Nanoactuators and nanomachines have long been sought after, but key bottlenecks remain. Forces at submicrometer scales are weak and slow, control is hard to achieve, and power cannot be reliably supplied. Despite the increasing complexity of nanodevices such as DNA origami and molecular machines, rapid mechanical operations are not yet possible. Here, we bind temperatureresponsive polymers to charged Au nanoparticles, storing elastic energy that can be rapidly released under light control for repeatable isotropic nanoactuation. Optically heating above a critical temperature T c = 32°C using plasmonic absorption of an incident laser causes the coatings to expel water and collapse within a microsecond to the nanoscale, millions of times faster than the base polymer. This triggers a controllable number of nanoparticles to tightly bind in clusters. Surprisingly, by cooling below T c their strong van der Waals attraction is overcome as the polymer expands, exerting nanoscale forces of several nN. This large force depends on van der Waals attractions between Au cores being very large in the collapsed polymer state, setting up a tightly compressed polymer spring which can be triggered into the inflated state. Our insights lead toward rational design of diverse colloidal nanomachines.ctuators are needed to turn energy sources into physical movement. These can be for microrobotics, sensing, storage devices, smart windows and walls, or more general functional and active materials. Such artificial muscles have gained rapidly increasing interest (1, 2) leading to micropropellers (3, 4), gas jets from catalytic surfaces (5), and DNA machines (6). However, the actuation methods, delivery of energy, and forces obtained (typically 10 fN/nm 2 ) are limited so far (7): Magnetic fields are inconvenient to apply locally for actuation, as is >200°C heating to actuate polymer fibers; the nanocatalysis of chemical fuels lacks controllability, whereas DNA machines rely on "fuel" DNA strands to competitively bind and operate on very slow (second) timescales. Piezoelectric-type materials used in high-end instrumentation (such as atomic force microscopy or nanopositioning stages) provide short travel but with inorganic materials that are dense, delicate, expensive, hard to fabricate, and demand high voltages (150-300 V), as is also true for electrostrictive rubbers and relaxor ferroelectrics (8, 9). Many biological systems such as Escherichia coli (10), cilia (11), or nematocysts (12) provide sophisticated models for nanomachines (13). Although molecular motors and artificial muscles from hydrogels (14, 15), colloids (16), or liquid crystalline elastomers (17, 18) successfully mimic such behaviors, they are very slow (on the order of seconds) and the forces generated are very small (∼ pN). This is because either the energy density stored in the system is low or the energy release is inefficient.To overcome this we design a colloidal actuating transducer system with high-energy storage (1,000 k B T/cycle) and fast (>MHz) release mechanism....

Many natural silks produced by spiders and insects are unique materials in their exceptional toughness and tensile strength, while being lightweight and biodegradable–properties that are currently unparalleled in synthetic materials. Myriad approaches have been attempted to prepare artificial silks from recombinant spider silk spidroins but have each failed to achieve the advantageous properties of the natural material. This is because of an incomplete understanding of the in vivo spidroin-to-fiber spinning process and, particularly, because of a lack of knowledge of the true morphological nature of spidroin nanostructures in the precursor dope solution and the mechanisms by which these nanostructures transform into micrometer-scale silk fibers. Herein we determine the physical form of the natural spidroin precursor nanostructures stored within spider glands that seed the formation of their silks and reveal the fundamental structural transformations that occur during the initial stages of extrusion en route to fiber formation. Using a combination of solution phase diffusion NMR and cryogenic transmission electron microscopy (cryo-TEM), we reveal direct evidence that the concentrated spidroin proteins are stored in the silk glands of black widow spiders as complex, hierarchical nanoassemblies (∼300 nm diameter) that are composed of micellar subdomains, substructures that themselves are engaged in the initial nanoscale transformations that occur in response to shear. We find that the established micelle theory of silk fiber precursor storage is incomplete and that the first steps toward liquid crystalline organization during silk spinning involve the fibrillization of nanoscale hierarchical micelle subdomains.

Fibrillar collagens have mechanical and biological roles, providing tissues with both tensile strength and cell binding sites which allow molecular interactions with cell-surface receptors such as integrins. A key question is: how do collagens allow tissue flexibility whilst maintaining well-defined ligand binding sites? Here we show that proline residues in collagen glycine-proline-hydroxyproline (Gly-Pro-Hyp) triplets provide local conformational flexibility, which in turn confers well-defined, low energy molecular compression-extension and bending, by employing two-dimensional 13C-13C correlation NMR spectroscopy on 13C-labelled intact ex vivo bone and in vitro osteoblast extracellular matrix. We also find that the positions of Gly-Pro-Hyp triplets are highly conserved between animal species, and are spatially clustered in the currently-accepted model of molecular ordering in collagen type I fibrils. We propose that the Gly-Pro-Hyp triplets in fibrillar collagens provide fibril “expansion joints” to maintain molecular ordering within the fibril, thereby preserving the structural integrity of ligand binding sites.

Melanin is a ubiquitous natural pigment found in a diverse array of organisms. Allomelanin is a class of nitrogen-free melanin often found in fungi. Herein, we find artificial allomelanin analogues exhibit high intrinsic microporosity and describe an approach for further increasing and tuning that porosity. Notably, the synthetic method involves an oxidative polymerization of 1,8-DHN in water, negating the need for multiple complex templating steps and avoiding expensive or complex chemical precursors. The well-defined morphologies of these nanomaterials were elucidated by a combination of electron microscopy and scattering methods, yielding to high-resolution 3D reconstruction based on small-angle X-ray scattering (SAXS) results. Synthetic allomelanin nanoparticles exhibit high BET areas, up to 860 m 2 /g, and are capable of ammonia capture up to 17.0 mmol/g at 1 bar. In addition, these nanomaterials can adsorb nerve agent simulants in solution and as a coating on fabrics with high breathability where they prevent breakthrough. We also confirmed that naturally derived fungal melanin can adsorb nerve gas simulants in solution efficiently despite lower porosity than synthetic analogues. Our approach inspires further analysis of yet to be discovered biological materials of this class where melanins with intrinsic microporosity may be linked to evolutionary advantages in relevant organisms and may in turn inspire the design of new high surface area materials.