It is known that in large vessels (whole) blood behaves as a Navier-Stokes (Newtonian) fluid; however, in a vessel whose characteristic dimension (e.g., a diameter in the range of 20 to 500 microns) is about the same size as the characteristic size of the blood cells, blood behaves as a non-Newtonian fluid, exhibiting complex phenomena, such as shear-thinning, stress relaxation, the Fahraeus effect, the plasma-skimming, etc.. Using the framework of mixture theory an Eulerian-Eulerian two phase model is applied to model blood flow, where the plasma is treated as Newtonian fluid and the RBCs are treated as shear thinning fluid.[5]

Mechanically-induced blood trauma such as hemolysis and thrombosis often occurs at microscopic channels, steps and crevices within cardiovascular devices. A predictive mathematical model based on a broad understanding of hemodynamics at micro scale is needed to mitigate these effects, and is the motivation of this research project.

Fibroblast cells mechanically interact with their environment through several mechanisms, including the formation of focal adhesion complexes (FACs) with adjacent ligands. A quasi-3D (Q3D) experimental device was devised to investigate chemo-mechanical stimulation of these cells. It employed a novel microscopic fixture featuring micropolymer arrays positioned just above a cellular monolayer, enabling mechanical stimulation through dorsal attachment to FACs. This protocol demonstrated the ability to preserve the normal stellate morphology of fibroblasts. Live-cell imaging during mechanical stimulation revealed robust calcium elevation in cells interacting with the Q3D device. This system provides a simple alternative to existing 3D culture methods yet allows dynamic, real-time mechanical probing of cells in a physiologically significant environment as compared to optical or magnetic tweezers.

Cells translate environmental mechanical stimuli into biochemical reactions that govern a range of cellular processes such as proliferation, death and tissue matrix remodeling. Mechanical activation of individual focal adhesions formed between the cell and its environment directly correspond to several internal responses. Intracellular calcium concentration, [Ca 2+ ] in , has been shown to profoundly change during force sensing. In order to understand this dynamic in cells, we compared calcium mobilization resulting from chemical stimulation and that resulting from mechanical stimulation. We have analyzed the response of fibroblasts to membrane displacements of over 5 μm resulting in eventual spikes in [Ca 2+ ] in . Our data initially indicates that fibroblasts may process mechanical calcium events in unique manner in comparison to other cell types. This finding has implications in a range of fields including mechanobiology and magnetics based activation.

Flow visualization techniques provide the opportunity to observe the fluid dynamics phenomena that occur in vascular geometries under specific, known conditions. These conditions can then be used to calibrate computational models of identical geometries, a validation that is useful in the assessment of prospective interventions and perturbations. The present study investigated the flow dynamics within both a rigid abdominal aortic aneurysm (AAA) model with an iliac bifurcation and a compliant replica. Velocity fields were experimentally measured in vitro using particle image velocimetry (PIV) and compared with transient CFD and FSI analyses. The results show that the CFD approach is able to predict the patterns of flow from the PIV experiments, which arise from the geometry of the AAA. The FSI representation of the compliant wall PIV experiments showed that the in-plane dynamics visualized by PIV matched by FSI in a qualitative manner. Wall deformation, assessed by means of diameter changes in the cardiac cycle at the midsection of the compliant AAA model, was matched by the FSI analysis with a maximum relative difference of 8%.

Left ventricular assist device (LVAD) therapy has become an established treatment for patients with end-stage heart failure as either a bridge to transplant (BTT) or as permanent support (destination therapy: DT) [1]. For a small portion of patients, LVAD could be used as a bridge to cardiac recovery (BTR). Recent clinical studies have demonstrated the advantages of continuous-flow LVADs over pulsatile-flow counterparts with respect to higher survival rates and lower incidence of major adverse events [2]. However, the control challenge of continuous-flow LVADs has been not fully addressed: most of the devices are driven at a constant speed, which does not take into account changes in patient physiologic demands [3, 4].

Mechanical circulatory support for the smallest newborn pediatric patients has historically been limited to extracorporeal membrane oxygenation, which can only provide several days to weeks of full cardiac support; far short of the median waiting time for pediatric heart transplantation of nearly three months [1]. Recently, new technologies have been developed, including the PediaFlow pediatric ventricular assist device, to address this need. The PediaFlow device is a magnetically levitated (mag lev), mixed flow turbodynamic blood pump which has been developed in large part in silico using CFD-based inverse design optimization and closed form rotor dynamics models [2, 3]. Each prototype undergoes a series of in vitro and in vivo tests to verify the accuracy of the simulations in predicting performance and biocompatibility. The overall goal is continued refinement and progress towards an implantable pump that produces 0.3 −1.5 L/min for up to 6 months in pediatric heart failure patients from 5 to 15 kg. We describe here the design principles and test procedures for the first three prototypes as well as the predicted performance for a fourth prototype currently being prepared for testing ( Figure 1 ).

