High-fidelity Transducers Research Articles

The organic electrochemical transistor for biological applications

ABSTRACTThe rising field of bioelectronics, which couples the realms of electronics and biology, holds huge potential for the development of novel biomedical devices for therapeutics and diagnostics. Organic electronic devices are particularly promising; the use of robust organic electronic materials provides an ideal biointerface due to their reported biocompatibility, and mechanical matching between the sensor element and the biological environment, are amongst the advantages unique to this class of materials. One promising device emerging from this field is the organic electrochemical transistor (OECT). Arguably, the most important feature of an OECT is that it provides local amplification and as such can be used as a high fidelity transducer of biological events. Additionally, the OECT combines properties and characteristics that can be tuned for a wide spectrum of biological applications. Here, we frame the development of the OECT with respect to its underlying optimization for a variety of different applications, including ion sensing, enzymatic sensing, and electrophysiology. These applications have allowed the development of OECTs to sense local ionic/biomolecular and single cell activity, as well characterization of tissue and even monitoring of function of whole organs. The body of work reviewed here demonstrates that the OECT is an extremely versatile device that emerges as an important player for therapeutics and diagnostics. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41735.

Mechanical properties of arteries cryopreserved at −80 °C and −150 °C

A new protocol for cryopreservation of arteries frozen at −80 °C was compared to the reference protocol for cryopreservation at −150 °C and to freshly harvested arteries. The aim of the study is to evaluate both protocols as global procedures to freeze and thaw arteries commonly used in tissue banks. Changes in mechanical properties of rabbit common carotid arteries were studied. Vascular segments were tested in vitro under dynamics loading conditions. Pressure and diameter were recorded simultaneously by a high fidelity transducer and an echotracking device, respectively. The pressure–diameter relationship was fitted by the arctangent Langewouters’ model and the arterial thickness was derived from histological measurements. Histological sections showed that the fresh and −80 °C groups were less damaged by hemodynamic load and histological preparation than the −150 °C group ( p < 0.05). No differences between fresh and cryopreserved arteries regarding the structural (diameter, intimal-media thickness) and mechanical parameters (distensibility, circumferential stress, elastic modulus) were found. The isobaric circumferential stress was reduced in frozen arteries. These results demonstrate that the cryopreservation at −80 °C preserves the histological structure and mechanical properties better than the cryopreservation at −150 °C, suggesting that the new cryopreservation protocol at −80 °C is a method of choice for treating vessel replacement in vascular surgery.

Effects of endotoxic shock on right ventricular systolic function and mechanical efficiency.

To investigate the effects of endotoxin infusion on right ventricular (RV) systolic function and mechanical efficiency. Six anesthetized pigs (Endo group) received a 0.5 mg/kg endotoxin infusion over 30 min and were compared with six other anesthetized pigs (Control group) receiving placebo for 5 h. RV pressure-volume (PV) loops were obtained by the conductance catheter technique and pulmonary artery flow and pressure were measured with high-fidelity transducers. RV adaptation to increased afterload during the early phase of endotoxin-induced pulmonary hypertension (T30) was obtained by both homeometric and hetereometric regulations: the slope of the end-systolic PV relationship of the right ventricle increased from 1.4+/-0.2 mmHg/ml to 2.9+/-0.4 mmHg/ml (P<0.05) and RV end-diastolic volume increased from 56+/-6 ml to 64+/-11 ml (P<0.05). Consequently, right ventricular-vascular coupling was maintained at a maximum efficiency. Ninety minutes later (T120), facing the same increased afterload, the right ventricle failed to maintain its contractility to such an elevated level and, as a consequence, right ventricular-vascular uncoupling occurred. PV loop area, which is known to be highly correlated with oxygen myocardial consumption, increased from 1154+/-127 mmHg/ml (T0) to 1798+/-122 mmHg/ml (T180) (P<0.05) while RV mechanical efficiency decreased from 63+/-2% (T0) to 45+/-5% (T270) (P<0.05). In the very early phase of endotoxinic shock, right ventricular-vascular coupling is preserved by an increase in RV contractility. Later, myocardial oxygen consumption and energetic cost of RV contractility are increased, as evidenced by the decrease in RV efficiency, and right ventricular-vascular uncoupling occurs. Therefore, therapies aiming at restoring right ventricular-vascular coupling in endotoxic shock should attempt to increase RV contractility and to decrease RV afterload but also to preserve RV mechanical efficiency.

