On-chip magnetophoretic capture in a model of malaria-infected red blood cells

The search for new rapid diagnostic tests for malaria is a priority for developing an efficient strategy to fight this endemic disease, which affects more than 3 billion people worldwide. In this paper, we characterize systematically an easy-to-operate lab-on-chip, designed for the magnetophoretic capture of malaria-infected red blood cells. The method relies on the positive magnetic susceptibility of infected red blood cells with respect to blood plasma. A matrix of nickel posts fabricated in a silicon chip placed face down is aimed at attracting infected cells, while healthy cells sediment on a glass slide under the action of gravity. Using a model of infected red blood cells, i.e. erythrocytes with methaemoglobin, we obtained a capture efficiency of about 70% after 10 minutes in static conditions. By proper agitation, the capture efficiency reached 85% after just 5 minutes. Sample preparation requires only a 1:10 volume dilution of whole blood, previously treated with heparin, in a phosphate buffered solution. Nonspecific attraction of untreated red blood cells was not observed in the same time interval. This article is protected by copyright. All rights reserved.

Fluid dynamics characterization and thrombogenicity assessment of a levitating centrifugal pump with different impeller designs

Technical guidelines nowadays recommend and regulate the use Computational Fluid Dynamics (CFD) to assess the performance of medical devices. CFD coupled to blood damage models has emerged as a powerful tool to evaluate the hemocompatibility of blood recirculating devices. The present study is aimed at evaluating the hydrodynamic performance and the thrombogenic potential of two prototypes of magnetically levitating centrifugal pumps. The two devices differ in the impeller configuration - 6-blades vs. 12-blades - and have been designed to be used in Cardiopulmonary Bypass (CPB) circuits during open heart surgery and in Extracorporeal Membrane Oxygenation (ECMO) to support patients with severe cardiac or respiratory failure. The pumps have been modelled using Direct Numerical Simulation coupled to Lagrangian analysis to predict platelet activation due to abnormal shear stress histories. Numerical results have been compared with experimental data in terms of head generation for different working points. Results show that the 6-blades pump has i) smaller stagnation areas, ii) lower stress levels and iii) higher strain rate, resulting in a lower thrombogenic potential, whereas the 12-blade impeller guarantees a more stable performance at high flow rates, suggesting its preferential use for more demanding applications, such as CPB.

Coronary artery mechanics induces human saphenous vein remodelling via recruitment of adventitial myofibroblast-like cells mediated by Thrombospondin-1

Rationale: Despite the preferred application of arterial conduits, the greater saphenous vein (SV) remains indispensable for coronary bypass grafting (CABG), especially in multi-vessel coronary artery disease (CAD). The objective of the present work was to address the role of mechanical forces in the activation of maladaptive vein bypass remodeling, a process determining progressive occlusion and recurrence of ischemic heart disease.

Methods: We employed a custom bioreactor to mimic the coronary shear and wall mechanics in human SV vascular conduits and reproduce experimentally the biomechanical conditions of coronary grafting and analyzed vein remodeling process by histology, histochemistry and immunofluorescence. We also subjected vein-derived cells to cyclic uniaxial mechanical stimulation in culture, followed by phenotypic and molecular characterization using RNA and proteomic methods. We finally validated our results in vitro and using a model of SV carotid interposition in pigs.

Results: Exposure to pulsatile flow determined a remodeling process of the vascular wall involving reduction in media thickness. Smooth muscle cells (SMCs) underwent conversion from contractile to synthetic phenotype. A time-dependent increase in proliferating cells expressing mesenchymal (CD44) and early SMC (SM22α) markers, apparently recruited from the SV adventitia, was observed especially in CABG-stimulated vessels. Mechanically stimulated SMCs underwent transition from contractile to synthetic phenotype. MALDI-TOF-based secretome analysis revealed a consistent release of Thrombospondin-1 (TSP-1), a matricellular protein involved in TGF-β-dependent signaling. TSP-1 had a direct chemotactic effect on SV adventitia resident progenitors (SVPs); this effects was inhibited by blocking TSP-1 receptor CD47. The involvement of TSP-1 in adventitial progenitor cells differentiation and graft intima hyperplasia was finally contextualized in the TGF-β-dependent pathway, and validated in a saphenous vein into carotid interposition pig model.

Conclusions: Our results provide the evidence of a matricellular mechanism involved in the human vein arterialization process controlled by alterations in tissue mechanics, and open the way to novel potential strategies to block VGD progression based on targeting cell mechanosensing-related effectors.

Prothrombotic activity of cytokine-activated endothelial cells and shear-activated platelets in the setting of ventricular assist device support

BACKGROUND

We systematically analyzed the synergistic effect of: (i) cytokine-mediated inflammatory activation of endothelial cells (ECs) with and (ii) shear-mediated platelet activation (SMPA) as a potential contributory mechanism to intraventricular thrombus formation in the setting of left ventricular assist device (LVAD) support.

METHODS

Intact and shear-activated human platelets were exposed to non-activated and cytokine-activated ECs. To modulate the level of LVAD-related shear activation, platelets were exposed to shear stress patterns of varying magnitude (30, 50, and 70 dynes/cm², 10 minutes) via a hemodynamic shearing device. ECs were activated via exposure to inflammatory tumor necrosis factor-α (TNF-α 10 and 100 ng/ml, 24 hours), consistent with inflammatory activation recorded in patients on LVAD circulatory support.

RESULTS

Adhesivity of shear-activated platelets to ECs was significantly higher than that of intact/unactivated platelets, regardless of the initial activation level (70 dynes/cm² shear-activated platelets vs intact platelets: +80%, p < 0.001). Importantly, inflammatory activation of ECs amplified platelet prothrombinase activity progressively with increasing shear stress magnitude and TNF-α concentration: thrombin generation of 70 dynes/cm² shear-activated platelets was 2.6-fold higher after exposure and adhesion to 100 ng/ml TNF-α‒activated ECs (p < 0.0001).

CONCLUSIONS

We demonstrated synergistic effect of SMPA and cytokine-mediated EC inflammatory activation to enhance EC‒platelet adhesion and platelet prothrombotic function. These mechanisms may contribute to intraventricular thrombosis in the setting of mechanical circulatory support.

