Locally Gated SnS2/hBN Thin Film Transistors with a Broadband Photoresponse.

Next-generation flexible and transparent electronics demand newer materials with superior characteristics. Tin dichalcogenides, Sn(S,Se)2, are layered crystal materials that show promise for implementation in flexible electronics and optoelectronics. They have band gap energies that are dependent on their atomic layer number and selenium content. A variety of studies has focused in particular on tin disulfide (SnS2) channel transistors with conventional silicon substrates. However, the effort of interchanging the gate dielectric by utilizing high-quality hexagonal boron nitride (hBN) still remains. In this work, the hBN coupled SnS2 thin film transistors are demonstrated with bottom-gated device configuration. The electrical transport characteristics of the SnS2 channel transistor present a high current on/off ratio, reaching as high as 105 and a ten-fold enhancement in subthreshold swing compared to a high-κ dielectric covered device. We also demonstrate the spectral photoresponsivity from ultraviolet to infrared in a multi-layered SnS2 phototransistor. The device architecture is suitable to promote diverse studied on flexible and transparent thin film transistors for further applications.

Enhancement of near-infrared detectability from InGaZnO thin film transistor with MoS2 light absorbing layer.

We report an enhancement of near-infrared (NIR) detectability from amorphous InGaZnO (α-IGZO) thin film transistor in conjunction with randomly distributed molybdenum disulfide (MoS2) flakes. The electrical characteristics of the α-IGZO grown by radio-frequency magnetron sputtering exhibit high effective mobility exceeding 15 cm2 V-1 s-1 and current on/off ratio up to 107. By taking advantages of the high quality α-IGZO and MoS2 light absorbing layer, photodetection spectra are able to extend from ultra-violet to NIR range. The α-IGZO channel detector capped by MoS2 show a photo-responsivity of approximately 14.9 mA W-1 at 1100 nm wavelength, which is five times higher than of the α-IGZO device without MoS2 layer.

Electrical and photovoltaic properties of residue-free MoS2 thin films by liquid exfoliation method.

Molybdenum disulfide (MoS2) film fabricated by a liquid exfoliation method has significant potential for various applications, because of its advantages of mass production and low-temperature processes. In this study, residue-free MoS2 thin films were formed during the liquid exfoliation process and their electrical properties were characterized with an interdigitated electrode. Then, the MoS2 film thickness could be controlled by centrifuge condition in the range of 20 âˆ¼ 40 nm, and its carrier concentration and mobility were measured at about 7.36 × 1016 cm-3 and 4.67 cm2 V-1 s-1, respectively. Detailed analysis on the films was done by atomic force microscopy, Raman spectroscopy, and high-resolution transmission electron microscopy measurements for verifying the film quality. For application of the photovoltaic device, a Au/MoS2/silicon/In junction structure was fabricated, which then showed power conversion efficiency of 1.01% under illumination of 100 mW cm-2.

Linearly and Highly Pressure-Sensitive Electronic Skin Based on a Bioinspired Hierarchical Structural Array.

Pressure-sensitive electronic skin composed of a hierarchical structural array exhibits outstanding linear and high sensitivity in the pressure range exerted by gentle touch. By virtue of monolayer graphene acting as electrode material, this device can be operated with low voltage. Especially, its high transparency enables an accurate placement of the device on the target position when it is used for health monitoring.

Thermal annealing effects on ZnO films grown on graphene buffered Si substrates.

ZnO films deposited on SiO2/Si substrate with a graphene single layer (GSL) were studied by using an ultra-high vacuum sputter. The as-prepared films were annealed at temperature ranges from 500 degrees C to 800 degrees C for 1 min under ambient N2 gas. When the annealing temperature was increased up to 800 degrees C, the root mean square roughness of the ZnO/Si sample surface decreased down to 3.4 nm, and the grain sizes increased about 50.8 nm with a clear grain boundary. From the photoluminescence (PL) spectra, the high intensity of near-band-edge UV emission at 380 nm (3.26 eV) and the broad band emission between 450 and 650 nm, known as the visible defect related PL band, decreased with increasing annealing temperature up to 800 degrees C. The ZnO thin films on the growth on the GSL and post-annealing at 700 degrees C for 1 min under ambient N2 gas had the best structural and optical properties.

