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Superficial Modulus, Water-Content, and Mesh-Size at Hydrogel Surfaces

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Abstract

The most distal surfaces of lubricious high water-content aqueous gels may have decreasing concentrations and gradients of macromolecular chains on the surface that emanate outward into the environment. This superficial zone of extended polymer chains has a water-content that approaches 100% over the final few hundred nanometers, and the superficial modulus is the elastic modulus of this superficial surface. Micro-rheology using high-speed microscopy with fluorescent nanospheres enabled measurements of both the storage modulus G′ and the loss modulus G″ over a frequency range of 0.4 1/s–50 1/s. 100 µm-thick control samples of polyacrylamide gels with equilibrium water-content of 97.9%, 98.4%, and 98.9% had measured storage moduli of 70.3 ± 26.9 Pa, 53.3 ± 22.4 Pa, and 38.8 ±14 Pa, respectively. Master curves based on meta-data analysis from published measurements of mesh-size, water-content, and elastic modulus were created and used to relate rheological measurements of the superficial modulus to water-content and mesh-size. This interfacial microrheological measurement method was further used to quantify the superficial modulus and water-content of two commercial contact lens materials that have water-gradient gels on their surfaces: delefilcon A (E = 48 ± 11 Pa, > 99.6% water) and lehfilcon A (E = 10 ± 8 Pa, > 99.7% water). The micro-rheology method on Gemini gel interfaces facilitates measurements of the most distal superficial zone of aqueous gels and the quantification of the superficial modulus and water-content of these surfaces.

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Funding

The research leading to these results received funding from Alcon Laboratories. Author DTN is supported by a National Science Foundation Graduate Research Fellowship.

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Authors and Affiliations

  1. Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, 32611, USA

    Diego I. Pedro, Duy T. Nguyen, Lucca Trachsel, Jose G. Rosa, Britney Chu & W. Gregory Sawyer

  2. Department of Chemistry, University of Florida, Gainesville, FL, 32611, USA

    Brent S. Sumerlin

  3. Department of Astronomy, University of Florida, Gainesville, FL, 32611, USA

    Stephen Eikenberry

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  1. Diego I. Pedro
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  2. Duy T. Nguyen
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  3. Lucca Trachsel
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Pedro, D.I., Nguyen, D.T., Trachsel, L. et al. Superficial Modulus, Water-Content, and Mesh-Size at Hydrogel Surfaces. Tribol Lett 69, 160 (2021). https://doi.org/10.1007/s11249-021-01538-3

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