Sex-Specific and Dose-Dependent Effects of Drag-Reducing Polymers on Microcirculation and Tissue Oxygenation in Rats After Traumatic Brain Injury.

Traumatic brain injury (TBI) ultimately leads to a reduction in the cerebral metabolic rate for oxygen due to ischemia. Previously, we showed that 2 ppm i.v. of drag-reducing polymers (DRP) improve hemodynamic and oxygen delivery to tissue in a rat model of mild-to-moderate TBI. Here we evaluated sex-specific and dose-dependent effects of DRP on microvascular CBF (mvCBF) and tissue oxygenation in rats after moderate TBI. In vivo two-photon laser scanning microscopy over the rat parietal cortex was used to monitor the effects of DRP on microvascular perfusion, tissue oxygenation, and blood-brain barrier (BBB) permeability. Lateral fluid-percussion TBI (1.5 ATA, 100 ms) was induced after baseline imaging and followed by 4 h of monitoring. DRP was injected at 1, 2, or 4 ppm within 30 min after TBI. Differences between groups were determined using a two-way ANOVA analysis for multiple comparisons and post hoc testing using the Mann-Whitney U test. Moderate TBI progressively decreased mvCBF, leading to tissue hypoxia and BBB degradation in the pericontusion zone (p < 0.05). The i.v. injection of DRP increased near-wall flow velocity and flow rate in arterioles, leading to an increase in the number of erythrocytes entering capillaries, enhancing capillary perfusion and tissue oxygenation while protecting BBB in a dose-dependent manner without significant difference between males and females (p < 0.01). TBI resulted in an increase in intracranial pressure (20.1 ± 3.2 mmHg, p < 0.05), microcirculatory redistribution to non-nutritive microvascular shunt flow, and stagnation of capillary flow, all of which were dose-dependently mitigated by DRP. DRP at 4 ppm was most effective, with a non-significant trend to better outcomes in female rats.

Hemorheological Approach to Improve Perfusion of Red Blood Cells with Reduced Deformability Using Drag-Reducing Polymer (In Vitro Study).

Drag-reducing polymers (DRPs) are nontoxic water-soluble blood additives that have been shown to beneficially alter hemodynamics when delivered intravenously in nanomolar concentrations. This study examines the ability of DRPs to alter the traffic of mixtures of normal and less-deformable red blood cells (RBCs) through branched microchannels and is intended to support and expand upon previous experiments within straight capillary tubes to promote DRPs for future clinical use. Branched polydimethylsiloxane microchannels were perfused with a mixture of normal bovine RBCs also containing heat-treated less-deformable RBCs at a hematocrit of 30% with 10 ppm of the DRP poly(ethylene oxide) (MW 4M Da). Suspensions were driven by syringe pump, collected at outlets, and RBC dimensions measured while subject to shear stress to determine the proportion of healthy RBCs in each sample. DRPs eliminated evidence of the plasma skimming phenomena and significantly increased the pressure drop across microchannels. Further, DRPs were found to cause an increase in the proportion of healthy RBCs exiting the branch outlet from -8.5 ± 2.5% (control groups) to +12.1 ± 5.4% (n = 6, p = 0.02). These results suggest DRP additives may be used to improve the perfusion of less-deformable RBCs in vivo and indicates their potential for future clinical use.

Addition of Drag-Reducing Polymers to Colloid Resuscitation Fluid Enhances Cerebral Microcirculation and Tissue Oxygenation After Traumatic Brain Injury Complicated by Hemorrhagic Shock.

