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Evaluation of transport properties of a drug in a hydrogel matrix is of engineering importance in the assessment of drug delivery systems. Water sorption and solute release are the two important aspects that determine the transport of water/solute in a hydrogel. A novel custom-made diffusion cell is used to examine the transport properties in the hydrogels by chemically cross-linking hyaluronic acid in various alkaline solutions at different cross-linker-to-polymer ratios. The tracer diffusion coefficient in the swollen hydrogel matrix in its rubbery state is estimated using a custom-made diffusional cell. The release kinetics is followed at perfect sink conditions, which transform from a glassy polymer dry membrane state to a swollen rubbery gel state. It is shown that the diffusion of solvent (water) through the hydrogel is case II transport, while the diffusion through the swollen hydrogel is case I (Fickian). The diffusion coefficient is proved to be independent of mesh size and pH of the initial solution. However, the release kinetics is influenced by the diffusion of solute and the relaxation of the polymer in hydrogel. The relaxation coefficient is a function of alkalinity in the solution with which the gel is being made. The contribution of relaxation to the transport during solvent sorption and solute release is found to be similar.

Numerous methods have been adopted to alter the interfacial tension during the enhanced oil recovery (EOR) system. Much emphasis was given to the conventional methods of EOR because of its ease in operation and understanding. Efforts were made to use surfactants along with Nano particles as they could modify the rheological properties to a great extent with their complexion in the structure and properties. The combination of a cationic polymer (polyacrylamide) (PAM) in the presence of anionic surfactant (sodium dodecyl sulfate) (SDS) with varied concentrations of anionic Nano particle (silicon dioxide) in their complex aqueous solution form is investigated. At a known concentration of polymer and surfactant, the changes in rheological properties of fluid are studied for varied concentrations of silica Nanoparticles. Hydrated and un-hydrated polyacrylamide solutions were subjected to analysis at the well resembling temperature of 90OC, to know the effect of thermal stability of the polymer. It is observed that the fluid viscosity is reduced by two orders of magnitude with the addition of Nano particles, at low shears. However, the fluid showed shear thickening properties due to the complex structure among the polymer, surfactant and particle. The ionic charges interplay leading to the formation of complex structures at the hydrated state of polymer affects the viscosity of the fluid to a great extent.

Hyaluronic acid (HA)-based materials are being investigated because of their role in biological fluids and tissues. Poly(vinyl alcohol) (PVA) when blended with HA at different compositions leads to superior mechanical properties compared to pure HA. The PVAHA blend hydrogels are potential candidates for pharmaceutical, biomedical, and cosmetic applications. It is essential to understand the structure, gelation time, and morphological properties of these hydrogels. In this work, a blend system of PVA crosslinked with glutaraldehyde in the presence of HA is studied. Semidilute solutions of PVA and HA are blended, followed by gelation due to crosslinking. The crosslinked gels as well as the gel cast membranes were examined. The effect of HA on the gelation process is investigated using rheological characterization. It is shown that kinetics of gelation is influenced by HA content, though storage modulus of the gels is influenced marginally. The structural features of PVAHA gels were also probed with scanning electron microscopy and dynamic light scattering. It is argued that there is a complex interplay between intra- and intermolecular crosslinking of PVA and PVA–HA interactions during the gel formation. Based on the insights obtained from various probing techniques for PVAHA gels with different HA content, three broad structural features were identified. It is shown that the hydrogel is semi-interpenetrating network at lower HA content ( 20% HA). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41081.

There is an increasing demand for designing controlled drug delivery systems with materials which are more biocompatible, economical and materials which can be processed easily. Poly (vinyl alcohol) (PVA) and hyaluronic acid (HA) are promising polymers for applications in drug delivery. PVA forms gel based on the acetal bridges when crosslinked with glutaraldehyde (GA). On the other hand, HA a natural polymer, forms gel with divinyl sulfone (DVS) as a crosslinker. PVA and HA blends upon crosslinking PVA with GA or HA with DVS, in the presence of the other polymer, form gels that are more adaptable to the drug delivery systems. In this work, the mechanical properties and swelling behaviour of PVAHA gels were characterized. The effect of composition on viscoelastic moduli and degree of swelling was determined. The storage modulus (G") of various gels made of PVA, HA and PVAHA blends were measured using rheology and compared with the values available in the literature. Swelling properties were measured and compared among various PVA and HA gels. Collagen is added to PVA solution and the rheological properties were measured in the gel state. Based on the values of storage modulus, gels of various compositions of PVA, HA and collagen might be selected as potential biomaterials for drug delivery system depending on careful understanding the type of application. � 2014, DESIDOC.