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E.D. Sendler, G.W. Abrams, R. Iezzi; Fabrication and Characterization of Multichannel Microfluidic Devices for Controlled Release of Neurotransmitter to Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1505.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To develop fabrication methods and characterize the release dynamics of flexible multichannel microfluidic devices for the controlled release of neurotransmitter to the retina. Methods: Multiple microchannels were patterned in SU–8 layer on 2 cm2 polymer or glass substrate after photopolymerization via mercury vapor arc lamp. Channels were sealed with a 2nd polymer, glass, or SU–8 layer, and apertures of 10–40 microns diameter, spaced 100 microns were laser drilled through the 1st substrate layer to serve as release orifices. Fluorescein ejection was measured via high–speed video microscopy. Temporal and volumetric release characteristics of apertures were compared according to orifice size using multichannel pneumatic pump and iontophoretic release methods. Results:Uniform microfluidic channels were fabricated within SU–8 polymer layers of 20 to 100 microns thickness. Substrate thickness ranged between 12.5um to 100um. YAG–laser drilling produced uniform release apertures ranging in size from 10 to 40 microns in diameter. Pneumatic puff ejection demonstrated that fluorescein could be released with a minimum pulse of 20 milliseconds. Fluorescein dosing control could be attained by modulating the puff pressure between 2 and 20 PSI and the release time between 20 to 100 milliseconds. Iontophoretic ejection was possible in 10–micron holes using 500 nanoamperes of current. Fluorescein leakage was dependent upon aperture size and hydrostatic pressure due to the height of the fill tube. Conclusions: Microfluidic devices scaleable to high channel counts were successfully fabricated and evaluated. Fluid release characteristics were modified by varying release orifice diameters. Release from individual channels was selectively controlled according to the duration of ejection and the magnitude of applied pressure or iontophoretic current. An array such as this may be used as a model for neurotransmitter stimulation in retinal prostheses and in controlled drug release applications.
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