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The pure and composite hydrogels of chitosan with sodium alginate were synthesized at various pH values and characterized by rheology and IR-spectroscopy. Chitosan shows gelation at neutral and basic pH while sodium alginate remains in solution form at all pH values. By careful adjustment of mixing weight fraction ratio and pH, an array of hydrogels with modulated structural dynamics and viscoelasticity, mechanical strength and encapsulation capacity were obtained. At acidic pH, a higher weight fraction of alginate increased the elasticity of the hydrogels while at basic pH more percentage of chitosan stabilized the hydrogel. Strongest composite hydrogels were obtained at acidic pH and gel strength decreased on increasing pH of the synthetic medium. The synthesized hydrogels were studied for their encapsulation capability towards Citral. The pure chitosan hydrogels showed maximum encapsulation capacity followed by the composite hydrogels prepared at neutral pH. This study highlights that a range of composite hydrogels with modified properties can be obtained by simple changes in experimental conditions exploiting physical interactions and can help in better understanding of niche of its applicability in research and industry., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Synthesis and structural characterization of hydrogels composed of sodium alginate, polyethylene oxide and acrylic acid with cyclodextrin as the hydrocolloid prepared at different pH values is presented. The hydrogels synthesized show significant variations in rheological properties, drug encapsulation capability and release kinetics. The hydrogels prepared at lower pH (pH 1) are more elastic, have high tensile strength and remain almost unaffected by varying temperature or frequency. Further, their Ibuprofen encapsulation capacity is low and releases it slowly. The hydrogel prepared at neutral pH (pH 7) is viscoelastic, thermo-reversible and also exhibits sol-gel transition on applying frequency and changing temperature. It shows highest Ibuprofen encapsulation capacity and also optimum drug release kinetics. The hydrogel prepared at higher pH (pH 12) is more viscous, has low tensile strength, is unstable to change in temperature and has fast drug release rate. The study highlights the pH responsiveness of three composite alginate hydrogels prepared under different conditions to be employed in drug delivery applications., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The interaction of cetyltrimethylammoium bromide (CTAB) and its gemini homologue (butanediyl-1,4-bis (dimethylcetylammonium bromide), 16-4-16 with biocompatible polymer sodium alginate (SA) has been investigated in aqueous medium. Addition of K2CO3 influences viscoelastic properties of surfactant impregnated SA via competition between electrostatic and hydrophobic interactions. Viscosity of these polymer-surfactant systems increases with increase in concentration of K2CO3, and a cryogel is formed at about 0.5M K2CO3 concentration. The thermal stability of gel (5% SA+0.5M K2CO3) decreases with increase in surfactant concentration, a minimum is observed with increase in 16-4-16 concentration. The impact of surfactant addition on the alginate structure vis-à-vis its drug loading capability and release thereof was studied using Ibuprofen (IBU) as the model drug. The hydrogel with 16-4-16 exhibits higher IBU encapsulation and faster release in comparison to the one containing CTAB. This higher encapsulation-cum-faster release capability has been related to micelle mediated solubilization and greater porosity of the hydrogel with gemini surfactant., (Copyright © 2015 Elsevier Ltd. All rights reserved.)