Versican is differentially regulated in the adventitial and medial layers of human vein grafts

Changes in extracellular matrix proteins may contribute significantly to the adaptation of vein grafts to the arterial circulation. We examined the production and distribution of versican and hyaluronan in intact human vein rings cultured ex vivo, veins perfused ex vivo, and cultured venous adventitial and smooth muscle cells. Immunohistochemistry revealed higher levels of versican in the intima/media compared to the adventitia, and no differences in hyaluronan. In the vasa vasorum, versican and hyaluronan associated with CD34⁺ progenitor cells. Culturing the vein rings for 14 days revealed increased versican immunostaining of 30–40% in all layers, with no changes in hyaluronan. Changes in versican accumulation appear to result from increased synthesis in the intima/media and decreased degradation in the adventitia as versican transcripts were increased in the intima/media, but unchanged in the adventitia, and versikine (the ADAMTS-mediated cleavage product of versican) was increased in the intima/media, but decreased in the adventitia. In perfused human veins, versican was specifically increased in the intima/media in the presence of venous pressure, but not with arterial pressure. Unexpectedly, cultured adventitial cells express and accumulate more versican and hyaluronan than smooth muscle cells. These data demonstrate a differential regulation of versican and hyaluronan in human venous adventitia vs. intima/media and suggest distinct functions for these extracellular matrix macromolecules in these venous wall compartments during the adaptive response of vein grafts to the arterial circulation.

Microfluidic flow-based platforms for induction and analysis of dynamic shear-mediated platelet activation-Initial validation versus the standardized hemodynamic shearing device

A microfluidic flow-based platform (μFP), able to stimulate platelets via exposure of shear stress patterns pertinent to cardiovascular devices and prostheses, was compared to the Hemodynamic Shearing Device (HSD)-a state-of-the-art bench-top system for exposure of platelets to defined levels and patterns of shear. Platelets were exposed to time-varying shear stress patterns in the two systems; in detail, platelets were recirculated in the μFP or stimulated in the HSD to replicate comparable exposure time. Shear-mediated platelet activation was evaluated via (i) the platelet activity state assay, allowing the measurement of platelet-mediated thrombin generation and associated prothrombotic tendencies, (ii) scanning electron microscopy to evaluate morphological changes of sheared platelets, and (iii) flow cytometry for the determination of platelet phosphatidylserine exposure as a marker of shear activation. The results revealed good matching and comparability between the two systems, with similar trends of platelet activation, formation of microaggregates, and analogous trends of activation marker exposure for both the HSD and microfluidic-stimulated samples. These findings support future translation of the microfluidic platform as a Point-of-Care facsimile system for the diagnosis of thrombotic risk in patients implanted with cardiovascular devices.

A Mechanical Model Lung for Hydraulic Testing of Total Liquid Ventilation Circuits

A new model lung (ML), designed to reproduce the tracheal pressure vs. fluid flow relationship in animals undergoing total liquid ventilation (TLV) trials, was developed to be used as a mock bench test for neonatal TLV circuits.

The ML is based on a linear inertance-resistance-compliance (LRC) lumped-parameter model of the respiratory system with different resistance values for inspiration (Rinsp) or expiration (Rexp). The resistant element was set up using polypropylene hollow fibres packed inside a tube. A passive oneway valve was used to control the resistance cross-section area provided for the liquid to generate different values for Rinsp or Rexp, each adjustable by regulating the active length of the respective fibre pack. The compliant element consists of a cylindrical column reservoir, in which bars of different diameter were inserted to adjust compliance (C). The inertial phenomena occurring in the central airways during TLV were reproduced by specifically dimensioned conduits into which the endotracheal tube connecting the TLV circuit to the ML was inserted. A number of elements with different inertances (L) were used to simulate different sized airways.

A linear pressure drop-to-flow rate relationship was obtained for flow rates up to 5 l/min. The measured C (0.8 to 1.3 mL cmH2O−1 kg−1), Rinsp (90 to 850 cmH2O s l−1), and Rexp (50 to 400 cmH2O s l −1) were in agreement with the literature concerning animals weighing from 1 to 12 kg. Moreover, features observed in data acquired during in vivo TLV sessions, such as pressure oscillations due to fluid inertia in the upper airways, were similarly obtained in vitro thanks to the inertial element in the ML.

Clinical Evaluation of Internal Hemodiafiltration (iHDF): A Diffusive-Convective Technique Performed with Internal Filtration Enhanced High-Flux Dialyzers

Aim

Efficiency in removing middle molecules such as ß2-microglobulin (ß2-MG) is one of the main purposes of modern dialytic therapy. In order to achieve this, techniques requiring complex machines and substitution fluid have been developed over recent years. Alternatively, the internal filtration / back filtration phenomenon can be used. The recent development of a so-called “internal filtration enhanced dialyser” prompted us to compare the removal of ß2-MG together with other small molecules when the dialyser was used either in standard hemodiafiltration (HDF) or internal hemodiafiltration (iHDF).

Methods

Ten stable, anuric, hemodialysis (HD) patients treated by thrice weekly standard bicarbonate HD using low-flux synthetic membrane entered the study. A new high-flux polysulfone dialyser designed with the specific aim of enhancing internal filtration (BS-1.6 UL, 1.6 m2, Toray Industries) was used. Post dilution HDF (2.5 l/hour of substitution fluid, dialysate flow 500 ml/min) was compared with iHDF (dialysate flow 750 ml/min), with blood flow at 300 ml/min. Samples were obtained at the start and at the end of the session in order to measure the % removal of urea, creatinine, uric acid, phosphate and ß2-MG (corrected for total protein concentration). In addition, after 20 min of dialysis the clearances of the same molecules were measured. A mathematical model has been developed for the description of the hydrodynamic phenomena taking place within the dialyser and of fluid filtration across the membrane.

Results

No significant differences have been observed in removal rate switching from HDF to iHDF except for ß2-MG removal, which was slightly higher in HDF than in iHDF. Phosphate clearance is significantly higher than those obtained with creatinine in both HDF (p<0.005) and iHDF (p<0.01) modalities. The total convection calculated with the model is reduced with respect to HDF only by 24% (4100 ml/h vs. 5400 ml/h on the average).

