Mechanical characterization of oligo(ethylene glycol)-based hydrogels by dynamic nanoindentation experiments.
Oligo(ethylene glycol)-based (OEG) hydrogel samples of varying cross-link densities and degrees of swelling were characterized through dynamic nanoindentation testing. Experiments were performed using a non-standard nanoindentation method, which was validated on a standard polystyrene sample. This method maximizes the capability of the instrument to measure the stiffness and damping of highly compliant, viscoelastic materials. Experiments were performed over the frequency range of 1 to 50 Hz, using a 1mm diameter flat punch indenter. A hydration method was adopted to avoid sample dehydration during testing. Values of storage modulus (E') ranged from 3.5 to 8.9 MPa for the different OEG-hydrogel samples investigated. Samples with higher OEG concentrations showed greater scatter in the modulus measurements and it is attributed to inhomogeneities in these materials. The (E') values did not show a strong variation over frequency for any of the samples. Values of loss modulus (E") were two orders of magnitude lower than the storage modulus, resulting in very low values of loss factor (E"/E'<0.1). These are characteristics of strong gels, which present negligible viscous properties.
Helmholtz-Zentrum Geesthacht, Institute of Materials Research, Materials Mechanics, 21502 Geesthacht, Germany. Electronic address: paula.guglielmi@hzg.de.
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Guglielmi
Michigan Technological University, College of Engineering, Department of Materials Science and Engineering, Houghton, MI 49931, USA.
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Herbert
Helmholtz-Zentrum Geesthacht, Institute of Biomaterial Science, 14513 Teltow-Seehof, Germany.
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Tartivel
Helmholtz-Zentrum Geesthacht, Institute of Biomaterial Science, 14513 Teltow-Seehof, Germany.
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Behl
Helmholtz-Zentrum Geesthacht, Institute of Biomaterial Science, 14513 Teltow-Seehof, Germany.
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Lendlein
Helmholtz-Zentrum Geesthacht, Institute of Materials Research, Materials Mechanics, 21502 Geesthacht, Germany.
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Huber
Helmholtz-Zentrum Geesthacht, Institute of Materials Research, Materials Mechanics, 21502 Geesthacht, Germany.
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Lilleodden
D004548:Elasticity; D020100:Hydrogels; D008422:Materials Testing / Q000379:methods*; D055595:Mechanical Phenomena; D036103:Nanotechnology / Q000379:methods*; D011092:Polyethylene Glycols / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry; D014783:Viscosity
D020100:Hydrogels; D011137:Polystyrenes; D011092:Polyethylene Glycols
Dynamical testing; Hydrogel; Mechanical properties; Nanoindentation