A self-powered kinesin-microtubule system for smart cargo delivery

Molecular Machines and Microrobots: Nanoarchitectonics Developments and On-Water Performances

This review will focus on micromachines and microrobots, which are objects at the micro-level with similar machine functions, as well as nano-level objects such as molecular machines and nanomachines. The paper will initially review recent examples of molecular machines and microrobots that are not limited to interfaces, noting the diversity of their functions. Next, examples of molecular machines and micromachines/micro-robots functioning at the air-water interface will be discussed. The behaviors of molecular machines are influenced significantly by the specific characteristics of the air-water interface. By placing molecular machines at the air-water interface, the scientific horizon and depth of molecular machine research will increase dramatically. On the other hand, for microrobotics, more practical and advanced systems have been reported, such as the development of microrobots and microswimmers for environmental remediations and biomedical applications. The research currently being conducted on the surface of water may provide significant basic knowledge for future practical uses of molecular machines and microrobots.

Polymer-Carrying Ability of Actin Filaments Interacting with Myosin Motors in a Biological Motility System In Vitro

The reconstituted motility system of actin-myosin is expected to be used in bioinspired transport devices, in which carried materials are attached to either moving actin filaments or walking myosin molecules. However, the dependence of the ability to transport on the size of the attached materials is still inadequately understood. Here, as carried materials, polyethylene glycols (PEGs) of various sizes are covalently bound to actin filaments, and the motility of PEG-attached filaments on a heavy meromyosin immobilized on a glass surface is observed via fluorescence microscopy. Full attachment of 2 kDa PEG, with an approximately 2 nm gyration radius, decreases the velocity and fraction of moving actin filaments by approximately 10% relative to unattached filaments. For the 5 kDa PEG, the fraction of moving filaments is decreased by approximately 70% even when the filaments contain only 20% PEG-attached actin. The attachment of both sizes of PEGs suppresses the actin-activated ATPase activity at the same level. These results suggest that actin filaments can carry PEGs up to 2 kDa having the same size as actin monomers, while the rate of ATP hydrolysis is limited. The size-dependence may provide a criterion for material delivery via actin filaments in nanotransport applications. This article is protected by copyright. All rights reserved.

Nanoarchitectonics beyond Self-Assembly: Challenges to Create Bio-Like Hierarchic Organization

Incorporation of non-equilibrium actions in the sequence of self-assembly processes would be an effective means to establish bio-like high functionality hierarchical assemblies. As a novel methodology beyond self-assembly, nanoarchitectonics, which has as its aim the fabrication of functional materials systems from nanoscopic units through the methodological fusion of nanotechnology with other scientific disciplines including organic synthesis, supramolecular chemistry, microfabrication, and bio-process, has been applied to this strategy. The application of non-equilibrium factors to conventional self-assembly processes is discussed on the basis of examples of directed assembly, Langmuir-Blodgett assembly, and layer-by-layer assembly. In particular, examples of the fabrication of hierarchical functional structures using bio-active components such as proteins or by the combination of bio-components and two-dimensional nanomaterials, are described. Methodologies described in this review article highlight possible approaches using the nanoarchitectonics concept beyond self-assembly for creation of bio-like higher functionalities and hierarchical structural organization.

Synchronous operation of biomolecular engines

Biomolecular motor systems are the smallest natural machines with an ability to convert chemical energy into mechanical work with remarkably high efficiency. Such attractive features enabled biomolecular motors to become classic tools in soft matter research over the past decade. For designing suitably engineered biomimetic systems, the biomolecular motors can potentially be used as molecular engines that can transform energy and ensure great advantages for the construction of bio-nanodevices and molecular robots. From the optimization of their prolonged lifetime to coordinate them into highly complex and ordered structures, enormous efforts have been devoted to make them useful in the synthetic environment. Synchronous operation of the biomolecular engines is one of the key criteria to coordinate them into certain different patterns, which depends on the local interaction of biomolecular motors. Utilizing chemical and physical stimuli, synchronization of biomolecular motor systems has become possible, which allows them to coordinate into different higher ordered patterns with different modes of functionality. Recently, programmed synchronous operation of the biomolecular engines has also been demonstrated, using a smart biomaterial to build up swarms reminiscent of nature. Here, we review the recent progress in the synchronized operation of biomolecular motors in engineered systems to explicitly program their interaction and further their applications. Such developments in the coordination of biomolecular motors have opened a broad way to explore the construction of future autonomous molecular machines and robots based on synchronization of biomolecular engines.