Hemorrhagic shock (HS) is a severe complication of traumatic brain injury (TBI) that doubles mortality due to severely compromised microvascular cerebral blood flow (mvCBF) and oxygen delivery reduction, as a result of hypotension. Volume expansion with resuscitation fluids (RF) for HS does not improve microvascular CBF (mvCBF); moreover, it aggravates brain edema. We showed that the addition of drag-reducing polymers (DRP) to crystalloid RF (lactated Ringer's) significantly improves mvCBF, oxygen supply, and neuronal survival in rats suffering TBI+HS. Here, we compared the effects of colloid RF (Hetastarch) with DRP (HES-DRP) and without (HES). Fluid percussion TBI (1.5 ATA, 50 ms) was induced in rats and followed by controlled HS to a mean arterial pressure (MAP) of 40 mmHg. HES or HES-DRP was infused to restore MAP to 60 mmHg for 1 h (prehospital period), followed by blood reinfusion to a MAP of 70 mmHg (hospital period). In vivo two-photon microscopy was used to monitor cerebral microvascular blood flow, tissue hypoxia (NADH), and neuronal necrosis (i.v. propidium iodide) for 5 h after TBI+HS, followed by postmortem DiI vascular painting. Temperature, MAP, blood gases, and electrolytes were monitored. Statistical analyses were done using GraphPad Prism by Student's t-test or Kolmogorov-Smirnov test, where appropriate. TBI+HS compromised mvCBF and tissue oxygen supply due to capillary microthrombosis. HES-DRP improved mvCBF and tissue oxygenation (p < 0.05) better than HES. The number of dead neurons in the HES-DRP was significantly less than in the HES group: 76.1 ± 8.9 vs. 178.5 ± 10.3 per 0.075 mm3 (P < 0.05). Postmortem visualization of painted vessels revealed vast microthrombosis in both hemispheres that were 33 ± 2% less in HES-DRP vs. HES (p < 0.05). Thus, resuscitation after TBI+HS using HES-DRP effectively restores mvCBF and reduces hypoxia, microthrombosis, and neuronal necrosis compared to HES. HES-DRP is more neuroprotective than lactated Ringer's with DRP and requires an infusion of a smaller volume, which reduces the development of hypervolemia-induced brain edema.

Improved Cerebral Perfusion Pressure and Microcirculation by Drag Reducing Polymer-Enforced Resuscitation Fluid After Traumatic Brain Injury and Hemorrhagic Shock.

Hemorrhagic shock (HS) after traumatic brain injury (TBI) reduces cerebral perfusion pressure (CPP) and cerebral blood flow (CBF), increasing hypoxia and doubling mortality. Volume expansion with resuscitation fluids (RFs) for HS does not improve CBF and tissue oxygen, while hypervolemia exacerbates brain edema and elevates intracranial pressure (ICP). We tested whether drag-reducing polymers (DRPs), added to isotonic Hetastarch (HES), would improve CBF but prevent ICP increase. TBI was induced in rats by fluid percussion, followed by controlled hemorrhage to mean arterial pressure (MAP) = 40 mmHg. HES-DRP or HES was infused to MAP = 60 mmHg for 1 h, followed by blood reinfusion to MAP = 70 mmHg. Temperature, MAP, ICP, cortical Doppler flux, blood gases, and electrolytes were monitored. Microvascular CBF, tissue hypoxia, and neuronal necrosis were monitored by two-photon laser scanning microscopy 5 h after TBI/HS. TBI/HS reduced CPP and CBF, causing tissue hypoxia. HES-DRP (1.9 ± 0.8 mL) more than HES (4.5 ± 1.8 mL) improved CBF and tissue oxygenation (p < 0.05). In the HES group, ICP increased to 23 ± 4 mmHg (p < 0.05) but in HES-DRP to 12 ± 2 mmHg. The number of dead neurons, microthrombosis, and the contusion volume in HES-DRP were significantly less than in the HES group (p < 0.05). HES-DRP required a smaller volume, which reduced ICP and brain edema.

Resuscitation with Drag Reducing Polymers after Traumatic Brain Injury with Hemorrhagic Shock Reduces Microthrombosis and Oxidative Stress.

