Poster N13 - Investigating Complex Modulus and Swelling Effects on PEGDA Hydrogel Vitreous Humor Substitute Compared to Native Vitreous

Introduction: The vitreous humor is the largest chamber of the eye, occupying over 80% of the space. Over time the collagen and fibers within the vitreous break down and liquefy, which leads to vitreous liquification. To avoid retinal detachment, the damaged vitreous is extracted and a substitute is placed inside through a surgery called vitrectomy. With over a quarter of a million vitrectomies performed each year, the only long-term FDA approved vitreous substitute is silicone oil. Unlike the native vitreous, silicone oil is not viscoelastic and can lead to lasting problems including cataract. In this study we are looking to compare a native vitreous with a variety of PEGDA gels to determine whether a hydrogel-based substitute with designed viscoelastic properties would be an appropriate long-term choice. We are investigating the complex modulus of the hydrogel pre and post swelling under pressure to mimic IOP physiologic effect.

Materials and

Methods: To mimic the liquefication behavior of the vitreous humor, solutions containing DI Water, APS and TEMED were created. PEDGA (MW 575) w/v 2%, 2.81%, 4% and 6% were added to said solutions, and polymerized. A sample of these gels were then swelled, and the free absorbance capacity was measured. The free absorbance capacity is the maximum amount of water that a hydrogel can hold when submerged. When lyophilized, the hydrogels did not turn to powder, so a non-standard swelling method was used. The samples were pre-weighed and post hydration, aspirated to determine swelled weight. Shear rheological tests to measure the complex modulus, complex viscosity and damping factor were conducted pre and post swelling. Additional tests will be done to determine swelling capacity under pressure at 10 mmHg and 15 mmHg. Testing performed on the PEGDA hydrogels will mirror the tests performed on the native vitreous.

Results, Conclusions, and Discussions: Through previous experimentations, it was determined that 2.81% w/v PEGDA solutions are closest to the native vitreous and we anticipate the rheological data to mirror that hypothesis. Early data shows a difference in the complex modulus of the pre and post swollen PEGDA hydrogels. Preliminary testing displays a trend in the swelling capacity compared to the w/v% PEGDA; the higher the PEGDA percentage, the larger the swelling capacity. Through the swelling tests, we will determine the free absorbance capacity of the PEGDA gels, compare them to published data, and compare the effect of IOP on the native vitreous and PEGDA hydrogels.

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