Nano-and Micromotors Designed for Cancer Therapy

Biohybrid Micro/Nanorobots: Pioneering the Next Generation of Medical Technology

Biohybrid micro/nanorobots hold a great potential for advancing biomedical research. These tiny structures, designed to mimic biological organisms, offer a promising method for targeted drug delivery, tissue engineering, biosensing/imaging, and cancer therapy, among other applications. The integration of biology and robotics opens new possibilities for minimally invasive surgeries and personalized healthcare solutions. The key challenges in the development of biohybrid micro/nanorobots include ensuring biocompatibility, addressing manufacturing scalability, enhancing navigation and localization capabilities, maintaining stability in dynamic biological environments, navigating regulatory hurdles, and successfully translating these innovative technologies into clinical applications. Herein, the recent advancements, challenges, and future perspectives related to the biomedical applications of biohybrid micro/nanorobots are described. Indeed, this review sheds light on the cutting-edge developments in this field, providing researchers with an updated overview of the current potential of biohybrid micro/nanorobots in the realm of biomedical applications, and offering insights into their practical applications. Furthermore, it delves into recent advancements in the field of biohybrid micro/nanorobotics, providing a comprehensive analysis of the current state-of-the-art technologies and their future applications in the biomedical field.

Recent advances in the development of tumor microenvironment-activatable nanomotors for deep tumor penetration

Cancer represents a significant threat to human health, with the use of traditional chemotherapy drugs being limited by their harsh side effects. Tumor-targeted nanocarriers have emerged as a promising solution to this problem, as they can deliver drugs directly to the tumor site, improving drug effectiveness and reducing adverse effects. However, the efficacy of most nanomedicines is hindered by poor penetration into solid tumors. Nanomotors, capable of converting various forms of energy into mechanical energy for self-propelled movement, offer a potential solution for enhancing drug delivery to deep tumor regions. External force-driven nanomotors, such as those powered by magnetic fields or ultrasound, provide precise control but often necessitate bulky and costly external equipment. Bio-driven nanomotors, propelled by sperm, macrophages, or bacteria, utilize biological molecules for self-propulsion and are well-suited to the physiological environment. However, they are constrained by limited lifespan, inadequate speed, and potential immune responses. To address these issues, nanomotors have been engineered to propel themselves forward by catalyzing intrinsic "fuel" in the tumor microenvironment. This mechanism facilitates their penetration through biological barriers, allowing them to reach deep tumor regions for targeted drug delivery. In this regard, this article provides a review of tumor microenvironment-activatable nanomotors (fueled by hydrogen peroxide, urea, arginine), and discusses their prospects and challenges in clinical translation, aiming to offer new insights for safe, efficient, and precise treatment in cancer therapy.

Breaking barriers in cancer treatment: nanobiohybrids empowered by modified bacteria and vesicles

Cancer, the leading global cause of mortality, poses a formidable challenge for treatment. The effectiveness of cancer therapies, ranging from chemotherapy to immunotherapy, relies on the precise delivery of therapeutic agents to tumor tissues. Nanobiohybrids, resulting from the fusion of bacteria with nanomaterials, constitute a promising delivery system. Nanobiohybrids offer several advantages, including the ability to target tumors, genetic engineering capabilities, programmed product creation, and the potential for multimodal treatment. Recent advances in targeted tumor treatments have leveraged bacteria-based nanobiohybrids. Here, we outline the progress in cancer treatment using nanobiohybrids. Our focus is particularly on various therapeutic approaches within the context of nanobiohybrid systems, where bacteria are integrated with nanomaterials to combat cancer. It has been demonstrated that bacteria-based nanobiohybrids present a robust and effective method for tumor theranostics.

Active osmoticlike pressure on permeable inclusions

We use a standard minimal active Brownian model to investigate the osmotic-like effective pressure generated by active fluids on fixed hollow inclusions. These inclusions are enclosed by a permeable (albeit nonflexible) membrane, and the interior and exterior regions of the inclusions have different particle motility strengths. We consider both rectangular and disklike inclusions and analyze the effects of various system parameters, such as excluded volume interaction between active particles, hardness of membrane, and active particle density, on the effective pressure produced on the enclosing membrane. We focus on the range of intermediate to high motility strengths and analyze the effective pressure in the steady state. Our findings for the active pressure produced in the interior and exterior regions of the inclusion indicate that the pressure is higher in the region with lower motility due to the relatively stronger accumulation of active particles.

