Topography of Hydrophilic Contact Lens in Liquid Environment

 Atomic force microscopy (AFM) is a nondestructive, nanometer scale, surface metrology technique with applications in various industries.  Utilizing an additional scanner accessory enables the Cerium Laboratories’ AFM to perform surface measurement when samples are moist or completely immersed within a liquid.  This is an important capability where a soft or wet surface requires analysis reflecting the conditions of real time use.  For example, a hydrophilic polymer immersed in water or saline experiences comparable conditions to a contact lens being worn by a consumer.  The measured lens’ topography may be presented in either 2D or 3D image representations.  Using software, polymer defects, peak-to-peak values and root-mean-square (RMS) surface roughness are quantifiable.  The polymer surface is not damaged during examination allowing further experimentation and/or analysis after AFM measurement.

Figure 1 shows 2D and 3D representations, left and right respectively, of AFM data obtained from a commercially available soft contact lens in contact mode.  The data was obtained while the lens was fully immersed in deionized water.  The dark red lines and white spots are typical surface features of contact lens.  Polymer defects are observable in a similar manner during imaging.  Figure 2 is a plot of multiple RMS surface roughness measurements from the same data.  The internal software algorithm uses RMS which prevents weighting during the average.  The AFM roughness precision is of high quality since scans were obtained at various points across the random surface and the instrument has a ± 0.1 nm uncertainty.

Figure 1:  20 × 20 µm area, vertical scale bar is 25 nm, 2D (left), 3D (right).

Figure 2:  Multiple RMS surface roughness measurements, 20 × 20 µm area, horizontal line represents the average RMS surface roughness at 2.5 nm.

• Cerium Laboratories’ AFM is a Digital Instruments Dimension 5000 AFM accepting samples up to 200 mm diameter and 1 cm height.  Measurement capabilities include contact mode and the more versatile TappingMode (TM).