Nature Materials

Tissue-engineered skeletal muscle offers robotics unique advantages in energy density, adaptability, and self-repair, but current biohybrid machines couple muscle directly to artificial skeletons, limiting net force output and requiring continuous stimulation maintain mechanism positions. Here, we introduce a biohybrid bistable switching mechanism that converts antagonistic muscle contractions to snap-through actuation of an elastomeric four-bar flexure, maintaining stable positions without energy consumption. We decouple passive muscle pre-tensioning from flexure operation with thin-film elastomer resistance bands, enabling fine tuning of spring stiffness and force to match muscle mechanical output envelopes. Leveraging mesoscale additive manufacturing, spin coating, and replica molding techniques, components are integrated into a millimeter-scale linear stage to axially align muscles with artificial components. Our prototype achieves reversible toggling between bistable states with a 130 ms switching time, establishing skeletal muscle actuators as viable electromechanical switches, and broadening biohybrid robotics towards novel applications such as grippers, valves, and mechanical computers.

The actin cytoskeleton is a self-assembled material that acts as the mechanical scaffold of the cell. Within the cell, protein cross-linkers organize actin filaments into assemblies with various microstructures that support distinct physiological functions. These protein cross-linkers differ in structural features. To decouple the role of individual cross-linker properties in actin assembly microstructure and mechanics, we synthesize programmable cross-linkers using a DNA linker coupled to binding domains. We find that high affinity cross-linkers induce actin bundling, while low affinity cross-linkers form actin networks. Myosin II motors remodel and contract all cross-linked networks tested in distinct ways from uncross-linked networks. We find that networks with high affinity cross-linkers have different myosin induced dynamics than networks with low affinity cross-linkers. This research expands our understanding of how cells regulate their mechanics and microstructures, while also providing insight towards the structure-property relationship in complex soft materials.

Engineered human neuromuscular models are limited by a trade-off between biological fidelity and architectural control: self-assembled organoids organize stochastically, while engineered 3D tissues impose anisotropy through passive tension at the edges without internal guidance. Here we encode architectural guidance into human neuromuscular tissues by coupling a three-dimensional, cell-laden biomatrix to a xolographically printed hydrogel substrate featuring sub-millimeter surface topography. We demonstrate that grooved substrates increase human primary myotube alignment and maturation in the overlying 3D tissue, while guiding directional axon extension from human iPSC-derived motor neuron spheroids. We show that combining both cell types along a shared alignment axis establishes functional neuromuscular connectivity, evidenced by acetylcholine receptor clustering, glutamate-evoked contraction and its blockade by d-tubocurarine (curare), and yields innervation coverage of centimeter scale tissues. Overall, this platform combines compliant substrates, mesoscale tissue architectural guidance, and human-relevant cell biology in a single untethered construct for studies of neuromuscular tissue development and function.

Matrix stiffness is a hallmark of aggressive solid tumors and strongly associated with therapeutic resistance and poor prognosis. This mechanical barrier represents a major unmet challenge in oncology, as current strategies rarely address how matrix mechanics themselves drive treatment resistance. Here, we identified ferroptosis, an iron-dependent form of cell death, as a potential long-sought vulnerability that can be exploited to eliminate mechanically resistant tumors. Using genetic and chemical approaches, we investigated how matrix stiffness sensitizes cancer cells to ferroptosis and whether this vulnerability can be therapeutically targeted. We found that cancer cells cultured on stiff matrices were more sensitive to ferroptosis than those on soft matrices, as evidenced by reduced cell viability and elevated lipid peroxidation. Furthermore, we found that matrix stiffness induced YAP activation, which upregulated its target gene SKP2, a key mediator required for the heightened ferroptosis sensitivity observed under stiff conditions. Finally, using an injectable hydrogel system, we demonstrated that stiffened tumors were resistant to chemotherapy but remained highly susceptible to ferroptosis induction, resulting in markedly reduced tumor volume and weight. Our findings established ferroptosis as a stiffness-dependent vulnerability mediated by a YAP-SKP2 signaling axis, revealing a mechanotransductive pathway that may be leveraged to target treatment-refractory tumors.

