Flies developed smaller cells when temperature fluctuated more frequently

Changes in cell size might be an important component of adaptation to thermal heterogeneity. Although Drosophila melanogaster develops smaller cells at fluctuating temperatures, we do not know whether this response depends on the frequency or amplitude of thermal change. In a laboratory experiment, we exposed flies to either frequent or infrequent fluctuations between 17 and 27 °C, while controlling the total exposure to each temperature. Flies emerged from these treatments with similar body sizes, but flies at more frequent fluctuations emerged earlier and had smaller epidermal cells for a given body size. Tissue built from small cells has more nuclei for transcription, shorter distances between cell compartments, and a larger surface area for transport across membranes. Therefore, we hypothesize that physiological effects of small cells reduce lags in metabolic activity and enhance performance of flies during warming. For plasticity of cell size to confer a fitness advantage, this hypothetical benefit must outweigh the cost of maintaining a greater area of plasma membrane.

Role of subunit III and its lipids in the molecular mechanism of cytochrome c oxidase

The terminal respiratory enzyme cytochrome c oxidase (CcO) reduces molecular oxygen to water, and pumps protons across the inner mitochondrial membrane, or the plasma membrane of bacteria. A two-subunit CcO harbors all the elements necessary for oxygen reduction and proton pumping. However, it rapidly undergoes turnover-induced irreversible damage, which is effectively prevented by the presence of subunit III and its tightly bound lipids. We have performed classical atomistic molecular dynamics (MD) simulations on a three-subunit CcO, which show the formation of water wires between the polar head groups of lipid molecules bound to subunit III and the proton uptake site Asp91 (Bos taurus enzyme numbering). Continuum electrostatic calculations suggest that these lipids directly influence the proton affinity of Asp91 by 1-2pK units. We surmise that lipids bound to subunit III influence the rate of proton uptake through the D-pathway, and therefore play a key role in preventing turnover-induced inactivation. Atomistic MD simulations show that subunit III is rapidly hydrated in the absence of internally bound lipids, which is likely to affect the rate of O2 diffusion into the active-site. The role of subunit III with its indigenous lipids in the molecular mechanism of CcO is discussed.

In vivo oximetry of human bulbar conjunctival and episcleral microvasculature using snapshot multispectral imaging

Multispectral imaging (MSI) is a well-established technique for non-invasive oximetry of retinal blood vessels, which has contributed to the understanding of a variety of retinal conditions, including glaucoma, diabetes, vessel occlusion, and retinal auto-regulation. We report the first study to use snapshot multi-spectral imaging (SMSI) for oximetry of the bulbar conjunctival and episcleral microvasculature in the anterior segment of the eye. We report the oxygen dynamics of the bulbar conjunctival and episcleral microvasculature at normoxia and at acute mild hypoxia conditions. A retinal-fundus camera fitted with a custom Image-Replicating Imaging Spectrometer was used to image the bulbar conjunctival and episcleral microvasculature in ten healthy human subjects at normoxia (21% Fraction of Inspired Oxygen [FiO2]) and acute mild hypoxia (15% FiO2) conditions. Eyelid closure was used to control oxygen diffusion between ambient air and the sclera surface. Four subjects were imaged for 30 seconds immediately following eyelid opening. Vessel diameter and Optical Density Ratio (ODR: a direct proxy for oxygen saturation) of vessels was computed automatically. Oximetry capability was validated using a simple phantom that mimicked the scleral vasculature. Acute mild hypoxia resulted in a decrease in blood oxygen saturation (SO2) (i.e. an increase in ODR) when compared with normoxia in both bulbar conjunctival (p < 0.001) and episcleral vessels (p = 0.03). Average episcleral diameter increased from 78.9 ± 8.7 μm (mean ± standard deviation) at normoxia to 97.6 ± 14.3 μm at hypoxia (p = 0.02). Diameters of bulbar conjunctival vessels showed no significant change from 80.1 ± 7.6 μm at normoxia to 80.6 ± 7.0 μm at hypoxia (p = 0.89). When exposed to ambient air, hypoxic bulbar conjunctival vessels rapidly reoxygenated due to oxygen diffusion from ambient air. Reoxygenation occured in an exponential manner, and SO2 reached normoxia baseline levels. The average ½ time to full reoxygenation was 3.4 ± 1.4 s. As a consequence of oxygen diffusion, bulbar conjunctival vessels will be highly oxygenated (i.e. close to 100% SO2) when exposed to ambient air. Episcleral vessels were not observed to undergo any significant oxygen diffusion, instead behaving similarly to pulse oximetry measurements. This is the first study to the image oxygen dynamics of bulbar conjunctival and episcleral microvasculature, and consequently, the first study to directly observe the rapid reoxygenation of hypoxic bulbar conjunctival vessels when exposed to ambient air. Oximetry of bulbar conjunctival vessels could potentially provide insight into conditions where oxygen dynamics of the microvasculature are not fully understood, such as diabetes, sickle-cell diseases, and dry-eye syndrome. Oximetry in the bulbar conjunctival and episcleral microvasculature could be complimentary or alternative to retinal oximetry.

