Melt Electrospinning Writing of Magnetic Microrobots

Recent Advances in Electrospinning Techniques for Precise Medicine

In the realm of precise medicine, the advancement of manufacturing technologies is vital for enhancing the capabilities of medical devices such as nano/microrobots, wearable/implantable biosensors, and organ-on-chip systems, which serve to accurately acquire and analyze patients' physiopathological information and to perform patient-specific therapy. Electrospinning holds great promise in engineering materials and components for advanced medical devices, due to the demonstrated ability to advance the development of nanomaterial science. Nevertheless, challenges such as limited composition variety, uncontrollable fiber orientation, difficulties in incorporating fragile molecules and cells, and low production effectiveness hindered its further application. To overcome these challenges, advanced electrospinning techniques have been explored to manufacture functional composites, orchestrated structures, living constructs, and scale-up fabrication. This review delves into the recent advances of electrospinning techniques and underscores their potential in revolutionizing the field of precise medicine, upon introducing the fundamental information of conventional electrospinning techniques, as well as discussing the current challenges and future perspectives.

The Past, Present, and Future of Tubular Melt Electrowritten Constructs to Mimic Small Diameter Blood Vessels - A Stable Process?

Melt Electrowriting (MEW) is a continuously growing manufacturing platform. Its advantage is the consistent production of micro- to nanometer fibers, that stack intricately, forming complex geometrical shapes. MEW allows tuning of the mechanical properties of constructs via the geometry of deposited fibers. Due to this, MEW can create complex mechanics only seen in multi-material compounds and serve as guiding structures for cellular alignment. The advantage of MEW is also shown in combination with other biotechnological manufacturing methods to create multilayered constructs that increase mechanical approximation to native tissues, biocompatibility, and cellular response. These features make MEW constructs a perfect candidate for small-diameter vascular graft structures. Recently, studies have presented fascinating results in this regard, but is this truly the direction that tubular MEW will follow or are there also other options on the horizon? This perspective will explore the origins and developments of tubular MEW and present its growing importance in the field of artificial small-diameter vascular grafts with mechanical modulation and improved biomimicry and the impact of it in convergence with other manufacturing methods and how future technologies like AI may influence its progress.

Free-Boundary Microfluidic Platform for Advanced Materials Manufacturing and Applications

Microfluidics, with its remarkable capacity to manipulate fluids and droplets at the microscale, has emerged as a powerful platform in numerous fields. In contrast to conventional closed microchannel microfluidic systems, free-boundary microfluidic manufacturing (FBMM) processes continuous precursor fluids into jets or droplets in a relatively spacious environment. FBMM is highly regarded for its superior flexibility, stability, economy, usability, and versatility in the manufacturing of advanced materials and architectures. In this review, a comprehensive overview of recent advancements in FBMM is provided, encompassing technical principles, advanced material manufacturing, and their applications. FBMM is categorized based on the foundational mechanisms, primarily comprising hydrodynamics, interface effects, acoustics, and electrohydrodynamic. The processes and mechanisms of fluid manipulation are thoroughly discussed. Additionally, the manufacturing of advanced materials in various dimensions ranging from zero-dimensional to three-dimensional, as well as their diverse applications in material science, biomedical engineering, and engineering are presented. Finally, current progress is summarized and future challenges are prospected. Overall, this review highlights the significant potential of FBMM as a powerful tool for advanced materials manufacturing and its wide-ranging applications.

Spreadable Magnetic Soft Robots with On-Demand Hardening

Magnetically actuated mobile robots demonstrate attractive advantages in various medical applications due to their wireless and programmable executions with tiny sizes. Confronted with complex application scenarios, however, it requires more flexible and adaptive deployment and utilization methods to fully exploit the functionalities brought by magnetic robots. Herein, we report a design and utilization strategy of magnetic soft robots using a mixture of magnetic particles and non-Newtonian fluidic soft materials to produce programmable, hardened, adhesive, reconfigurable soft robots. For deployment, their ultrasoft structure and adhesion enable them to be spread on various surfaces, achieving magnetic actuation empowerment. The reported technology can potentially improve the functionality of robotic end-effectors and functional surfaces. Experimental results demonstrate that the proposed robots could help to grasp and actuate objects 300 times heavier than their weight. Furthermore, it is the first time we have enhanced the stiffness of mechanical structures for these soft materials by on-demand programmable hardening, enabling the robots to maximize force outputs. These findings offer a promising path to understanding, designing, and leveraging magnetic robots for more powerful applications.

