Assessing Mouse Lens Elasticity and Viscoelasticity Using Atomic Force Microscopy

Abstract

Purpose : Lens elasticity has been shown to decrease significantly with age in multiple animal models. Given the widespread use of mice as a model organism in ophthalmologic research, characterization of this relationship in the mouse is needed for use as a reference. Therefore, the purpose of this study is to measure mouse lens elasticity and viscoelasticity as a function of age using Atomic Force Microscopy (AFM).

Methods : 8 whole lenses from 5 mice (age range: 9-20 months) were extracted immediately following euthanasia. 1mL of 5% agarose (g/ml) was placed in Petri dishes, and the intact lenses were placed anterior side up so that only the posterior half was contained within the agarose; after it gelled, the Petri dish was filled with DMEM until the intact lens was fully submerged to prevent dehydration. Mechanical properties were immediately characterized with a custom AFM optimized for microindentation studies (Ziebarth et al. Mol Vis 2007 Apr; 13:504-510). The AFM cantilever (5mm diameter borosilicate glass particle, silicon nitride cantilever, 0.12N/m) was lowered onto the lens. To measure elasticity, the cantilever was raised after coming into contact with the sample. Young’s modulus of elasticity was found by fitting the Hertz model to the resultant force vs. indentation graph. To measure viscosity, the cantilever was held in contact with the sample for between 3 and 5 seconds. Viscosity was found by fitting the Darling model to the resultant force vs. time graph during the hold period.

Results : The mouse lens elasticity was 27.52±14.60kPa (range: 4.41-52.80kPa). In all but three of the lenses, we could not discern any viscoelastic effects; the viscosity of the three lenses measured were 50.29Pa-s, 83.1Pa-s, and 217.06Pa-s.

Conclusions : These experiments demonstrate the AFM’s ability to measure the elasticity and viscoelasticity of the mouse lens. Preliminary data suggest that the younger mice tend to have less stiff lenses.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.