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Abstract Many biological and synthetic systems are suspensions of oriented actively-moving components. Unlike in passive suspensions, the interplay between orientational order, active flows, and interactions with boundaries gives rise to fascinating new phenomena in such active suspensions. Here, we examine the paradigmatic example of a surface-attached drop of an active fluid (an “active drop”), which has so far only been studied in the idealized limit of thin drops. We find that such surface-attached active drops can exhibit a wide array of stable steady-state shapes and internal flows that are far richer than those documented previously, depending on boundary conditions and the strength of active stresses. Our analysis uncovers quantitative principles to predict and even rationally control the conditions under which these different states arise—yielding design principles for next-generation active materials. 

Abstract Antibiotic resistance is a growing global health threat. Although antibiotic activity is well studied in homogeneous liquid cultures, many infections are caused by spatially structured multicellular populations where consumption of scarce nutrients establishes strong spatial variations in their abundance. These nutrient variations have long been hypothesized to help bacterial populations tolerate antibiotics, since liquid culture studies link antibiotic tolerance to metabolic activity, and thus, local nutrient availability. Here, we test this hypothesis by visualizing cell death in structuredEscherichia colipopulations exposed to select nutrients and antibiotics. We find that nutrient availability acts as a bottleneck to antibiotic killing, causing death to propagate through the population as a traveling front. By integrating our measurements with biophysical theory and simulations, we establish quantitative principles that explain how collective nutrient consumption can limit the progression of this “death front,” protecting a population from a nominally deadly antibiotic dose. While increasing nutrient supply can overcome this bottleneck, in some cases, excess nutrient unexpectedlypromotesthe regrowth of resistant cells. Altogether, this work provides a key step toward predicting and controlling antibiotic treatment of spatially structured bacterial populations, yielding biophysical insights into collective behavior and guiding strategies for effective antibiotic stewardship. 

Abstract The experimental discovery of fractional Chern insulators (FCIs) in moiré materials raises the question of whether their time-reversal invariant analogs, fractional topological insulators (FTIs), can also be realized in these platforms. We address this via exact diagonalization calculations in both a Landau level (LL) model and continuum model for twisted MoTe₂, and extract principles for engineering FTIs in realistic conditions. For the spinful LL model at filling$$\nu =\frac{1}{3}+\frac{1}{3}$$ $\nu =\frac{1}{3}+\frac{1}{3}$ , we show that a suppression of the short-range component of the interaction is important to stabilize the FTI. For twisted MoTe₂at$$\nu =-\frac{4}{3}$$ $\nu =-\frac{4}{3}$ , we find that a short-range attractiongon top of the screened Coulomb interaction is needed to realize an FTI. We discuss how this threshold value ofgcould be reduced by examining larger system sizes, incorporating band-mixing effects, exploiting Landau level character, and engineering the dielectric environment. While our study highlights the challenges, at least for the fillings considered, for obtaining FTIs, we also provide potential sample-engineering routes to improve the stability of FTI phases. 

ABSTRACT 3D printing (3DP) is leveraged in cutting‐edge research across disparate disciplines, with block copolymers (BCPs) frequently playing key roles in state‐of‐the‐art techniques. Here we review basic block copolymer physics and properties, highlighting the applications they have enabled across many 3DP subfields. We emphasize promising areas for optical, mechanical, electronic, templating, and bioengineering advancements in applications of BCPs in 3DP. We envision these advancements will largely be enabled through using 3DP to direct self‐assembly of these nanostructured materials in 3D to enable hierarchical structural control, ultimately using BCPs either as templates for further functionalization or as inherently anisotropic materials. This review examines established and emerging applications of block copolymers in 3DP. Block copolymers are widely utilized in inks for extrusion‐based 3DP and as support matrices and sacrificial inks for embedded 3DP. New methods are being actively developed to facilitate printing of BCPs via vat photopolymerization, electric‐field‐driven deposition techniques, and other emerging techniques. We highlight the subset of BCP 3DP studies which move beyond rheological and interfacial modification to leverage the functionality of these inherently nanostructured materials. We focus on the potential to couple bottom‐up BCP self‐assembly with top‐down patterning via 3DP to achieve on‐the‐fly tunability of BCP material structure and function. 

Abstract The cell nucleus is a soft composite material with a shell-like nuclear cortex enclosing chromatin, comprised of roughly 2 meters of DNA and associated proteins. Assembling on and around chromatin are droplet-like structures known as biomolecular condensates, which form via phase separation, and facilitate vital roles in gene expression. From studies in non-living materials, the driving forces for phase separation are expected to be sensitive to the local mechanical environment, which often exhibits significant spatial heterogeneity. However, the relationship between chromatin heterogeneity and the phase equilibrium and dynamics of nuclear condensates remains unclear. Here, we investigate the interplay between chromatin organization and the formation, dynamics, and size of engineered model condensates and endogenous nuclear bodies in living cells. We demonstrate that decreasing chromatin heterogeneity with epigenetic modifying drugs correlates with decreased mobility of both endogenous and engineered condensates, and is associated with impaired condensate growth and shifts in the binodal phase boundary of engineered condensates. These findings illustrate how the cell nucleus behaves as a heterogeneous composite material with mechanically permissive chromatin micro-environments. 