Biohybrid magnetic microrobots: An intriguing and promising platform in biomedicine

Biohybrid magnetic microrobots (BMMs) have emerged as an exciting class of microrobots and have been considered as a promising platform in biomedicine. Many microorganisms and body's own cells show intriguing properties, such as morphological characteristics, biosafety, and taxis abilities (e.g., chemotaxis, aerotaxis), which have made them attractive for the fabrication of microrobots. For remote controllability and sustainable actuation, magnetic components are usually incorporated onto these biological entities, and other functionalized non-biological components (e.g., therapeutic agents) are also included for specific applications. This review highlights the latest developments in BMMs with a focus on their biomedical applications. It starts by introducing the fundamental understanding of the propulsion system at the microscale in a magnetically driven manner, followed by a summary of diverse BMMs based on different microorganisms and body's own cells along with their relevant applications. Finally, the review discusses how BMMs contribute to the advancements of microrobots, the current challenges of using BMMs in practical clinical settings, and the future perspectives of this exciting field. STATEMENT OF SIGNIFICANCE: Biohybrid magnetic microrobots (BMMs), composed of biological entities and functional parts, hold great potential and serve as a novel and promising platform for biomedical applications such as targeted drug delivery. This review comprehensively summarizes the recent advancements in BMMs for biomedical applications, mainly focused on the representative propulsion modalities in a magnetically propelled manner and diverse designs of BMMs based on different biological entities, including microorganisms and body's own cells. We hope this review can provide ideas for the future design, development, and innovation of micro/nanorobots in the field of biomedicine.

A bioengineered trachea-like structure improves survival in a rabbit tracheal defect model

A practical strategy for engineering a trachea-like structure that could be used to repair or replace a damaged or injured trachea is an unmet need. Here, we fabricated bioengineered cartilage (BC) rings from three-dimensionally printed fibers of poly(ɛ-caprolactone) (PCL) and rabbit chondrocytes. The extracellular matrix (ECM) secreted by the chondrocytes combined with the PCL fibers formed a "concrete-rebar structure," with ECM deposited along the PCL fibers, forming a grid similar to that of native cartilage. PCL fiber-hydrogel rings were then fabricated and alternately stacked with BC rings on silicone tubes. This trachea-like structure underwent vascularization after heterotopic transplantation into rabbits for 4 weeks. The vascularized bioengineered trachea-like structure was then orthotopically transplanted by end-to-end anastomosis to native rabbit trachea after a segment of trachea had been resected. The bioengineered trachea-like structure displayed mechanical properties similar to native rabbit trachea and transmural angiogenesis between the rings. The 8-week survival rate in transplanted rabbits was 83.3%, and the respiratory rate of these animals was similar to preoperative levels. This bioengineered trachea-like structure may have potential for treating tracheal stenosis and other tracheal injuries.

Exact and Computationally Robust Solutions for Cylindrical Magnets Systems with Programmable Magnetization

Magnetic systems based on permanent magnets are receiving growing attention, in particular for micro/millirobotics and biomedical applications. Their design landscape is expanded by the possibility to program magnetization, yet enabling analytical results, crucial for containing computational costs, are lacking. The dipole approximation is systematically used (and often strained), because exact and computationally robust solutions are to be unveiled even for common geometries such as cylindrical magnets, which are ubiquitously used in fundamental research and applications. In this study, exact solutions are disclosed for magnetic field and gradient of a cylindrical magnet with generic uniform magnetization, which can be robustly computed everywhere within and outside the magnet, and directly extend to magnets systems of arbitrary complexity. Based on them, exact and computationally robust solutions are unveiled for force and torque between coaxial magnets. The obtained analytical solutions overstep the dipole approximation, thus filling a long-standing gap, and offer strong computational gains versus numerical simulations (up to 106 , for the considered test-cases). Moreover, they bridge to a variety of applications, as illustrated through a compact magnets array that could be used to advance state-of-the-art biomedical tools, by creating, based on programmable magnetization patterns, circumferential and helical force traps for magnetoresponsive diagnostic/therapeutic agents.

