A microfluidic model to study the effects of arrhythmic flows on endothelial cells
Lab on a chip, 2024
Atrial fibrillation (AF) is the most common type of cardiac arrhythmia and an important contribut... more Atrial fibrillation (AF) is the most common type of cardiac arrhythmia and an important contributor to morbidity and mortality. Endothelial dysfunction has been postulated to be an important contributing factor in cardiovascular events in patients with AF. However, how vascular endothelial cells respond to arrhythmic flow is not fully understood, mainly due to the limitation of current in vitro systems to mimic arrhythmic flow conditions. To address this limitation, we developed a microfluidic system to study the effect of arrhythmic flow on the mechanobiology of human aortic endothelial cells (HAECs). The system utilises a computer-controlled piezoelectric pump for generating arrhythmic flow with a unique ability to control the variability in both the frequency and amplitude of pulse waves. The flow rate is modulated to reflect physiological or pathophysiological shear stress levels on endothelial cells. This enabled us to systematically dissect the importance of variability in the frequency and amplitude of pulses and shear stress level on endothelial cell mechanobiology. Our results indicated that arrhythmic flow at physiological shear stress level promotes endothelial cell spreading and reduces the plasma membrane-to-cytoplasmic distribution of β-catenin. In contrast, arrhythmic flow at low and atherogenic shear stress levels does not promote endothelial cell spreading or redistribution of β-catenin. Interestingly, under both shear stress levels, arrhythmic flow induces inflammation by promoting monocyte adhesion via an increase in ICAM-1 expression. Collectively, our microfluidic system provides opportunities to study the effect of arrhythmic flows on vascular endothelial mechanobiology in a systematic and reproducible manner.
Bioengineered Vascular Model of Foam Cell Formation
ACS Biomaterials Science & Engineering, Nov 28, 2023
Foam cell formation is a complex blood vessel pathology, which is characterized by a series of ev... more Foam cell formation is a complex blood vessel pathology, which is characterized by a series of events, including endothelium dysfunction, inflammation, and accumulation of immune cells underneath the blood vessel walls. Novel bioengineered models capable of recapitulating these events are required to better understand the complex pathological processes underlying the development of foam cell formation and, consequently, advanced bioengineered platforms for screening drugs. Here, we generated a microfluidic blood vessel model, incorporating a three-dimensional (3D) extracellular matrix coated with an endothelial layer. This system enables us to perform experiments under a dynamic microenvironment that recapitulates the complexities of the native vascular regions. Using this model, we studied the effectors that regulate monocyte adhesion and migration, as well as foam cell formation inside vessel walls. We found that monocyte adhesion and migration are regulated by both the endothelium and monocytes themselves. Monocytes migrated into the extracellular matrix only when endothelial cells were cultured in the vessel model. In addition, the exposure of an endothelial layer to tumor necrosis factor α (TNF-α) and low shear stress both increased monocyte migration into the subendothelial space toward the matrix. Furthermore, we demonstrated the process of foam cell formation, 3 days after transmigration of peripheral blood mononuclear cells (PBMCs) into the vessel wall. We showed that pre-exposure of PBMCs to high shear rates increases their adhesion and migration through the TNF-α-treated endothelium but does not affect their capacity to form foam cells. The versatility of our model allows for mechanistic studies on foam cell formation under customized pathological conditions.
Microfluidic platforms enable a variety of physical or chemical stimulation of single or multiple... more Microfluidic platforms enable a variety of physical or chemical stimulation of single or multiple cells to be examined and monitored in real-time. To date, intracellular calcium signalling research is, however, predominantly focused on observing the response of cells to a single mode of stimulation; consequently, the sensitising/desensitising of cell responses under concurrent stimuli is not well studied. In this paper, we provide an extended Discontinuous Dielectrophoresis procedure to investigate the sensitising of chemical stimulation, over an extensive range of shear stress, up to 63 dyn/cm 2 , which encompasses shear stresses experienced in the arterial and venus systems (10 to 60 dyn/cm 2 ). Furthermore, the TRPV4-selective agonist GSK1016790A, a form of chemical stimulation, did not influence the ability of the cells' to remain immobilised under high levels of shear stress; thus, enabling us to investigate shear stress stimulation on agonism. Our experiments revealed that shear stress sensitises GSK1016790A-evoked intracellular calcium signalling of cells in a shear-stimulus dependent manner, as observed through a reduction in the cellular response time and an increase in the pharmacological efficacy. Consequently, suggesting that the role of TRPV4 may be underestimated in endothelial cells-which experience high levels of shear stress. This study highlights the importance of conducting studies at high levels of shear stress. Additionally, our approach will be valuable for examining the effect of high levels of shear on different cell types under different conditions, as presented here for agonist activation. V
This review discusses the current trends in self-contained microfluidic systems, and classifies s... more This review discusses the current trends in self-contained microfluidic systems, and classifies such systems based on their operating mechanism into passive, hand-powered and active groups.