The CentriMag ventricular assist device in acute heart failure refractory to medical management.

BACKGROUND: The CentriMag ventricular assist device (VAD) has gained popularity in the last several years as rescue support for patients with decompensated heart failure. We have used the CentriMag VAD as a bridge to decision device. We describe our experience with device placement, use and outcomes. METHODS: This is a retrospective study of all patients who underwent CentriMag placement at our institution from January 2007 to August 2009. Sixty-three patients had placement of a CentriMag device, with 43% (n = 27) of these being placed due to failure of medical management. These cases were the focus of our study. RESULTS: Primary diagnoses were ischemic cardiomyopathy (n = 17), dilated cardiomyopathy (n = 7) or other (n = 3). Mean age was 47.1 (range 7 to 72) years. Prior to implant, 85% of patients were on intra-aortic balloon pump (IABP) support, 70% were on vasopressors, and 44% were on more than one inotrope. INTERMACS score was 1 in 67% of patients and 2 in 33% of patients. Six patients were bridged to a long-term device, 8 to transplantation and 10 to recovery. Eighty-nine percent (24 of 27) of patients survived to explant and 74% (20 of 27) survived to hospital discharge, with a 1-year survival of 68%. Thromboembolic complications occurred in 10 patients, including 6 strokes. Compared with patients who survived to discharge, those who died had a significantly higher body mass index (30.8 vs 24.1 kg/m(2), p = 0.003). Survivors to discharge demonstrated significant improvements in hepatic and renal function over the course of device support while non-survivors did not. CONCLUSIONS: The CentriMag demonstrates promising results when used in patients with acute heart failure refractory to medical management.

Incidence and predictors of pacemaker placement after surgical ablation for atrial fibrillation.

BACKGROUND: Bradyarrhythmia requiring pacemaker placement is a relatively common complication after surgical ablation for atrial fibrillation (AF). We report our experience with surgical ablation procedures using various energy modalities and lesion sets in an attempt to identify the risk factors associated with postoperative pacemaker requirement. METHODS: Intraoperative data were collected prospectively, and preoperative and postoperative data were collected retrospectively. Energy modality and lesion sets used were dependent on availability on the date of the procedure and surgeon preference. RESULTS: From October 1999 to October 2009, 701 patients underwent surgical ablation for AF at our institution. Forty-five patients (7.6%) required early postoperative pacemaker placement. There were no significant differences in baseline characteristics or associated procedures between patients who required pacemaker placement and those who did not. Ninety-day mortality was greater in patients requiring pacemaker placement (15.6% versus 6.6%; p = 0.025). In multivariable analysis, a pacemaker requirement was more likely with the use of microwave energy (odds ratio [OR] 2.87; confidence interval [CI], 1.41 to 5.84; p = 0.004) and a right atrial lesion set (OR, 2.82; CI, 1.07 to 7.45; p = 0.036). CONCLUSIONS: In conclusion, over our 10-year experience with surgical AF ablations, the incidence of pacemaker requirement was much lower than that reported in series of classic "cut and sew" Maze procedures, even among patients undergoing full biatrial ablations. Although biatrial ablation is currently our favored approach to patients with long-standing or persistent AF, right atrial lesion sets increase the risk of this complication and should be used judiciously.

Predictors of mortality after short-term ventricular assist device placement.

BACKGROUND: Risk assessment prior to long-term ventricular assist device (VAD) placement has been shown to be crucial for successful outcomes and efficient resource utilization. Short-term VADs are often used as salvage therapy in acute heart failure when the clinical scenario precludes such thorough preoperative assessment. Our goal was to devise a risk stratification system that may be used shortly after stabilization of hemodynamics with a short-term VAD to predict the likelihood of survival. METHODS: A retrospective study was performed of all patients undergoing Abiomed (Abiomed Cardiovascular Inc., Danvers, MA) or CentriMag (Levitronix LLC, Waltham, MA) placement at our institution or transferred to our institution with the device in place. From January 2001 until August 2009, 93 patients were identified. Preoperative and early postoperative variables were analyzed for their correlation with in-hospital mortality. RESULTS: Multivariable logistic regression analysis identified factors that were associated with death. A three-point scoring system, utilizing a diagnosis of postcardiotomy shock or graft failure, female sex, and postoperative day 3 total bilirubin greater than 5.2 mg/dL was devised. A score of 2 or greater was associated with an 86% mortality rate, whereas a score of 0 was associated with a 13% mortality rate. CONCLUSIONS: A simple scoring system based on readily available data may predict mortality after short-term VAD placement. Such a scoring system may be of prognostic value for physicians and patient families early in the support period and may help guide decisions.

