Sol-Gel Silica Particles for Controlled Release Applications
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Sol-Gel Silica Particles for Controlled Release Applications
Christophe Barbé, Sandrine Calleja, Linggen Kong, Elizabeth Drabarek, Alexandra Bush, Erden Sizgek and Kim Finnie Materials and Engineering Sciences, Australian Nuclear Science and Technology Organization, Menai NSW 2234, Australia [email protected] ABSTRACT Using sol-gel technology combined with water-in-oil (W/O) emulsions, we have developed an innovative method for producing ceramic particles with independent control over the release rate and particle size. The average particle size can be varied from 10 nm to 100 µm and is controlled by the emulsion chemistry. The release rate can be independently varied from mg/hours to mg/month, and is controlled by the internal microstructure of the particles and the initial sol-gel chemistry. INTRODUCTION An increasing number of applications require the production of delivery systems in particulate form. Although a wide range of organic compounds has been used to manufacture these capsules or particles, very few inorganic controlled release systems have found their way into industrial products. This is typically the case for ceramics which, despite several intrinsic advantages such as their resistance to corrosion, their thermal and electrical stability, as well as their important bio-compatibility and environmental-friendliness, remain an untapped resource for the manufacture of controlled release systems. The relative difficulty in manipulating their internal microstructure (compared to polymers), as well as high processing temperatures being incompatible with the encapsulation of organic molecules, are possible reasons for their lack of popularity as a controlled release matrix. Both these limitations can be overcome by using sol-gel technology, which can be described as an inorganic, ambient temperature, polymerization technique. Sol-gel processes, combined with emulsion chemistry, enables facile encapsulation of active molecules inside spherical micro and nano-particles [1,2]. EXPERIMENTAL METHODS Typically, a sol-gel solution is prepared by combining tetramethylorthosilicate (TMOS), an aqueous solution of the active molecule at the desired pH, and methanol. The resulting solution is stirred for 30 min at 300 rpm and left to age for one day at ambient temperature. In parallel, a surfactant solution is prepared by dissolving a surfactant (e.g. sorbitan monoleate) in a non-polar solvent (e.g. cyclohexane) followed by homogenization using a high-speed blender (1200 rpm for 60 s) to form a clear surfactant/solvent solution. The sol-gel solution is then added to the surfactant/solvent solution and the resulting emulsion stirred at 500 rpm for 90 min. A suspension of microspheres forms and is filtered and washed three times with the solvent to remove the surfactant. The resulting microspheres are then dried at room temperature for 1 day, before further drying at 80°C for 5 days. Several surfactant/solvent combinations have been explored to study the influence of the emulsion parameters on the final particle
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