Surface mechanical properties of pHEMA contact lenses: Viscoelastic and adhesive property changes on exposure to controlled humidity

Aric Opdahl, Seong Kim, Telly S. Koffas, Chris Marmo, Gabor A. Somorjai

Research output: Contribution to journalArticle

65 Scopus citations

Abstract

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.

Original languageEnglish (US)
Pages (from-to)350-356
Number of pages7
JournalJournal of Biomedical Materials Research - Part A
Volume67
Issue number1
DOIs
StatePublished - Oct 1 2003

All Science Journal Classification (ASJC) codes

  • Ceramics and Composites
  • Biomaterials
  • Biomedical Engineering
  • Metals and Alloys

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