An early assessment of silicone hydrogel safety : pearls and pitfalls, and current status

The contact lens industry has evolved and now provides many choices, including continuous wear, overnight orthokeratology, frequent-replacement lenses, daily-disposable lenses, and many alternatives in systems of care and maintenance. Epidemiologic studies to date have shown that how a lens is worn, particularly if worn overnight, can increase the risk of microbial keratitis. However, the risk of silicone hydrogel contact lenses worn on a continuous-wear basis has been evaluated only recently. This article summarizes the recent research data on extended-wear silicone hydrogel lenses and discusses the challenges of early evaluations of silicone hydrogel lens safety. Finally, the relevance of this information is discussed to practitioners and contact lens wearers making choices about the risks and benefits of different products and how they are used.

In response: Changes in ultraviolet transmittance of hydrogel and silicone hydrogel contact lenses induced by wear

We thank Dr Shedden and Dr Pall for their insightful comments and the opportunity to clarify a number of points from our work.1 The “protection factor” (PF) expressed as the inverse of the transmittance of contact lens (CL) material (1/Tλ), where T is the percentage transmittance of ultraviolet radiation (UVR) in a given waveband (UVC, UVB or UVA) of the UV spectrum for contact lenses is the standard method for reporting PF values and as such there should not be any controversy. We have calculated the PF for each wavelength across the entire UV spectrum (UVC, UVB, UVA) as presented in figure 3 of our previous publication.1 In that article, we were simply stating the observation when transmission in the UVC spectra band is considered especially because appreciable amounts of potentially carcinogenic short UV wavelengths was shown to be present in sunlight in our region three decades ago2 and these short wavelength photons are reported to be more biologically damaging to ocular tissues.3 In addition, the depletion of the Ozone layer is still continuing. Nevertheless, we understand the concern of the authors that the results of the PF might be confusing to those who are not familiar with the science of UVR and as such we have made some revisions to the findings of the calculated PF...

Persistent anterior chamber silicone oil and myopia

A 60-year-old male experienced a marked unilateral myopic shift of 20 D following attempted removal of intravitreal heavy silicone oil (HSO) used in the treatment of inferior proliferative vitreous retinopathy following retinal detachment. Examination revealed HSO adherent to the corneal endothelium forming a convex interface with the aqueous, obscuring the entire pupil, which required surgical intervention to restore visual acuity. This case highlights the potential ocular complications associated with silicone oil migration into the anterior chamber, which include corneal endothelial decompensation and a significant increase in myopia.

Studies on the Tracking and Erosion Resistance of RTV Silicone Rubber Nanocomposite

One of the problems associated with outdoor polymeric insulators is tracking and erosion of the weathershed which can directly influence the reliability of the power system. Flame retardants are added to the base material to enhance its tracking and erosion resistance. Hydroxide fillers are regarded as the best flame retardants. This paper deals with studies related to nano - sized magnesium dihydroxide (MDH) and micron-sized Alumina Trihydrate (ATH) fillers as flame retardants in RTV silicone rubber. Tracking and erosion resistance studies were carried out on MDH and ATH silicone rubber composites using an inclined plane tracking and erosion (IPT) resistance tester. The MDH filled (5% by wt) composites performed much better than ATH composites in terms of eroded mass, depth of erosion, width and length of erosion. The eroded mass of MDH composite is 49.8 % that of ATH composite which can be attributed to high surface area and higher thermal stability of MDH nanofillers.

Hybrid Materials Combining Photoactive 2,3-Didecyloxy Anthracene Physical Gels and Gold Nanoparticles

Organic/inorganic hybrid gels have been developed in order to control the three-dimensional structure of photoactive nanofibers and metallic nanoparticles (NPs). These materials are prepared by simultaneous self-assembly of the 2,3-didecyloxyanthracene (DDOA) gelator and of thiol-capped gold nanoparticles (AuNPs). TEM and fluorescence measurements show that alkane-thiol capped AuNPs are homogeneously dispersed and tightly attached to the thermoreversible fibrillar network formed by the organogelator in n-butanol or n-decanol. Rheology and thermal stability measurements reveal moreover that the mechanical and thermal stabilities of the DDOA organogels are not significantly altered and that they remain strong, viscoelastic materials. The hybrid materials display a variable absorbance in the visible range because of the AuNPs, whereas the strong luminescence of the DDOA nanofibers is efficiently quenched by micromolar amounts of AuNPs. Besides, we obtained hybrid aerogels using supercritical CO2. These arc very low-density porous materials showing fibrillar networks oil which fluorinated gold NPs arc dispersed. These hybrid materials are of high interest because of their tunable optical properties and are under investigation for efficient light scattering.

Supramolecular gels `in action'

n recent years, self-assembly has emerged as a powerful tool for the construction of functional nanostructures. Myriad applications of these nanoscale architectures, especially the supramolecular gels derived from low molecular mass compounds, in fields such as optoelectronics, light harvesting, organic–inorganic hybrid materials, tissue engineering and regenerative medicine are being envisaged. This review attempts to present a succinct overview of the current state of research on functional nano-scale systems—the design, synthesis and applications of self-assembled nanomaterials engineered to carry out precise functions, with an emphasis on supramolecular gel phase materials.

