The effect of hydrophobicity on the viscoelastic creep characteristics of poly(ethylene glycol)-acrylate hydrogels

The creep behavior of hydrophobic poly(ethylene glycol)acrylate hydrogels was well characterized by two Kelvin units in series, compared to the other various combinations of the linear viscoelastic elements investigated. The hydrogels were synthesized by reacting acrylate derivatives of poly(ethylene glycol) [PEG] with PEG-diacrylate as the crosslinking agent. By using different amounts of omega-phenoxy-PEG-acrylate in the monomer feed ratio, the hydrophobicity was varied. The extent of monomer conversion was greater than 95%, as determined by Raman spectroscopy. With increasing hydrophobicity, the elastic modulus of the hydrogels increased from 10.92 kPa to 35.10 kPa, and the density increased from 1.0004 g/cm(3) to 1.0091 g/cm(3), while the dimensional stability decreased from 1.55 to 1.48. Two Kelvin units in series well characterized the creep curve for various loads and time durations. The time constants were in the range of 1-2 s and approximately 300 s for the two Kelvin units. These hydrophobic hydrogels may be used as model tissues to determine the viscoelasticity of the human lens. (C) 2003 American Chemical Society.