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R. Parke-Houben, Y. Hu, L. Zheng, C. N. Ta, J. R. Cochran, C. W. Frank; Development of Porous Interpenetrating Network Hydrogels for High Strength Artificial Cornea Periphery. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1154.
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To develop a highly porous three-dimensional scaffold at the periphery of the high-strength artificial cornea hydrogel based on polyethylene glycol and polyacrylic acid (PEG/PAA). The porous periphery will promote integration of the hydrogel implant with native tissue and improve retention of the device.
A crystal templating technique was used to create close-packed, three-dimensional arrays of uniform polymer microspheres. PEG solution was allowed to percolate through the voids between the microspheres and crosslinked to form a gel. The resulting material was soaked in acrylic acid solution overnight and polymerized. Thus an interpenetrating network (IPN) was formed around the microsphere template. The template was then removed by etching with organic solvent. The porous PEG/PAA hydrogel was washed copiously with water and swollen in phosphate buffered saline. The templates and porous hydrogels were examined using variable pressure scanning electron microscopy (VP-SEM). This technique allowed the observation of the porous hydrogel structures while fully hydrated, without the need for sputter coating.
Polystyrene was selected as an appropriate material for the microsphere template because it is resistant to dissolution by acrylic acid. It was found that during the acrylic acid synthesis step, dramatic swelling of the hydrogel occurred around each microsphere. The resulting hydrogel contained isolated pockets rather than highly interconnected pathways through which cells could migrate, because contact between microspheres was lost. To maintain contact between microspheres, the templates were subjected to oven-sintering at 130°C for five to 60 minutes. This additional step preserved contact between microspheres by fusing them together. The success of the sintering and leaching steps, and the optimization of these steps, in producing highly porous IPN hydrogels was demonstrated using VP-SEM. Using an annular template, we successfully produced single-piece hydrogels containing both a clear PEG/PAA central optic and a porous peripheral region for biointegration.
Using a crystal templating technique, oven-sintering, and organic etch, highly porous PEG/PAA interpenetrating network hydrogels were produced with well defined, controlled microchannel sizes. This makes possible the seamless one-piece fabrication of PEG/PAA artificial cornea implants, without the need for a junction between the central optic and the peripheral region.
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