Absolute Partial Pressures Research Articles

In vitro oxygen imaging of acellular and cell-loaded beta cell replacement devices

Type 1 diabetes (T1D) is an autoimmune disease that leads to the loss of insulin-producing beta cells. Bioartificial pancreas (BAP) or beta cell replacement strategies have shown promise in curing T1D and providing long-term insulin independence. Hypoxia (low oxygen concentration) that may occur in the BAP devices due to cell oxygen consumption at the early stages after implantation damages the cells, in addition to imposing limitations to device dimensions when translating promising results from rodents to humans. Finding ways to provide cells with sufficient oxygenation remains the major challenge in realizing BAP devices’ full potential. Therefore, in vitro oxygen imaging assessment of BAP devices is crucial for predicting the devices’ in vivo efficiency. Electron paramagnetic resonance oxygen imaging (EPROI, also known as electron MRI or eMRI) is a unique imaging technique that delivers absolute partial pressure of oxygen (pO2) maps and has been used for cancer hypoxia research for decades. However, its applicability for assessing BAP devices has not been explored. EPROI utilizes low magnetic fields in the mT range, static gradients, and the linear relationship between the spin–lattice relaxation rate (R1) of oxygen-sensitive spin probes such as trityl OX071 and pO2 to generate oxygen maps in tissues. With the support of the Juvenile Diabetes Research Foundation (JDRF), an academic-industry partnership consortium, the “Oxygen Measurement Core” was established at O2M to perform oxygen imaging assessment of BAP devices originated from core members’ laboratories. This article aims to establish the protocols and demonstrate a few examples of in vitro oxygen imaging of BAP devices using EPROI. All pO2 measurements were performed using a recently introduced 720 MHz/25 mT preclinical oxygen imager instrument, JIVA-25™. We began by performing pO2 calibration of the biomaterials used in BAPs at 25 mT magnetic field since no such data exist. We compared the EPROI pO2 measurement with a single-point probe for a few selected materials. We also performed trityl OX071 toxicity studies with fibroblasts, as well as insulin-producing cells (beta TC6, MIN6, and human islet cells). Finally, we performed proof-of-concept in vitro pO2 imaging of five BAP devices that varied in size, shape, and biomaterials. We demonstrated that EPROI is compatible with commonly used biomaterials and that trityl OX071 is nontoxic to cells. A comparison of the EPROI with a fluorescent-based point oxygen probe in selected biomaterials showed higher accuracy of EPROI. The imaging of typically heterogenous BAP devices demonstrated the utility of obtaining oxygen maps over single-point measurements. In summary, we present EPROI as a quality control tool for developing efficient cell transplantation devices and artificial tissue grafts. Although the focus of this work is encapsulation systems for diabetes, the techniques developed in this project are easily transferable to other biomaterials, tissue grafts, and cell therapy devices used in the field of tissue engineering and regenerative medicine (TERM). In summary, EPROI is a unique noninvasive tool to experimentally study oxygen distribution in cell transplantation devices and artificial tissues, which can revolutionize the treatment of degenerative diseases like T1D.

Critical Thermodynamic Conditions for the Formation of p-Type β-Ga2O3 with Cu Doping.

As a promising third-generation semiconductor, is facing bottleneck for its p-type doping. We investigated the electronic structures and the stability of various Cu doped structures of . We found that Cu atoms substituting Ga atoms result in p-type conductivity. We derived the temperature and absolute oxygen partial pressure dependent formation energies of various doped structures based on first principles calculation with dipole correction. Then, the critical thermodynamic condition for forming the abovementioned substitutional structure was obtained.

Thermodynamics of Vaporization in the Li2O–Ta2O5 system: The Standard Enthalpies of Formation of Lithium Tantalates

Vaporization in the Li2O–Ta2O5 system is studied using the Knudsen effusion method in combination with mass-spectrometric analysis of the gas phase in the temperature range of 1570–1860 K. Saturated vapor above the system is found to consist of lithium atoms, oxygen molecules, and lithium oxide Li2O molecules over the entire range of condensed phase compositions. The absolute partial pressures are calculated, and a p–x section of the complete p–T–x phase diagram at T = 1753 K is constructed. The experimental data made it possible to calculate the standard enthalpies of a number of heterophase reactions and the standard enthalpies of formation of lithium tantalates using the second and third laws of thermodynamics: $${{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }$$ (Li3TaO4) = –2074.6 ± 62.9 kJ/mol, $${{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }$$ (LiTaO3) = –1403.5 ± 57.4 kJ/mol, and $${{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }$$ (LiTa3O8) = –3466.4 ± 47.3 kJ/mol. Activities of the components at T = 1473 K and the standard enthalpy of formation of lithium heptatantalate ( $${{\Delta }_{f}}H_{{{\text{298}}}}^{^\circ }$$ (Li7TaO6) = –3383.0 kJ/mol) are estimated from the p–x section of the phase diagram.