Superparamagnetic Artificial Cells PLGA-Fe3O4 Micro/Nanocapsules for Cancer Targeted Delivery

Artificial cells have been extensively used in many fields, such as nanomedicine, biotherapy, blood substitutes, drug delivery, enzyme/gene therapy, cancer therapy, and the COVID-19 vaccine. The unique properties of superparamagnetic Fe3O4 nanoparticles have contributed to increased interest in using superparamagnetic artificial cells (PLGA-Fe3O4 micro/nanocapsules) for targeted therapy. In this review, the preparation methods of Fe3O4 NPs and superparamagnetic artificial cell PLGA-drug-Fe3O4 micro/nanocapsules are discussed. This review also focuses on the recent progress of superparamagnetic PLGA-drug-Fe3O4 micro/nanocapsules as targeted therapeutics. We shall concentrate on the use of superparamagnetic artificial cells in the form of PLGA-drug-Fe3O4 nanocapsules for magnetic hyperthermia/photothermal therapy and cancer therapies, including lung breast cancer and glioblastoma.

Sideways propelled bimetallic rods at the water/oil interface

The motion of self-propelling microswimmers is significantly affected by confinement, which can enhance or reduce their mobility and also steer the direction of their propulsion. While their interactions with solid boundaries have already received considerable attention, many aspects of the influence of liquid-liquid interfaces (LLI) on active particle propulsion still remain unexplored. In this work, we studied the adsorption and motion of bimetallic Janus sideways propelled rods dispersed at the interface between an aqueous solution of hydrogen peroxide and oil. The wetting properties of the bimetallic rods result in a wide distribution of their velocities at the LLI. While a fraction of rods remain immotile, we note a significant enhancement of motility for the rest of the particles with velocities of up to 8 times higher in comparison to those observed near a solid wall. Liquid-liquid interfaces, therefore, can provide a new way to regulate the propulsion of bimetallic particles.

Visible Light-Driven Micromotors in Fuel-Free Environment with Promoted Ion Tolerance

Light-driven electrophoretic micromotors have gained significant attention recently for applications in drug delivery, targeted therapy, biosensing, and environmental remediation. Micromotors that possess good biocompatibility and the ability to adapt to complex external environments are particularly attractive. In this study, we have fabricated visible light-driven micromotors that could swim in an environment with relatively high salinity. To achieve this, we first tuned the energy bandgap of rutile TiO₂ that was hydrothermally synthesized, enabling it to generate photogenerated electron-hole pairs under visible light rather than solely under UV. Next, platinum nanoparticles and polyaniline were decorated onto the surface of TiO₂ microspheres to facilitate the micromotors swimming in ion-rich environments. Our micromotors exhibited electrophoretic swimming in NaCl solutions with concentrations as high as 0.1 M, achieving a velocity of 0.47 μm/s without the need for additional chemical fuels. The micromotors' propulsion was generated solely by splitting water under visible light illumination, therefore offering several advantages over traditional micromotors, such as biocompatibility and the ability to operate in environments with high ionic strength. These results demonstrated high biocompatibility of photophoretic micromotors and high potential for practical applications in various fields.

A Biomolecular Toolbox for Precision Nanomotors

The application of nanomotors for cancer diagnosis and therapy is a new and exciting area of research, which when combined with precision nanomedicine, promises to solve many of the issues encountered by previous development of passive nanoparticles. The goal of this article is to introduce nanomotor and nanomedicine researchers to the deep pool of knowledge available regarding cancer cell biology and biochemistry, as well as provide a greater appreciation of the complexity of cell membrane compositions, extracellular surfaces, and their functional consequences. A short description of the nanomotor state-of-art for cancer therapy and diagnosis is first provided, as well as recommendations for future directions of the field. Then, a biomolecular targeting toolbox has been collated for researchers looking to apply their nanomaterial of choice to a biological setting, as well as providing a glimpse into currently available clinical therapies and technologies. This toolbox contains an overview of different classes of targeting molecules available for high affinity and specific targeting and cell surface targets to aid researchers in the selection of a clinical disease model and targeting methodology. It is hoped that this review will provide biological context, inspiration, and direction to future nanomotor and nanomedicine research.