Conclusions

iHDF is a high flux dialysis method, which, if performed with a dialyser designed to enhance internal filtration, obtains a much higher removal rate in comparison with dialysers in traditional high flux dialysis, as previously reported in the literature. Provided that the dialyser is used on a dialysis machine working with ultra pure dialysate and UF control, this dialyser line can perform reliable internal HDF without the need for replacement solution. Considering the narrow difference in performance observed between iHDF and HDF, and the increasing number (and age) of patients leading to higher dialysis costs, iHDF represents a cost-effective alternative to other diffusive-convective techniques.

Routine clinical anti-platelet agents have limited efficacy in modulating hypershear-mediated platelet activation associated with mechanical circulatory support

INTRODUCTION

Continuous flow ventricular assist devices (cfVADs) continue to be limited by thrombotic complications associated with disruptive flow patterns and supraphysiologic shear stresses. Patients are prescribed complex antiplatelet therapies, which do not fully prevent recurrent thromboembolic events. This is partially due to limited data on antiplatelet efficacy under cfVAD-associated shear conditions.

MATERIALS AND METHODS

We investigated the efficacy of antiplatelet drugs directly acting on three pathways: (1) cyclooxygenase (aspirin), (2) phosphodiesterase (dipyridamole, pentoxifylline, cilostazol), and (3) glycoprotein IIb-IIIa (eptifibatide). Gel-filtered platelets treated with these drugs were exposed for 10min to either constant shear stresses (30dyne/cm² and 70dyne/cm²) or dynamic shear stress profiles extracted from simulated platelet trajectories through a cfVAD (Micromed DeBakey). Platelet activation state (PAS) was measured using a modified prothrombinase-based assay, with drug efficacy quantified based on PAS reduction compared to untreated controls.

RESULTS AND CONCLUSIONS

Significant PAS reduction was observed for all drugs after exposure to 30dyne/cm² constant shear stress, and all drugs but dipyridamole after exposure to the 30th percentile shear stress waveform of the cfVAD. However, only cilostazol was significantly effective after 70dyne/cm² constant shear stress exposure, though no significant reduction was observed upon exposure to median shear stress conditions in the cfVAD. These results, coupled with the persistence of reported clinical thrombotic complication, suggest the need for the development of new classes of drugs that are especially designed to mitigate thrombosis in cfVAD patients, while reducing or eliminating the risk of bleeding.

A novel system for the treatment of aortic annular dilation: an ex vivo investigation

OBJECTIVES

The main reason for aortic repair failures is recurrent annular dilatation. The fibrous portion of left ventricular outflow tract dilates. A novel device was designed to tackle this problem.

METHODS

The device consists of an internal ring applied at the aortic annulus plus an external flexible band at the level of the aortic root. The internal ring has a semi-rigid portion (40%, placed at ventriculo-arterial junction) and a flexible portion to allow it to conform along the curves of the non-coronary/right coronary leaflet and right coronary/left coronary leaflet commissures. The external band acts as a reinforcement to the internal ring. A pulsatile mock loop capable of housing porcine aortic valve was used. Working conditions were 60 bpm of heart rate, 75 of stroke volumes and 120-80 mmHg of simulated pressure. Mean gradient, effective orifice area, annular diameter, coaptation height and length were recorded on 11 aortic root units (ARUs). High-speed video and standard echocardiographic images were also recorded. All data were acquired in the following conditions: (i) basal (untreated ARU); (ii) pathological condition (left coronary/non-coronary triangle was dilated by suturing an aortic patch); and (iii) ARU treated with the device.

RESULTS

Gradients and effective orifice area were respectively 0.9 ± 0.64 mmHg and 3.1 ± 0.7cm2 (pathological) and 3.7 ± 1.1 mmHg and 1.5 ± 0.2cm2 (treated, P < 0.05). Left coronary/non-coronary diameter decreased from 2.4 ± 0.2 cm (pathological) to 2.0 ± 0.2 (treated, P < 0.05). Coaptation length and height were fully restored to basal values following treatment. Visual inspection showed proper dynamics of the leaflet, confirmed by high-speed video and echocardiography.

CONCLUSIONS

The device allowed for restoring physiologic-like coaptation in the experimental model, without inducing clinically relevant worsening of the haemodynamics of the treated ARU.

Microfludic platforms for the evaluation of anti-platelet agent efficacy under hyper-shear conditions associated with ventricular assist devices

Thrombus formation is a major adverse event affecting patients implanted with ventricular assist devices (VADs). Despite anti-thrombotic drug administration, thrombotic events remain frequent within the first year post-implantation. Platelet activation (PA) is an essential process underling thrombotic adverse events in VAD systems. Indeed, abnormal shear forces, correlating with specific flow trajectories of VADs, are strong agonists mediating PA. To date, the ability to determine efficacy of anti-platelet (AP) agents under shear stress conditions is limited. Here, we present a novel microfluidic platform designed to replicate shear stress patterns of a clinical VAD, and use it to compare the efficacy of two AP agents in vitro. Gel-filtered platelets were incubated with i) acetylsalicylic acid (ASA) and ii) ticagrelor, at two different concentrations (ASA: 125 and 250 µM; ticagrelor: 250 and 500 nM) and were circulated in the VAD-emulating microfluidic platform using a peristaltic pump. GFP was collected after 4 and 52 repetitions of exposure to the VAD shear pattern and tested for shear-mediated PA. ASA significantly inhibited PA only at 2-fold higher concentration (250 µM) than therapeutic dose (125 µM). The effect of ticagrelor was not dependent on drug concentration, and did not show significant inhibition with respect to untreated control. This study demonstrates the potential use of microfluidic platforms as means of testing platelet responsiveness and AP drug efficacy under complex and realistic VAD-like shear stress conditions.

Abstract 373: Effects of Coronary Wall Mechanics on Smooth Muscle Cell Phenotypic Switch and CD44 + Mesenchymal Cell Repopulation in Saphenous Vein Grafts

Background: Despite the preferred application of arterial conduits, the greater saphenous vein (SV) remains indispensable for bypass grafting, especially in multi-vessel coronary artery disease. Early remodeling induced by altered wall mechanics has been recognized to play a key role in SV graft disease. The mechanism remains, however, unknown.