Atherosclerosis is associated with a decrease in cerebral microvascular blood flow and tissue oxygenation.

Chronic atherosclerosis may cause cerebral hypoperfusion and inadequate brain oxygenation, contributing to the progression of cognitive decline. In this study, we exploited two-photon phosphorescence lifetime microscopy to measure the absolute partial pressure of oxygen (PO2) in cortical tissue in both young and old LDLR-/-, hApoB100+/+ mice, spontaneously developing atherosclerosis with age. Capillary red-blood-cell (RBC) speed, flux, hematocrit and capillary diameter were also measured by two-photon imaging of FITC-labelled blood plasma. Our results show positive correlations between RBC speed, flux, diameter and capillary-adjacent tissue PO2. When compared to the young mice, we observed lower tissue PO2, lower RBC speed and flux, and smaller capillary diameter in the old atherosclerotic mice. The old mice also exhibited a higher spatial heterogeneity of tissue PO2, and RBC speed and flux, suggesting a less efficient oxygen extraction.

VGAM: Compact and Low‐Power Mass Spectrometer‐Based Instrumentation for Volcanic Gas Monitoring

AbstractCompact mass spectrometers (MSs) can provide simultaneous multispecies analysis with high sensitivity and precision. For volcanic gas monitoring in situ, instrumental mass spectrometry requires reliability and ruggedness combined with low power usage and portability. The Volcanic Gas Analytical Monitor (VGAM) is capable of quantitative molecular analysis of a variety of atmospheric and volcanic gases in a single sensor by ion trap mass spectrometry. These gases include H2, He, H2O, N2, O2, Ar, NO, N2O, CO, CO2, H2S, SO, SO2, and CH4. Unlike previous field instruments using magnetic sector and quadrupole MSs with vacuums backed by compact turbomolecular pumps, the VGAM uses a low‐power autoresonant ion trap MS and nonevaporable getter‐ion pumped vacuum that operates at only 25‐W total power, which is often the power requirement for just the MS. Ratiometric mass spectral response is combined with total pressure measurements to report absolute partial pressures. Data are generated in real time and are recorded to internal flash memory. Relatively low power (<1 W) data telemetry to remote sites is possible. Analysis of volcanic plumes, fumaroles, and solfatara fields is accomplished by direct inlet of gases, after trapping as much excess water vapor in both the external and internal foreline as possible. We report herein on the VGAM autorun and postprocessing procedures, initial calibration results for CO2, and the results of a brief field deployment at Sulfur Banks solfatara field, Kilauea Volcano, Hawaii.

Substitution reactions of gaseous ions in a three-dimensional quadrupole ion trap.

Substitution reactions between gaseous ions and neutral substrate molecules are of ongoing high interest. To investigate these processes in a qualitative and quantitative manner, we have constructed a device, with which a defined amount of a volatile substrate can be mixed with a defined amount of helium gas and added into a three-dimensional quadrupole ion trap. From the known inner volume of the device, the known ratio nsubstrate :nHe of the mixture, and the determined absolute partial pressure of helium in the ion trap, we can derive the partial pressure of the substrate in the ion trap and, thus, convert the directly observable pseudo-first-order rate constants of the substitution reactions into absolute bimolecular rate constants. We have tested the device by investigating a series of SN 2 reactions of Br- and CF3 CH2 O- anions as well as ligand exchange reactions of ligated Na+ cations. As the obtained results suggest, the described device makes it possible to determine the bimolecular rate constants of substitution reactions as well as other ion-molecule reactions with satisfactory accuracy and reliability.

Two-photon phosphorescence lifetime microscopy of retinal capillary plexus oxygenation in mice.

