ResearchTopics

Furst Group Research Poster

An overview of current research activities in the Furst Research Group.

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Current projects

Nanomechanics of particle contacts

The rheology of a colloidal suspension depends on the interaction forces between particles. At high volume fractions and conditions of strong attraction, particles are separated by a fraction of their size, which may be on the order of nanometers. Dispersion, electrostatic, depletion, steric, and hydrodynamic interactions, as well as geometrical characteristics such as shape and roughness, all potentially contribute to interparticle forces. We use laser tweezers to measure the contact and sliding mechanics between micrometer-size colloidal particles. With these, we’ve gained new insights into the nature of cohesion and contact, the aging of contacts, and their mechanics, including the existence of a critical bending moment, stick slip motion, contact line pinning, particle rolling, the ability to tune these forces by reducing the interfacial energy of the particles, and their overall effect on bulk rheology. Such measurements of colloidal-scale interactions and mechanics should be informative for developing models of suspension rheology, including the elasticity and modulus of colloidal gels and the contact mechanics underlying discontinuous shear thickening of suspensions. Of key interest: can we develop computational models that incorporate these experimental observations? These are central problems for developing and advancing new sustainable processes, especially with the goal of reducing the environmental burden of cements.

Representative publications

Francesco Bonacci, Xavier Chateau, Eric M. Furst, Julie Goyon, and Anäel Lemaître, “Yield stress aging in attractive colloidal suspensions,” Phys. Rev. Lett., 128, 018003 (2022). DOI:10.1103/PhysRevLett.128.018003.
Francesco Bonacci, Xavier Chateau, Eric M. Furst, Jennifer Fusier, Julie Goyon, and Anäel Lemaître, “Contact and macroscopic aging in dense colloidal suspensions,” Nat. Mater., 19, 775–780 (2020). DOI: 10.1038/s41563- 020-0624-9
Kathryn A. Whitaker, Lilian Hsiao, Zsigmond Varga, Michael J. Solomon, James W. Swan, and Eric M. Furst, “Colloidal gel elasticity arises from the packing of locally glassy clusters,” Nat. Comm., 10, 2237 (2019). DOI: 10.1038/s41467-019-10039-w

Dissipative self-assembly

Colloids and nanoparticles self-assemble in external fields, a property which enables functional and smart materials like magnetorheological fluids and potentially new ones in which structure controls the transport of heat, light, or chemical species. Suspensions of paramagnetic colloids are a model to study these phenomena. In experiments conducted in the microgravity environment of the International Space Station and earth-based experiments, we find that several factors govern the kinetics of phase separation of paramagnetic colloids and the steady-state structures that they form in periodically toggled fields, including the field strength, toggle frequency, and duty ratio. The suspension structures observed over many toggle cycles are in good agreement with those predicted by the theoretical and computational work of Sherman et al. (Sherman, Z. M.; Rosenthal, H.; Swan, J. W. Langmuir 2018, 34, 1029−1041), including a dependence on the field duty. Our results are important experimental tests for models of dissipative self-assembly -- processes in which ordered structures form far from equilibrium by continuously absorbing energy and dissipating it into their surroundings. Such active assembly processes offer promising methods to generate complex structures and circumvent arrest in undesirable metastable states.

Representative publications

Hojin Kim, Moujhuri Sau, and Eric M. Furst, “An expanded state diagram for the directed self-assembly of colloidal suspensions in toggled fields,” Langmuir, 36, 9926-9934 (2020). DOI: 10.1021/acs.langmuir.0c01616
James W. Swan, Jonathan L. Bauer, Yifei Liu and Eric M. Furst, “Directed colloidal self-assembly in toggled magnetic fields,” Soft Matter, 10, 1102–1109 (2014). DOI 10.1039/c3sm52663a
J. W. Swan, P. A. Vasquez, P. A. Whitson, E. M. Fincke, K. Wakata, S. H. Magnus, F. De Winne, M. R. Barratt, J. H. Agui, R. D. Green, N. R. Hall, D. Y. Bohman, C. T. Bunnell, A. P. Gast and E. M. Furst, “Multi-scale kinetics of a field-directed colloidal phase transition,” Proc. Natl. Acad. Sci. USA, Early Edition (2012). DOI: 10.1073/pnas.1206915109

Bundlemer solution assembly

Coiled-coil peptide bundles [1] (or bundlemers) self-assemble in aqueous solution into nanometer-scale filaments. Our current research examines the bundlemer interactions in solution, the kinetics of assembly, and the nanomechanical forces of these peptide-based nanorods. Bundlemers can be chemically functionalized to form rods that are orders of magnitude longer than their individual bundlemer segments. One unique property of these rods is their persistence length, a measure of rigidity, which is comparable to that of single-wall carbon nanotubes (SWCNTs) based on electron micrographs. Using microrheological and micromanipulation techniques, such as dynamic light scattering and optical tweezers, we seek to understand the mechanism governing rod growth and assembly, as well as combine this information to measure the persistence length and other mechanical properties of these synthetic nanofilaments.