Use of ventricular assist devices in patients with mitral valve prostheses.

BACKGROUND: Use of ventricular assist devices (VADs) in patients with prosthetic valves may carry an increased risk of thromboembolism; however, clinical information is lacking. The aim of this study was to report our experience of the use of VADs in patients with prosthetic mitral valves. METHODS: A retrospective analysis of 747 VAD patients from January 1995 to May 2010 was performed. RESULTS: Thirteen patients with a prosthetic mitral valve (average age 56 ± 10 years of age, nine mechanical valve, four biological valve) were identified. Indications for VAD implantation were as a bridge to transplant in 11 patients and destination therapy in two patients. At the time of VAD implant, no intervention to the prosthetic mitral valve was performed. Eight patients received a HeartMate I (Thoratec Corporation, Pleasanton, CA, USA), three patients received a HeartMate II (Thoratec Corporation), and two patients received a Thoratec VAD (Thoratec Corporation). Among nine mechanical valve patients, six patients were anticoagulated with warfarin, and one patient with heparin, while two patients did not receive anticoagulation due to bleeding. Ten patients were successfully transplanted at an average of 123 days post-VAD implant, one died after 48 days from multiorgan failure, and two remained on VAD support. No clinical thromboembolic events were observed. No intracardiac thrombus was detected by echocardiogram or on the pathology of the explanted hearts. Five patients had experienced a bleeding event (postoperative mediastinal bleeds, gastrointestinal bleedings, retroperitoneal hematoma, and subconjuctival bleeding). CONCLUSIONS: In patients with mitral valve prostheses who require VAD support, leaving the prosthesis intact does not increase the incidence of adverse events.

Aortic valve procedures at the time of ventricular assist device placement.

BACKGROUND: Placement of a ventricular assist device (VAD) may lead to reduced or absent opening of the aortic valve and thus increase risk of thrombus formation in the aortic root as well as on the valve itself. The outcome of additional procedures to the aortic valve at the time of VAD placement is unclear. METHODS: A retrospective analysis of 712 VAD patients from 1995 to 2009 was performed. RESULTS: Twenty-eight patients were identified who underwent aortic valve procedures in addition to VAD placement. Indication for VAD placement was bridge to transplant in 23 patients, destination therapy in 4, and postcardiotomy shock in 1. Aortic valve procedures were performed for preexisting mechanical aortic prosthesis in 8 (7 closure and 1 aortic valve replacement with biological prosthesis), and for moderate or severe aortic insufficiency in 20 patients (10 repair, 9 closure, and 1 aortic valve replacement with biological prosthesis). At the last follow-up, 16 patients had undergone heart transplant, 6 remained on VAD support, and 5 had died. While on VAD support, no adverse events related to the aortic valve procedures occurred. The 30-day operative mortality was 0.4%. No clinical thromboembolic events were observed. In 2 patients, there was evidence of thrombus formation in the explanted heart. Four patients had bleeding complications. Of the 9 patients who received aortic valve repair, 2 had recurrent aortic insufficiency on echocardiograms during an average follow-up of 118 days. CONCLUSIONS: Additional procedures to the aortic valve at the time of VAD placement are feasible. Overall outcomes are comparable to those seen in patients without the need for aortic valve manipulation at the time of VAD placement.

Improved diabetic control in advanced heart failure patients treated with left ventricular assist devices.