Impaired oxygen delivery and/or consumption in the retinal tissue underlies the pathophysiology of many retinal diseases. However, the essential tools for measuring oxygen concentration in retinal capillaries and studying oxygen transport to retinal tissue are still lacking. We show that two-photon phosphorescence lifetime microscopy can be used to map absolute partial pressures of oxygen (pO2) in the retinal capillary plexus. Measurements were performed at various retinal depths in anesthetized mice under systemic normoxic and hyperoxic conditions. We used a newly developed two-photon phosphorescent oxygen probe, based on a two-photon absorbing platinum tetraphthalimidoporphyrin, and commercially available optics without correction for optical aberrations of the eye. The transverse and axial distances within the tissue volume were calibrated using a model of the eye's optical system. We believe this is the first demonstration of in vivo depth-resolved imaging of pO2 in retinal capillaries. Application of this method has the potential to advance our understanding of oxygen delivery on the microvascular scale and help elucidate mechanisms underlying various retinal diseases.

In vivo imaging and analysis of cerebrovascular hemodynamic responses and tissue oxygenation in the mouse brain.

Cerebrovascular dysfunction has an important role in the pathogenesis of multiple brain disorders. Measurement of hemodynamic responses in vivo can be challenging, particularly as techniques are often not described in sufficient detail and vary between laboratories. We present a set of standardized in vivo protocols that describe high-resolution two-photon microscopy and intrinsic optical signal (IOS) imaging to evaluate capillary and arteriolar responses to a stimulus, regional hemodynamic responses, and oxygen delivery to the brain. The protocol also describes how to measure intrinsic NADH fluorescence to understand how blood O2 supply meets the metabolic demands of activated brain tissue, and to perform resting-state absolute oxygen partial pressure (pO2) measurements of brain tissue. These methods can detect cerebrovascular changes at far higher resolution than MRI techniques, although the optical nature of these techniques limits their achievable imaging depths. Each individual procedure requires 1-2 h to complete, with two to three procedures typically performed per animal at a time. These protocols are broadly applicable in studies of cerebrovascular function in healthy and diseased brain in any of the existing mouse models of neurological and vascular disorders. All these procedures can be accomplished by a competent graduate student or experienced technician, except the two-photon measurement of absolute pO2 level, which is better suited to a more experienced, postdoctoral-level researcher.

Critical conditions for the formation of p-type ZnO with Li doping.

The stability of Li dopants in ZnO is studied via first-principles calculations with electric dipole correction. The formation energies of substitutional Li (LiZn), interstitial Li (Lii) and the LiZn + Lii complex are calculated in large supercells and the results are extrapolated to the limit of an infinite-sized supercell. The stabilities of 2LiZn and the LiZn + Lii complex are found to depend on the temperature and absolute oxygen partial pressure. At normal experimental temperature (900 K), an extremely high absolute oxygen partial pressure (194 bar) is needed to break the coupling between LiZn and Lii and thus form p-type ZnO. The reaction barrier and the absorbance spectra are also discussed.

Quantitative Micro-Raman Spectroscopy for Partial Pressure Measurement in Small Volumes.

We demonstrate the quantitative capabilities of Raman confocal microscopy as a nondestructive method to measure the partial pressure of molecular gases in mm3 range sealed volume having an optical access. Thanks to a calibration procedure, we apply this technique for the characterization of the absolute nitrogen partial pressure inside buffered micro electromechanical system (MEMS) atomic vapor cells developed for atomic clocks. Our results are compared with measurements obtained by rubidium hyperfine frequency spectroscopy and a good agreement is demonstrated between the two methods, with a three-sigma detection limit below 10 mbar for a 1 h integration time, using a 33 mW 532 nm excitation laser. These results prove the potential of confocal micro-Raman spectroscopy as a simple and nondestructive method for small-scale pressure measurements.

Thermodynamics of vaporization of the mixed-ligand complex of sodium dipivaloylmethanate with o-phenanthroline Na(thd)(phen)

Vaporization of the complex between sodium dipivaloylmethanate and o-phenanthroline Na(thd)(phen) is studied using the Knudsen effusion method and mass spectral analysis of the gas-phase composition. Sublimation of the compound is found to occur congruently. Saturated vapor predominantly consists of o-phenanthroline molecules C12H8N2, trimeric molecules Na3(thd)3, and a minor amount of Na4(thd)4 and Na(thd)(phen) molecules. The absolute partial pressures and enthalpies of sublimation of the gas-phase components, as well as the ΔfG0(T) of formation of the complex from Na(thd)(s) and Phen(l), are calculated. The standard enthalpy of dissociation of gaseous Na(thd)(phen) into Na3(thd)3(g) and Phen(g) is estimated.