Outcome after traumatic brain injury (TBI) is worsened by hemorrhagic shock (HS); however, the existing volume expansion approach with resuscitation fluids (RF) is controversial as it does not adequately alleviate impaired microvascular cerebral blood flow (mCBF). We previously reported that resuscitation fluid with drag reducing polymers (DRP-RF) improves CBF by rheological modulation of hemodynamics. Here, we evaluate the efficacy of DRP-RF, compared to lactated Ringers resuscitation fluid (LR-RF), in reducing cerebral microthrombosis and reperfusion mitochondrial oxidative stress after TBI complicated by HS. Fluid percussion TBI (1.5 ATA, 50 ms) was induced in rats and followed by controlled HS to a mean arterial pressure (MAP) of 40 mmHg. DRP-RF or LR-RF was infused to restore MAP to 60 mmHg for 1 h (pre-hospital period), followed by blood re-infusion to a MAP = 70 mmHg (hospital period). In vivo 2-photon laser scanning microscopy over the parietal cortex was used to monitor microvascular blood flow, nicotinamide adenine dinucleotide (NADH) for tissue oxygen supply and mitochondrial oxidative stress (superoxide by i.v. hydroethidine [HEt], 1 mg/kg) for 4 h after TBI/HS, followed by Dil vascular painting during perfusion-fixation. TBI/HS decreased mCBF resulting in capillary microthrombosis and tissue hypoxia. Microvascular CBF and tissue oxygenation were significantly improved in the DRP-RF compared to the LR-RF treated group (p < 0.05). Reperfusion-induced oxidative stress, reflected by HEt fluorescence, was 32 ± 6% higher in LR-RF vs. DRP-RF (p < 0.05). Post-mortem whole-brain visualization of DiI painted vessels revealed multiple microthromboses in both hemispheres that were 29 ± 3% less in DRP-RF vs. LR-RF group (p < 0.05). Resuscitation after TBI/HS using DRP-RF effectively restores mCBF, reduces hypoxia, microthrombosis formation, and mitochondrial oxidative stress compared to conventional volume expansion with LR-RF.

Preclinical performance of a pediatric mechanical circulatory support device: The PediaFlow ventricular assist device.

OBJECTIVES: The PediaFlow (HeartWare International, Inc, Framingham, Mass) is a miniature, implantable, rotodynamic, fully magnetically levitated, continuous-flow pediatric ventricular assist device. The fourth-generation PediaFlow was evaluated in vitro and in vivo to characterize performance and biocompatibility. METHODS: Supported by 2 National Heart, Lung, and Blood Institute contract initiatives to address the limited options available for pediatric patients with congenital or acquired cardiac disease, the PediaFlow was developed with the intent to provide chronic cardiac support for infants as small as 3 kg. The University of Pittsburgh-led Consortium evaluated fourth-generation PediaFlow prototypes both in vitro and within a preclinical ovine model (n = 11). The latter experiments led to multiple redesigns of the inflow cannula and outflow graft, resulting in the implantable design represented in the most recent implants (n = 2). RESULTS: With more than a decade of extensive computational and experimental efforts spanning 4 device iterations, the AA battery-sized fourth-generation PediaFlow has an operating range of 0.5 to 1.5 L/min with minimal hemolysis in vitro and excellent hemocompatibility (eg, minimal hemolysis and platelet activation) in vivo. The pump and finalized accompanying implantable components demonstrated preclinical hemodynamics suitable for the intended pediatric application for up to 60 days. CONCLUSIONS: Designated a Humanitarian Use Device for "mechanical circulatory support in neonates, infants, and toddlers weighing up to 20 kg as a bridge to transplant, a bridge to other therapeutic intervention such as surgery, or as a bridge to recovery" by the Food and Drug Administration, these initial results document the biocompatibility and potential of the fourth-generation PediaFlow design to provide chronic pediatric cardiac support.

Heart valve scaffold fabrication: Bioinspired control of macro-scale morphology, mechanics and micro-structure.