Dielectrophoresis is a versatile tool for the sorting, immobilization, and characterization of ce... more Dielectrophoresis is a versatile tool for the sorting, immobilization, and characterization of cells in microfluidic systems. The performance of dielectrophoretic systems strongly relies on the configuration of microelectrodes, which produce a nonuniform electric field. However, once fabricated, the microelectrodes cannot be reconfigured to change the characteristics of the system. Here, we show that the reorientation of the microfluidic channel with respect to the microelectrodes can be readily utilized to alter the characteristics of the system. This enables us to change the location and density of immobilized viable cells across the channel, release viable cells along customized numbers of streams within the channel, change the deflection pattern of nonviable cells along the channel, and improve the sorting of viable and nonviable cells in terms of flow throughput and efficiency of the system. We demonstrate that the reorientation of the microfluidic channel is an effective tool to create versatile dielectrophoretic platforms using the same microelectrode design.
The International Journal of Biochemistry & Cell Biology, Sep 1, 2016
Transient receptor potential ion channels (TRP) are a superfamily of non-selective ion channels w... more Transient receptor potential ion channels (TRP) are a superfamily of non-selective ion channels which are opened in response to a diverse range of stimuli. The TRP vanilloid 4 (TRPV4) ion channel is opened in response to heat, mechanical stimuli, hypo-osmolarity and arachidonic acid metabolites. However, recently TRPV4 has been identified as an ion channel that is modulated by, and opened by intracellular signalling cascades from other receptors and signalling pathways. Although TRPV4 knockout mice show relatively mild phenotypes, some mutations in TRPV4 cause severe developmental abnormalities, such as the skeletal dyplasia and arthropathy. Regulated TRPV4 function is also essential for healthy cardiovascular system function as a potent agonist compromises endothelial cell function, leading to vascular collapse. A better understanding of the signalling mechanisms that modulate TRPV4 function is necessary to understand its physiological roles. Post translational modification of TRPV4 by kinases and other signalling molecules can modulate TRPV4 opening in response to stimuli such as mechanical and hyposmolarity and there is an emerging area of research implicating TRPV4 as a transducer of these signals as opposed to a direct sensor of the stimuli. Due to its wide expression profile, TRPV4 is implicated in multiple pathophysiological states. TRPV4 contributes to the sensation of pain due to hypo-osmotic stimuli and inflammatory mechanical hyperalsgesia, where TRPV4 sensitizaton by intracellular signalling leads to pain behaviors in mice. In the vasculature, TRPV4 is a regulator of vessel tone and is implicated in hypertension and diabetes due to endothelial dysfunction. TRPV4 is a key regulator of epithelial and endothelial barrier function and signalling to and opening of TRPV4 can disrupt these critical protective barriers. In respiratory function, TRPV4 is involved in cystic fibrosis, cilary beat frequency, bronchoconstriction, chronic obstructive pulmonary disease, pulmonary hypertension, acute lung injury, acute respiratory distress syndrome and cough.In this review we highlight how modulation of TRPV4 opening is a vital signalling component in a range of tissues and why understanding of TRPV4 regulation in the body may lead to novel therapeutic approaches to treating a range of disease states.
