Vitreous Medium Research Articles

Reflecting Picasso in Glass

Whereas Picasso’s work in ceramics, wood and bronze is rather well known, the body of his sculptures in glass remains an object of little research. In fact, as a thorough analysis reveals, they rarely find mention in publications or catalogues on Picasso and seldom are included in exhibitions or retrospectives on the great Spanish artist. This may on the one hand be attributed to a still prevailing perception of glass as a medium for industrial, functional or everyday purposes—hence discounting the material in terms of artistic output—while on the other to controversies of authorship, related to the question of ideation versus creation. Unlike ceramics or bronze, the realisation of blown glass sculpture hinges on the involvement of the maestro vetraio as the mediator between thought and form—thus resulting in a distancing between artwork and artist conditioned by the nature of the medium. Against this background, the paper aims at a better understanding of Picasso’s vision of sculpture through an examination of his creations in the vitreous medium. On these grounds, a closer look at Picasso’s works in glass is meant to highlight his unique ‘hand’ in terms of idiom, line and form.

Models and Algorithms for the Refinement of Therapeutic Approaches for Retinal Diseases.

We are developing a Virtual Eye for in silico therapies to accelerate research and drug development. In this paper, we present a model for drug distribution in the vitreous body that enables personalized therapy in ophthalmology. The standard treatment for age-related macular degeneration is anti-vascular endothelial growth factor (VEGF) drugs administered by repeated injections. The treatment is risky, unpopular with patients, and some of them are unresponsive with no alternative treatment. Much attention is paid to the efficacy of these drugs, and many efforts are being made to improve them. We are designing a mathematical model and performing long-term three-dimensional Finite Element simulations for drug distribution in the human eye to gain new insights in the underlying processes using computational experiments. The underlying model consists of a time-dependent convection-diffusion equation for the drug coupled with a steady-state Darcy equation describing the flow of aqueous humor through the vitreous medium. The influence of collagen fibers in the vitreous on drug distribution is included by anisotropic diffusion and the gravity via an additional transport term. The resulting coupled model was solved in a decoupled way: first the Darcy equation with mixed finite elements, then the convection-diffusion equation with trilinear Lagrange elements. Krylov subspace methods are used to solve the resulting algebraic system. To cope with the large time steps resulting from the simulations over 30 days (operation time of 1 anti-VEGF injection), we apply the strong A-stable fractional step theta scheme. Using this strategy, we compute a good approximation to the solution that converges quadratically in both time and space. The developed simulations were used for the therapy optimization, for which specific output functionals are evaluated. We show that the effect of gravity on drug distribution is negligible, that the optimal pair of injection angles is (50∘,50∘), that larger angles can result in 38% less drug at the macula, and that in the best case only 40% of the drug reaches the macula while the rest escapes, e.g., through the retina, that by using heavier drug molecules, more of the drug concentration reaches the macula in an average of 30 days. As a refined therapy, we have found that for longer-acting drugs, the injection should be made in the center of the vitreous, and for more intensive initial treatment, the drug should be injected even closer to the macula. In this way, we can perform accurate and efficient treatment testing, calculate the optimal injection position, perform drug comparison, and quantify the effectiveness of the therapy using the developed functionals. We describe the first steps towards virtual exploration and improvement of therapy for retinal diseases such as age-related macular degeneration.

Synthesis and Characterization of Nanoparticle-Based Dexamethasone-Polypeptide Conjugates as Potential Intravitreal Delivery Systems