Plasma treatment of PDMS for applications of in vitro motility assays

In vitro motility assays are readily used to simplify the complex environments within the cell and in muscle tissue. These assays have afforded considerable insight into the fundamentals of their underlying biophysics, interactions with cargo, intracellular regulation, and motor cooperation/competition. Extension of the standard in vitro motility assay into a more automated and cost-effective fluidic design while providing availability to the scientific community without expertise in lithographic fabrication is critical for the continued advancement of the field. In this work, we utilized a standard plasma cleaner to oxidize the widely prevalent material polydimethylsiloxane (PDMS) to create flow cells that could be used for in vitro motility assays. Our analysis indicated that a 40 min pre-treatment of the PDMS with plasma exposure resulted in optimal bundle motility. This finding was attributed to the condition at which the least amount of oxygen permeates the PDMS slab, enters the motility buffer, and oxidizes the motor proteins. Based on these findings, we developed a method for constructing microfluidic devices from glass and plasma-treated PDMS molds in which motility could be observed.

New approach to measuring oxygen diffusion and consumption in encapsulated living cells, based on electron spin resonance microscopy

Cell microencapsulation within biocompatible polymers is an established technology for immobilizing living cells that secrete therapeutic products.  These can be transplanted into a desired site in the body for the controlled and continuous delivery of the therapeutic molecules.  One of the most important properties of the material that makes up the microcapsule is its oxygen penetrability, which is critical for the cells' survival.  Oxygen reaches the cells inside the microcapsules via a diffusion process.  The diffusion coefficient for the microcapsules' gel material is commonly measured using bulk techniques, where the gel in a chamber is first flushed with nitrogen and the subsequent rate of oxygen diffusion back into it is measured by an oxygen electrode placed in the chamber.  This technique does not address possible heterogeneities between microcapsules, and also cannot reveal O₂ heterogeneity inside the microcapsule resulting from the living cells' activity.  Here we develop and demonstrate a proof of principle for a new approach to measuring and imaging the partial pressure of oxygen (pO₂) inside a single microcapsule by means of high-resolution and high-sensitivity electron spin resonance (ESR).  The proposed methodology makes use of biocompatible paramagnetic microparticulates intercalated inside the microcapsule during its preparation.  The new ESR approach was used to measure the O₂ diffusion properties of two types of gel materials (alginate and extracellular matrix - ECM), as well as to map a 3D image of the oxygen inside single microcapsules with living cells. STATEMENT OF SIGNIFICANCE: The technology of cell microencapsulation offers major advantages in the sustained delivery of therapeutic agents used for the treatment of various diseases ranging from diabetes to cancer. Despite the great advances made in this field, it still faces substantial challenges, preventing it from reaching the clinical practice. One of the primary challenges in developing cell microencapsulation systems is providing the cells with adequate supply of oxygen in the long term. Nevertheless, there is still no methodology good enough for measuring O2 distribution inside the microcapsule with sufficient accuracy and spatial resolution without affecting the microcapsule and/or the cells' activity in it. In the present work, we introduce a novel magnetic resonance technique to address O2 availability within cell-entrapping microcapsules. For the first time O2 distribution can be accurately measured and imaged within a single microcapsule. This new technique may be an efficient tool in the development of more optimal microencapsulation systems in the future, thus bringing this promising field closer to clinical application.