Dielectrophoretically patterned carbon nanotubes to sort microparticles
Electrophoresis, Sep 24, 2010
This article compares the operation of a dielectrophoretic (DEP) platform before and after patter... more This article compares the operation of a dielectrophoretic (DEP) platform before and after pattering carbon nanotubes (CNTs) between its microelectrodes. The diverse performance of the DEP system is assessed by separating 1 and 5 μm polystyrene particles. In the absence of CNTs, both particles can only be trapped by operating the system at low medium conductivities, (<10(-3) S/m) and frequencies (<75 kHz). Alternatively, applying CNTs to the system, some CNTs coat the surface of particles and increase their overall conductivity and permittivity, whereas the rest of them are patterned between the microelectrodes and induce strong DEP forces at their free ends, which can effectively trap the coated particles. The first development extends the range of medium conductivities and frequencies at which the trapping of both particles is achievable, whereas the second development facilitates the selective deposition of particles along the surface of curved microelectrodes. Setting the medium conductivity to 2×10(-3) S/m and the frequency to 20 MHz, most of 5 μm particles are trapped at the entry region of the first microelectrode pair, whereas most of 1 μm particles are trapped at the tips, and this distinction facilitates their separation. The trapping of 1 μm particles can be improved by decreasing the frequency to 1.5 MHz. This study demonstrates how the integration of CNTs into microfluidic systems enables them to operate beyond their capabilities.
Currently, there are no known treatments for protection of axonal loss associated with neuroinfla... more Currently, there are no known treatments for protection of axonal loss associated with neuroinflammatory diseases such as multiple sclerosis (MS). Survivin is a member of the inhibitors of the apoptosis (IAP) family of proteins that its neuroprotective effects have not been studied. We demonstrate here that SurR9-C84A, a survivin mutant, exhibits a neuroprotective role against the cytotoxic effects of activated T-cell infiltrates, such as granzyme B (GrB). The activated T-cell supernatants induce toxicity on differentiated SK-N-SH cells, which is associated with the loss of Ca 2+ homeostasis, the increased population of dead cells, mitochondrial membrane depolarisation, and the accelerated expression of cyclinD1, caspase3 and Fas, as observed for most apoptotic cells. Alternatively, the pre-treatment with SurR9-C84A reduces the population of dead cells by balancing the cytosolic Ca 2+ homeostasis, decreasing the level of mitochondrial depolarisation, and also reducing the expression of cyclinD1 and caspase3. Our findings suggest that SurR9-C84A has a neuroprotective effect against the cytotoxins existing in activated T-cell supernatants including GrB.
Immobilisation of cells is an important feature of many cellular assays, as it enables the physic... more Immobilisation of cells is an important feature of many cellular assays, as it enables the physical/ chemical stimulation of cells; whilst, monitoring cellular processes using microscopic techniques. Current approaches for immobilising cells, however, are hampered by time-consuming processes, the need for specific antibodies or coatings, and adverse effects on cell integrity. Here, we present a dielectrophoresis-based approach for the robust immobilisation of cells, and analysis of their responses under high shear flows. This approach is quick and label-free, and more importantly, minimises the adverse effects of electric field on the cell integrity, by activating the field for a short duration of 120 s, just long enough to immobilise the cells, after which cell culture media (such as HEPES) is flushed through the platform. In optimal conditions, at least 90% of the cells remained stably immobilised, when exposed to a shear stress of 63 dyn/cm 2 . This approach was used to examine the shear-induced calcium signalling of HEK-293 cells expressing a mechanosensitive ion channel, transient receptor potential vaniloid type 4 (TRPV4), when exposed to the full physiological range of shear stress. The ability to stably immobilise cells is an important feature in cellular assays, as it enables the physical/ chemical stimulation of cells and monitoring of cellular processes using a variety of microscopic techniques 1 . Classically, the immobilisation of non-adherent cells is acieved by surface modification 2 , which can be accomplished in different ways: such as coating the substrate surface with biomimetic peptides like poly L-lysine or poly ornithine ; cell adhesive proteins like laminin or fibronectin 5 ; or patterning a suitable ligand onto the substrate which