research a type of nanorobots currently under development

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• Review Article
• Published: 06 February 2023

Smart micro- and nanorobots for water purification

• Mario Urso   ORCID: orcid.org/0000-0001-7993-8138 1   na1 ,
• Martina Ussia   ORCID: orcid.org/0000-0002-3248-6725 1   na1 &
• Martin Pumera   ORCID: orcid.org/0000-0001-5846-2951 1  

Nature Reviews Bioengineering volume  1 ,  pages 236–251 ( 2023 ) Cite this article

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Less than 1% of Earth’s freshwater reserves is accessible. Industrialization, population growth and climate change are further exacerbating clean water shortage. Current water-remediation treatments fail to remove most pollutants completely or release toxic by-products into the environment. The use of self-propelled programmable micro- and nanoscale synthetic robots is a promising alternative way to improve water monitoring and remediation by overcoming diffusion-limited reactions and promoting interactions with target pollutants, including nano- and microplastics, persistent organic pollutants, heavy metals, oils and pathogenic microorganisms. This Review introduces the evolution of passive micro- and nanomaterials through active micro- and nanomotors and into advanced intelligent micro- and nanorobots in terms of motion ability, multifunctionality, adaptive response, swarming and mutual communication. After describing removal and degradation strategies, we present the most relevant improvements in water treatment, highlighting the design aspects necessary to improve remediation efficiency for specific contaminants. Finally, open challenges and future directions are discussed for the real-world application of smart micro- and nanorobots.

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Introduction

Water is vital for all forms of life. However, of the Earth’s freshwater, less than 1% is estimated to be accessible, and its contamination represents one of the most severe ecological threats 1 , 2 . Furthermore, clean water shortage is intensifying owing to the increasing global demand associated with population growth, industrialization and climate change 3 . Contaminants such as plastic waste, heavy metals, persistent organic pollutants (including pharmaceuticals and pesticides) and oil spills are associated with substantial ecological risks. Once within the aquatic ecosystem, contaminants can cause irreversible accumulative, recurrent, carcinogenic, mutagenic and other detrimental effects on the aquatic flora and fauna, while their propagation through the food chain further amplifies the associated risks 4 . Moreover, aqueous protozoan, bacterial and viral pathogens can cause the spread of typhoid, cholera, salmonella and other diseases. In addition, higher global temperatures increase the concentration of nutrients such as carbon, nitrogen and phosphate in raw water, which favours the regrowth of opportunistic pathogens mainly caused by antimicrobial-resistant pathogens 1 , 2 . In this context, bacterial biofilm formation onto industrial pipes and water lines results in a slower water flow and corrosion of the tubes, thus reducing the hydraulic efficiency of power plants and further compromising the safety of drinking-water distribution systems 5 , 6 , 7 . Although these biological risks might seem more relevant for developing regions, industrialized regions will also need to adapt to the scarcity of clean water resources, requiring innovative solutions for frequent (re)use of grey water (such as from washing machines and dishwashers) and natural water bodies to ensure drinking water supplies.

The concept of ‘water remediation’ dates back to Sanskrit, ancient Greek and Egyptian writings around 2000  bc , from Hippocrates with the discovery of water’s healing properties, the Roman aqueducts and Archimedes’ screw, up to modern-era treatments, including filtration systems with coagulation and sedimentation. Furthermore, water chlorination and desalination methods, as well as the use of advanced oxidation processes and nanotechnologies, have reduced the hazards and illnesses related to contaminated drinking-water distribution systems 3 . Despite these advances, 75% of water bodies remain at ecological risk 1 . During water remediation, most pollutants are not completely removed from contaminated areas or are merely degraded, releasing toxic by-products into the environment.

Owing to their active motion, self-propelled programmable micro- and nanoscale synthetic robots provide exciting opportunities to improve water monitoring and remediation processes, enhancing treatment efficiency by overcoming diffusion-limited reactions and promoting interactions with target pollutants 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 . In this Review, we describe the path to engineering small-scale materials into intelligent micro- and nanorobotic machines that can autonomously move to accomplish predetermined tasks. In particular, we focus on micro- and nanorobots that remove and degrade water contaminants, ranging from nano- and microplastics to organic molecules, heavy metals, oil spills and microorganisms. Finally, we discuss practical challenges and future research directions, proposing systems suitable for real-world applications.

From materials to robots

Robots are machines programmed to perform specific tasks autonomously or under human supervision. Small-scale robots (<100 µm), initially referred to as ‘micro- and nanomotors’, are micro- and nanostructured materials capable of harvesting energy from the surrounding environment and converting it into locomotion 16 , 17 . These tiny devices benefit from the synergy between their motion attributes and their unique size-, shape- and structure-dependent physicochemical properties at the micro- and nanoscale. Furthermore, they show superior performance compared to passive matter (for example, conventional static micro- and nanomaterials) in all areas, including water remediation 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 . The active motion of micro- and nanomotors drives the movement of the surrounding fluid, improving the mass transfer of chemical reactions, which are limited to passive diffusion in static approaches. This process facilitates the interaction between the motors and the water contaminants, resulting in shorter purification times. As the complexity of the required functions increased, for example, catching selected pollutants or moving the robots in groups to improve removal and degradation efficiency, the design of micro- and nanomotors became more sophisticated 10 , 26 . The introduction of propulsion, multifunctionality, adaptation to the environment, collective behaviours and mutual communication have transformed micro- and nanomaterials into intelligent micro- and nanorobots (Fig.  1 ). To realize self-propulsion, reliable fabrication methods are needed to induce asymmetry in the material’s structure, allowing it to break the symmetry of a local field and ‘swim’ 27 , 28 , 29 , 30 (Table  1 ). Therefore, depending on the motion mechanism, micro- and nanorobots can be classified as fuel-driven or externally driven 31 (Fig.  2 ).

Micro- and nanorobots are designed using micro- and nanomaterials and introducing: propulsion, the ability to move spontaneously by consuming a chemical fuel or under exposure to an external field; multifunctionality, the ability to perform multiple specific tasks; taxis, the adaptive response to environmental stimuli such as gradients of chemical species (chemotaxis), light (phototaxis) or magnetic fields (magnetotaxis); collective behaviour, the cooperative action of robot ensembles to improve the efficacy of a process or to perform complicated tasks beyond an individual’s capability; communication, through which neighbouring robots can operate in a coordinated and synchronized manner and exchange information. The scheme illustrates an example of a bubble-propelled Janus robot in which the red and blue hemispheres represent the structural–functional and engine sides, respectively. The sizes of microrobots and nanorobots are 1–100 µm and <1 µm, respectively.

a , Pt microrockets self-propel owing to the catalysed decomposition of H 2 O 2 into O 2 bubbles, whose expulsion results in a powerful thrust. b , Enzyme-powered nanorobots are based on the uneven immobilization of an enzyme (such as urease), catalysing the hydrolysation of a substrate (urea), resulting in a product gradient that drives their motion by self-phoresis. c , The engine of disintegrating robots decomposes during propulsion, such as for Mg-based microrobots, whose reaction in water produces a stream of H 2 bubbles at the expense of the Mg core. d , Metal–semiconductor Janus micro- and nanorobots move under light irradiation owing to the photogenerated electron–hole (e − –h + ) pairs within the semiconductor. Oxidation and reduction of water occur at both sides of the robot, establishing a gradient of protons (H + ) and the resulting local electric field, which induces motion by self-electrophoresis. e , Upon exposure to a rotating magnetic field, magnetic helical robots translate the rotational motion generated by orthogonal coil pairs into a translational motion that can be wirelessly navigated with high precision. f , Micro- and nanorobots can move upon pressure exerted by acoustic fields. Red and blue structures represent the structural–functional component and the engine of the robot, respectively.

Fuel-driven micro- and nanorobots

Fuel-driven micro- and nanorobots, also known as ‘chemical’ or ‘catalytic’, exploit the reaction between a catalyst and a chemical fuel (or substrate) to move 32 , 33 , 34 , 35 . Despite its toxicity, hydrogen peroxide (H 2 O 2 ) is the most frequently used fuel and the expensive noble metal platinum (Pt) is its most efficient decomposition catalyst, resulting in micro- and nanorobotic propulsion by bubble ejection or self-phoresis 36 . The latter is the spontaneous motion of a particle in response to the generation of a quantity gradient, such as solute concentration (self-diffusiophoresis), electric potential (self-electrophoresis) or temperature (self-thermophoresis). For example, Pt microrockets self-propel in H 2 O 2 owing to the continuous jet stream of O 2 bubbles (Fig.  2a ), which also produce powerful thrusts and motility in high-ionic-strength media, such as seawater 37 , 38 . Enzymes, such as catalase, urease and glucose oxidase, are the biological counterpart of inorganic catalysts 39 , 40 , 41 . Micro- and nanorobots with uneven distribution of catalase (an enzyme catalysing the decomposition of H 2 O 2 ) undergo bubble propulsion in H 2 O 2 , whereas urease and glucose oxidase hydrolyse more biocompatible substrates, like urea and glucose, generating a product gradient for micro- and nanorobotic self-phoresis (Fig.  2b ). However, their use is restricted to biomedical applications where the substrates are naturally present, for example, the bladder for urea 42 . Disintegration of the robots is mediated by catalytic reactions that simultaneously consume the robot’s engine and fuel, similar to the reaction between Mg and water 43 , 44 , 45 (Fig.  2c ). However, fuel-driven micro- and nanorobots suffer from poor control over the motion (on–off, directionality) and limited life span.