Controlling the kinetics of interaction between microtubules and kinesins over a wide temperature range using the deep-sea osmolyte trimethylamine N-oxide

Trimethylamine N-oxide is found to be effective in regulating the interaction between microtubules and kinesins over a wide temperature range. The lifetime of the motility of microtubules on kinesins at high temperatures is prolonged using trimethylamine N-oxide. The activation energy of microtubule motility is increased by trimethylamine N-oxide. Prolonged operation at high temperatures decreased the activation energy of MT motility despite the increase in concentration of trimethylamine N-oxide.

Enzyme catalysis powered micro/nanomotors for biomedical applications

This review provides insights on enzyme powered motors using fuels present in biological environments for biomedical applications.

Molecular Assemblies of Biomimetic Microcapsules

Layer-by-layer (LbL) assembly is a most commonly used method to prepare various microcapsules based on the electrostatic interactions, hydrogen bonding, covalent bonding, and so on. Among these interactions, Schiff base bond formed in covalent assembly not only has an advantage in stability, but also enables the assembled microcapsules with autofluorescence and pH sensitivity. In this Article, we will mainly describe the construction of biomimetic microcapsules through Schiff base mediated LbL assembly. The structures and properties of the assembled microcapsules are introduced and their applications as drug carriers are highlighted.

From isolated structures to continuous networks: A categorization of cytoskeleton-based motile engineered biological microstructures

As technology at the small scale is advancing, motile engineered microstructures are becoming useful in drug delivery, biomedicine, and lab-on-a-chip devices. However, traditional engineering methods and materials can be inefficient or functionally inadequate for small-scale applications. Increasingly, researchers are turning to the biology of the cytoskeleton, including microtubules, actin filaments, kinesins, dyneins, myosins, and associated proteins, for both inspiration and solutions. They are engineering structures with components that range from being entirely biological to being entirely synthetic mimics of biology and on scales that range from isotropic continuous networks to single isolated structures. Motile biological microstructures trace their origins from the development of assays used to study the cytoskeleton to the array of structures currently available today. We define 12 types of motile biological microstructures, based on four categories: entirely biological, modular, hybrid, and synthetic, and three scales: networks, clusters, and isolated structures. We highlight some key examples, the unique functionalities, and the potential applications of each microstructure type, and we summarize the quantitative models that enable engineering them. By categorizing the diversity of motile biological microstructures in this way, we aim to establish a framework to classify these structures, define the gaps in current research, and spur ideas to fill those gaps. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Nanotechnology Approaches to Biology > Cells at the Nanoscale Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Molecular Assembly of Rotary and Linear Motor Proteins

Molecular machines are an important and emerging frontier in research encompassing interdisciplinary subjects of chemistry, physics, biology, and nanotechnology. Although there has been major interest in creating synthetic molecular machines, research on natural molecular machines is also crucial. Biomolecular motors are natural molecular machines existing in nearly every living systems. They play a vital role in almost every essential process ranging from intracellular transport to cell division, muscle contraction and the biosynthesis of ATP that fuels life processes. The construction of biomolecular motor-based biomimetic systems can help not only to deeply understand the mechanisms of motor proteins in the biological process but also to push forward the development of bionics and biomolecular motor-based devices or nanomachines. From combination of natural biomolecular motors with supramolecular chemistry, great opportunities could emerge toward the development of intelligent molecular machines and biodevices. In this Account, we describe our efforts to design and reconstitute biomolecular motor-based active biomimetic systems, in particular, the combination of motor proteins with layer-by-layer (LbL) assembled cellular structures. They are divided into two parts: (i) reconstitution of rotary molecular motor F_OF₁-ATPase, which is coated on the surface of LbL assembled microcapsules or multilayers and synthesizes adenosine triphosphate (ATP) through creating a proton gradient; (ii) molecular assembly of linear molecular motors, the kinesin-based active biomimetic systems, which are coated on a planar surface or LbL assembled tubular structure and drive the movement of microtubules. LbL assembled structures offer motor proteins with an environment that resembles the natural cell. This enables high activity and optimized function of the motor proteins. The assembled biomolecular motors can mimic their functionalities from the natural system. In addition, LbL assembly provides facile integration of functional components into motor protein-based active biomimetic systems and achieves the manipulation of F_OF₁-ATPase and kinesin. For F_OF₁-ATPase, the light-driven proton gradient and controlled ATP synthesis are highlighted. For kinesin, the strategies used for the direction and velocity control of kinesin-based molecular shuttles are discussed. We hope this research can inspire new ideas and propel the actual applications of biomolecular motor-based devices in the future.

