Using dioxane and water as mixed solvents to prepare pH and temperature dual responsive poly(N-isopropyl acrylamide-co-itaconic acid) hydrogels

AbstractpH and temperature dual responsive hydrogels based on itaconic acid (IA) and N-isopropylacrylamide (NIPAAm) were prepared by means of water and dioxane as mixed solvents. The chemical compositions, structures and morphologies of these hydrogels were characterized by FTIR, TGA and SEM, and their pH and temperature responsive behaviours were investigated through equilibrium swelling ratios, deswelling and reswelling kinetics. The results showed the hydrogels fabricated in this condition had expanded chain conformations and macroporous network structures, and exhibited the larger swelling ratios as well as improved deswelling/reswelling dynamics.

Effect of Carbon Black on Crosslinking

For a number of different vulcanization systems, the equilibrium swelling ratios for carbon-black-filled and unfilled samples are shown to be linearly related, as found by Lorenz and Parks, indicating that the degree of crosslinking is not changed by incorporating carbon black. However, filled compounds swell less, and thus the apparent degree of crosslinking is significantly greater. For example, it is about twice as large for compounds containing 50 phr of HAF carbon black. This is confirmed by measurements of the elastic modulus of swollen samples. Relatively strong bonds appear to be formed between rubber molecules and the surface of carbon black particles - bonds that can withstand swelling stresses and temperatures of up to 120 °C. Bonding between rubber and carbon black is also indicated by the limited swelling of filled rubber compounds even before vulcanization, although in this case the apparent degree of crosslinking is smaller. Thus, vulcanization appears to enhance the contribution of rubber-particle bonding to the elastic modulus and restricted swelling of carbon-black-filled vulcanizates. Simple procedures are suggested for estimating the actual degree of crosslinking in filled rubber vulcanizates from measurements of equilibrium swelling or elastic modulus.

Design of pH Sensitive Materials for On/Off Release of Thrombolytic and Anticoagulant Drugs

An experimental study was conducted to determine the mechanisms of transport for delivery of cardiovascular agents using a pH-sensitive hydrogel as the carrier. Copolymer gels based on hydrophilic (2-hydroxyethyl methacrylate) and polybasic (N,N-diethylaminoethyl methacrylate) monomers were formed as membranes and analyzed for their potential to control the diffusion of model solutes as well as heparin and streptokinase. The polybasic materials were selected because they would allow drug delivery to be triggered by microenvironmental pH fluctuations around the site of a blood clot. In slightly basic solutions, the polymers remained in a thermodynamic state of phase-separation, while the polymer absorbed more solution and the mesh size increased once the pH was less than the pKb of the polybasic moiety. The hydrogels' equilibrium swelling ratios were determined as a function of pH, and the mesh sizes were determined by rubber elasticity measurements. Diffusion of model solutes, as well as heparin, was studied using side-by-side diffusion cells to determine the influence of gel morphology and mesh size on the screening of the solutes. Streptokinase release from these gels was modulated by environmental pH.