Synthetic micro/nanomotors in drug delivery

Stability Analysis for Large-Scale Multi-Agent Molecular Communication Systems

Molecular communication (MC) is recently featured as a novel communication tool to connect individual biological nanorobots. It is expected that a large number of nanorobots can form large multi-agent MC systems through MC to accomplish complex and large-scale tasks that cannot be achieved by a single nanorobot. However, most previous models for MC systems assume a unidirectional diffusion communication channel and cannot capture the feedback between each nanorobot, which is important for multi-agent MC systems. In this paper, we introduce a system theoretic model for large-scale multi-agent MC systems using transfer functions, and then propose a method to analyze the stability for multi-agent MC systems. The proposed method decomposes the multi-agent MC system into multiple single-input and single-output (SISO) systems, which facilitates the application of simple analysis technique for SISO systems to the large-scale multi-agent MC system. Finally, we demonstrate the proposed method by analyzing the stability of a specific large-scale multi-agent MC system and clarify a parameter region to synchronize the states of nanorobots, which is important to make cooperative behaviors at a population level.

Boosting the Efficiency of Photoactive Rod-Shaped Nanomotors via Magnetic Field-Induced Charge Separation

Photocatalytic nanomotors have attracted a lot of attention because of their unique capacity to simultaneously convert light and chemical energy into mechanical motion with a fast photoresponse. Recent discoveries demonstrate that the integration of optical and magnetic components within a single nanomotor platform offers novel advantages for precise motion control and enhanced photocatalytic performance. Despite these advancements, the impact of magnetic fields on energy transfer dynamics in photocatalytic nanomotors remains unexplored. Here, we introduce dual-responsive rod-like nanomotors, made of a TiO2/NiFe heterojunction, able to (i) self-propel upon irradiation, (ii) align with the direction of an external magnetic field, and (iii) exhibit enhanced photocatalytic performance. Consequently, when combining light irradiation with a homogeneous magnetic field, these nanomotors exhibit increased velocities attributed to their improved photoactivity. As a proof-of-concept, we investigated the ability of these nanomotors to generate phenol, a valuable chemical feedstock, from benzene under combined optical and magnetic fields. Remarkably, the application of an external magnetic field led to a 100% increase in the photocatalytic phenol generation in comparison with light activation alone. By using various state-of-the-art techniques such as photoelectrochemistry, electrochemical impedance spectroscopy, photoluminescence, and electron paramagnetic resonance, we characterized the charge transfer between the semiconductor and the alloy component, revealing that the magnetic field significantly improved charge pair separation and enhanced hydroxyl radical generation. Consequently, our work provides valuable insights into the role of magnetic fields in the mechanisms of light-driven photocatalytic nanomotors for designing more effective light-driven nanodevices for selective oxidations.

H2S-Powered Nanomotors for Active Therapy of Tumors by Inducing Ferroptosis and Lactate-Pyruvate Axis Disorders

Disruption of the symbiosis of extra/intratumoral metabolism is a good strategy for treating tumors that shuttle resources from the tumor microenvironment. Here, we report a precision treatment strategy for enhancing pyruvic acid and intratumoral acidosis to destroy tumoral metabolic symbiosis to eliminate tumors; this approach is based on PEGylated gold and lactate oxidase-modified aminated dendritic mesoporous silica with lonidamine and ferrous sulfide loading (PEG-Au@DMSNs/FeS/LND@LOX). In the tumor microenvironment, LOX oxidizes lactic acid to produce pyruvate, which represses tumor cell proliferation by inhibiting histone gene expression and induces ferroptosis by partial histone monoubiquitination. In acidic tumor conditions, the nanoparticles release H2S gas and Fe2+ ions, which can inhibit catalase activity to promote the Fenton reaction of Fe2+, resulting in massive ·OH production and ferroptosis via Fe3+. More interestingly, the combination of H2S and LND (a monocarboxylic acid transporter inhibitor) can cause intracellular acidosis by lactate, and protons overaccumulate in cells. Multiple intracellular acidosis is caused by lactate-pyruvate axis disorders. Moreover, H2S provides motive power to intensify the shuttling of nanoparticles in the tumor region. The findings confirm that this nanomedicine system can enable precise antitumor effects by disrupting extra/intratumoral metabolic symbiosis and inducing ferroptosis and represents a promising active drug delivery system candidate for tumor treatment.

Buoyancy-Driven Micro/-Nanomotors: From Fundamentals to Applications

The progression of self-powered micro/-nanomotors (MNMs) has rapidly evolved over the past few decades, showing applications in various fields such as nanotechnology, biomedical engineering, microfluidics, environmental science, and energy harvesting. Miniaturized MNMs transduce chemical/biochemical energies into mechanical motion for navigating through complex fluidic environments with directional control via external forces fields such as magnetic, photonic, and electric stimuli. Among various propulsion mechanisms, buoyancy-driven MNMs have received noteworthy recognition due to their simplicity, efficiency, and versatility. Buoyancy force-driven motors harness the principles of density variation-mediated force to overcome fluidic resistance to navigate through complex environments. Restricting the propulsion in one direction helps to control directional movement, making it more efficient in isotropic solutions. The changes in pH, ionic strength, chemical concentration, solute gradients, or the presence of specific molecules can influence the motion of buoyancy-driven MNMs as evidenced by earlier reports. This review aims to provide a fundamental and detailed analysis of the current state-of-the-art in buoyancy-driven MNMs, aiming to inspire further research and innovation in this promising field.

Chemical herding as a multiplicative factor for top-down manipulation of colloids

Colloidal particles can create reconfigurable nanomaterials, with applications such as color-changing, self-repairing, and self-regulating materials and reconfigurable drug delivery systems. However, top-down methods for manipulating colloids are limited in the scale they can control. We consider here a new method for using chemical reactions to multiply the effects of existing top-down colloidal manipulation methods to arrange large numbers of colloids with single-particle precision, which we refer to as chemical herding. Using simulation-based methods, we show that if a set of chemically active colloids (herders) can be steered using external forces (i.e., electrophoretic, dielectrophoretic, magnetic, or optical forces), then a larger set of colloids (followers) that move in response to the chemical gradients produced by the herders can be steered using the control algorithms given in this paper. We also derive bounds that predict the maximum number of particles that can be steered in this way, and we illustrate the effectiveness of this approach using Brownian dynamics simulations. Based on the theoretical results and simulations, we conclude that chemical herding is a viable method for multiplying the effects of existing colloidal manipulation methods to create useful structures and materials.