The use of dexamethasone for eye disease treatment is limited by its low solubility, bioavailability, and rapid elimination when applied topically. The covalent conjugation of dexamethasone with polymeric carriers is a promising strategy to overcome existing drawbacks. In this work, amphiphilic polypeptides capable of self-assembly into nanoparticles were proposed as potential delivery systems for intravitreal delivery. The nanoparticles were prepared and characterized using poly(L-glutamic acid-co-D-phenylalanine) and poly(L-lysine-co-D/L-phenylalanine) as well as poly(L-lysine-co-D/L-phenylalanine) covered with heparin. The critical association concentration for the polypeptides obtained was in the 4.2-9.4 μg/mL range. The hydrodynamic size of the formed nanoparticles was between 90 and 210 nm, and they had an index of polydispersity between 0.08 and 0.27 and an absolute zeta-potential value between 20 and 45 mV. The ability of nanoparticles to migrate in the vitreous humor was examined using intact porcine vitreous. Conjugation of DEX with polypeptides was performed by additional succinylation of DEX and activation of carboxyl groups introduced to react with primary amines in polypeptides. The structures of all intermediate and final compounds were verified by 1H NMR spectroscopy. The amount of conjugated DEX can be varied from 6 to 220 µg/mg of polymer. The hydrodynamic diameter of the nanoparticle-based conjugates was increased to 200-370 nm, depending on the polymer sample and drug loading. The release of DEX from the conjugates due to hydrolysis of the ester bond between DEX and the succinyl moiety was studied both in a buffer medium and a vitreous/buffer mixture (50/50, v/v). As expected, the release in the vitreous medium was faster. However, the release rate could be controlled in the range of 96-192 h by varying the polymer composition. In addition, several mathematical models were used to assess the release profiles and figure out how DEX is released.

The Backscattering Polarization for a Sphere with a Two-Scale Relief of Rough Surface

The paper presents the results of studies of the polarization of backscattered optical radiation for a model of a sphere with a wavy surface covered with arbitrarily oriented ellipsoidal pores. The calculations were performed by the Monte Carlo method (ROKS-RG program, geometrical optics approximation). Surface roughness of objects is taken into account using local geometries. It is shown that for structures whose pores contain a vitreous medium, the presence of vacuum voids between a transparent and opaque medium determines the nature of the phase dependence of the degree of polarization. In the absence of vacuum, the polarization is always positive and, for small phase angles, depends significantly on the optical characteristics of an opaque medium. The presence of vacuum is a catalyst for the growth of the p-component of the reflected radiation. This leads to a significant decrease in the amplitude of the positive polarization branch. Differences in the optical characteristics of opaque materials are also leveled out, and in some cases negative values of the degree of polarization are observed in the region of small phase angles. Keywords: polarization, geometrical optics approximation, Monte Carlo method, rough surface, Two-Scale Relief.

Implementation of optical quantum gate for polarization-encoded qubits via acousto-optic diffraction by shear acoustic waves in vitreous media

Implementation of optical quantum gate for polarization-encoded qubits via acousto-optic diffraction by shear acoustic waves in vitreous media

Fabrication, Optimization, and In Vitro and In Vivo Characterization of Intra-vitreal Implant of Budesonide Generally Made of PHBV.

Drug delivery to vitreous in comparison with drug delivery to the other parts of the eye is complicated and challenging due to the existence of various anatomical and physiological barriers. Developing injectable intra-vitreal implant could be beneficial in this regard. Herein, poly(hydroxybutyrate-co-valerate) (PHBV) implants were fabricated and optimized using response surface method for budesonide (BZ) delivery. The acquired implants were characterized in regard to the stability of the ingredients during fabrication process, drug loading amount, and drug release pattern (in PBS-HA-A and in vitreous medium). According to this research and statistical analysis performed, first HV% (hydroxyvalerate) then molecular weight and ratio of PEG as pore former affect respectively release rate and burst strength of BZ with different coefficients. Drug release profile in rabbit eye correlated well with that of in vitro (R2 = 0.9861, p˂0.0001). No significant changes were seen in ERG waves, intraocular pressure, and histological studies during the in vivo part of the project. Using 8% HV, 20% PEG/PHBV, and higher molecular weight PEG (i.e., 6000), the optimum formulation was achieved. Toxicity and biocompatibility of the optimized formulation, which were evaluated in vivo, indicated the suitability of design implant for intra-vitreal BZ delivery. Grapical abstract.