[1] Wu, D.; Sinha, N.; Lee, J.; Sutherland, B. P.; Halaszynski, N. I.; Tian, Y.; Caplan, J.; Zhang, H. V.; Saven, J. G.; Kloxin, C. J.; et al. Polymers with Controlled Assembly and Rigidity Made with Click-Functional Peptide Bundles. Nature 2019, 574, 658–662.

Representative publications

Coming soon!

Material and cellular response in 3D cell culture

The objective of this project is to develop and apply innovative rheological and microrheological methods as a characterization toolbox that captures bulk and local, dynamic pericellular changes in complex stimuli responsive biomaterials. The approach includes determining effective limitations and optimal resolution of current microrheological and bulk material characterization methods for responsive hydrogels. Additionally, rather than analyzing these methods individually, we seek a transformative, synergistic approach to characterize materials from the nano scale up to the bulk scale.

Representative publications

Coming soon!

Salt-induced local ordering in amorphous protein dense phases

Relatively little is known about biopolymer phase behavior, despite their presence both in vivo and during protein solution processing. The physical nature of the dense phase, whether crystal, dense liquid, or a nonequilibrium phase such as a gel, is strongly dependent on the solution conditions. Achieving desired phase behavior can require extensive empirical study, and unwanted phases may prove difficult to eliminate. Our goal is to provide a reliable knowledge base of biopolymer behavior under both ambient and high-pressure conditions [1]. We optimize these studies with a novel high-pressure sample environment for simultaneous structural and rheological measurements. Greene et al showed for the first time that macroscopically amorphous salted-out protein dense phases contain nanocrystalline regimes [2]. The work presented here completes the structural investigation of salted-out ovalbumin under ambient conditions, with the dual purpose of validating the novel sample environment with a well-characterized protein dense phase. Small-angle neutron scattering (SANS), static light scattering (SLS), and small-angle x-ray scattering (SAXS) data are combined to provide a full structural profile. Attention is given to trends in microstructure development with aging time and how structural observations may serve as a predictor for macroscopic properties. The results provide insights into local crystallinity within amorphous protein dense phases and build the groundwork for an in-depth study of pressure effects on biopolymer material properties.

[1] Teixeira, S. C. M., High-pressure small-angle neutron scattering for food studies. Current Opinion in Colloid & Interface Science 2019, 42, 99-109. [2] Greene, D. G. M., S.; Wagner, N.J.; Sandler, S.I.; Lenhoff, A.M., Local Crystalline Structure in an Amorphous Protein Dense Phase. Biophysical Journal 2015, 109, 1716-1723.

Representative publications

Coming soon!

MAb adsorption and interfacial rheology

Monoclonal antibodies (MAbs) encounter a range of physical and chemical stresses during development, manufacturing, transportation, and storage. Such stresses can promote different aggregation mechanisms in bulk solution and at solid-liquid, liquid-liquid, and vapor-liquid interfaces. Aggregation in bulk solution has been studied extensively in a mechanistic context, but the understanding of surface-mediated aggregation remains largely speculative, in part because of the limited experiments capable of resolving interfacial processes. We focus on mechanistic insight into surface-mediated aggregation of MAbs by using microbubble tensiometry and interfacial rheology at the air-liquid interface. Interfacial creep measurements and oscillatory strain and frequency sweep measurements reveal that an adsorbed MAb layers at the air-water interface form soft solid films. For each sub-phase condition (pH, concentration), the creep compliance from different applied stresses can be horizontally shifted for superposition onto a master curve, consistent with soft glassy rheology. The viscoelastic moduli, creep compliance, and superimposed master curves of the MAb layers were dependent on solution pH and bulk concentration in a manner that indicated that adsorbed MAbs form stronger interfacial films as the solution pH approaches the pI of the MAb, and at higher bulk concentrations, which is likely a consequence of irreversible adsorption kinetics analogous to nanoparticle adsorption at air-liquid and liquid-liquid interfaces.

Representative publications

Caitlin V. Wood, Vladimir I. Razinkov, Wei Qi, Christopher J. Roberts, Jan Vermant, and Eric M. Furst, “Antibodies adsorbed to the air-water interface form soft glasses," Langmuir, 39, 22, 7775–7782 (2023). DOI: 10.1021/ acs.langmuir.3c00616
Caitlin V. Wood, Sean McEvoy, Vladimir I. Razinkov, Wei Qi, Eric M. Furst, and Christopher J. Roberts, “A rapid, small-volume approach to evaluate protein aggregation at air-water interfaces,” J. Pharm. Sci., 110, 1083¬–1092 (2021). DOI: 10.1016/j.xphs.2020.11.024
Caitlin V. Wood, Sean McEvoy, Vladimir I. Razinkov, Wei Qi, Eric M. Furst, and Christopher J. Roberts, “Kinetics and competing mechanisms of antibody aggregation via bulk and surface-mediated pathways,” J. Pharm. Sci. 109, 1449–1459 (2020). DOI: 10.1016/j.xphs.2020.01.005