(93e) Biocompatible Polymers Characterization by Igc

The use of polymers in the modern pharmaceutical industry is quite wide and needs a lot of different information. One of the more recent applications is the impregnation of a polymeric system with a drug using as carrier a supercritical fluid. This process is based on dissolving the active principle in a supercritical fluid, the supercritical solvent swells and reduces the glass transition temperature (Tg) of the polymer and the solute splits between the solvent and the matrix itself. The process is feasible only if the impregnating agent is soluble in the supercritical fluid, if the polymer is swollen by the supercritical solvent and the partition coefficient is favorable to charge the matrix with enough active principle. The inverse gas chromatography (IGC) can be employed for studying the plasticization. In the IGC the obtained experimental data are the specific retention volumes Vg0 of a solute injected in the stationary phase (the polymer in this case) at different temperatures: the plot of the retention volume logarithm versus the reciprocal of the temperature is called retention diagram from which it is possible to observe the phase transitions of the polymer investigated. The experimentally determined specific retention volumes Vg0 can be used to characterize the investigated stationary phases in terms of dipolarity/polarizability, hydrogen-bond, basicity/acidity and lipophilicity by means of the equation of solvation proposed by Abraham. Experimental values of fugacity coefficients can be determined and utilized in connection of an equation of state model to predict the behavior of the substances investigated in different solvents and in carbon dioxide at high pressure. This thermodynamic approach has been applied to polyvinylpyrrolidones (PVP) which are polymers widely used in pharmaceutical and chemical formulations, in cosmetics, in paper and textile processes since they are physically and chemically inert, to copolymers of glycolide, a dimer of glycolic acid, and lactide, a dimer of lactic acid, (PLGA) which have been utilised in the medical industry for numerous biological applications including polymeric drug delivery devices, synthetic bone scaffolding, and even dental prosthetic devices and finally to different Eudragit® polymers. This investigation has been made on different biodegradable polymers: linear poly vinyl pyrrolidones (PVP), (PVP K25 (BASF, Mw=29.000), PVP K30 (BASF, Mw=40.000), and PVP K90 (BASF, Mw=360.000)), two biodegradable copolymers, poly(DL-lactide/glycolyde) (PLGA), with different lactide-glycolyde ratios, 50:50 (PLGA 5050) and 85:15 (PLGA 8515) and the corresponding pure polymers and four Eudragit® (Eudragit® E100 and L100 and Eudragit® RL and RS).