Externally driven micro- and nanorobots

Externally driven micro- and nanorobots overcome the limitations of fuel-driven ones by gathering energy from external fields, including light, acoustic and electromagnetic fields. Of these sources, sunlight is particularly beneficial, being a natural, abundant and renewable form of energy that can trigger several degradation mechanisms at the same time 46 , 47 , 48 , 49 . The motion of light-powered robots originates from the generation of electron–hole pairs (e − –h + ) in an irradiated photoactive material. For example, by illuminating a semiconductor material with photon energies larger than its bandgap, electrons are promoted to the conduction band, leaving holes in the valence band. These photogenerated carriers catalyse photochemical reactions that result in motion by bubble propulsion or self-phoresis. A metal–semiconductor junction is often required to prevent photogenerated carriers recombining within the semiconductor or to break the semiconducting material’s symmetry 50 , 51 . The motion mechanism of a typical metal–semiconductor Janus micro- or nanorobot comprises photogenerated carriers that lead to the oxidation and reduction of water at the two sides of the robot (Fig.  2d ). Specifically, the semiconductor side acts as a source of protons (H + ), which are consumed at the metal side (the proton sink), establishing a gradient of charges, and consequently, a local electric field driving the micro- or nanorobot’s movement by self-electrophoresis. However, single-component metal-coating-free micro- and nanorobots can also move under light owing to their inherent asymmetry or asymmetric illumination 52 . The main limitation of light-powered robots is the decreasing light intensity with depth and the inefficient self-electrophoresis in high-ionic-strength media (seawater). By contrast, magnetic fields can operate micro- and nanorobots in any medium with great manoeuvrability 53 , 54 . Rather than mere magnetic-mediated attraction–repulsion, these robots move by magnetophoresis in magnetic-field gradients or by torque transfer under rotating magnetic fields. For example, helical propellers in a rotating magnetic field convert their rotation into a translational movement 55 (Fig.  2e ). Unlike light-driven robots, magnetically driven robots are not autonomous and are limited by the high cost and size constraints associated with the magnetic setup 56 . Electric field propulsion, achieved by combining materials with different polarizability, is similar to magnetic propulsion, including fuel-free controllable motion 57 . Acoustic fields can also actuate different micro- and nanorobot designs, such as bimetallic microrods or asymmetric nanowires, owing to the pressure exerted by acoustic radiation 58 , 59 , 60 , 61 (Fig.  2f ). Ultrasound fields are harmless to the human body, which is why they have been principally used for biomedical applications, allowing rapid cell internalization, intracellular propulsion and delivery of therapeutic agents 62 , 63 .

Multifunctional micro- and nanorobots

In addition to simple swimming, robots are also required to perform tailored tasks in specific applications. Multifunctionality is imparted to micro- and nanorobots by integrating different modules, such as organic or inorganic molecules and materials 64 , 65 , 66 , 67 . Each micro- and nanorobot’s module has a defined role: the structural material provides a robust scaffold, the engine is responsible for the motion, the imaging material enables traceability, the magnetic material introduces magnetic properties (such as collectability under magnetic fields) and the surface material interacts with the environment, including water contaminants in the robot’s proximity through intrinsic properties or surface functional groups (ranging from simple molecules to supramolecular structures and polymers). For example, DNA-engineered micro- and nanorobots exploit the self-propulsion, programmability and specificity of Watson–Crick base pairing for the intracellular detection of cancer biomarkers or gene delivery 68 . However, the choice of single-task or multi-purpose robots must be thoroughly assessed, because integrating multiple units entails several fabrication, assembly and scaling challenges 69 .

Although small-scale robots have shown promising results in laboratory settings, real-world scenarios are complex and dynamic. Propulsion and movement can easily be influenced by variations in the chemical composition of the swimming media or from exposure to unexpected stimuli. Therefore, similar to living organisms, smart robots need to exhibit adaptive responses to dynamically changing environments. For example, the Escherichia coli bacterium uses receptors to sense the concentration of chemicals (such as nutrients) in its surroundings and move towards richer spots 70 . Another example is the diel vertical migration of plankton in aquatic ecosystems; these organisms move to the surface at night to access food and avoid predators and return to the bottom region during the day 71 . Taxis (mainly chemotaxis, phototaxis and magnetotaxis) in micro- and nanorobots relies on stimulus-mediated mechanisms 72 , 73 . For example, chemotactic robots move according to concentration gradients of chemicals, such as their fuel 74 , 75 , 76 . As they move along the gradient, their diffusivity increases owing to the enhanced catalytic reaction rate at higher fuel concentrations (Fig.  3a ). Phototactic micro- and nanorobots sense the direction of light, orient and move towards (positive phototaxis) or away from it (negative phototaxis) 77 , 78 , 79 (Fig.  3b ). Phototaxis has generally been observed in highly asymmetric structures. The most renowned example of an artificial phototactic microswimmer consists of a Janus nanotree formed by a silicon trunk and titanium dioxide (TiO 2 ) branches with chemically programmable negative or positive phototaxis, mimicking the behaviour of natural green algae 80 . Gravitaxis, the movement in response to gravity, is another form of behavioural response. This phenomenon is observed in micro- and nanorobots with asymmetric mass distribution or structure, in which they move in the opposite direction of gravity. For example, some light-driven micro- and nanorobots show a form of gravitaxis in response to light (like the diel vertical migration), typically referred to as ‘negative photogravitaxis’ 81 , 82 , 83 (Fig.  3c ). Magnetotactic micro- and nanorobots adjust their motion according to the direction of magnetic field gradients or dynamic magnetic fields to minimize energy consumption 84 , 85 , 86 . For example, they can be attracted or repelled by a magnetic field upon polarity inversion (Fig.  3d ).

a , Positive chemotaxis of bubble-propelled Janus micro- and nanorobots moving towards the region with a higher fuel concentration. b , Light-driven Janus micro- and nanorobots move towards (positive phototaxis) or away from (negative phototaxis) the light source on a plane. c , A light-driven Janus robot irradiated from beneath moves upwards (opposite to gravity ( g )), leading to negative photogravitaxis. d , Magnetotaxis of a magnetic helical robot moving towards or away from a magnetic field upon inverting its polarity. Red and blue structures represent the structural–functional component and the engine of the robot, respectively.

Collective micro- and nanorobots

Collective animal behaviour involves the execution of tasks beyond the single animal’s capability. For example, ant colonies self-assemble into robust ‘bridges’ to march across gaps in terrains, whereas starlings’ synchronized motion as shape-shifting clouds allows them to frighten predators. These behaviours have inspired artificial swarming micro- and nanorobots 87 . Compared to single robots, micro- and nanorobot swarms provide superior efficiency, robustness and flexibility. For example, a group of robots can perform a desired task faster than a single robot can and accomplish size-dependent operations, such as the transport of large cargoes, which requires the cooperation of several robots. The group perceives broader environmental variations compared to single robots, and, in the event of a robot’s failure, it can still complete the assigned task 88 . The fundamental feature of micro- and nanorobot swarms is the collective motion of its constituents. Typically, tactic micro- and nanorobots manifest coordinated movements in response to energy gradients 89 . However, practical applications require swarms to adapt to environmental changes through self-organization and reconfigurability in shape and function. All these behaviours rely on physico-chemical interactions between the robots 90 , 91 , 92 , 93 . For example, light-powered magnetic microrobots spontaneously assemble into self-motile ‘snake-like’ microchains owing to the particles’ shape-modulated magnetic dipole–dipole interactions 94 . Furthermore, using external magnetic fields, microrobots can reversibly switch from a dispersed to an aggregate state, allowing them to explore their surroundings, move as a group to overcome obstacles and rotate or transport microscale objects 95 . Integrating the functions of contaminant removal and degradation into robotic swarms can thus be a promising approach.

Communication between micro- and nanorobots or with the environment is another essential feature to ensure synchronized maneuvering of swarms, which still remains one of the main challenges in micro- and nanorobotics. For example, robots exchange chemical signals, such as the release of small molecules or ions, producing a chemical gradient to attract, repel, accelerate or decelerate other robots 96 . Moreover, long-range hydrodynamic communication between micro- and nanorobots produces a ‘hit and run’ response whereby a robot acts as a ‘leader’, collecting smaller particles (‘followers’) and fighting to gather the followers of a competitor 97 . This intriguing response could be used to design micro- and nanorobots capable of recognizing more persistent and toxic pollutants in water and communicating this information to other robots in the swarm, gathering them around the targeted contaminant to ensure its removal or degradation. However, exchanging such complex information and functions between robots in real-world settings is still far from being accessible.

Robots for water remediation

Micro- and nanorobots aim to accelerate and improve the water decontamination process. The synergistic action between their active motion and their material properties enhances the adsorption of soluble organic pollutants and heavy metals at the solid–liquid interface (Table  2 ). Specifically, once the target contaminants approach the robots’ surface, a stable network of weak interactions is established through a physisorption mechanism, primarily electrostatic, without any external agitation. Electrostatic interactions refer to the positive or negative surface charge that molecules or particles acquire when immersed in a liquid medium and are strongly influenced by its pH and ionic strength 98 . Micro- and nanorobots can be programmed to possess a surface charge opposite to that of the target contaminants by functionalizing them with specific molecules or polymers or by modifying the solution parameters 99 (Fig.  4a ). Impurities also possess a surface charge, allowing their capture, transport and release by electrostatic forces. For example, plastic-based debris is composed of polymers with negatively or positively charged functional end-groups. By properly modifying the micro- or nanorobot’s surface charge through adjustments to the solution pH, it is possible to promote a reversible ‘on the fly’ adsorption or desorption of contaminants.

a , Electrostatic adsorption between the robot’s surface and pollutants with opposite surface charge. b , Marine-mussel-inspired chemical adhesion of pollutants to a polydopamine-coated robot. c , Migration of pollutants toward a robot through phoretic interactions induced by the generated gradients. d , Degradation of pollutants by the hydroxyl radicals (OH • ) produced by the Fenton reaction between Fe 2+ ions released from a Fe-based robot and H 2 O 2 . e , Photocatalytic degradation of pollutants owing to reactive oxygen species (ROS) produced by photochemical reactions involving photogenerated electron–hole (e − –h + ) pairs in a photocatalyst, water and O 2 . The photo-Fenton reaction between photogenerated electrons and H 2 O 2 further enhances ROS production for iron-oxide-based photocatalysts. f , Enzymes immobilized on the robot’s surface lower the activation energy necessary to degrade pollutants. g , Bacteria killed by the controlled release of bactericidal agents, such as Ag + , by a Ag-based robot. h , Physical erosion of a bacterial biofilm from a surface by a self-propelled robot. i , ‘Kill-n-clean’ approach based on the erosion and complete elimination of a bacterial biofilm from a surface upon release of antibiotics. Removal and degradation strategies are depicted for spherical or bubble-propelled Janus robots, but the concepts can be extended to other classes of micro- and nanorobots. Red and blue hemispheres represent the structural–functional and engine sides of the robot, respectively.  E C , energy level of the conduction band of the semiconductor; E V , energy level of the valence band of the semiconductor.

