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J. M. Morris, S. A. Barker, J. Sanderson; Development of a Performance Matched Vitreous Substitute. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5796.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a performance-matched vitreous replacement for use in vitrectomy procedures. Feasibility studies have been carried out using porcine vitreous.
Fresh (< 4 h post-mortem) porcine eyes were obtained from a local slaughter-house, with the animals having been processed under standard UK regulations for animals for human consumption. Texture Analysis (TA) was used to test force in compression of the vitreous in situ. The physical nature of the vitreous samples was tested using oscillatory rheological methods including torque and flow profiles. Potential replacement gels were produced from various concentrations of sodium hyaluronic acid (NaHA), sodium carboxymethylcellulose (NaCMC) and poloxamer F127, with either a balanced salt or glucose solution. Gels were assessed for similarity to the native material using the same rheological techniques as above. Gels were also tested for optical clarity using light scattering procedures and for acute cytotoxicity using a lactate dehydrogenase (LDH) assay on human ARPE-19 cells.
TA results (mean ± sd, n=25) for individual samples tested when fresh were 35.94 ± 11.84g This indicated a wide natural variability of the materials. Repeated TA tests on the same sample showed a trend of steadily decreasing values of the force required, indicating that repeated stress will permanently damage the vitreous. Oscillatory rheometric measurements confirmed previous studies using different rheological techniques that the vitreous behaves predominantly as a visco-elastic material. All gel formulations tested showed excellent optical clarity and promising results in the acute cytotoxicity challenge test. Cell death over 24 hours was comparable to that observed in control, 14.32%; 16% w/w poloxamer F127, 11.35%; 1%w/v NaHA, 8.62%; 1% w/v high viscosity NaCMC, 8.76%; and 2 %w/v medium viscosity NaCMC, 10.09%. Rheologically, the NaHA and NaCMC gels behaved in a more fluid-like fashion than the native porcine vitreous, whereas the poloxamer gels showed a similar visco-elastic rheological profile to the natural material. The numerical response was related to the concentration.
Initial physical characterisation studies on several apparently bio-compatible gel formulations suggest that the development of a performance-matched vitreous substitute is feasible.
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