Human-scale navigation of magnetic microrobots in hepatic arteries

Advances in Magnetically Controlled Medical Robotics: A Review of Actuation Systems, Continuum Designs, and Clinical Prospects for Minimally Invasive Therapies

Magnetically controlled micro-robots hold immense potential for revolutionizing advanced medical applications, garnering significant research interest. This potential is underscored by the dual focus on magnetic control systems-both as driving forces and manipulation field sources-and magnetic continuums that have demonstrated clinical therapeutic efficacy. This comprehensive review delves into the actuation characteristics of permanent magnet systems, electromagnetic systems, and commercially available magnetic control systems. It also explores innovative designs of magnetic wires and tubes serving as continuum structures and investigates the variable stiffness properties of magnetic continua, informed by material and structural attributes. Furthermore, the discussion extends to their prospective roles and future applications within the medical realm. The objective is to elucidate emerging trends in the study of magnetic control systems and magnetic continua, marked by an expanding operational scope and enhanced precision in manipulation. By aligning these trends with clinical challenges and requirements, this review seeks to refine research trajectories, expedite practical implementations, and ultimately advocate for minimally invasive therapies. These therapies, leveraging magnetic control systems and magnetic continuums as cutting-edge treatment modalities, promise transformative impacts on the future of healthcare.

Magnetic Micro/nanorobots in Cancer Theranostics: From Designed Fabrication to Diverse Applications

Cancer poses a substantial threat and a serious challenge to public human health, driving the promotion of sophisticated technologies for cancer therapy. While conventional chemotherapy has bottlenecks such as low delivery efficiency, strong toxic side effects, and tumor enrichment barriers, magnetic micro/nanorobots (MNRs) emerge as promising therapeutic candidates that provide alternative strategies for cancer therapy. MNR is a kind of human-made machine that is micro- or nanosized, is reasonably designed, and performs command tasks through self-actuated or externally controlled propulsion mechanisms, which can be potentially applied in cancer theranostics. Here, this review first introduces the components that constitute a typical magnetic MNR, including the body part, the driving part, the control part, the function part, and the sensing part. Subsequently, this review elucidates representative fabrication methods to construct magnetic MNRs from top-down approaches to bottom-up approaches, covering injection molding, self-rolling, melt electrospinning writing, deposition, biotemplate method, lithography, assembling, 3D printing, and chemical synthesis. Furthermore, this review focuses on multiple applications of magnetic MNRs facing cancer diagnosis and treatment, encompassing imaging, quantification, drug release, synergy with typical therapies, cell manipulation, and surgical assistance. Then, this review systematically elaborates on the biocompatibility and biosafety of magnetic MNRs. Finally, the challenges faced by magnetic MNRs are discussed alongside future research directions. This review is intended to provide scientific guidance that may improve the comprehension and cognition of cancer theranostics through the platform of magnetic MNRs, promoting and prospering the practical application development of magnetic MNRs.

Nanozyme-Shelled Microcapsules for Targeting Biofilm Infections in Confined Spaces

Bacterial infections in irregular and branched confinements pose significant therapeutic challenges. Despite their high antimicrobial efficacy, enzyme-mimicking nanoparticles (nanozymes) face difficulties in achieving localized catalysis at distant infection sites within confined spaces. Incorporating nanozymes into microrobots enables the delivery of catalytic agents to hard-to-reach areas, but poor nanoparticle dispersibility and distribution during fabrication hinder their catalytic performance. To address these challenges, a nanozyme-shelled microrobotic platform is introduced using magnetic microcapsules with collective and adaptive mobility for automated navigation and localized catalysis within complex confinements. Using double emulsions produced from microfluidics as templates, iron oxide and silica nanoparticles are assembled into 100-µm microcapsules, which self-organize into multi-unit, millimeter-size assemblies under rotating magnetic fields. These microcapsules exhibit high peroxidase-like activity, efficiently catalyzing hydrogen peroxide to generate reactive oxygen species (ROS). Notably, microcapsule assemblies display remarkable collective navigation within arched and branched confinements, reaching the targeted apical regions of the tooth canal with high accuracy. Furthermore, these nanozyme-shelled microrobots perform rapid catalysis in situ and effectively kill biofilms on contact via ROS generation, enabling localized antibiofilm action. This study demonstrates a facile method of integrating nanozymes onto a versatile microrobotic platform to address current needs for targeted therapeutic catalysis in complex and confined microenvironments.

Cooperative Magnetic Interfacial Microrobot Couple for Versatile Non-Contact Biomedical Applications

Magnetic interfacial microrobots are increasingly recognized as a promising approach for potential biomedical applications ranging from electronic functionalization to minimally invasive surgery and targeted drug delivery. Nevertheless, existing research faces challenges, including less cooperative interactions, contact-based cargo manipulation, and slow transport velocity. Here, the cooperative magnetic interfacial microrobot couple (CMIMC) is proposed to address the above challenges. The CMIMC can be maneuvered by a single magnet and readily switched between capture and release states. By leveraging cooperative interactions and meticulous engineering of capillary forces through shape design and surface treatment, the CMIMC demonstrates the ability to perform non-contact cargo manipulation. Using the synergy of preferred magnetization directions and magnetic field distribution, along with optimization of the resistance-reducing shape, the CMIMC significantly enhances the cargo transport velocity, reaching 12.2 body length per second. The studies demonstrate various biomedical applications like targeted drug delivery and myomectomy, paving the way for the broad implementation of interfacial microrobots in biomedical fields.