Nanoengineering of biohybrid micro/nanobots for programmed biomedical applications

Biohybrid micro/nanobots have emerged as an innovative resource to be employed in the biomedical field due to their biocompatible and biodegradable properties. These are tiny nanomaterial-based integrated structures engineered in a way that they can move autonomously and perform the programmed tasks efficiently even at hard-to-reach organ/tissues/cellular sites. The biohybrid micro/nanobots can either be cell/bacterial/enzyme-based or may mimic the properties of an active molecule. It holds the potential to change the landscape in various areas of biomedical including early diagnosis of disease, therapeutics, imaging, or precision surgery. The propulsion mechanism of the biohybrid micro/nanobots can be both fuel-based and fuel-free, but the most effective and easiest way to propel these micro/nanobots is via enzymes. Micro/nanobots possess the feature to adsorb/functionalize chemicals or drugs at their surfaces thus offering the scope of delivering drugs at the targeted locations. They also have shown immense potential in intracellular sensing of biomolecules and molecular events. Moreover, with recent progress in the material development and processing is required for enhanced activity and robustness the fabrication is done via various advanced techniques to avoid self-degradation and cause cellular toxicity during autonomous movement in biological medium. In this review, various approaches of design, architecture, and performance of such micro/nanobots have been illustrated along with their potential applications in controlled cargo release, therapeutics, intracellular sensing, and bioimaging. Furthermore, it is also foregrounding their advancement offering an insight into their future scopes, opportunities, and challenges involved in advanced biomedical applications.

Establishment of ultrasound-responsive SonoBacteriaBot for targeted drug delivery and controlled release

Bacteria-driven biohybrid microbots have shown great potential in caⁿcer treatment. However, how precisely controlling drug release at the tumor site is still an issue. To overcome the limitation of this system, we proposed the ultrasound-responsive SonoBacteriaBot (DOX-PFP-PLGA@EcM). Doxorubicin (DOX) and perfluoro-n-pentane (PFP) were encapsulated in polylactic acid-glycolic acid (PLGA) to form ultrasound-responsive DOX-PFP-PLGA nanodroplets. Then, DOX-PFP-PLGA@EcM is created by DOX-PFP-PLGA amide-bonded to the surface of E. coli MG1655 (EcM). The DOX-PFP-PLGA@EcM was proved to have the characteristics of high tumor-targeting efficiency, controlled drug release capability, and ultrasound imaging. Based on the acoustic phase change function of nanodroplets, DOX-PFP-PLGA@EcM enhance the signal of US imaging after ultrasound irradiation. Meanwhile, the DOX loaded into DOX-PFP-PLGA@EcM can be released. After being intravenously injected, DOX-PFP-PLGA@EcM can efficiently accumulate in tumors without causing harm to critical organs. In conclusion, the SonoBacteriaBot has significant benefits in real-time monitoring and controlled drug release, which has significant potential applications for therapeutic drug delivery in clinical settings.

Photothermal Nanoheaters-Modified Spores for Safe and Controllable Antitumor Therapy

Introduction

To present a safer tumor therapy based on bacteria and identify in detail how the activation and infection behavior of spores can be controlled remotely by near-infrared light (NIR-irradiation) based on nanoheaters' modification.

Methods

Spores bring a better tolerance to surface modification. Transitive gold-nanorods-allied-nanoclusters-modified spores (Spore@NRs/NCs) were constructed by covalent glutaraldehyde crosslink. The photothermal properties of nanoheaters before and after attachment to spores were studied by recording temperature-irradiation time curves. The controlled viability and infection behavior of Spore@NRs/NCs were investigated by NIR-irradiation.

Results

In this work, a controllable sterilizing effect to activated vegetative bacteria was obtained obviously. When met with a suitable growth-environment, Spore@NRs/NCs could germinate, activate into vegetative bacteria and continue to reproduce. Without NIR-irradiation, nanoheaters could not affect the activity of both spores and vegetative bacterial cells. However, with NIR-irradiation after incubating in growth medium, nanoheaters on spores could control the spores' germination and affect the growth curve as well as the viability of the vegetative bacterial cells. For Spore@NRs/NCs (Spore:NCs:NRs=1:1:4, 67.5 μg mL^-1), a ~98% killing rate of vegetative bacterial cells was obtained with NIR-irradiation (2.8 W cm^-2, 20 min) after 2 h-incubation. In addition, these nanoheaters modified on spores could be taken not only to the vegetative bacteria cells, but also to the first-generation bacteria cells with their excellent photothermal and bactericidal performance, as well as synergetic anticancer effect. NIR-irradiation after 2 h-incubation could also trigger Spore@NRs/NCs (1:1:4, 6 μL) to synergistically reduce the viability of HCT116 cells to 15.63±2.90%.

Conclusion

By using NIR-irradiation, the "transitive" nanoheaters can remotely control the activity of both bacteria (germinated from spore) and cancer cells. This discovery provides basis and a feasible plan for controllable safer treatment of bacteria therapy, especially anaerobes with spores in hypoxic areas of the malignant solid tumors.