Establishing a stable and robust contact between the active robot and the passive contaminant is crucial for the removal process, but pH-dependent electrostatic forces might lack sufficient strength. To improve adherence, polydopamine (PDA) has been used as a sticky coating on robots to mimic the adhesive properties of marine mussels 100 (Fig.  4b ). PDA has a structure similar to 3,4-dihydroxy- l -phenylalanine (DOPA), a natural polyaminoacid secreted by mussels that allows them to firmly adhere to solid surfaces and resist sea waves 10 . An alternative approach to facilitate contact with contaminants exploits strong and attractive phoretic interactions (Fig.  4c ), which induce collective behaviours, assemblies or migration of passive particles owing to the generated (or modified) local gradients around the robots in response to diffusiophoretic, electrophoretic or thermophoretic mechanisms 100 , 101 . However, these strategies fail to permanently remove the adsorbed contaminants and further disposal is required. To overcome this issue, an ecofriendly approach that avoids the generation of secondary pollutants is to use advanced oxidation processes; these were introduced in 1987 as a class of water-treatment methods involving the production of highly reactive chemical species in “sufficient quantity to affect water purification” 102 , 103 , including O 2 , O 3 or H 2 O 2 as oxidants, light irradiation and catalysts. The process consists of producing strong oxidizing agents called ‘reactive oxygen species’ (ROS), such as OH • , O 2 •− , O 2 2• and 1 O 2 , through chemical or photochemical reactions. These ROS react with water contaminants, which are then cleaved into smaller compounds until their complete mineralization into CO 2 and water.

Fenton, Fenton-like, photo-Fenton reactions and heterogeneous photocatalysis are the most recurrent advanced oxidation processes used in water remediation by micro- and nanorobots. Fenton reactions are activated by Fe 2+ or Fe 3+ in H 2 O 2 , resulting in the production of OH • . Robots composed of Fe-based materials undergo corrosion in H 2 O 2 , catalysing the Fenton reaction (Fig.  4d ). Similarly, a Fenton-like reaction refers to the same process induced by other catalysts, such as metals at lower oxidation states (for example, Pt). By contrast, heterogeneous photocatalysis is based on irradiating a photocatalytic material (semiconductor or photosensitizer) with photons having energy equal to or greater than its bandgap, generating electron-hole (e − –h + ) pairs that migrate to the photocatalyst’s surface and produce ROS upon reaction with water and O 2 (Fig.  4e ). Micro- and nanorobots made of photocatalytic iron oxides, such as α-Fe 2 O 3 (haematite), can also catalyse the photo-Fenton process in H 2 O 2 by generating ROS through the reaction of photogenerated electrons with H 2 O 2 (Fig.  4e ). It is worth noting that light-powered micro- and nanorobots are particularly advantageous for water remediation because they use light both to move and simultaneously to degrade pollutants by photocatalysis or the photo-Fenton reaction. However, considering that adsorption is necessary to initiate the photocatalytic process, it is often challenging to distinguish the effective contribution of the motion-enhanced adsorption from the degradation. A low-cost and sustainable alternative to advanced oxidation processes is to use enzyme-mediated bioremediation. This method relies on natural enzymes, such as those secreted by microorganisms, to lower the activation energy required ‘to digest’ pollutants 104 . Moreover, enzymes can also be immobilized on synthetic micro- and nanorobots to use this mechanism (Fig.  4f ).

Water decontamination from pathogenic microorganisms using micro- and nanorobots also benefits from complementary approaches. While moving, robots can rapidly release bactericidal agents (for example, silver ions (Ag + )) in a controllable manner, resulting in bacteria elimination 105 , 106 , 107 (Fig.  4g ). Self-propelled micro- and nanorobots can also erode bacterial biofilms from surfaces through a ‘brush-like’ effect 108 (Fig.  4h ). In this case, the bacteria are only physically removed from the surface, therefore an additional step is required for their elimination. For example, selected antibacterial agents (such as antibiotics) can be chemically linked or physically adsorbed on the robots’ surface. The carried antibiotic is then released on the residual bacteria to trigger a ‘kill-n-clean’ method that destroys all debris while avoiding recolonization 109 (Fig.  4i ).

Nano- and microplastics

Plastics are synthetic materials made of polymer chains, that is, monomers linked by covalent bonds. Owing to their high adaptability, durability, flexibility, low weight and cost, plastics manufacturing has increased exponentially since the 1950s, making them ubiquitous in our lives. However, plastics are difficult to eliminate and they mainly accumulate in marine environments 110 , where they fragment into smaller and more hazardous particles, namely, microplastics (<5 mm) and nanoplastics (<1 μm) 111 . Polyethylene, polypropylene and polystyrene are among the most recurrent ones. Their physicochemical properties mean that nano- and microplastics adsorb pollutants on their surfaces and support the growth of bacterial biofilms. They can propagate through the food chain or directly contaminate drinking-water distribution systems, posing a danger to the health of all living beings. Microplastics have already been detected in human blood, highlighting the importance of developing effective and definitive strategies for their elimination 112 .

The first attempts at using micro- and nanorobots for microplastic sequestration exploited the active movement of light-driven Au–Ni–TiO 2 microrobots as self-propelled micromachines 101 . These microrobots propel themselves under ultraviolet (UV) light irradiation in water and H 2 O 2 by self-electrophoresis, capturing microplastics on their way, including microplastics extracted from personal-care products and those present in Baltic seawater samples, through phoretic interactions. Moreover, they can assemble into microchains upon exposure to an external magnetic field and move in a coordinated manner. This configuration maximizes the contact area for the capture of microplastics and their removal by shovelling, in this case, by directly pushing them out of the water sample. Similarly, bio-inspired magnetic microrobots made of sunflower pollen grains enable plastic removal on a large scale and at a low cost 113 . These microrobots exhibit three different motion modes (rolling, spinning and wobbling) depending on the applied magnetic field. By tuning the latter, the ‘microsubmarines’ can cooperate to capture, transport and release a large polystyrene bead (100 μm) or form chains to shovel smaller polystyrene beads owing to the fluid flow generated by their movement.

Adsorptive bubble separation is an alternative approach for the removal of microplastics 114 . This mechanism is based on the bubble propulsion of hydrothermally synthesized Fe 2 O 3 –MnO 2 core–shell microrobots. Microplastics are trapped in the O 2 bubbles generated by H 2 O 2 decomposition during the microrobots’ motion. The microplastic-containing bubbles are then pushed toward the solution’s surface, creating a foam that can be easily separated. However, the adsorptive bubble separation requires a high H 2 O 2 concentration (5%) and a surfactant, and yielded a lower removal efficiency ( ∼ 10% in 2 h) compared to light-driven Au–Ni–TiO 2 microrobots (67% in 40 s). By contrast, bismuth tungstate (Bi 2 WO 6 ) microrobots swarm under visible light irradiation in 0.025% H 2 O 2 , attach to textile fibres (a source of microplastic pollution) and destroy them by photocatalysis 115 . This microrobot is particularly advantageous as it does not require expensive metal coatings to move because its motion mechanism is based on asymmetric illumination.

Similar noble-metal-free light-powered and magnetic Fe 3 O 4 –BiVO 4 microrobots have been used to remove and degrade microplastics in a confined space 116 . These microrobots consist of star-shaped microparticles that move under visible light irradiation in 0.1% H 2 O 2 as a result of their inherent asymmetry. Their mechanism of action consists of firmly anchoring to large polylactic acid, polycaprolactone (PCL), polyethylene terephthalate (PET) and polypropylene plastic pieces, allowing their transport and removal from a maze of macroscale channels with remarkable efficiencies ( ∼ 70% for polylactic acid and PCL, ∼ 40% for PET, ∼ 20% for polypropylene in a 10-cm-long hallway). After seven days of exposure to visible light and H 2 O 2 , the surface chemical and morphological properties of the microplastics start to deteriorate; however, only a poor degradation efficiency (3% for polylactic acid) was estimated as the microplastics’ weight loss. Alternatively, PDA-coated Fe 3 O 4 microrobots were functionalized with lipase to promote enzymatic degradation of microplastics 100 . Upon actuation by a transversal rotating magnetic field, microrobot swarms adhere to and transport large microplastic pieces (up to 140 µm) owing to PDA’s sticky properties. Optical microscopy revealed the enzymatic digestion of PCL microplastics after overnight incubation with the microrobots.

The ultimate goal of plastic sequestration is to completely mineralize the micro- and nanoplastics and their constituent polymer chains into H 2 O and CO 2 . Micro- and nanorobots can break the strong covalent bonds in polymer chains, as shown by using light-powered Pt–Pd–haematite Janus microrobots 117 . Haematite is a particularly beneficial component because it is a visible-light photoactive semiconductor, a catalyst for Fenton and photo-Fenton reactions and a magnetically navigable material owing to its ferromagnetic properties. These microrobots propel themselves in water and H 2 O 2 under light irradiation by self-electrophoresis. The electrostatic attraction between the microrobots and PEG is amplified by adjusting the solution pH, so that at pH 3 the microrobots are positively charged to attract the negatively charged PEG chains. Furthermore, introducing 1% H 2 O 2 accelerates the Fenton and photo-Fenton reactions, resulting in total high-molecular-weight polyethylene glycol (PEG) degradation within 24 h. Compared to single-component microrobots, these robots are more expensive because of the noble-metal coating. However, they are more effective owing to the synergy between multiple degradation mechanisms.

Organic molecules

The majority of micro- and nanorobots used for water purification from organic molecules are assessed by their ability to remove or degrade dyes such as methylene blue and rhodamine B 30 , 118 , 119 , 120 . However, these robots are also effective against more persistent and toxic pollutants, including chemical warfare agents 106 , phenolic 121 , 122 and nitroaromatic compounds 123 , 124 , antibiotics 125 , 126 , hormones 127 and psychoactive substances 128 . Nonetheless, several challenges related to their manufacturing and operational costs and performance (removal or degradation efficiencies, reusability) limit the translation of micro- and nanorobots to real-world settings.