α,ε-Hybrid Peptide-Stabilized Magnetic Nanoparticle-Coated Paper-Based Actuators

The development of α,ε-hybrid peptide-stabilized magnetic nanoparticles and their application to fabricate a paper-based actuator has been reported. From single-crystal diffraction analysis, the nitropeptide 2 has an extended structure with a trans geometry. The one-pot in situ multiple oxidation-reduction reaction of a synthetic nitropeptide solution in ammonium hydroxide and FeCl₂ leads to the formation of Fe₃O₄ nanoparticles. The reduction reaction replaces the nitro group with an amine group, which finally acts as capping agent for the stabilization of the Fe₃O₄ nanoparticles. Paper-based soft magneto machines with multivariant actuation modes such as contraction-expansion, bending, and uplifting locomotion have been studied. The device has potential as controllable paper-based soft robots.

A Dual-Responsive Magnetoactive and Electro-Ionic Soft Actuator Derived from a Nickel-Based Metal-Organic Framework

There is growing demand for multiresponsive soft actuators for the realization of natural, safe, and complex motions in robotic interactions. In particular, soft actuators simultaneously stimulated by electrical and magnetic fields are always under development owing to their simple controllability and reliability during operation. Herein, magnetically and electrically driven dual-responsive soft actuators (MESAs) derived from novel nickel-based metal-organic frameworks (Ni-MOFs-700C), are reported. Nanoscale Ni-MOFs-700C has excellent electrochemical and magnetic properties that allow it to be used as a multifunctional material under both magnetoactive and electro-ionic actuations. The dual-responsive MESA exhibits a bending displacement of 30 mm and an ultrafast rising time of 1.5 s under a very low input voltage of 1 V and also exerts a bending deflection of 12.5 mm at 50 mT under a high excitation frequency of 5 Hz. By utilizing a dual-responsive MESA, the hovering motion of a hummingbird robot is demonstrated under magnetic and electrical stimuli.

Dip-Printed Microneedle Motors for Oral Macromolecule Delivery

Micromotors have demonstrated values in drug delivery, and recent attempts focus on developing effective approaches to generate functional micromotors to improve this area. Here, with the integration of microfluidic droplet printing and wettability-induced drawing photolithography, we present an innovative spatiotemporal serial multistep dip-printing strategy to generate novel independent microneedle motors (IMNMs) for orally delivering macromolecular drugs. As the strategy combines the advantages of the hydrophilic wettability, extension effects, and capillary effects, the IMNMs with an oblate basement and a needle-shaped head or a core-shell structured multicomponent head can be created by simply printing pregel droplets layer by layer, following with simultaneous wiredrawing and solidification. Owing to the polarized magnetic particles in the bottom basement and the rapidly dissolvable polymers as the middle basement, the resultant IMNMs can respond to magnetic fields, move to desired places under a magnet, penetrate tissue-like substrates, induce head-basement separation, and leave only the needles for cargo release. Based on these features, we have demonstrated that these IMNMs can deliver insulin via intestinal tracts to realize effective blood glucose control of diabetic rabbit models. These results indicate the practical values and bright future of the dip-printing stratagem and these IMNMs in clinical applications.

A Biodegradable Magnetic Microrobot Based on Gelatin Methacrylate for Precise Delivery of Stem Cells with Mass Production Capability

A great deal of research has focused on small-scale robots for biomedical applications and minimally invasive delivery of therapeutics (e.g., cells, drugs, and genes) to a target area. Conventional fabrication methods, such as two-photon polymerization, can be used to build sophisticated micro- and nanorobots, but the long fabrication cycle for a single microrobot has limited its practical use. This study proposes a biodegradable spherical gelatin methacrylate (GelMA) microrobot for mass production in a microfluidic channel. The proposed microrobot is fabricated in a flow-focusing droplet generator by shearing a mixture of GelMA, photoinitiator, and superparamagnetic iron oxide nanoparticles (SPIONs) with a mixture of oil and surfactant. Human nasal turbinate stem cells (hNTSCs) are loaded on the GelMA microrobot, and the hNTSC-loaded microrobot shows precise rolling motion in response to an external rotating magnetic field. The microrobot is enzymatically degraded by collagenase, and released hNTSCs are proliferated and differentiated into neuronal cells. In addition, the feasibility of the GelMA microrobot as a cell therapeutic delivery system is investigated by measuring electrophysiological activity on a multielectrode array. Such a versatile and fully biodegradable microrobot has the potential for targeted stem cell delivery, proliferation, and differentiation for stem cell-based therapy.

