Microrheology of Drug Particulates in Drying Polymeric Films

The introduction of nano- and micro-scale particles into polymer blends creates a large internal surface between the solid particles and the polymer, changing substantially the thermodynamic and mechanical properties of the polymer matrix Adsorption of polymers from solutions of their mixtures on solids plays an important role in the formation of API composite structures with evenly distributed i.e. non-aggregated particulate materials.

The effect of the particles on the phase separation in forming polymeric networks can be  related to the selectivity of the component adsorption at the interface with a solid phase, leading to the redistribution of the system components between the bulk and the surface layers. We have studied the filmgel-formation process of several drug loadedhydroxypropyl methylcellulose formulations using a new optical technology based on diffusing-wave spectroscopy. This unique and simple technique allows a non-destructive real-time monitoring of the drying process providing unique information on rheological properties at the particle lenghth scale. Measured kinetics of film formation provide a new vision of the successive steps of the mechanisms taking place (evaporation, packing, etc.). Obtained data are in good corellation with the data on the phase behavior of the polymeric solution.We also present experimental data and theoretical models that predict transport properties and stability of this colloidal system.