Optimization of Atomic Force Microscopy Cantilever Specifications for Pressure Measurement in Biological Tissues

Atomic Force Microscopy (AFM) is an established technique to measure the mechanical properties of cells and tissues. Measurements are based on force interactions between cantilever and sample. These measurements can be influenced by the underlying substrate. Published literature has utilized this phenomenon to measure the turgor pressure of eukaryotic cells through the cell membrane. The purpose of the current study was to determine how to increase measurement sensitivity of pressure in larger-scale biological tissues, specifically intraocular pressure.

AFM was used to measure pressurized artificial corneas. Tipless and tipped cantilevers were used to acquire measurements of Young's modulus of elasticity and apparent stiffness over the pressure range: 15, 25, and 35 mmHg to represent normal, elevated, and uncontrolled IOP.

In this study, fourteen tipless cantilevers and eight modified cantilevers were tested to determine which cantilever parameters best measured the pressure beneath the tissue. The parameters evaluated were spring constant, indenter tip radius, and effective working length. Spring constant had a more pronounced effect on apparent stiffness than any other parameter examined for both unmodified and modified cantilevers. For modified cantilevers, the ratio of working length to indenter radius enhances the bottom-substrate effect, with lower ratios being more advantageous.

The results of this study suggest that AFM could be used to quantify pressure beneath biological tissues, but care must be taken to select a cantilever with appropriate specifications.