Bio-hybrid microrobots, which combine living microorganisms with synthetic structures, can overcome limitations associated with toxic fuels and expensive noble metal catalysts. For example, self-propelled microrobots based on marine rotifers (microorganisms that live in aquatic environments) have efficiently cleaned the insecticide and nerve agent methyl paraoxon 129 , a phosphate triester that is extremely dangerous and difficult to degrade owing to the high chemical stability of its P–O bond. For this purpose, organophosphorus hydrolase (OPH)-functionalized microbeads are accumulated inside the rotifers. The cilia in the rotifers’ mouth generate strong fluid flow, which pushes the polluted water toward the microbeads to accelerate the hydrolyzation of the methyl paraoxon into the electrochemically detectable p-nitrophenol, reaching an eightfold increase in degradation efficiency compared to bare OPH-functionalized microbeads. This strategy does not require any fuel and can be extended to other types of contaminants by changing the functional group on the microbeads.

An interesting approach for removing the synthetic hormone α-oestradiol is to use polypyrrole–Fe 3 O 4 –Pt tubular microrobots. While the inner Pt layer and the Fe 3 O 4 nanoparticles enable microrobotic bubble propulsion in H 2 O 2 and magnetic steering, respectively, the polypyrrole surface charge can be programmed by adjusting the solution’s pH to intensify the electrostatic attraction of the hormone. Surprisingly, once introduced into the α-oestradiol solution, the hormone’s adsorption and accumulation on the moving microrobots generates macroscopic spiderweb-like fibres. The microrobots and the woven α-oestradiol webs can then be converted into a single compact piece under an external magnetic field and easily separated from the treated water 130 .

The propulsion of micro- and nanorobots enhances fluid mixing, which has been known to accelerate the remediation process. Therefore, it is reasonable to expect that the greater the speed of the micro- and nanorobots, the higher the removal or degradation efficiency. However, a counterintuitive example has been reported, in which light-powered Pt–haematite Janus microrobots with different Pt coating thicknesses degrade picric acid, a model for nitroaromatic explosives, in H 2 O 2  by the photo-Fenton reaction 131 . The thicker and more compact Pt coating increases the microrobots’ speed at the expense of faster H 2 O 2 consumption. Therefore, less H 2 O 2 is available for the photo-Fenton reaction, reducing the degradation efficiency. By contrast, in a process termed ‘microrobots in sponge’, the porous structure of cobalt ferrite microrobots embedded in a polyurethane-based sponge allows more pollutants to be captured, which are then degraded in situ by the microrobots through the Fenton reaction using only 0.13% H 2 O 2 (ref. 132 ). The microrobots’ bubble propulsion enhances fluid mixing and creates a pressure gradient that promotes fluid pumping inside the sponge. The synergy between the properties of the sponge and the microrobots results in methylene blue degradation in large volumes (1 litre in 15 min), allowing the microrobots to be recovered and re-used.

Another strategy aimed at removing organic molecules from water is to digest them enzymatically using laccase 133 , 134 . Although laccase suffers from loss of enzymatic activity upon exposure to UV light, linking photosensitive azobenzene molecules to microrobots protects enzymes such as horseradish peroxidase, laccase and catalase, enabling enzymatic decomposition of various substrates under direct UV light irradiation 135 .

Micro- and nanorobots need to be selective to be able to recognize and treat the most dangerous pollutants in wastewaters. Molecularly imprinted polymers (MIPs) are promising candidates to address this issue. This technique consists of imprinting a molecule (template) on a material (matrix) during its preparation, followed by the template’s removal, which leaves complementary cavities that allow selective adsorption of the template 136 . For example, imprinting the antibiotic erythromycin (template) on a thermoresponsive poly( N -isopropylacrylamide) (PNIPAM) hydrogel coating (matrix) of Mn 3 O 4 –CoFe 2 O 4 microrobots prepared using lotus pollen as a porous bio-template 137 allows MIP-mediated selective recognition and temperature-controlled adsorption and release of erythromycin.

One of the main limitations of micro- and nanorobots for water purification is their short navigation distance (only a few millimetres) when required to operate in large water volumes (cubic metres). Self-propelled ‘aircraft-like’ carriers of photocatalytic microrobots could solve this problem 138 . For example, a 3D-printed millimetre-scale robot with a conical head and tubular structure filled with ethanol and Pt–TiO 2 microrobots can move for tens of metres by asymmetrically and simultaneously releasing the stored ethanol fuel and the microrobots, a process known as the Marangoni effect. This approach allows the photocatalytic microrobots’ slow and distributed release, resulting in picric acid degradation over a large area.

Water-purification studies by micro- and nanorobots are principally conducted using deionized water samples 139 . However, the robots’ motion is substantially obstructed or poisoned by solid impurities present in sewage samples, highlighting the need to use real-world specimens in future studies.

Heavy metals

Heavy metals, such as arsenic, cadmium, mercury, lead and copper, are water pollutants of major concern 140 . They tend to accumulate in organisms, causing severe health issues, including metal-induced ROS-mediated oxidative damage 141 . The use of self-propelled micro- and nanorobots is a viable way to remove heavy metals 142 , 143 .

Using natural and abundant materials as the primary building blocks for micro- and nanorobots reduces their fabrication costs. Halloysite nanoclay is an excellent absorber, which forms when rolling kaolin clay sheet into tubes owing to the strain caused by a lattice mismatch between the adjacent silicon dioxide and aluminum oxide layers over millions of years. Pt-coated nanoclay robots show rapid removal of Zn 2+ and Cd 2+ owing to their bubble propulsion in H 2 O 2 and electrostatic attraction of the metal cations 144 . Pollen grains are another advantageous material for formulating micro- and nanorobots, owing to their biocompatibility, stability and monodispersity. For example, Pt-covered pollen grains remove Hg 2+ in H 2 O 2 with a remarkable efficiency ( ∼ 80% in 2 h) 145 . As an alternative to membrane-assisted electrodeposition, kapok fibres can be used as a sacrificial template on which to prepare bubble-propelled tubular microrobots for Cu 2+ removal 146 . Similarly, spirulina, an edible alga, has been employed as a scaffold on which to fabricate magnetically actuated microrobots, owing to its peculiar helical structure 147 . For example, growing Fe 3 O 4 and MnO 2 nanoparticles on spirulina results in swarms of magnetic microrobots that remove Pb 2+ in H 2 O 2 -free water under a rotating magnetic field. To reduce dependence on expensive Pt engines, metal-free light-driven C 3 N 4 tubular microrobots have been proposed 148 . Under visible-light irradiation, photogenerated carriers in the semiconductor decompose H 2 O 2 , leading to bubble evolution and self-propulsion. These microrobots remove Cu 2+ by complex formation with N- and C-based functional groups. Interestingly, the adsorbed metal ions display Fenton-like activity, which increases the decomposition rate of H 2 O 2 and, thereby, the speed of the microrobots. Furthermore, this strategy can be extended to capture precious metal ions (Ag + and Pd 2+ ) 149 .

One simple yet effective approach to improve remediation efficiency is to increase the adsorptive area of the micro- and nanorobots. Metal–organic frameworks (MOFs) are attractive materials for this purpose, owing to their large surface area, tuneable pore size and functionalities related to the organic linker, which can be selected according to the targeted application. For example, superstructures with large surface area (~600 m 2  g −1 ) consisting of asymmetric hollow silica nanobottles, coated with Fe 3 O 4 nanoparticles and a catalase-modified mesoporous silica layer, self-propel in H 2 O 2 , resulting in the rapid removal of Cu 2+ (80% in 1 h) 150 . Similar MOF-based microrobots can be used to remove metal ions from water, including the radioactive UO 2 2+ (refs. 151 , 152 ). Another strategy to improve the performance of micro- and nanorobots is to design robots that can selectively remove pollutants. For example, microrobots with a tunable polyaminoacid outer layer selectively eliminate inorganic (Cd 2+ ) or organic (methylmercury) heavy metals, owing to the electrostatic interaction and coordination effect between amino and carboxyl groups in polyaspartic acid and Cd 2+ , or the stronger bonds between sulfhydryl groups in polycysteine and Hg for methylmercury 153 . Functionalization of Au tubular microrobots with thymine–thymine (T–T) mismatched base pairs is another way to remove Hg 2+ selectively, preferentially forming the complex T–Hg 2+ –T (ref. 154 ). Similarly, minerals with intrinsic affinity to specific heavy metals can be used to design robots with selective adsorption ability, as in the case of illite and zeolite with the radionuclide Cs + (refs. 155 , 156 ).

To be recyclable, micro- and nanorobots must release the captured pollutant in a complete and controlled manner. For example, magnetically actuated nanorobots with thermoresponsive polymeric ‘hands’ can pick up and dispose of pollutants, including As metal ions, by modulating the water temperature 157 . These nanorobots are made of Fe 3 O 4 nanoparticles coated with a pluronic tri-block copolymer formed by a hydrophobic polypropylene oxide core and a thermoresponsive hydrophilic polyethylene oxide shell. Exposure to 5 mg per litre As for 100 min in water at 25 °C under a rotating magnetic field results in 65% pickup efficiency, followed by a disposal efficiency of 48% in water at 5 °C. After ten cycles, these efficiencies drop slightly to 38% and 31% for pickup and disposal, respectively.

Inspired by the supercapacitors’ charge storage mechanism, graphite nanofibre–Ni–Pt or Bi–Ni–Pt bubble-propelled tubular microrobots can also be used for the selective electroadsorption of heavy metals 158 . Upon collision with a negatively charged electrode, electrons are transferred to the microrobots, allowing the adsorption of the metal cations by electrostatic forces in an O 2 -free solution. Unlike previous examples, adsorption is not limited to the microrobots’ surface, but includes the layered structure of graphite and Bi to intercalate the metal cations in the interlayer spacing up to ~400 layers from the microrobots’ surface. Furthermore, owing to their different interlayer distance, graphite-based microrobots selectively capture Li + , whereas Bi-based microrobots removed larger cations such as Na + and Ca 2+ . By magnetically transferring the microrobots to an O 2 -saturated solution, the cations are promptly released, allowing their multiple use.

