Search

Continuous-flow ventricular assist devices (CFVAD) and counterpulsation devices (CPD) are used to treat heart failure (HF). CFVAD can diminish pulsatility, but pulsatile modes have been implemented to increase vascular pulsatility. The effects of CFVAD in a pulsatile mode and CPD support on the function of endothelial cells (ECs) are yet to be investigated. In this study, two in vitro microfluidic models for culturing ECs are proposed to reproduce blood pressure (BP) and wall shear stress (WSS) on the arterial endothelium while using these medical devices. The layout and parameters of the two microfluidic systems were optimized based on the principle of hemodynamic similarity to efficiently simulate physiological conditions. Moreover, the unique design of the double-pump and double afterload systems could successfully reproduce the working mode of CPDs in an in vitro microfluidic system. The performance of the two systems was verified by numerical simulations and in vitro experiments. BP and WSS under HF, CFVAD in pulsatile modes, and CPD were reproduced accurately in the systems, and these induced signals improved the expression of Ca2+, NO, and reactive oxygen species in ECs, proving that CPD may be effective in normalizing endothelial function and replacing CFVAD to a certain extent to treat non-severe HF. This method offers an important tool for the study of cell mechanobiology and a key experimental basis for exploring the potential value of mechanical circulatory support devices in reducing adverse events and improving outcomes in the treatment of HF in the future. [ABSTRACT FROM AUTHOR]

Rotary blood pumps (RBPs) operating at a constant speed generate non-physiologic blood pressure and flow rate, which can cause endothelial dysfunction, leading to adverse clinical events in peripheral blood vessels and other organs. Notably, pulsatile working modes of the RBP can increase vascular pulsatility to improve arterial endothelial function. However, the laws and related mechanisms of differentially regulating arterial endothelial function under different pulsatile working modes are still unclear. This knowledge gap hinders the optimal selection of the RBP working modes. To address these issues, this study developed a multi-element in vitro endothelial cell culture system (ECCS), which could realize in vitro cell culture effectively and accurately reproduce blood pressure, shear stress, and circumferential strain in the arterial endothelial microenvironment. Performance of this proposed ECCS was validated with numerical simulation and flow experiments. Subsequently, this study investigated the effects of four different pulsation frequency modes that change once every 1-4-fold cardiac cycles (80, 40, 80/3, and 20 cycles per min, respectively) of the RBP on the expression of nitric oxide (NO) and reactive oxygen species (ROS) in endothelial cells. Results indicated that the 2-fold and 3-fold cardiac cycles significantly increased the production of NO and prevented the excessive generation of ROS, potentially minimizing the occurrence of endothelial dysfunction and related adverse events during the RBP support, and were consistent with animal study findings. In general, this study may provide a scientific basis for the optimal selection of the RBP working modes and potential treatment options for heart failure. [ABSTRACT FROM AUTHOR]

Antagonizing TNF-α signaling attenuates chronic inflammatory disease, but is associated with adverse effects on the cardiovascular system. Therefore the impact of TNF-α on basal control of redox signaling events needs to be understand in more depth. This is particularly important for the Keap1/Nrf2 pathway in the heart and in the present study we hypothesized that inhibition of a low level of TNF-α signaling attenuates the TNF-α dependent activation of this cytoprotective pathway. HL-1 cardiomyocytes and TNF receptor1/2 (TNFR1/2) double knockout mice (DKO) were used as experimental models. TNF-α (2–5 ng/ml, for 2 h) evoked significant nuclear translocation of Nrf2 with increased DNA/promoter binding and transactivation of Nrf2 targets. Additionally, this was associated with a 1.5 fold increase in intracellular glutathione (GSH). Higher concentrations of TNF-α (>10–50 ng/ml) were markedly suppressive of the Keap1/Nrf2 response and associated with cardiomyocyte death marked by an increase in cleavage of caspase-3 and PARP. In vivo experiments with TNFR1/2-DKO demonstrates that the expression of Nrf2-regulated proteins (NQO1, HO-1, G6PD) were significantly downregulated in hearts of the DKO when compared to WT mice indicating a weakened antioxidant system under basal conditions. Overall, these results indicate that TNF-α exposure has a bimodal effect on the Keap1/Nrf2 system and while an intense inflammatory activation suppresses expression of antioxidant proteins a low level appears to be protective.

