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Heterogeneity and its Influence on the Properties of Difunctional Poly(ethylene glycol) Hydrogels: Structure and Mechanics
journal contribution
posted on 2015-08-11, 00:00 authored by Paula Malo de Molina, Sahger Lad, Matthew E. HelgesonDifunctional polymer hydrogels, such
as those prepared from poly(ethylene
glycol) diacrylate (PEGDA) macromers, are widely used for a number
of potential applications in biotechnology and advanced materials
due to their low cost, mild cross-linking conditions, and biocompatibility.
The microstructure of such hydrogels is known to be heterogeneous,
yet little is known about the specific structure itself, how it is
impacted by the molecular parameters of the macromer, or its impact
on macroscopic gel properties. Here, we determine the structure of
PEGDA hydrogels using small-angle neutron scattering over a significant
range of macromer molecular weights and volume fractions. From this,
we propose a structural model for PEGDA hydrogels based on self-excluded,
highly branched star polymers arranged into a fractal network. The
primary implication of this structure is that heterogeneity arises
not from defects in the cross-linking network, as is commonly assumed,
but rather from a heterogeneous distribution of polymer concentration.
This structural model provides a systematic explanation of the linear
elasticity and swelling of PEGDA hydrogels.