Rac1 modulates the vitreous‐induced plasticity of mesenchymal movement in retinal pigment epithelial cells

The vitreous has been shown to induce epithelial-mesenchymal transdifferentiation because it induces fibroblast-like morphology, enhanced migration and invasion in retinal pigment epithelial cells in proliferative vitreoretinopathy. Rac1 is the principal mediator of cell migration. In the current study, the relationship between Rac1 and cell migration, and invasion in vitreous-transformed retinal pigment epithelial cells was investigated using NSC23766, a specific inhibitor of Rac guanosine-5'-triphosphatase activity, and the involvement of a Rac1 guanosine-5'-triphosphatase-dependent pathway was detected. One-way design with multiple levels and repeated measurement design. The vitreous humor was collected from 20 healthy donor eyes and the retinal pigment epithelial cells were obtained from 9 healthy donor eyes. Human low-passage retinal pigment epithelial cells were treated with normal medium or 25% vitreous medium. Rac1 activity was measured using a pull-down assay. The cytotoxicity of NSC23766 was measured using the trypan blue dye exclusion test. Cell migration was measured using a wound healing assay. Cell invasion was determined using a transwell invasion assay. Protein expression of Rac1 and phosphorylation of LIM kinase 1 and cofilin were detected by Western blot analysis. Cell migration, invasion, Rac1 activity and phosphorylation of LIM kinase 1 and cofilin. Rac1guanosine-5'-triphosphatase was activated in vitreous-transformed retinal pigment epithelial cells. A Rac inhibitor suppressed vitreous-induced migration and invasion in retinal pigment epithelial cells. Cofilin phosphorylation was activated by vitreous treatment but blocked by NSC23766. Rac1 mediates vitreous-transformed retinal pigment epithelial cells' plasticity of mesenchymal movement via Rac1 guanosine-5'-triphosphatase-dependent pathways that modulate LIM kinase 1 and cofilin activity. Rac inhibition may be considered a novel treatment for proliferative vitreoretinopathy.

Computational modeling of intravitreal drug delivery in the vitreous chamber with different vitreous substitutes

Intravitreal injection of drug is commonly used to treat vitreoretinal diseases. In order to assess the effectiveness of the injected drug, it is critical to know the drug distribution within the eye following the injection. This is particularly important when the vitreous medium has been replaced by fluid substitutes. The main objective of this paper is to characterize the spatio-temporal evolution of drug distribution following intravitreal injection into a vitreous substitute such as silicone oil. In addition, water is considered as an intravitreal fluid to represent the liquefaction of vitreous that occurs with aging. Both direct injection of drugs and injection of time-released drugs are studied. The results show that the concentration distribution depends on the properties of the vitreous substitute, the diffusion coefficient of the drug and the permeability of the retinal surface. For drugs with high diffusion coefficients, convection plays a small role in the drug transport. For drugs with low diffusion coefficients and in low viscosity vitreous fluids, convection is seen to play a more important role and can lead to high drug concentrations on the retina which can be potentially toxic. Time-released drug injection is shown to avoid conditions of retinal toxicity, and to provide lower drug concentrations with sustained residence times along the retinal surface. For drugs with high diffusivity and retinal permeability, uniform distribution of the drug is obtained along the surface of the retina, while for drugs with low diffusion coefficient and retinal permeability the concentration of drug is localized along the posterior surface of the retina.

