Applications of Atomic Force Microscopy
for Contact Lens Manufacturing
Atomic Force Microscopy (AFM)
has advanced biomaterials R&D by
offering the unique ability to analyze
surface properties non-destructively with
nanometer-level resolution in ambient
air or liquids. Polymer products used
as biomaterials, including intra-occular
implants and contact lenses, have
represented one of the fastest growing
sectors in the medical device industry.
Significant increases in manufacturing
output of contact lenses, especially
in disposable products, are driving
demand for better quality control and
innovative new designs. Surface
characterization is an integral part of
contact lens R&D and quality control.
Optical and electron microscopy, and
stylus and optical profilometry are
some of the conventional techniques
used for characterizing the lenses
and for developing and improving
production processes. This application
note describes some areas where the
AFM provides new capabilities for
surface characterizations that help
speed product development efforts
and, improve product quality,
performance and yields.
The AFM Techniques
Contact mode is the original
AFM imaging mode and can be
implemented in both air and liquid.
The AFM tip, at the end of a flexible
cantilever, is brought into light contact
with the sample surface and raster-
scanned across the surface by a
piezoelectric scanner. Changes in the
cantilever deflection during scanning
are monitored and kept constant
using electro-mechanical feedback.
Topographic images are generated
by mapping the distance the scanner
moves vertically to maintain a constant
deflection at every lateral data point.
TappingMode AFM is a more recent
development in which the imaging
probe is vertically oscillated at or near
the resonant frequency of the cantilever
(Figure 1). Electro-mechanical
feedback maintains the oscillation at
a constant amplitude during scanning.
The image is produced by mapping
the distance the scanner moves
vertically, to maintain the constant
Figure 1. Schem