The microstructure of polyacrylamide hydrogel matrices was probed by turbidity measurements, and by fluorescence recovery after photobleaching (FRAP) of fluorescently labeled bovine serum albumin (fBSA), as a function of polymer concentration and crosslink density. Turbidity increased with increasing polymer and/or crosslinker concentration. At low polymer and crosslinker concentrations, FRAP dynamics were well described by diffusion through a single polymer phase. However for higher concentrations of polymer and crosslinker, the diffusion model was inadequate, and a second mode, likely corresponding to release of fBSA from regions of relatively dense polymer, was observed. At low network concentrations, probe diffusivity (inversely related to FRAP relaxation time) decreased with increasing polymer and crosslinker concentrations. Following onset of the second mode, however, diffusivity increased with increasing monomer concentration, suggesting that the network through which fBSA diffused became looser. The optical and FRAP measurements, while showing qualitatively similar trends, were not directly correlated, and they likely reflected different modes of network phase separation.

The effect of varying initial monomer concentration on the microstructure and rheological properties of poly (sodium acrylate) hydrogel was investigated. It was seen that as polymer concentration increased, mechanical strength and elasticity of the network also increased till 25 wt% beyond which it saturates. In the case of loss modulus a similar increase is observed with increase in polymer concentration upto 25 wt%, past which there is a minor drop for 30 wt% gel indicating marginal drop in gel strength. The frequency sweep results showed predominant elastic response typical for a strong gel. A solid-like mechanical response was also confirmed by analyzing complex viscosity of respective hydrogels.

The dynamics of polyacrylamide hydrogels with and without entrapped anionic polyelectrolyte chains have been investigated using dynamic light scattering measurements. A non - ergodic treatment of the data suggests a striking alteration in system dynamics for gels embedded with polyelectrolytes when compared with parent gel. The gels exhibited an increasingly non - ergodic behaviour with maximum frozen in structure for gels with highest concentration of polyelectrolyte chains indicating stiffening of network junction. The analysis by short time expansion of intermediate scattering function suggests there is a decrease in mesh size with increase in polyelectrolyte concentration.

This work describes purification and characterisation of a monocot mannose-specific lectin from Hyacinth bulbs. The purified lectin has a molecular mass of ∼30kDa in reducing as well as in non-reducing SDS-PAGE. In hydrodynamic studies by Dynamic Light Scattering (DLS) showed that purified lectin was monomeric in nature with a molecular size of 2.38±0.03nm. Agglutination activity of purified lectin was confirmed by rabbit erythrocytes and its agglutination activity was inhibited by d-mannose and a glycoprotein (ovalbumin). Glycoprotein nature of purified lectin was confirmed by Periodic Acid Schiff's (PAS) stain. Purified lectin showed moderate pH and thermal stability by retaining hemagglutination activity from pH 6-8 and temperature up to 60°C. It also suppressed the growth of human colon cancer cells (Caco-2) and cervical cancer cells (HeLa) with IC50 values of 127μg/mL and 158μg/mL respectively, after 24-h treatment. Morphological studies of treated cells (Caco-2 and HeLa) with hyacinth lectin by AO/EB dual staining indicated that purified lectin is capable of inducing apoptosis.

Probe diffusion of fluorescently labeled Dextran 40 inside polyelectrolyte solution of polyacrylic acid (PAA) was investigated using Fluorescence Recovery After Photobleaching technique. The crowding and interaction effects on probe diffusion were controlled by tuning background polymer and added external electrolyte concentration. For all the salt concentration, an overall decrease in diffusion coefficient is observed with rise in polymer concentration. The diffusion coefficient decreases with decrease in salt concentration whereas the solution viscosity increases, indicating a competition between viscous drag and electrostatic interaction. A large positive deviation from the ideal Stokes-Einstein relation is observed for high polymer and low salt concentration, which reduces markedly with addition of salt confirming polyelectrolyte effects, plays a major role in deciding the probe diffusion.

