Efficient navigation and precise localization of Brownian micro/nano self-propelled motor particles within complex landscapes could enable future high-tech applications involving for example drug delivery, precision surgery, oil recovery, and environmental remediation. Here we employ a model-free deep reinforcement learning algorithm based on bio-inspired neural networks to enable different types of micro/nano motors to be continuously controlled to carry out complex navigation and localization tasks. Micro/nano motors with either tunable self-propelling speeds or orientations or both, are found to exhibit strikingly different dynamics. In particular, distinct control strategies are required to achieve effective navigation in free space and obstacle environments, as well as under time constraints. Our findings provide fundamental insights into active dynamics of Brownian particles controlled using artificial intelligence and could guide the design of motor and robot control systems with diverse application requirements.
Motor proteins display widely different stepping patterns as they move on microtubule tracks, from the deterministic linear or helical motion performed by the protein kinesin to the uncoordinated random steps made by dynein. How these different strategies produce an efficient navigation system needed to ensure correct cellular functioning is still unclear. Here, we show by numerical simulations that deterministic and random motor steps yield different outcomes when random obstacles decorate the microtubule tracks: kinesin moves faster on clean tracks but its motion is strongly hindered on deco…
We use molecular dynamics simulations to investigate the displacement of a simple butterfly-like molecular motor inside nanopores of various radii filled with a viscous medium. The medium is modeled with a versatile potential that may be adjusted to represent a large number of materials. It was found previously that the motor folding not only increases its displacement but also creates elementary diffusion processes inside the medium, related to the opening angle of the motor folding. The presence of these processes changes the medium dynamics and in turn affects the motor displacement. Theref…
Control and transport of nanoscale objects in fluids is challenging because of the unfavorable scaling of most interaction mechanisms to small length scales. We design energy landscapes for nanoparticles by accurately shaping the geometry of a nanofluidic slit and exploiting the electrostatic interaction between like charged particles and walls. Directed transport is performed by combining asymmetric potentials with an oscillating electric field to achieve a rocking Brownian motor. Using 60\,nm diameter gold spheres, we investigate the physics of the motors with high spatio-temporal resolution…
Several designs for micro-devices for chemotaxis based on nano-motors are proposed. The nano- or micro-motors are the conventional Janus rods or spheres that are powered by the catalytic reaction of fuels such as hydrogen peroxide. It is shown how these can be linked to make a device that can follow a concentration gradient of the fuel. The feasibility of assembling the devices using micromanipulation or metallic deposition is discussed. A possible design principle is suggested for a device that follows the concentration gradient of an analyte other than the fuel.
Motion of active particles, such as catalytic micro- and nano-motors, is usually characterized via either dynamic light scattering or optical microscopy. In both cases, speed of particles is obtained from the calculus of the mean square displacement (MSD) and typically, the theoretical formula of the MSD is derived from the motion equations of an active Brownian particle. One of the most commonly reported parameters is the speed of the particle, usually attributed to its propulsion, and is widely used to compare the motion efficiency of catalytic motors. However, it is common to find different…
Biological motors are marvels of nature that inspire creation of their synthetic counterparts with comparable nanoscale dimensions, high efficiency and diverse functions. Molecular motors have been synthesized, but obtaining nanomotors through self-assembly remains challenging. Here we describe a self-assembled colloidal motor with a repetitive light-driven rotation of transparent micro-particles immersed in a liquid crystal and powered by a continuous exposure to unstructured ~1 nW light. A monolayer of azobenzene molecules defines how the liquid crystal's optical axis mechanically couples to…
Like their larger micron-scale counterparts, Ångström-scale chemically self-propelled motors use asymmetric catalytic activity to produce self-generated concentration gradients that lead to directed motion. Unlike their micron-scale counterparts, the sizes of Ångström-scale motors are comparable to the solvent molecules in which they move, they are dominated by fluctuations, and they operate on very different time scales. These new features are studied using molecular dynamics simulations of small sphere dimer motors. We show that the ballistic regime is dominated by the thermal speed but the …
We have developed a two dimensional stochastic molecular dynamics model for the description of intra cellular collective motion of bio motors, in particular Kinesins, on a microtubular track. The model is capable or reproducing the hand-over-hand mechanism of the directed motion along the microtubule. The model gives the average directed velocity and the current of Kinesins along the microtubule. It is shown that beyond a certain density of Kinesins, the average velocity and current undergo notable decrease which is due to formation of traffic jams in the system.
