Drug release profiles and microstructural characterization of cast and freeze dried vitamin B12 buccal films by positron annihilation lifetime spectroscopy

• Cast and freeze dried buccal films containing vitamin B12 were prepared.
• Sodium alginate and Carbopol 71G were selected for the buccal film formulation.
• PALS was applied to compare the microstructural characteristics of the films.
• Korsmeyer–Peppas kinetic model was used to determine the drug release mechanism.
• Correlation was found between the o-Ps lifetime values and the changes of release rate of samples.

Solvent cast and freeze dried films, containing the water-soluble vitamin B12 as model drug were prepared from two polymers, sodium alginate (SA), and Carbopol 71G (CP). The proportion of the CP was changed in the films. The microstructural characterization of various samples was carried out by positron annihilation lifetime spectroscopy (PALS). The drug release kinetics of untreated and stored samples was evaluated by the conventionally applied semi-empirical power law.Correlation was found between the changes of the characteristic parameters of the drug release and the ortho-positronium (o-Ps) lifetime values of polymer samples. The results indicated that the increase of CP concentration, the freeze-drying process and the storage at 75% R.H. decreased the rate of drug release.The PALS method enabled the distinction between the micro- and macrostructural factors influencing the drug release profile of polymer films.

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