Free volume properties of drug delivery polymers studied by positron annihilation spectroscopy

The effect of free-volume on the drug delivery polymeric materials has been investigated by using positron annihilation spectroscopy (PAS). The objective of this research work is to characterize the chemical and physical properties of drug delivery polymeric materials, so that the obtained scientific information could be used to improve the drug delivery processes. In this study, the experimental techniques of Doppler broadening energy spectra (DBES) of positron annihilation and positron annihilation lifetime (PAL) coupled with a slow positron beam were used to measure the difference of free-volumes at the atomic level as a function of positron incident energy (0--30 keV).; A variety of polymeric drug delivery materials, including biodegradable polymers blends and copolymers, such as poly (vinyl-pyrrolidone) (PVP) and poly (ethylene glycol) (PEG), with desirable hydrophilic/hydrophobic groups and the relevant copolymers were chosen as the studied materials. The free-volume hole-radii and hole-volume distributions were obtained from positron annihilation lifetime measurements. Glass transition temperatures were obtained from the free volume data and heat capacity rate (DSC) with the temperature. Results of free-volume depth profile were obtained in different composition of polymers blends, chemical composition, polymer molecular weight and the hydrogen bonding replacement to covalent bonding etc.; A variety of drugs dissolved in PVP-PEG mixtures were studied by DBES and PAL coupled with a slow positron beam. Free-volume properties from the surface to the bulk of PVP-PEG polymers with drugs were obtained from the S parameter using DBES and o-Ps lifetime from PAL. The depth profile of drug distribution was measured and it provides useful information about delivery efficiencies. A correlation between the change of free volume and the drug concentration was obtained. Different types of drugs interact with polymeric materials differently and show different results of positron annihilation signals. From this study, we demonstrate that a combined use of DBES and PAL and a slow positron beam could be a novel method to investigate the drug delivery mechanism and transport efficiency for pharmaceutical applications.