The increase in tanker operations with the associated leakage of petroleum and other oil spills into water bodies (and lack of suitable discharge thereof), has become a substantial environmental problem 159 . Oil release counts for more than one million metric tons per year, calling for urgent and practical solutions. One of the first examples of micro- and nanorobots used for oil remediation involved Au–Ni–poly(3,4-ethylenedioxythiophene) (PEDOT)–Pt microtubes modified with a self-assembled monolayer of long alkanethiol chains 160 . Owing to their strong hydrophobic interactions with oil droplets, the microrobots capture and transport oil spills in H 2 O 2 . Replacing Pt and H 2 O 2 with a disintegrating engine reduces the cost and toxicity of microrobots at the expense of their lifetime 161 . Therefore, new fabrication and propulsion methods have been proposed to develop hydrophobic microrobots. For example, tuning the evolution of microfluidic double emulsions asymmetrically loaded with Fe 3 O 4 –Ag nanoparticles results in hierarchically porous polymeric spheres containing two microscale pores in a nanoporous matrix 162 . The nanoparticles ensure powerful bubble propulsion in H 2 O 2 (~1,600 μm s −1 ) while capturing oil, and magnetic collectability to enable the washing and re-use of the microrobots. Similarly, walnut-like microrobots composed of PCL, Fe 3 O 4 nanoparticles and catalase have been fabricated through a one-step electrospinning process 163 . The microrobots move by catalase-induced bubble propulsion in H 2 O 2 , assisted by the photothermal effect produced by the Fe 3 O 4 nanoparticles under light irradiation, whereas the PCL hydrophobic surface ensures the adsorption of spilled oil.

Magnetically powered micro- and nanorobots have emerged in oil removal owing to their effective and environmentally friendly actuation mode. For example, 3D porous magnetic oil collectors formulated by modifying a commercial polyurethane sponge with PDA nanoparticles, can be used as a navigable bifunctional platform on which to link Fe 3 O 4 nanoparticles and 1H,1H,2H,2H-perfluorodecanethiol (PFDT), changing the sponge’s wettability from hydrophilic to superhydrophobic 164 . Similarly, magnetic microsubmarines based on sunflower pollen grains can move at the liquid–liquid interface (water–oil) and the liquid–solid interface (the bottom of the vessel) 113 . The highly ordered nanospikes and super-oleophilicity of the microsubmarines enable adsorption and transport of oil droplets 37 times larger than their own volume.

In these examples, the removed oil spills were not completely degraded. To overcome this issue, enzyme-modified bio-inspired nanorobots have been proposed for the in situ degradation of oils. For example, using triacetin as fuel, mesoporous silica nanoparticles decorated with lipase obtained from Candida rugosa decompose dissolvable and slightly dissolvable triglyceride substrates, a model for oil pollutants 165 . Interestingly, the enzyme undergoes conformational changes depending on the different orientation and accessibility of the catalytic centre 166 . Furthermore, designing lipase-modified nanorobots in a yolk@spiky–shell structure endowed with near-infrared light responsiveness allows precise navigation towards oil droplets, showing a high degradation efficiency of ∼ 90% in 20 min owing to the synergistic combination of enzymatic and photothermal mechanisms 167 .

Microorganisms

Biological pollution in water arises from pathogenic microorganisms like viruses, bacteria, fungi and protozoa 168 . These pathogens pose severe risks for humans and animals, causing large-scale morbidity and mortality. Microorganisms can adapt to their surroundings, switch to a dormant state in which they can survive for extended periods without nutrients and resume proliferation under favourable conditions. Furthermore, they release toxins as secondary metabolites and acquire resistance to decontaminants, hindering their complete removal 169 . Contamination of aquatic resources is mostly of faecal origin, which spreads owing to poor water quality, lack of sanitation and inadequate hygiene 170 . Current disinfection methods are based on UV treatments and chlorine, chloramines or ozone 171 . However, these processes consume a substantial amount of energy (UV treatment), produce harmful by-products and require high doses of disinfectants to avoid pathogenic recolonization, a treatment that favours the establishment of resistant microbial biofilms. Furthermore, the effectiveness of traditional disinfection techniques against new fungal, bacterial and viral species is unknown and must be evaluated to avoid future outbreaks 172 .

The first attempts to remove aqueous pathogens focused on killing bacteria ‘on the fly’ by modifying microrobots with anti-bactericidal agents such as antibiotics, enzymes, protein receptors and metal ions 173 . However, bacterial biofilms preferentially grow in inaccessible locations, which requires the ability to control the movement of robots through, for example, using an external magnetic field. In this regard, catalytic antimicrobial robots (CARs) that incorporate iron oxide nanoparticles have been designed to remove bacterial biofilm grown at the end of conical tubings, mimicking a clogging plaque 174 . Exposing helicoidal CARs to H 2 O 2 , mutanase–dextranase enzyme solution and a rotating magnetic field prompts CARs to rapidly move in a corkscrew-like fashion (5 mm s −1 ), resulting in biofilm matrix drilling and removal. Simultaneously, the catalytic action of CARs removes the remaining biofilm clogs by killing all bacterial debris, thereby avoiding regrowth. Persistent bacterial biofilms can also be removed using the ‘kill-n-clean’ method (Fig.  4i ). For example, magnetic microrobots derived from biocompatible porous tea buds, loaded with ciprofloxacin and decorated with Fe 3 O 4 nanoparticles, exploit the acidic microenvironment of bacterial biofilms to release antibiotics in a pH-dependent manner, resulting in the simultaneous eradication and degradation of the biofilm 109 . Similarly, magnetically actuated helical microswimmers with an inner carbon core synergistically combine light and magnetic fields to kill E. coli bacteria through a photothermal effect under near-infrared light irradiation 175 .

Light-propelled micro- and nanorobots are another valuable solution for eliminating bacterial biofilms. These robots can move and simultaneously generate ROS, inducing substantial damage to the biofilm and preventing its regrowth. For example, intrinsically asymmetric Ag-doped ZnO microrobots demonstrate autonomous motion under UV light irradiation while destroying gram-negative Pseudomonas aeruginosa and gram-positive methicillin-resistant Staphylococcus aureus (MRSA) bacterial biofilms with higher efficiency ( ∼ 50% in 5 min) than in the static condition without light irradiation ( ∼ 10% in 5 min), as indicated by live–dead assay 105 . To avoid using UV light, bactericidal nanorobots consisting of Ag-coated TiO 2 nanotubes allow eradication of multispecies bacterial biofilms firmly attached to metallic surfaces (40% efficiency in 30 min). Owing to their broad light absorption from the UV to the visible region, these nanorobots vary in speed and motion type, resulting in modes such as clock-like rotation (up to 500 rpm) and swimming along random trajectories (30 µm s −1 ) 176 . Interestingly, upon visible light exposure, star-shaped light-powered BiVO 4 microrobots generate chemical gradients that allow them to swim and assemble into swarms to capture and kill fungal microbes ( Saccharomyces cerevisiae ) in water, rendering them photocatalytically inactivated 177 .

To remove pathogens on a large scale, biohybrid robots can be used 178 . For example, self-motile Chlamydomonas reinhardtii microalgae, covalently bound to the angiotensin-converting enzyme 2 (ACE2) receptor through a click-chemistry reaction, efficiently remove the SARS-CoV-2 viral spike protein (95%) and pseudovirus (89%). Moreover, these biohybrid microbots display fast (>100 μm s −1 ) and long-lasting motion (24 h) and reusability for five consecutive cycles in different water matrices, including acetate phosphate medium, phosphate-buffered saline, drinking water and river water, without needing fuel.

Self-propulsion has provided micro- and nanomaterials with an additional engineering dimension, allowing the development of swarms of intelligent small-scale robots that move in response to external stimuli and cooperate to accomplish selected tasks. For water-remediation applications, where the efficacy and speed of the purification process are crucial, micro- and nanorobots have proved effective owing to the synergy between active motion and programmable pollutant removal–degradation mechanisms through material design. Despite the breadth of efficacy of micro- and nanorobots against contaminants differing in nature and size (millimetre- to atomic-scale), several challenges must still be faced for real-world applications.

The main limitation is related to their applicability in open-water bodies such as oceans, seas, lakes and rivers. In principle, fuel-free sunlight-powered micro- and nanorobots are suitable for offshore water treatment because their activation does not require expensive and bulky apparatus (as for the magnetic actuation) or a chemical fuel that would be dispersed in an open space. However, their propulsion might be hindered by the decreasing light penetration with depth, restricting their use to surface-water treatment. Moreover, the motility of light-driven self-electrophoretic robots is hampered in high-salinity waters owing to the higher solution conductivity, which decreases the autogenerated electric field 179 . In addition, marine currents could overcome the motion of the robots, impeding their recovery and re-use. Alternatively, micro- and nanorobots can be actuated in a confined space (for example, a tub or tank), constraining potential secondary pollution phenomena (Box  1 ). Providing sufficient light intensity over the whole water volume using additional light sources could simultaneously sustain robotic movement and pollutant removal and degradation. ‘Hybrid’ robots exploiting multiple motion modes could further improve water-purification performance. For example, chemical fuels and electric fields can be used to boost the speed of light-driven robots 180 . Alternatively, magnetic fields allow us to control swarms of robots whose propulsion is not affected by the properties of the medium, such as its conductivity, after which fuels and light might be required to degrade the removed pollutants. Such a system must ensure a more efficient, safer and cheaper operation than current water-purification plants before it can be commercialized. Accordingly, for a proper estimation of production efficiency, quality, robustness and costs, the energy consumption associated with micro- and nanorobot operation must also be evaluated (Box  1 ).