A system to perform quantitative fluorescein angiography

Abstract Purpose: To develop a system with which fluorescein angiograms may be quantitatively compared across time, patients and laboratories. Methods: Sets of standard solutions of the fluorescein were developed in media that mimics the physical and chemical environments of compartments of the eye, i.e., serum and vitreous, in which the measurement is taken. Images from these sets of standards were obtained at exactly the same time and under the same instrument settings as the data from the eye on the same angiogram. Computer software was developed to quantitatively analyze the angiogram that established calibration plots and converted the grey image to an absolute color scale image of the data, as well as provide quality control information as to the performance of the instrument. Results: The position and shape of the excitation and emission spectra of the fluorescein standards matched those of fluorescein in serum and vitreous media. The 80% reduction in quantum efficiency of fluorescein in serum compared to fluorescein in PBS at pH 7.4 was equal to fluorescein in synthetic serum and/or PBS at pH 5.5. The reduction in quantum efficiency of fluorescein in vitreous was only 3% and equal to fluorescein in PBS at pH 7.3.The resulting computer generated color scale angiogram images were directly compared across time and patients and the initial results appeared consistent and reasonable. In addition, by evaluating the calculated instrument performance parameters, e.g., linearity, dynamic range, detection threshold and Window of Anaylsis, a determination of the quality of the angiogram could be made. Conclusions: This system provides data that is independent of the instrument and operator, and promises that quantitative comparisons can be made across time, patients and laboratories.

Heat treatments versus microstructure in a molybdenum-rich borosilicate

A new glass formulation, a calcium and zirconium-enriched alumino-boro-silicate matrix, able to incorporate 12 wt% of molybdenum oxide has been developed in order to trap molybdenum as CaMoO 4, a stable phase in a vitreous medium. Laboratory studies on this matrix have shown the impact of the glass thermal treatment on its microstructure. Thus, four cooling rates and heat treatments presented in this paper were investigated to determine if Ca and Mo totally reacted to give CaMoO 4 and to localize the powellite phase in the different glasses. Using X-ray diffraction and Rietveld refinements, we were able to quantify both crystallized and amorphous CaMoO 4 in all the samples. EDS analyses allowed us to localize it in the glass microstructure. Then coupling together the micrograph analysis and the X-ray diffraction results proved the presence of amorphous powellite and showed its place in the glasses.

Photoviscous flow and glass macroproperties

The interest in glass photosensitivity has been renewed due to the importance of photosensitivity phenomena in potical fibers devices which promise a host of novel applications. Among these developments, one is the ability to imprint periodic and permanent refractive-index changes (Bragg gratings) on monomode germanosilicate optical fibers using excimer lasers. Defect formation in the structure of the glass core mainly germanium GODC (germanium-related oxygen-deficient centers) defects are supposed to be responsible for the grating formation. Here the phenomena are analyzed under another perspective that is related with high temperature gradient inside monomode optical fibers and its consequences. Because temperatures much higher than the germanium silicate glass softening point could be achieved during exposure to excimer lasers, the formation of Bragg gratings is a two step process to modify vitreous media. First, UV energy should be absorbed at the fiber core - by defects, dopants and glass components - and a second step where this energy is thermalised. There is no ablation in the glass core and energy transfer is governed by viscous flow or photoviscous flow and internal structural rearrangements. Alternatives to enhance optical fiber glass photosensitivity via glass composition and viscous behaviour are discussed.

Investigation of energy structure of lead silicate glasses by non-linear absorption spectroscopy technique

Regularities of color center formation in the lead silicate glasses under photoexcitation have been studied. It is shown for the first time that the long-wave boundary of carrier mobility of vitreous media can be placed considerably higher then the fundamental absorption edge of the material matrix. For this reason the detection of linear formation of color centers in the lead silicate glasses is not possible. Their coloration arises only from the multi-photon matrix ionization and the excitation occurs through virtual states that are located in the fundamental absorption region. The numerical estimates of the three-photon absorption coefficient and the forming color centers cross-section at 527 nm are obtained for the glasses with different content of lead oxide.

Possible use of low-frequency esr to estimate the quadrupole coupling constant in copper(II) complexes in vitreous media

Possible use of low-frequency esr to estimate the quadrupole coupling constant in copper(II) complexes in vitreous media

THE ELECTRICAL CONDUCTIVITY OF SODIUM CHLORIDE IN MOLTEN GLASS1

Precipitation of collodial suspensions in glass by dissolved salts leads to the assumption that they ionize. In this investigation the Conductivity of glass alone and with dissolved salts confirms the theory. A special cell has been devised for conductivity work in glass at high temperatures. This is the first study of the electrical conductivity of salts in vitreous media.