The influence of structure and morphology on ion permeation in commercial silicone hydrogel contact lenses

Virginia Saez-Martinez, Aisling Mann*, Fiona Lydon, Frank Molock Jr, Sian Layton, Daniel Thomas William Toolan, Jonathan R. Howse, Paul Topham, Brian Tighe

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The importance of the microstzructure of silicone hydrogels is widely appreciated but is poorly understood and minimally investigated. To ensure comfort and eye health, these materials must simultaneously exhibit both high oxygen and high water permeability. In contrast with most conventional hydrogels, the water content and water structuring within silicone hydrogels cannot be solely used to predict permeability. The materials achieve these opposing requirements based on a composite of nanoscale domains of oxygen‐permeable (silicone) and water‐permeable hydrophilic components. This study correlated characteristic ion permeation coefficients of a selection of commercially available silicone hydrogel contact lenses with their morphological structure and chemical composition. Differential scanning calorimetry measured the water structuring properties through subdivision of the freezing water component into polymer‐associated water (loosely bound to the polymer matrix) and ice‐like water (unimpeded with a melting point close to that of pure water). Small‐angle x‐ray scattering, and environmental scanning electron microscopy techniques were used to investigate the structural morphology of the materials over a range of length scales. Significant, and previously unrecognized, differences in morphology between individual materials at nanometer length scales were determined; this will aid the design and performance of the next generation of ocular biomaterials, capable of maintaining ocular homeostasis.
Original languageEnglish
Pages (from-to)137-148
Number of pages12
JournalJournal of biomedical materials research: part B
Issue number1
Early online date24 Jul 2020
Publication statusPublished - Jan 2021

Bibliographical note

© 2020 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals LLC.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.


  • ESEM
  • SAXS
  • contact lens
  • ion permeation
  • silicone hydrogels


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