Morphological Properties of Siloxane-Hydrogel Contact Lens Surfaces.
The aim of this study was to quantitatively characterize the micromorphology of contact lens (CL) surfaces using atomic force microscopy (AFM) and multifractal analysis.



AFM and multifractal analysis were used to characterize the topography of new and worn siloxane-hydrogel CLs made of Filcon V (I FDA group). CL surface roughness was studied by AFM in intermittent-contact mode, in air, on square areas of 25 and 100 μm2, by using a Nanoscope V MultiMode (Bruker). Detailed surface characterization of the surface topography was obtained using statistical parameters of 3-D (three-dimensional) surface roughness, in accordance with ISO 25178-2: 2012.



Before wear, the surface was found to be characterized by out-of-plane and sharp structures, whilst after a wear of 8 h, two typical morphologies were observed. One morphology (sharp type) has a similar aspect as the unworn CLs and the other morphology (smooth type) is characterized by troughs and bumpy structures. The analysis of the AFM images revealed a multifractal geometry. The generalized dimension Dqand the singularity spectrum f(α) provided quantitative values that characterize the local scale properties of CL surface geometry at nanometer scale.



Surface statistical parameters deduced by multifractal analysis can be used to assess the CL micromorphology and can be used by manufacturers in developing CLs with improved surface characteristics. These parameters can also be used in understanding the tribological interactions of the back surface of the CL with the corneal surface and the front surface of the CL with the under-surface of the eyelid (friction, wear, and micro-elastohydrodynamic lubrication at a nanometer scale).
a Department of Biomedical Computer Systems , University of Silesia, Faculty of Computer Science and Materials Science, Institute of Informatics , Sosnowiec , Poland.
Sebastian
S
Stach
b Department of Automotive Engineering and Transportation, Faculty of Mechanical Engineering, Discipline of Descriptive Geometry and Engineering Graphics , Technical University of Cluj-Napoca , Cluj-Napoca , Cluj , Romania.
Ştefan
Ş
Ţălu
c Department of Materials Science , University of Milano Bicocca , Milano , Italy.
Silvia
S
Trabattoni
c Department of Materials Science , University of Milano Bicocca , Milano , Italy.
Silvia
S
Tavazzi
a Department of Biomedical Computer Systems , University of Silesia, Faculty of Computer Science and Materials Science, Institute of Informatics , Sosnowiec , Poland.
Alicja
A
Głuchaczka
a Department of Biomedical Computer Systems , University of Silesia, Faculty of Computer Science and Materials Science, Institute of Informatics , Sosnowiec , Poland.
Patrycja
P
Siek
a Department of Biomedical Computer Systems , University of Silesia, Faculty of Computer Science and Materials Science, Institute of Informatics , Sosnowiec , Poland.
Joanna
J
Zając
d Department of Materials Science , University of Milano Bicocca, Piazza dell'Ateneo Nuovo , Milano , Italy.
Stefano
S
Giovanzana
D000328:Adult; D003263:Contact Lenses, Hydrophilic; D004209:Disposable Equipment; D005260:Female; D017709:Fractals; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000737:chemistry*; D008297:Male; D008422:Materials Testing; D018625:Microscopy, Atomic Force; D012833:Siloxanes / Q000737:chemistry*; D013499:Surface Properties; D055815:Young Adult
D012833:Siloxanes; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate
Atomic force microscopy; disposable contact lenses; multifractal analysis; siloxane-hydrogel material; surface roughness; wear of contact lenses