allows cells to attach, spread and migrate along the surface . Important drawbacks of such surface modification approaches are the protein adsorption into the substrate, and the interaction between the cell-substrate may be influenced by different parameters such as surface free energy, charge, roughness, and thickness of modifying layer. Consequently, these surface modifications are often unstable and uneven, and can lead to cellular rearrangement when exposed to a high magnitude of mechanical forces 5 . Furthermore, any surface modification can affect the biology of cells and consequently change cellular responses to the experimental conditions. As such, this approach is not ideal for immobilisation of non-adherent cells, especially when high levels of mechanical stress such as flow-induced shear is required. Microfluidic systems are widely considered, as enabling technologies in cellular biology research . Microfluidic platforms offer reduced sample and reagent volumes, sample diversity, short reaction times, enhanced sensitivity, and the capacity for multiplexing and automation . Moreover, microfluidic systems enable the quick and controllable immobilisation of cells using a variety of mechanisms, including hydrodynamics 12 , optical tweezing 13 , acoustophoresis 14 , magnetophoresis 15 , and dielectrophoresis . The use of hydrodynamic filters can lead to clogging of the microfluidic channel by trapped cells or debris . Moreover, the performance of such filters depends on the size and deformability of the cells,
A self-sufficient droplet generation system using highly porous polymeric sponges is introduced... more A self-sufficient droplet generation system using highly porous polymeric sponges is introduced. Upon manual compression, hundreds of droplets are generated with 64% of them falling in the range of 5 to 50 µm. Facilitates the simple encapsulation, chemical stimulation and microscopic analysis of cells inside droplets. Is potentially suitable for conducing cellular assays in educational and research laboratories.
TRPV4 is a non-selective cation channel that tunes the function of different tissues including th... more TRPV4 is a non-selective cation channel that tunes the function of different tissues including the vascular endothelium, lung, chondrocytes, and neurons. GSK1016790A is the selective and potent agonist of TRPV4 and a pharmacological tool that is used to study the TRPV4 physiological function in vitro and in vivo. It remains unknown how the sensitivity of TRPV4 to this agonist is regulated. The spatial and temporal dynamics of receptors are the major determinants of cellular responses to stimuli. Membrane translocation has been shown to control the response of several members of the transient receptor potential (TRP) family of ion channels to different stimuli. Here, we show that TRPV4 stimulation with GSK1016790A caused an increase in [Ca 2+ ] i that is stable for a few minutes. Single molecule analysis of TRPV4 channels showed that the density of TRPV4 at the plasma membrane is controlled through two modes of membrane trafficking, complete, and partial vesicular fusion. Further, we show that the density of TRPV4 at the plasma membrane decreased within 20 min, as they translocate to the recycling endosomes and that the surface density is dependent on the release of calcium from the intracellular stores and is controlled via a PI3K, PKC, and RhoA signaling pathway.
Water jacket systems are routinely used to control the temperature of Petri dish cell culture cha... more Water jacket systems are routinely used to control the temperature of Petri dish cell culture chambers. Despite their widespread use, the thermal characteristics of such systems have not been fully investigated. In this study, we conducted a comprehensive set of theoretical, numerical and experimental analyses to investigate the thermal characteristics of Petri dish chambers under stable and transient conditions. In particular, we investigated the temperature gradient along the radial axis of the Petri dish under stable conditions, and the transition period under transient conditions. Our studies indicate a radial temperature gradient of 3.3 • C along with a transition period of 27.5 min when increasing the sample temperature from 37 to 45 • C for a standard 35 mm diameter Petri dish. We characterized the temperature gradient and transition period under various operational, geometric, and environmental conditions. Under stable conditions, reducing the diameter of the Petri dish and incorporating a heater underneath the Petri dish can effectively reduce the temperature gradient across the sample. In comparison, under transient conditions, reducing the diameter of the Petri dish, reducing sample volume, and using glass Petri dish chambers can reduce the transition period.