Valvular heart disease is currently treated with mechanical valves, which benefit from longevity, but are burdened by chronic anticoagulation therapy, or with bioprosthetic valves, which have reduced thromboembolic risk, but limited durability. Tissue engineered heart valves have been proposed to resolve these issues by implanting a scaffold that is replaced by endogenous growth, leaving autologous, functional leaflets that would putatively eliminate the need for anticoagulation and avoid calcification. Despite the diversity in fabrication strategies and encouraging results in large animal models, control over engineered valve structure-function remains at best partial. This study aimed to overcome these limitations by introducing double component deposition (DCD), an electrodeposition technique that employs multi-phase electrodes to dictate valve macro and microstructure and resultant function. Results in this report demonstrate the capacity of the DCD method to simultaneously control scaffold macro-scale morphology, mechanics and microstructure while producing fully assembled stent-less multi-leaflet valves composed of microscopic fibers. DCD engineered valve characterization included: leaflet thickness, biaxial properties, bending properties, and quantitative structural analysis of multi-photon and scanning electron micrographs. Quasi-static ex-vivo valve coaptation testing and dynamic organ level functional assessment in a pressure pulse duplicating device demonstrated appropriate acute valve functionality.

Drag reducing polymers decrease hepatic injury and metastases after liver ischemia-reperfusion.

INTRODUCTION: Surgery, a crucial therapeutic modality in the treatment of solid tumors, can induce sterile inflammatory processes which can result in metastatic progression. Liver ischemia and reperfusion (I/R) injury, an inevitable consequence of hepatic resection of metastases, has been shown to foster hepatic capture of circulating cancer cells and accelerate metastatic growth. Efforts to reduce these negative consequences have not been thoroughly investigated. Drag reducing polymers (DRPs) are blood-soluble macromolecules that can, in nanomolar concentrations, increase tissue perfusion, decrease vascular resistance and decrease near-wall microvascular concentration of neutrophils and platelets thereby possibly reducing the inflammatory microenvironment. We hypothesize that DRP can potentially be used to ameliorate metastatic capture of tumor cells and tumor growth within the I/R liver. METHODS: Experiments were performed utilizing a segmental ischemia model of mice livers. Five days prior or immediately prior to ischemia, murine colon adenocarcinoma cells (MC38) were injected into the spleen. DRP (polyethylene oxide) or a control of low-molecular-weight polyethylene glycol without drag reducing properties were administered intraperitoneally at the onset of reperfusion. RESULTS: After three weeks from I/R, we observed that liver I/R resulted in an increased ability to capture and foster growth of circulating tumor cells; in addition, the growth of pre-existing micrometastases was accelerated three weeks later. These effects were significantly curtailed when mice were treated with DRPs at the time of I/R. Mechanistic investigations in vivo indicated that DRPs protected the livers from I/R injury as evidenced by significant decreases in hepatocellular damage, neutrophil recruitment into the liver, formation of neutrophil extracellular traps, deposition of platelets, formation of microthrombi within the liver sinusoids and release of inflammatory cytokines. CONCLUSIONS: DRPs significantly attenuated metastatic tumor development and growth. DRPs warrant further investigation as a potential treatment for liver I/R injury in the clinical setting to improve cancer-specific outcomes.

Development of a High-Throughput Magnetic Separation Device for Malaria-Infected Erythrocytes.

This study describes a non-dilutive high-gradient magnetic separation (HGMS) device intended to continuously remove malaria-infected red blood cells (iRBCs) from the circulation. A mesoscale prototype device with disposable photo-etched ferromagnetic grid and reusable permanent magnet was designed with a computationally-optimized magnetic force. The prototype device was evaluated in vitro using a non-pathogenic analog for malaria-infected blood, comprised of 24% healthy RBCs, 6% human methemoglobin RBCs (metRBCs), and 70% phosphate buffer solution (PBS). The device provided a 27.0 ± 2.2% reduction of metRBCs in a single pass at a flow rate of 77 µL min-1. This represents a clearance rate over 380 times greater throughput than microfluidic devices reported previously. These positive results encourage development of a clinical scale system that would economize time and donor blood for treating severe malaria.

Nanomolar concentration of blood-soluble drag-reducing polymer inhibits experimental metastasis of human breast cancer cells.