Abstract We report the discovery of (Al,Cu)‐bearing metallic alloys in two micrometeorites found in the Project Stardust collection gathered from urban rooftop environments in Norway. Most of the alloys are the same as those found in the Khatyrka meteorite and other micrometeorites, though one has a composition that has not been reported previously. Oxygen isotope ratio measurements using secondary ion mass spectrometry show that the Project Stardust samples reported here, like all earlier examples of natural (Al,Cu)‐bearing alloys, contain material of chondritic affinity. 

Abstract The intrinsic frustrated nature of a kagome lattice is amenable to the realization of exotic phases of matter, such as quantum spin liquids or spin ices, and the multiple-qcharge density waves (CDW) in the kagome metals. Despite intense efforts to understand the mechanism driving the electronic modulations, its origin is still unknown and obscured by competing interactions and intertwined orders. Here, we identify a dimerization-driven 2D hexagonal charge-diffuse precursor in the antiferromagnetic kagome metal FeGe and demonstrate that the fraction of dimerized/undimerized states is the relevant order parameter of the multiple-qCDW of a continuous phase transition. The pretransitional charge fluctuations with propagation vectorq = q_Mat T_CDW < T < T^*(125 K) are anisotropic, hence holding a quasi-long-range bond-orientational order. The broken translational symmetry emerges from the anisotropic diffuse precursor, akin to the Ising scenario of antiferromagnetic triangular lattices. The temperature and momentum dependence of the critical scattering show parallels to the stacked hexatic B-phases reported in liquid crystals and transient states of CDWs and highlight the key role of the topological defect-mediated melting of the CDW in FeGe. 

Summary Pyrenoids are algal CO₂‐fixing organelles that mediate approximately one‐third of global carbon fixation. Most pyrenoids are traversed by membranes that are thought to supply them with concentrated CO₂. Despite the critical nature of these membranes for pyrenoid function, they are poorly understood, with few protein components known in any species.Here, we identify protein components of the pyrenoid‐traversing membranes from the leading model alga,Chlamydomonas reinhardtii,by affinity purification and mass spectrometry of membrane fragments. Our proteome includes previously known proteins as well as novel candidates.We further characterize two of the novel pyrenoid‐traversing membrane‐resident proteins: Cre10.g452250, which we name Pyrenoid Membrane Enriched 1 (PME1), and Cre02.g143550, also known as Low‐CO₂‐Induced 16 (LCI16). We confirm the pyrenoid‐traversing membrane localization of LCI16 and observe that PME1 and LCI16 physically interact. We find that neither protein is required for normal membrane morphology or growth under CO₂‐limiting conditions, but that both mutants show a similar proteomic profile to those of established pyrenoid mutants.Taken together, our study identifies the proteome of the pyrenoid‐traversing membranes and initiates the characterization of a novel pyrenoid‐traversing membrane complex, building toward a mechanistic understanding of the pyrenoid. 

Abstract Under heat stress, proteins have been shown to organize into biomolecular condensates in living cells. Recent experiments suggest that this response may be encoded in the chemical makeup of proteins. In particular, specific sequences undergo phase separation at elevated temperatures, exhibiting lower critical solution temperatures (LCST). However, the precise role of LCST‐type transitions in heat‐induced condensation remains largely unknown. This knowledge gap is further compounded by a lack of approaches that can quantitatively predict LCST‐type phase behavior in proteins. To address this, we have developed Mpipi‐T—a residue‐resolution model for predicting LCST‐type transitions in proteins. By integrating atomistic free energy of solvation data with experimental cloud point measurements, we parameterize short‐range non‐bonded interactions to capture the entropically driven phase separation that occurs upon heating, while analytically scaling long‐range electrostatic interactions as a function of temperature. We show that Mpipi‐T predicts LCST‐type behavior, including both single‐molecule properties and collective phase separation. Using Mpipi‐T, we analyze three key proteins postulated to exhibit LCST: Alzheimer's disease‐associated hTau40, stress granule‐binding Pab1, and circadian clock regulator ELF3. Strikingly, our model predicts that each protein encodes an LCST near the physiological growth temperature of its respective organism. These findings highlight a potential mechanism by which proteins encode stress resilience in living systems, providing principles that can be harnessed in synthetic biology to engineer thermoresponsive behavior. Beyond mechanistic insight, Mpipi‐T's computational efficiency also makes it a potentially useful tool for designing such proteins directly from their sequence. 

Abstract Tissue homeostasis, the biological process of maintaining a steady state in tissue via control of cell proliferation and death, is essential for the development, growth, maintenance, and proper function of living organisms. Disruptions to this process can lead to serious diseases and even death. In this study, we use the vertex model for the cell-level description of tissue mechanics to investigate the impact of the tissue environment and local mechanical properties of cells on homeostasis in confined epithelial tissues. We find a dynamic steady state, where the balance between cell divisions and removals sustains homeostasis, and characterise the homeostatic state in terms of cell count, tissue area, homeostatic pressure, and the cells’ neighbour count distribution. This work, therefore, sheds light on the mechanisms underlying tissue homeostasis and highlights the importance of mechanics in its control.