Electrospray-printed nanostructured graphene oxide gas sensors

We report low-cost conductometric gas sensors that use an ultrathin film made of graphene oxide (GO) nanoflakes as transducing element. The devices were fabricated by lift-off metallization and near-room temperature, atmospheric pressure electrospray printing using a shadow mask. The sensors are sensitive to reactive gases at room temperature without requiring any post heat treatment, harsh chemical reduction, or doping with metal nanoparticles. The sensors’ response to humidity at atmospheric pressure tracks that of a commercial sensor, and is linear with changes in humidity in the 10%–60% relative humidity range while consuming <6 μW. Devices with GO layers printed by different deposition recipes yielded nearly identical response characteristics, suggesting that intrinsic properties of the film control the sensing mechanism. The gas sensors successfully detected ammonia at concentrations down to 500 ppm (absolute partial pressure of ∼5 × 10−4 T) at ∼1 T pressure, room temperature conditions. The sensor technology can be used in a great variety of applications including air conditioning and sensing of reactive gas species in vacuum lines and abatement systems.

Application of the perturbed chain-SAFT equation of state for modeling CO2 solubility in aqueous monoethanolamine solutions

CO2 removal by treatment of acid gases by aqueous alkanolamines is a very significant operation from industrial and environmental point of view. To attain a comprehensive thermodynamic model of the CO2–MEA–H2O in a wide range of temperature and CO2 partial pressures, Perturbed Chain-Statistical Associating Fluid Theory (PC-SAFT) EOS is applied to predict the absorption of carbon dioxide by MEA (MonoEthanolAmine). In order to find the best association scheme for MEA in PC-SAFT EOS, three pure parameter sets for MEA in the 2B, 3B and 4C association schemes are determined in temperature range 303.15–443.15K. Temperature independent binary interaction parameters have been adjusted in the VLE calculation for three schemes of MEA and two schemes of water. Binary VLE calculations show the 3B scheme for MEA and the 4C scheme for water indicate the best prediction in the MEA–H2O system. Excess enthalpy data for aqueous MEA are predicted by kij, which has been adjusted in VLE calculations. The 3B scheme for MEA and the 4C scheme for water also are used to find CO2 solubility in the ternary system of CO2–MEA–H2O system. Ideal Smith–Missen algorithm has been applied to find the concentration of all species in chemical equilibrium. Results show the 3B association scheme for MEA and the 4C association scheme for water in PC-SAFT EOS have better agreement with binary and ternary experimental data. PC-SAFT EOS is able to anticipate the CO2 solubility in the CO2–MEA–H2O system without any regression in the ternary system. The CO2 solubility in ternary system is compared to e-NRTL as a common thermodynamics model. The average absolute partial pressure deviations for PC-SAFT and e-NRTL are calculated around 36% and 42%, respectively.

Thermodynamics and vapor formation features of zinc(II) and tin(II) pivalates

Vapor formation of tin(II) and zinc(II) pivalates were studied using the Knudsen effusion method and mass spectrometry analysis of the gas phase. Sublimation of the tin complex is shown to be accompanied by polymerization of the condensed phase, changing its thermodynamic parameters. The vapor formation of zinc pivalate in the presence of trace amounts of water is accompanied by partial hydrolysis of the condensed phase and sublimation of the sample in the form of Zn4O(piv)6 and Zn2piv4. The absolute partial pressures and heats of sublimation of the components of the gas phase above tin and zinc complexes are calculated.

In vivo intracellular oxygen dynamics in murine brain glioma and immunotherapeutic response of cytotoxic T cells observed by fluorine-19 magnetic resonance imaging.

Noninvasive biomarkers of anti-tumoral efficacy are of great importance to the development of therapeutic agents. Tumor oxygenation has been shown to be an important indicator of therapeutic response. We report the use of intracellular labeling of tumor cells with perfluorocarbon (PFC) molecules, combined with quantitative 19F spin-lattice relaxation rate (R1) measurements, to assay tumor cell oxygen dynamics in situ. In a murine central nervous system (CNS) GL261 glioma model, we visualized the impact of Pmel-1 cytotoxic T cell immunotherapy, delivered intravenously, on intracellular tumor oxygen levels. GL261 glioma cells were labeled ex vivo with PFC and inoculated into the mouse striatum. The R1 of 19F labeled cells was measured using localized single-voxel magnetic resonance spectroscopy, and the absolute intracellular partial pressure of oxygen (pO2) was ascertained. Three days after tumor implantation, mice were treated with 2×107 cytotoxic T cells intravenously. At day five, a transient spike in pO2 was observed indicating an influx of T cells into the CNS and putative tumor cell apoptosis. Immunohistochemistry and quantitative flow cytometry analysis confirmed that the pO2 was causally related to the T cells infiltration. Surprisingly, the pO2 spike was detected even though few (∼4×104) T cells actually ingress into the CNS and with minimal tumor shrinkage. These results indicate the high sensitivity of this approach and its utility as a non-invasive surrogate biomarker of anti-cancer immunotherapeutic response in preclinical models.