Self-propelled micro- and nanorobots are more efficient than static materials for water-remediation applications. Furthermore, the removal and degradation efficiency is not satisfactory for all the pollutants investigated. For example, achieving total decomposition of plastic waste is particularly challenging, because plastics contain UV stabilizers to improve their stability. One practical solution is to combine multiple degradation mechanisms in the same robot or to program it to target the most persistent contaminant selectively. These features require the integration of multiple components, resulting in higher complexity and production costs. Therefore, the design of micro- and nanorobots must be kept as simple as possible while meeting the requirements of mass production, such as by using high-throughput fabrication methods (for example, 3D bioprinting). An associated risk to take into account is the accumulation of small-scale robots in the environment. In this context, using abundant, biocompatible and biodegradable natural materials such as microalgae is an attractive option.

Micro- and nanorobots can also be used to remediate soil and plants, which are at great risk of contamination owing to the extensive application of toxic pesticides in agriculture to improve crop yield. Environmentally friendly and biocompatible small-scale robots could decompose pesticides into harmless products in situ. As in water remediation, the robots need a liquid medium to facilitate their active movement and to enable removal and degradation of contaminants. One strategy could be to suspend the robots in water sprayed on the soil or plants’ surface, degrading the pesticides at the water–soil and water–plant interfaces under sunlight. Alternatively, they can be designed to target pests directly, thereby replacing the role of toxic pesticides.

Numerous studies have proved the immense potential of using micro- and nanorobots for water remediation. However, translation of this technology to real-world applications needs the combined efforts of scientists from different backgrounds, including physicists, chemists, biologists and engineers, to meet market demands.

Box 1 Robot-based water-remediation systems

Micro- and nanorobots are not suitable for remediation of open-water bodies (such as oceans), but can be used to remove or degrade contaminants in confined spaces, for example, by integration onboard a ship for offshore operations. Any small-scale robot-based water-remediation system should include a tank with an inlet pipe for contaminated water and an outlet pipe for clean water, equipped with sensors to assess post-treatment water quality (see the figure). The tank can be exposed to direct sunlight or arrays of ultraviolet lights to power light-driven robots, with the assistance of H 2 O 2 fuel if necessary. However, magnetic actuation might be preferred over light-driven actuation, especially for salty water where the high conductivity reduces the self-generated electric field that enables the movement of most light-driven micro- and nanorobots. Therefore, the tank could also be surrounded by a set of orthogonal magnetic coil pairs directed by the operator through an external controller. This system facilitates the movement of the robots to accelerate the adsorption (or degradation) of the pollutants and for collecting the robots at a preset location at the end of the treatment to let purified water exit. Moreover, magnetic actuation can be used to direct robots toward a second vessel where non-degradable pollutants can be controllably released, enabling re-use of the robots. Therefore, an ideal micro- or nanorobot must include several components with specific functions to meet these technical requirements (see the figure). For example, it could contain a magnetic engine as the core to ensure control over its location, speed and trajectory by regulating the magnetic field parameters. The engine could be surrounded by an adsorber with a large surface area (for example, a highly porous material) to maximize adsorption efficiency. The adsorber can be, in turn, coated by a shell of a photoresponsive material capable of undergoing one or multiple photodegradation pathways. If necessary, the robots’ surface can be further functionalized with enzymes to facilitate pollutants’ decomposition thereby boosting degradation efficiency 181 . Importantly, enzymes’ stability under exposure to light and photogenerated reactive oxygen species (ROS) needs to be evaluated. Such a system must be environmentally safe, with competitive production costs compared to conventional drinking-water distribution systems. In addition, a complete economic assessment of a system similar to the one described here should consider the energy consumption of pumping water, sensors to monitor the water quality, the controller of the magnetic setup, light sources and, importantly, the exact treatment duration. These parameters depend on the removal efficiency, which, in turn, is a function of other variables, including the nature of the pollutant, the number of robots, the parameters of the magnetic field and the light intensity.

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M.P. is supported by the Grant Agency of the Czech Republic (19-26896X).

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Urso, M., Ussia, M. & Pumera, M. Smart micro- and nanorobots for water purification. Nat Rev Bioeng 1 , 236–251 (2023). https://doi.org/10.1038/s44222-023-00025-9

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Tsuda, S. (2016). Nanorobotics. In: Bhushan, B. (eds) Encyclopedia of Nanotechnology. Springer, Dordrecht. https://doi.org/10.1007/978-94-017-9780-1_137

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What Is Nanorobotics?

Nanorobotics refers to the emerging field of science and technology that deals with the design, development and control of robots at the nanoscale. 

The nanoscale includes the size range of 1 to 100 nanometers, where one nanometer (nm) is equal to one billionth of a meter. 

Since nanorobots are robots built to operate at the nanoscale, they could perform tasks that are beyond the capabilities of conventional macro-scale robots. Nanorobots would have unique properties and capabilities that allow them to control and manipulate materials at the nanoscale, which would make them highly valuable for a wide range of applications and industries. 

Is Nanorobotics Real?

Much of what we know about nanorobotics is theoretical at this point. Nanorobotics is an interdisciplinary field that combines the principles of robotics, nanotechnology and material science to develop robots at the nanoscale. The use of nanorobots could lead to significant advancements in fields like medicine , manufacturing, energy production and environmental cleanup. Nanorobotics could also lead to new scientific discoveries and a deeper understanding of the nanoscale world . 

Using nanorobots can also lead to cost savings and improved efficiency. For example, in healthcare , nanorobots could be used for targeted drug delivery, which can reduce the amount of medication a patient needs and minimize side effects, thereby resulting in cost savings for patients and healthcare providers. Nanorobots could also be used for non-invasive surgeries to reduce the need for lengthy hospital stays and recovery times. It’s clear the field of nanorobotics has the potential to bring significant, positive changes and benefit society in numerous ways.

Related Reading From This Expert What Is Nanotechnology?

How Do Nanorobotics Work?

Nanorobotics work by using robots at nanoscale, which are also known as nanorobots. The design and operation of nanorobots can vary depending on their intended use. In general, nanorobots would work by using various technologies like nanoscale sensors, control systems and nanoscale actuators. 

The sensors in nanorobots could detect specific signals or conditions like the presence of a certain type of molecule or material, and then transmit this information to the control system. The control system could then use this information to decide on the proper action for the nanorobot. We could use the nanorobots’ actuators to perform a wide range of actions including movement, releasing of drugs in the human body or the manipulation of structures and materials (more on this below). 

In order to perform their intended tasks, nanorobots need to be able to navigate and interact with their environment. This can be accomplished by a variety of methods like self-propulsion, remote control, or through chemical or biological means.

What Are the Challenges of Nanorobotics?

The development and implementation of nanorobotics faces several challenges, including:

• Technical Complexity : Designing and operating nanorobots is a complicated process that involves many technical difficulties like development of nanoscale components, controlling the movement of the nanorobots and ensuring their stability.
• Safety Concerns : The potential for nanorobots in medical applications and the environment raises concerns about their safety. For example, nanorobots, designed for medical treatments, could harm patients in the case of a malfunction.
• Regulatory Issues : There are currently few regulations in place to govern the development and use of nanorobots, which may slow their widespread adoption by public and private sector entities.
• Funding and Resources : The development of nanorobotics is quite expensive and requires significant funding and resources, as well as specialized equipment and human expertise.
• Scalability : The development and production of large numbers of nanorobots can be challenging due to the complex and time-consuming nature of the manufacturing process.

Are Nanorobotics Dangerous?

If not properly designed and controlled, nanobots could cause harm to a living organism or the environment . Let’s say, hypothetically, that nanobots are designed and programmed to target and remove a specific type of cellular debris in a human body. Instead, the nanobots could end up attacking healthy cells or tissues, which will cause harm to the patient. This situation could occur if the nanobots cannot properly distinguish between the targeted debris and healthy cells, or in the case of the nanobots malfunction. Another risk would involve the potential for the harmful use of nanorobots. For example, nanorobots could be used as weapons or for industrial espionage. 

Due to these mentioned challenges, the development of nanorobotics has been slow so far and commercial use seems far away. However, we’ve seen progress and it’s likely that these challenges will be overcome in the coming decades.

More in Nanotechnology 10 Nanotechnology Examples Making a Big Impact

Applications of Nanorobotics

The field of nanorobotics has a wide range of potential applications across various industries. It’s important to note that many of these applications are still theoretical.

• Improved Medical Treatments : Nanorobots could perform medical procedures with higher accuracy and precision than humans. This could result in more effective patient treatment with fewer side effects and shorter recovery time.
• Environmental Cleanup : Nanorobots could potentially help humans clean up toxic waste, oil spills and other substances harmful to the environment. This could reduce the impact of pollution while also reducing the risk to humans who will engage with toxic waste less.
• Enhanced Manufacturing : Using nanorobots, manufacturers could improve the efficiency and quality of manufacturing processes. Nanorobots could perform tasks with a level of precision and accuracy that’s difficult to achieve with traditional manufacturing methods. This could help to improve the quality and consistency of products, reduce waste, improve worker safety and minimize errors.
• Increased Scientific Knowledge : Nanorobots can act as research tools to help scientists understand the nanoscale world, thereby leading to new technological breakthroughs. The nanoscale world refers to the scale of matter that is typically measured in nanometers (nm), which is one billionth of a meter.
• Advancements in Materials Science : We could use nanorobots to manipulate and assemble materials at the nanoscale, which could lead to new and improved materials with unique properties. For example, we could develop materials with enhanced strength, durability and conductivity by arranging atoms and molecules in specific ways using nanorobots.
• Space Exploration : We could use nanorobots for in-space manufacturing, repair and maintenance of satellites and other spacecraft. For example, the nanorobots could be used to close micro-holes in spacecrafts .

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The Use of Nanorobotics in the Treatment Therapy of Cancer and Its Future Aspects: A Review

Muskan aggarwal.