Aim: To investigate mechanical factors involved in early graft remodeling, we characterized SV-derived smooth muscle cells (SMCs) after both ex vivo coronary-like mechanical stimulation of SV segments and in vitro unidirectional strain.

Methods: SV segments from patients receiving coronary artery bypass grafts were stimulated in a custom-made coronary pulse-duplicator bioreactor. After 7 (n=6) or 14 (n=5) days, stretched and control SVs were fixed and stained for immunofluorescence. Additionally, SMCs isolated from SVs of 7 patients undergoing saphenectomy were subjected to uniaxial cyclic strain (10% elongation, 1 Hz) for 24 or 72 hours using a Flexcell platform. SMCs analysis was performed by western blotting and mass spectrometry-based secretome analysis.

Results: Coronary stimulation elevated apoptosis of SV medial cells after 7 days, and consistently reduced the percentage of cells positive for contractile markers α-SMA and calponin. Conversely, synthetic phenotype marker tropomyosin-4 (TM4) and early contractile marker SM22α were elevated at T14. Mesenchymal marker CD44 was markedly upregulated in cells populating the media after 14 days of stimulation. In accordance, strained SMCs displayed decreased α-SMA and SM22α, and increased TM4 protein expression after 72h. Analysis of the supernatant showed a significant increase of plasminogen activator inhibitor-1 and thrombospondin 1.

Conclusions: Mechanical stimulation of SVs leads to apoptosis of medial cells and a decrease of contractile SMC markers, followed by repopulation with cells expressing the mesenchymal marker CD44. In addition, unidirectional strain induces a switch of SMC phenotype and secretion of proteins related to vascular remodeling. We are currently investigating whether CD44 + cells derive from SMCs undergoing phenotypic switch, or from progenitor cells localized in the adventitia.

Modelling of Lesions Associated with Functional Mitral Regurgitation in an Ex Vivo Platform

Functional mitral regurgitation (FMR) is a complex pathology involving valvular and subvalvular structures reconfiguration, and its treatment is considered challenging. There is a lack of experimental models allowing for reliable preclinical FMR treatments' evaluation in a realistic setting. A novel approach to simulate FMR was developed and incorporated into an ex vivo passive beating heart platform. FMR was obtained by dilating the mitral annulus (MA) mainly in the antero-posterior direction and displacing the papillary muscles (PMs) apically and laterally by ad hoc designed and 3D printed dilation and displacing devices. It caused hemodynamic and valve morphology alterations. Isolated MA dilation (MAD) led to significantly increased antero-posterior distance (A-P) and decreased coaptation height (CH), tenting area (TA) and systolic leaflets angulation, resembling clinically recognized type I of mitral regurgitation with normal leaflet motion. Whereas concomitant MAD with PM displacement caused an increase in A-P, TA, CH. This geometrical configuration replicated typical determinants of type IIIb lesion with restricted leaflet motion. The proposed methods provided a realistic and repeatable ex vivo FMR model featuring two lesions clinically associated with the pathology. It bears a promise to be successfully utilized in preclinical studies, clinical training and medical education.

High Frequency Components of Hemodynamic Shear Stress Profiles are a Major Determinant of Shear-Mediated Platelet Activation in Therapeutic Blood Recirculating Devices

We systematically analyzed the relative contributions of frequency component elements of hemodynamic shear stress waveforms encountered in cardiovascular blood recirculating devices as to overall platelet activation over time. We demonstrated that high frequency oscillations are the major determinants for priming, triggering and yielding activated “prothrombotic behavior” for stimulated platelets, even if the imparted shear stress has low magnitude and brief exposure time. Conversely, the low frequency components of the stress signal, with limited oscillations over time, did not induce significant activation, despite being of high magnitude and/or exposure time. In vitro data were compared with numerical predictions computed according to a recently proposed numerical model of shear-mediated platelet activation. The numerical model effectively resolved the correlation between platelet activation and the various frequency components examined. However, numerical predictions exhibited a different activation trend compared to experimental results for different time points of a stress activation sequence. With this study we provide a more fundamental understanding for the mechanobiological responsiveness of circulating platelets to the hemodynamic environment of cardiovascular devices, and the importance of these environments in mediating life-threatening thromboembolic complications associated with shear-mediated platelet activation. Experimental data will guide further optimization of the thromboresistance of cardiovascular implantable therapeutic devices.

In vitro and in silico approaches to quantify the effects of the Mitraclip® system on mitral valve function

Mitraclip^® implantation is widely used as a valid alternative to conventional open-chest surgery in high-risk patients with severe mitral valve (MV) regurgitation. Although effective in reducing mitral regurgitation (MR) in the majority of cases, the clip implantation produces a double-orifice area that can result in altered MV biomechanics, particularly in term of hemodynamics and mechanical stress distribution on the leaflets. In this scenario, we combined the consistency of in vitro experimental platforms with the versatility of numerical simulations to investigate clip impact on MV functioning. The fluid dynamic determinants of the procedure were experimentally investigated under different working conditions (from 40bpm to 100bpm of simulated heart rate) on six swine hearts; subsequently, fluid dynamic data served as realistic boundary conditions in a computational framework able to quantitatively assess the post-procedural MV biomechanics. The finite element model of a human mitral valve featuring an isolated posterior leaflet prolapse was reconstructed from cardiac magnetic resonance. A complete as well as a marginal, sub-optimal grasping of the leaflets were finally simulated. The clipping procedure resulted in a properly coapting valve from the geometrical perspective in all the simulated configurations. Symmetrical complete grasping resulted in symmetrical distribution of the mechanical stress, while uncomplete asymmetrical grasping resulted in higher stress distribution, particularly on the prolapsing leaflet. This work pinpointed that the mechanical stress distribution following the clipping procedure is dependent on the cardiac hemodynamics and has a correlation with the proper execution of the grasping procedure, requiring accurate evaluation prior to clip delivery.

