Abstract
Purpose :
Atomic Force Microscopy (AFM) is an established technique to measure the mechanical properties of cells and tissues. AFM measurements are based on force interactions between a cantilever and a sample. These measurements are dependent on the underlying substrate stiffness: samples seem overly stiff or soft depending on what is underneath it. Our group’s previous experiments have already shown that AFM measurements on the corneal surface are dependent on the intraocular pressure (IOP). This interdependency could expand the scope of AFM as a diagnostic tool for IOP. However, there are additional specifications of the AFM cantilever that need to be considered. The purpose of this current study is to determine how cantilever stiffness in particular impacts the ability of AFM to sense changes in IOP.
Methods :
To avoid variability associated with cadaver tissue, experiments were conducted on an artificial cornea from Bioniko. To restore hydration, the model was placed in deionized water for 30 minutes, and then mounted in a custom IOP chamber that fits in the AFM set-up. The pressure chamber functions as a sealed-end manometer: deionized water is added until the target pressure is reached, with pressure recorded using a transducer (Keller). Measurements were performed using a custom AFM system that has been optimized for biomechanical studies of ophthalmic tissues. Testing was performed using cantilevers of spring constants ranging from 0.6-10.94N/m (HQ:NSC series, MikroMasch). Thirteen cantilevers with different spring constants were used. Fifteen repeat measurements were acquired every 2mmHg from 15mmHg to 39mmHg. The values were recorded using IgorPro (WaveMetrics) and analyzed using custom MATLAB code. Statistical outlier analysis was performed on the output values for each pressure increment, and outliers were omitted. Measurements were analyzed as a function of pressure.
Results :
A linear trend correlating AFM measurements and IOP was found for 6 of the 13 cantilevers tested. These trends are more consistent when the cantilever has a higher spring constant (>2N/m). Only 1 cantilever with a spring constant lower than 2N/m was able to detect a trend with IOP. Repeat measurements using the same cantilevers confirmed this.
Conclusions :
Selection of appropriate cantilever specifications is an essential prerequisite in establishing AFM as a reliable and repeatable IOP measurement technique.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.