1 Medicine, Jawaharlal Nehru Medical College, Datta Meghe Institute of Medical Sciences, Wardha, IND

Sunil Kumar

The late Nobel Physicist Richard P. Feynman, in a dinner talk in 1959, very rightly said that there is enough room for the betterment of technology beyond our scope of imagination, proposing utilizing mechanical tools to make those that are relatively smaller than the others, which further can be rendered fruitful in making even more compact mechanical devices, all the way down to the level of the smallest known atom, emphasizing that this is "a progress which I believe cannot be avoided". Feynman proposed that nanomachines, nanorobots, and nanodevices may eventually be utilized to construct a huge range of atomically accurate microscopic instruments and manufacturing equipment, as well as a large number of ultra-small devices and other nanoscale and microscale robotic structures. Biotechnology, molecular biology, and molecular medicine could be used to create totally self-sufficient nanorobots/nanobots. Nanorobotics includes sophisticated submicron devices constructed of nanocomponents that are viewed as a magnificent desired future of health care. It has a promising potential in medication delivery technology for cancer, the top cause of mortality among those under the age of 85 years. Nanorobots might transport and distribute vast volumes of anticancer medications into diseased cells without hurting normal cells, decreasing the adverse effects of existing therapies such as chemotherapy damage. The ultimate development of this innovation, which will be accomplished via a close partnership among specialists in robotics, medicine, and nanotechnology, will have a significant influence on illness detection, therapy, and prophylaxis. This report includes a study on several ways to cancer therapy utilizing nanorobots. Furthermore, it offers insight into the future breadth of this area of research.

Introduction and background

Researchers have emphasised nanotechnology as an outstanding technological trend in the last few decades, and it is characterized by the fast proliferation of electronics for applications in communication, known as nanomedicine, and environmental monitoring. Studies are now being conducted on the scientific bottlenecks that affect the lifespan of the living, particularly humans. Among these constraints are illnesses with few or no alternatives for treatment and healing. A drug delivery system (DDS) refers to an alternative diagnosis and/or therapy that has been shown in the medical fraternity [ 1 , 2 ]. Nanorobots are nanoelectromechanical systems (NEMS), a recently developed chapter in miniaturisation, similar to microelectromechanical systems (MEMS), which is already a multibillion-dollar business. Designing, architecting, producing, programming, and implementing such biomedical nanotechnology are all part of nanorobotics and NEMS research. Any scale of robotics includes calculations, commands, actuation and propulsion, power, data-sharing, interface, programming, and coordination. There is heavy stress on actuation, which is a key prerequisite for robotics [ 1 ]. The similarity in size of nanorobots to that of organic human cells and organelles brings up a huge variety of its possible uses in the field of health care and environmental monitoring of microorganisms. Other potential uses, such as cell healing, may be possible if nanorobots are tiny enough to reach the cells. Furthermore, it is still to be realised that the tiny sensors and actuators' square measures are necessary for the growing concept of a strongly connected ascending information technology infrastructure; the envision of artificial cells (nanorobots) that patrol the cardiovascular system, thus, detecting and destroying infections in minute quantities. This might be a programmable system with approachable ramifications in medicine, creating a revolutionary replacement from therapy to bar [ 1 ]. Chemotherapeutic substances employed in cancer treatment measure disseminates non-specifically throughout the body, where they exert an influence on both malignant and normal cells, restricting the drug quantity feasible within the growth and also resulting in unsatisfactory medication due to excessive toxic hazards of the chemotherapy drugs on normal cells of the body. It is safe to say that molecularly focused medical care has evolved as a collaborative method to overcome the lack of specificity of traditional cancer therapy drugs [ 3 ]. With the help of nanotechnology, intercellular aggregation of the drugs in cancer cells can be increased while minimising the risk of unwanted drug toxicity in normal cells by utilising various drug targeting mechanisms [ 4 ].

This review article focuses on the recent advancements, technological growth, and expansion in the field of nanorobotics and nanotechnology and its application in the discipline of bio-healthcare systems, principally for the DDS in the medication of cancer. Existing research literature and relevant studies regarding the topic of concern were read and a detailed analysis was undertaken in the indexes of PubMed, Science Direct, MEDLINE, Scopus, and Google Scholar. Hardly any language or time constraints were applied. To obtain a detailed search, more articles, synonyms, and derivatives of the phrases were employed; the following evaluation phrases were used: "drug delivery", "cancer", "neoplasms", and "cancer therapy".

Nanorobots and their types

Nanorobots are miniaturised machines that have the ability to perform work at par with that of current existing machines, having applications in the aspects of medicine, industry, and other areas like the development of nanomotors employed for the conservation of energy; nanorobots have also proved to be serviceable in reducing infertility problems by acting as an engine and giving a boost to the sperm motility when attached to them [ 2 ]. Organic and inorganic nanorobots are by far the most commonly studied. Organic nanorobots, also known as bio-nanorobots, are created by combining virus and bacterium DNA cells. This type of nanorobot is less harmful to the organism. Diamond structures, synthetic proteins, and other materials are used to make inorganic nanobots, which are more hazardous than organic nanobots. To overcome this hurdle of toxicity, researchers have devised a way involving encapsulating the robot, thus decreasing its chances of being destructed by the body's self-defence mechanism [ 5 , 6 ]. Scientists can gain an understanding of how to energise micro and nano-sized devices using reactionary processes if they understand the biological motors of live cells [ 7 ]. The Chemistry Institute of the Federal Fluminense University created a nano valve, which is made up of a tank covered with a shutter in which dye molecules are housed and may leave in a uniform fashion whenever the cover is opened. This gadget is also natural, made of silica (SiO2), beta-cyclodextrins, and organo-metallic molecules, and shall be used in therapeutic applications [ 1 ]. Proteins are employed in certain studies to feed nanomotors that can move huge objects, as well as the use of DNA hybridisation and antibody protein in the development of nanorobots. DNA hybridisation is defined as a process by which two complementary single-stranded DNA and/or RNA molecules bond together to form a double-stranded molecule. A nanorobot can be functionalized using a variety of chemical compounds [ 8 ]. It has been investigated in nanomedicine in DDS, which operates directly on targeted cells of the human body. Researchers create devices that can administer medications to precise places while simultaneously adjusting the dose and amount of release. This DDS using nanorobots can be used to treat joint disorders, dental problems, diabetes, cancer, hepatitis and other conditions [ 2 , 9 - 12 ]. One of the benefits of this technology is the potential to diagnose and treat illnesses with minimal impact on normal tissues, minimizing the likelihood of negative effects and guiding healing and remodelling therapy at the cellular and sub-cellular levels [ 13 , 14 ].

Chemotherapy drug delivery using nanorobots in cancer treatment

New advances in medication delivery have resulted in greater quality in targeted drug delivery that uses nanosensors to detect particular cells and regulate discharges through the use of smart medicines [ 1 ]. Traditional chemotherapeutic drugs act by eliminating swiftly replicating cells, which is a primary feature of malignant cells. Most anticancer medications have a limited therapeutic boundary, often resulting in cytotoxicity to normal stem cells that proliferate quickly, such as bone marrow, macrophages, gastrointestinal tract (GIT), and hair follicles, causing adverse effects like myelosuppression (lower synthesis of WBCs, producing immunosuppression), mucositis (inflammation of the GIT lining), alopecia (hair loss), organ malfunction, thrombocytopenia/anaemia, and haematological side effects, among other things. Doxorubicin is used to treat numerous forms of cancer, including Hodgkin's disease, when it is combined with other antineoplastic medicines to minimize its toxicity [ 15 , 16 ]. Paclitaxel is a drug that is injected intravenously and is used to treat breast cancer. Some of the significant side effects include bone marrow suppression and progressive neurotoxicity. Cisplatin is an alkylating drug that results in the intra-DNA binding filament. Its negative effects include giddiness and severe vomiting, and it can be nephrotoxic [ 1 ]. Camptothecin is applied to treat neoplasia by inhibiting type 1 topoisomerases, an enzyme required for cellular duplication of genetic information. Numerous initiatives have been launched with the goal of employing nanotechnology to build DDS that can reduce the negative impacts of traditional therapy. On the surface of single-walled carbon nanotubes (SWNTs), doxorubicin was layered [ 17 ]. Doxorubicin was used in metastatic tumour cells as a polymer prodrug/collagen hybrid. The use of polymeric pro-drug nanotechnology in the therapy of rapidly dividing abnormal cells is a novel advance in the field [ 18 ]. Nanotechnology is continually looking for biocompatible materials that may be used as a DDS. The nanoparticle hydroxyapatite (HA), a significant component of bone and teeth, was employed to deliver paclitaxel, an anti-neoplastic medication, and the out-turn implies that therapy should begin with hydrophobic medicines [ 19 ]. Various initiatives have been launched with the goal of employing nanotechnology to build DDS, which can reduce the negative influence of traditional chemotherapy. The limitation of conservative chemotherapeutics is that it is unable to target malignant cells exclusively. These above-listed adverse effects often result in a delay in treatment, reduced drug dose or intermittent stopping of the therapy [ 20 ]. Given the ability of nanorobots to travel as blood-borne devices, they can aid in crucial therapy procedures such as early diagnostics and smart medication administration [ 21 ]. A nanorobot can aid with smart chemotherapy for medication administration and give an efficient early dissolution of cancer by targeting only the neoplastic-specific cells and tissues and preventing the surrounding healthy cells from the toxicity of the chemotherapy drugs so being used. Nanorobots as drug transporter for timely dose administration allow chemical compounds to be kept in the bloodstream for as long as essential, giving expected pharmacokinetic characteristics for chemotherapy in the therapies for anti-cancer as shown in Figure ​ Figure1 1 [ 22 - 25 ]. The clinical use of nanorobots for diagnostic, therapy, and surgery can be accomplished by injecting them via an intravenous route. The nanorobots may be getting intravenously injected into the body of the recipient. The chemotherapy pharmacokinetics comprises uptake, metabolism, and excretion, as well as a rest period to allow the body to re-establish itself ahead of the succeeding chemotherapy session. For tiny tumours, patients are often treated in two-week cycles [ 26 ]. As a primary time threshold for medical purposes, nanorobots can be used to assess and diagnose the tumour within a short span of time using proteomic-based sensors. The magnetic resonance contrast-agent uptake kinetics of a very small molecular weight can forecast the transport of protein medicines to solid tumours [ 27 ]. Testing and diagnostics are critical components of nanorobotics study. It provides speedy testing diagnosis at the initial visit, eliminating the need for a follow-up appointment following the lab result, and illness identification at an earlier stage. The demand for energy for propulsion is a restriction in the usage of nanorobots in vivo. Because small inertia and strong viscous forces are associated with less productivity and less convective motion, higher quantities of energy are required [ 28 ]. Drug retention in the tumour will decide the medication's effectiveness after nanorobots pass cellular membranes for targeted administration. Depending on its structure, medication transport pathways from plasma to tissue impact chemotherapy to achieve more effective tumour chemotherapy [ 27 ]. According to the latest research, nanotechnology, DNA production of molecular-scale devices with superior control over shape, and site-specific functionalisation assures interesting benefits in the advancement of nanomedicine. However, biological milieu uncertainty and innate immune activation continue to be barriers to in vivo deployment. Thus, the primary benefit of nanorobots for cancer medicine administration is that they reduce chemotherapeutic side effects. The nanorobot design integrates carbon nanotubes and DNA, which are current contenders for the latest types of nanoelectronics, as the optimum method [ 29 ]. As a compound bio-sensor with sole-chain antigen-binding proteins, a complementary metal oxide semiconductor (CMOS) is used for building circuits with characteristic sizes in tens of nanometres [ 30 ]. For medicament release, this approach employs stimulation elicited upon proteomics and bioelectronics signals. As a result, nanoactuators are engaged to adjust medication delivery whenever the nanorobot detects predetermined modifications in protein gradients [ 1 , 31 ]. Thermal and chemical signal changes are relevant circumstances directly connected to significant medical target identification. Nitric oxide synthase (NOS), E-cadherin, and B cell lymphoma-2 (Bcl-2) are some instances of fluctuating protein aggregation within the body near a medical target under diseased conditions. Furthermore, temperature changes are common in tissues with inflammation [ 32 ]. The framework integrates chemical and thermal characteristics as the most essential clinical and therapeutic recommendations for nanorobot template analysis. It also integrates chemical and thermal characteristics as the most essential diagnostic and therapeutic recommendations for nanorobot framework evaluation. The simulation in a three-dimensional real-time setting attempts to provide a viable model for nanorobot foraging within the body. One of the breakthroughs describes a hardware structure rooted in nano-bioelectronics for the use of nanorobots in neoplasia therapy [ 33 , 34 ]. The continuous venture in building medical micro-robots has led to the initial conceptual framework research of a full medical nanorobot until now issued in a peer-reviewed publication, "Respirocytes", detailed a theoretical unnatural mechanical red blood cell, or "Respiro-cytes", consisting of 18 billion perfectly ordered architectural atoms proficient in delivering 236 times extra oxygen to the tissues and cells of the body per unit volume than normal red blood cells [ 35 ]. Microbivores, or unnatural phagocytes, might monitor the circulation, searching for and eliminating pathogens such as bacteria, viruses, or fungi. These nanobots may use up to 200 pW continuously. This capability is employed to break down germs that have been entrapped. Microbivores have biological phagocytic defences that are either organic or antibiotic-assisted, and they can operate up to 1,000 times quicker. Even the most serious septicaemic diseases will be eliminated by microbivores within a short span of time. Because virulent microorganisms are entirely digested into harmless sugars and amino acids, which are the nanorobot’s sole discharge, the nanorobots reject the advanced possibility of sepsis or septic shock [ 36 , 37 ].