Reshapable Osteogenic Biomaterials Combining Flexible Melt Electrowritten Organic Fibers with Inorganic Bioceramics

Ever-growing various applications, especially for tissue regeneration, cause a pressing need for novel methods to functionalize melt electrowritten (MEW) microfibrous scaffolds with unique nanomaterials. Here, two novel strategies are proposed to modify MEW polycaprolactone (PCL) grids with ZnO nanoparticles (ZP) or ZnO nanoflakes (ZF) to enhance osteogenic differentiation. The calcium mineralization levels of MC3T3 osteoblasts cultured on PCL/ZP 0.1 scaffolds are ∼3.91-fold higher than those cultured on nonmodified PCL scaffolds, respectively. Due to the nanotopography mimicking bone anatomy, the PCL/ZF scaffolds (∼2.60 times higher in ALP activity compared to PCL/ZP 1 and ∼2.17 times higher in mineralization compared to PCL/ZP 0.1) achieved superior results. Moreover, the flexible feature inherited from PCL grids makes it possible for them to act as a reshapable osteogenic bioscaffold. This study provides new strategies for synthesizing nanomaterials on microscale surfaces, opening up a new route for functionalizing MEW scaffolds to fulfill the growing demand of tissue engineering.

3D Printing Ultraflexible Magnetic Actuators via Screw Extrusion Method

Soft magnetic actuators with programmable structure design and controllable deformation ability based on 3D printing technology have attracted extensive attention. In this paper, a novel 3D printing strategy is developed to manufacture the ultraflexible magnetic actuator, in which the printed material is composed of magnetic particles and thermoplastic rubber materials. Different from the traditional fused deposition printing, this printing strategy introduces screw extrusion technology to the heating components of the printer to overcome the problem of filament buckling in the flexible material. Thus, the tensile modulus of the printed products can be reduced to as low as ≈2 MPa. Based on the above method, biomimetic magnetic actuators of the sucker and the pump are constructed for adhering and releasing object and pumping liquid. The contraction performance of the magnetic actuator is studied via a series of experiments and the magnetic field-induced deformation is analyzed by the multiphysics-based finite element model. This work proves that ultraflexible magnetic actuators fabricated by this 3D printing strategy show broad prospects in the fields of soft robotics and bionics.

Inorganic-Organic Hybrid Copolymeric Colloids as Multicolor Emission, Fuel-Free, UV- and Visible-Light-Actuated Micropumps

Light-actuated micromachines are of enormous interest due to their ability to harvest light for triggering catalytic reactions to acquire free energy for mechanical work. This work presents an inorganic-organic hybrid copolymeric poly(cyclotriphosphazene-co-barbituric acid) colloid, which displays multiwavelength excited emission and catalytic activities, exploiting the unique structural, chemical, and optical features of inorganic heterocyclic ring hexachlorocyclotriphosphazene and organic co-monomer barbituric acid. Specifically, this work reveals particle-resolved unusual multicolor emission under excitation with the same or different wavelengths of light using fluorescence microscopy. The result is rationalized by density functional theory studies. In this work, the authors find that emission is coincident with fluorometric measurements, and the photocatalytic properties are anticipated from the overall band structure. This work also demonstrates the use of these colloids as micropumps, which can be remotely activated by UV, blue, and green lights under fuel-free conditions, and ascribe the behavior to ionic diffusiophoresis arising from light-triggered generation of H⁺ and other charged species. This work offers a new class of polymeric colloids with multiple-wavelength excited emission and catalytic activities, which is expected to open new opportunities in the design of fuel-free, photo-actuated micromachines and active systems.