Micro/Nano motors are micro to nano-sized particles and systems that are capable of motion in fluidic systems. Their motion can be a result of many mechanisms, one of the most well-known of which is electrolyte diffusiophoresis, in which asymmetric production of charged ions across the surface of the particle leads to phoresis. The focus of this work is to construct Urease motors with careful control of their Janus balance, i.e., to control the percentage of surface covered with the enzyme and study the effect of this asymmetry on the propulsion velocity of the particles. In that regard, we we…
In this article, we develop a mathematical model for the rotary bacterial flagellar motor (BFM) based on the recently discovered structure of the stator complex (MotA$_5$MotB$_2$). The structure suggested that the stator also rotates. The BFM is modeled as two rotating nano-rings that interact with each other. Specifically, translocation of protons through the stator complex drives rotation of the MotA pentamer ring, which in turn drives rotation of the FliG ring in the rotor via interactions between the MotA ring of the stator and the FliG ring of the rotor. Preliminary results from the struc…
Flow-driven rotary motors drive functional processes in human society such as windmills and water wheels. Although examples of such rotary motors also feature prominently in cell biology, their synthetic construction at the nanoscale has thus far remained elusive. Here, we demonstrate flow-driven rotary motion of a self-organized DNA nanostructure that is docked onto a nanopore in a thin solid-state membrane. An elastic DNA bundle self assembles into a chiral conformation upon phoretic docking onto the solid-state nanopore, and subsequently displays a sustained unidirectional rotary motion of …
Active media, whose constituents are able to move autonomously, display novel features that differ from those of equilibrium systems. In addition to naturally-occurring active systems such as populations of swimming bacteria, active systems of synthetic self-propelled nanomotors have been developed. These synthetic systems are interesting because of their potential applications in a variety of fields. Janus particles, synthetic motors of spherical geometry with one hemisphere that catalyzes the conversion of fuel to product and one noncatalytic hemisphere, can propel themselves in solution by …
Micromotor and nanomotor particles are typically made using dense solid particles that can sediment or be trapped in confined flow environments. Creation of much larger motors should be possible if a very low-density system is used with sufficient strength to carry liquid and still experience propulsive motion. Light, dense millimotors should also be able to deform more than dense solid ones in constrictions. Millimotors are created from permeable capsules of bacterial cellulose that are coated with catalase-containing metal-organic frameworks, enabling reactive propulsion in aqueous hydrogen …
A computational method for magnetically guided drug delivery is presented and the results are compared for the aggregation process of magnetic particles within a fluid environment. The model is developed for the simulation of the aggregation patterns of magnetic nanoparticles under the influence of MRI magnetic coils. A novel approach for the calculation of the drag coefficient of aggregates is presented. The comparison against experimental and numerical results from the literature is showed that the proposed method predicts well the aggregations in respect to their size and pattern dependance…
Using molecular dynamics simulations we compare the motion of a nano-swimmer based on Purcell suggested motor with a time asymmetrical cycle with the motion of the same molecular motor with a time symmetrical cycle. We show that Purcell theorem still holds at the nanoscale, despite the local structure and the medium fluctuations. Then, with the purpose of both orienting the swimmer displacement and increasing the breakdown of the theorem, we study the effect of an electric field on a polarized version of these swimmers. For small and large fields, the time asymmetrical swimmer is more efficien…
A reversal of the particle current in rocking Brownian motors was predicted more than 20 years ago; however, an experimental verification and a deeper insight into the underlying mechanisms remained elusive. Here, we investigate the high frequency behaviour of a rocking Brownian motor for charged nanoparticles based on electrostatic interactions in a 3D shaped nanofluidic slit and electro-osmotic forcing of the particles. A sub ms temporal and $\approx\,10\,$nm spatial resolution of the 60 nm gold spheres allows us to measure the time-resolved and frequency dependent evolution of the particle …
A Brownian Motor is a nanoscale or molecular device that combines the effects of thermal noise, spatial or temporal asymmetry, and directionless input energy to drive directed motion. Because of the input energy, Brownian motors function away from thermodynamic equilibrium and concepts such as linear response theory, fluctuation dissipation relations, and detailed balance do not apply. The {\em generalized} fluctuation-dissipation relation, however, states that even under strongly thermodynamically non-equilibrium conditions the ratio of the probability of a transition to the probability of th…
Self-propelling bacteria are a dream of nano-technology. These unicellular organisms are not just capable of living and reproducing, but they can swim very efficiently, sense the environment and look for food, all packaged in a body measuring a few microns. Before such perfect machines could be artificially assembled, researchers are beginning to explore new ways to harness bacteria as propelling units for micro-devices. Proposed strategies require the careful task of aligning and binding bacterial cells on synthetic surfaces in order to have them work cooperatively. Here we show that asymmetr…
The more we learn about the cytoplasm of cells, the more we realise that the cytoplasm is not uniform but instead is highly inhomogeneous. In any inhomogeneous solution, there are concentration gradients, and particles move either up or down these gradients due to a mechanism called diffusiophoresis. I estimate that inside metabolically active cells, the dynamics of particles can be strongly accelerated by diffusiophoresis, provided that they are at least tens of nanometres across. The dynamics of smaller objects, such as single proteins are largely unaffected.
We show that the correlated stochastic fluctuation of the friction coefficient can give rise to long-range directional motion of a particle undergoing Brownian random walk in a constant periodic energy potential landscape. The occurrence of this motion requires the presence of two additional independent bodies interacting with the particle via friction and via the energy potential, respectively, which can move relative to each other. Such three-body system generalizes the classical Brownian ratchet mechanism, which requires only two interacting bodies. In particular, we describe a simple two-l…
The efficiency of bio-molecular motors stems from reversible interactions $\sim$ $k_B T$; weak bonds stabilizing intermediate states (enabling $direct$ conversion of chemical into mechanical energy). For their (unknown) origins, we suggest that a magnetically structured phase (MSP) formed via accretion of super-paramagnetic particles (S-PPs) by magnetic rocks on the Hadean Ocean floor had hosted motor-like diffusion of ligand-bound S-PPs through its template-layers; its ramifications range from optical activity to quantum coherence. A gentle flux gradient offers both detailed-balance breaking …