Artifactual staining of proteins on polyacrylamide gels by nitrobluetetrazolium chloride and phenazine methosulfate

Different purified proteins were shown to give purple formazan bands corresponding to the protein stain following electrophoresis on polyacrylamide gels, in the presence of nitrobluetetrazolium (NBT) and phenazine methosulfate (PMS). Both PMS and NBT are needed for formazan production which has a favorable pH at 8.5. Sulfhydryl blockers in the incubation medium inhibited this color development to different extents. While proteins with free SH groups like bovine serum albumin, ovalbumin, and urease showed this pyridine nucleotide independent artifact, nonthiol proteins, viz., bovine pancreatic ribonuclease A, and riboflavin-binding protein from chicken egg white failed to do so. The nonenzymatic formazan formation observed with different proteins could also be shown in an in vitro assay system. It is clear that the “nothing dehydrogenase” phenomenon observed in several cases may be due to the thiol group-mediated artifactual staining of proteins.

Disc electrophoresis of sorghum seed proteins in polyacrylamide gels

Electrophoretic analyses of sorghum flour protein by disc electrophoresis in polyacrylamide gels containing urea have been described. The albumin, globulin, and prolamin fractions of sorghum endosperm meal have been investigated, using pH 9.5 and 4.3 gel systems with four different buffers. Highly complex patterns were observed for all three protein fractions. It has been suggested that this method can provide a convenient tool for the analyses of seed proteins which are relatively insoluble in aqueous buffers.

Crystallization Studies of ZrO2-SiO2 Composite Gels

Composite ZrO2-SiO2 powders were prepared using a gel route. Morphological and crystallographic features of ZrO2 particles formed during the heat treatment, and the particle sizes of the composites have been investigated. The following polymorphic changes have been observed during the heat treatment: amorphous -> metastable-cubic/tetragonal ZrO2 -> tetragonal ZrO2 -> monoclinic ZrO2. SiO2 crystallizes above 1273 K. The martensitic transformation of ZrO2 (t -> m) was observant in situ, when exposed to a high-energy electron beam. These results are important in the production of ZrO2-toughened ceramics of controlled microstructure.

Carbon nanotube reinforced supramolecular gels with electrically conducting, viscoelastic and near-infrared sensitive properties

Pristine and long-chain functionalized single-walled carbon nanotubes (SWNTs) were incorporated successfully in supramolecular organogels formed by an all-trans tri(p-phenylenevinylene) bis-aldoxime to give rise to new nanocomposites with interesting mechanical, thermal and electrical properties. Variable-temperature UV-vis and fluorescence spectra reveal both pristine and functionalized SWNTs promote aggregation of the gelator molecules and result in quenching of the UV-vis and fluorescence intensity. Electron microscopy and confocal microscopy show the existence of a densely packed and directionally aligned fibrous network in the resulting nanocomposites. Differential scanning calorimetry (DSC) of the composites shows that incorporation of SWNTs increases the gel formation temperature. The DSC of the xerogels of 1-SWNT composites indicates formation of different thermotropic mesophases which is also evident from polarized optical microscopy. The reinforced aggregation of the gelators on SWNT doping was reflected in the mechanical properties of the composites. Rheology of the composites demonstrates the formation of a rigid and viscoelastic solid-like assembly on SWNT incorporation. The composites from gel-SWNTs were found to be semiconducting in nature and showed enhanced electrical conductivity compared to that of the native organogel. Upon irradiation with a near IR laser at 1064 nm for 5 min it was possible to selectively induce a gel-to-sol phase transition of the nanocomposites, while irradiation for even 30 min of the native organogel under identical conditions did not cause any gel-to-sol conversion.

Corona Aging Studies on Silicone Rubber Nanocomposites

In EHV and UHV power transmission lines, corona could occur even on well designed transmission line hardware and insulators especially under wet conditions. Corona if allowed to occur continuously can significantly damage the polymeric insulators used in such lines in the long run. This paper presents the experimental results of corona aging studies conducted on unfilled silicone rubber as well as filled silicone rubber nanocomposites. Corona aging studies were conducted on silicone rubber samples with filler concentrations of 0, 1, 2 and 3 % by wt of nanosilica for 25 h and 50 h. Needle-plane electrode geometry has been used to create the corona on the samples. Different characterization techniques such as Scanning Electron Microscopy, Energy Dispersive X-ray analysis, Hydrophobicity, Fourier Transform Infrared Spectroscopy, and Optical Profilometry have been used to assess the relative performance of the samples with respect to corona aging. Results indicate that at 3 wt %, the performance of the nanocomposite is much better than the unfilled silicon rubber which can be attributed to the modifications in the material caused by the size factor of the filler.

Chiral gels derived from secondary ammonium salts of (1R, 3S)-(+)-camphoric acid

In order to have access to chiral gels, a series of salts derived from (1R, 3S)-(+)-camphoric acid and various secondary amines were prepared based on supramolecular synthon rationale. Out of seven salts prepared, two showed moderate gelation abilities. The gels were characterized by differential scanning calorimetry, table top rheology, scanning electron microscopy, single crystal and powder X-ray diffraction. Structure property correlation based on X-ray diffraction techniques remain inconclusive indicating that some of the integrated part associated with the gelation phenomena requires a better understanding.

Supramolecular Chirality in Organogels: A Detailed Spectroscopic, Morphological, and Rheological Investigation of Gels (and Xerogels) Derived from Alkyl Pyrenyl Urethanes

This Article addresses the formation of chiral supramolecular structures in the organogels derived from chiral organogelator 1R (or 2R), and its mixtures with its enantiomer (1S) and achiral analogue 3 by extensive circular dichroism (CD) spectroscopic measurements. Morphological analysis by atomic force microscopy (AFM) and scanning electron microscopy (SEM) were complemented by the measurements of their bulk properties by thermal stability and rheological studies. Specific molecular recognition events (1/3 vs 2/3) and solvent effects (isooctane vs dodecane) were found to be critical in the formation of chiral aggregates. Theoretical studies were also carried out to understand the interactions responsible for the formation of the superstructures.