Metastasis is the leading cause of cancer mortality. Extravasation of cancer cells is a critical step of metastasis. We report a novel proof-of-concept study that investigated whether non-toxic blood-soluble chemical agents capable of rheological modification of the near-vessel-wall blood flow can reduce extravasation of tumor cells and subsequent development of metastasis. Using an experimental metastasis model, we demonstrated that systemic administration of nanomolar concentrations of so-called drag-reducing polymer dramatically impeded extravasation and development of pulmonary metastasis of breast cancer cells in mice. This is the first proof-of-principle study to directly demonstrate physical/rheological, as opposed to chemical, way to prevent cancer cells from extravasation and developing metastasis and, thus, it opens the possibility of a new direction of adjuvant interventional approach in cancer.

Rheological effects of drag-reducing polymers improve cerebral blood flow and oxygenation after traumatic brain injury in rats.

Cerebral ischemia has been clearly demonstrated after traumatic brain injury (TBI); however, neuroprotective therapies have not focused on improvement of the cerebral microcirculation. Blood soluble drag-reducing polymers (DRP), prepared from high molecular weight polyethylene oxide, target impaired microvascular perfusion by altering the rheological properties of blood and, until our recent reports, has not been applied to the brain. We hypothesized that DRP improve cerebral microcirculation and oxygenation after TBI. DRP were studied in healthy and traumatized rat brains and compared to saline controls. Using in-vivo two-photon laser scanning microscopy over the parietal cortex, we showed that after TBI, nanomolar concentrations of intravascular DRP significantly enhanced microvascular perfusion and tissue oxygenation in peri-contusional areas, preserved blood-brain barrier integrity and protected neurons. The mechanisms of DRP effects were attributable to reduction of the near-vessel wall cell-free layer which increased near-wall blood flow velocity, microcirculatory volume flow, and number of erythrocytes entering capillaries, thereby reducing capillary stasis and tissue hypoxia as reflected by a reduction in NADH. Our results indicate that early reduction in CBF after TBI is mainly due to ischemia; however, metabolic depression of contused tissue could be also involved.

A Reusable, Compliant, Small Volume Blood Reservoir for In Vitro Hemolysis Testing.

Bench-top in vitro hemolysis testing is a fundamental tool during the design and regulatory safety evaluation of blood-contacting medical devices. While multiple published experimental protocols exist, descriptions of the test loop reservoir remain ambiguous. A critical fixture within the circuit, there is no readily available blood reservoir that ensures thorough mixing and complete air evacuation: two major factors which can affect results. As part of the Food and Drug Administration (FDA) Critical Path Initiative, we developed a three-piece reservoir consisting of a 3D-printed base, a plastic clamp set, and a medical-grade blood bag. This simple, reusable, and cost-effective design was used successfully in the hemolysis assessment of FDA benchmark nozzles and prototype rotary blood pumps, and may be useful as an integral component to any in vitro blood circulation loop.

Red Blood Cell Mechanical Fragility Test for Clinical Research Applications.

Red blood cell (RBC) susceptibility to mechanically induced hemolysis, or RBC mechanical fragility (MF), is an important parameter in the characterization of erythrocyte membrane health. The rocker bead test (RBT) and associated calculated mechanical fragility index (MFI) is a simple method for the assessment of RBC MF. Requiring a minimum of 15.5 mL of blood and necessitating adjustment of hematocrit (Ht) to a "standard" value (40%), the current RBT is not suitable for use in most studies involving human subjects. To address these limitations, we propose a 6.5 mL reduced volume RBT and corresponding modified MFI (MMFI) that does not require prior Ht adjustment. This new method was assessed for i) correlation to the existing text, ii) to quantify the effect of Ht on MFI, and iii) validation by reexamining the protective effect of plasma proteins on RBC MF. The reduced volume RBT strongly correlated (r = 0.941) with the established large volume RBT at matched Hts, and an equation was developed to calculate MMFI: a numerical estimation (R2 = 0.923) of MFI if performed with the reduced volume RBT at "standard" (40%) Ht. An inversely proportional relationship was found between plasma protein concentration and RBC MF using the MMFI-reduced volume method, supporting previous literature findings. The new reduced volume RBT and modified MFI will allow for the measurement of RBC MF in clinical and preclinical studies involving humans or small animals.

Ex Vivo Assessment of a Parabolic-Tip Inflow Cannula for Pediatric Continuous-Flow VADs.

