MAE Colloquium: Vicky Nguyen
B11 Kimball Hall B11 Kimball Hall
Talk: Computational design of functional composite hydrogel structures and devices
Nature is full of examples of soft functional composite structures with arrangements of active and passive materials of dissimilar properties. Biological organisms exploit the swelling and growth mismatch inherent in these structures to enable complex shape change and motion. Our work has been focused on developing computational models of stimuli-responsive hydrogel composite structures to investigate how soft active and stiff passive material segments can be arranged in two-dimensional and three-dimensional structures to achieve a targeted shape change and, furthermore, a coordinated sequence of shape changes to achieve locomotion. In this presentation, I will describe the experimental and computational modeling investigation of two types of stimuli-responsive hydrogel materials, poly(N-isopropylacrylamide) (pNIPAM) and DNA polymerization hydrogels, and their structures. pNIPAM is a common thermoresponsive hydrogel that undergoes a transition from a hydrophilic state to a hydrophobic state when the temperature increases above the lower critical solution temperature (LCST), resulting in a dramatic change in volume. DNA polymerization gel is a co-polymer of large stiff DNA hairpins and smaller flexible chains, such (e.g., PEDGA and PAAM). The DNA hairpins act as dynamic crosslinkers that bind to complementary hairpins. Successive hairpins can be inserted to lengthen the crosslink and increase hydrogel swelling until the reaction site is closed by a terminating hairpin. The DNA-activated swelling permits spatial patterning of different DNA sequences in the gel for complex shape changes and for programming a sequence of shape changes. Our modeling approach develops coupled chemo-mechanical models to describe the physical mechanisms of swelling for each system. We then apply the models to investigate the interplay between geometry, material properties, and surface interactions in hydrogel shape-changing structures.
Thao (Vicky) Nguyen received her S.B. from MIT in 1998, and M.S. and Ph.D. from Stanford in 2004, all in mechanical engineering. She was a research scientist at Sandia National Laboratories in Livermore from 2004-2007, before joining the Mechanical Engineering Department at Johns Hopkins University, where she is currently a Professor and Marlin U. Zimmerman Faculty Scholar in the Department of Mechanical Engineering with secondary appointments in Materials Science and Ophthalmology. Dr. Nguyen’s research encompasses the biomechanics of soft tissues and the mechanics of active polymers and biomaterials. Dr. Nguyen received the 2008 Presidential Early Career Award for Scientists and Engineers (PECASE), 2008 NNSA Office of Defense Programs Early Career Scientists and Engineer Award, 2013 NSF CAREER, 2013 Eshelby Mechanics Award for Young Faculty, 2013 ASME Sia Nemat-Nasser Early Career Award, and the 2015 T.J.R. Hughes Young Investigator Award from the Applied Mechanics Division of ASME. She was elected Fellow of ASME in 2022 and AIMBE in 2023. She served as President of the Board of Directors of the Society of Engineering Science in 2020 and is currently Editor-in-Chief of the Journal of Biomechanics.