AIMS: Left ventricular assist devices (LVADs) are increasingly used as therapeutic options for patients with advanced congestive heart failure (CHF), many of whom suffer from diabetes mellitus (DM). The aim of this study was to evaluate the effect of restoration of normal cardiac output using LVAD support on diabetes control in patients with advanced CHF. METHODS AND RESULTS: A retrospective chart review of all clinic patients supported with long-term LVADs between July 2008 and July 2009 at Columbia University Medical Center was performed. Patients with DM diagnosed prior to device implantation were included in this analysis. Clinical and laboratory data within 1 month preceding and 6 months following LVAD implantation were collected. Of 43 LVAD patients followed in our clinic during the study period, 15 had a diagnosis of DM. Thirteen of the 15 patients were male, mean age was 63 ± 11 years, and the pre-LVAD left ventricular ejection fraction (LVEF) was 16.5 ± 5.7%. Fasting glucose levels, HbA1c, and daily insulin requirement within 1 month before and an average of 4.0 ± 2.3 months after LVAD placement were 157.7 ± 50.6 vs. 104.1 ± 21.4 mg/dL, 7.7 ± 0.9 vs. 6.0 ± 0.8.%, and 53.3 ± 51.7 vs. 24.2 ± 27.2 IU, respectively (P < 0.05 for all comparisons). Six of the 15 patients were completely free of antidiabetic medications and had blood glucose < 126 mg/dL as well as HbA1c < 6% after LVAD. Body mass index (BMI) was slightly increased after LVAD (28.7 ± 5.3 vs. 30.2 ± 4.1 kg/m², P NS). CONCLUSION: Restoration of normal cardiac output after LVAD implantation improves diabetic control in patients with advanced CHF. Additional studies are warranted to determine the mechanisms that worsen or possibly induce DM in patients with advanced CHF.

Prevalence of de novo aortic insufficiency during long-term support with left ventricular assist devices.

BACKGROUND: Left ventricular assist devices (LVADs) are increasingly used as long-term therapy for end-stage heart failure patients. We compared the prevalence of aortic insufficiency (AI) after HeartMate II (HMII) vs HeartMate XVE (HMI) support and assessed the role of aortic root diameter and aortic valve opening in the development of AI. METHOD: Pre-operative and post-operative echocardiograms of 93 HMI and 73 HMII patients who received implants at our center between January 2004 and September 2009 were retrospectively reviewed. After excluding patients with prior or concurrent surgical manipulation of the aortic valve, with baseline AI, or without baseline echoes, 67 HMI and 63 HMII patients were studied. AI was deemed significant if mild to moderate or greater. Pathology reports were reviewed for 77 patients who underwent heart transplant. RESULTS: AI developed in 4 of 67 HMI (6.0%) and in 9 of 63 HMII patients (14.3%). The median times to AI development were 48 days for HMI patients and 90 days for HMII patients. For patients who remained on device support at 6 and 12 months, freedom from AI was 94.5% and 88.9% in HMI patients and 83.6% and 75.2% in HMII patients (log rank p = 0.194). Aortic root diameters, as determined by echocardiography for the patients with AI, trended to be larger at baseline (3.43 ± 0.43 vs 3.15 ± 0.40; p = 0.067) and follow-up (3.58 ± 0.54 vs 3.29 ± 0.50; p = 0.130) compared with those who did not have AI. Aortic root circumferences were assessed directly by a pathologist in those patients who underwent transplant and were significantly larger in HMII patients who had developed AI compared with those patients who did not (8.44 ± 0.89 vs 7.36 ± 1.02 cm; p = 0.034). Lastly, AI was more common in patients whose aortic valve did not open (11 of 26 vs 1 of 14; p = 0.03). CONCLUSION: Aortic insufficiency occurs frequently in patients who receive continuous-flow support with a HMII LVAD, and may be associated with aortic root diameter enlargement and aortic valve opening. These findings warrant a more thorough preoperative patient evaluation and additional studies to investigate the factors, that may be associated with AI development.

Acquired von Willebrand syndrome after continuous-flow mechanical device support contributes to a high prevalence of bleeding during long-term support and at the time of transplantation.

