Atomic Force Microscopy as a Characterization Tool for Contact Lenses: Indentation Tests and Grain Analysis

Abstract

Nondestructive methods for testing mechanical properties of soft contact lenses allow quality control and testing to be performed on same sample by considering various parameters. A novel alternative to conventional mechanical test technique for contact lenses is presented implementing atomic force microscopy (AFM) and force spectroscopy (FS) technique as pico-indentation and mechanical characterization tool. This technique gives nN force resolution with producing nm range elastic deformation. FS and AFM topography results are evaluated simultaneously to compare mechanical and topographical properties of contact lenses such as Young's modulus, grain size evaluation, surface roughness, and adhesion force. Mechanical properties of soft contact lenses were reported by considering equilibrium water content of contact lens.

Keywords:

• AFM
• force spectroscopy
• grain analysis
• Pico-indentation
• soft contact lenses

Notes

^a Surface area ratio is calculated via Surface Area Analysis tool, reported value is ratio of calculated area/scanning area. Mean value of nine measurements for each sample.

^b R_pv value is peak to valley surface topography (i.e., mean height of surface structures) calculated as mean value of height of structures over a sampling area. Mean value of at least 18 measurements for each sample.

^c R_q value is root mean square (RMS) roughness of sampling area. Mean value of at least 18 measurements for each sample.

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