A study of the frictional properties of senofilcon-A contact lenses.

The frictional property of soft contact lenses could have a great impact on their clinical performance. However, to date, only a handful of studies have been conducted to understand the friction mechanism(s) of the soft contact lens. In the current paper, the friction of senofilcon-A contact lenses has been studied with a stainless steel ball as the counterface in a saline solution. The load applied was between 0.5 mN and 100 mN and the sliding velocity ranges from 0.01 cm/s to 0.5 cm/s. It was found that the friction force is proportional to normal load as described by Amonton's law and this unexpected behavior can be attributed to the fact that viscous flow contributes little to the overall friction and that solid-solid contact dominates the friction of senofilcon-A. It was also found that the coefficient of the friction increases with the velocity and the quantitative relationship between them can be explained reasonably well with a previously proposed "repulsion-adsorption" model. The impacts of material chemistry, water content, test media, applied load and the sliding velocity on the friction mechanism(s) are also discussed.

[1]  Carson,et al.  Relaxation time of confined liquids under shear. , 1991, Physical review letters.

[2]  T. Kurokawa,et al.  Friction between like-charged hydrogels—combined mechanisms of boundary, hydrated and elastohydrodynamic lubrication , 2009 .

[3]  K. Zadnik,et al.  Twenty-five Years of Contact Lenses: The Impact on the Cornea and Ophthalmic Practice , 2000, Cornea.

[4]  M. E. R. Real Oliveira,et al.  Soft Contact Lens Surface Profile by Atomic Force Microscopy , 2010, Optometry and vision science : official publication of the American Academy of Optometry.

[5]  G. Somorjai,et al.  Friction studies of hydrogel contact lenses using AFM: non-crosslinked polymers of low friction at the surface. , 2001, Biomaterials.

[6]  J. Nairn.  MEASUREMENT OF THE FRICTION AND LUBRICITY PROPERTIES OF CONTACT LENSES , 1995 .

[7]  G. Young,et al.  The effect of soft contact lens care products on lens modulus. , 2010, Contact lens & anterior eye : the journal of the British Contact Lens Association.

[8]  S. Granick,et al.  Motions and Relaxations of Confined Liquids , 1991, Science.

[9]  J. Gong,et al.  Friction of Gels. 3. Friction on Solid Surfaces , 1999 .

[10]  U. Raviv,et al.  Fluidity of water confined down to subnanometer films. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[11]  J. Gong,et al.  Gel friction: A model based on surface repulsion and adsorption , 1998 .

[12]  G. Somorjai,et al.  AFM and SFG studies of pHEMA-based hydrogel contact lens surfaces in saline solution: adhesion, friction, and the presence of non-crosslinked polymer chains at the surface. , 2002, Biomaterials.

[13]  F. P. Bowden,et al.  The Friction and Lubrication of Solids , 1964 .

[14]  W. Sawyer,et al.  Friction coefficient of soft contact lenses: measurements and modeling , 2005 .

[15]  D. Xiong,et al.  Friction Behavior of Poly (Vinyl Alcohol) Gel Against Stainless Steel Ball in Different Lubricant Media , 2008 .

[16]  S. Maximovitch,et al.  Streaming potential measurements on stainless steels surfaces: evidence of a gel-like layer at the steel/electrolyte interface , 2004 .

[17]  Tongsheng Li,et al.  A study on the friction properties of PAAc hydrogel under low loads in air and water , 2004 .

[18]  J. Gong,et al.  Effect of substrate adhesion and hydrophobicity on hydrogel friction. , 2008, Soft matter.

[19]  G. Somorjai,et al.  Surface mechanical properties of pHEMA contact lenses: viscoelastic and adhesive property changes on exposure to controlled humidity. , 2003, Journal of biomedical materials research. Part A.

[20]  O. Wichterle,et al.  Hydrophilic Gels for Biological Use , 1960, Nature.

[21]  Jian Ping Gong,et al.  Friction and lubrication of hydrogels-its richness and complexity. , 2006, Soft matter.

[22]  M. Radmacher,et al.  Imaging soft samples with the atomic force microscope: gelatin in water and propanol. , 1995, Biophysical journal.

[23]  K. Sabet,et al.  Effect of Infection by Xanthomonas malvacearum (E.F.S.) Dowson on Respiration-rate of Cotton Leaves , 1960, Nature.

[24]  Uri Raviv,et al.  Fluidity of water confined to subnanometre films , 2001, Nature.

[25]  U. Raviv,et al.  Fluidity of Bound Hydration Layers , 2002, Science.

[26]  G. Somorjai,et al.  Effect of Equilibrium Bulk Water Content on the Humidity-Dependent Surface Mechanical Properties of Hydrophilic Contact Lenses Studied by Atomic Force Microscopy , 2003 .