New approach to determine absolute partial pressures of ions in saturated vapors of inorganic materials

A new complex approach to determine absolute partial pressures of molecular and ionic components of vapor is advanced on the basis of a combination of mass-spectrometric and quantum-chemical methods using sodium bromide as an example. Thermodynamic parameters of molecules and ions and the electron work function are determined for crystalline NaBr.

Simultaneous imaging of cerebral partial pressure of oxygen and blood flow during functional activation and cortical spreading depression.

We developed a novel imaging technique that provides real-time two-dimensional maps of the absolute partial pressure of oxygen and relative cerebral blood flow in rats by combining phosphorescence lifetime imaging with laser speckle contrast imaging. Direct measurement of blood oxygenation based on phosphorescence lifetime is not significantly affected by changes in the optical parameters of the tissue during the experiment. The potential of the system as a novel tool for quantitative analysis of the dynamic delivery of oxygen to support brain metabolism was demonstrated in rats by imaging cortical responses to forepaw stimulation and the propagation of cortical spreading depression waves. This new instrument will enable further study of neurovascular coupling in normal and diseased brain.

Effusion of positive and negative ions from a Knudsen cell with weak electric field and ionic conductivity of the sample

The studies on absolute partial pressure measurements of ionic components of the high temperature vapors over inorganic fluorides by means of Knudsen cell mass spectrometry are summarized. The problems arising when the ions are extracted directly from the effusion cell with electric field are discussed. The conditions for correct determination of the equilibrium constants for gaseous reactions, involving both positive and negative ions, are established.

Absolute oxygen tension (pO2) in murine fatty and muscle tissue as determined by EPR

The absolute partial pressure of oxygen (pO(2)) in the mammary gland pad and femoral muscle of female mice was measured using EPR oximetry at 700 MHz. A small quantity of lithium phthalocyanine (LiPc) crystals was implanted in both mammary and femoral muscle tissue of female C3H mice. Subsequent EPR measurements were carried out 1-30 days after implantation with or without control of core body temperature. The pO(2) values in the tissue became stable 2 weeks after implantation of LiPc crystals. The pO(2) level was found to be higher in the femoral muscle than in the mammary tissue. However, the pO(2) values showed a strong dependence on the core body temperature of the mice. The pO(2) values were responsive to carbogen (95% O(2), 5% CO(2)) breathing even 44-58 days after the implantation of LiPc. The LiPc linewidth was also sensitive to changes in the blood supply even 60 days after implantation of the crystals. This study further validates the use of LiPc crystals and EPR oximetry for long-term non-invasive assessment of pO(2) levels in tissues, underscores the importance of maintaining normal body core temperature during the measurements, and demonstrates that mammary tissue functions at a lower pO(2) level than muscle in female C3H mice.

Kinetic investigations on methanol steam reforming on PdZn catalysts in microchannel reactors and model transfer into the pressure gap region

In the present study, a microchannel reactor was used in an integral mode of reactor operation to investigate parameter influences on the steam reforming of methanol on PdZn catalysts prepared by washcoating the microchannels with ZnO nanoparticles. Different models derived from significant concentration parameters were evaluated concerning their suitability to describe the kinetics of the methanol reforming reaction in the examined parameter range. Water gas shift reaction was found to be negligible in the reaction network. Methanol decomposition, even though it was influenced by the reactor material, was neglected for the modelling since CO was present only at a minor extent at the reactor outlet. Superior isothermal behaviour of the microchannel reactor is supposed to be responsible for good correlations of the derived models with experimental results. One of the models, the “global model”, was transferred to results from experiments in the pressure gap region obtained in a similar microchannel reactor suitable for low-pressure application. Although this was a model extrapolation, model and experiment were in good accordance for a wide range of absolute and methanol partial pressures, molar ratios of water to methanol and temperatures.