Sub-Nanogram Resolution Measurement of Inertial Mass and Density Using Magnetic-Field-Guided Bubble Microthruster

Artificial micro/nanomotors using active particles hold vast potential in applications such as drug delivery and microfabrication. However, upgrading them to micro/nanorobots capable of performing precise tasks with sophisticated functions remains challenging. Bubble microthruster (BMT) is introduced, a variation of the bubble-driven microrobot, which focuses the energy from a collapsing microbubble to create an inertial impact on nearby target microparticles. Utilizing ultra-high-speed imaging, the microparticle mass and density is determined with sub-nanogram resolution based on the relaxation time characterizing the microparticle's transient response. Master curves of the BMT method are shown to be dependent on the viscosity of the solution. The BMT, controlled by a gamepad with magnetic-field guidance, precisely manipulates target microparticles, including bioparticles. Validation involves measuring the polystyrene microparticle mass and hollow glass microsphere density, and assessing the mouse embryo mass densities. The BMT technique presents a promising chip-free, real-time, highly maneuverable strategy that integrates bubble microrobot-based manipulation with precise bioparticle mass and density detection, which can facilitate microscale bioparticle characterizations such as embryo growth monitoring.

Light-Triggered Inflation of Microdroplets

Driven systems composed largely of droplets and fuel make up a significant portion of microbiological function. At the micrometer scale, fully synthetic systems that perform an array of tasks within a uniform bulk are much more rare. In this work, we introduce an innovative design for solid-in-oil composite microdroplets. These microdroplets are engineered to nucleate an internal phase, undergo inflation, and eventually burst, all powered by a steady and uniform energy input. We show that by altering the background input, volumetric change and burst time can be tuned. When the inflated droplets release the inner contents, colloidal particles are shown to transiently attract to the release point. Lastly, we show that the system has the ability to perform multiple inflation-burst cycles. We anticipate that our conceptual design of internally powered microdroplets will catalyze further research into autonomous systems capable of intricate communication as well as inspire the development of advanced, responsive materials.

Putting Hybrid Nanomaterials to Work for Biomedical Applications

Hybrid nanomaterials have found use in many biomedical applications. This article provides a comprehensive review of the principles, techniques, and recent advancements in the design and fabrication of hybrid nanomaterials for biomedicine. We begin with an introduction to the general concept of material hybridization, followed by a discussion of how this approach leads to materials with additional functionality and enhanced performance. We then highlight hybrid nanomaterials in the forms of nanostructures, nanocomposites, metal-organic frameworks, and biohybrids, including their fabrication methods. We also showcase the use of hybrid nanomaterials to advance biomedical engineering in the context of nanomedicine, regenerative medicine, diagnostics, theranostics, and biomanufacturing. Finally, we offer perspectives on challenges and opportunities.

Pair Interactions of Self-Propelled SiO2-Pt Janus Colloids: Chemically Mediated Encounters

Driven by the necessity to achieve a thorough comprehension of the bottom-up fabrication process of functional materials, this experimental study investigates the pairwise interactions or collisions between chemically active SiO2-Pt Janus colloids. These collisions are categorized based on the Janus colloids' orientations before and after they make physical contact. In addition to the hydrodynamic interactions, the Janus colloids are also known to affect each other's chemical field, resulting in chemophoretic interactions, which depend on the degree of surface anisotropy in reactivity of Janus colloid and the solute-surface interaction at play. Our study reveals that these interactions lead to a noticeable decrease in particle speed and changes in orientation that correlate with the contact duration and yield different collision types. Distinct configurations of contact during collisions were found, whose mechanisms and likelihood are found to be dependent primarily on the chemical interactions. Such estimates of collision and their characterization in dilute suspensions shall have a key impact in determining the arrangement and time scales of dynamical structures and assemblies of denser suspensions and potentially the functional materials of the future.

Multifunctional Chiral Chemically-Powered Micropropellers for Cargo Transport and Manipulation

Practical applications of synthetic self-propelled nano and microparticles for microrobotics, targeted drug delivery, and manipulation at the nanoscale are rapidly expanding. However, fabrication limitations often hinder progress, resulting in relatively simple shapes and limited functionality. Here, taking advantage of 3D nanoscale printing, chiral micropropellers powered by the hydrogen peroxide reduction reaction are fabricated. Due to their chirality, the propellers exhibit multifunctional behavior controlled by an applied magnetic field: spinning in place (loitering), directed migration in the prescribed direction, capture, and transport of polymer cargo particles. Design parameters of the propellers are optimized by computation modeling based on mesoscale molecular dynamics. It is predicted by computer simulations, and confirmed experimentally, that clockwise rotating propellers attract each other and counterclockwise repel. These results shed light on how chirality and shape optimization enhance the functionality of synthetic autonomous micromachines.

Enhanced phoretic self-propulsion of active colloids through surface charge asymmetry

Charged colloidal particles propel themselves through asymmetric fluxes of chemically generated ions on their surface. We show that asymmetry in the surface charge distribution provides an additional mode of self-propulsion at the nanoscale for chemically active particles that produce ionic species. Particles of sizes smaller than or comparable to the Debye length achieve directed self-propulsion through surface charge asymmetry even when ionic flux is uniform over its surface. Janus nanoparticles endowed with both surface charge and ionic flux asymmetries result in enhanced propulsion speeds of the order of μm/s or higher. Our work suggests an alternative avenue for specifying surface properties that optimize self-propulsion in ionic media.

Acoustic Bubble and Magnetic Actuation-Based Microrobot for Enhanced Multiphase Drug Delivery Efficiency

This paper proposes an acoustic bubble and magnetic actuation-based microrobot for enhancing multiphase drug delivery efficiency. The proposed device can encapsulate multiphase drugs, including liquids, using the two bubbles embedded within the microtube. Additionally, using the magnetic actuation of the loaded magnetic liquid metal, it can deliver drugs to target cells. This study visualized the flow patterns generated by the oscillating bubble within the tube to validate the drug release principle. In addition, to investigate the effect of the oscillation properties of the inner bubble on drug release, the oscillation amplitude of the inner bubble was measured under various experimental variables using a high-speed camera. Subsequently, we designed a microrobot capable of encapsulating bubbles, drugs, and magnetic liquid metal and fabricated it using microfabrication technology based on ultra-precision 3D printing. As a proof of concept, we demonstrated the transport and drug release of the microrobot encapsulating the drug in a Y-shaped channel simulating a blood vessel. The proposed device is anticipated to enhance the efficiency of drug therapy by minimizing drug side effects, reducing drug administration frequency, and improving the stability of the drug within the body. This paper is expected to be applicable not only to targeted drug delivery but also to various biomedical fields, such as minimally invasive surgery and cell manipulation, by effectively delivering multiphase drugs using the simple structure of a microrobot.

