Highlights
Highlights of IRG research are reported on an ongoing basis to the NSF MRSEC program. Publications supported by Brandeis MRSEC funding are recorded here.
2025
Triangular subunits with chemically specific interactions self-assemble into two-dimensional tilings with large unit cells comprised of many unique subunit species, which could find applications in photonics and plasmonics. New design algorithms show how to define the mutual interactions between the various particle species to produce a user-specified complex crystal with a multicomponent unit cell by exploiting symmetry. Experiments using DNA-origami subunits verify this design approach and produce two-dimensional tilings with unit-cell dimensions approaching the wavelength of visible light, as quantified by electron microscopy. An investigation of the design ecomomy, i.e., the number of unique subunits required to produce a tiling with a given unit-cell area, reveals a set of economical design rules to guide future experiments.
Triangular monomers with programmable local curvature and specific interactions assemble into self-closing cylindrical tubules. Self-closing assemblies are prone to polymorphism due to the large number of self-closing states with similar energies, such as tubules with different diameter or pitch. Adding complexity, by using multiple unique assembly subunits, can increase the free-energy landscape of off-target structures, improving the yield of a particular assembly outcome (the selectivity). Experimental realizations of tubule assembly show that the selectivity first increases and then plateaus with increasing complexity; the cross-over point denotes the optimal economy for assembly, where one can achieve maximum selectivity using the minimum number of distinct subunit species. A theoretical elastic energy model predicts how this cross-over point depends upon the self-closing size, the number of unique subunits, and the mechanical properties of the subunit assemblies.
The formation of contractile asters composed of biopolymers is ubiquitous in living systems. In vitro, it is unclear why asters coalescence is slowing down and why asters display either liquid-like or solid-like properties. Sometimes, asters only appear transiently. This knowledge gap is unexplained by current active matter theories and precludes the rational design of steady-state contractile materials. Here, MRSEC IRG2 members Duclos, Baskaran, and Hagan combined experiments and computer simulations to explain the origin of the arrested coalescence, aging, and stability of asters composed of microtubules and molecular motors. They identified the origin of asters’ solidification and developed alternative formulations to assemble liquid-like asters. Complementary work by Dogic and Fraden investigates how the mechanical contribution of actin filaments impacts the aster’s dynamics.
Spontaneous flows are defining features of active nematics. They’ve been reported in various 2D experimental systems that share the same conserved and broken symmetries, from biofilms to active layers of biopolymers. Quiescent active nematics are more uncommon, despite their biological relevance for cell cytoskeleton and tissue dynamics. The active Fréedericksz transition predicts that confinement can stabilize active nematics in a quiescent out-of-equilibrium phase. Duclos, Yevick, and Baskaran combined microscopy, biochemical assays, microfluidics, and simulations to test this fundamental prediction of active hydrodynamic theory using a simple and tunable model system composed of microtubules and molecular motors dispersed in a 3D colloidal liquid crystal.
This year, the MRSEC celebrates 10 years of collaborating with Waltham High School to provide ”The Brandeis MRSEC and Waltham High School Science Pizza Talk” series! These extremely popular talks occur monthly during the academic year and invites WHS students to listen to a science talk during their lunch periods.
Once a month during the academic year, Brandeis University scientists from diverse backgrounds travel to Waltham High School for “Science Pizza Talks” to share their unique personal journeys into science careers while high school students ask questions and enjoy free pizza. A long-term goal is to ignite a passion for science in high school students and support their persistence in STEM.
Since launching the series in 2015, over 70 talks have been held including a number of Spanish-language science talks and talks for middle school students. Talks were delivered virtually during COVID. Attendance for talks regularly reaches 100 students meaning that over the course of 10 years, thousands of high school students have attended this series.
In Fall 2024, the Brandeis MRSEC organized an inaugural field trip for the Waltham High School Science Club with the goal of introducing high school students to research experiences at Brandeis University and supporting university enrollment.
In small groups, high school students were rotated through Brandeis research labs where they participated in a hands-on activity led by MRSEC trainees. Research discussed topics such as self-assembly, epigenetics, and microscopy. Students were then given a guided tour which introduced them to campus life but also discussed application support that is available for WHS students.
For the inaugural field trip, 45 high school students were in attendance and five research labs were engaged. Due to the success of this event, the MRSEC plans to expand engagement in upcoming years.