Intelligent Micro-/Nanorobots for Cancer Theragnostic

Cancer is one of the most intractable diseases owing to its high mortality rate and lack of effective diagnostic and treatment tools. Advancements in micro-/nanorobot (MNR)-assisted sensing, imaging, and therapeutics offer unprecedented opportunities to develop MNR-based cancer theragnostic platforms. Unlike ordinary nanoparticles, which exhibit Brownian motion in biofluids, MNRs overcome viscous resistance in an ultralow Reynolds number (Re << 1) environment by effective self-propulsion. This unique locomotion property has motivated the advanced design and functionalization of MNRs as a basis for next-generation cancer-therapy platforms, which offer the potential for precise distribution and improved permeation of therapeutic agents. Enhanced barrier penetration, imaging-guided operation, and biosensing are additionally studied to enable the promising cancer-related applications of MNRs. Herein, the recent advances in MNR-based cancer therapy are comprehensively addresses, including actuation engines, diagnostics, medical imaging, and targeted drug delivery; promising research opportunities that can have a profound impact on cancer therapy over the next decade is highlighted.

Contemporary Tools for the Cure against Pernicious Microorganisms: Micro-/Nanorobots

One of the most pressing concerns to global public health is the emergence of drug-resistant pathogenic microorganisms due to increased unconscious antibiotic usage. With the rising antibiotic resistance, existing antimicrobial agents lose their effectiveness over time. This indicates that newer and more effective antimicrobial agents and methods should be investigated. Many studies have shown that micro-/nanorobots exhibit promise in the treatment of microbial infections with their great properties, such as the intrinsic antimicrobial activities owing to their oxidative stress induction and metal ion release capabilities, and effective and autonomous delivery of antibiotics to the target area. In addition, they have multiple simultaneous mechanisms of action against microbes, which makes them remarkable in antimicrobial activity. This review focuses on the antimicrobial micro-/nanorobots and their strategies to impede biofilm formation, following a brief introduction of the latest advancements in micro-/nanorobots, and their implementations against various bacteria, and other microorganisms.

Spatiotemporal control of engineered bacteria to express interferon-γ by focused ultrasound for tumor immunotherapy

Bacteria-based tumor therapy has recently attracted wide attentions due to its unique capability in targeting tumors and preferentially colonizing the core area of the tumor. Various therapeutic genes are also harbored into these engineering bacteria to enhance their anti-tumor efficacy. However, it is difficult to spatiotemporally control the expression of these inserted genes in the tumor site. Here, we engineer an ultrasound-responsive bacterium (URB) which can induce the expression of exogenous genes in an ultrasound-controllable manner. Owing to the advantage of ultrasound in tissue penetration, an acoustic remote control of bacterial gene expression can be realized by designing a temperature-actuated genetic switch. Cytokine interferon-γ (IFN-γ), an important immune regulatory molecule that plays a significant role in tumor immunotherapy, is used to test the system. Our results show that brief hyperthermia induced by focused ultrasound promotes the expression of IFN-γ gene, improving anti-tumor efficacy of URB in vitro and in vivo. Our study provides an alternative strategy for bacteria-mediated tumor immunotherapy.

Beyond Janus Geometry: Characterization of Flow Fields around Nonspherical Photocatalytic Microswimmers

Catalytic microswimmers that move by a phoretic mechanism in response to a self-induced chemical gradient are often obtained by the design of spherical janus microparticles, which suffer from multi-step fabrication and low yields. Approaches that circumvent laborious multi-step fabrication include the exploitation of the possibility of nonuniform catalytic activity along the surface of irregular particle shapes, local excitation or intrinsic asymmetry. Unfortunately, the effects on the generation of motion remain poorly understood. In this work, single crystalline BiVO₄ microswimmers are presented that rely on a strict inherent asymmetry of charge-carrier distribution under illumination. The origin of the asymmetrical flow pattern is elucidated because of the high spatial resolution of measured flow fields around pinned BiVO₄ colloids. As a result the flow from oxidative to reductive particle sides is confirmed. Distribution of oxidation and reduction reactions suggests a dominant self-electrophoretic motion mechanism with a source quadrupole as the origin of the induced flows. It is shown that the symmetry of the flow fields is broken by self-shadowing of the particles and synthetic surface defects that impact the photocatalytic activity of the microswimmers. The results demonstrate the complexity of symmetry breaking in nonspherical microswimmers and emphasize the role of self-shadowing for photocatalytic microswimmers. The findings are leading the way toward understanding of propulsion mechanisms of phoretic colloids of various shapes.

