Porous silica microshells from diatoms as biocarrier for drug delivery applications

The use of porous silica microshells (microparticles) generated from fossilised diatoms known as diatomite or diatomaceous earth (DE) as a natural drug carrier for drug delivery application is presented. The structure, morphology, particle size distribution, porosity, surface area and crystallinity of diatom microshells obtained from Australian mine (Mount Sylvia Diatomite Pty. Ltd.) were characterised using scanning electron microscopy, particle size measurements, BET analysis and X-ray powder diffraction analysis. To prove the drug delivery concept based on diatoms for implant and oral drug delivery, indomethacin as a model of water poorly soluble drug was investigated. Results show the effectiveness of diatom silica for drug delivery application, with about 22 wt.% drug loading capacity and sustained drug release over two weeks. Two steps drug release from diatom structures were observed: the first is rapid release (over 6 h) attributed to the surface deposited drug and the second is slow and sustained release over two weeks with zero order kinetics, as a result of release from diatom pores and internal hollow structure. These results confirm that natural material based on diatom silica can be successfully applied as a biocarrier for both oral and implant drug delivery applications, offering considerable potential to replace synthetic silica based materials.