Oxygen, water and sodium chloride transport in Soft Contact Lenses Materials

[EN] Oxygen permeability, diffusion coefficient of the sodium ions and water flux and permeability in different conventional hydrogel (Hy) and silicone-hydrogel (Si-Hy) contact lenses have been measured experimentally. The results showed that oxygen permeability and transmissibility requirements of the lens have been addressed through the use of siloxane containing hydrogels. In general, oxygen and sodium chloride permeability values increased with the water content of the lens but there was a percolation phenomenon from a given value of water uptake mainly in the Si-Hy lenses which appeared to be related with the differences between free water and bound water contents. The increase of ion permeability with water content did not follow a unique trend indicating a possible dependence of the chemical structure of the polymer and character ionic and non-ionic of the lens. Indeed, the salt permeability values for silicone hydrogel contact lenses were one order of magnitude below those of conventional hydrogel contact lenses, which can be explained by a diffusion of sodium ions occurring only through the hydrophilic channels. The increase of the ionic permeability in Si-Hy materials may be due to the confinement of ions in nanoscale water channels involving possible decreased degrees of freedom for diffusion of both water and ions. In general, ionic lenses presented values of ionic permeability and diffusivity higher than most non-ionic lenses. The tortuosity of the ionic lenses is lower than the non-ionic Si-Hy lenses. Frequency 55 and PureVision exhibited the highest water permeability and flux values and, these parameters were greater for ionic Si-Hy lenses than for ionic conventional hydrogel lenses.Gavara, R.; Compañ Moreno, V. (2016). Oxygen, water and sodium chloride transport in Soft Contact Lenses Materials. Journal of Biomedical Materials Research Part B Applied Biomaterials. 105(8):2218-2231. doi:10.1002/jbm.b.33762S22182231105

A three-dimensional model to describe complete human corneal oxygenation during contact lens wear

We perform a novel 3D study to quantify the corneal oxygen consumption and diffusion in each part of the cornea with different contact lens materials. The oxygen profile is calculated as a function of oxygen tension at the cornea-tear interface and the oxygen transmissibility of the lens, with values used in previous studies. We aim to determine the influence of a detailed geometry of the cornea in their modeling compared to previous low dimensional models used in the literature. To this end, a 3-D study based on an axisymmetric volume element analysis model was applied to different contact lenses currently on the market. We have obtained that the model provides a valuable tool for understanding the flux and cornea oxygen profiles through the epithelium, stroma, and endothelium. The most important results are related to the dependence of the oxygen flux through the cornea-lens system on the contact lens thickness and geometry. Both parameters play an important role in the corneal flux and oxygen tension distribution. The decline in oxygen consumption experienced by the cornea takes place just inside the epithelium, where the oxygen tension falls to between 95 and 16 mmHg under open eye conditions, and 30 to 0.3 mmHg under closed eye conditions, depending on the contact lens worn. This helps to understand the physiological response of the corneal tissue under conditions of daily and overnight contact lens wear, and the importance of detailed geometry of the cornea in the modeling of diffusion for oxygen and other species

A three-dimensional model to describe complete human corneal oxygenation during contact lens wear

[EN] We perform a novel 3D study to quantify the corneal oxygen consumption and diffusion in each part of the cornea with different contact lens materials. The oxygen profile is calculated as a function of oxygen tension at the cornea-tear interface and the oxygen transmissibility of the lens, with values used in previous studies. We aim to determine the influence of a detailed geometry of the cornea in their modeling compared to previous low dimensional models used in the literature. To this end, a 3-D study based on an axisymmetric volume element analysis model was applied to different contact lenses currently on the market. We have obtained that the model provides a valuable tool for understanding the flux and cornea oxygen profiles through the epithelium, stroma, and endothelium. The most important results are related to the dependence of the oxygen flux through the cornea-lens system on the contact lens thickness and geometry. Both parameters play an important role in the corneal flux and oxygen tension distribution. The decline in oxygen consumption experienced by the cornea takes place just inside the epithelium, where the oxygen tension falls to between 95 and 16 mmHg under open eye conditions, and 30 to 0.3 mmHg under closed eye conditions, depending on the contact lens worn. This helps to understand the physiological response of the corneal tissue under conditions of daily and overnight contact lens wear, and the importance of detailed geometry of the cornea in the modeling of diffusion for oxygen and other species.This research was funded by the Universitat Jaume I (UJI) under the project UJI-B2018-53. We thanks to Robert Jones for the English language revision.Aguilella-Arzo, M.; Compañ Moreno, V. (2023). A three-dimensional model to describe complete human corneal oxygenation during contact lens wear. Journal of Biomedical Materials Research Part B Applied Biomaterials. 111(3):610-621. https://doi.org/10.1002/jbm.b.35180610621111

A Deep Insight into Different Acidic Additives as Doping Agents for Enhancing Proton Conductivity on Polybenzimidazole Membranes

The use of phosphoric acid doped polybenzimidazole (PBI) membranes for fuel cell applications has been extensively studied in the past decades. In this article, we present a systematic study of the physicochemical properties and proton conductivity of PBI membranes doped with the commonly used phosphoric acid at different concentrations (0.1, 1, and 14 M), and with other alternative acids such as phytic acid (0.075 M) and phosphotungstic acid (HPW, 0.1 M). The use of these three acids was reflected in the formation of channels in the polymeric network as observed by cross-section SEM images. The acid doping enhanced proton conductivity of PBI membranes and, after doping, these conducting materials maintained their mechanical properties and thermal stability for their application as proton exchange membrane fuel cells, capable of operating at intermediate or high temperatures. Under doping with similar acidic concentrations, membranes with phytic acid displayed a superior conducting behavior when compared to doping with phosphoric acid or phosphotungstic acid

