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A porous polymer is required to sustain corneal epithelial tissue on the anterior surface of an implantable contact lens (corneal onlay). Porosity creates topography on the polymer surface and, if defined, this can be manipulated to elicit a particular tissue response. Previous work identified pores of 100-nm diameter to be the critical size of a discontinuity in a polymer surface to facilitate the migration, stratification, and sustained adhesion of corneal epithelial tissue. Now we address the issue of pore density. Corneal epithelial tissue was grown for 21 days on nonporous polycarbonate and polycarbonate track-etched with pores 100-nm diameter with pore densities ranging from 0.27 and 14.4% of the total polymer surface area. Histology was used to score epithelial structure, and electron microscopy was used to quantitate the formation of adhesive structures (basal lamina and hemidesmosomes) at the tissue-polymer interface. Data showed that epithelial tissue stratified and epithelial adhesive structures formed on polycarbonate surfaces with pore densities between 0.52 and 14.4% inclusive. This means that epithelial tissue can be maintained on a polymer where up to 14.4% of the surface is dedicated to small discontinuities in the form of pores 100-nm diameter. These figures can be used to specify the design of a polymer for applications requiring epithelial cover.

The capacity factor k' is defined ask' = V( V -Vo)/Vo, where Vis the elution volume of the eluate and V , is the elution volume of a nonretained compound.