(302b) Mobility of Particles in Gelling Matrices

The mobility of active pharmaceutical ingredient (API) particles in gels reveals how the particles are packaged in the polymeric matrix. So far, Stokes – Einstein equation has been widely applied to characterize the mobility of particles in fluid media. However, Stoke – Einstein equation cannot be applied to describe the mobility of particle in condense polymer solution and gel because the diffusivity of particle is not inversely proportional to the bulk viscosity. Therefore, the modified Stokes – Einstein equation is applied. The key factor in modified Stockes – Einstein equation is that the microviscosity of polymer solution is used instead of the bulk viscosity. Diffusing Wave Spectroscopy (DWS) technique is used to characterize the dynamic mobility of APIs with the size from hundreds nanometer to micron size in hydroxypropyl methyl cellulose network. Our results show that, the relationship between diffusion coefficients of the imbedded particles to the viscosity of media is not reversely proportional.