Control of vitamin B12 release from poly(ethylene glycol)/poly(butylene terephthalate) multiblock copolymers

The release of vitamin B-12 (1355 Da) from matrices based on multiblock copolymers was studied. The copolymers were composed of hydrophilic poly(ethylene glycol)-terephthalate (PEGT) blocks and hydrophobic poly(butylene terephthalate) (PBT) blocks. Vitamin B-12 loaded films were prepared by using a water-in-oil emulsion method. The copolymer properties, like permeability, could be varied by increasing the PEG-segment length from 300 up to 4000 g/mol and by changing the wt% of PEGT. From permeation and release experiments, the diffusion coefficient of vitamin B-12 through PEGT/PBT films of different compositions was determined. The diffusion coefficient of vitamin B-12 was strongly dependent on the composition of the copolymers. Although an increased wt% of PEGT (at a constant PEG-segment length) resulted in a higher diffusion coefficient, a major effect was observed at increasing PEG-segment length. By varying the copolymer composition, a complete release of vitamin B-12 in 1 day up to a constant release for over 12 weeks was obtained. The release rate could be effectively tailored by blending copolymers with different PEG-segment lengths. The swelling and the crystallinity of the matrix could explain the effect of the matrix composition on the release behavior. (C) 2002 Elsevier Science Ltd. All rights reserved.