving the fluid velocity gradient tensor measured along the RBC trajectory as the input. To resolve the fluid velocity in the immediate vicinity of the RBC as well as the motion of the membrane, we employ the boundary integral method coupled to a structural solver. The governing equations are discretized in space using spherical harmonics, yielding spectral integration accuracy. The predictions produced by this formulation are in good agreement with those obtained from simulations of spherical capsules in shear flows and optical tweezers experiments. The accuracy of the present method is evaluated using unbounded shear flow as a benchmark. Its computational cost grows proportional to p ⁵, where p is the degree of the spherical harmonic. It also exhibits a fast convergence rate that is approximately O ( p 6 ) for p ⪅ 20.

A new membrane formulation for modelling the flow of stomatocyte, discocyte, and echinocyte red blood cells

In this work, a numerical model that enables simulation of the deformation and flow behaviour of differently aged Red Blood Cells (RBCs) is developed. Such cells change shape and decrease in deformability as they age, thus impacting their ability to pass through the narrow capillaries in the body. While the body filters unviable cells from the blood naturally, cell aging poses key challenges for blood stored for transfusions. Therefore, understanding the influence RBC morphology and deformability have on their flow is vital. While several existing models represent young Discocyte RBC shapes well, a limited number of numerical models are developed to model aged RBC morphologies like Stomatocytes and Echinocytes. The existing models are also limited to shear and stretching simulations. Flow characteristics of these morphologies are yet to be investigated. This paper aims to develop a new membrane formulation for the numerical modelling of Stomatocyte, Discocytes and Echinocyte RBC morphologies to investigate their deformation and flow behaviour. The model used represents blood plasma using the Lattice Boltzmann Method (LBM) and the RBC membrane using the discrete element method (DEM). The membrane and the plasma are coupled by the Immersed Boundary Method (IBM). Previous LBM-IBM-DEM formulations represent RBC membrane response based on forces generated from changes in the local area, local length, local bending, and cell volume. In this new model, two new force terms are added: the local area difference force and the local curvature force, which are specially incorporated to model the flow and deformation behaviour of Stomatocytes and Echinocytes. To verify the developed model, the deformation behaviour of the three types of RBC morphologies are compared to well-characterised stretching and shear experiments. The flow modelling capabilities of the method are then demonstrated by modelling the flow of each cell through a narrow capillary. The developed model is found to be as accurate as benchmark Smoothed Particle Hydrodynamics (SPH) approaches while being significantly more computationally efficient.

Hemolysis Testing In Vitro: A Review of Challenges and Potential Improvements

Many medical devices such as cardiopulmonary bypass systems, mechanical heart valves, or ventricular assist devices are intended to come into contact with blood flow during use. In vitro hemolysis testing can provide valuable information about the hemocompatibility of prototypes and thus help reduce the number of animal experiments required. Such tests play an important role as research and development tools for objective comparisons of prototypes and devices as well as for the extrapolation of their results to clinical outcomes. Therefore, it is important to explore and provide new ways to improve current practices. In this article, the main challenges of hemolysis testing are described, namely the difficult blood sourcing, the high experimental workload, and the low reproducibility of test results. Several approaches to address the challenges identified are proposed and the respective literature is reviewed. These include the replacement of blood as the "shear-sensitive fluid" by alternative test fluids, the replacement of sparse, manual sampling and blood damage assessment by a continuous and automated monitoring, as well as an analysis of categories and causes of variability in hemolysis test results that may serve as a structural template for future studies.