The heart is a dynamic organ, and the cardiac tissue experiences changes in pressure and stretch during the cardiac cycle. Existing cell culture and animal models are limited in their capacity to decouple and tune specific hemodynamic stresses implicated in the development of physiological and pathophysiological cardiac tissue remodeling. This study focused on creating a system to subject engineered cardiac tissue to either pressure or stretch stimuli in isolation and the subsequent evaluation of acute tissue remodeling. We developed a cardiac tissue chip containing three-dimensional (3-D) cell-laden hydrogel constructs and cultured them within systems where we could expose them to either pressure changes or volume changes as seen in the left ventricle. Acute cellular remodeling with each condition was qualitatively and quantitatively assessed using histology, immunohistochemistry, gene expression studies, and soluble factor analysis. Using our unique model system, we isolated the effects of pressure and stretch on engineered cardiac tissue. Our results confirm that both pressure and stretch mediate acute stress responses in the engineered cardiac tissue. However, both experimental conditions elicited a similar acute phase injury response within this timeframe. This study demonstrates our ability to subject engineered cardiac tissue to either pressure or stretch stimuli in isolation, both of which elicited acute tissue remodeling responses. [ABSTRACT FROM AUTHOR]

Continuous flow ventricular assist device (CFVAD) support in advanced heart failure patients causes diminished pulsatility, which has been associated with adverse events including gastrointestinal bleeding, end organ failure, and arteriovenous malformation. Recently, pulsatility augmentation by pump speed modulation has been proposed as a means to minimize adverse events. Pulsatility primarily affects endothelial and smooth muscle cells in the vasculature. To study the effects of pulsatility and pulse modulation using CFVADs, we have developed a microfluidic co-culture model with human aortic endothelial (ECs) and smooth muscle cells (SMCs) that can replicate physiologic pressures, flows, shear stresses, and cyclical stretch. The effects of pulsatility and pulse frequency on ECs and SMCs were evaluated during (1) normal pulsatile flow (120/80 mmHg, 60 bpm), (2) diminished pulsatility (98/92 mmHg, 60 bpm), and (3) low cyclical frequency (115/80 mmHg, 30 bpm). Shear stresses were estimated using computational fluid dynamics (CFD) simulations. While average shear stresses (4.2 dynes/cm2) and flows (10.1 mL/min) were similar, the peak shear stresses for normal pulsatile flow (16.9 dynes/cm2) and low cyclic frequency (19.5 dynes/cm2) were higher compared to diminished pulsatility (6.45 dynes/cm2). ECs and SMCs demonstrated significantly lower cell size with diminished pulsatility compared to normal pulsatile flow. Low cyclical frequency resulted in normalization of EC cell size but not SMCs. SMCs size was higher with low frequency condition compared to diminished pulsatility but did not normalize to normal pulsatility condition. These results may suggest that pressure amplitude augmentation may have a greater effect in normalizing ECs, while both pressure amplitude and frequency may be required to normalize SMCs morphology. The co-culture model may be an ideal platform to study flow modulation strategies. [ABSTRACT FROM AUTHOR]

Background: Patients on continuous flow ventricular assist devices (CF‐VADs) are at high risk for the development of Acquired von‐Willebrand Syndrome (AVWS) and non‐surgical bleeding. von Willebrand Factor (vWF) plays an essential role in maintaining hemostasis via platelet binding to the damaged endothelium to facilitate coagulation. In CF‐VAD patients, degradation of vWF into low MW multimers that are inefficient in facilitating coagulation occurs and has been primarily attributed to the supraphysiological shear stress associated with the CF‐VAD impeller. Methods: In this review, we evaluate information from the literature regarding the unraveling behavior of surface‐immobilized vWF under pulsatile and continuous flow pertaining to: (A) the process of arterial endothelial vWF production and release into circulation, (B) the critical shear stress required to unravel surface bound versus soluble vWF which leads to degradation, and (C) the role of pulsatility in on the production and degradation of vWF. Results and Conclusion: Taken together, these data suggests that the loss of pulsatility and its impact on arterial endothelial cells plays an important role in the production, release, unraveling, and proteolytic degradation of vWF into low MW multimers, contributing to the development of AVWS. Restoration of pulsatility can potentially mitigate this issue by preventing AVWS and minimizing the risk of non‐surgical bleeding. [ABSTRACT FROM AUTHOR]

