Dynamic behavior of glucose oxidase-containing microparticles of poly(ethylene glycol)-grafted cationic hydrogels in an environment of changing pH.

Poly(diethylaminoethyl-g-ethylene glycol) microparticles were prepared by suspension polymerization of diethylaminoethyl methacrylate, poly(ethylene glycol) monomethacrylate and the crosslinking agent tetra(ethylene glycol) dimethacrylate in silicone oil using redox initiators. Particles of different sizes, crosslinking ratios and graft molecular weights were prepared. The changes in the swelling of the particles were studied as the pH was changed between 3.0 and 7.4. The particles showed rapid swelling/deswelling dynamics in response to changes in pH. It was evident that faster response could be obtained from smaller particles. Changing the crosslinking ratio resulted in changes in the extent of swelling, as well as the speed of response. It was also found that longer graft lengths were responsible for increasing the effect of relaxation of the swelling of the network.

Glucose-sensitivity of glucose oxidase-containing cationic copolymer hydrogels having poly(ethylene glycol) grafts.

Glucose oxidase and catalase were immobilized on poly(diethylaminoethyl methacrylate-g-ethylene glycol) gels by copolymerization of the constituent monomers and the functionalized enzyme solutions. The hydrogels were prepared in the form of discs and microparticles. The amount and the activity of enzymes immobilized in the matrix were determined. The hydrogels were tested for their response to glucose by exposing microparticles to varying concentrations of glucose. The generation of gluconic acid as a result of the reaction of glucose with oxygen was investigated as a function of polymer parameters, such as crosslinking ratio and enzyme loading. Pulsatile variation of the glucose concentration was used to confirm the glucose-dependent swelling properties of these hydrogels.

A new model describing the swelling and drug release kinetics from hydroxypropyl methylcellulose tablets.

A novel mathematical model for the water transport into and drug release from hydroxypropyl methylcellulose (HPMC) tablets is presented. Fick's second law of diffusion is used to describe the mass transfer processes in the three-component system drug/polymer/water. Numerical solutions of the respective set of partial differential equations are provided, considering axial and radial diffusion within cylindrical tablets. It is shown that the diffusion coefficients strongly depend on the water concentration (parameters quantifying this dependence have been determined). Swelling of the device is considered using moving boundary conditions, whereas dissolution processes are neglected. Experiments proved the applicability of the theory. The practical benefit of the new model is to calculate the required shape and dimensions of HPMC tablets to achieve a desired release profile.