Unraveling the role of mechanical stimulation on smooth muscle cells: A comparative study between 2D and 3D models

A thorough understanding of cell response to combined culture configuration and mechanical cues is of paramount importance in vascular tissue engineering applications. Herein, we investigated and compared the response of vascular smooth muscle cells (vSMCs) cultured in different culture environments (2D cell monolayers and 3D cellularized collagen-based gels) in combination with mechanical stimulation (7% uniaxial cyclic strain, 1 Hz) for 2 and 5 days. When cyclic strain was applied, two different responses, in terms of cell orientation and expression of contractile-phenotype proteins, were observed in 2D and 3D models. Specifically, in 2D configuration, cyclic strain caused ∼50% of cell population to align nearly perpendicular (80-90 degrees) to the strain direction, while not influencing the contractile-phenotype protein expression, as compared to the 2D static controls. Conversely, the application of uniaxial strain to 3D constructs induced a ∼60% cell alignment almost parallel (0-10 degrees) to the strain direction. Moreover, 3D mechanical stimulation applied for 5 days induced a twofold increase of SM α-actin level and a 14-fold increase of calponin expression as compared to 3D static controls. Altogether these findings provide a new insight into the potential to drive cell behavior by modulating the extracellular matrix and the biomechanical environment. Biotechnol. Bioeng. 2016;113: 2254-2263. © 2016 Wiley Periodicals, Inc.

In vitro assessment of mitral valve function in cyclically pressurized porcine hearts

Recent approaches to the in vitro experimental study of cardiac fluid mechanics involve the use of whole biological structures to investigate in the lab novel therapeutic approaches for the treatment of heart pathologies. To enhance reliability and repeatability, the influence of the actuation strategy of the experimental apparatuses on the biomechanics of biological structures needs to be assessed. Using echography and intracardiac high-speed imaging, we compared the mitral valve (MV) anatomo-functional features (coaptation areas/lengths, papillary muscles-valvular plane distances) in two passive-beating-heart mock loops with internal (IPML) or external (EPML) pressurization of the ventricular chamber. Both apparatuses showed fluid dynamic conditions that closely resembled the physiology. The MVs analyzed in the EPML presented coaptation areas and lengths that were systematically higher, and exhibited greater variability from early-to peak-systole, as compared to those in the IPML. Moreover, in the EPML, the MV leaflets exhibited a convexity with high curvature toward the atrium. With the IPML, MV coaptation lengths ranged similar to available clinical data and the papillary muscles-valve plane distances were more stable throughout systole. In conclusion, both the apparatuses allow for reproducing in vitro the left heart hemodynamics, in terms of flow rates and pressures, with proper mitral valve continence. Results suggest that the IPML is more suitable for replicating the physiological MV functioning, while the EPML may have more potential as a model for the study of MV pathologies.

Aspirin has limited ability to modulate shear-mediated platelet activation associated with elevated shear stress of ventricular assist devices

Continuous flow ventricular assist devices (cfVADs) while effective in advanced heart failure, remain plagued by thrombosis related to abnormal flows and elevated shear stress. To limit cfVAD thrombosis, patients utilize complex anti-thrombotic regimens built upon a foundation of aspirin (ASA). While much data exists on ASA as a modulator of biochemically-mediated platelet activation, limited data exists as to the efficacy of ASA as a means of limiting shear-mediated platelet activation, particularly under elevated shear stress common within cfVADs. We investigated the ability of ASA (20, 25 and 125 μM) to limit shear-mediated platelet activation under conditions of: 1) constant shear stress (30 dynes/cm(2) and 70 dynes/cm(2)); 2) dynamic shear stress, and 3) initial high shear exposure (70 dynes/cm(2)) followed by low shear exposure - i.e. a platelet sensitization protocol, utilizing a hemodynamic shearing device providing uniform shear stress in vitro. The efficacy of ASA to limit platelet activation mediated via passage through a clinical cfVAD system (DeBakey Micromed) in vitro was also studied. ASA reduced platelet activation only under conditions of low shear stress (38% reduction compared to control, n=10, p<0.004), with minimal protection at higher shear stress and under dynamic conditions (n=10, p>0.5) with no limitation of platelet sensitization. ASA had limited ability (25.6% reduction in platelet activation rate) to modulate shear-mediated platelet activation induced via cfVAD passage. These findings, while performed under "deconstructed" non-clinical conditions by utilizing purified platelets alone in vitro, provide a potential contributory mechanistic explanation for the persistent thrombosis rates experienced clinically in cfVAD patients despite ASA therapy. An opportunity exists to develop enhanced pharmacologic strategies to limit shear-mediated platelet activation at elevated shear levels associated with mechanical circulatory support devices.

A novel passive left heart platform for device testing and research

Integration of biological samples into in vitro mock loops is fundamental to simulate real device's operating conditions. We developed an in vitro platform capable of simulating the pumping function of the heart through the external pressurization of the ventricle. The system consists of a fluid-filled chamber, in which the ventricles are housed and sealed to exclude the atria from external loads. The chamber is connected to a pump that drives the motion of the ventricular walls. The aorta is connected to a systemic impedance simulator, and the left atrium to an adjustable preload. The platform reproduced physiologic hemodynamics, i.e. aortic pressures of 120/80 mmHg with 5 L/min of cardiac output, and allowed for intracardiac endoscopy. A pilot study with a left ventricular assist device (LVAD) was also performed. The LVAD was connected to the heart to investigate aortic valve functioning at different levels of support. Results were consistent with the literature, and high speed video recordings of the aortic valve allowed for the visualization of the transition between a fully opening valve and a permanently closed configuration. In conclusion, the system showed to be an effective tool for the hemodynamic assessment of devices, the simulation of surgical or transcatheter procedures and for visualization studies.

A lumped-parameter approach for designing a novel pulsatile bioreactor for ex-vivo studies of human saphenous vein remodeling

After coronary artery bypass grafting (CABG), the hemodynamic conditions experienced by the saphenous veins are similar to those experienced by coronary arteries: pulsatile pressure (80-120 mmHg), pulsatile flow (mean flow rate of 250 ml/min), and elevated shear stress (1-7 Pa). Here we present a novel pulsatile platform for studying the human saphenous vein early remodeling events after CABG. The system was designed in order to apply CABG-like pressure/flow stimulation patterns to the hosted human saphenous vein segments, i.e. a pulsatile pressure oscillating between a diastolic minimum and a systolic maximum in counter-phase with a pulsatile flow rate. Functional tests revealed good fitting of simulated and measured tracings and the ability of the pulsatile platform to mimic the complexity of the coronary hemodynamic environment with good fidelity in comparison with state-of-the-art devices. This system will enable us to study the biological response of human saphenous veins to CABG conditioning ex vivo, in currently ongoing experiments.

