Contact lenses have to fulfil a number of contradictory functions while remaining optically clear – they need to be flexible enough to make them comfortable, but must also maintain their shape in saline conditions. Current mechanical characterisation of lens materials is based solely on tensile tests, which measure only the averaged elastic modulus of the entire lens. With coatings and wetting agents widely used in the latest multiphase lenses, it is becoming increasingly important to measure the local mechanical properties of these materials.

Led by Vladimir V. Tsukruk, Georgia Tech engineers turned to AFM-based surface force spectroscopy (SFS) to characterise the micromechanical properties of commercial contact lenses at the nanoscale. This technique has been used to study surface topography, friction, and protein absorption in contact lens materials and in eye tissue, but the paper from Tsukruk (Polymer 55 (2014) 6091–6101 [DOI: 10.1016/j.polymer.2014.09.053]) is the first to probe the surface mechanical properties in wet conditions. The team’s technique combined two AFM modes - high frequency (tapping mode) measurements, which provide high resolution maps of topography and mechanical properties, and static (force volume) nanoindentation, which utilises tip sample interactions to accurately calculate mechanical properties.

Read more about the research here.