Visualizing Facets Asymmetry Induced Directional Movement of Cadmium Chloride Nanomotor

Nanomotors in solution have many potential applications. However, it has been a significant challenge to realize the directional motion of nanomotors. Here, we report cadmium chloride tetrahydrate (CdCl2·4H2O) nanomotors with remarkable directional movement under electron beam irradiation. Using in situ liquid phase transmission electron microscopy, we show that the CdCl2·4H2O nanoparticle with asymmetric surface facets moves through the liquid with the flat end in the direction of motion. As the nanomotor morphology changes, the speed of movement also changes. Finite element simulation of the electric field and fluid velocity distribution around the nanomotor assists the understanding of ionic self-diffusiophoresis as a driving force for the nanomotor movement; the nanomotor generates its own local ion concentration gradient due to different chemical reactivities on different facets.

pH-Responsive swimming behavior of light-powered rod-shaped micromotors

Micromotors have emerged as promising devices for a wide range of applications e.g., microfluidics, lab-on-a-chip devices, active matter, environmental monitoring, etc. The control over the activity of micromotors with the ability to exhibit multimode swimming is one of the most desirable features for many of the applications. Here, we demonstrate a rod-shaped light-driven micromotor whose activity and swimming behavior can easily be controlled. The rod-shaped micromotors are fabricated through the dynamic shadowing growth (DSG) technique, where a 2 μm long arm of titanium dioxide (TiO2) is grown over spherical silica (SiO2) particles (1 μm diameter). Under low-intensity UV light exposure, the micromotors exhibit self-propulsion in an aqueous peroxide medium. When activated, the swimming behavior of micromotors greatly depends on the pH of the medium. The swimming direction, i.e., forward or backward movement, as well as swimming modes like translational or rotational motion, can be controlled by changing the pH values. The observed dynamics has been rationalized using a theoretical model incorporating chemical activity, hydrodynamic flow, and the effect of gravity for a rod-shaped active particle near a planar wall. The pH-dependent translational and rotational dynamics of micromotors provide a versatile platform for achieving controlled and responsive behaviors. Continued research and development in this area hold great promise for advancing micromotors and enabling novel applications in microfluidics, micromachining, environmental sciences, and biomedicine.

Doxorubicin-Loaded Microrobots for Targeted Drug Delivery and Anticancer Therapy

Micro-sized magnetic particles (also known as microrobots [MRs]) have recently been shown to have potential applications for numerous biomedical applications like drug delivery, microengineering, and single cell manipulation. Interdisciplinary studies have demonstrated the ability of these tiny particles to actuate under the action of a controlled magnetic field that not only drive MRs in a desired trajectory but also precisely deliver therapeutic payload to the target site. Additionally, optimal concentrations of therapeutic molecules can also be delivered to the desired site which is cost-effective and safe especially in scenarios where drug dose-related side effects are a concern. In this study, MRs are used to deliver anticancer drugs (doxorubicin) to cancer cells and subsequent cell death is evaluated in different cell lines (liver, prostate, and ovarian cancer cells). Cytocompatibility studies show that MRs are well-tolerated and internalized by cancer cells. Doxorubicin (DOX) is chemically conjugated with MRs (DOX-MRs) and magnetically steered toward cancer cells using the magnetic controller. Time-lapsed video shows that cells shrink and eventually die when MRs are internalized by cells. Taken together, this study confirms that microrobots are promising couriers for targeted delivery of therapeutic biomolecules for cancer therapy and other non-invasive procedures that require precise control.

Motion of nanovehicles on pristine and vacancy-defected silicene: implications for controlled surface motion

Understanding the motion of surface-rolling nanomachines has attracted lots of attention in recent studies, due to their ability in carrying molecular payloads and nanomaterials on the surface. Controlling the surface motion of these nanovehicles is beneficial in the fabrication of nano-transportation systems. In the present study, molecular dynamics (MD) simulations alongside the potential energy analysis have been utilized to investigate the motion of C60 and C60-based nanovehicles on the silicene monolayer. Nano-machine simulations are performed using molecular mechanic forcefield. Compared with graphene and hexagonal boron-nitride, the molecules experience a higher energy barrier on the silicene, which leads to a lower diffusion coefficient and higher activation energy of C60 and nanomachines. Overcoming the maximum energy barrier against sliding motion is more probable at higher temperatures where the nanomachines receive higher thermal energy. After evaluating the motion of molecules around local vacancies, we introduce a nanoroad structure that can restrict surface motion. The motion of C60 and nanovehicles over the surface is limited to the width of nanorods up to a certain temperature. To increase the controllability of the motion, a thermal gradient has been applied to the surface and the molecules move toward the lower temperature regions, where they find lower energy levels. Comparing the results of this study with other investigations regarding the surface motion of molecules on boron-nitride and graphene surfaces brings forth the idea of controlling the motion by silicene-based hybrid substrates, which can be further investigated.

Strategies in design of self-propelling hybrid micro/nanobots for bioengineering applications

Micro/nanobots are integrated devices developed from engineered nanomaterials that have evolved significantly over the past decades. They can potentially be pre-programmed to operate robustly at numerous hard-to-reach organ/tissues/cellular sites for multiple bioengineering applications such as early disease diagnosis, precision surgeries, targeted drug delivery, cancer therapeutics, bio-imaging, biomolecules isolation, detoxification, bio-sensing, and clearing up clogged arteries with high soaring effectiveness and minimal exhaustion of power. Several techniques have been introduced in recent years to develop programmable, biocompatible, and energy-efficient micro/nanobots. Therefore, the primary focus of most of these techniques is to develop hybrid micro/nanobots that are an optimized combination of purely synthetic or biodegradable bots suitable for the execution of user-defined tasks more precisely and efficiently. Recent progress has been illustrated here as an overview of a few of the achievable construction principles to be used to make biomedical micro/nanobots and explores the pivotal ventures of nanotechnology-moderated development of catalytic autonomous bots. Furthermore, it is also foregrounding their advancement offering an insight into the recent trends and subsequent prospects, opportunities, and challenges involved in the accomplishments of the effective multifarious bioengineering applications.

