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Driving macro-scale transformations in three-dimensional-printed biopolymers through controlled induction of molecular anisotropy at the nanoscale
Full text linkMotivated by the need to harness the properties of renewable and biodegradable polymers for the design and manufacturing of multi-scale structures with complex geometries, we have employed our additive manufacturing platform that leverages molecular self-assembly for the production of metre-scale structures characterized by complex geometries and heterogeneous material composition. As a precursor material, we used chitosan, a chemically modified form of chitin, an abundant and sustainable structural polysaccharide. We demonstrate the ability to control concentration-dependent crystallization as well as the induction of the preferred orientation of the polymer chains through the combination of extrusion-based robotic fabrication and directional toolpathing. Anisotropy is demonstrated and assessed through high-resolution micro-X-ray diffraction in conjunction with finite element simulations. Using this approach, we can leverage controlled and user-defined small-scale propagation of residual stresses to induce large-scale folding of the resulting structures
Orientational Behavior and Vibrational Response of Glycine at Aqueous Interfaces
Full text linkAqueous glycine plays many different roles in living systems, from being a building block for proteins to being a neurotransmitter. To better understand its fundamental behavior, we study glycine's orientational behavior near model aqueous interfaces, in the absence and presence of electric fields and biorelevant ions. To this purpose, we use a surface-specific technique called heterodyne-detected vibrational sum-frequency generation spectroscopy (HD-VSFG). Using HD-VSFG, we directly probe the symmetric and antisymmetric stretching vibrations of the carboxylate group of zwitterionic glycine. From their relative amplitudes, we infer the zwitterion's orientation near surfactant-covered interfaces and find that it is governed by both electrostatic and surfactant-specific interactions. By introducing additional ions, we observe that the net orientation is altered by the enhanced ionic strength, indicating a change in the balance of the electrostatic and surfactant-specific interactions
Temperature Effects and Activation Barriers in Aqueous Proton-Uptake Reactions
Full text linkAqueous proton transfer reactions are fundamental in biology and chemistry, yet kinetics and mechanisms of strong base-weak acid reactions are not well understood. In this work, we present a temperature-dependent reaction kinetic study of the water-soluble photobase actinoquinol, in the presence and absence of succinimide, a weak acid reaction partner. We study the temperature dependence of the reaction and connect the observed dynamics to the reaction’s thermodynamics. We find that actinoquinol reacts in associated complexes with water/succinimide, creating an intermediate complex that can undergo either dissociation to create products, or reverse proton transfer within the complex to recreate the initial reactants. We find that the intermediates’ formation is energetically unfavorable with both reaction partners, which impacts the net reaction rates. We also find that the net reaction rate is additionally strongly influenced by the competition between the dissociation of the intermediates and their reverse reaction
Nano-optomechanical fiber-tip sensing
Full text linkNano-optomechanical sensors exploit light confinement at the nanoscale to enable very precise measurements of displacement, force, acceleration, and mass. Their application is hampered by the complex optical set-ups or packaging schemes required to couple light to and from the nano-optomechanical resonator. In this work, we present a fiber-coupled nano-optomechanical sensor that requires no coupling optics. This is achieved by directly placing a nano-optomechanical structure, a double membrane photonic crystal (DM-PhC), on the facet of a fiber, using a simple and scalable wafer-to-fiber transfer method. The device is probed in reflection and has a resonance at telecom wavelengths with a relatively broad spectral width of 3–10 nm, which is advantageous for a simple read-out and achieves a displacement imprecision of . Using resonant driving and a ringdown measurement, we can induce and monitor mechanical oscillations with an nm-scale amplitude via the fiber, which allows for tracking the mechanical resonant frequency and the mechanical linewidth with imprecisions of 79 and 12 Hz, respectively, at integration times of 4.5 s. We further demonstrate the application of this fiber-tip sensor to the measurement of pressure, using the effect of collisional damping on the mechanical linewidth, leading to the imprecision of with an integration time of 290 s. This combination of optomechanics and fiber-tip sensing may open the way to a new generation of fiber sensors with unprecedented functionality, ultrasmall footprint, and low-cost readout
Bio-inspired autonomy in soft robots
Full text linkSoft robotic actuation concepts meet and sometimes exceed their natural counterparts. In contrast, artificially recreating natural levels of autonomy is still an unmet challenge. Here, we come to this conclusion after defining a measure of energy- and control-autonomy and classifying a representative selection of soft robots. We argue that, in order to advance the field, we should focus our attention on interactions between soft robots and their environment, because in nature autonomy is also achieved in interdependence. If we better understand how interactions with an environment are leveraged in nature, this will enable us to design bio-inspired soft robots with much greater autonomy in the future
With the leisure of time, kinetic proofreading can still perform reliable ligand discrimination