Electrical conditioning of adipose-derived stem cells in a multi-chamber culture platform

In tissue engineering, several factors play key roles in providing adequate stimuli for cells differentiation, in particular biochemical and physical stimuli, which try to mimic the physiological microenvironments. Since electrical stimuli are important in the developing heart, we have developed an easy-to-use, cost-effective cell culture platform, able to provide controlled electrical stimulation aimed at investigating the influence of the electric field in the stem cell differentiation process. This bioreactor consists of an electrical stimulator and 12 independent, petri-like culture chambers and a 3-D computational model was used to characterize the distribution and the intensity of the electric field generated in the cell culture volume. We explored the effects of monophasic and biphasic square wave pulse stimulation on a mouse adipose-derived stem cell line (m17.ASC) comparing cell viability, proliferation, protein, and gene expression. Both monophasic (8 V, 2 ms, 1 Hz) and biphasic (+4 V, 1 ms and -4 V, 1 ms; 1 Hz) stimulation were compatible with cell survival and proliferation. Biphasic stimulation induced the expression of Connexin 43, which was found to localize also at the cell membrane, which is its recognized functional mediating intercellular electrical coupling. Electrically stimulated cells showed an induced transcriptional profile more closely related to that of neonatal cadiomyocytes, particularly for biphasic stimulation. The developed platform thus allowed to set-up precise conditions to drive adult stem cells toward a myocardial phenotype solely by physical stimuli, in the absence of exogenously added expensive bioactive molecules, and can thus represent a valuable tool for translational applications for heart tissue engineering and regeneration.

In-vitro study of a porcine quadricuspid aortic valve

BACKGROUND AND AIM OF THE STUDY

Quadricuspid aortic valve (QAV) is an extremely rare congenital defect in which the valve features an additional fourth cusp. It is often associated with an alteration in valve functionality such as valve regurgitation, stenosis and coronary disease. These associated pathologies entail surgical correction in about 50% of patients at a mean age of 50 years.

METHODS

A swine QAV was studied in a pulsatile mock loop in the laboratory. Rest (70 bpm) and exercise (100 bpm) conditions were simulated, and opening and closing kinematics were evaluated from a high-speed video. Short- and long-axis echocardiograms were recorded. The pressure drop across the valve, valve competence and effective orifice area were evaluated and compared to data from healthy samples tested in the same experimental apparatus.

RESULTS

Hemodynamic quantities were physiologic-like, despite the QAV showing an altered kinematics (longer closing and opening times compared to healthy samples) and an asynchronous closing phase (the extra cusps reached the closed configuration at the end of systole systematically earlier with respect to the other three cusps). Echocardiographic data showed an increased coaptation height between the left and right coronary cusps, and a mismatch between the lunule of the extra cusp and the non-coronary cusp.

CONCLUSION

The altered kinematics, together with incorrect coaptation, can alter the biomechanics of the structure, inducing an anomalous distribution of local stress which could lead to structural failure over time.

A dynamic distention protocol for whole-organ bladder decellularization: histological and biomechanical characterization of the acellular matrix

A combined physical-chemical protocol for whole full-thickness bladder decellularization is proposed, based on organ cyclic distention through repeated infusion/withdrawal of the decellularization agents through the urethra. The dynamic decellularization was intended to enhance cell removal efficiency, facilitating the delivery of detergents within the inner layers of the tissue and the removal of cell debris. The use of mild chemical detergents (hypotonic solution and non-ionic detergent) was employed to limit adverse effects upon matrix 3D ultrastructure. Inspection of the presence of residual DNA and RNA was carried out on decellularized matrices to verify effective cell removal. Histological investigation was focused on assessing the retention of adequate structural and functional components that regulate the biomechanical behaviour of the acellular tissue. Biomechanical properties were evaluated through uniaxial tensile loading tests of tissue strips and through ex vivo filling cystometry to evaluate the whole-organ mechanical response to a physiological-like loading state. According to our results, a dynamic decellularization protocol of 17 h duration with a 5 ml/min detergent infusion flow rate revealed higher DNA removal efficiency than standard static decellularization, resulting in residual DNA content < 50 ng/mg dry tissue weight. Furthermore, the collagen network and elastic fibres distribution were preserved in the acellular ECM, which exhibited suitable biomechanical properties in the perspective of its future use as an implant for bladder augmentation.

A microfluidic platform for controlled biochemical stimulation of twin neuronal networks

Spatially and temporally resolved delivery of soluble factors is a key feature for pharmacological applications. In this framework, microfluidics coupled to multisite electrophysiology offers great advantages in neuropharmacology and toxicology. In this work, a microfluidic device for biochemical stimulation of neuronal networks was developed. A micro-chamber for cell culturing, previously developed and tested for long term neuronal growth by our group, was provided with a thin wall, which partially divided the cell culture region in two sub-compartments. The device was reversibly coupled to a flat micro electrode array and used to culture primary neurons in the same microenvironment. We demonstrated that the two fluidically connected compartments were able to originate two parallel neuronal networks with similar electrophysiological activity but functionally independent. Furthermore, the device allowed to connect the outlet port to a syringe pump and to transform the static culture chamber in a perfused one. At 14 days invitro, sub-networks were independently stimulated with a test molecule, tetrodotoxin, a neurotoxin known to block action potentials, by means of continuous delivery. Electrical activity recordings proved the ability of the device configuration to selectively stimulate each neuronal network individually. The proposed microfluidic approach represents an innovative methodology to perform biological, pharmacological, and electrophysiological experiments on neuronal networks. Indeed, it allows for controlled delivery of substances to cells, and it overcomes the limitations due to standard drug stimulation techniques. Finally, the twin network configuration reduces biological variability, which has important outcomes on pharmacological and drug screening.