Polymer matrix: A good substrate material for oxygen probes used in pressure sensitive paints

Over the past few years, surface pressure measurement has fundamental importance in many areas, particularly, aerodynamic research. Conventional methods involve pressure taps, but due to the nature of these pressure taps, only pressure information of isolated points on model surface is available, which limit their applications in aerodynamics studies. Recently the newly developed approach, pressure sensitive paint (PSP) has revolutionized such pressure measurements and various PSP materials have been developed for aerodynamics research. Hence, the main focus of this review is to study the interactions of polymers with different oxygen probes and polymeric role as supporting material in the maturation of PSP. In this review, the selected PSP materials are categorically elucidated in terms of their advantages and limitations to give a fair insight about their applicability. Further, we have summarized and articulated such particular optical oxygen sensing materials either that have been used as PSP or have potential to be used as PSP materials.

Transformation of sludge Si to nano-Si/SiOx structure by oxygen inward diffusion as precursor for high performance anodes in lithium ion batteries

Although several Si/C composite structures have been proposed for high-performance lithium-ion batteries (LIBs), they have still suffered from expensive and complex processes of nano-Si production. Herein, a simple, controllable oxygen inward diffusion was utilized to transform Si sludge obtained from the photovoltaic (PV) industry into the nano-Si/SiO_x structure as a result of the high diffusion efficiency of O inside Si and high surface area of the sludge. After further process, a yolk/shell Si/C structure was obtained as an anode material for LIBs. This composite demonstrated an excellent cycling stability, with a high reversible capacity (∼ 1250 mAh/g for 500 cycles), by void space originally left by the SiO_x accommodate inner Si expansion. We believe this is a rather simple way to convert the waste Si into a valuable nano-Si for LIB applications.

Application of interface material and effects of oxygen gradient on the performance of single-chamber sediment microbial fuel cells (SSMFCs)

Single-chamber sediment microbial fuel cells (SSMFCs) have received considerable attention nowadays because of their unique dual-functionality of power generation and enhancement of wastewater treatment performance. Thus, scaling up or upgrading SSMFCs for enhanced and efficient performance is a highly crucial task. Therefore, in order to achieve this goal, an innovative physical technique of using interface layers with four different pore sizes embedded in the middle of SSMFCs was utilized in this study. Experimental results showed that the performance of SSMFCs employing an interface layer was improved regardless of the pore size of the interface material, compared to those without such layers. The use of an interface layer resulted in a positive and significant effect on the performance of SSMFCs because of the effective prevention of oxygen diffusion from the cathode to the anode. Nevertheless, when a smaller pore size interface was utilized, better power performance and COD degradation were observed. A maximum power density of 0.032mW/m² and COD degradation of 47.3% were obtained in the case of an interface pore size of 0.28μm. The findings in this study are of significance to promote the future practical application of SSMFCs in wastewater treatment plants.

Rectification of oxygen transfer through the rat colonic epithelium

AIM

To assess whether higher sensitivity of colonic epithelium to hypoxia at the serosal side is associated with oxygen transfer asymmetry.

METHODS

Rats were fed either with normal chow or a low-sodium diet. Tissues were mounted as flat sheets in a modified, airtight Ussing chamber with oxygen meters in each hemichamber. Mucosal samples from normal diet animals were studied under control conditions, in low-chloride solution and after adding chloride secretion inhibitors and chloride secretagogues. Samples from sodium-deprived rats were studied before and after ouabain addition. In separate experiments, the correlation between short-circuit current and oxygen consumption was analyzed. Finally, hypoxia was induced in one hemichamber to assess the relationship between its oxygen content and the oxygen pressure difference between both hemichambers.

