In situ gels are systems which are applied as solutions or suspensions and are capable of undergoing rapid sol-to-gel transformation triggered by external stimulus such as temperature, pH etc. on instillation. The aim of the present study was to formulate and evaluate pH responsive in-situ gel for ophthalmic delivery. Ciprofloxacin hydrochloride is popularly used as a broad spectrum antibiotic in the treatment of corneal ulcers of ocular infections. However, rapid dilution on instillation, wash out, poor retention of drug concentration delimit the therapeutic benefits of the drug when used in form of conventional eye drops. Sodium alginate, an ophthalmic gel forming mucoadhesive polymer was chosen as polymer which undergoes instantaneous gel formation due to formation of calcium alginate by virtue of its interaction with divalent cation (Ca+2) present in lachrymal fluid. Hydroxy Propyl Methyl Cellulose (HPMC K4M and E5 0LV) was further incorporated as a viscosity enhancer in order to achieve the desired consistency so as to facilitate sustained drug release. The developed formulations were evaluated for clarity, pH measurement, gelling capacity, drug content, rheological study, and in vitro drug release. Thus, in situ gel based systems containing gums can be a valuable approach for ophthalmic drug delivery when compared to conventional systems.

Strontium tartrate trihydrate (STT) crystals have been grown in silica hydrogel. Various polarization mechanisms such as atomic polarization of lattice, orientational polarization of dipoles and space charge polarization in the grown crystals have been understood using results of the measurements of dielectric constant (ε ε′ ′) and dielectric loss (tan δ δ) as functions of frequency and temperature. Ion core type polarization is seen in the temperature range 75-180°C, and above 180°C, there is interfacial polarization for relatively lower frequency range. One observes dielectric dispersion at lower frequency presumably due to domain wall relaxation.

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Results of a study on nucleation kinetics, growth, and characterization of strontium tartrate trihydrate single crystals in silica hydrogel are described. The basic structure, composition, and perfection of the grown crystals were determined by XRD, EDAX, and laser scattering tomography. It was found that experimental conditions, such as pH and density of gel, concentration and volume of supernatant liquid, aging and quality of gel, have a strong influence on the nucleation kinetics and growth of the crystals. The effect of experimental conditions on growth kinetics has been qualitatively explained from the standpoint of the classical nucleation theory.

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