A novel environmental chamber for neuronal network multisite recordings

Environmental stability is a critical issue for neuronal networks in vitro. Hence, the ability to control the physical and chemical environment of cell cultures during electrophysiological measurements is an important requirement in the experimental design. In this work, we describe the development and the experimental verification of a closed chamber for multisite electrophysiology and optical monitoring. The chamber provides stable temperature, pH and humidity and guarantees cell viability comparable to standard incubators. Besides, it integrates the electronics for long-term neuronal activity recording. The system is portable and adaptable for multiple network housings, which allows performing parallel experiments in the same environment. Our results show that this device can be a solution for long-term electrophysiology, for dual network experiments and for coupled optical and electrical measurements.

In vitro hemodynamics and valve imaging in passive beating hearts

Due to their high complexity, surgical approaches to valve repair may benefit from the use of in vitro simulators both for training and for the investigation of those measures which can lead to better clinical results. In vitro tests are intrinsically more effective when all the anatomical substructures of the valvular complexes are preserved. In this work, a mock apparatus able to house an entire explanted porcine heart and subject it to pulsatile fluid-dynamic conditions was developed, in order to enable the hemodynamic analysis of simulated surgical procedures and the imaging of the valvular structures. The mock loop's hydrodynamic design was based on an ad-hoc defined lumped-parameter model. The left ventricle of an entire swine heart was dynamically pressurized by an external computer-controlled pulse duplicator. The ascending aorta was connected to a hydraulic circuit which simulated the input impedance of the systemic circulation; a reservoir passively filled the left atrium. Accesses for endoscopic imaging were located in the apex of the left ventricle and in the aortic root. The experimental pressure and flow tracings were comparable with the typical in vivo curves; a mean flow of 3.5±0.1l pm and a mean arterial pressure of 101±2 mmHg was obtained. High-quality echographic and endoscopic video recordings demonstrated the system's excellent potential in the observation of the cardiac structures dynamics. The proposed mock loop represents a suitable in vitro system for the testing of minimally-invasive cardiovascular devices and surgical procedures for heart valve repair.

Simulation of functional tricuspid regurgitation using an isolated porcine heart model

BACKGROUND AND AIM OF THE STUDY

The results of tricuspid annuloplasty to treat functional tricuspid regurgitation (FTR) are sometimes suboptimal, and alternative techniques are needed. In the absence of reliable FTR models, and in an effort to minimize the need for animal experiments, a reproducible bench-model was developed of FTR, that allowed the simulation of the anatomic features of the condition.

METHODS

A fresh porcine heart was mounted on a rigid support that was placed into a basin filled with saline; a closed circuit was then created with a centrifugal pump, equipped with connection tubes. The inflow tube of the pump conveyed saline from the basin to the pump; the outflow cannula was inserted through the pulmonary artery, across the pulmonary valve, into the right ventricle. The pump was activated to pressurize the right ventricle, thus inducing tricuspid valve regurgitation (TVR). The regurgitant flow through the valve was quantified using a flow-meter. Radiopaque markers were sutured to the head of each papillary muscle and to the tricuspid annulus, in order to trace the geometric changes of the tricuspid valve at increasing pump rates, using fluoroscopy. The efficacy of the bench-model was validated with 10 hearts.

RESULTS

The TVR was increased proportionally with the right ventricular pressure (RVP) (TVR = 0.089xRVP - 1.515; R2 = 0.89). The increase in TVR was associated with increases in the annular-to-papillary muscles distance (APML) (TVR = 0.059xAPML - 2.94; R2 = 0.96), of the inter-papillary muscles distance (PMD) (TVR = 0.058xPMD - 8.58; R2 = 0.94), and of the triscuspid annular dilatation (TAD) (TVR = 0.05xTAD - 1.85; R2 = 0.89). Of these parameters, APML was the strongest predictor of TVR.

CONCLUSION

The porcine heart bench model represents a reproducible system to simulate the physiopathology of FTR, and has the potential to serve as a complementary method for the evaluation of new 'in vitro' technologies and therapies for FTR.

Validation of long-term primary neuronal cultures and network activity through the integration of reversibly bonded microbioreactors and MEA substrates

In vitro recording of neuronal electrical activity is a widely used technique to understand brain functions and to study the effect of drugs on the central nervous system. The integration of microfluidic devices with microelectrode arrays (MEAs) enables the recording of networks activity in a controlled microenvironment. In this work, an integrated microfluidic system for neuronal cultures was developed, reversibly coupling a PDMS microfluidic device with a commercial flat MEA through magnetic forces. Neurons from mouse embryos were cultured in a 100 µm channel and their activity was followed up to 18 days in vitro. The maturation of the networks and their morphological and functional characteristics were comparable with those of networks cultured in macro-environments and described in literature. In this work, we successfully demonstrated the ability of long-term culturing of primary neuronal cells in a reversible bonded microfluidic device (based on magnetism) that will be fundamental for neuropharmacological studies.

How to embed three-dimensional flexible electrodes in microfluidic devices for cell culture applications

This communication describes a simple, rapid and cost effective method of embedding a conductive and flexible material within microfluidic devices as a means to realize uniform electric fields within cellular microenvironments. Fluidic channels and electrodes are fabricated by traditional soft-lithography in conjunction with chemical etching of PDMS. Devices can be deformable (thus allowing for a combination of electro-mechanical stimulation), they are made from inexpensive materials and easily assembled by hand; this method is thus accessible to a wide range of laboratories and budgets.

Beat-rate dependent mitral flow patterns for in vitro hemodynamic applications

The conservative surgery approach for restoring the functionality of heart valves has predominated during the last two decades, particularly for the mitral valve. In vitro pulsatile testing is a key methodology for the investigation of heart valve hemodynamics, and particularly for the ideation, validation and optimization of novel techniques in heart valve surgery. Traditionally, however, pulsatile mock loops have been developed for the study of aortic valve substitutes, and scarce attention has been paid in replicating the mitral flow patterns with due hemodynamic fidelity. In this work we provide detailed analytical expressions to produce beat-rate dependent, physiologic-like mitral flow patterns for in vitro applications. The approach we propose is based on a biomechanical analysis of the factors which govern hemodynamic changes in the mitral flow pattern, namely in terms of E and A wave contours and E/A peaks ratio, when switching from rest to mild exercise conditions. The patterns from the model we obtained were in good agreement with clinical literature data in terms of i) gradual superimposition of the E and A wave, which yielded a single peak at 96 bpm; ii) decrease in the E/A ratio with increasing heart rate; iii) amount of flow delivered by each of the two waves. The proposed method provides a physiologically representative, beat-rate dependent analytical expression of the mitral flow pattern, which can be used in in vitro hydrodynamic investigations to accurately replicate the changes that the flow waves experience when the heart rate shifts from rest to mild exercise conditions.