Reconstituting organ development in vitro requires reproducing dynamic developmental transitions rather than only terminal tissue structures. Here, we developed MoSAIC (Modular Spatial Assembly and Integration of Cues), a modular platform that decomposes complex culture operations and subsequently integrates them to reconstruct multimodal mechano-chemical spatial cues. Using human induced pluripotent stem cells, MoSAIC enabled independent control of tissue geometry, extracellular matrix localization, physical boundaries, and morphogen gradients, while also permitting defined mechanical and chemical perturbations during development. Their integration guided a continuous ectodermal sheet through neural induction, tissue bending, and bifurcation into neural and epidermal tissues, followed by formation of a polarized neural tube structure. Spatially controlled morphogen exposure further established dorsoventral patterning, while the resulting tissue exhibited posterior neural tube identity. Using the developed model recapitulating the transition of human neurulation, MoSAIC further enables non-genetic perturbation of mechanical and chemical cues to interrogate the mechanisms governing neural tube closure.

Precise organization of bioactive ligands at material-cell interfaces is critical for directing integrin-mediated cell behavior, yet tuning supramolecular organization commonly necessitates orchestrated redesign of molecular composition or ligand sequence. Here we establish terminal modification as a minimal, sequence-preserving strategy to reprogram the organization and function of self-assembling integrin ligands. Using FFFIKVAV as a model system, N- and C-terminal modifications generated distinct supramolecular states with markedly different integrin activation and cell migration responses. Notably, stronger intermolecular association did not produce stronger biological activity, as N-terminal acetylation promoted scaffold consolidation while reducing the configurational freedom of the exposed IKVAV ligand and diminishing integrin activation and cell migration. Alongside modulating migration magnitude, terminal chemistry also diversified the cellular programs supporting migration, with the parent peptide and its C-terminally amidated analogue favoring protrusion-dominant and stress-fiber-dominant adhesion-cytoskeletal programs, respectively. These functional states were reproduced when the assemblies were introduced directly to pre-adherent cells, extending their activity beyond preformed material coatings. Our findings identify terminal chemistry as a compact molecular design variable that links supramolecular organization to ligand function while diversifying the biological output of a shared bioactive sequence.

Centromeric heterochromatin is maintained by a self-reinforcing loop between DNA methylation (5mC) and histone H3 lysine 9 trimethylation (H3K9me3), yet whether this coupling is preserved at the level of individual chromosomes in cancer has been inaccessible to conventional epigenomic assays, which average signals across cell populations and cannot resolve single-chromosome heterogeneity. Here, we use antibody-functionalized atomic force spectroscopy to simultaneously map 5mC and H3K9me3 at the centromeres of individual metaphase chromosomes from non-tumorigenic, luminal, and triple-negative breast cancer (TNBC) cell models. Co-localized 5mC/H3K9me3 sites are mechanically stiffer than sites carrying either mark alone across the panel, revealing a cooperative biophysical signature of epigenetic crosstalk. Luminal chromosomes acquire the highest mark density, co-localization, and stiffness, whereas TNBC chromosomes show reduced density and diminished, though not absent, co-localization and stiffness, converging toward the low baseline of non-tumorigenic epithelium. TGF-{beta}1-induced epithelial-mesenchymal transition reproduces this attenuated phenotype in luminal cells, linking it directly to a process central to TNBC aggressiveness. These biophysical parameters classify cancer versus non-tumorigenic chromosomes with near-perfect, cross-validated accuracy, and further resolve the two TNBC subtypes using colocalization-derived features alone (macro-F1 = 0.933). These results establish the mechanical consequence of epigenetic mark co-localization as a single-chromosome-resolvable signature of centromeric organization, attenuated in aggressive breast cancer, and demonstrate a force-spectroscopy platform for mechano-epigenetic profiling of cancer chromosomes.