Biodegradable Microrobots for DNA Vaccine Delivery

The delivery of nucleic acid vaccine to stimulate host immune responses against Coronavirus disease 2019 shows promise. However, nucleic acid vaccines have drawbacks, including rapid clearance and poor cellular uptake, that limit their therapeutic potential. Microrobots can be engineered to sustain vaccine release and further control the interactions with immune cells that are vital for robust vaccination. Here, the 3D fabrication of biocompatible and biodegradable microrobots via the two-photon polymerization of gelatin methacryloyl (GelMA) and their proof-of-concept application for DNA vaccine delivery is reported. Programmed degradation and drug release by varying the local exposure dose in 3D laser lithography and further functionalized the GelMA microspheres with polyethyleneimine for DNA vaccine delivery to dendritic cell and primary cells is demonstrated. In mice, the DNA vaccine delivered by functionalized microspheres elicited fast, enhanced, and durable antigen expression, which may lead to prolonged protection. Furthermore, we demonstrate the maneuverability of microrobots by fabricating GelMA microspheres on magnetic skeletons. In conclusion, GelMA microrobots may provide an efficient vaccination strategy by controlling the expression duration of DNA vaccines.

How Nanotherapeutic Platforms Play a Key Role in Glioma? A Comprehensive Review of Literature

Glioblastoma (GBM), a highly aggressive form of brain cancer, is considered one of the deadliest cancers, and even with the most advanced medical treatments, most affected patients have a poor prognosis. However, recent advances in nanotechnology offer promising avenues for the development of versatile therapeutic and diagnostic nanoplatforms that can deliver drugs to brain tumor sites through the blood-brain barrier (BBB). Despite these breakthroughs, the use of nanoplatforms in GBM therapy has been a subject of great controversy due to concerns over the biosafety of these nanoplatforms. In recent years, biomimetic nanoplatforms have gained unprecedented attention in the biomedical field. With advantages such as extended circulation times, and improved immune evasion and active targeting compared to conventional nanosystems, bionanoparticles have shown great potential for use in biomedical applications. In this prospective article, we endeavor to comprehensively review the application of bionanomaterials in the treatment of glioma, focusing on the rational design of multifunctional nanoplatforms to facilitate BBB infiltration, promote efficient accumulation in the tumor, enable precise tumor imaging, and achieve remarkable tumor suppression. Furthermore, we discuss the challenges and future trends in this field. Through careful design and optimization of nanoplatforms, researchers are paving the way toward safer and more effective therapies for GBM patients. The development of biomimetic nanoplatform applications for glioma therapy is a promising avenue for precision medicine, which could ultimately improve patient outcomes and quality of life.

Velocity and Out-Step Frequencies for a Micro-Swimmer Based on Spiral Carbon Nanotubes

The existing producing processes of micro spiral swimmers are complex. Here, a microswimmer with a magnetic layer on the surface of the spiral carbon nanotubes is proposed, which has a simple producing process. For the microswimmer, its equations of the velocities and out-step frequency are deduced. Using these equations, the velocities and out-step frequency of the microswimmer and their changes with related parameters are investigated. Results show that its velocities are proportional to the radius and helix angle of the spiral carbon nanotubes, and its out-step frequencies are proportional to magnetic field strength, the helix angle and magnetic layer thicknesses of the spiral carbon nanotubes, and inversely proportional to the fluid viscosity. The out-step frequency of the microswimmer is measured, which is in good agreement with the calculative ones.

Light-Triggered Mechanical Disruption of Extracellular Barriers by Swarms of Enzyme-Powered Nanomotors for Enhanced Delivery

Targeted drug delivery depends on the ability of nanocarriers to reach the target site, which requires the penetration of different biological barriers. Penetration is usually low and slow because of passive diffusion and steric hindrance. Nanomotors (NMs) have been suggested as the next generation of nanocarriers in drug delivery due to their autonomous motion and associated mixing hydrodynamics, especially when acting collectively as a swarm. Here, we explore the concept of enzyme-powered NMs designed as such that they can exert disruptive mechanical forces upon laser irradiation. The urease-powered motion and swarm behavior improve translational movement compared to passive diffusion of state-of-the-art nanocarriers, while optically triggered vapor nanobubbles can destroy biological barriers and reduce steric hindrance. We show that these motors, named Swarm 1, collectively displace through a microchannel blocked with type 1 collagen protein fibers (barrier model), accumulate onto the fibers, and disrupt them completely upon laser irradiation. We evaluate the disruption of the microenvironment induced by these NMs (Swarm 1) by quantifying the efficiency by which a second type of fluorescent NMs (Swarm 2) can move through the cleared microchannel and be taken up by HeLa cells at the other side of the channel. Experiments showed that the delivery efficiency of Swarm 2 NMs in a clean path was increased 12-fold in the presence of urea as fuel compared to when no fuel was added. When the path was blocked with the collagen fibers, delivery efficiency dropped considerably and only depicted a 10-fold enhancement after pretreatment of the collagen-filled channel with Swarm 1 NMs and laser irradiation. The synergistic effect of active motion (chemically propelled) and mechanical disruption (light-triggered nanobubbles) of a biological barrier represents a clear advantage for the improvement of therapies which currently fail due to inadequate passage of drug delivery carriers through biological barriers.

Active control of equilibrium, near-equilibrium, and far-from-equilibrium colloidal systems

The development of top-down active control over bottom-up colloidal assembly processes has the potential to produce materials, surfaces, and objects with applications in a wide range of fields spanning from computing to materials science to biomedical engineering. In this review, we summarize recent progress in the field using a taxonomy based on how active control is used to guide assembly. We find there are three distinct scenarios: (1) navigating kinetic pathways to reach a desirable equilibrium state, (2) the creation of a desirable metastable, kinetically trapped, or kinetically arrested state, and (3) the creation of a desirable far-from-equilibrium state through continuous energy input. We review seminal works within this framework, provide a summary of important application areas, and present a brief introduction to the fundamental concepts of control theory that are necessary for the soft materials community to understand this literature. In addition, we outline current and potential future applications of actively-controlled colloidal systems, and we highlight important open questions and future directions.

Bioinspired microrobots: Opportunities and challenges in targeted cancer therapy

Chemotherapy is still the most effective technique to treat many forms of cancer. However, it also carries a high risk of side effects. Numerous nanomedicines have been developed to avoid unintended consequences and significant negative effects of conventional therapies. Achieving targeted drug delivery also has several challenges. In this context, the development of microrobots is receiving considerable attention of formulation scientists and clinicians to overcome such challenges. Due to their mobility, microrobots can infiltrate tissues and reach tumor sites more quickly. Different types of microrobots, like custom-made moving bacteria, microengines powered by small bubbles, and hybrid spermbots, can be designed with complex features that are best for precise targeting of a wide range of cancers. In this review, we mainly focus on the idea of how microrobots can quickly target cancer cells and discuss specific advantages of microrobots. A brief summary of the microrobots' drug loading and release behavior is provided in this manuscript. This manuscript will assist clinicians and other medical professionals in diagnosing and treating cancer without surgery.