From radial to unidirectional water pumping in zeta-potential modulated Nafion nanostructures

Chemically propelled micropumps are promising wireless systems to autonomously drive fluid flows for many applications. However, many of these systems are activated by nocuous chemical fuels, cannot operate at high salt concentrations, or have difficulty for controlling flow directionality. In this work we report on a self-driven polymer micropump fueled by salt which can trigger both radial and unidirectional fluid flows. The micropump is based on the cation-exchanger Nafion, which produces chemical gradients and local electric fields capable to trigger interfacial electroosmotic flows. Unidirectional pumping is predicted by simulations and achieved experimentally by nanostructuring Nafion into microarrays with a fine tune modulation of surrounding surface zeta potentials. Nafion micropumps work in a wide range of salt concentrations, are reusable, and can be fueled by different salt cations. We demonstrate that they work with the common water-contaminant cadmium, using the own capture of this ion as fuel to drive fluid pumping. Thus, this system has potential for efficient and fast water purification strategies for environmental remediation. Unidirectional Nafion pumps also hold promise for effective analyte delivery or preconcentration for (bio)sensing assays.

Chemically propelled micropumps are wireless fluid flow driving systems with many potential applications. Here, the authors report a self-driven reusable Nafion micropump fueled by different salt cations in a wide range of concentrations that triggers both radial and unidirectional flows, showing efficient water remediation capabilities.

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.

Multifunctional micro/nanomotors as an emerging platform for smart healthcare applications

Self-propelling micro- and nano-motors (MNMs) are emerging as a multifunctional platform for smart healthcare applications such as biosensing, bioimaging, and targeted drug delivery with high tissue penetration, stirring effect, and rapid drug transport. MNMs can be propelled and/or guided by chemical substances or external stimuli including ultrasound, magnetic field, and light. In addition, enzymatically powered MNMs and biohybrid micromotors have been developed using the biological components in the body. In this review, we describe emerging MNMs focusing on their smart propulsion systems, and diagnostic and therapeutic applications. Finally, we highlight several MNMs for in vivo applications and discuss the future perspectives of MNMs on their current limitations and possibilities toward further clinical applications.

Multi-Functional Liposome: A Powerful Theranostic Nano-Platform Enhancing Photodynamic Therapy

Although photodynamic therapy (PDT) has promising advantages in almost non-invasion, low drug resistance, and low dark toxicity, it still suffers from limitations in the lipophilic nature of most photosensitizers (PSs), short half-life of PS in plasma, poor tissue penetration, and low tumor specificity. To overcome these limitations and enhance PDT, liposomes, as excellent multi-functional nano-carriers for drug delivery, have been extensively studied in multi-functional theranostics, including liposomal PS, targeted drug delivery, controllable drug release, image-guided therapy, and combined therapy. This review provides researchers with a useful reference in liposome-based drug delivery.

Microfluidics for Microswimmers: Engineering Novel Swimmers and Constructing Swimming Lanes on the Microscale, a Tutorial Review

This paper provides an updated review of recent advances in microfluidics applied to artificial and biohybrid microswimmers. Sharing the common regime of low Reynolds number, the two fields have been brought together to take advantage of the fluid characteristics at the microscale, benefitting microswimmer research multifold. First, microfluidics offer simple and relatively low-cost devices for high-fidelity production of microswimmers made of organic and inorganic materials in a variety of shapes and sizes. Microscale confinement and the corresponding fluid properties have demonstrated differential microswimmer behaviors in microchannels or in the presence of various types of physical or chemical stimuli. Custom environments to study these behaviors have been designed in large part with the help of microfluidics. Evaluating microswimmers in increasingly complex lab environments such as microfluidic systems can ensure more effective implementation for in-field applications. The benefits of microfluidics for the fabrication and evaluation of microswimmers are balanced by the potential use of microswimmers for sample manipulation and processing in microfluidic systems, a large obstacle in diagnostic and other testing platforms. In this review various ways in which these two complementary technology fields will enhance microswimmer development and implementation in various fields are introduced.

The emerging technology of biohybrid micro-robots: a review

Abstract

In the past few decades, robotics research has witnessed an increasingly high interest in miniaturized, intelligent, and integrated robots. The imperative component of a robot is the actuator that determines its performance. Although traditional rigid drives such as motors and gas engines have shown great prevalence in most macroscale circumstances, the reduction of these drives to the millimeter or even lower scale results in a significant increase in manufacturing difficulty accompanied by a remarkable performance decline. Biohybrid robots driven by living cells can be a potential solution to overcome these drawbacks by benefiting from the intrinsic microscale self-assembly of living tissues and high energy efficiency, which, among other unprecedented properties, also feature flexibility, self-repair, and even multiple degrees of freedom. This paper systematically reviews the development of biohybrid robots. First, the development of biological flexible drivers is introduced while emphasizing on their advantages over traditional drivers. Second, up-to-date works regarding biohybrid robots are reviewed in detail from three aspects: biological driving sources, actuator materials, and structures with associated control methodologies. Finally, the potential future applications and major challenges of biohybrid robots are explored.

