In situ gelling systems are polymeric formulations that are in sol forms before entering in the body, but change to gel forms under the physiological conditions. The sol-gel transition depends on one or a combination of different stimuli, like pH change, temperature modulation, solvent exchange, ultra violet irradiation and the presence of specific ions or molecules. Drug delivery systems having such properties can be widely used for sustained delivery vehicle preparation of the bioactive molecules. Some important advantages of these smart systems are ease of application and reduced frequency of administration, as well as protection of drug from environmental condition changes.

Background and purpose of the study: Several polymeric systems have been used to fabricate ocular inserts for better ocular bioavailability and retention to drug of which gelling systems have shown advantages of convenient administration and increased contact time. The purpose of the present study was to develop a bioadhesive in-situe gelling ocular insert of Gatifloxacin using polymeric system of sodium alginate as gelling and chitosan as bioadhesive agent.Materials and methods: Polymeric ocular inserts of Gatifloxacin sesquehydrate (GS) were composed using sodium alginate and chitosan with glycerin as plasticizer by solvent casting method. The ocular inserts were investigated for physicochemical properties (thickness, weight variation, folding endurance and surface pH), mechanical strength (tensile strength, elongation at break), swelling index, and bioadhesion parameters. In vitro release studies were carried using a fabricated donor-receptor compartment model.Results: Cumulative drug released from the formulation ranged from 95-99% within 8-12h.The formulation D (2% sodium alginate and 1% chitosan) sustained the drug release for the longest period of time (12h). Zero-order release of the drug was from optimized formulation D. A high correlation coefficient (r=0.9845) was recorded between in vitro and in vivo drug release.Conclusion: Gatifloxacin sesquehydrate inserts have appreciable film forming properties and were found to posses good antimicrobial efficacy.

Gellan gum was exploited to modulate the stability of sesame oil-in-water emulsion and fabricated stable droplets with mean size of ̴ 9 μm till 30 days, then gelified by CaCl2 solution with final concentration of 55mM or 1% GDL. Enrichment with CaCl2 increased the amount of compact structures in gels in conjunction with decreasing WHC values and textural features modification. Gellan bundles as visualised by microscopic images conferred a remarkable influence to gel samples; enrichment with GDL or control gels increased the WHC value and formed less coarse networks. Based on Fourier transform infrared (FTIR) spectroscopy it was suggested that was no major changes in the functional groups of different gel samples, also according to the results of XRD analysis all the emulsion gels had an amorphous nature. The results indicated close relationships between physicochemical properties and microstructures of gellan-stabilized emulsion gels and would be of vital importance for extending the present knowledge about the preparation and properties of emulsion gels from gellan gum.