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D. Waters, D. Myung, P. Huie, J. Noolandi, J. R. Cochran, C. N. Ta, C. W. Frank; Oxygen and Oligosaccharide Diffusion in Interpenetrating Network Hydrogels for Replacement of Corneal Tissue. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5720.
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The development and characterization of a fully synthetic biocompatible material that mimics the mechanical strength, nutrient permeability, and water content of natural human corneal tissue is presented. The permeability of the cornea to cell nutrients such as glucose and oxygen is critical for supporting a corneal epithelial cell layer for keratoprosthesis, corneal inlay and onlay applications. Oligosaccharide diffusion is used as a means to examine the effects of increased solute size and as a probe of the network structure.
Interpenetrating polymer networks (IPNs) of poly(ethylene glycol) (PEG) and poly(acrylic acid) (PAA) are fabricated by polymerization and crosslinking of acrylic acid monomers in the presence of a polyethylene glycol (PEG) hydrogel network. Diffusion coefficients of glucose and oligosaccharides in the hydrogel network are determined by measuring solute flux through the gels. Oxygen Dk values are determined by the polarographic method. The effect of varying the molecular weight and initial water content of the PEG network on permeability is examined.
The synthesized PEG/PAA interpenetrating networks are pH and ionic strength sensitive with water contents varying from 75-95 wt.% in pH 7.4 phosphate buffered saline. The tensile strength of the PEG/PAA IPN is on the order of 1 MPa, an order of magnitude increase over single networks of PEG and PAA alone. The diffusion coefficients of glucose and oligosaccharides are found to increase linearly with increased water content. Increasing the molecular weight and initial water content of the PEG network increased the equilibrium water content of the hydrogel and subsequently increased nutrient permeability. The glucose and oligosaccharide diffusion coefficients were on the order of 1x10-6 cm2/s.
PEG/PAA interpenetrating networks can be tuned to have high nutrient permeability as well as high mechanical strength. The mechanical strength and permeability of these materials mimics that of natural cornea tissue and therefore present an interesting material for use in corneal tissue replacement applications.
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