Hydrogels are increasingly being used as biomaterials, tissue engineered scaffolds and soft flexible actuators. These materials exhibit significant time-dependent behaviour resulting from the flow of water through the permeable polymer network and through the molecular rearrangement of polymer bonds. The mechanical response exhibits intrinsic length-scale effects due to the size of pores and the interaction between pore walls and the liquid phase flowing. Here, mechanical characterization of hydrogels is explored with indentation and tensile testing techniques across a range of length-scales, from nanometer—comparable to the pore size—to macroscopic. Composite hydrogels are created by mixing two hydrogel phases that exhibit substantially different time-dependent behaviours, and by infiltrating electrospun fibrous polymer scaffolds with hydrogels. The results from these tests are analyzed using both viscoelastic and poroelastic mechanical frameworks and compared with scaling laws based on rubber elasticity. While the elastic behaviour of the composite gels largely scales as expected with the volume fractions of the phases, the time-dependent behaviour is more complex. The approach allows for the targeted design of custom hydrogels with combinations of mechanical properties optimized for their application.
Dr Michelle Oyen is a University Lecturer at Cambridge University. Her research area covers nanoindentation, biomaterials and biomechanics. She received her PhD from the University of Minnesota in 2005 and joined Cambridge in 2006. She has 50 Journal papers and 35 conference proceeding papers. She has served as Principal Editor of the Journal of Materials Research since 2006. She has also served on the Editorial Board of the Journal of the Mechanical Behavior of Biomedical Materials and Acta Mechanica Sinica since 2011.
published on: 3rd April 2012