OBJECTIVES: The objective of the study was to determine the prevalence of bleeding during continuous-flow left ventricular assist device support and to identify potential mechanisms for those bleeding events. BACKGROUND: Bleeding is frequently reported with continuous-flow left ventricular assist devices and may result from anticoagulation coupled with bleeding diathesis such as acquired von Willebrand syndrome. Accordingly, the prevalence of coagulation abnormalities including laboratory assessment for von Willebrand syndrome, bleeding events during device support, and at heart transplantation were evaluated. METHODS: A retrospective study in all HeartMate II (HM II) (Thoratec Corp., Pleasanton, California) patients who underwent implantation between April 1, 2004, and August 1, 2009, was performed. Bleeding was defined as the need for transfusion >7 days after device insertion of 1 U of packed red blood cells. Transfusion at heart transplantation was compared with that in HeartMate XVE patients. RESULTS: Seventy-nine HM II devices were implanted. Anticoagulation included warfarin in 68.3%, aspirin in 55.7%, and dipyridamole in 58.2% of the patients. Of the patients, 44.3% had bleeding episodes at 112 ± 183 days after left ventricular assist device implantation, with 50% experiencing an event within 2 months. Gastrointestinal bleeding was the most frequent event. At the index event, the international normalized ratio averaged 1.67 ± 0.53, and the platelet count was 237 ± 119 × 10(9)/l. Comparison of the transfusion requirements at heart transplantation of 35 HM II patients with 62 HeartMate XVE patients demonstrated twice the transfusion requirements in HM II patients (packed red blood cells, 6.3 ± 0.8 U vs. 3.8 ± 0.5 U; platelets, 12.5 ± 5.4 U vs. 8.6 ± 6.4 U; fresh frozen plasma, 9.6 ± 4.9 U vs. 4.9 ± 3.6 U; and cryoprecipitate, 4.3 ± 3.6 U vs. 2.2 ± 3.5 U; p < 0.05 for all). High molecular weight von Willebrand factor multimers were measured in 31 HM II patients and were reduced in all patients; 18 of these 31 (58%) patients had bleeding. CONCLUSIONS: Patients with the HM II had a high incidence of bleeding events during device support and at heart transplantation. All HM II patients had reduced high molecular weight von Willebrand factor multimers. The role of these abnormalities in the high incidence of bleeding deserves further investigation. Furthermore, alterations in anticoagulation should be considered during device support and before surgery in patients supported with the HM II.

Activation of endogenous GABAA channels on airway smooth muscle potentiates isoproterenol-mediated relaxation.

Reactive airway disease predisposes patients to episodes of acute smooth muscle mediated bronchoconstriction. We have for the first time recently demonstrated the expression and function of endogenous ionotropic GABA(A) channels on airway smooth muscle cells. We questioned whether endogenous GABA(A) channels on airway smooth muscle could augment beta-agonist-mediated relaxation. Guinea pig tracheal rings or human bronchial airway smooth muscles were equilibrated in organ baths with continuous digital tension recordings. After pretreatment with or without the selective GABA(A) antagonist gabazine (100 muM), airway muscle was contracted with acetylcholine or beta-ala neurokinin A, followed by relaxation induced by cumulatively increasing concentrations of isoproterenol (1 nM to 1 muM) in the absence or presence of the selective GABA(A) agonist muscimol (10-100 muM). In separate experiments, guinea pig tracheal rings were pretreated with the large conductance K(Ca) channel blocker iberiotoxin (100 nM) after an EC(50) contraction with acetylcholine but before cumulatively increasing concentrations of isoproterenol (1 nM to 1 uM) in the absence or presence of muscimol (100 uM). GABA(A) activation potentiated the relaxant effects of isoproterenol after an acetylcholine or tachykinin-induced contraction in guinea pig tracheal rings or an acetylcholine-induced contraction in human endobronchial smooth muscle. This muscimol-induced potentiation of relaxation was abolished by gabazine pretreatment but persisted after blockade of the maxi K(Ca) channel. Selective activation of endogenous GABA(A) receptors significantly augments beta-agonist-mediated relaxation of guinea pig and human airway smooth muscle, which may have important therapeutic implications for patients in severe bronchospasm.