This image throws light on the various challenges that different shaped nanorobots face when employed for drug delivery [ 38 ].

Image reprinted from [ 38 ] under Creative Commons Attribution 4.0 International License.

Future of nanotechnology in the area of medicine

To bring in combination the required collaborative skills to produce these unique technologies, numerous conventional streams of science, such as medicine, chemistry, physics, materials science, and biology, have come together to form the expanding field of nanotechnology. Nanotechnology has a vast span of possible applications (Figure ​ (Figure2) 2 ) [ 39 ], from improvements to current practices to the creation of entirely new tools and skills. The last few years have observed an exponential increase of interest in the topic of nanotechnology and research, which has led to the identification of novel applications for nanotechnology in medicine and the emergence of an advanced branch called nanomedicine. It includes the science and technology of diagnosing, treating, and preventing illness, traumatic injury, and alleviating pain; conserving and enhancing human health using nanoscale architectured materials, biotechnology, and genetic engineering; eventually, complex machine systems and nanorobots, known as "nanomedicine" (Figure ​ (Figure3) 3 ) [ 40 , 41 ].

The discovery of nanoparticles with the help of nanotechnology has led to its various uses in the area of medicine. The nanoparticle so created can be employed for various uses like in the manufacturing of nano implants, tissue engineering for drug delivery systems, gene delivery systems, drug screening, theranostics, cancer therapy, biomarker mapping, disease detection, and bio-imaging [ 39 ].

Image reprinted from [ 39 ] under Creative Commons Attribution 4.0 International License.

Nanorobots are being used in various domains of pre-clinical and clinical medicine. In pre-clinical medicine, nanorobots are being employed in bioimaging and various delivery systems of drugs, gene therapy, living cells, and inorganic therapeutics. Similarly, nanorobots in clinical medicine are being extensively used in disease diagnosis and surgeries for biopsy, biofilm degradation, tissue collection, and sampling [ 41 ].

Image reprinted from [ 41 ] under Creative Commons Attribution 4.0 International License.

In vivo diagnostics, nanomedicine might create technologies that can act within the human body to diagnose ailments earlier and identify and measure toxic chemicals and tumour cells. In the surgical aspect, when launched into the body through the intravenous route or cavities, a surgical nanorobot controlled or led by a human surgeon might work as a semi-autonomous on-site surgeon. An inbuilt computer might manage the device's operations, such as looking for disease and identifying and fixing injury by nanomanipulation while maintaining communication with the supervising surgeon via coded ultrasonic signals [ 37 ]. By transforming mechanical energy from bodily movement, muscle stretching, or water flow into electricity, scientists were able to design a new generation of self-sustained implanted medical devices, sensors, and portable gadgets [ 39 ]. Nanogenerators generate electricity by bending and then releasing piezoelectric and semiconducting zinc oxide nanowires. Nanowires may be produced on polymer-based films, and the utilization of flexible polymer substrates may one day allow portable gadgets to be powered by their users' movement [ 39 ]. Fluorescent biological labelling, medication and gene delivery, pathogen identification, protein sensing, DNA structure probing, tissue engineering, tumour identification, separation and purification of biological molecules and cells, MRI contrast enhancement, and phagokinetic research are among the uses. The extended duration effect of nanomedicine study is to describe quantitative molecular-scale components called nanomachinery. Accurate command and manipulation of nanomachinery in cells can lead to a more diverse and advanced gain in the interpretation of cellular processes in organic cells, as well as the creation of new technologies for disease detection and medication. The advantage of this research is the formation of a platform technology that will affect nanoscale imaging methodologies aimed to investigate molecular pathways in organic cells [ 40 , 42 ].

Conclusions

The main target of writing this review was to provide an outline of the technological development of nanotechnology in medicine by making a nanorobot and introducing it in the medication of cancer as a new mode of drug delivery. Cancer is described as a collection of diseases characterised by the unregulated development and spread of malignant cells in the body, and the number of people diagnosed every year keeps adding up. Cancer treatment is most likely the driving force behind the creation of nanorobotics; it can be auspiciously treated using existing medical technology and therapeutic instruments, with the major help of nanorobotics. To decide the prognosis and chances of survival in a cancer patient, consider the following factors: better prognosis can be achieved if the evolution of the disease is time-dependent and a timely diagnosis is made. Another important aspect is to reduce the side effects of chemotherapy on the patients by forming efficient targeted drug delivery systems. Programmable nanorobotic devices working at the cellular and molecular level would help doctors to carry out precise treatment. In addition to resolving gross cellular insults caused by non-reversible mechanisms or to the biological tissues stored cryogenically, mechanically reversing the process of atherosclerosis, enhancing the immune system, replacing or re-writing the DNA sequences in cells at will, improving total respiratory capacity, and achieving near-instant homeostasis, medically these nanorobots have been put forward for use in various branches of dentistry, research in pharmaceuticals, and aid and abet clinical diagnosis. When nanomechanics becomes obtainable, the ideal goal of physicians, medical personnel, and every healer throughout known records would be realized. Microscale robots with programmable and controllable nanoscale components produced with nanometre accuracy would enable medical physicians to perform at the cellular and molecular levels to heal and carry out rehabilitating surgeries. Nanomedical doctors of the 21st century will continue to make effective use of the body's inherent therapeutic capacities and homeostatic systems, since, all else being equal, treatments that intervene the least are the best.

Acknowledgments

The author would like to acknowledge the combined efforts of Mr. Harsh Verma, a medical student at Jawaharlal Nehru Medical College, Wardha, India, and that of Capt. Bachwala Rohit, Regimental Medical Officer, The Ladakh Scouts Regiment, in contributing to this article.

The content published in Cureus is the result of clinical experience and/or research by independent individuals or organizations. Cureus is not responsible for the scientific accuracy or reliability of data or conclusions published herein. All content published within Cureus is intended only for educational, research and reference purposes. Additionally, articles published within Cureus should not be deemed a suitable substitute for the advice of a qualified health care professional. Do not disregard or avoid professional medical advice due to content published within Cureus.

The authors have declared that no competing interests exist.

Nanorobots: A Developmental Tool for the Treatment of Cancer

Article sidebar, main article content.

This review paper aims at presenting the overall scenario of the present trends and advancements in development in the treatment of cancer. Nanorobots help us in bridging the technological gap between the different fields of sciences on the nanoscale. According to the World Health Organisation, the leading cause of the death in the present scenario is the Cancer. Currently there are two types of treatment processes used for cancer treatment: chemotherapy and radiotherapy. But with the advancement in technology, the nanotechnology has come up with an excellent idea of introducing Nanorobots that use cadherin signals and chemicals along with body heat as their fuel to target and kill the tumour cells. This is a revolution in the field of medical technology and also an alternative to the chemo and radio-therapy, therefore finding a solution to one of the most challenging problems without any side effects.

Article Details

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License .

Ankit Kumar Dubey

Department of Biotechnology, School of Applied Sciences, REVA University, Bangalore

Ligi Milesh