Two-dimensional-Ti3C2 magnetic nanocomposite for targeted cancer chemotherapy

Introduction: Cervical cancer is the leading cause of cancer-related death in women, so novel therapeutic approaches are needed to improve the effectiveness of current therapies or extend their activity. In recent decades, graphene analogs, such as Mxene, an emerging class of two-dimensional (2D) graphene analogs, have been drawing considerable attention based on their intrinsic physicochemical properties and performance as potential candidates for tumor therapy, particularly for therapeutic purposes. Here we explored the targeted drug delivery in cervical cancer in in vivo model. Mxene-based nanocarriers are not able to be precisely controlled in cancer treatment. Method: To solve this problem, the titanium carbide-magnetic core-shell nanocarrier (Ti₃C₂-Fe₃O₄@SiO₂-FA) is also developed to provide synergetic anticancer with magnetic controlling ability along with pH-responsive drug release. A xenograft model of the cervix was used to investigate the effects of Cisplatin alone, or in combination with Ti₃C₂@FA and Ti₃C₂@ Fe₃O₄@SiO₂-FA, on tumor growth following histological staining for evaluation of necrosis. Result and Discussion: A significant tumor-growth suppression effect is shown when the Ti₃C₂-Fe₃O₄@SiO₂-FA nanocarrier is magnetically controlled Cisplatin drug release. It reveals a synergistic therapeutic efficacy used in conjunction with pharmaceuticals (p < .001). According to the in vivo study, the Ti₃C₂@FA@Cisplatin nanocomposite exhibits less tumor growth than the drug alone or Ti₃C₂@FA@Cisplatin via increasing necrosis effect (p < .001). Through this study, Mxene nanosheets are expanded for biomedical applications, not only through the fabrication of biocompatible magnetic Mxene nanocomposite but also through the development of functionalization strategies that enable the magnetic Ti₃C₂ nanocomposite to load high levels of Cisplatin for cervical cancer treatment (242.5%). Hence, Ti₃C₂-Fe₃O₄@SiO₂-FA nanocarriers would be promising candidates to improve cancer treatment efficiency.

Advanced medical micro-robotics for early diagnosis and therapeutic interventions

Recent technological advances in micro-robotics have demonstrated their immense potential for biomedical applications. Emerging micro-robots have versatile sensing systems, flexible locomotion and dexterous manipulation capabilities that can significantly contribute to the healthcare system. Despite the appreciated and tangible benefits of medical micro-robotics, many challenges still remain. Here, we review the major challenges, current trends and significant achievements for developing versatile and intelligent micro-robotics with a focus on applications in early diagnosis and therapeutic interventions. We also consider some recent emerging micro-robotic technologies that employ synthetic biology to support a new generation of living micro-robots. We expect to inspire future development of micro-robots toward clinical translation by identifying the roadblocks that need to be overcome.

Biomedical Nanosystems for In Vivo Detoxification: From Passive Delivery Systems to Functional Nanodevices and Nanorobots

The problem of low efficiency of nanotherapeutic drugs challenges the creation of new alternative biomedical nanosystems known as robotic nanodevices. In addition to encapsulating properties, nanodevices can perform different biomedical functions, such as precision surgery, in vivo detection and imaging, biosensing, targeted delivery, and, more recently, detoxification of endogenous and xenobiotic compounds. Nanodevices for detoxification are aimed at removing toxic molecules from biological tissues, using a chemical- and/or enzyme-containing nanocarrier for the toxicant to diffuse inside the nanobody. This strategy is opposite to drug delivery systems that focus on encapsulating drugs and releasing them under the influence of external factors. The review describes various kinds of nanodevices intended for detoxification that differ by the type of poisoning treatment they provide, as well as the type of materials and toxicants. The final part of the review is devoted to enzyme nanosystems, an emerging area of research that provides fast and effective neutralization of toxins in vivo.

Gauging Nanoswimmer Dynamics via the Motion of Large Bodies

Nanoswimmers are ubiquitous in biotechnology and nanotechnology but are extremely challenging to measure due to their minute size and driving forces. A simple method is proposed for detecting the elusive physical features of nanoswimmers by observing how they affect the motion of much larger, easily traceable particles. Modeling the swimmers as hydrodynamic force dipoles, we find direct, easy-to-calibrate relations between the observable power spectrum and diffusivity of the tracers and the dynamic characteristics of the swimmers-their force dipole moment and correlation times.

Controlled propulsion of micro/nanomotors: operational mechanisms, motion manipulation and potential biomedical applications

Inspired by natural mobile microorganisms, researchers have developed micro/nanomotors (MNMs) that can autonomously move by transducing different kinds of energies into kinetic energy. The rapid development of MNMs has created tremendous opportunities for biomedical fields including diagnostics, therapeutics, and theranostics. Although the great progress has been made in MNM research, at a fundamental level, the accepted propulsion mechanisms are still a controversial matter. In practical applications such as precision nanomedicine, the precise control of the motion, including the speed and directionality, of MNMs is also important, which makes advanced motion manipulation desirable. Very recently, diverse MNMs with different propulsion strategies, morphologies, sizes, porosities and chemical structures have been fabricated and applied for various uses. Herein, we thoroughly summarize the physical principles behind propulsion strategies, as well as the recent advances in motion manipulation methods and relevant biomedical applications of these MNMs. The current challenges in MNM research are also discussed. We hope this review can provide a bird's eye overview of the MNM research and inspire researchers to create novel and more powerful MNMs.

Microscopic robots with onboard digital control

Autonomous robots-systems where mechanical actuators are guided through a series of states by information processing units to perform a predesigned function-are expected to revolutionize everything from health care to transportation. Microscopic robots are poised for a similar revolution in fields from medicine to environmental remediation. A key hurdle to developing these microscopic robots is the integration of information systems, particularly electronics fabricated at commercial foundries, with microactuators. Here, we develop such an integration process and build microscopic robots controlled by onboard complementary metal oxide semiconductor electronics. The resulting autonomous, untethered robots are 100 to 250 micrometers in size, are powered by light, and walk at speeds greater than 10 micrometers per second. In addition, we demonstrate a microscopic robot that can respond to an optical command. This work paves the way for ubiquitous autonomous microscopic robots that perform complex functions, respond to their environments, and communicate with the outside world.

