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Lingyun Cheng, Huiyuan Hou, Alejandra Nieto, Gordon Miskelly, Dirk-Uwe Bartsch, William Freeman, Michael Sailor; Correlation between release of rapamycin from Porous Silicon (pSi) and the color shifting of pSi monitored by a digital camera: a prototype of non-invasive remote monitoring system for intravitreal drug release. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1084. doi: https://doi.org/.
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pSi photonic crystals can be created through etching with a periodically varying current to impart a color to these particles. Drug loading and release can be measured by reflectance spectroscopy. The current study aims to investigate the feasibility of monitoring drug release from pSi photonic crystals by in vitro digital imaging of the color changes associated with pSi degradation and drug release.
pSi was prepared by electrochemical etch of a silicon wafer. pSi microparticles were prepared by ultrasonic fracture. The pSi surface was chemically modified with undecylenic acid and then partially oxidized before rapamycin loading through infiltration (pore size ~15 nm). Rapamycin-loaded pSi particles were added to 4.5mL of HBSS in a petri dish which was incubated at 37°C. At predetermined time points, the pSi particles in the dish were photographed using a digital camera with coaxial lighting and the dissolution medium was sampled for rapamycin quantitation. The photographs were imported into Image J and the color of the particles was measured after thresholding of the images.
Hydrolytic and oxidative degradation of pSi, and release of rapamycin from pSi caused an observable change of the pSi particles from reddish to yellowish and then to transparent. The corresponding changes in the reflected light intensity was correlated with the cumulative drug release (r=0.93, p<0.0001; Figure). These optical effects result from a blue-shift in the spectral peaks displayed by the photonic crystals during the pSi degradation/drug release process. At the early stage the reflected light intensity increased mainly due to the drug release while the light intensity decline at later stage mainly from degradation of pSi.
Rapamycin release from pSi photonic crystals can be quantitatively monitored with a digital camera which will allow a non-invasive and remote monitoring for an intravitreally injected drug and pSi delivery system.
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