Biohybrid Flexible Sperm-like Microrobot for Targeted Chemo-Photothermal Therapy.

Magnetic micro/nanorobots are promising platforms for targeted drug delivery, and their construction with soft and flexible features has received extensive attention for practical applications. Despite significant efforts in this field, facile fabrication of magnetic microrobots with flexible structures and versatility in targeted therapy remains a big challenge. Herein, we proposed a novel universal strategy to fabricate a biohybrid flexible sperm-like microrobot (BFSM) based on a Chlorella (Ch.) cell and artificial flagella, which showed great potential for targeted chemo-photothermal therapy for the first time. In this approach, microspherical Ch. cells were utilized to construct the microrobotic heads, which were intracellularly deposited with core-shell Pd@Au, extracellularly magnetized with Fe3O4, and further loaded with anticancer drug. The magnetic heads with excellent photothermal and chemotherapeutic capability were further assembled with flexible polypyrrole nanowires via biotin-streptavidin bonding to construct the BFSMs. Based on the exquisite head-to-tail structures, the BFSMs could be effectively propelled under precessing magnetic fields and move back and forth without a U-turn. Moreover, in vitro chemo-photothermal tests were conducted to verify their performance of targeted drug delivery toward localized HeLa cells. Due to this superior versatility and facile fabrication, the BFSMs demonstrated great potential for targeted anticancer therapy.

Magnetic Biohybrid Microrobot Multimers Based on Chlorella Cells for Enhanced Targeted Drug Delivery.

Magnetic micro-/nanorobots have been regarded as a promising platform for targeted drug delivery, and tremendous strategies have been developed in recent years. However, realizing precise and efficient drug delivery in vivo still remains challenging, in which the versatile integration of good biocompatibility and reconfiguration is the main obstacle for micro-/nanorobots. Herein, we proposed a novel strategy of magnetic biohybrid microrobot multimers (BMMs) based on Chlorella (Ch.) and demonstrated their great potential for targeted drug delivery. The spherical Ch. cells around 3-5 µm were magnetized with Fe3O4 to fabricate biohybrid microrobots and then loaded with doxorubicin (DOX). Using magnetic dipolar interactions, the microrobot units could reconfigure into chain-like BMMs as tiny dimers, trimers, and so forth via attraction-induced self-assembly and disassemble reversibly via repulsion. The BMMs exhibited diverse swimming modes including rolling and tumbling with high maneuverability, and the rolling dimer's velocity could reach 107.6 µm/s (∼18 body length/s) under a 70 Gs precessing magnetic field. Furthermore, the BMMs exhibited low cell toxicity, high DOX loading capacity, and pH-triggered drug release, which were verified by chemotherapy experiments toward HeLa cancer cells. Due to the remarkable versatility and facile fabrication, the BMMs demonstrate great potential for targeted anticancer therapy.

Artificial flexible sperm-like nanorobot based on self-assembly and its bidirectional propulsion in precessing magnetic fields.

Sperm cells can move at a high speed in biofluids based on the flexible flagella, which inspire novel flagellar micro-/nanorobots to be designed. Despite progress in fabricating sperm-type robots at micro scale, mass fabrication of vivid sperm-like nanorobots with flagellar flexibility is still challenging. In this work, a facile and efficient strategy is proposed to produce flexible sperm-like nanorobots with self-assembled head-to-tail structure, and its bidirectional propulsion property was studied in detail. The nanorobots were composed of a superparamagnetic head and a flexible Au/PPy flagellum, which were covalently linked via biotin-streptavidin bonding with a high yield. Under precessing magnetic fields, the head drove the flexible tail to rotate and generated undulatory bending waves propagating along the body. Bidirectional locomotion was investigated, and moving velocity as well as direction varied with the actuating conditions (field strength, frequency, direction) and the nanorobot's structure (tail length). Effective flagellar propulsion was observed near the substrate and high velocities were attained to move back and forth without U-turn. Typical modelling based on elastohydrodynamics and undulatory wave propagation were utilized for propulsion analysis. This research presents novel artificial flexible sperm-like nanorobots with delicate self-assembled head-to-tail structures and remarkable bidirectional locomotion performances, indicating significant potentials for nanorobotic design and future biomedical application.

Efficient Removal of Pb(II) from Aqueous Systems Using Spirulina-Based Biohybrid Magnetic Helical Microrobots.

Wastewater remediation toward heavy metal pollutants has attracted considerable attention, and various adsorption-based materials were employed in recent years. However, it is still challenging to explore low-cost and high-efficient adsorbents with superior removal performance, nontoxicity, flexible operation, and good reusability. Herein, Fe3O4- and MnO2-loaded biohybrid magnetic helical microrobots (BMHMs) based on Spirulina cells were presented for the first time, and their performance on Pb(II) removal was studied in detail. Intracellular synthesis of Fe3O4 and MnO2 nanoparticles into Spirulina cells was successively conducted to obtain the BMHMs with superparamagnetism and high surface activity. The BMHMs could be flexibly propelled under magnetic actuation, and collective cork-screw spinning was performed to enhance fluidic diffusion with intensive adsorption. Rapid and significant removal of Pb(II) in wastewater was achieved using the swarming microrobots, and a high adsorption capacity could be reached at 245.1 mg/g. Moreover, the BMHMs could be cyclically reutilized after simple regeneration, and good specificity toward Pb(II) was verified. The adsorption mechanism was further studied, which revealed that the pseudo-second-order kinetics dominated in the adsorption process, and the Langmuir isothermal model also fitted the experimental results well. The intriguing properties of the BMHMs enable them to be versatile platforms with significant potentials in wastewater remediation.