Cardiomyocyte contraction is essential for the pumping action of the heart and deteriorates after myocardial damage, either as a consequence of irreversible cardiomyocyte injury or stiffening of the extracellular matrix, a process described as fibrosis. Cell geometry and substrate stiffness not only influence sarcomere architecture and contractility, they also determine how much work the cardiomyocytes can transfer to their environment. Human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes provide a model system to examine these effects in a controlled manner, enabling us to mimic key features of the cardiac environment in vitro. Here we show that geometric confinement and substrate stiffness influence different aspects of cardiomyocyte force generation. By combining traction force microscopy and live-cell imaging of hiPSC-derived cardiomyocytes on soft and patterned substrates, we find that geometric confinement leads to longer resting sarcomeres and more pronounced sarcomere shortening on substrates with both physiological (10 kPa) and fibrotic (30 kPa) stiffness. Interestingly, the substrate stiffness itself has little effect on resting sarcomere length, but influences the peak contractile stress. On 10 kPa substrates, confined cells generate higher peak contractile stresses than unconfined cells, whereas this difference is not observed at 30 kPa. Confinement also results in faster mechanical relaxation at 10 kPa, with no detectable difference at 30 kPa. The combination of defined cell geometry and physiological stiffness leads to longer resting sarcomere lengths, more pronounced sarcomere shortening, higher peak contractile stress, and faster relaxation, features associated with a more mature cardiomyocyte phenotype. These findings show that the mechanical consequences of cell geometry depend on substrate stiffness and, therefore, both aspects have to be considered when employing hiPSC-derived cardiomyocytes as a model system in mechanobiology research, disease modeling and drug testing.

From flocking birds to swarming insects, collective motion enables groups to accomplish tasks beyond the capabilities of individuals. These behaviors emerge from local interactions among group members, but the interaction rules that organize collectives at the cellular scale remain poorly understood, in part because they are difficult to manipulate experimentally. Here we develop a cell-machine interface that enables us to rewrite the rules of collective migration. Cell-cell interaction rules are specified in software and implemented in living cells through real-time computer vision and closed-loop optogenetic control. Using a single engineered cell line, we program cells to self-organize into flocks, to propagate regenerative signal relays that recapitulate the interaction logic of immune-cell swarms, and to collectively navigate guidance cues that individual cells cannot. Our work shows that altering simple rules of cell-cell interaction is sufficient to generate new emergent collective capabilities. This approach provides an experimental framework for discovering the organizational principles of multicellular coordination and designing synthetic collectives with capabilities beyond those of their individual members.

The actin cytoskeleton drives shape changes and transport in cells and supports mechanical signal transmission. However, how cells control and use active cytoskeletal flows at the mesoscale is not well understood. We reconstituted an active cytoskeleton in water-in-oil emulsion droplets of Xenopus laevis egg extract and observed, above a critical droplet size, the emergence of a 3D radially convergent steady-state flow of polymeric actin, maintained by continuous actin turnover. The flow condensed lipid-rich cellular debris into a centered inclusion. Steady-state F-actin density and flow velocity profiles roughly collapse onto scale-invariant master curves. This behavior can be explained by a physical model representing the network as an isotropic active viscous fluid with a percolation threshold. The contracting network behaves as an active swimmer with complex internal dynamics that centers itself and the central inclusion inside the droplets without physical boundary attachment. Active contraction, crosslinking and polymerization dynamics in an actin network can thus generate cell-scale flow patterns that sense the confining geometry and external signals and exert forces that are likely sufficient to move and localize organelles in cells.

Compressive stress is a pervasive feature of solid tumour growth, and mechanical loading is known to activate calcium signalling through the mechanosensitive channel Piezo1. How this signal is converted into changes in cellular biosynthetic capacity, however, remains unclear. Here we show that compressive stress engages a Piezo1-dependent calcium checkpoint that reduces translational output with increasing mechanical load, independently of mTORC1 and the integrated stress response. Compression triggers Piezo1-dependent release of endoplasmic reticulum Ca2, activating eEF2 kinase to slow translational elongation. This same Ca2 signal drives mitochondrial remodelling and reactive oxygen species production, which reinforce translational repression through redox-dependent oxidation of the translation initiation factor eIF2{beta}. In parallel, Ca2-dependent AMPK activation triggers autophagic ribosome degradation, alleviating compression-induced macromolecular crowding and restoring cytoplasmic rheology despite sustained mechanical load. These mechanisms act at distinct levels of translational control: initiation, elongation and ribosome abundance; yet converge to limit biosynthetic output under compression. Consistent with a role for this pathway in tumour adaptation to mechanical constraint, eEF2K expression correlates with poor overall survival in a public PDAC patient dataset. Together, these findings define a mechano-metabolic checkpoint through which cells actively tune biosynthetic capacity to their physical environment.

