BACKGROUND: The cornea is the outer portion of the eye and protects the eye from infection or debris. When the cornea becomes compromised due to age and disease (specifically Diabetes Mellitus), it becomes impaired and can have profound impacts on an individual’s quality of life by leading to vision loss or blindness. The different layers of the cornea all contain many proteins and collagen, and have varying degrees of thickness and biomechanical properties. Stiffness in the cornea has either been measured via the use of AFM (Atomic Force Microscopy) which involves removing a slice of the cornea and adhering to the surface, as a function of IOP (Intraocular Pressure), or tensile testing. Previous research has also used the nanoindenter to measure the stiffness of different layers in the intact globe (eyeball) within the mouse head or by adhering to PEG submerged in PBS. However, no studies to our knowledge have used the intact globe exposed to air and placed on a 3D printed model to measure different corneal layers via the use of nanoindentation.
METHODS: 6 C57BL/6J mice were obtained between 8-12 and 27 weeks of age, had the eyes extracted, and half remained with intact epithelium while the other half had the epithelium abraded with a 1.5 mm trephine. The eyes were placed in keratinocyte solution (KCM) for preservation while they were transported to the site with a nanoindenter. The globes were then placed on a 3D printed holder, cornea facing up, and irrigated with KCM solution in between indentation measurements. The PIUMA Optics 11 Nanoindenter was used to measure the Effective Young’s Modulus of the epithelium, basement membrane, and stroma. The Oliver & Pharr modeling was used as opposed to the Hertzian Model due to the biomechanical and adhesion properties of the eye.
RESULTS: A comparison of control mice at 9 weeks shows an average Effective Young’s Modulus of 30.73 kPa, and an average Effective Young’s Modulus for 15 week old mice of 62.50 kPa for the epithelium. The average Effective Young’s Modulus of the basement membrane for 9 week control mice was ~6.2 kPa and for older 27 week mice was ~6 kPa. The Effective Young’s modulus for the stroma of 9 week old mice was ~68.3 kPa and for 27 week old mice was ~ 222.7 kPa.
CONCLUSION: It was observed that stiffer substrates (in this instance, stiffer layers) require stiffer probes. The opposite is true of softer substrates, which require softer probes. It is beneficial in either instance to use a larger tip radius as there will be more contact and surface area measurement, so the probe has less recoil due to the adhesion from the corneal layers. The values observed in this study correlated with the values seen in the study conducted by Xu et al. However, the basement membrane values were different and could be due to probe specifications or layer thinness. Additional studies are needed to observe changes in Young’s Modulus based on probe characteristics with diseases such as Diabetes Mellitus (DM).
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/45556 |
| Date | 01 February 2023 |
| Creators | Gomez, Stephanie A. |
| Contributors | Trinkaus-Randall, Vickery |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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