Graphic abstract

Impact of Segmented Magnetization on the Flagellar Propulsion of Sperm-Templated Microrobots

Technical design features for improving the way a passive elastic filament produces propulsive thrust can be understood by analyzing the deformation of sperm-templated microrobots with segmented magnetization. Magnetic nanoparticles are electrostatically self-assembled on bovine sperm cells with nonuniform surface charge, producing different categories of sperm-templated microrobots. Depending on the amount and location of the nanoparticles on each cellular segment, magnetoelastic and viscous forces determine the wave pattern of each category during flagellar motion. Passively propagating waves are induced along the length of these microrobots using external rotating magnetic fields and the resultant wave patterns are measured. The response of the microrobots to the external field reveals distinct flow fields, propulsive thrust, and frequency responses during flagellar propulsion. This work allows predictions for optimizing the design and propulsion of flexible magnetic microrobots with segmented magnetization.

'Sweeping rods': cargo transport by self-propelled bimetallic microrods moving perpendicular to their long axis

A possible application of self-propelling particles is the transport of microscopic cargo. Maximizing the collection and transport efficiency of particulate matter requires the area swept by the moving particle to be as large as possible. One such particle geometry are rods propelled perpendicular to their long axis, that act as "sweepers" for collecting particles. Here we report on the required Janus coating to achieve such motion, and on the dynamics of the collection and transport of microscopic cargo by sideways propelled Janus rods.

Fully Steerable Symmetric Thermoplasmonic Microswimmers

A cornerstone of the directed motion of microscopic self-propelling particles is an asymmetric particle structure defining a polarity axis along which these tiny machines move. This structural asymmetry ties the orientational Brownian motion to the microswimmers directional motion, limiting their persistence and making the long time motion effectively diffusive. Here, we demonstrate a completely symmetric thermoplasmonic microswimmer, which is propelled by laser-induced self-thermophoresis. The propulsion direction is imprinted externally to the particle by the heating laser position. The orientational Brownian motion, thus, becomes irrelevant for the propulsion, allowing enhanced control over the particles dynamics with almost arbitrary steering capability. We characterize the particle motion in experiments and simulations and also theoretically. The analysis reveals additional noise appearing in these systems, which is conjectured to be relevant for biological systems. Our experimental results show that even very small particles can be precisely controlled, enabling more advanced applications of these micromachines.

Biomedical Micro-/Nanomotors: From Overcoming Biological Barriers to In Vivo Imaging

Self-propelled micro- and nanomotors (MNMs) have shown great potential for applications in the biomedical field, such as active targeted delivery, detoxification, minimally invasive diagnostics, and nanosurgery, owing to their tiny size, autonomous motion, and navigation capacities. To enter the clinic, biomedical MNMs request the biodegradability of their manufacturing materials, the biocompatibility of chemical fuels or externally physical fields, the capability of overcoming various biological barriers (e.g., biofouling, blood flow, blood-brain barrier, cell membrane), and the in vivo visual positioning for autonomous navigation. Herein, the recent advances of synthetic MNMs in overcoming biological barriers and in vivo motion-tracking imaging techniques are highlighted. The challenges and future research priorities are also addressed. With continued attention and innovation, it is believed that, in the future, biomedical MNMs will pave the way to improve the targeted drug delivery efficiency.

A Journey of Nanomotors for Targeted Cancer Therapy: Principles, Challenges, and a Critical Review of the State-of-the-Art

A nanomotor is a miniaturized device that converts energy stored in the environment into mechanical motion. The last two decades have witnessed a surge of research interests in the biomedical applications of nanomotors, but little clinical translation. To accelerate this process, targeted cancer therapy is used as an example to describe a "survive, locate, operate, and terminate" (SLOT) mission of a nanomotor, where it must 1) survive in the unfriendly in vivo environment, 2) locate its target as well as be located by human operators, 3) carry out specific operations, and 4) terminate after the mission is completed. Along this journey, the challenges presented to a nanomotor, including to power, navigate, steer, target, release, control, image, and communicate are discussed, and how state-of-the-art nanomotors meet or fall short of these requirements is critically reviewed. These discussions are then condensed into a table for easy reference. In particular, it is argued that chemically powered nanomotors are intrinsically ill-positioned for targeted cancer therapy, while nanomotors powered by magnetic fields or ultrasound show more promises. Following this argument, a tentative nanomotor design is then presented in the end to conform to the SLOT guideline, and to inspire practical, functional nanorobots that are yet to come.

