Biomedical and Chemical Engineering Research Seminar Series - Molecular-Scale Engineering of Stimuli-Responsive Polymer Hydrogels

Molecular-Scale Engineering of Stimuli-Responsive Polymer Hydrogels

Polymer hydrogels that respond to external stimuli including pH, light, and heat have attracted broad interest as soft materials with controlled release profiles, 3D printability, and sensing and actuation capabilities. This presentation will explore the molecular-scale engineering of two stimuli-responsive polymer hydrogels. First, we evaluate the impact of functional nanomaterials on photo-responsive hydrogel formation by embedding nanocapsules into solutions containing anthracene-functionalized poly(ethylene glycol) star polymers. Nanocapsules that protect interior cargo and disperse readily through polymeric matrices have drawn particular interest for their ability to integrate chemically incompatible systems, such as organic photon upconversion materials for sustainable additive manufacturing. Using in situ photo-rheology, we observe an unexpected non-monotonic dependence of gel formation dynamics on polymer concentration, as well as faster gel formation and enhanced mechanical properties upon addition of nanocapsules. This study suggests synergistic mechanical reinforcement of hydrogels by nanocapsules, despite not being crosslinked into the polymer network. Second, we investigate the ion-responsive behavior of repetitive proteins that undergo conformational changes in response to calcium ions. Calcium ions trigger numerous biological phenomena including bone growth, muscle contraction, and neurotransmitter release. We modify hydrophobicity, electrostatics, and sequence heterogeneity of calcium-responsive proteins to demonstrate sequence-dependent, reversible folding in the presence of calcium ions by circular dichroism, as well as domain size changes by small-angle X-ray scattering. Hydrogels comprising calcium-responsive proteins reveal the impact of sequence on hydrogel stability, calcium sensitivity, shear modulus, and characteristic relaxation time. Overall, molecular-scale engineering enables the rational design of stimuli-responsive polymer hydrogels for sustainable manufacturing and dynamic biomaterials. Website: https://mailab.stanford.edu/