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 favourable to charge the matrix with enough active principle. In order to overcome these limitations other technological approaches have been suggested. In the Supercritical AntiSolvent Precipitation (SAS) process the drug co precipitates with a polymer from a drug solution in which the antisolvent (the supercritical fluid) is added: a uniform dispersion of the drug in the polymer matrix is obtained. Whatever process is used the compatibilities between the different components plays a predominant role. Inverse gas chromatography (IGC) can be employed for collecting information useful for the characterization of the polymers and for the investigation of the equilibria involved. In the IGC the obtained experimental data are the specific retention volumes Vg 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 plasticization and the phase transitions of the polymer investigated. The experimentally determined specific retention volumes Vg 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 with 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.