Cilia-Mimic Locomotion of Magnetic Colloidal Collectives Enhanced by Low-Intensity Ultrasound for Thrombolytic Drug Penetration

Rapid thrombolysis is very important to reduce complications caused by vascular blockage. A promising approach for improving thrombolysis efficiency is utilizing the permanent magnetically actuated locomotion of nanorobots. However, the thrombolytic drug transportation efficiency is challenged by in-plane rotating locomotion and the insufficient drug penetration limits further improvement of thrombolysis. Inspired by ciliary movement for cargo transportation in human body, in this study, cilia-mimic locomotion of magnetic colloidal collectives is realized under torque-force vortex magnetic field (TFV-MF) by a designed rotating permanent magnet assembly. This cilia-mimic locomotion mode can generate more disturbances to the fluids to improve thrombolytic drug transportation and the increased height and area of colloidal collectives boosted the imaging capability. In addition, low-intensity ultrasound is applied to enhance colloids infiltration by producing the fiber breakage and inducing erythrocyte deformation. In vitro thrombolytic experiments demonstrate that the thrombolysis efficiency increased by 16.2 times compared with that of pure tissue plasminogen activator (tPA) treatments. Furthermore, in vivo rat models of femoral vein thrombosis confirmed that this approach can achieve blood flow recanalization more quickly. The proposed cilia-mimic locomotion of magnetic colloidal collectives combined with low-intensity ultrasound irradiation mode provides a new insight of therapeutic interventions for vascular thrombus by enhancing drug penetration.

Superselective embolic particle guidance in vessel networks via shape-adaptive acoustic manipulation

Interventional embolization has been widely used as a clinical cancer therapy, which deactivates the tumors by occluding their blood supply vessels. However, conventional methods lack active control over the embolic particles, thus having a limited selectivity of millimeter-scale vessels and the issue of missing embolization. Here, we propose an ultrasound-based method for embolic particle control in submillimeter vessels. The biocompatible ultrasound generated from an extrasomatic source can transmit through biological tissues, and exert forces on the intravital embolic particles. We show that the particles, influenced by these forces, are steerable to the target branch at vascular bifurcations. By modulating the ultrasound to adapt the vascular bifurcation distribution, the particles flowing in the micro-vessel networks are steered to the target branch and embolize it. The acoustic steering within ex vivo and in vivo models both verify the potential of this non-invasive particle control for precise and safe interventional therapy.

Magnetic soft microrobots for erectile dysfunction therapy

Erectile dysfunction (ED) is a major threat to male fertility and quality of life, and mesenchymal stromal cells (MSCs) are a promising therapeutic option. However, therapeutic outcomes are compromised by low MSC retention and survival rates in corpus cavernosum tissue. Here, we developed an innovative magnetic soft microrobot comprising an ultrasoft hydrogel microsphere embedded with a magnetic nanoparticle chain for MSC delivery. This design also features phenylboronic acid groups for scavenging reactive oxygen species (ROS). With a Young's modulus of less than 1 kPa, the ultrasoft microrobot adapts its shape within narrow blood vessels, ensuring a uniform distribution of MSCs within the corpus cavernosum. Our findings showed that compared with traditional MSC injections, the MSC delivery microrobot (MSC-Rob) significantly enhanced MSC retention and survival. In both rat and beagle ED models, MSC-Rob treatment accelerated the repair of corpus cavernosum tissue and restored erectile function. Single-cell RNA sequencing (scRNA-seq) revealed that MSC-Rob treatment facilitates nerve and blood vessel regeneration in the corpus cavernosum by increasing the presence of regenerative macrophages. Overall, our MSC-Rob not only advances the clinical application of MSCs for ED therapy but also broadens the scope of microrobots for other cell therapies.

X-ray fluoroscopy guided localization and steering of miniature robots using virtual reality enhancement

In developing medical interventions using untethered milli- and microrobots, ensuring safety and effectiveness relies on robust methods for real-time robot detection, tracking, and precise localization within the body. The inherent non-transparency of human tissues significantly challenges these efforts, as traditional imaging systems like fluoroscopy often lack crucial anatomical details, potentially compromising intervention safety and efficacy. To address this technological gap, in this study, we build a virtual reality environment housing an exact digital replica (digital twin) of the operational workspace and a robot avatar. We synchronize the virtual and real workspaces and continuously send the robot position data derived from the image stream into the digital twin with short average delay time around 20-25 ms. This allows the operator to steer the robot by tracking its avatar within the digital twin with near real-time temporal resolution. We demonstrate the feasibility of this approach with millirobots steered in confined phantoms. Our concept demonstration herein can pave the way for not only improved procedural safety by complementing fluoroscopic guidance with virtual reality enhancement, but also provides a platform for incorporating various additional real-time derivative data, e.g., instantaneous robot velocity, intraoperative physiological data obtained from the patient, e.g., blood flow rate, and pre-operative physical simulation models, e.g., periodic body motions, to further refine robot control capacity.

Magnetically Driven Quadruped Soft Robot with Multimodal Motion for Targeted Drug Delivery

Untethered magnetic soft robots show great potential for biomedical and small-scale micromanipulation applications due to their high flexibility and ability to cause minimal damage. However, most current research on these robots focuses on marine and reptilian biomimicry, which limits their ability to move in unstructured environments. In this work, we design a quadruped soft robot with a magnetic top cover and a specific magnetization angle, drawing inspiration from the common locomotion patterns of quadrupeds in nature and integrating our unique actuation principle. It can crawl and tumble and, by adjusting the magnetic field parameters, it adapts its locomotion to environmental conditions, enabling it to cross obstacles and perform remote transportation and release of cargo.