High-Voltage Wave Induced a Unique Structured Percolation Network with a Negative Gauge Factor

Nanocomposite percolation networks have attracted increasing attention in the field of wearable devices. Generally, the large junction resistance caused by the small contact area in the percolation network is considered as the bottleneck in preparing high-performance electronics. In such electronics, an applied strain will lead to deformation on the fiber junction, subsequently increasing the sheet resistance. However, taking advantage of the dominant role of the contact resistance in the percolation network, the overall resistance of the network can be controlled by skillfully adjusting the contact area. Here, we designed a combined gold-polycaprolactone (Au-PCL) network with a unique buckling net structure. When the thickness of the gold nanolayer is 50 nm, the network shows typical percolation behavior with high transparency (93%), good conductivity (20 Ω/sq), and good ductility. Moreover, the networks show a unique positive relationship between the conductivity and strain due to the variation of contact resistance. By designing different waving angles, the network can be used as a dynamic strain sensor with a tunable gauge factor ranging from -0.8 to -1.8. Overall, these highly stretchable and transparent Au-PCL networks show promising applications in the field of high-performance electronic and optoelectronic nanodevices.

Powering and Fabrication of Small-Scale Robotics Systems

Purpose of Review

The increasing number of contributions in the field of small-scale robotics is significantly associated with the progress in material science and process engineering during the last half century. With the objective of integrating the most optimal materials for the propulsion of these motile micro- and nanosystems, several manufacturing strategies have been adopted or specifically developed. This brief review covers some recent advances in materials and fabrication of small-scale robots with a focus on the materials serving as components for their motion and actuation.

Recent Findings

Integration of a wealth of materials is now possible in several micro- and nanorobotic designs owing to the advances in micro- and nanofabrication and chemical synthesis. Regarding light-driven swimmers, novel photocatalytic materials and deformable liquid crystal elastomers have been recently reported. Acoustic swimmers are also gaining attention, with several prominent examples of acoustic bubble-based 3D swimmers being recently reported. Magnetic micro- and nanorobots are increasingly investigated for their prospective use in biomedical applications. The adoption of different materials and novel fabrication strategies based on 3D printing, template-assisted electrodeposition, or electrospinning is briefly discussed.

Summary

A brief review on fabrication and powering of small-scale robotics is presented. First, a concise introduction to the world of small-scale robotics and their propulsion by means of magnetic fields, ultrasound, and light is provided. Recent examples of materials and fabrication methodologies for the realization of these devices follow thereafter.

Design, fabrication and application of magnetically actuated micro/nanorobots: a review

Magnetically actuated micro/nanorobots are typical micro- and nanoscale artificial devices with favorable attributes of quick response, remote and contactless control, harmless human-machine interaction and high economic efficiency. Under external magnetic actuation strategies, they are capable of achieving elaborate manipulation and navigation in extreme biomedical environments. This review focuses on state-of-the-art progresses in design strategies, fabrication techniques and applications of magnetically actuated micro/nanorobots. Firstly, recent advances of various robot designs, including helical robots, surface walkers, ciliary robots, scaffold robots and biohybrid robots, are discussed separately. Secondly, the main progresses of common fabrication techniques are respectively introduced, and application achievements on these robots in targeted drug delivery, minimally invasive surgery and cell manipulation are also presented. Finally, a short summary is made, and the current challenges and future work for magnetically actuated micro/nanorobots are discussed.

Magnetorheological Elastomer-Based Self-Powered Triboelectric Nanosensor for Monitoring Magnetic Field

The adaptable monitoring of the ubiquitous magnetic field is of great importance not only for scientific research but also for industrial production. However, the current detecting techniques are unwieldly and lack essential mobility owing to the complex configuration and indispensability of the power source. Here, we have constructed a self-powered magnetic sensor based on a subtle triboelectric nanogenerator (TENG) that consists of a magnetorheological elastomer (MRE). This magnetic sensor relies on triboelectrification and electrostatic induction to produce electrical signals in response to the MRE's deformation induced by the variational magnetic field without using any external power sources. The fabricated magnetic sensor shows a fast response of 80ms and a desirable sensitivity of 31.6 mV/mT in a magnetic field range of 35-60 mT as well as preliminary vectorability enabled by the multichannel layout. Our work provides a new route for monitoring dynamic magnetic fields and paves a way for self-powered electric-magnetic coupled applications.