Small numbers of cells can determine the fate of an entire organism. For example, metastatic cancer cells seed distant organs, therapy-resistant clones repopulate tumors, and T cells infiltrate and expand in tissues with matching antigens. Visualizing the activity of such cells in living organisms requires highly sensitive, specific and repeatable imaging in optically opaque tissues. Here we introduce cell chirp, an ultrasound imaging method for real-time imaging of single cells in living organs inaccessible to light. Cell chirp exploits the harmonic response of genetically encoded gas vesicles to frequency-coded ultrasound to sensitively and specifically visualize single cells in scattering background. We first develop this method in tissue-mimicking phantoms, demonstrating the ability to quantitatively detect single cells as validated by optical cell counts. We then establish the ability of cell chirp to image thousands of genetically labeled cells within a million-cell background tissue, track reporter gene expression over days, and suppress background signals by more than two orders of magnitude. Finally, we use cell chirp to track the fate of antigen-positive or antigen-negative tumor-cell minorities during weeks-long T-cell engager treatments. Cell chirp reveals the dynamics of sparsely distributed, genetically defined cells in opaque tissues.

Extracellular matrix (ECM)-mediated cell adhesion and tension regulate development and disease through crosstalk with Receptor Tyrosine Kinases (RTKs). RTKs stimulate proliferation, survival, and metabolic reprogramming via Ras/ERK and PI3K/Akt signaling. Emerging evidence identify the biophysical and biochemical integration of integrin-mediated adhesions with RTK signaling, however, the molecular mechanisms regulating this phenotype remain poorly understood. Here, we demonstrate that ECM stiffness potentiates ligand-mediated epidermal growth factor receptor (EGFR) signaling at scales ranging from the single adaptor protein, Grb2 upward to multicellular spheroids and tissues. We show that ECM stiffness-driven RTK signaling is mediated by integrin adhesions that reshape the membrane to induce the formation of RTK signaling hotspots distributed globally across the cell membrane. A parsimonious computational model and biochemical membrane perturbations causally implicate membrane curvature and topography in tension-dependent integrin-EGFR crosstalk. The results demonstrate how the mechanical properties of the ECM direct molecular recruitment and confinement of signaling molecules to regulate growth factor-dependent RTK signaling. Given that many RTK-driven solid tumors develop a stiff stroma, the findings could explain why many therapeutic tyrosine kinase inhibitors develop clinical resistance. The findings suggest clarifying how tension regulates transmembrane receptor signaling could identify unique force-dependent molecular regulators towards which new antitumor therapies could be applied.

Protein nanofibers are hold great promise as genetically programmable scaffolds for constructing functional material interfaces. AtaA, a giant trimeric autotransporter adhesin from Acinetobacter sp. Tol 5, forms an elongated architecture from the bacterial cell surface, enabling the cells to adhere directly to a wide variety of abiotic surfaces. However, the potential use of AtaA as a scaffold with additional biological functions remains largely unexplored. In this study, we investigated the use of AtaA as a self-immobilizing scaffold for constructing enzymatically active surfaces via horseradish peroxidase (HRP)-catalyzed tyrosine coupling. We prepared a recombinant AtaA nanofiber fragment (NhNs-AtaA) and its derivative containing two tyrosine-containing loop structures (YL-NhNs-AtaA). Both recombinant proteins retained their adhesive properties. Treatment with HRP and H2O2 generated high-molecular-weight products from both proteins, and dityrosine fluorescence emission indicated the formation of tyrosine-derived covalent cross-links. Y-Loop insertion further increased the consumption of monomeric AtaA and promoted the formation of high-molecular-weight products. The removal of arginine, which was included during purification, further increased the loss of monomeric AtaA in both constructs, indicating that intermolecular protein association influenced productive AtaA cross-linking. NhNs-AtaA and YL-NhNs-AtaA were combined with Y-tagged bacterial alkaline phosphatase (BAP-Y). HRP-mediated coupling generated high-molecular-weight products consistent with the cross-linked AtaA-BAP-Y conjugates and enabled the retention of BAP activity on AtaA-coated surfaces without prior chemical modification. Although Y-Loop insertion enhanced polymerization in solution, it reduced AtaA adhesion and consequently lowered surface-bound phosphatase activity, revealing a trade-off between cross-linking reactivity and native adhesive function. These findings establish AtaA as a self-immobilizing protein nanofiber scaffold for constructing enzymatically active surfaces, and suggest the potential extension of this strategy to other AtaA-based interfaces.