Physiological heart development and cardiac function rely on the response of cardiac cells to mechanical stress during hemodynamic loading and unloading. These stresses, especially if sustained, can induce changes in cell structure, contractile function, and gene expression. Current cell culture techniques commonly fail to adequately replicate physical loading observed in the native heart. Therefore, there is a need for physiologically relevant in vitro models that recreate mechanical loading conditions seen in both normal and pathological conditions. To fulfill this need, we have developed a microfluidic cardiac cell culture model ([micro]CCCM) that for the first time allows in vitro hemodynamic stimulation of cardiomyocytes by directly coupling cell structure and function with fluid induced loading. Cells are cultured in a small (1 cm diameter) cell culture chamber on a thin flexible silicone membrane. Integrating the cell culture chamber with a pump, collapsible pulsatile valve and an adjustable resistance element (hemostatic valve) in series allow replication of various loading conditions experienced in the heart. This paper details the design, modeling, fabrication and characterization of fluid flow, pressure and stretch generated at various frequencies to mimic hemodynamic conditions associated with the normal and failing heart. Proof-of-concept studies demonstrate successful culture of an embryonic cardiomyoblast line (H9c2 cells) and establishment of an in vivo like phenotype within this system. 10.1021/ac1012893

Technologies that enable the isolation of cell subtypes from small samples of complex populations will greatly facilitate the implementation of proteomics and genomics to human diseases. Transcriptome analysis of blood requires the depletion of contaminating erythrocytes. We report an automated microfluidic device to rapidly deplete erythrocytes from whole blood via deionized water lysis and to collect enriched leukocytes for phenotype and genomic analyses. Starting with blood from healthy subjects, we demonstrate the utility of this microfluidic cassette and lysis protocol to prepare unstimulated leukocytes, and lenkocytes stimulated ex vivo with Staphylococcal enterotoxin B, which mimics some of the cellular effects seen in patients with severe bacterial infections. Microarrays are used to assess the global gene expression response to enterotoxin B. The results demonstrate that this system can isolate unactivated leukocytes from small blood samples without any significant loss, which permits more information to be obtained from subsequent analysis, and will be readily applicable to clinical settings.

Leukocyte isolation from whole blood to study inflammation requires the removal of contaminating erythrocytes. Leukocytes, however, are sensitive to prolonged exposure to hyper/hypoosmotic solutions, temperature changes, mechanical manipulation, and gradient centrifugation. Even though care is taken to minimize leukocyte activation and cell loss during erythrocyte lysis, it is often not possible to completely avoid it. Most procedures for removal of contaminating erythrocytes from leukocyte preparations are designed for bulk processing of blood, where the sample is manipulated for longer periods of time than necessary at the single-cell level. Ammonium chloride-mediated lysis is the most commonly used method to obtain enriched leukocyte populations but has been shown to cause some activation and selective loss of certain cell types. The leukocyte yield and subsequent activation status of residual leukocytes after N[H.sub.4]Cl-mediated lysis have been shown to depend on the time of exposure to the lysis buffer. We have developed a microfluidic lysis device that deals with erythrocyte removal at nearly the single-cell level. We can achieve complete lysis of erythrocytes and ~ 100% recovery of leukocytes where the cells are exposed to an isotonic lysis buffer for less than 40 s, after which the leukocytes are immediately returned to physiological conditions. Theoretically, this process can be made massively parallel to process several milliliterss of whole blood to obtain a pure leukocyte population in less than 15 min.