RESULTS

In all studied conditions, oxygen consumption was larger in the serosal hemichamber than in the mucosal one (P = 0.0025 to P < 0.0001). Short-circuit current showed significant correlation with both total oxygen consumption (r = 0.765; P = 0.009) in normoxia and oxygen consumption in the serosal hemichamber (r = 0.754; P = 0.011) during mucosal hypoxia, but not with oxygen consumption in the mucosal hemichamber. When hypoxia was induced in the mucosal hemichamber, an oxygen pressure difference of 13 kPa with the serosal hemichamber was enough to keep its oxygen content constant. However, when hypoxia was induced in the serosal hemichamber, the oxygen pressure difference with the mucosal hemichamber necessary to keep its oxygen content constant was 40 kPa (P < 0.0001).

CONCLUSION

Serosal oxygen supply is more readily available to support short-circuit current. This may be partly due to a rectifying behavior of transepithelial oxygen transfer.

Optimized aeration strategies for nitrogen removal efficiency: application of end gas recirculation aeration in the fixed bed biofilm reactor

Aeration strategy played an important role in reactor performance. In this study, when superficial upflow air velocity (SAV) decreased from 0.16 to 0.08 cm s^-1, low dissolved oxygen concentration (DO) of 2.0 mg L^-1 occurred in reactor. The required depth for anoxic microenvironment in biofilm decreased from 902.3 to 525.9 μm, which enhanced the growth of denitrifying bacteria and total nitrogen (TN) removal efficiency. However, decreasing aeration intensity resulted in insufficient hydraulic shear stress, which led to weak biofilm matrix structure. Mass biofilm detachment and reactor deterioration then occurred after 87 days of operation. An end gas recirculation aeration strategy was proposed to separately manipulate DO and aeration intensity. Low DO and high aeration intensity were simultaneously achieved, which enhanced the metabolism of denitrifying bacteria (such as Flavobacterium sp., Pseudorhodobacter sp., and Dok59 sp.) and EPS-producing bacteria (such as Zoogloea sp. and Rhodobacter sp.). Consequently, high TN removal performance (82.1 ± 2.7%) and stable biofilm structure were achieved.

Impact of hypothermia on the biomechanical effect of epithelium-off corneal cross-linking

Background

The corneal cross-linking (CXL) photochemical reaction is essentially dependent on oxygen and hypothermia, which usually leads to higher dissolved oxygen levels in tissues, with potentially greater oxygen availability for treatment. Here, we evaluate whether a reduction of corneal temperature during CXL may increase oxygen availability and therefore enhance the CXL biomechanical stiffening effect in ex vivo porcine corneas.

Methods

One hundred and twelve porcine corneas had their epithelium manually debrided before being soaked with 0.1% hypo-osmolaric riboflavin. These corneas were equally assigned to one of four groups. Groups 2 and 4 underwent accelerated epithelium-off CXL using 9 mW/cm² irradiance for 10 min, performed either in a cold room temperature (group 2, 4 °C) or at standard room temperature (group 4, 24 °C). Groups 1 and 3 served as non-cross-linked, temperature-matched controls. Using a stress-strain extensometer, the elastic moduli of 5-mm wide corneal strips were analyzed as an indicator of corneal stiffness.

Results

Accelerated epithelium-off CXL led to significant increases in the elastic modulus between 1 and 5% of strain when compared to non-cross-linked controls (P < 0.05), both at 4 °C (1.40 ± 0.22 vs 1.23 ± 0.18 N/mm) and 24 °C (1.42 ± 0.15 vs 1.19 ± 0.11 N/mm). However, no significant difference was found between control groups (P = 0.846) or between groups in which CXL was performed at low or standard room temperature (P = 0.969).

Conclusions

Although initial oxygen availability should be increased under hypothermic conditions, it does not appear to play a significant role in the biomechanical strengthening effect of epithelium-off CXL accelerated protocols in ex vivo porcine corneas.

