Controlled release of insulin from plasma-irradiated sandwitch device using poly-DL-lactic acid.

The release behavior of insulin from a plasma-irradiated sandwitch (PIS) device using poly-DL-lactic acid (PLA) was studied. The controlled release device can be obtained by oxygen plasma irradiation (radiofrequency discharge operating at 13.56 MHz) on the outer layer of the sandwitch device which was fabricated from an insulin-PLA matrix tablet as a core material and a mixture of plasma-degradable polyoxymethylene (POM) and biodegradable PLA as a wall material. The release test indicated that insulin was released through the micropores formed by the vaporization of POM, and that the release behavior of insulin was affected largely by the molecular weight of PLA used as the outer layer rather than the plasma operational condition. The release of insulin can be controlled by the use of PLA with an average molecular weight of 11000 as the outer layer of the PIS device. Insulin from the PIS device maintained normal blood glucose levels for 10 d in diabetic rats as an implantable dosage form. The duration of insulin effectiveness was relatively short considering the degradation rate of PLA, indicating that the degradation characteristics of biodegradable PLA were not well reflected in the PIS device.