To address the challenge of unloading the left ventricle during pediatric mechanical circulatory support using next-generation rotary blood pumps, a novel inflow cannula was developed. This unique inflow cannula for pediatric, continuous-flow, left ventricular assist devices (VADs) with a parabolic-shaped inlet entrance was evaluated alongside a bevel-tip and fenestrated-tip cannula via an ex vivo, isolated-heart experimental setup. Performance was characterized using two clinical scenarios of over-pumping and hypovolemia, created by varying pump speed and filling preload pressure, respectively, at ideal and off-axis cannula placement to assess ventricular unloading and positional sensitivity. Quantitative and qualitative assessments were performed on the resultant hemodynamics and intra-ventricular boroscopic images to classify conditions of nonsuction, partial, gradual or severe entrainment, and ventricular collapse. The parabolic-tip cannula was found to be significantly less sensitive to placement position (p < 0.001) than the bevel-tip cannula under all conditions, while not statistically different from the fenestrated cannula. Visual analysis of the parabolic-tip cannula showed complete resistance to entrainment, whereas the fenestrated-tip had partial entrainment in 90% and 87% of the over-pumping and hypovolemic studies, respectively. We conclude that future pediatric VAD designs may benefit from incorporating the parabolic-tip inflow cannula design to maximize unloading of the left ventricle in ideal and nonoptimal conditions.

Drag-Reducing Polymer Enhances Microvascular Perfusion in the Traumatized Brain with Intracranial Hypertension.

Current treatments for traumatic brain injury (TBI) have not focused on improving microvascular perfusion. Drag-reducing polymers (DRP), linear, long-chain, blood-soluble, nontoxic macromolecules, may offer a new approach to improving cerebral perfusion by primary alteration of the fluid dynamic properties of blood. Nanomolar concentrations of DRP have been shown to improve hemodynamics in animal models of ischemic myocardium and ischemic limb, but have not yet been studied in the brain. We recently demonstrated that DRP improved microvascular perfusion and tissue oxygenation in a normal rat brain. We hypothesized that DRP could restore microvascular perfusion in hypertensive brain after TBI. Using in vivo two-photon laser scanning microscopy we examined the effect of DRP on microvascular blood flow and tissue oxygenation in hypertensive rat brains with and without TBI. DRP enhanced and restored capillary flow, decreased microvascular shunt flow, and, as a result, reduced tissue hypoxia in both nontraumatized and traumatized rat brains at high intracranial pressure. Our study suggests that DRP could constitute an effective treatment for improving microvascular flow in brain ischemia caused by high intracranial pressure after TBI.

Mechanical blood trauma in assisted circulation: sublethal RBC damage preceding hemolysis.

After many decades of improvements in mechanical circulatory assist devices (CADs), blood damage remains a serious problem during support contributing to variety of adverse events, and consequently affecting patient survival and quality of life. The mechanisms of cumulative cell damage in continuous-flow blood pumps are still not fully understood despite numerous in vitro, in vivo, and in silico studies of blood trauma. Previous investigations have almost exclusively focused on lethal blood damage, namely hemolysis, which is typically negligible during normal operation of current generation CADs. The measurement of plasma free hemoglobin (plfHb) concentration to characterize hemolysis is straightforward, however sublethal trauma is more difficult to detect and quantify since no simple direct test exists. Similarly, while multiple studies have focused on thrombosis within blood pumps and accessories, sublethal blood trauma and its sequelae have yet to be adequately documented or characterized. This review summarizes the current understanding of sublethal trauma to red blood cells (RBCs) produced by exposure of blood to flow parameters and conditions similar to those within CADs. It also suggests potential strategies to reduce and/or prevent RBC sublethal damage in a clinically-relevant context, and encourages new research into this relatively uncharted territory.

Multilaboratory study of flow-induced hemolysis using the FDA benchmark nozzle model.