Design and Absolute Calibration of an Embedded, Wideband Velocity Sensor

A unique embeddable high-fidelity transducer is introduced here, presenting design parameters and National Institute of Standards and Technology (NIST) calibration. Traditionally, acoustic emission studies are conducted by placing an array of sensors on the surface of the specimen being tested, but the physical constraints of many practical testing geometries preclude surface placement of sensors. Advantages of embedded sensors include the following: ( a) mode conversion is avoided so the measured waveforms are simpler and easier to interpret; ( b) the sensor(s) can be located close to the area of crack growth; ( c) a greater length of signal can be recorded before being contaminated by surface reflections/mode conversions; ( d) embedded sensors may be less susceptible to accidental movement or damage; and ( e) embedded sensors can be used when free surfaces are not accessible. To date no such transducers have been available. As a surface sensor, the device is sensitive to partial displacement; as an embedded sensor, the device is sensitive to particle velocity. The presented design yields sensitivity equal to commercial resonant devices (2.34-V output per mm per s embedded; 2.8 V/nm surface) while maintaining the high-fidelity of the NIST displacement sensors (±2.5 dB from 10 KHz to 1 MHz). The embedded response is calibrated with the theoretical solution for Lamb’s problems.

Multiplexer displays two pressure signals on single oscilloscope channel.

High-fidelity pressure transducers may drift during long experiments. To correct for this drift, many investigators periodically rebalance the high-fidelity transducer, comparing the results from the high-fidelity transducer with those from a fluid-filled catheter connected to an external transducer. This procedure is subject to error because the high-fidelity and reference signals have to be displayed on different oscilloscope channels; thus these channels can drift differently, being subject to parallax and other problems. This procedure also requires two display channels, which are often in short supply during two display channels, which are often in short supply during complex experiments. We present a design for a multiplexer that will display two pressure signals on one oscilloscope channel, thereby solving these problems and saving one channel to display other information.

Regional pressure differences in the left ventricle

Theoretically, if blood is to have directional flow and different magnitudes of velocity, pressure should be distributed in the left ventricle (LV) as a function of both space and time. Thus, regional pressure differences (RPD) were examined in the LV of 20 open-chested dogs. High-fidelity transducers were implanted through stab wounds at three positions in the LV: the base (B), equator (EQ), and apex (APX). Simultaneous, high-fidelity LV pressures were compared in each region under rest conditions and during graded infusions of isoproterenol and propranolol. In the baseline condition, there were slight but significant differences between the APX and B in end-diastolic pressure (EDP), peak systolic pressure (PSP), peak dp/dt and Vmax. At rest, the largest RPD between the APX and B in PSP was 9 mm Hg (mean +/- 1 SE = 2.1 +/- 0.5), and the largest during diastole was 5.1 mm Hg (mean +/- 1 SE = 1.2 +/- 0.4); the largest difference in Vmax was 30.5% (mean +/- 1 SE = 10.8 +/- 2.4). During isoproterenol infusion the RPD in PSP were accentuated; the largest seen was 84 mm Hg between APX and B (mean +/- 1 SE = 15.7 +/- 4.5). The largest difference in Vmax between B and APX was 188% (mean +/- 1 SE = 48.5 +/- 9.4). Propranolol obliterated these RPD. These results indicate that there are significant RPD in the LV cavity; during systole the highest pressures decrease sequentially from the apex to the equator and to the base; during diastole these RPD are of lesser magnitude. These RPD affect all derived pressure indices, and these changes can be increaed or decreased by drug intervention. These results are important for two reasons: 1) the position of catheters in the LV cavity is important when pressure-dependent LV parameters are compared in different conditions; and 2) in any force balance analysis of the left ventricle it is important to note that force generation by the left ventricle is an active process that transmits regional pressure differences to the LV cavity.