Holten-Andersen Group Research

Metal Ion Coordinate Polymer Networks


The viscoelastic mechanical properties of hydrogel network can be programmed using bio-inspired metal-coordinate crosslinks sensitive to UV light. Depending on the metal ion used to crosslink the hydrogel, the stiffness can be increased by 1000x, decreased by 100x, or remain unchanged by UV-irradiation.

Grindy, Holten-Andersen, Bio-inspired metal-coordinate hydrogels with programmable viscoelastic material functions controlled by longwave UV light, Soft Matter, 2017.

Polymer-Nanoparticle Composites


Interactions between polymer molecules and inorganic nanoparticles can play a dominant role in nanocomposite material mechanics, yet control of such interfacial interaction dynamics remains a significant challenge particularly in water. This study presents insights on how to engineer hydrogel material mechanics via nanoparticle interface-controlled cross-link dynamics. Inspired by the adhesive chemistry in mussel threads, we have incorporated iron oxide nanoparticles (Fe3O4 NPs) into a catechol-modified polymer network to obtain hydrogels cross-linked via reversible metal-coordination bonds at Fe3O4 NP surfaces. The structurally controlled hierarchical mechanics presented here suggest how to develop hydrogels with remote-controlled self-healing dynamics.

Li, Barrett, Messersmith, Holten-Andersen, Controlling Hydrogel Mechanics via Bio-Inspired Polymer–Nanoparticle Bond Dynamics, ACS Nano, 2015.

Expanding the stoichiometric window for metal cross-linked gel assembly using competition


Polymer networks with dynamic cross-links have generated widespread  interest as tunable and responsive viscoelastic materials. However,  narrow stoichiometric limits in cross-link compositions are typically  imposed in the assembly of these materials to prevent excess free  cross-linker from dissolving the resulting polymer networks. Here we  demonstrate how the presence of molecular competition allows for vast  expansion of the previously limited range of cross-linker concentrations  that result in robust network assembly. Specifically, we use  metal-coordinate cross-linked gels to verify that stoichiometric  excessive metal ion cross-linker concentrations can still result in  robust gelation when in the presence of free ion competing ligands, and  we offer a theoretical framework to describe the coupled dynamic  equilibria that result in this effect. We believe the insights presented  here can be generally applied to advance engineering of the broadening  class of polymer materials with dynamic cross-links.

Cazzell, Holten-Andersen, Expanding the stoichiometric window for metal cross-linked gel assembly using competition, PNAS, 2019.

Cross-Linking Metal Coordination Gels


The change from wet and soft to dry and hard is a visco-elastic to solid material transition widely displayed in nature, in particular in materials rich in metal-coordinate cross-linking. How metal-coordinate cross-link dynamics contribute to macromolecular material mechanics upon solidification by dehydration remains an open question.  Using mussel-inspired Fe-catechol cross-linked polymer hydrogels, we address this question. In addition to a nearly two-fold increase in stiffness, we find that the presence of Fe-catechol coordination bonds in a dehydrated polymer gel also provides the bulk network with a significantly increased energy dissipation with over three times higher loss factor.    

Kim, Peterson, Holten-Andersen, Enhanced  Water Retention Maintains Energy Dissipation in Dehydrated  Metal-Coordinate Polymer Networks: Another Role for Fe-Catechol  Cross-Links?, Chemistry of Materials, 2018.

Hybrid Lanthanide Metal–Coordinate Complex


Samples that show the effect of mixing different lanthanide ions with a ligand material called terpyridine in a solvent. In the top three vials, the lanthanides used are (left to right) lanthanum, europium, and terbium. The fluids display the characteristic colors of those elements. The white-light-emitting fluid in the lower vial was formed by mixing together equal volumes of the blue, red, and green samples above.

Chen, Holten-Andersen, Multistimuli-responsive White Luminescent Fluids Using Hybrid Lanthanide Metal–Coordinate Complex Probes, Advanced Optical Materials, 2015.


Paper in prep. Update soon.