Micro-scale investigations of the flow and deformation of blood and its formed elements have been studied for many years. Early in vitro investigations in the rotational viscometers or small glass tubes revealed important rheological properties such as the reduced blood apparent viscosity, Fahraeus effect and Fahraeus-Lindqvist effect [1], exhibiting the nonhomogeneous property of blood in microcirculation. We have applied Mixture Theory , also known as Theory of Interacting Continua , to study and model this property of blood [2, 3]. This approach holds great promise for predicting the trafficking of RBCs in micro-scale flows (such as the depletion layer near the wall), andother unique hemorheological phenomena relevant to blood trauma. The blood is assumed to be composed of an RBC component modeled as a nonlinear fluid, suspended in plasma, modeled as a linearly viscous fluid.

Ventricular Assist Devices (VADs) have emerged as the standard of care for advanced heart failure (HF) patients, requiring mechanical circulatory support [1]. Regardless of the intended use, a small — yet significant — portion of implanted patients exhibits signs of recovery of the left ventricular function [2].

In recent years, CFD has become an increasingly used tool in the design of blood-based devices. However, the estimation of red blood cells damage (hemolysis) remains a very important challenge due to the complex rheology of blood and the turbulence present in most pumping devices. The objective of this study was to identify an appropriate turbulence model suitable for predicting hemolysis in Hemodialysis cannula. Several modern turbulence models were evaluated in comparison to Direct Numerical Simulation (DNS), which was used as the gold standard. The fluid dynamics in the cannula was modeled as a coaxial jet in which Reynolds’ number approached 2800. Based on comparison of velocity and stress time-averaged profiles, the Shear Stress Transport (SST) model with Gamma-Theta transition was identified as an optimal compromise between accuracy and computational cost.

This paper describes a design process for a new pediatric ventricular assist device (VAD), the PediaFlow. The VAD is a magnetically levitated turbodynamic pump design for chronic support of infants and small children. The design entailed the consideration of multiple pump topologies, from which an axial mixed-flow configuration was chosen for further optimization via computation fluid dynamics. The magnetic design includes permanent-magnet (PM) passive bearings for radial support of the rotor, an actively controlled thrust actuator for axial support, and a brushless DC motor for rotation. These components are closely coupled both geometrically and magnetically, and were therefore optimized in parallel, using electromagnetic, rotordynamic and fluid models. Multiple design objectives were considered including efficiency, size, and margin between critical speed to operating speed. The former depends upon the radial and yaw stiffnesses of the PM bearings. Analytical expressions for the stiffnesses were derived and verified through FEA. A toroidally-wound motor was designed for high efficiency and minimal additional negative radial stiffness. The design process relies heavily on optimization at the component-level and system-level. The results of this preliminary design optimization yielded a pump design with an overall stability margin of 15 percent, based on a pressure rise of 100 mmHg at 0.5 lpm running at 16,000 RPM.

The Left Ventricular Assist Device (LVAD) is a mechanical device that can assist an ailing natural heart in performing its functions. The latest generation of such devices is a rotary-type pump which is generally much smaller, lighter, and quieter than the conventional pulsatile-type pump. The rotary-type pumps are controlled by varying the rotor (impeller) speed. If the patient is in a health care facility, the pump speed can be adjusted manually by a trained clinician. However, an important challenge facing the increased use of these LVADs, is the desire to allow the patient to return home. The development of an appropriate patient adaptive feedback speed controller for the pump is therefore crucial to meet this challenge. In addition to being able to adapt to changes in the patient’s daily activities by automatically regulating the pump speed, the controller must also be able to prevent the occurrence of suction. In this paper we will discuss the theoretical and practical issues associated with the development of such a controller. As a flrst step, we will present a state-space mathematical model, based on a nonlinear equivalent circuit flow model, which represents the interaction of the pump with the left ventricle of the heart. The associated state space model is a 5-dimensional vector of time varying nonlinear difierential equations. The time variation occurs over 4 consecutive intervals representing the contraction, ejection, relaxation, and fllling phases of the left ventricle. The pump in the model is represented by a nonlinear equation which relates the pump rotational speed and the pump flow to the pressure difierence across the pump. Using this model, we will discuss a gradient based feedback controller which increases the pump speed to meet the patient requirements up to the point where suction may occur. At that point the controller will maintain a constant pump speed keeping the gradient of the minimum pump flow at zero. Simulation results using the model equipped with the feedback controller are presented for two cases representing two levels of patient activities. Performance of the controller for noisy measurements of pump blood flow is also investigated. Our results show that such a feedback controller performs very well and is fairly robust against measurements noise.