Light-driven microrobots: capture and transport of bacteria and microparticles in a fluid medium

The design of simple microrobotic systems with capabilities to address various applications like cargo transportation, as well as biological sample capture and manipulation in an individual unit, provides a novel route for designing advanced multifunctional microscale systems. Here, we demonstrate a facile approach to fabricate such multifunctional and fully controlled light-driven microrobots. The microrobots are titanium dioxide-silica Janus particles that are propelled in aqueous hydroquinone/benzoquinone fuel when illuminated by low-intensity UV light. The application of light provides control over the speed as well as activity of the microrobots. When modified with additional thin film coatings of nickel and gold, the microrobots exhibit the capturing and transportation of silica microparticles and E. coli bacteria. While transporting, they also show guided swimming under an external uniform magnetic field, which is interesting for deciding their moving path or the start/end positions. The fluorescent dye-based live/dead tests confirm that in the microrobot system almost no bacteria were harmed during the capturing or transportation. The simplistic design and steerable swimming with the ability to capture and transport are the important features of the microrobots. These features make them an ideal candidate for in vitro or lab-on-a-chip based studies, e.g., drug delivery, bacterial sensing, cell treatment, etc., where the capturing and transport of microscopic entities play a crucial role.

Recent Process in Microrobots: From Propulsion to Swarming for Biomedical Applications

Recently, robots have assisted and contributed to the biomedical field. Scaling down the size of robots to micro/nanoscale can increase the accuracy of targeted medications and decrease the danger of invasive operations in human surgery. Inspired by the motion pattern and collective behaviors of the tiny biological motors in nature, various kinds of sophisticated and programmable microrobots are fabricated with the ability for cargo delivery, bio-imaging, precise operation, etc. In this review, four types of propulsion-magnetically, acoustically, chemically/optically and hybrid driven-and their corresponding features have been outlined and categorized. In particular, the locomotion of these micro/nanorobots, as well as the requirement of biocompatibility, transportation efficiency, and controllable motion for applications in the complex human body environment should be considered. We discuss applications of different propulsion mechanisms in the biomedical field, list their individual benefits, and suggest their potential growth paths.

Quantitative Analysis of Drag Force for Task-Specific Micromachine at Low Reynolds Numbers

Micromotors have spread widely in order to meet the needs of new applications, including cell operation, drug delivery, biosensing, precise surgery and environmental decontamination, due to their small size, low energy consumption and large propelling power, especially the newly designed multifunctional micromotors that combine many extra shape features in one device. Features such as rod-like receptors, dendritic biosensors and ball-like catalyzing enzymes are added to the outer surface of the tubular micromotor during fabrication to perform their special mission. However, the structural optimization of motion performance is still unclear. The main factor restricting the motion performance of the micromotors is the drag forces. The complex geometry of a micromotor makes its dynamic behavior more complicated in a fluid environment. This study aimed to design the optimum structure of tubular micromotors with minimum drag forces and obtain the magnitude of drag forces considering both the internal and external fluids of the micromotors. By using the computational fluid dynamics software Fluent 18.0 (ANSYS), the drag force and the drag coefficient of different conical micromotors were calculated. Moreover, the influence of the Reynolds numbers Re, the semi-cone angle δ and the ratios ξ and η on the drag coefficient was analyzed. The results show the drag force monotonically increased with Reynolds numbers Re and the ratio η. The extreme point of the drag curve is reached when the semi-cone angle δ is 8° and the ratio ξ is 3.846. This work provides theoretical support and guidance for optimizing the design and development of conical micromotors.

Active colloidal molecules in activity gradients

We consider a rigid assembly of two active Brownian particles, forming an active colloidal dimer, in a gradient of activity. We show analytically that depending on the relative orientation of the two particles the active dimer accumulates in regions of either high or low activity, corresponding to, respectively, chemotaxis and antichemotaxis. Certain active dimers show both chemotactic and antichemotactic behavior, depending on the strength of the activity. Our coarse-grained Fokker-Planck approach yields an effective potential, which we use to construct a nonequilibrium phase diagram that classifies the dimers according to their tactic behavior. Moreover, we show that for certain dimers a higher persistence of the motion is achieved similar to the effect of a steering wheel in macroscopic devices. This work could be useful for designing autonomous active colloidal structures which adjust their motion depending on the local activity gradients.

Nanoswimmers Based on Capped Janus Nanospheres

Nanoswimmers are synthetic nanoscale objects that convert the available surrounding free energy to a directed motion. For example, bacteria with various flagella types serve as textbook examples of the minuscule swimmers found in nature. Along these lines, a plethora of artificial hybrid and non-hybrid nanoswimmers have been introduced, and they could find many uses, e.g., for targeted drug delivery systems (TDDSs) and controlled drug treatments. Here, we discuss a certain class of nanoparticles, i.e., functional, capped Janus nanospheres that can be employed as nanoswimmers, their subclasses and properties, as well as their various implementations. A brief outlook is given on different fabrication and synthesis methods, as well as on the diverse compositions used to prepare nanoswimmers, with a focus on the particle types and materials suitable for biomedical applications. Several recent studies have shown remarkable success in achieving temporally and spatially controlled drug delivery in vitro using Janus-particle-based TDDSs. We believe that this review will serve as a concise introductory synopsis for the interested readers. Therefore, we hope that it will deepen the general understanding of nanoparticle behavior in biological matrices.

Self-propelled micro/nanobots: A new insight into precisely targeting cancerous cells through intelligent and deep cancer penetration

Cancer overlooks are globally one of the most dangerous and life-threatening tribulations. While significant advances have been made in the targeted delivery of anti-cancer medications over the last few years, several challenges, such as low efficacy and strong toxic effects, remain to be addressed. Micro/nanomotors have been thoroughly studied for both effective cancer detection and treatment, as demonstrated by significant advancements in the architecture of smart and functional micro/nanomotor biomedical systems. Able to self-propelled within fluid media, micro/nanomotors have attractive vehicles to maximize the efficacy of tumor delivery. Here, we present the current developments in the delivery, detection, and imaging-guided treatment of micro/nanomotors in the clinical field, including cancer-related specific targeted drug delivery, and then discuss the barriers and difficulties encountered by micro/nanomotors throughout the medical process. Furthermore, this paper addresses the potential growth of micro/nanomotors for medical applications, and sets out the current drawbacks and future research directions for more advancement.

Light-driven microdrones

When photons interact with matter, forces and torques occur due to the transfer of linear and angular momentum, respectively. The resulting accelerations are small for macroscopic objects but become substantial for microscopic objects with small masses and moments of inertia, rendering photon recoil very attractive to propel micro- and nano-objects. However, until now, using light to control object motion in two or three dimensions in all three or six degrees of freedom has remained an unsolved challenge. Here we demonstrate light-driven microdrones (size roughly 2 μm and mass roughly 2 pg) in an aqueous environment that can be manoeuvred in two dimensions in all three independent degrees of freedom (two translational and one rotational) using two overlapping unfocused light fields of 830 and 980 nm wavelength. To actuate the microdrones independent of their orientation, we use up to four individually addressable chiral plasmonic nanoantennas acting as nanomotors that resonantly scatter the circular polarization components of the driving light into well-defined directions. The microdrones are manoeuvred by only adjusting the optical power for each motor (the power of each circular polarization component of each wavelength). The actuation concept is therefore similar to that of macroscopic multirotor drones. As a result, we demonstrate manual steering of the microdrones along complex paths. Since all degrees of freedom can be addressed independently and directly, feedback control loops may be used to counteract Brownian motion. We posit that the microdrones can find applications in transport and release of cargos, nanomanipulation, and local probing and sensing of nano and mesoscale objects.