The effect of crowding, background and probe charges and chain flexibility on probe dynamics of Green Fluorescent Protein in polyelectrolyte solutions of poly-l-lysine was investigated using Fluorescence Recovery After Photobleaching (FRAP). An interesting double diffusive behavior in FRAP recovery curve was observed at low polymer concentration resulting in two relaxation modes, which disappears with rise in polymer concentration. The fast relaxation mode attributes to diffusion of free protein molecules alone, where as slow mode is credited to polymer adsorbed protein molecules. Absence of double diffusive behavior at higher polymer concentration is argued in terms of varying host chain conformation and the only relaxation mode present is due to movement of free probes alone rather than that of adsorbed proteins. We noticed only a marginal decrease in diffusion coefficient with rise in salt concentration and the trend is reversed when variation in sample viscosity with salt is taken into account. In addition a small but systematic decrease in diffusion coefficient is seen with increase in magnitude of probe charge. Comparison of results with ideal Stoke – Einstein relation brings out the importance of polyelectrolyte effect and indicates ∼200 – fold positive deviations from predicted value for both variation in ionic strength and solution pH.

We have investigated the effect of ionic and non – ionic surfactants on the structure and rheological properties of polyacrylamide hydrogels. With addition of ionic and non-ionic surfactants, just below and above their critical micellar concentration (CMC), there is a significant decrease in hydrogels mechanical strength as compared to the parent hydrogels alone. In oscillatory measurements, no frequency dependence is observed in the case of polyacrylamide hydrogels. However with the addition of surfactants, just below and above CMC, noticeable frequency dependence is observed.

Rheological measurements on gellan gum hydrogels were carried out to investigate the effect of an anionic surfactant, sodium dodecyl sulfate (SDS) on hydrogel structure. The gel strength was found to be strongly correlated to surfactant concentration. Below the Critical Micellar Concentration (CMC), we observed an increase in gel strength with rise in surfactant concentration and a reverse trend is observed for surfactant concentration above CMC. The gel network structure is found to be highly elastic below CMC, while an aggregated network is observed at higher concentration of surfactant. With the addition of surfactant, sol to gel transition temperature of Gellan Gum is shifted to higher temperature, suggesting addition of surfactant promotesas well as stabilizes the helix formation.

Hydroxypropyl Cellulose (HPC) microgels were prepared by emulsion polymerization method. The volume phase transition temperature (VPTT) and swelling properties were investigated using Dynamic Light Scattering (DLS). The VPTT for the HPC microgels was found to be similar to 44 degrees C. Microgel particles swelled similar to'3' times of their original size on decreasing temperature from 50 degrees C to 25 degrees C. In addition we have also studied the effect of salts, sodium nitrate and sodium bromide in the Hofmeister series on deswelling and colloidal stability of HPC microgels using DLS and turbidity measurements respectively. Microgel particles swelled in presence of NaNO3 when its concentration was increased from 10(-4) to 0.5 M and deswelled beyond it. As oppose to this, swelling of microgels in presence of NaBr was seen only upto 10(-3) and beyond which deswelling of microgels was observed. The results obtained are consistent with Hofmeister series of anions. Turbidity results showed that the colloidal stability of HPC microgel dispersion was dependent on ionic strength and type of added salt. For both salts, stability of microgels was found to decrease with rise in salt concentration.

Diffusion of labeled BSA in polyacrylamide hydrogels was studied with variation of polymer and crosslinker concentration in order to probe the microstructure of the hydrogels. With the rise in polymer concentration beyond a certain threshold, single exponential recovery shifted to double exponential, suggesting structural changes in the hydrogel matrix. A similar shift from single to double diffusive behavior was seen on increasing crosslinker concentration at a given polymer concentration.

The diffusion of green fluorescent protein (GFP) in non-dilute polyelectrolyte solutions of Poly-L-lysine was studied using fluorescence recovery after photobleaching (FRAP) technique. The effect of background charges on probe diffusion of GFP was studied with varying ionic strength of the solution. With increase in polyelectrolyte concentration, increase in solution viscosity and decrease in probe diffusion coefficient was observed. At the same time, we observed the diffusion coefficient increased with increase in salt concentration, while solution viscosity decreased, indicating a competition between electrostatic force between background and probe and viscosity drag. When the probe diffusion coefficient was compared with the predicted Stokes-Einstein (S-E) relation, strong positive deviations were observed for all the solutions with highest deviation observed for solution with zero salt concentration.