Influence of 1-D silica nanotubes as drug adsorbent on release behaviors of tulobuterol-loaded porous microcapsules

Porous poly(ɛ-caprolactone) (PCL)/Eudragit RS 100 (ERS-100) microcapsules containing tulobuterol-adsorbed silica nanotubes (S-NTs) were prepared using a solvent evaporation method. The release behaviors of the PCL/ERS-100 microcapsules were investigated as a function of S-NT content. The PCL/ERS-100 microcapsules showed a stable and porous surface compared to the PCL microcapsules prepared without ERS-100. The drug loading and encapsulation efficiencies of the microcapsules were increased slightly by the addition of S-NTs due to the adsorption of the drugs on the S-NTs. In an acidic release medium, the PCL/ERS-100 microcapsules containing the tulobuterol-loaded S-NTs showed a slow drug release, which was dependent on the S-NT content. These behaviors are most likely due to the reduced diffusion rate of the drug from the hydrated microcapsules, which results from the strong interaction between the porous S-NTs and the drug.