Reperfusion injury after extended ischemia accounts for approximately 50% of myocardial infarct size, and there is no standard therapy. HDAC inhibition reduces infarct size and enhances cardiomyocyte autophagy and PGC1α-mediated mitochondrial biogenesis when administered at the time of reperfusion. Furthermore, a specific autophagy-inducing peptide, Tat-Beclin 1 (TB), reduces infarct size when administered at the time of reperfusion. However, since SAHA affects multiple pathways in addition to inducing autophagy, whether autophagic flux induced by TB maintains mitochondrial homeostasis during ischemia/reperfusion (I/R) injury is unknown. We tested whether the augmentation of autophagic flux by TB has cardioprotection by preserving mitochondrial homeostasis both in vitro and in vivo. Wild-type mice were randomized into two groups: Tat-Scrambled (TS) peptide as the control and TB as the experimental group. Mice were subjected to I/R surgery (45 min coronary ligation, 24 h reperfusion). Autophagic flux, mitochondrial DNA (mtDNA), mitochondrial morphology, and mitochondrial dynamic genes were assayed. Cultured neonatal rat ventricular myocytes (NRVMs) were treated with a simulated I/R injury to verify cardiomyocyte specificity. The essential autophagy gene, ATG7, conditional cardiomyocyte-specific knockout (ATG7 cKO) mice, and isolated adult mouse ventricular myocytes (AMVMs) were used to evaluate the dependency of autophagy in adult cardiomyocytes. In NRVMs subjected to I/R, TB increased autophagic flux, mtDNA content, mitochondrial function, reduced reactive oxygen species (ROS), and mtDNA damage. Similarly, in the infarct border zone of the mouse heart, TB induced autophagy, increased mitochondrial size and mtDNA content, and promoted the expression of PGC1α and mitochondrial dynamic genes. Conversely, loss of ATG7 in AMVMs and in the myocardium of ATG7 cKO mice abolished the beneficial effects of TB on mitochondrial homeostasis. Thus, autophagic flux is a sufficient and essential process to mitigate myocardial reperfusion injury by maintaining mitochondrial homeostasis and partly by inducing PGC1α-mediated mitochondrial biogenesis. [ABSTRACT FROM AUTHOR]

Background: Patients with continuous flow ventricular assist devices (CF‐VADs) are at high risk for non‐surgical bleeding, speculated to associate with the loss of pulsatility following CF‐VAD placement. It has been hypothesized that continuous shear stress causes elongation and increased enzymatic degradation of von Willebrand Factor (vWF), a key player in thrombus formation at sites of vascular damage. However, the role of loss of pulsatility on the unravelling behavior of vWF has not been widely explored. Methods: vWF molecules were immobilized on the surface of microfluidic devices and subjected to various pulsatile flow profiles, including continuous flow and pulsatile flow of different magnitudes, dQ/dt (i.e., first derivative of flow rate) of pulsatility and pulse frequencies to mimic in vivo shear flow environments with and without CF‐VAD support. VWF elongation was observed using total internal reflection fluorescence (TIRF) microscopy. Besides, the vWF level is measured from the patients' blood sample before and after CF‐VAD implantation from a clinical perspective. To our knowledge, this work is the first in providing direct, visual observation of single vWF molecule extension under controlled‐pulsatile shear flow. Results: Unravelling of vWF (total sample size n ~ 200 molecules) is significantly reduced under pulsatile flow (p < 0.01) compared to continuous flow. An increase in the magnitude of pulsatility further reduces unravelling lengths, while lower frequency of pulsatility (20 vs. 60 pulses per min) does not have a major effect on the maximum or minimum unravelling lengths. Evaluation of CF‐VAD patient blood samples (n = 13) demonstrates that vWF levels decreased by ~40% following CF‐VAD placement (p < 0.01), which correlates to single‐molecule observations from a clinical point of view. Conclusions: Pulsatile flow reduces unfolding of vWF compared to continuous flow and a lower pulse frequency of 20 pulses/minute yielded comparable vWF unfolding to 60 pulses/minute. These findings could shed light on non‐surgical bleeding associated with the loss of pulsatility following CF‐VAD placement. [ABSTRACT FROM AUTHOR]

