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C. Kim, A. Vieira, K. I. Forward, I. R. Schwab; Analysis of the Oxygen and Molecular Permeability of Silk Fibroin Films. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4623.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the oxygen and molecular permeability of silk fibroin films created using various techniques.
Four varieties of silk films were obtained from collaborators in Boston, MA and Queensland, AU.Oxygen permeability was calculated using the average water content of the silk films, as outlined by the International Standard method. Quantitative values were then compared between silk films, as well as amniotic membrane and therapeutic soft contact lenses.Molecular permeability was assessed by measuring the rate of movement of fluorescein dextran across silk films at multiple molecular weights. Membranes from cell culture inserts were stripped and replaced with circular silk discs, which were securely attached to the perimeter of the inserts using cyanoacrylate glue.Following construction, the cell inserts with silk were placed into buffered saline solution. Standard amounts of fluorescein dextran at 20-, 40-, and 70-kDa were added to the center of each cell insert. After incubation for one hour, samples of the surrounding saline solution were collected and immediately read on a flourescence spectrophotometer.
Oxygen permeability varied greatly amongst the types of silk tested. Two of the groups demonstrated an average water content of approximately 90%, with calculated oxygen permeabilities exceeding 100x10^-11 mlO2*cm/(sec*cm2*mmHg). The oxygen permeability of these films was higher than that of soft contact lenses, and similar to that of amniotic membrane. Conversely, the other two groups were found to have much lower oxygen permeabilities of 14x10^-11 and 27x10^-11 mlO2*cm/(sec*cm2*mmHg), respectively.Similarly, there was significant variation in molecular permeability amongst the silk groups examined. An inverse relationship between molecular weight and flow rate was noted across all samples tested. Molecular permeability was greatest across mechanically perforated silk and a brittle, less transparent preparation. Flow was approximately 86ng/hr at 20-kDa and 39ng/hr at 70-kDa across the former, and 42ng/hr to 19ng/hr across the latter. A thin transparent preparation of silk allowed a flow rate of 30ng/hr at 20-kDa and 6ng/hr at 70-kDa. In contrast, flow across a thicker analogue was about 15ng/hr at 20-kDa and negligible at 70-kDa.
We have previously demonstrated the potential of silk fibroin film as a delivery scaffold for cultivated corneal epithelial cells to injured ocular surfaces. While a major advantage of silk over amniotic membrane lies in its modifiability, this also affects its permeability to oxygen and certain molecules.
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