Research Progress of Micro/Nanomotors for Cancer Treatment

Nanomaterials have been widely used in cancer treatment and have achieved remarkable results. However, the specificity of the tumor microenvironment and a series of biological barriers (such as blood flow, cell membrane, dense tissue, etc.) have caused many obstacles faced by nanomaterials after entering the human body, which makes traditional drug delivery vehicles have insurmountable difficulties, such as low delivery efficiency, poor permeability, etc. The micro/nanomotors with autonomous movement capabilities provide the possibility to solve the above problems. Therefore, this review summarizes the current researches of micro/nanomotors strategies to overcome the different biological barriers of nanomaterials in cancer treatment. The advantages and disadvantages of three typical micro/nanomotors (biological, physical and chemical micro/nanomotors) in cancer treatment are summarized separately, and the future design of micro/nanomotors more suitable for tumor environment was discussed.

Engineering microrobots for targeted cancer therapies from a medical perspective

Systemic chemotherapy remains the backbone of many cancer treatments. Due to its untargeted nature and the severe side effects it can cause, numerous nanomedicine approaches have been developed to overcome these issues. However, targeted delivery of therapeutics remains challenging. Engineering microrobots is increasingly receiving attention in this regard. Their functionalities, particularly their motility, allow microrobots to penetrate tissues and reach cancers more efficiently. Here, we highlight how different microrobots, ranging from tailor-made motile bacteria and tiny bubble-propelled microengines to hybrid spermbots, can be engineered to integrate sophisticated features optimised for precision-targeting of a wide range of cancers. Towards this, we highlight the importance of integrating clinicians, the public and cancer patients early on in the development of these novel technologies.

Active Assembly of Spheroidal Photocatalytic BiVO4 Microswimmers

We create single-component photocatalytic bismuth vanadate (BiVO₄) microswimmers with a spheroidal shape that move individually upon irradiation without any asymmetrization step. These particles form active assemblies which we investigate combining an experimental approach with numerical simulations and analytical calculations. We systematically explore the speed and assembly of the swimmers into clusters of up to four particles and find excellent agreement between experiment and theory, which helps us to understand motion patterns and speed trends. Moreover, different batches of particles can be functionalized separately, making them ideal candidates to fulfill a multitude of tasks, such as sensing or environmental remediation. To exemplify this, we coat our swimmers with silica (SiO₂) and selectively couple some of their modules to fluorophores in a way which does not inhibit self-propulsion. The present work establishes spheroidal BiVO₄ microswimmers as a versatile platform to design multifunctional microswimmers.

Catalytic/magnetic assemblies of rolled-up tubular nanomembrane-based micromotors

Nano/-micromotors self-assembling into static and dynamic clusters are of considerable promise to study smart, interactive, responsive, and adaptive nano/-micromaterials that can mimic spatio-temporal patterns, swarming, and collective behaviors widely observed in nature. Previously, the dynamic self-assembly of bubble-propelled catalytic micromotors initiated by capillary forces has been reported. This manuscript shows novel self-assembly modes of magnetic/catalytic Ti/FeNi/Pt tubular micromotors. When chemical fuel (hydrogen peroxide) is added it is decomposed on contact with Pt catalyst into oxygen and water. Here, the non-bubbling motion and autonomous assembly of catalytic/magnetic nanomembranes, i.e. without nucleation/generation of oxygen bubbles, are shown. Moreover, magnetic Ti/FeNi/Pt micromotors are spun using an external magnetic field and they form dynamic clusters balanced by attractive magnetic and repulsive hydrodynamic interactions. Micromotors form dynamic clusters, undergo precession and rapidly propagate through the solution.

Effective interactions mediated between two permeable disks in an active fluid

We study steady-state properties of a bath of active Brownian particles (ABPs) in two dimensions in the presence of two fixed, permeable (hollow) disklike inclusions, whose interior and exterior regions can exhibit mismatching motility (self-propulsion) strengths for the ABPs. We show that such a discontinuous motility field strongly affects spatial distribution of ABPs and thus also the effective interaction mediated between the inclusions through the active bath. Such net interactions arise from soft interfacial repulsions between ABPs that sterically interact with and/or pass through permeable membranes assumed to enclose the inclusions. Both regimes of repulsion and attractive (albeit with different mechanisms) are reported and summarized in overall phase diagrams.