Multilaboratory in vitro blood damage testing was performed on a simple nozzle model to determine how different flow parameters and blood properties affect device-induced hemolysis and to generate data for comparison with computational fluid dynamics-based predictions of blood damage as part of an FDA initiative for assessing medical device safety. Three independent laboratories evaluated hemolysis as a function of nozzle entrance geometry, flow rate, and blood properties. Bovine blood anticoagulated with acid citrate dextrose solution (2-80 h post-draw) was recirculated through nozzle-containing and paired nozzle-free control loops for 2 h. Controlled parameters included hematocrit (36 ± 1.5%), temperature (25 °C), blood volume, flow rate, and pressure. Three nozzle test conditions were evaluated (n = 26-36 trials each): (i) sudden contraction at the entrance with a blood flow rate of 5 L/min, (ii) gradual cone at the entrance with a 6-L/min blood flow rate, and (iii) sudden-contraction inlet at 6 L/min. The blood damage caused only by the nozzle model was calculated by subtracting the hemolysis generated by the paired control loop test. Despite high intralaboratory variability, significant differences among the three test conditions were observed, with the sharp nozzle entrance causing the most hemolysis. Modified index of hemolysis (MIHnozzle ) values were 0.292 ± 0.249, 0.021 ± 0.128, and 1.239 ± 0.667 for conditions i-iii, respectively. Porcine blood generated hemolysis results similar to those obtained with bovine blood. Although the interlaboratory hemolysis results are only applicable for the specific blood parameters and nozzle model used here, these empirical data may help to advance computational fluid dynamics models for predicting blood damage.

Real time visualization and characterization of platelet deposition under flow onto clinically relevant opaque surfaces.

Although the thrombogenic nature of the surfaces of cardiovascular devices is an important aspect of blood biocompatibility, few studies have examined platelet deposition onto opaque materials used for these devices in real time. This is particularly true for the metallic surfaces used in current ventricular assist devices (VADs). Using hemoglobin depleted red blood cells (RBC ghosts) and long working distance optics to visualize platelet deposition, we sought to perform such an evaluation. Fluorescently labeled platelets mixed with human RBC ghosts were perfused across six opaque materials (a titanium alloy (Ti6Al4V), silicon carbide (SiC), alumina (Al2O3, 2-methacryloyloxyethyl phosphorylcholine polymer coated Ti6Al4V (MPC-Ti6Al4V), yttria partially stabilized zirconia (YZTP), and zirconia toughened alumina (ZTA)) for 5 min at wall shear rates of 400 and 1000 s(-1). Ti6Al4V had significantly increased platelet deposition relative to MPC-Ti6Al4V, Al2 O3 , YZTP, and ZTA at both wall shear rates (p < 0.01). For all test surfaces, increasing the wall shear rate produced a trend of decreased platelet adhesion. The described system can be a utilized as a tool for comparative analysis of candidate blood-contacting materials with acute blood contact.

Biocompatibility Assessment of the CentriMag-Novalung Adult ECMO Circuit in a Model of Acute Pulmonary Hypertension.

Extracorporeal membrane oxygenation (ECMO) is rarely used in patients with severe pulmonary hypertension (PH) as a bridge to lung transplantation. In this study, we assess the blood biocompatibility of the integrated CentriMag-Novalung ECMO system (venoarterial) in an acute model of PH. Severe PH (≥2/3 systemic) was induced in eight sheep through progressive ligation of the main pulmonary artery. System performance, platelet activation, thromboelastography (TEG) parameters, fibrinogen, plasma-free hemoglobin, and total plasma protein were measured at initiation, 3, and 6 hr of support in the ECMO (N = 4) and sham (N = 4) groups. A stable ECMO flow (2.2 ± 0.1 L/min), low transmembrane pressure gradient, and steady blood O2 and CO2 levels were maintained. Platelet activation was low (<4%) in both the groups, whereas platelet responsiveness to agonist (platelet activating factor) was reduced in the sham group when compared with the ECMO group. There were no differences in the TEG parameters, fibrinogen concentration, plasma-free hemoglobin (<10 mg/dl), and plasma total protein between the two groups. The findings of low levels of platelet activation and plfHb suggest adequate blood biocompatibility of the integrated CentriMag-Novalung circuit use for short-term support in a model of PH.