Due to the rapidly growing number of older people worldwide and the concomitant increase in cardiovascular complications, there is an urgent need for age-related cardiac disease modeling and drug screening platforms. In the present study, we developed a cardiac tissue chip model that incorporates hemodynamic loading and mimics essential aspects of the infarcted aging heart. We induced cellular senescence in H9c2 myoblasts using low-dose doxorubicin treatment. These senescent cells were then used to engineer cardiac tissue fibers, which were subjected to hemodynamic stresses associated with pressure-volume changes in the heart. Myocardial ischemia was modeled in the engineered cardiac tissue via hypoxic treatment. Our results clearly show that acute low-dose doxorubicin treatment-induced senescence, as evidenced by morphological and molecular markers, including enlarged and flattened nuclei, DNA damage response foci, and increased expression of cell cycle inhibitor p16INK4a, p53, and ROS. Under normal hemodynamic load, the engineered cardiac tissues demonstrated cell alignment and retained cardiac cell characteristics. Our senescent cardiac tissue model of hypoxia-induced myocardial infarction recapitulated the pathological disease hallmarks such as increased cell death and upregulated expression of ANP and BNP. In conclusion, the described methodology provides a novel approach to generate stress-induced aging cardiac cell phenotypes and engineer cardiac tissue chip models to study the cardiovascular disease pathologies associated with aging. [ABSTRACT FROM AUTHOR]

Cardiopulmonary bypass (CPB) results in short-term (3–5 h) exposure to flow with diminished pulsatility often referred to as "continuous flow". It is unclear if short-term exposure to continuous flow influences endothelial function, particularly, changes in levels of pro-inflammatory and pro-angiogenic cytokines. In this study, we used the endothelial cell culture model (ECCM) to evaluate if short-term (≤5 h) reduction in pulsatility alters levels of pro-inflammatory/pro-angiogenic cytokine levels. Human aortic endothelial cells (HAECs) cultured within the ECCM provide a simple model to evaluate endothelial cell function in the absence of confounding factors. HAECs were maintained under normal pulsatile flow for 24 h and then subjected to continuous flow (diminished pulsatile pressure and flow) as observed during CPB for 5 h. The ECCM replicated pulsatility and flow morphologies associated with normal hemodynamic status and CPB as seen with clinically used roller pumps. Levels of angiopoietin-2 (ANG-2), vascular endothelial growth factor-A (VEGF-A), and hepatocyte growth factor were lower in the continuous flow group in comparison to the pulsatile flow group whereas the levels of endothelin-1 (ET-1), granulocyte colony stimulating factor, interleukin-8 (IL-8) and placental growth factor were higher in the continuous flow group in comparison to the pulsatile flow group. Immunolabelling of HAECs subjected to continuous flow showed a decrease in expression of ANG-2 and VEGF-A surface receptors, tyrosine protein kinase-2 and Fms-related receptor tyrosine kinase-1, respectively. Given that the 5 h exposure to continuous flow is insufficient for transcriptional regulation, it is likely that pro-inflammatory/pro-angiogenic signaling observed was due to signaling molecules stored in Weible-Palade bodies (ET-1, IL-8, ANG-2) and via HAEC binding/uptake of soluble factors in media. These results suggest that even short-term exposure to continuous flow can potentially activate pro-inflammatory/pro-angiogenic signaling in cultured HAECs and pulsatile flow may be a successful strategy in reducing the undesirable sequalae following continuous flow CPB. [ABSTRACT FROM AUTHOR]

Objective: Continuous Flow Left Ventricular Assist Devices (CFLVAD) are circulatory support devices that are implanted in patients with end-stage heart failure. We developed a novel control algorithm for CFLVAD to maintain physiologic perfusion while avoiding ventricular suction using only the intrinsic pump measurement of pump speed and without utilizing model-based estimation. Methods: The controller objective is to maintain a differential pump speed setpoint. A mathematical model of the circulatory system coupled with a model of a CFLVAD was used to test the control algorithm in silico. Robustness and efficacy were evaluated by comparing the proposed control algorithm to constant speed control, differential pump pressure control, mean aortic pressure control, and ventricular end diastolic pressure control during (1) rest and exercise conditions, (2) a rapid eight-fold increase in pulmonary vascular resistance under rest and exercise, (3) transitions from rest to exercise, and exercise to rest, (4) safe mode during left ventricular asystole, and (5) RPM measurement noise of 1% to 10% for (1) to (4). Results and conclusion: The control algorithm provided adequate perfusion while preventing ventricular suction for all test conditions. Performance did not deteriorate significantly with pump speed measurement noise of up to 6%. The safe mode successfully detected asystole and maintained adequate perfusion to sustain life even when the differential pump speed was low. Significance: Maintaining a constant differential pump speed can simultaneously achieve physiologic perfusion and suction prevention without needing unreliable, direct measurements of flow or pressure, or complex parameter or model-based estimation techniques. [ABSTRACT FROM AUTHOR]