Granular hydrogels, made of jammed soft microparticles, are of great interest for 3D (bio)printing, as they combine ideal rheological properties and extensive modularity, yielding favorable microstructures for tissue engineering. Typically, the yield-stress properties of these materials, which facilitate printability, are defined by the preparation state and the initial particle content of the hydrogel. Here, we propose a granular hydrogel whose yield-stress and, consequently, printability and printed scaffolds shape retention can be controlled not only by the initial weight fraction of particles but also by their stimuli-responsive swelling. The responsive microgels are prepared from poly(N-isopropylacrylamide) crosslinked by dynamic covalent disulfide bonds. The particles swelling is triggered by reduction-induced cleavage of the disulfide bonds into two pendant thiol groups, enabling printing of multilayer scaffolds with high shape fidelity. Without chemically induced swelling, the same formulation requires higher particle concentrations to be printable. Importantly, the printed structures can be annealed by oxidizing the thiol units back into disulfide inter-particle bonds. The printed scaffolds are compatible with human dermal fibroblasts (HDF) and support cell-material interactions. This system offers a unique opportunity for on-demand modulation of both printability and scaffold microstructure, enabling unique control over local stiffness, packing density, and porosity in granular scaffolds.

Many protein kinases, ubiquitous signal transducers across all kingdoms of life, are activated by phosphorylation of one or more conserved residues in their activation loops. This reaction is widely considered to be intermolecular (trans) in nature, dependent on the transient dimerization of two kinase domains. However, since the substrate, product and reaction chemistry are identical, bulk solution kinase assays cannot distinguish between intra- and inter-molecular reactions. Discriminating between these two mechanisms is crucial because they impose different requirements on the cell for acute, high-fidelity signal transduction. Using single-molecule reaction chambers fabricated from DNA origami, we show that the paradigmatic insulin receptor kinase (IRK) undergoes intramolecular (cis) autophosphorylation with kinetics indistinguishable from those in free solution. Furthermore, we demonstrate that the bacterial serine/threonine kinase protein kinase B (PknB) undergoes intramolecular autophosphorylation, allosterically stimulated by intermolecular (trans) interactions. Our findings establish that intramolecular activation loop autophosphorylation is not only possible, but likely an ancient and conserved feature of protein kinase signaling. More broadly, our work provides new tools for single-molecule enzymology.

Membrane tension, defined as the energy cost to expand the membrane surface area, is a fundamental mechanical property of the lipid bilayer and an important modulator of various cellular processes. Liposomes provide model systems to study protein-mediated membrane dynamics, where membrane tension can be controlled by osmotic pressure and micropipette aspiration. However, it is challenging to individually control membrane tension of nanometer-sized liposomes, such as small unilamellar vesicles (SUVs), that are widely used for modeling subcellular membrane structures and drug delivery. To bridge this technological gap, we present reconfigurable DNA origami rings for dynamically controlling membrane tension of sub-100 nm liposomes. The DNA nanorings template the formation of uniformly sized SUVs and undergo trigger-responsive dilation and contraction, thus applying controlled and reversible mechanical stress to the SUV membranes. Electron microscopy analyses show deformed liposomes with ~2.5% expanded membrane area following ring dilation. The corresponding increase in membrane tension opens a mechanosensitive ion channel MscL with gating tension of ~10 mN/m. Selectively manipulating a mixture of SUV populations enables timed release of their distinct molecular cargos, either concurrently or one at a time. Furthermore, vesicles with expanded membranes are more conducive to SNARE-mediated fusion. The nanomechanical device thus provides a programmable platform for engineering the mechanics of synthetic nano-vesicles and studying membrane tension modulated processes at the molecular level.

