Advanced Hydrogels Based Drug Delivery Systems for Ophthalmic Delivery

Hydrogels are aqueous gels composed of cross-linked networks of hydrophilic polymers. Stimuli-responsive based hydrogels have gained focus over the past 20 years for treating ophthalmic diseases. Different stimuli-responsive mechanisms are involved in forming polymer hydrogel networks, including change in temperature, pH, ions, and others including light, thrombin, pressure, antigen, and glucose-responsive. Incorporation of nanocarriers with these smart stimuli-responsive drug delivery systems that can extend the duration of action by increasing ocular bioavailability and reducing the dosing frequency. This review will focus on the hydrogel drug delivery systems highlighting the gelling mechanisms and emerging stimuli-responsive hydrogels from preformed gels, nanogels, and the role of advanced 3D printed hydrogels in vision-threatening diseases like age-related macular degeneration and retinitis pigmentosa. It also provides insight into the limitations of hydrogels along with the safety and biocompatibility of the hydrogel drug delivery systems.

Synthesis and characterization of a novel sugar based cross-linker

There are very few literature reports on the synthesis of monosaccharide based cross-linkers. A novel monosaccharide sugar-based cross-linker was synthesized by using D-mannitol, and allyl chloride in basic medium at low temperature (40°C) under inert atmospheric conditions. We have used a new synthetic scheme which does not involve the use of autoclave at high temperature and pressure for carrying out allylation with allyl chloride. The synthesized product has been characterized by, Fourier-transform infrared (FT-IR) spectra and 1 H Nuclear magnetic resonance (1 HNMR) spectra. The formation of allyl mannitol was also confirmed with the help of elemental analysis of C, H and O. Cross linked polymer gel samples were prepared by polymerizing acrylic acid monomer alongwith the synthesized cross-linker at different concentrations. Aqueous gels have been prepared from the cross-linked polymers and their swelling capacity has been studied. It has been found that these gels act as superabsorbent materials. The optimum ratio of cross-linker and acrylic acid monomer for the preparation of gel having highest swelling capacity (~ 28000% of water) was found to be 0.03 g crosslinker with 12.0 g. monomer.

Isolation and utilization of cellulosic elements from the plant cell wall

Two very different types of cellulosic materials that may be isolated from plant-based sources are reviewed herein. We have shown that long helical cellulosic coils may be isolated by gentle chemical treatment of leaf petioles. The coils stem from protoxylem elements and are readily distinguished from other cellulosic components by polarized light microscopy, forming single- or multistranded left-handed helices. More widely known are the nanometer thickness cellulosic elements that may also be isolated from plant cell walls. These nanocelluloses can be subdivided into two main families. Cellulose nanocrystals (CNCs) are less than 250 nm long and are usually made by sulfuric acid hydrolysis. CNCs form stable liquid crystalline suspensions in water that dry to give iridescent coloured films, analogous to those found in some tropical plants. Cellulose nanofibrils (CNFs) are much longer and may have carboxyl groups on the surface. Both CNCs and CNFs are intrinsically hydrophilic and form useful aqueous gels and viscosity modifiers. By altering the surface chemistry, the nanocelluloses can also be incorporated as strengthening agents in composite materials. A wide range of commercial applications for these renewable materials has been proposed.

Il Salterio di San Romualdo (secolo IX), primi interventi di restauro e indagini conoscitive

The San Romualdo Psalter is a manuscript dating back to the 9th century, which for a long time has been thought to have been written by the saint himself. Its rubrication turned white making it completely unreadable, the previous repairs led to distortions of the parchment. The codex was dismantled and reproduced using UV fluorescence, with a remarkable improvement in the text’s readability. Previous repairs have been removed using rigid aqueous gels; distortions have been treated with humidification and tensioning with neodymium magnets. The manuscript has been resewn using a Japanese paper concertina and double thread technique, and bound on beech boards and full alum tawed goatskin.

Exfoliated sheets of MoS2 trigger formation of aqueous gels with acute NIR light responsiveness

We have developed a unique class of MoS2 entrapped aqueous gels where the exfoliated sheets trigger physical cross-linking of nanofibers of peptide amphiphiles.