Objective: Cardiovascular research and regenerative strategies have been significantly limited by the lack of relevant cell culture models that can recreate complex hemodynamic stresses associated with pressure–volume changes in the heart. Methods: To address this issue, we designed a biomimetic cardiac tissue chip (CTC) model where encapsulated cardiac cells can be cultured in three-dimensional (3-D) fibres and subjected to hemodynamic loading to mimic pressure–volume changes seen in the left ventricle. These 3-D fibres are suspended within a microfluidic chamber between two posts and integrated within a flow loop. Various parameters associated with heart function, like heart rate, peak-systolic pressure, end-diastolic pressure and volume, end-systolic pressure and volume, and duration ratio between systolic and diastolic, can all be precisely manipulated, allowing culture of cardiac cells under developmental, normal, and disease states. Results: We describe two examples of how the CTC can significantly impact cardiovascular research by reproducing the pathophysiological mechanical stresses associated with pressure overload and volume overload. Our results using H9c2 cells, a cardiomyogenic cell line, clearly show that culture within the CTC under pathological hemodynamic loads accurately induces morphological and gene expression changes, similar to those seen in both hypertrophic and dilated cardiomyopathy. Under pressure overload, the cells within the CTC see increased hypertrophic remodeling and fibrosis, whereas cells subject to prolonged volume overload experience significant changes to cellular aspect ratio through thinning and elongation of the engineered tissue. Conclusions: These results demonstrate that the CTC can be used to create highly relevant models where hemodynamic loading and unloading are accurately reproduced for cardiovascular disease modeling. [ABSTRACT FROM AUTHOR]

We developed a novel model for studying hyperparathyroidism by growing ex vivo 3-dimensional human parathyroids as part of a microphysiological system (MPS) that mimics human physiology. The purpose of this study was to validate the parathyroid portion of the MPS. We prospectively collected parathyroid tissue from 46 patients with hyperparathyroidism for growth into pseudoglands. We evaluated pseudogland architecture and calcium responsiveness. Following 2 weeks in culture, dispersed cells successfully coalesced into pseudoglands ∼500–700 µm in diameter that mimicked the appearance of normal parathyroid glands. Functionally, they also appeared similar to intact parathyroids in terms of organization and calcium-sensing receptor expression. Immunohistochemical staining for calcium-sensing receptor revealed 240–450/cell units of mean fluorescence intensity within the pseudoglands. Finally, the pseudoglands showed varying levels of calcium responsiveness, indicated by changes in parathyroid hormone (PTH) levels. In summary, we successfully piloted the development of a novel MPS for studying the effects of hyperparathyroidism on human organ systems. We are currently evaluating the effect of PTH on adverse remodeling of tissue engineered cardiac, skeletal, and bone tissue within the MPS. [ABSTRACT FROM AUTHOR]

Human induced pluripotent stem cell (hiPSC)-derived cardio-myocytes (hiPSC-CMs) hold great promise for cardiovascular disease modeling and regenerative medicine. However, these cells are both structurally and functionally -immature, primarily due to their differentiation into cardiomyocytes occurring under static culture which only reproduces biomolecular cues and ignores the dynamic hemo-dynamic cues that shape early and late heart development during cardiogenesis. To evaluate the effects of hemodynamic stimuli on hiPSC-CM maturation, we used the biomimetic cardiac tissue model to reproduce the hemodynamics and pressure/volume changes associated with heart development. Following 7 days of gradually increasing stimulation, we show that hemodynamic loading results in (a) enhanced alignment of the cells and extracellular matrix, (b) significant increases in genes associated with physiological hypertrophy, (c) noticeable changes in sarcomeric organization and potential changes to cellular metabolism, and (d) a significant increase in fractional shortening, suggestive of a positive force frequency response. These findings suggest that culture of hiPSC-CMs under conditions that accurately reproduce hemodynamic cues results in structural orga-nization and molecular signaling consistent with organ growth and functional maturation. [ABSTRACT FROM AUTHOR]