Wheel-like Magnetic-Driven Microswarm with a Band-Aid Imitation for Patching Up Microscale Intestinal Perforation

Microscale intestinal perforation can cause considerable mortality and is very difficult to treat using conventional methods owing to the numerous challenges associated with microscale operations, which require the development of new body-friendly and effective treatment methods. Swarming micro- and nanomotors have shown great potential in biomedical applications in complex and hard-to-reach environments. Herein, we present a wheel-like magnetic-driven microswarm (WLM) with a band-aid imitation to patch microscale intestinal perforations by pasting on the perforation point in mucus-filled environments. A method called "packing under rolling" was applied to make the formed microswarms denser and rounder. Microswarms with variable aspect ratios can be fabricated by tuning the frequency and strength of the external magnetic field. Actuation and navigation in a confined complex environment, locomotion on three-dimensional surfaces, and multiple switchable motion modes have been realized by combining AC and DC magnetic fields. Moreover, we demonstrated WLM controllable navigation, movement, and microscale perforation patching in the chicken intestines ex vivo. The proposed strategy will contribute to the treatment of microscale intestinal perforation and may be applicable to novel, precise topical medication and microsurgery.

Polymeric Micro/Nanocarriers and Motors for Cargo Transport and Phototriggered Delivery

Smart polymer-based micro/nanoassemblies have emerged as a promising alternative for transporting and delivering a myriad of cargo. Cargo encapsulation into (or linked to) polymeric micro/nanocarrier (PC) strategies may help to conserve cargo activity and functionality when interacting with its surroundings in its journey to the target. PCs for cargo phototriggering allow for excellent spatiotemporal control via irradiation as an external stimulus, thus regulating the delivery kinetics of cargo and potentially increasing its therapeutic effect. Micromotors based on PCs offer an accelerated cargo-medium interaction for biomedical, environmental, and many other applications. This review collects the recent achievements in PC development based on nanomicelles, nanospheres, and nanopolymersomes, among others, with enhanced properties to increase cargo protection and cargo release efficiency triggered by ultraviolet (UV) and near-infrared (NIR) irradiation, including light-stimulated polymeric micromotors for propulsion, cargo transport, biosensing, and photo-thermal therapy. We emphasize the challenges of positioning PCs as drug delivery systems, as well as the outstanding opportunities of light-stimulated polymeric micromotors for practical applications.

General Thermodynamic-Controlled Coating Method to Prepare Janus Mesoporous Nanomotors for Improving Tumor Penetration

Artificial nanomotors are undergoing significant developments in several biomedical applications. However, current experimental strategies for producing nanomotors still have inherent drawbacks such as the requirement for expensive equipment, strict controlling of experimental conditions, and strenuous processes with several complex procedures. In this study, we describe for the first time a facile single-step thermodynamic-controlled coating method to prepare Janus mesoporous organosilica nanomotors. By controlling the total free energy of organosilica oligomers (G) from a low development level to a high level in the reaction system, the nonspontaneous nucleation on the platinum (Pt) nanosurface and the spontaneous nucleation in a solvent can be controlled, respectively. More importantly, we reveal that the molecular arrangement and contact angle of deposited organosilica on Pt cores vary with the total free energy of organosilica oligomers (G). Different values of θ would change the trend of detachment from Pt for organosilica nucleated cores and carry out diverse coating modes. These are indicated by the morphology evolution of platinum/organosilica hybrids, from naked platinum nanoparticles, evenly distributed organosilica shell/core, nonconcentric to typical Janus nanomotor. The prepared Janus mesoporous nanomotor (JMN) showed typical mesopore structures and active propelling behaviors under H₂O₂ stimulation. In addition, the JMN modified with hyaluronic acid exhibited excellent biocompatibility and improved tumor penetration under H₂O₂ stimulation. The successful construction of other nanomotor frameworks based on a gold-templated core proves the perfect applicability of the thermodynamic-coating method for the production of nanomotors. In conclusion, this work establishes a manufacturing methodology for nanomotors and drives nanomotors for promising biomedical applications.

In vitro models to evaluate ingestible devices: Present status and current trends

Orally ingestible medical devices offer significant opportunity in the diagnosis and treatment of gastrointestinal conditions. Their development necessitates the use of models that simulate the gastrointestinal environment on both a macro and micro scale. An evolution in scientific technology has enabled a wide range of in vitro, ex vivo and in vivo models to be developed that replicate the gastrointestinal tract. This review describes the landscape of the existing range of in vitro tools that are available to characterize ingestible devices. Models are presented with details on their benefits and limitations with regards to the evaluation of ingestible devices and examples of their use in the evaluation of such devices is presented where available. The multitude of models available provides a suite of tools that can be used in the evaluation of ingestible devices that should be selected on the functionality of the device and the mechanism of its function.

Cooperative transport by flocking phototactic micromotors

Cargo delivery by micro/nanomotors provides enormous opportunities for micromanipulation, environmental cleaning, drug delivery, etc. However, due to the limited driving force, it is usually difficult for single micro/nanomotors to transport cargoes much larger or heavier than themselves. Here, we demonstrate that flocking phototactic TiO2 micromotors can cooperatively transport multiple and different types of large cargoes based on light-responsive diffusiophoresis. Utilizing spontaneous diffusiophoretic attraction, flocking TiO2 micromotors can load large cargoes. Under UV light navigation, flocking TiO2 micromotors cooperatively carry and transport cargoes via collective diffusiophoretic repulsion in open space or complex microenvironments. After reaching the destination, the carried cargoes can also be unloaded from the flock and be deployed at a predetermined destination by disassembling or reversing the flock. This study may pave the way for developing intelligent swarming micro/nanorobots for cooperative targeting micromanipulation and advancing their applications in drug delivery and microengineering.