Full text linkKinetic proofreading is a canonical scheme believed to be
responsible for the high ligand discrimination capacity of
many biochemical processes. In a recent PNAS publication,
Kirby and Zilman studied kinetic proofreading for receptor
signaling and argued that when stochasticity is taken into
account, having more proofreading steps does not generally
improve the discrimination of different receptor-binding lig-
ands based on counts of signaling molecules produced (1)
Path Weight Sampling: Exact Monte Carlo Computation of the Mutual Information between Stochastic Trajectories
Full text linkMost natural and engineered information-processing systems transmit information via signals that vary in time. Computing the information transmission rate or the information encoded in the temporal characteristics of these signals requires the mutual information between the input and output signals as a function of time, i.e., between the input and output trajectories. Yet, this is notoriously difficult because of the high-dimensional nature of the trajectory space, and all existing techniques require approximations. We present an exact Monte Carlo technique called path weight sampling (PWS) that, for the first time, makes it possible to compute the mutual information between input and output trajectories for any stochastic system that is described by a master equation. The principal idea is to use the master equation to evaluate the exact conditional probability of an individual output trajectory for a given input trajectory and average this via Monte Carlo sampling in trajectory space to obtain the mutual information. We present three variants of PWS, which all generate the trajectories using the standard stochastic simulation algorithm. While direct PWS is a brute-force method, Rosenbluth-Rosenbluth PWS exploits the analogy between signal trajectory sampling and polymer sampling, and thermodynamic integration PWS is based on a reversible work calculation in trajectory space. PWS also makes it possible to compute the mutual information between input and output trajectories for systems with hidden internal states as well as systems with feedback from output to input. Applying PWS to the bacterial chemotaxis system, consisting of 182 coupled chemical reactions, demonstrates not only that the scheme is highly efficient but also that the number of receptor clusters is much smaller than hitherto believed, while their size is much larger
Dual-color DNA-PAINT single-particle tracking enables extended studies of membrane protein interactions
Full text linkDNA-PAINT based single-particle tracking (DNA-PAINT-SPT) has recently significantly enhanced observation times in in vitro SPT experiments by overcoming the constraints of fluorophore photobleaching. However, with the reported implementation, only a single target can be imaged and the technique cannot be applied straight to live cell imaging. Here we report on leveraging this technique from a proof-of-principle implementation to a useful tool for the SPT community by introducing simultaneous live cell dual-color DNA-PAINT-SPT for quantifying protein dimerization and tracking proteins in living cell membranes, demonstrating its improved performance over single-dye SPT
Hydrogel Microrobots Self‐Assembled into Ordered Structures with Programmable Actuation
Full text linkSub-millimeter robots—microrobots—that can autonomously perform mechanical work at the microscale would radically change new areas of human activity such as micromanipulation, microfabrication, or healthcare. Sets of identical microrobots that can connect into different, larger structures open the possibility for a “universal” microrobotic unit that fulfills a large variety of functions derived from the structure that multiple units can be assembled into. The capability of individual hydrogel microcrawlers to self-assemble under confinement into periodically ordered planar structures is demonstrated. Subsequently, these can be bound together using light to form a solid porous sheet. The lateral shape of the sheet is imprinted during the binding process. Furthermore, the sheets bend into 3D structures, where the bending direction can be programmed. The resulting structures actuate anisotropically when exposed to heat or laser illumination and can be designed for various modes of operation, such as manipulation or untethered locomotion. The formation of ordered microstructures from individual mobile robots enables easier transport and remote assembly of these structures at the place of interest without the need for direct intervention
Chiral Seeded Growth of Gold Nanorods Into Fourfold Twisted Nanoparticles with Plasmonic Optical Activity
Full text linkA robust and reproducible methodology to prepare stable inorganic nanoparticles with chiral morphology may hold the key to the practical utilization of these materials. An optimized chiral growth method to prepare fourfold twisted gold nanorods is described herein, where the amino acid cysteine is used as a dissymmetry inducer. Four tilted ridges are found to develop on the surface of single-crystal nanorods upon repeated reduction of HAuCl4, in the presence of cysteine as the chiral inducer and ascorbic acid as a reducing agent. From detailed electron microscopy analysis of the crystallographic structures, it is proposed that the dissymmetry results from the development of chiral facets in the form of protrusions (tilted ridges) on the initial nanorods, eventually leading to a twisted shape. The role of cysteine is attributed to assisting enantioselective facet evolution, which is supported by density functional theory simulations of the surface energies, modified upon adsorption of the chiral molecule. The development of R-type and S-type chiral structures (small facets, terraces, or kinks) would thus be non-equal, removing the mirror symmetry of the Au NR and in turn resulting in a markedly chiral morphology with high plasmonic optical activity