• A control system to enhance vascular pulsatility for rotary blood pump was proposed. • Switching two differential pump speed setpoints to raise vascular pulsatility. • The proposed control algorithm was only based on intrinsic pump speed measurements. • This algorithm augmented vascular pulsatility, provided flow rates, avoided suction. Continuous flow rotary blood pumps (RBP) operating clinically at constant rotational speeds cannot match cardiac demand during varying physical activities, are susceptible to suction, diminish vascular pulsatility, and have an increased risk of adverse events. A sensorless, physiologic feedback control strategy for RBP was developed to mitigate these limitations. The proposed algorithm used intrinsic pump speed to obtain differential pump speed (Δ RPM). The proposed gain-scheduled proportional-integral controller, switching of setpoints between a higher pump speed differential setpoint (Δ RPM Hr) and a lower pump speed differential setpoint (Δ RPM Lr), generated pulsatility and physiologic perfusion, while avoiding suction. The switching between Δ RPM Hr and Δ RPM Lr setpoints occurred when the measured Δ RPM reached the pump differential reference setpoint. In-silico tests were implemented to assess the proposed algorithm during rest, exercise, a rapid 3-fold pulmonary vascular resistance increase, rapid change from exercise to rest, and compared with maintaining a constant pump speed setpoint. The proposed control algorithm augmented aortic pressure pulsatility to over 35 mmHg during rest and around 30 mmHg during exercise. Significantly, ventricular suction was avoided, and adequate cardiac output was maintained under all simulated conditions. The performance of the sensorless algorithm using estimation was similar to the performance of sensor-based method. This study demonstrated that augmentation of vascular pulsatility was feasible while avoiding ventricular suction and providing physiological pump outflows. Augmentation of vascular pulsatility can minimize adverse events that have been associated with diminished pulsatility. Mock circulation and animal studies would be conducted to validate these results. [ABSTRACT FROM AUTHOR]

Keywords: Disease modeling; In vitro culture; Microphysiological systems EN Disease modeling In vitro culture Microphysiological systems 267 268 2 06/27/22 20220501 NES 220501 In vitro cell and tissue culture models represent an important starting point for disease modeling, drug discovery, and drug toxicity testing. Cell-, tissue-, and organ-on-a-chip models and MPS are increasing being used to develop human models of human disease to provide an alternative to animal models for drug development and toxicity testing. Finally, Shahin-Shamsabadi et al. (pp. 304-312) developed a novel method that utilizes cell sheet engineering to assemble complex tissue structures in a layer-by-layer format and build tissue in a scalable fashion that is necessary for sustainable lab-grown meat alternatives. [Extracted from the article]

Flow cytometry is a powerful technique capable of simultaneous multi-parametric analysis of heterogeneous cell populations for research and clinical applications. In recent years, the flow cytometer has been miniaturized and made portable for application in clinical- and resource-limited settings. The sample preparation procedure, i.e. labeling of cells with antibodies conjugated to fluorescent labels, is a time consuming (∼45 min) and labor-intensive procedure. Microfluidics provides enabling technologies to accomplish rapid and automated sample preparation. Using an integrated microfluidic device consisting of a labeling and washing module, we demonstrate a new protocol that can eliminate sample handling and accomplish sample and reagent metering, high-efficiency mixing, labeling and washing in rapid automated fashion. The labeling module consists of a long microfluidic channel with an integrated chaotic mixer. Samples and reagents are precisely metered into this device to accomplish rapid and high-efficiency mixing. The mixed sample and reagents are collected in a holding syringe and held for up to 8 min following which the mixture is introduced into an inertial washing module to obtain ‘analysis-ready’ samples. The washing module consists of a high aspect ratio channel capable of focusing cells to equilibrium positions close to the channel walls. By introducing the cells and labeling reagents in a narrow stream at the center of the channel flanked on both sides by a wash buffer, the elution of cells into the wash buffer away from the free unbound antibodies is accomplished. After initial calibration experiments to determine appropriate ‘holding time’ to allow antibody binding, both modules were used in conjunction to label MOLT-3 cells (T lymphoblast cell line) with three different antibodies simultaneously. Results confirm no significant difference in mean fluorescence intensity values for all three antibodies labels (p < 0.01) between the conventional procedure (45 min) and our microfluidic approach (12 min). [ABSTRACT FROM AUTHOR]