Current status of micro/nanomotors in drug delivery

Synthetic micro/nanomotors (MNMs) are novel, self-propelled nano or microscale devices that are widely used in drug transport, cell stimulation and isolation, bio-imaging, diagnostic and monitoring, sensing, photocatalysis and environmental remediation. Various preparation methods and propulsion mechanisms make MNMs "tailormade" nanosystems for the intended purpose or use. As the one of the newest members of nano carriers, MNMs open a new perspective especially for rapid drug transport and gene delivery. Although there exists limited number of in-vivo studies for drug delivery purposes, existence of in-vitro supportive data strongly encourages researchers to move on in this field and benefit from the manoeuvre capability of these novel systems. In this article, we reviewed the preparation and propulsion mechanisms of nanomotors in various fields with special attention to drug delivery systems.

Bacteria and bacterial derivatives as drug carriers for cancer therapy

The application of bacteria and bacteria-derived membrane vesicles (MVs) has promising potential to make a great impact on the development of controllable targeted drug delivery for combatting cancer. Comparing to most other traditional drug delivery systems, bacteria and their MVs have unique capabilities as drug carriers for cancer treatment. They can overcome physical barriers to target and accumulate in tumor tissues and initiate antitumor immune responses. Furtherly, they are able to be modified both genetically and chemically, to produce and transport anticancer agents into tumor tissues with improved safety and efficacy of cancer treatment but decreased cytotoxic effects to normal cells. In this review, we present some examples of tumor-targeting bacteria and bacteria-derived MVs for the delivery of anticancer drugs, including chemo-therapeutic, radio-therapeutic, photothermal-therapeutic, and immuno-therapeutic agents. We also discuss the advantages as well as the limitations of these tumor-targeting bacteria and their MVs used as platforms for controlled delivery of anticancer therapeutic agents, and further highlight their great potential on clinical translation.

Biocatalytic Micro- and Nanomotors

Enzyme-powered micro- and nanomotors are tiny devices inspired by nature that utilize enzyme-triggered chemical conversion to release energy stored in the chemical bonds of a substrate (fuel) to actuate it into active motion. Compared with conventional chemical micro-/nanomotors, these devices are particularly attractive because they self-propel by utilizing biocompatible fuels, such as glucose, urea, glycerides, and peptides. They have been designed with functional material constituents to efficiently perform tasks related to active targeting, drug delivery and release, biosensing, water remediation, and environmental monitoring. Because only a small number of enzymes have been exploited as bioengines to date, a new generation of multifunctional, enzyme-powered nanorobots will emerge in the near future to selectively search for and utilize water contaminants or disease-related metabolites as fuels. This Minireview highlights recent progress in enzyme-powered micro- and nanomachines.

Targeted drug delivery therapies inspired by natural taxes

A taxis is the movement responding to a stimulus of an organism. This behavior helps organisms to migrate, to find food or to avoid dangers. By mimicking and using natural taxes, many bio-inspired and bio-hybrid drug delivery systems have been synthesized. Under the guidance of physical and chemical stimuli, drug-loaded carriers are led to a target, for example tumors, then locally release the drug, inducing a therapeutic effect without influencing other parts of the body. On the other hand, for moving targets, for example metastasis cancer cells or bacteria, taking advantage of their taxes behavior is a solution to capture and to eliminate them. For instance, several traps and ecological niches have been fabricated to attract cancer cells by releasing chemokines. Cancer cells are then eliminated by drug loaded inside the trap, by radiotherapy focusing on the trap location or by simply removing the trap. Further research is needed to deeply understand the taxis behavior of organisms, which is essential to ameliorate the performance of taxes-inspired drug delivery application.

Biohybrid robotics with living cell actuation

This review comprehensively discusses recent advances in the basic components, controlling methods and especially in the applications of biohybrid robots.

Nano/Micromotors for Diagnosis and Therapy of Cancer and Infectious Diseases

Micromotors are man-made nano/microscale devices capable of transforming energy into mechanical motion. The accessibility and force offered by micromotors hold great promise to solve complex biomedical challenges. This Review highlights current progress and prospects in the use of nano and micromotors for diagnosis and treatment of infectious diseases and cancer. Motion-based sensing and fluorescence switching detection strategies along with therapeutic approaches based on direct cell capture; killing by direct contact or specific drug delivery to the affected site, will be comprehensively covered. Future challenges to translate the potential of nano/micromotors into practical applications will be described in the conclusions.