Langmuir Nanoarchitectonics from Basic to Frontier

Methodology to combine nanotechnology and these organization processes has been proposed as a novel concept of nanoarchitectonics, which can fabricate functional materials with nanolevel units. As an instant nanoarchitectonics approach, confining systems within a two-dimensional plane to drastically reduce translational motion freedom can be regarded as one of the rational approaches. Supramolecular chemistry and nanofabrication and their related functions at the air-water interface with the concept of nanoarchitectonics would lead to the creation of a novel methodology of Langmuir nanoarchitectonics. In this feature article, we briefly summarize research efforts related to Langmuir nanoarchitectonics including the basics for anomalies in molecular interactions such as highly enhanced molecular recognition capabilities. It is also extended to frontiers including the fabrication of supramolecular receptors and two-dimensional patterns with subnanometer-scale structural regulation, manual control of molecular machines and receptors by hand-motion-like macroscopic actions, and the regulation of cell fates at nanoarchitected arrays of nanocarbon assemblies and at direct liquid interfaces.

Biological active matter aggregates: Inspiration for smart colloidal materials

Aggregations of social organisms exhibit a remarkable range of properties and functionalities. Multiple examples, such as fire ants or slime mold, show how a population of individuals is able to overcome an existential threat by gathering into a solid-like aggregate with emergent functionality. Surprisingly, these aggregates are driven by simple rules, and their mechanisms show great parallelism among species. At the same time, great effort has been made by the scientific community to develop active colloidal materials, such as microbubbles or Janus particles, which exhibit similar behaviors. However, a direct connection between these two realms is still not evident, and it would greatly benefit future studies. In this review, we first discuss the current understanding of living aggregates, point out the mechanisms in their formation and explore the vast range of emergent properties. Second, we review the current knowledge in aggregated colloidal systems, the methods used to achieve the aggregations and their potential functionalities. Based on this knowledge, we finally identify a set of over-arching principles commonly found in biological aggregations, and further suggest potential future directions for the creation of bio-inspired colloid aggregations.

Molecular Encapsulation Inside Microtubules Based on Tau-Derived Peptides

Microtubules are cytoskeletal filaments that serve as attractive scaffolds for developing nanomaterials and nanodevices because of their unique structural properties. The functionalization of the outer surface of microtubules has been established for this purpose. However, no attempts have been made to encapsulate molecules inside microtubules with 15 nm inner diameter. The encapsulation of various molecular cargos inside microtubules constitutes a new concept for nanodevice and nanocarrier applications of microtubules. Here, we developed peptide motifs for binding to the inner surface of microtubules, based on a repeat domain of the microtubule‐associated protein Tau. One of the four Tau‐derived peptides, 2_N, binds to a taxol binding pocket of β‐tubulin located inside microtubules by preincubation with tubulin dimer and subsequent polymerization of the peptide‐tubulin complex. By conjugation of 2_N to gold nanoparticles, encapsulation of gold nanoparticles inside microtubules was achieved. The methodology for molecular encapsulation inside microtubules by the Tau‐derived peptide is expected to advance the development of microtubule‐based nanomaterials and nanodevices.

Nano Trek Beyond: Driving Nanocars/Molecular Machines at Interfaces

In 2016, the Nobel Prize in Chemistry was awarded for pioneering work on molecular machines. Half a year later, in Toulouse, the first molecular car race, a "nanocar race", was held by using the tip of a scanning tunneling microscope as an electrical remote control. In this Focus Review, we discuss the current state-of-the-art in research on molecular machines at interfaces. In the first section, we briefly explain the science behind the nanocar race, followed by a selection of recent examples of controlling molecules on surfaces. Finally, motion synchronization and the functions of molecular machines at liquid interfaces are discussed. This new concept of molecular tuning at interfaces is also introduced as a method for the continuous modification and optimization of molecular structure for target functions.

Targeted Activation of Molecular Transportation by Visible Light

Regulated transportation of nanoscale objects with a high degree of spatiotemporal precision is a prerequisite for the development of targeted molecular delivery. In vitro integration of the kinesin-microtubule motor system with synthetic molecules offers opportunities to develop controllable molecular shuttles for lab-on-a-chip applications. We attempted a combination of the kinesin-microtubule motor system with push-pull type azobenzene tethered inhibitory peptides (azo-peptides) through which reversible, spatiotemporal control over the kinesin motor activity was achieved locally by a single, visible wavelength. The fast thermal relaxation of the cis-isomers of azo-peptides offered us quick and complete resetting of the trans-state in the dark, circumventing the requirement of two distinct wavelengths for two-way switching of kinesin-driven microtubule motility. Herein, we report the manipulation of selected, single microtubule movement while keeping other microtubules at complete rest. The photoresponsive inhibitors discussed herein would help in realizing complex bionanodevices.