Investigating effect of proton-exchange membrane on new air-cathode single-chamber microbial fuel cell configuration for bioenergy recovery from Azorubine dye degradation

One of the biggest challenges of using single-chamber microbial fuel cells (MFCs) that utilize proton-exchange membrane (PEM) air cathode for bioenergy recovery from recalcitrant organic compounds present in wastewater is mainly attributed to their high internal resistance in the anodic chamber of the single microbial fuel cell (MFC) configurations. The high internal resistance is due to the small surface area of the anode and cathode electrodes following membrane biofouling and pH splitting conditions as well as substrate and oxygen crossover through the membrane pores by diffusion. To address this issue, the fabrication of new PEM air-cathode single-chamber MFC configuration was investigated with inner channel flow open assembled with double PEM air cathodes (two oxygen reduction activity zones) coupled with spiral-anode MFC (2MA-CsS-AMFC). The effect of various proton-exchange membranes (PEMs), including Nafion 117 (N-117), Nafion 115 (N-115), and Nafion 212 (N-212) with respective thicknesses of 183, 127, and 50.08 μ, was separately incorporated into carbon cloth as PEM air-cathode electrode to evaluate their influences on the performance of the 2MA-CsS-AMFC configuration operated in fed-batch mode, while Azorubine dye was selected as the recalcitrant organic compound. The fed-batch test results showed that the 2MA-CsS-AMFC configuration with PEM N-115 operated at Azorubine dye concentration of 300 mg L^-1 produced the highest power density of 1022.5 mW m^-2 and open-circuit voltage (OCV) of 1.20 V coupled with enhanced dye removal (4.77 mg L h^-1) compared to 2MA-CsS-AMFCs with PEMs N-117 and N-212 and those in previously published data. Interestingly, PEM 115 showed remarkable reduction in biofouling and pH splitting. Apart from that, mass transfer coefficient of PEM N-117 was the most permeable to oxygen (K_O = 1.72 × 10^-4 cm s^-1) and PEM N-212 was the most permeable membrane to Azorubine (K_A = 7.52 × 10^-8 cm s^-1), while PEM N-115 was the least permeable to both oxygen (K_O = 1.54 × 10^-4) and Azorubine (K_A = 7.70 × 10^-10). The results demonstrated that the 2MA-CsS-AMFC could be promising configuration for bioenergy recovery from wastewater treatment under various PEMs, while application of PEM N-115 produced the best performance compared to PEMs N-212 and N-117 and those in previous studies of membrane/membrane-less air-cathode single-chamber MFCs that consumed dye wastewater.

COMSOL Multiphysics® modelling of oxygen diffusion through a cellulose nanofibril conduit employed for peripheral nerve repair

BACKGROUND

Peripheral nerve injury can cause significant impairment, and the current methods for facilitating repair, particularly over distances greater than approximately 1 mm, are not entirely effective. Allografts, autografts, and synthetic conduits are three of the most common surgical interventions for peripheral nerve repair; however, each has limitations including poor biocompatibility, adverse immune responses, and the need for successive surgeries. A potential new method for promoting peripheral nerve repair that addresses the shortcomings of current interventions is a biocompatible cellulose nanofibril (CNF) conduit that degrades in-vivo over time. Preliminary testing in multiple animal models has yielded positive results, but more information is needed regarding how the CNF conduit facilitates nutrient and gas flow.

RESULTS

The current work employs 3D modelling and analysis via COMSOL Multiphysics® to determine how the CNF conduit facilitates oxygen movement both radially through the conduit walls and axially along the length of the conduit. Various CNF wall permeabilities, conduit lengths, and nerve-to-conduit diameter ratios have been examined; all of which were shown to have an impact on the resultant oxygen profile within the conduit. When the walls of the CNF conduit were modeled to have significant oxygen permeability, oxygen diffusion across the conduit was shown to dominate relative to axial diffusion of oxygen along the length of the conduit, which was otherwise the controlling diffusion mechanism.