The functioning of cells under mechanical stress influences several cellular processes, for examp... more The functioning of cells under mechanical stress influences several cellular processes, for example proliferation, organogenesis, and transcription. Current techniques used to examine mechanical stress on loosely adherent cells, are however, primarily focused on single individual cells being stimulated, or require time-consuming surface coating techniques; and are limited in the level of shear stress that can be supplied to immobilised cells. Here we report the process of the technique, discontinuous dielectrophoresis; which enables high shear stress analysis of clusters of immobilised loosely adherent cells, we have analysed the performance of the system using Saccharomyces cerevisiae yeast cells, up to a shear stress of 42 dyn/cm 2 . Additionally, we provide application experimental results from investigating shear induced calcium signalling of HEK-293-TRPV4 cells at flow rates of 2.5, and 120 µl/min, corresponding to shear stress levels of 0.875 and 42 dyn/cm 2 , respectively. In summary, discontinuous dielectrophoresis will enable the investigation of the mechanotransduction behaviour of loosely adherent cells under physiologically relevant shear stresses. Additionally, discontinuous dielectrophoresis provides the capability for parallelism, and dynamic control over the microenvironment, as previously explored by different microfluidic platforms without the capacity for high shear stress analysis of loosely adherent cells.
We developed a platform, to investigate the influence spatial shear stress gradients on intracell... more We developed a platform, to investigate the influence spatial shear stress gradients on intracellular calcium signalling of non-adherent cells.
Oxidative stress is due to an imbalance of antioxidant/pro-oxidant homeostasis and is associated ... more Oxidative stress is due to an imbalance of antioxidant/pro-oxidant homeostasis and is associated with the progression of several neurological diseases, including Parkinson's and Alzheimer's disease and amyotrophic lateral sclerosis. Furthermore, oxidative stress is responsible for the neuronal loss and dysfunction associated with disease pathogenesis. Survivin is a member of the inhibitors of the apoptosis (IAP) family of proteins, but its neuroprotective effects have not been studied. Here, we demonstrate that SurR9-C84A, a survivin mutant, has neuroprotective effects against H 2 O 2 -induced neurotoxicity. Our results show that H 2 O 2 toxicity is associated with an increase in cell death, mitochondrial membrane depolarisation, and the expression of cyclin D1 and caspases 9 and 3. In addition, pre-treatment with SurR9-C84A reduces cell death by decreasing both the level of mitochondrial depolarisation and the expression of cyclin D1 and caspases 9 and 3. We further show that SurR9-C84A increases the antioxidant activity of GSH-peroxidase and catalase, and effectively counteracts oxidant activity following exposure to H 2 O 2 . These results suggest for the first time that SurR9-C84A is a promising treatment to protect neuronal cells against H 2 O 2 -induced neurotoxicity.
Particle trapping using dielectrophoretically patterned carbon nanotubes
Electrophoresis, Apr 1, 2010
This study presents the dielectrophoretic (DEP) assembly of multi‐walled carbon nanotubes (MWCNTs... more This study presents the dielectrophoretic (DEP) assembly of multi‐walled carbon nanotubes (MWCNTs) between curved microelectrodes for the purpose of trapping polystyrene microparticles within a microfluidic system. Under normal conditions, polystyrene particles exhibit negative DEP behaviour and are repelled from microelectrodes. Interestingly, the addition of MWCNTs to the system alters this situation in two ways: first, they coat the surface of particles and change their dielectric properties to exhibit positive DEP behaviour; second, the assembled MWCNTs are highly conductive and after the deposition serve as extensions to the microelectrodes. They establish an array of nanoelectrodes that initiates from the edge of microelectrodes and grow along the electric field lines. These nanoelectrodes can effectively trap the MWCNT‐coated particles, since they cover a large portion of the microchannel bottom surface and also create a much stronger electric field than the primary microelectrodes as confirmed by our numerical simulations. We will show that the presence of MWCNT significantly changes performance of the system, which is investigated by trapping sample polystyrene particles with plain, COOH and goat anti‐mouse IgG surfaces.
Targeting survivin has the ability to inhibit apoptosis and regulate mitosis for the protection o... more Targeting survivin has the ability to inhibit apoptosis and regulate mitosis for the protection of neuronal cells, and it offers several advantages for neuronal repair and protection. We found that the BIR motif mutant of survivin (SurR9-C84A) can bind to microtubules and regulate their stability, induce cell division, increase proliferation and activate the expression of cell cycle and neuronal markers in differentiated SK-N-SH and HCN-2 neurons. We further showed the protective effects of SurR9-C84A against post differentiation retinoic acid induced neurotoxicity. These abilities of SurR9-C84A offer a great potential for future neuronal repair therapy.
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Papers by Sara Baratchi