Non-equilibrium assembly of microtubules: from molecules to autonomous chemical robots

Biological systems have evolved to harness non-equilibrium processes from the molecular to the macro scale. It is currently a grand challenge of chemistry, materials science, and engineering to understand and mimic biological systems that have the ability to autonomously sense stimuli, process these inputs, and respond by performing mechanical work. New chemical systems are responding to the challenge and form the basis for future responsive, adaptive, and active materials. In this article, we describe a particular biochemical-biomechanical network based on the microtubule cytoskeletal filament - itself a non-equilibrium chemical system. We trace the non-equilibrium aspects of the system from molecules to networks and describe how the cell uses this system to perform active work in essential processes. Finally, we discuss how microtubule-based engineered systems can serve as testbeds for autonomous chemical robots composed of biological and synthetic components.

Spatiotemporal control of kinesin motor protein by photoswitches enabling selective single microtubule regulations

Artificial control of bio-nanomachines should have a major impact on the development of controllable transport systems for specific cargo transport on chips. Precise spatiotemporal control and local regulation of the bio-motor activity will, however, be necessary if we are to accomplish such a goal. In this study, we exploited the photoswitching properties of azobenzene-based high-energy molecules and inhibitors to control a single kinesin-driven microtubule that has potential to work as a nanocarrier for molecular cargos. In particular, we could influence the local concentration and dispersion of the microtubules at any desired position and time by irradiating a local area of the motility system at one wavelength, while irradiating the entire area at another wavelength, to enrich either cis or trans isomers of photoswitches in the selected region. Furthermore, various regulations (e.g., transporting, bending, breaking) of single microtubules were possible while almost arresting ambient microtubules-all without the need for any surface patterning.

Biomacromolecules based core/shell architecture toward biomedical applications

Polyelectrolyte multilayer capsules have become a novel and promising class of hybrid materials with great potential since they can be applied in various areas, such as pharmaceutical sciences, biotechnology, and biomedicine. The concept of using such carriers for biology application is diagnosis and treatment of diseases for convenience, safety and specific targeting. Therefore, the development of biocompatible, biodegradable and specific characteristic nanostructure material is highly desirable. Much effort has been devoted to exploring innovative and effective techniques to fabricate such materials. Among the available techniques, layer-by-layer (LbL) assembly capsules have attracted considerable attention attributing to the flexibly controlled size, shape, composition, wall thickness and functions. Protein, as the large class of biomacromolecules, was incorporated into capsules for improving the biocompatibility and specific function. In this review we provide an overview of the recent progress in biomacromolecular capsules or core/shell architecture with different diameters for the variety of purposes. The size ranging from micro-, sub-micro to nano scale based on the choice of the template. Their advantages are discussed here. The applications of these biomacromolecular capsules in biotechnological fields have also been summarized, for instance blood substitute, ATP carriers, photodynamic therapy and nanomedicines.

pH responsive ATP carriers to drive kinesin movement

Multilayer film coated CaCO3 microspheres were employed as pH responsive ATP carriers to drive kinesin movement. The production of oxygen scavengers in a kinesin-microtubule system induces the decomposition of ATP-loaded CaCO3 microspheres and then leads to the release of ATP.

Self-Assembled Smart Nanocarriers for Targeted Drug Delivery

Nanostructured drug-carrier systems promise numerous benefits for drug delivery. They can be engineered to precisely control drug-release rates or to target specific sites within the body with a specific amount of therapeutic agent. However, to achieve the best therapeutic effects, the systems should be designed for carrying the optimum amount of a drug to the desired target where it should be released at the optimum rate for a specified time. Despite numerous attempts, fulfilling all of these requirements in a synergistic way remains a huge challenge. The trend in drug delivery is consequently directed toward integrated multifunctional carrier systems, providing selective recognition in combination with sustained or triggered release. Capsules as vesicular systems enable drugs to be confined for controlled release. Furthermore, carriers modified with recognition groups can enhance the capability of encapsulated drug efficacy. Here, recent advances are reviewed regarding designing and preparing assembled capsules with targeting ligands or size controllable for selective recognition in drug delivery.

Self-Propelled Micro-/Nanomotors Based on Controlled Assembled Architectures

Synthetic micro-/nanomotors (MNMs) are capable of performing self-propelled motion in fluids through harvesting different types of energies into mechanical movement, with potential applications in biomedicine and other fields. To address the challenges in these applications, a promising strategy that combines controlled assembly (bottom-up approaches) with top-down approaches for engineering autonomous, multifunctionalized MNMs is under investigation, beginning in 2012. These MNMs, derived from layer-by-layer assembly or molecular self-assembly, display the advantages of: i) mass production, ii) response to the external stimuli, and iii) access to multifunctionality, biocompatibility, and biodegradability. The advance on how to integrate diverse functional components into different architectures based on controlled assemblies, to realize controlled fabrication, motion control (including the movement speed, direction, and state), and biomedical applications of MNMs, directed by the concept of nanoarchitectonics, are highlighted here. The remaining challenges and future research directions are also discussed.