Liquid-liquid phase separation is a vital and ubiquitous principle of subcellular organization. Several actin-binding proteins have recently been shown to undergo liquid-liquid phase separation, forming micron-sized droplets that assemble actin into distinct network shapes. However, our knowledge of how these phase-separated proteins organize actin filaments at the nanoscale is rather limited. Here, we seek to address this knowledge gap by investigating synapsin-1 condensates through a combination of computational simulations and nanoscale imaging experiments. Our results show that while synapsin-1 condensates by themselves lack any special structural organization, the addition of actin filaments results in the generation of a regularly organized actin scaffold within the condensates. The organized scaffold forms both when actin and synapsin-1 are added simultaneously and when actin is added after the formation of synapsin condensates. Dissolving the condensates, by synapsin-1 removal, leaves the actin scaffold largely unaffected in both simulations and experiments, implying that this scaffold should guide droplet reformation when synapsin-1 is added back. Taken together, our findings suggest that the actin-rich component of the condensate retains a structural memory that promotes and guides the reassembly of synapsin-actin condensates. This structural memory may be important in the long-term maintenance of synaptic function in vivo.

Reactive carbonyl metabolites such as methylglyoxal (MGO) accumulate in diabetes, aging, and metabolic disease, conditions frequently associated with pathological stiffening of human cells and tissues. While glycation of extracellular matrices and cytoskeletal proteins is known to contribute to these mechanical changes, whether the nucleus itself is a direct mechanical target of carbonyl stress remains unknown. Here, by combining advanced atomic force microscopy-based nanomechanical probing with correlative confocal imaging, we show that MGO-derived glycation directly remodels isolated cell nuclei, increasing stiffness, reducing fluidity, and restricting intranuclear deformation propagation. MGO-derived adducts accumulate prominently at the nuclear envelope, and perturbation of lamin A/C and chromatin state reveals that both structures contribute to glycation-induced stiffening. In cells, chronic MGO exposure induces nucleus-intrinsic stiffening and biases YAP nuclear localization in a substrate-stiffness-dependent manner, linking nuclear glycation to altered mechanosensitive regulation. In vivo, cardiac nuclear stiffening is only observed along with increased immunodetected MGO-adduct burden, while nuclear fluidity remains largely preserved. Together, these findings establish nonenzymatic glycation as a metabolic mechanism that remodels nuclear mechanics and alters cellular mechanosensing, revealing a previously unrecognized physical consequence of carbonyl stress.

Selectively perturbing pathogenic membranes while preserving host-cell integrity is a fundamental challenge in the design of membrane-active biomaterials. This challenge is particularly acute for enveloped viruses because their lipid membranes are derived from host cells and therefore share many of the same molecular constituents. Here, we demonstrate that engineered nanochirality provides a structural parameter for distinguishing virus-organized membrane nanodomains from host-cell membranes. Histidine-functionalized graphene quantum dots (His-GQDs) form enantiomeric nanoscale structures with distinct interfacial topologies despite closely matched size, composition, and surface charge. D-His-GQDs preferentially interact with cholesterol-rich ordered membrane nanodomains associated with S-acylated coronavirus Spike, penetrate more deeply into raft-like lipid bilayers, and induce lipid disordering, membrane leakage, and viral-envelope disruption. Reducing Spike S-acylation or depleting membrane cholesterol attenuated this stereoselective interaction, while molecular simulations revealed asymmetric lipid organization surrounding S-acylated Spike and preferential insertion of D-His-GQDs into the ordered membrane environment. Functionally, D-His-GQDs directly inactivated human coronavirus OC43 (HCoV-OC43), inhibited infection with an EC50 of 0.92 g/mL and exhibited a selectivity index of 361. Stereoselective antiviral activity extended to human cytomegalovirus, demonstrating activity across distinct enveloped-virus families, and intranasal D-His-GQDs protected HCoV-OC43-challenged mice under both prophylactic and early post-exposure regimens. Overall, these findings establish structural nanochirality as a biomaterial design parameter for recognizing higher-order membrane organization and converting virus-associated membrane states into selectively addressable therapeutic vulnerabilities.