Realization and efficiency evaluation of a micro-photocatalytic cell prototype for real-time blood oxygenation

A novel, miniaturized, high-efficiency photocatalytic cell, able to work in dynamic conditions, has been designed and validated in this study. Microfluidic channels were molded out of polydimethylsiloxane (PDMS) by means of standard soft lithography techniques, so as to work as photocatalytic cells, where the coupling of anatase titanium dioxide thin films and platinum electrodes, allows an electrically assisted photocatalytic reaction to produce dissolved oxygen gas from the water content of flowing fluid (e.g. blood). The thin films were deposited onto quartz glass substrates at room temperature (300 K) using reactive radio-frequency sputtering with a titanium metal target. The photocatalytic activity was evaluated through reduction rate of methylene blue solution. The results of the current study, as a proof of concept, have shown that the device can generate oxygen at a rate of 4.06 μM O(2)/(cm(2)min), thus extending its possible application range to the full oxygenation of flowing venous blood.

Mechanisms of polymyxin B endotoxin removal from extracorporeal blood flow: molecular interactions

The outer leaflet of Gram-negative bacteria membrane contains a great amount of lipopolysaccharides, also known as endotoxins, which play a central role in the pathogenesis of septic shock. It has been demonstrated that the polymyxin B (PMB) molecule has both antibacterial and antiendotoxin capabilities; in fact, it is able to compromise the bacterial outer membrane and bind lipopolysaccharides, thereby neutralizing its toxic effects. Extracorporeal hemoperfusion treatments based on cartridges containing PMB-immobilized fibers (Toraymyxin PMX-F; Toray Industries, Tokyo, Japan) are used to remove endotoxins circulating in the blood flow. In this study, we focused on the characterization of the interactions occurring in the formation of the PMB-endotoxin complex at the molecular level. In particular, the molecular mechanics approach was used to evaluate the interaction energy and eventually the interaction force between the two molecules. PMB was faced with five molecular portions of lipopolysaccharides differing in their structure. The interaction energy occurring for each molecular complex was calculated at different intermolecular distances and the binding forces were estimated by fitting interaction energy data. Results show that the short-range interactions between PMB and endotoxins are mediated mainly by hydrophobic forces, while in the long term, the complex formation is driven by ionic forces only. Maximum binding forces calculated via molecular mechanics for the PMB-endotoxin complex are in the range of 1.39-3.79 nN. Understanding the interaction mechanism of the single molecular complex is useful both in order to figure out the molecular features of such interaction and to perform higher scale level analysis, where such nanoscale detail is impractical but could be used to account for molecular behavior at a coarse level of discretization.

Beat-rate Dependent Mitral Flow Patterns for in Vitro Hemodynamic Applications

The conservative surgery approach for restoring the functionality of heart valves has predominated during the last two decades, particularly for the mitral valve. In vitro pulsatile testing is a key methodology for the investigation of heart valve hemodynamics, and particularly for the ideation, validation and optimization of novel techniques in heart valve surgery. Traditionally, however, pulsatile mock loops have been developed for the study of aortic valve substitutes, and scarce attention has been paid in replicating the mitral flow patterns with due hemodynamic fidelity. In this work we provide detailed analytical expressions to produce beat-rate dependent, physiologic-like mitral flow patterns for in vitro applications. The approach we propose is based on a biomechanical analysis of the factors which govern hemodynamic changes in the mitral flow pattern, namely in terms of E and A wave contours and E/A peaks ratio, when switching from rest to mild exercise conditions. The patterns from the model we obtained were in good agreement with clinical literature data in terms of i) gradual superimposition of the E and A wave, which yielded a single peak at 96 bpm; ii) decrease in the E/A ratio with increasing heart rate; iii) amount of flow delivered by each of the two waves. The proposed method provides a physiologically representative, beat-rate dependent analytical expression of the mitral flow pattern, which can be used in in vitro hydrodynamic investigations to accurately replicate the changes that the flow waves experience when the heart rate shifts from rest to mild exercise conditions.

A computational model for the optimization of transport phenomena in a rotating hollow-fiber bioreactor for artificial liver

A comprehensive computational study modelling the operation of a rotating hollow-fiber bioreactor for artificial liver (BAL) was performed to explore the interactions between the oxygenated culture medium and the cultured hepatocytes. Computational fluid dynamics investigations were carried out using two-dimensional (2D) and 3D time-dependent numerical simulations, integrating calculations of diffusion, convection, and multiphase fluid dynamics. The analysis was aimed at determining the rotational speed value of the chamber to ensure homogenous distribution of the floating microcarrier-attached aggregated cells (microCAACs) and avoid their sedimentation and excessive packing, analyzing oxygen (O(2)) delivery and cellular O(2) consumption as an index of cellular metabolic activity, and analyzing the fluid-induced mechanical stress experienced by cells. According to our results, homogeneous distribution of cells is reached at a rotational speed of 30 rpm; spreading of cellular concentration at around the initial value of 12% was limited (median = 11.97%, 5th percentile = 10.94%, 95th percentile = 13.2%), resulting in uniform suspension of microCAACs, which did not appear to be excessively packed. Mixing within the rotating fluid caused a maximum fluid-induced stress value of 0.05 Pa, which was neither endangering for liver-specific functions of cultured cells, nor causing disruption of the floating aggregates. Moreover, an inlet medium flow rate of 200 mL/m with a partial pressure of oxygen (pO(2)) value of 160 mmHg was found to guarantee an adequate O(2) supply for the hepatocytes (2.7 x 10(8) hepatocytes are simulated); under such conditions, the minimum pO(2) value (23 mmHg) is above the critical threshold value, causing the onset of cellular hypoxia (10 mmHg). We proved that numerical simulation of transport phenomena is a valuable tool for the computer-aided design of BALs, helping overcome the unsolved issues in optimizing the cell-environment conditioning procedure in rotating BALs.