CONCLUSIONS

The results of this study suggest that there is a complex relationship between axial and radial diffusion as the properties of the conduit such as length, diameter, and permeability are altered and when investigating various locations within the model. At low wall permeabilities the axial diffusion is dominant for all configurations, while for higher wall permeabilities the radial diffusion became dominant for smaller diameters. The length of the conduit did not alter the mechanism of diffusion, but rather had an inverse relationship with the magnitude of the overall concentration profile. As such the modeling results may be employed to predict and control the amount and distribution of oxygenation throughout the conduit, and hence to guide experimental conduit design.

Prototyping the Experimental Setup to Quantify the Tissue Oxygen Consumption Rate and Its Preliminary Test

In order to establish a reliable and practical method to make a diagnosis on the viability of an amputated extremity, we propose a method to evaluate the oxygen consumption rate. To validate this concept, we prototyped an experimental system with which the oxygen transfer rate into tissue can be assessed by the rate of change of the decrease in dissolved oxygen (DO) concentration within the buffer fluid surrounding the target tissue. The purpose of this study is to examine the feasibility of our prototyped experimental system by comparison between fresh and non-fresh rat skeletal muscles. The results show that the fresher tissue transferred more oxygen to the tissue, which suggests that tissue oxygen consumption is highly related to tissue freshness and can indirectly assess the tissue viability.

Influence of interfacial properties/structure on oxygen diffusion in oil-in-water emulsions

Oxygen diffusion played an important role in the lipid oxidation of food emulsions. In this study, a simple method was developed to quantitatively observe the oxygen diffusion in the oil-water biphasic system, and it was further applied to investigate the relationship between the oxygen diffusion and lipid oxidation in O/W emulsions. Various factors that related to the emulsion oxidation were considered, from their influence on the oxygen diffusion and lipid oxidation in the emulsions. Results showed that there was obvious correlation between the oxygen diffusion and lipid oxidation in O/W emulsions, which reveals the inhibition of oxygen diffusion could apparently slow down the lipid oxidation. Moreover, the changes of oil phase, water phase and interfacial layer of the emulsions, which were related to the oxygen diffusion, could improve the oxidative stability of the emulsions effectively. Our findings are helpful for deep understanding the mechanisms of the lipid oxidation in food emulsions.

Simulation of time-fractional oxygen diffusion in cornea coated by contact-lens

In this paper, the time-fractional oxygen diffusion has been simulated in a one-dimensional (1D) corneal-contact lens (CL) system. Different CLs have been employed as Balafilcon, thin- and thick-Polymacon. It is assumed that homogeneous and isotropic porous mediums of cornea and CL is saturated with compressible oxygen. The computations of the time-fractional derivations are done based on the Caputo method. The obtained results show that the fractional derivative order (FDO) severely affects pressure distribution in cornea and CL. Consequently, the magnitudes of post-lens-tear-film (PoLTF) pressure change due to diverse FDOs. Particularly, maximum changes have been observed in the results gained from the CLs with thicknesses more than 100 μm. The agreement of the results obtained from the time-fractional modeling with the experimental data compared to the standard diffusion modeling has been improved by more than 36%. Finally, it has been demonstrated that high-thickness CLs can cause exist anomalous diffusion process in cornea tissue.

Cerebral capillary oxygen diffusion: exploring the concept of intracapillary hemoglobin conformational changes

The mechanisms of oxygen diffusion in brain capillaries have not been fully clarified to date. According to the laws of physics, the well-documented phenomenon of hyperoxemia-induced excessive increases in brain tissue oxygen pressure (PbtO2) contradicts traditional models of cerebral capillary oxygen diffusion. Circulating models predict a significant drop in oxygen pressure (PO2), and some of them foresee the presence of hypoxic or anoxic corners near the capillary end, regardless of high PbtO2 levels. We propose that the cerebral intracapillary transformation of hemoglobin from the relaxed (R) to the tense (T) quaternary conformational state, driven by deoxygenation and an overload of negative allosteric effectors, and characterized by a lower, more hyperbolic dissociation curve, mitigates the oxygen pressure difference across cerebral capillaries, ensuring a homogeneous pericapillary distribution of oxygen. The hemoglobin R to T state transition is responsible for the high PbtO2 levels observed in viable cerebral tissue during hyperoxemia.