Evolution of the critical oxygen tension

Chang, A.; Compañ Moreno, V.; Weissman, BA. (2018). Evolution of the critical oxygen tension. Contact Lens Spectrum. 33(3):36-39. http://hdl.handle.net/10251/121358S363933

Dual Purpose Measurements with Displacement Sensors

[EN] In this paper we show a laboratory experience describing the possibility to build a sensor using a coil to measure small thicknesses of materials with the possibility of measuring temperature simultaneously, with the same built sensor. Its operation is based on the following facts: An electric current (a.c), flows through a coil and a magnetic field appears producing self-induction characterized by an electromotive force induced in the coil, when a conductive piece is situated in front of the coil. That permits us to obtain information about the distance between the coil and the conductive piece. When this separation thickness is changing, the magnetic field around the coil changes, because the self-induction coefficient (L) is also changing. Using resistance and impedance measurements (voltage in our case) in the coil, an expression has been obtained for the determination of the thickness of a non-conductive sheet placed between a metallic plate and the coil. Calibration measurements of resistance with temperature have been obtained. The thermodynamic analysis is also presented showing the equation of state of the system between the voltage, temperature and the thickness of the non-conductive sample. The linear thermal-expansion coefficient of the sample is also determined.The authors gratefully acknowledge the support provided by the projects ENE/2015-69203-R from Ministerio de Economia y Competitividad (MINECO) (Spain), and DGAPA-PAPIIT IG100618 and DGAPA-PAPIIT IN-114818 (México) and also thanks to Raúl Reyes Ortíz and Alberto López Vivas for technical assistance.Andrio, A.; Del Castillo, LF.; Compañ Moreno, V. (2020). Dual Purpose Measurements with Displacement Sensors. European Journal of Physics Education. 11(2):24-34. https://doi.org/10.20308/ejpe.v11i2.279S243411

Corneal Equilibrium Flux as a Function of Corneal Surface Oxygen Tension

[EN] Purpose Oxygen is essential for aerobic mammalian cell physiology. Oxygen tension (PO2) should reach a minimum at some position within the corneal stroma, and oxygen flux should be zero, by definition, at this point as well. We found the locations and magnitudes of this ¿corneal equilibrium flux¿ (xmin) and explored its physiological implications. Methods We used an application of the Monod kinetic model to calculate xmin for normal human cornea as anterior surface PO2 changes from 155 to 20 mmHg. Results We find that xmin deepens, broadens, and advances from 1.25 ¿m above the endothelial¿aqueous humor surface toward the epithelium (reaching a position 320 ¿m above the endothelial¿aqueous humor surface) as anterior corneal surface PO2 decreases from 155 to 20 mmHg. Conclusions Our model supports an anterior corneal oxygen flux of 9 ¿L O2 · cm¿2 · h¿1 and an epithelial oxygen consumption of approximately 4 ¿L O2 · cm¿2 · h¿1. Only at the highest anterior corneal PO2 does our model predict that oxygen diffuses all the way through the cornea to perhaps reach the anterior chamber. Of most interest, corneal oxygen consumption should be supported down to a corneal surface PO2 of 60 to 80 mmHg but declines below this range. We conclude that the critical oxygen tension for hypoxia induced corneal swelling is more likely this range rather than a fixed value.Compañ Moreno, V.; Aguilella-Arzo, M.; Weissman, BA. (2017). Corneal Equilibrium Flux as a Function of Corneal Surface Oxygen Tension. Optometry and Vision Science. 94(6):672-679. doi:10.1097/OPX.0000000000001083S67267994

Molecular Dynamics Simulations of Proton Conduction in Sulfonated Poly(phenyl sulfone)s

Full molecular dynamics was used to simulate separately the diffusion of naked protons and H₃O⁺ hydrated protons across sulfonated poly(phenyl sulfone)s. Simulations were carried out for wet membranes with the following characteristics:  ion-exchange capacity, 1.8 mequiv/g of dry membrane; water uptake, 10−30%; temperature range, 300−360 K. The diffusion coefficient of naked protons is nearly 1 order of magnitude higher than that of the hydrated protons for the membranes with the lower water uptake (10%). For the membranes with higher water uptake the ratio between the diffusion coefficients of the two particles reduces to about half an order of magnitude. The conductivity of the naked protons increases from 21.4 × 10⁻³ to 52.5 × 10⁻³ S/cm when the water uptake increases from 10% to 30%. For hydrated protons the conductivity increases from 1.54 × 10⁻³ to 7.57 × 10⁻³ S/cm. The conductivities obtained through simulations carried out at 300 K for the hydrated proton across membranes with water uptake 18% and 30% are roughly similar to those experimentally measured for a membrane with ion exchange capacity = 1.8 mequiv/g and water uptake = 24.3%. Simulated conductivities of both naked protons and hydrated protons follow Arrhenius behavior.This work was supported by the Comunidad de Madrid through the grant interfaces S-505/MAT-0227, Fondos Europeos de Desarrollo (FEDER), and Fondo Social Europeo (FSE). Financial support was also supplied by the Dirección General de Investigación Científica y Técnica (DGICYT) (grant MAT 2005-05648-C02-02)

Comments to paper entitled "Predicting scleral GP lens entrapped tear layer oxygen tensions"

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