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.

The surfaces of two types of soft contact lenses neutral and ionic hydrogels--were characterized by atomic force microscopy (AFM) and sum-frequency-generation (SFG) vibrational spectroscopy. AFM measurements in saline solution showed that the presence of ionic functional groups at the surface lowered the friction and adhesion to a hydrophobic polystyrene tip. This was attributed to the specific interactions of water and the molecular orientation of hydrogel chains at the surface. Friction and adhesion behavior also revealed the presence of domains of non-crosslinked polymer chains at the lens surface. SFG showed that the lens surface became partially dehydrated upon exposure to air. On this partially dehydrated lens surface, the non-crosslinked domains exhibited low friction and adhesion in AFM. Fully hydrated in saline solution, the non-crosslinked domains extended more than tens of nanometers into solution and were mobile.

[1]  M. Refojo.  Vapor Pressure and Swelling Pressure of Hydrogels , 1976 .

[2]  Kazunori Kataoka,et al.  Self-assembly of poly(ethylene glycol)-based block copolymers for biomedical applications , 2001 .

[3]  J. Gong,et al.  Friction of gels , 1997 .

[4]  A. Steel,et al.  Solvent Exclusion and Chemical Contrast in Scanning Force Microscopy , 1996 .

[5]  M. Refojo,et al.  Water Wettability of Hydrogels , 1976 .

[6]  J. Israelachvili,et al.  Molecular layering of water in thin films between mica surfaces and its relation to hydration forces , 1984 .

[7]  J. Baguet,et al.  Imaging surfaces of hydrophilic contact lenses with the atomic force microscope. , 1993, Biomaterials.

[8]  D. Ammon,et al.  Surface chemical structure for soft contact lenses as a function of polymer processing. , 1996, Journal of biomedical materials research.

[9]  A. F. Recum,et al.  The influence of micro-topography on cellular response and the implications for silicone implants , 1996 .

[10]  M. Lattimore.  An Apparent pH-lnduced Effect on Extended Wear Hydrogel Lens Water Content , 1996, Optometry and vision science : official publication of the American Academy of Optometry.

[11]  B. Milthorpe,et al.  Human serum albumin adsorption on hydrogel contact lenses in vitro. , 1996, Investigative ophthalmology & visual science.

[12]  J. Baguet,et al.  Characterization of lacrymal component accumulation on worn soft contact lens surfaces by atomic force microscopy. , 1995, Biomaterials.

[13]  Georges Hadziioannou,et al.  Acid-base properties and the chemical imaging of surface-bound functional groups studied with scanning force microscopy , 1997 .

[14]  Vladimir V. Tsukruk,et al.  Organic Molecular Films under Shear Forces: Fluid and Solid Langmuir Monolayers , 1996 .

[15]  G. Somorjai,et al.  Probing the Surface Structural Rearrangement of Hydrogels by Sum-Frequency Generation Spectroscopy , 1999 .

[16]  J. Gong,et al.  Heterogeneous Polymerization of Hydrogels on Hydrophobic Substrate , 2001 .

[17]  S. Biggs.  Non-equilibrium interaction forces between adsorbed polymer layers , 1996 .

[18]  S. Biggs,et al.  Direct measurement of the depletion force using an atomic force microscope , 1995 .

[19]  G. Hadziioannou,et al.  Nanotribological Properties of Unsymmetrical n-Dialkyl Sulfide Monolayers on Gold: Effect of Chain Length on Adhesion, Friction, and Imaging , 2000 .

[20]  Yaochun Shen,et al.  Liquid interfaces: A study by sum-frequency vibrational spectroscopy , 1999 .

[21]  V. V. Gorbunov,et al.  Probing of Micromechanical Properties of Compliant Polymeric Materials , 1998 .

[22]  Charles M. Lieber,et al.  Chemical Force Microscopy: Exploiting Chemically-Modified Tips To Quantify Adhesion, Friction, and Functional Group Distributions in Molecular Assemblies , 1995 .

[23]  J. Israelachvili,et al.  Molecular layering of water at surfaces and origin of repulsive hydration forces , 1983, Nature.

[24]  T. Williams,et al.  Modulation of Bacterial Adhesion to Hydrogel Contact Lenses by Albumin , 1998, Optometry and vision science : official publication of the American Academy of Optometry.

