These tubes were capped and then placed in water bath maintained at a temperature of 50��C for 48h. After this period, tubes were compound libraries taken out and cooled to room temperature. The hydrogels obtained were cut into discs of 6mm length and immersed into 50:50v/v ethanol-water solution for complete removal of catalyst and unreacted monomers. Gel discs were thoroughly washed until the pH of solution was same as the solution before washing. The hydrogels obtained were dried at 40��C until a constant weight was achieved and then were stored in vacuum desiccators for further use. Table 1Different formulations of AA/PVSA hydrogels.2.3. Swelling StudiesThe dynamic swelling ratio (Q) was evaluated gravimetrically in 100mL 0.05M USP phosphate buffer solutions of various pHs, that is, 1.2, 5.5, 6.5, and 7.
5. Preweighed dried hydrogels discs were immersed in solutions of desired pH at a temperature of 37��C. Swollen gels were removed from the medium at a predetermined interval of time for 8 hours, weighed after blotting them dry with filter paper, and placed in the same bath. The swelling ratio (Q) was calculated from the following [22]:Q=WS?WdWd,(1)where Ws and Wd are the weights of swollen and dried hydrogels, respectively.2.4. Characterization of Poly(AA-co-VSA) Hydrogels2.4.1. Structural Parameters The average molar mass of the chains between cross-links (Mc), directly related to the cross-link density, is an important parameter in characterizing the structural parameters ofhydrogels. Physical and mechanical properties of cross-linked hydrogels are significantly influenced by the Mc.
According to Flory-Rehners theory [23], Mc can be calculated usingMc=?V1dp(VS1/3?VS/2)ln?(1?VS)+VS+��VS2,(2)where VS is the volume fraction of the swollen hydrogel at equilibrium, V1 is the molar volume of the solvent (mLmol?1), �� is Flory-Huggin’s solvent interaction parameter between solvent and polymer [24], and dp is the density of gel (g mL?1).�� can be calculated from��=ln?(1?VS)+VSVS.(3)Volume fraction of the polymer (VS) was calculated by the following equation [25]:VS=[1+dpds(MaMb?1)]?1,(4)where dp and dsare densities (g mL?1) of gel and solvent, respectively. Ma and Mb are the masses (g) of the swollen and dry hydrogels, respectively.The number of links between two cross-linked chains is called cross-linked density (q) which was calculated from [26]q=dpNAMC,(5)where NA is Avogadro’s number (6.
023 �� 1023/mole).2.4.2. Fourier-Transformation Infrared Spectroscopy (FTIR) Dried discs of hydrogel samples were powdered in pestle and mortar. The powdered material was mixed with potassium bromide Drug_discovery (Merck IR spectroscopy grade) in 1:100 proportion and dried at 40��C. The mixture was compressed to semitransparent disc of 12mm diameter by applying a pressure of 65kN (pressure gauge, Shimadzu) for 2 minutes. The FTIR spectrum over the wave length range 4000�C400cm?1 was recorded using FTIR spectrometer (FTIR 8400 S, Shimadzu).2.4.3.