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Heterogeneity and length scale effects in PEG-based hydrogels



Brian G. Bush, Jenna M. Shapiro, Frank W. DelRio, Robert F. Cook, Michelle L. Oyen


Colloidal-probe spherical indentation load-relaxation experiments are conducted on poly(ethylene glycol) (PEG) hydrogel materials to quantify the steady-state mechanical properties and time-dependent transport properties in a single experiment. A probe radius of 3 µm was chosen to ensure experiments were conducted at biologically relevant length scales. PEG-based hydrogels are shown to be heterogeneous in both morphology and mechanical stiffness at this scale; a linear-harmonic interpolation of hyperelastic Mooney-Rivlin and Boussinesq flat-punch indentation models was used to describe the steady state response of the hydrogels and determine upper and lower bounds for indentation moduli. Analysis of the transient load-relaxation response during displacement-controlled hold period provides a means of extracting viscoelastic, τ1, and poroelastic, τ2, time constants. Approximate pore sizes on the order of 1 nm to 5 nm are calculated from τ2. In addition, outliers in the distribution of τ2 values at small indentation loads provide evidence of a near-equilibrium state characterized by a jamming phenomenon that restricts poroelastic fluid flow through the material. These results have important implications in the use of PEG-based hydrogels for bioengineering applications.
Soft Matter


Hydrogels, PEG, Viscoelasticity, Poroelasticity, time-dependent materials, contact mechanics


Bush, B. , Shapiro, J. , DelRio, F. , Cook, R. and Oyen, M. (2015), Heterogeneity and length scale effects in PEG-based hydrogels, Soft Matter, [online], (Accessed April 20, 2024)
Created August 10, 2015, Updated February 19, 2017