Macro- and Microscale Properties of the Vitreous Humor to Inform Substitute Design and Intravitreal Biotransport

ABSTRACT

Research on the vitreous humor and development of hydrogel vitreous substitutes have gained a rapid increase in interest within the past two decades. However, the properties of the vitreous humor and vitreous substitutes have yet to be consolidated. In this paper, the mechanical properties of the vitreous humor and hydrogel vitreous substitutes were systematically reviewed. The number of publications on the vitreous humor and vitreous substitutes over the years, as well as their respective testing conditions and testing techniques were analyzed. The mechanical properties of the human vitreous were found to be most similar to the vitreous of pigs and rabbits. The storage and loss moduli of the hydrogel vitreous substitutes developed were found to be orders of magnitude higher in comparison to the native human vitreous. However, the reported modulus for human vitreous, which was most commonly tested in vitro, has been hypothesized to be different in vivo. Future studies should focus on testing the mechanical properties of the vitreous in situ or in vivo. In addition to its mechanical properties, the vitreous humor has other biotransport mechanisms and biochemical functions that establish a redox balance and maintain an oxygen gradient inside the vitreous chamber to protect intraocular tissues from oxidative damage. Biomimetic hydrogel vitreous substitutes have the potential to provide ophthalmologists with additional avenues for treating and controlling vitreoretinal diseases while preventing complications after vitrectomy. Due to the proximity and interconnectedness of the vitreous humor to other ocular tissues, particularly the lens and the retina, more interest has been placed on understanding the properties of the vitreous humor in recent years. A better understanding of the properties of the vitreous humor will aid in improving the design of biomimetic vitreous substitutes and enhancing intravitreal biotransport.

KEYWORDS:

• Vitreous humor
• vitreous substitute
• mechanical properties
• hydrogel
• viscoelasticity
• modulus
• biotransport

Acknowledgments

We would like to acknowledge the past and present members of the Swindle-Reilly Lab for Biomimetic Polymeric Biomaterials for help and encouragement, and Drs. Matthew Reilly, Cynthia Roberts, and Jun Liu for advice and research guidance.

Data availability statement

The data that support the findings of this study are available from the corresponding author, KESR, upon request.

Patent Applications

Reilly KE, Reilly MA, Tram NK. Antioxidant-Releasing Vitreous Substitutes and Uses Thereof. US Patent Application PCT/US2020/017525, Feb. 10, 2020.

Supplementary material

Supplemental data for this article can be accessed on the publisher’s website.

Additional information

Funding

We would like to acknowledge The Ohio State University College of Engineering for funding.