A numerical study on drug delivery via multiscale synergy of cellular hitchhiking onto red blood cells

Red blood cell (RBC)-hitchhiking, in which different nanocarriers (NCs) shuttle on the erythrocyte membrane and disassociate from RBCs to the first organ downstream of the intravenous injection spot, has recently been introduced as a solution to enhance target site uptake. Several experimental studies have already approved that cellular hitchhiking onto the RBC membrane can improve the delivery of a wide range of NCs in mice, pigs, and ex vivo human lungs. In these studies, the impact of NC size, NC surface chemistry, and shear rate on the delivery process and biodistribution has been widely explored. To shed light on the underlying physics in this type of drug delivery system, we present a computational platform in the context of the lattice Boltzmann method, spring connected network, and frictional immersed boundary method. The proposed algorithm simulates nanoparticle (NP) dislodgment from the RBC surface in shear flow and biomimetic microfluidic channels. The numerical simulations are performed for various NP sizes and RBC-NP adhesion strengths. In shear flow, NP detachment increases upon increasing the shear rate. RBC-RBC interaction can also significantly boost shear-induced particle detachment. Larger NPs have a higher propensity to be disconnected from the RBC surface. The results illustrate that changing the interaction between the NPs and RBCs can control the desorption process. All the findings agree with in vivo and in vitro experimental observations. We believe that the proposed setup can be exploited as a predictive tool to estimate optimum parameters in NP-bound RBCs for better targeting procedures in tissue microvasculature.

Validation of a Miniaturized Test Loop for the Assessment of Human Blood Damage by Continuous-Flow Left-Ventricular Assist Devices

Despite improved hemocompatibility of left-ventricular assist devices (LVADs), assessment of blood damage remains mandatory in preclinical testing as standardized by ASTM-F1841. The most relevant test fluid is fresh, non-pooled human blood, but the limited volume of a standard donation requires significantly smaller loops than those commonly used with animal blood. In a recent study with porcine blood, we verified a miniaturized test loop with only 160 mL for the ASTM-conform paired testing of at least two LVADs and a static reference. Here, we validated this mini test loop for standardized assessment of blood damage with one 450-mL single donation of fresh human blood. Blood damage was assessed for HeartMate 3 and BPX-80 in 9 experiments with heparinized human blood for 6 hours. We analyzed plasma free hemoglobin, von Willebrand factor (vWF) concentration and collagen-binding functionality and calculated indices of hemolysis and vWF-ratios. Overall, we observed less blood damage compared to our previous study; however, the differences in mean indices of hemolysis and in mean normalized vWF-ratio between BPX-80 and HeartMate 3 were consistent for human blood. Thus, our mini test loop proved to be valid for preclinical standardized assessment of blood damage with only 450 mL of fresh human blood.

Numerical simulation of intracellular drug delivery via rapid squeezing

Intracellular drug delivery by rapid squeezing is one of the most recent and simple cell membrane disruption-mediated drug encapsulation approaches. In this method, cell membranes are perforated in a microfluidic setup due to rapid cell deformation during squeezing through constricted channels. While squeezing-based drug loading has been successful in loading drug molecules into various cell types, such as immune cells, cancer cells, and other primary cells, there is so far no comprehensive understanding of the pore opening mechanism on the cell membrane and the systematic analysis on how different channel geometries and squeezing speed influence drug loading. This article aims to develop a three-dimensional computational model to study the intracellular delivery for compound cells squeezing through microfluidic channels. The Lattice Boltzmann method, as the flow solver, integrated with a spring-connected network via frictional coupling, is employed to capture compound capsule dynamics over fast squeezing. The pore size is proportional to the local areal strain of triangular patches on the compound cell through mathematical correlations derived from molecular dynamics and coarse-grained molecular dynamics simulations. We quantify the drug concentration inside the cell cytoplasm by introducing a new mathematical model for passive diffusion after squeezing. Compared to the existing models, the proposed model does not have any empirical parameters that depend on operating conditions and device geometry. Since the compound cell model is new, it is validated by simulating a nucleated cell under a simple shear flow at different capillary numbers and comparing the results with other numerical models reported in literature. The cell deformation during squeezing is also compared with the pattern found from our compound cell squeezing experiment. Afterward, compound cell squeezing is modeled for different cell squeezing velocities, constriction lengths, and constriction widths. We reported the instantaneous cell center velocity, variations of axial and vertical cell dimensions, cell porosity, and normalized drug concentration to shed light on the underlying physics in fast squeezing-based drug delivery. Consistent with experimental findings in the literature, the numerical results confirm that constriction width reduction, constriction length enlargement, and average cell velocity promote intracellular drug delivery. The results show that the existence of the nucleus increases cell porosity and loaded drug concentration after squeezing. Given geometrical parameters and cell average velocity, the maximum porosity is achieved at three different locations: constriction entrance, constriction middle part, and outside the constriction. Our numerical results provide reasonable justifications for experimental findings on the influences of constriction geometry and cell velocity on the performance of cell-squeezing delivery. We expect this model can help design and optimize squeezing-based cargo delivery.

