Premium
Surface mechanical properties of pHEMA contact lenses: Viscoelastic and adhesive property changes on exposure to controlled humidity
Author(s) -
Opdahl Aric,
Kim Seong H.,
Koffas Telly S.,
Marmo Chris,
Somorjai Gabor A.
Publication year - 2003
Publication title -
journal of biomedical materials research part a
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.849
H-Index - 150
eISSN - 1552-4965
pISSN - 1549-3296
DOI - 10.1002/jbm.a.10054
Subject(s) - materials science , relative humidity , humidity , contact angle , composite material , adhesive , adhesion , contact lens , dehydration , viscoelasticity , lens (geology) , methacrylate , polymer , optics , layer (electronics) , copolymer , thermodynamics , biochemistry , chemistry , physics
The surface mechanical properties of poly(hydroxyethyl)methacrylate (pHEMA)‐based contact lenses were monitored as a function of humidity by atomic force microscopy (AFM). Surface viscoelastic and adhesion values were extracted from AFM force versus distance interaction curves and were found to be strongly dependent on the bulk water content of the lens and on the relative humidity. At low relative humidity, 40–50%, the dehydration rate from the surface is faster than the hydration rate from the bulk, leading to a rigid surface region that has mechanical properties similar to those measured on totally dehydrated lenses. At relative humidity values > 60%, the dehydration rate from the lens surface rapidly decreases, leading to higher surface water content and a softer surface region. The results indicate that, in an ocular environment, although the bulk of the pHEMA contact lens is hydrated, the surface region may be in a transition between a dehydrated glassy state and a hydrated rubbery state. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 350–356, 2003