Apoptotic Tumor DNA Activated Nanomotor Chemotaxis

Inspired by the tactic organisms in Nature that can self-direct their movement following environmental stimulus gradient, we proposed a DNase functionalized Janus nanoparticle (JNP) nanomotor system for the first time, which can be powered by ultralow nM to μM levels of DNA. The system exhibited interesting chemotactic behavior toward a DNA richer area, which is physiologically related with many diseases including tumors. In the presence of the subtle DNA gradient generated by apoptotic tumor cells, the cargo loaded nanomotors were able to sense the DNA signal released by the cells and demonstrate directional motion toward tumor cells. For our system, the subtle DNA gradient by a small amount (10 μL) of tumor cells is sufficient to induce the chemotaxis behavior of self-navigating and self-targeting ability of our nanomotor system, which promises to shed new light for tumor diagnosis and therapy.

Construction of Nanomotors with Replaceable Engines by Supramolecular Machine-Based Host-Guest Assembly and Disassembly

Micro/nanomotors (MNMs) are miniaturized devices capable of performing self-propelled motion and on-demand tasks, which have brought revolutionary renovations in nanomedicine, environmental remediation, biochemical sensing, etc. Numerous methods of either chemical synthesis or physical fabrications have been extensively investigated to prepare MNMs of various shapes and functions. However, MNMs with replaceable engines that can be flexibly assembled and disassembled, resembling that of a macroscopic machine, have not been achieved. Here, for the first time, we report a demonstration of control over the engine replacement of self-propelled nanomotors based on hollow mesoporous silica nanoparticles (HMSNPs) via supramolecular machine-based host-guest assembly and disassembly between azobenzene (Azo) and β-cyclodextrin (β-CD). Nanomotors with different driving mechanisms can be rapidly constructed by selecting corresponding β-CD-modified nanoengines of urease, Pt, or Fe₃O₄, to assemble with the azobenzene-modified HMSNPs (HMSNPs-Azo). In virtue of photoresponsive cis/trans isomer conversion of azobenzene molecules, engine switching can be accomplished by remote light triggered host-guest assembly or disassembly between HMSNPs-Azo and β-CD-modified engines. Moreover, this method can quickly include multiple engines on the surface of the HMSNPs-Azo to prepare a hybrid MNM with enhanced motion capability. This strategy not only is cost-effective for the rapid and convenient preparation of nanomotors with different propulsion mechanism but also paves a new path to future multiple functionalization of MNMs for on-demand task assignment.

Self-/Magnetic-Propelled Catalytic Nanomotors Based on a Janus SPION@PEG-Pt/PCL Hybrid Nanoarchitecture: Single-Particle versus Collective Motions

In this paper, we synthesized superparamagnetic iron oxide nanoparticles (NPs) functionalized with (3-aminopropyl)triethoxysilane (Fe₃O₄@APTES). The synthesized NPs were coated with succinic anhydride (Fe₃O₄@COOH) in the next step. Half the surface of the NPs was shielded with wax microparticles via the Pickering emulsion technique, and the unshielded side was covered with poly(ethylene glycol) methyl ether. Platinum nanoparticles (Pt NPs) were deposited between PEG chains by the oxidation-reduction method through an in situ procedure to obtain a metal-polymer composite. These deposited Pt NPs have the potential to catalyze the decomposition of hydrogen peroxide at the surface of Janus nanomotors (JNMs). After de-waxing of the NPs, Irgacure 2959 (as the initiator) was reacted with the bare side of the NPs to provide the opportunity to grow poly(ε-caprolactone) (PCL) chains on the surface of the nanomotors through the "grafting from" method. The diffusion coefficient and velocity of the JNMs (before and after the PCL reaction) in the aqueous solution of 1, 2, 3, 5, and 10% (w/w) hydrogen peroxide and in the presence of different concentrations of NaCl solutions (0, 5, and 10% (w/v)) were investigated by mean square displacement analysis for single-particle or collective motions of JNMs. In addition, the simultaneous effect of an external magnetic field and the NaCl concentration on the movement direction of JNMs was also evaluated in the presence of hydrogen peroxide (10%). Increasing the ionic strength through NaCl addition permits the JNMs to move with relatively lower amounts of fuel [i.e., 2% (w/w)]. The collective motion investigation of the JNMs showed the highest speed in the media with 10% (w/w) hydrogen peroxide and 5% (w/v) NaCl solution (about 1215.78 μm²/s) due to the surfactant effect of the Janus architecture.

Efficient Protein Transfection by Swarms of Chemically Powered Plasmonic Virus-Sized Nanorobots

Transfection is based on nonviral delivery of nucleic acids or proteins into cells. Viral approaches are being used; nevertheless, their translational capacity is nowadays decreasing due to persistent fear of their safety, therefore creating space for the field of nanotechnology. However, nanomedical approaches introducing static nanoparticles for the delivery of biologically active molecules are very likely to be overshadowed by the vast potential of nanorobotics. We hereby present a rapid nonviral transfection of protein into a difficult-to-transfect prostate cancer cell line facilitated by chemically powered rectangular virus-sized (68 nm × 33 nm) nanorobots. The enhanced diffusion of these biocompatible nanorobots is the key to their fast internalization into cells, happening in a matter of minutes and being up to 6-fold more efficient compared to static nanorobots in a nonfueled environment. The Au/Ag plasmonic nature of these nanorobots makes them simply traceable and allows for their detailed subcellular localization. Protein transfection mediated by such nanorobots is an important step forward, challenging the field of nanomedicine and having potential in future translational medical research.

Active, Yet Little Mobility: Asymmetric Decomposition of H2O2 Is Not Sufficient in Propelling Catalytic Micromotors

A popular principle in designing chemical micromachines is to take advantage of asymmetric chemical reactions such as the catalytic decomposition of H₂O₂. Contrary to intuition, we use Janus micromotors half-coated with platinum (Pt) or catalase as an example to show that this ingredient is not sufficient in powering a micromotor into self-propulsion. In particular, by annealing a thin Pt film on a SiO₂ microsphere, the resulting microsphere half-decorated with discrete Pt nanoparticles swims ∼80% more slowly than its unannealed counterpart in H₂O₂, even though they both catalytically produce comparable amounts of oxygen. Similarly, SiO₂ microspheres half-functionalized with the enzyme catalase show negligible self-propulsion despite high catalytic activity toward decomposing H₂O₂. In addition to highlighting how surface morphology of a catalytic cap enables/disables a chemical micromotor, this study offers a refreshed perspective in understanding how chemistry powers nano- and microscopic objects (or not): our results are consistent with a self-electrophoresis mechanism that emphasizes the electrochemical decomposition of H₂O₂ over nonelectrochemical pathways. More broadly, our finding is a critical piece of the puzzle in understanding and designing nano- and micromachines, in developing capable model systems of active colloids, and in relating enzymes to active matter.