Quantitative absorption imaging of red blood cells to determine physical and mechanical properties

Red blood cells or erythrocytes, constituting 40 to 45 percent of the total volume of human blood are vesicles filled with hemoglobin with a fluid-like lipid bilayer membrane connected to a 2D spectrin network. The shape, volume, hemoglobin mass, and membrane stiffness of RBCs are important characteristics that influence their ability to circulate through the body and transport oxygen to tissues. In this study, we show that a simple two-LED set up in conjunction with standard microscope imaging can accurately determine the physical and mechanical properties of single RBCs. The Beer–Lambert law and undulatory motion dynamics of the membrane have been used to measure the total volume, hemoglobin mass, membrane tension coefficient, and bending modulus of RBCs. We also show that this method is sensitive enough to distinguish between the mechanical properties of RBCs during morphological changes from a typical discocyte to echinocytes and spherocytes. Measured values of the tension coefficient and bending modulus are 1.27 × 10⁻⁶ J m⁻² and 7.09 × 10⁻²⁰ J for discocytes, 4.80 × 10⁻⁶ J m⁻² and 7.70 × 10⁻²⁰ J for echinocytes, and 9.85 × 10⁻⁶ J m⁻² and 9.69 × 10⁻²⁰ J for spherocytes, respectively. This quantitative light absorption imaging reduces the complexity related to the quantitative imaging of the biophysical and mechanical properties of a single RBC that may lead to enhanced yet simplified point of care devices for analyzing blood cells.

The constant thickness in the microfluidic channel is used for controlled absorption of red and blue light to measure red blood cell hemoglobin and height mapping. High speed recording of the height mapping provides us the membrane fluctuation.

Coarse-Grained Modeling of Pore Dynamics on the Red Blood Cell Membrane under Large Deformations

Transient pore formation on the membrane of red blood cells (RBCs) under high mechanical tensions is of great importance in many biomedical applications, such as RBC damage (hemolysis) and mechanoporation-based drug delivery. The dynamic process of pore formation, growth, and resealing is hard to visualize in experiments. We developed a mesoscale coarse-grained model to study the characteristics of transient pores on a patch of the lipid bilayer that is strengthened by an elastic meshwork representing the cytoskeleton. Unsteady molecular dynamics was used to study the pore formation and reseal at high strain rates close to the physiological ranges. The critical strain for pore formation, pore characteristics, and cytoskeleton effects were studied. Results show that the presence of the cytoskeleton increases the critical strain of pore formation and confines the pore growth. Moreover, the pore recovery process under negative strain rates (compression) is analyzed. Simulations show that pores can remain open for a long time during the high-speed tank-treading induced stretching and compression process that a patch of the RBC membrane usually experiences under high shear flow. Furthermore, complex loading conditions can affect the pore characteristics and result in denser pores. Finally, the effects of strain rate on pore formation are analyzed. Higher rate stretching of membrane patch can result in a significant increase in the critical areal strain and density of pores. Such a model reveals the dynamic molecular process of RBC damage in biomedical devices and mechanoporation that, to our knowledge, has not been reported before.