[25]  J. A. Hubbell,et al.  Surface Treatments of Polymers for Biocompatibility , 1996 .

[26]  E. Eckstein,et al.  Effects of low levels of methacrylic acid on the swelling behavior of poly(2-hydroxyethyl methacrylate) , 1984 .

[27]  Valery N. Bliznyuk,et al.  Adhesive and Friction Forces between Chemically Modified Silicon and Silicon Nitride Surfaces , 1998 .

[28]  H. D. Cavanagh,et al.  The relationship between contact lens oxygen permeability and binding of Pseudomonas aeruginosa to human corneal epithelial cells after overnight and extended wear. , 1999, The CLAO journal : official publication of the Contact Lens Association of Ophthalmologists, Inc.

[29]  M. Refojo,et al.  Wettability of hydrogels. I. Poly (2-hydroxyethyl methacrylate). , 1975, Journal of biomedical materials research.

[30]  Robert W. Carpick,et al.  Calibration of frictional forces in atomic force microscopy , 1996 .

[31]  J. Israelachvili.  Intermolecular and surface forces , 1985 .

[32]  J. Gong,et al.  A Possible Mechanism for the Substrate Effect on Hydrogel Formation , 2001 .

[33]  A Unsworth,et al.  Friction in hip prostheses. , 1997, Biomaterials.

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

[35]  N. Peppas,et al.  Physicochemical foundations and structural design of hydrogels in medicine and biology. , 2000, Annual review of biomedical engineering.

[36]  S. Biggs.  Steric and Bridging Forces between Surfaces Bearing Adsorbed Polymer: An Atomic Force Microscopy Study , 1995 .

[37]  N Pritchard,et al.  Dehydration, lens movement and dryness ratings of hydrogel contact lenses. , 1995, Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians.

[38]  V. V. Gorbunov,et al.  Micromechanical Properties of Elastic Polymeric Materials As Probed by Scanning Force Microscopy , 1998 .

[39]  D Fonn,et al.  Hydrogel lens dehydration and subjective comfort and dryness ratings in symptomatic and asymptomatic contact lens wearers. , 1999, Optometry and vision science : official publication of the American Academy of Optometry.

[40]  H. J. Griesser,et al.  Irreversible adsorption of human serum albumin to hydrogel contact lenses: a study using electron spin resonance spectroscopy. , 1999, Biomaterials.

[41]  D. Baude,et al.  Artificial tear adsorption on soft contact lenses: methods to test surfactant efficacy. , 2000, Biomaterials.

[42]  P. Luckham,et al.  Interactions between Poly(ethylene oxide) Layers Adsorbed to Glass Surfaces Probed by Using a Modified Atomic Force Microscope , 1996 .

[43]  B. Milthorpe,et al.  Lysozyme sorption in hydrogel contact lenses. , 1999, Investigative ophthalmology & visual science.

[44]  M. Maltarello,et al.  Disposable contact lenses and bacterial adhesion. In vitro comparison between ionic/high-water-content and non-ionic/low-water-content lenses. , 1995, Biomaterials.

[45]  H Takano,et al.  Chemical and biochemical analysis using scanning force microscopy. , 1999, Chemical reviews.

[46]  M. Wahlgren,et al.  Protein adsorption to solid surfaces. , 1991, Trends in biotechnology.

[47]  Goto,et al.  Nonlinear optical studies of liquid crystal alignment on a rubbed polyvinyl alcohol surface , 2000, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[48]  W. Gladfelter,et al.  Probing Biopolymers with Scanning Force Methods: Adsorption, Structure, Properties, and Transformation of Gelatin on Mica , 1994 .

[49]  Charles M. Lieber,et al.  Force Titrations and Ionization State Sensitive Imaging of Functional Groups in Aqueous Solutions by Chemical Force Microscopy , 1997 .

[50]  Daniel Chappard,et al.  2-Hydroxyethyl Methacrylate (HEMA): Chemical Properties and Applications in Biomedical Fields , 1992 .

[51]  P. Gatenholm,et al.  Surface Mobility of Grafted Hydrogels , 1999 .

[52]  B. Vincent,et al.  Depletion forces between silica surfaces in solutions of poly(acrylic acid) , 1997 .

[53]  J. Andrade.  Hydrogels for medical and related applications , 1976 .