title: Poly(lactic acid) microparticles coated with insulin-containing layer-by-layer films and their pH-dependent insulin release.
abstract: Poly(lactic acid) (PLA) microparticles were coated with layer-by-layer (LbL) films containing insulin and the pH-dependent release of insulin was studied. The LbL films were prepared on the surface of PLA microparticles by the alternate deposition of insulin and poly(allylamine hydrochloride) (PAH) through the electrostatic attraction between insulin and PAH. The insulin loading on the PLA microparticles depended on the film thickness, which corresponded to the number of insulin layers, and on the pH of the solution used to deposit insulin. The insulin loading increased with the film thickness and when the film was prepared at pH 7.4. The LbL films decomposed upon exposure to acidic solutions because the electrostatic attraction between the insulin and the PAH in the films disappeared when the charge on insulin changed from negative to positive at an acidic pH, which resulted in the release of insulin. The temperature and salt concentration did not affect the pH stability of the LbL films. The pH threshold for insulin release was pH 5.0-6.0, which corresponds to isoelectric point of insulin, 5.4. The release of insulin from the microparticles was rapid, and was almost complete within a few minutes. The circular dichroism spectra showed that the released insulin retained its original secondary structure. Our insulin-loaded PLA microparticles may be useful for the controlled release of insulin.
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Hashide
authors.forename: Kentaro
authors.initials: K
authors.lastname: Yoshida
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Hasebe
authors.forename: Masaru
authors.initials: M
authors.lastname: Seno
authors.forename: Shigehiro
authors.initials: S
authors.lastname: Takahashi
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Sato
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Anzai
mesh_terms: D002942:Circular Dichroism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000032:analysis* / Q000378:metabolism; D019344:Lactic Acid / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D008863:Microspheres; D011073:Polyamines / Q000737:chemistry; D011091:Polyesters; D011108:Polymers / Q000737:chemistry*; D055550:Protein Stability; D055672:Static Electricity
chemical_list: D007328:Insulin; D011073:Polyamines; D011091:Polyesters; D011108:Polymers; C063994:polyallylamine; D019344:Lactic Acid; C033616:poly(lactide)