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P. Ashton, H. Guo, J. Chen, L. Canham; Silicon Based Sustained Release Systems. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5989.
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To investigate the use of silicon in the preparation of small (<500nm) sustained release systems.
Silicon is a material that can be mechanically processed with extremely fine precision. Electronics grade silicon (purity 99.999%) was micro-machined to produce pores 390 µm in diameter and 250 µm in depth. These were filled with a polymer matrix of a test drug (fluocinolone acetonide) and after curing, coated with a permeable layer. Devices were then immersed in phosphate buffer (pH 7.4) at 37oC and samples were taken periodically and replaced with fresh buffer. Drug released was determined by HPLC. Due to the small size of these devices, release rates were determined from 9 devices at a time and the average release rate per device was calculated.
The devices provided linear release of fluocinolone acetonide with a mean release rate of 0.9µg/day.
Release from systems such as this has previously been found to be proportional to the surface area of the permeable layer. The extreme precision with which silicon can be machined (tolerances of less than 1 µm are usual) suggests that these systems can be used to provide great control over release rates. The systems tested here are significantly smaller than those approved for intra-ocular human use.
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