Magnetic Soft Millirobots 3D Printed by Circulating Vat Photopolymerization to Manipulate Droplets Containing Hazardous Agents for In Vitro Diagnostics

A Review of Droplet/Bubble Transportation on Bionic Superwetting Surface

The controllable droplets/bubble transportation has a wide range of applications in the fields of biomedical, chemistry, energy, and material applications, and has aroused great attention for its significant scientific and technology importance. The main challenges derived from the liquid/solid or gas/solid contact strength and actuating energy input. Artificial superwetting surfaces inspired by nature creatures have triggered technology revolution in many fields relevant to droplet operation, and the applied actuating force improve the controllability to preferential direction. In this review, we highlights recent advancements in droplets/bubble transportation on the superwetting surfaces driven by passive or active stimulation methods inspired by bionic function interfaces. The three main superwetting surfaces including superhydrophobic surface, slippery liquid-infused porous surface, hybrid surface, various stimuli methods including gravity/buoyance, chemical/morphology gradient, heat, magnetism, electricity, light, adhesion force, and prosperous applications including micro-reaction, biochemical analysis, fog collection/antifog, energy transfer, bubble/liquid micro-robot, self-cleaning, light/circle switch have been systematically summarized. Finally, the challenges and future perspectives of research innovations and practical applications are discussed.

Enhanced Digital Light Processing-Based One-Step 3-Dimensional Printing of Multifunctional Magnetic Soft Robot

Soft structures driven by magnetic fields exhibit the characteristics of being unencumbered and rapidly responsive, enabling the fabrication of various soft robots according to specific requirements. However, soft structures made from a single magnetic material cannot meet the multifunctional demands of practical scenarios, necessitating the development of soft robot fabrication technologies with composite structures of diverse materials. A novel enhanced digital light processing (DLP) 3-dimensional (3D) printing technology has been developed, capable of printing composite magnetic structures with different materials in a single step. Furthermore, a soft robot with a hard magnetic material-superparamagnetic material composite was designed and printed, demonstrating its thermal effect under high-frequency magnetic fields and the editability of the magnetic domains of the hard magnetic material. The robot exhibits a range of locomotive behaviors, including crawling, rolling, and swimming. Under the influence of a 1-Hz actuation magnetic field, the normalized velocities for these modes of motion are recorded as 0.31 body length per second for crawling, 1.88 body length per second for rolling, and 0.14 body length per second for swimming. The robot has demonstrated its capacity to navigate uneven terrain, surmount barriers, and engage in directed locomotion, along with the ability to capture and transport objects. Additionally, it has showcased swimming capabilities within environments characterized by low Reynolds numbers and high fluid viscosities, findings that corroborate simulation analyses. The multimaterial 3D printing technology introduced in this research presents extensive potential for the design and manufacturing of multifunctional soft robots.

Magnetic Miniature Soft Robot with Reprogrammable Drug-Dispensing Functionalities: Toward Advanced Targeted Combination Therapy

Miniature robots are untethered actuators, which have great prospects to transform targeted drug delivery because they can potentially deliver high concentrations of medicine to the disease site(s) with minimal complications. However, existing miniature robots cannot perform advanced targeted combination therapy; majority of them can at most transport one type of drug, while those that can carry multiple drugs are unable to change their drug-dispensing sequence and dosage. Furthermore, the latter robots cannot transport more than three types of drugs, selectively dispense their drugs, maintain their mobility, or release their drugs at multiple sites. Here, a millimeter-scale soft robot is proposed, which can be actuated by alternating magnetic fields to dispense four types of drugs with reprogrammable drug-dispensing sequence and dosage (dispensing rates: 0.0992-0.231 µL h-1). This robot has six degrees-of-freedom motions, and it can deliver its drugs to multiple desired sites by rolling and two-anchor crawling across unstructured environments with negligible drug leakage. Such dexterity is highly desirable and unprecedented for miniature robots with drug-dispensing capabilities. The soft robot therefore has great potential to enable advanced targeted combination therapy, where four types of drugs must be delivered to various disease sites, each with a specific sequence and dosage of drugs.

Ultrafast Sunlight-Induced Polymerization: Unveiling 2-Phenylnaphtho[2,3-d]Thiazole-4,9-dione as a Unique Scaffold for High-Speed and Precision 3D Printing

A series of 15 dyes based on the 2-phenylnaphtho[2,3-d]thiazole-4,9-dione scaffold and 1 compound based on the 2,3-diphenyl-1,2,3,4-tetrahydrobenzo[g]quinoxaline-5,10-dione scaffold are studied as photoinitiators. These compounds are used in two- and three-component high-performance photoinitiating systems for the free radical polymerization of trimethylolpropane triacrylate (TMPTA) and polyethylene glycol diacrylate (PEGDA) under sunlight. Remarkably, the conversion of TMPTA can reach ≈60% within 20 s, while PEGDA attains a 96% conversion within 90 s. To delve into the intricate chemical mechanisms governing the polymerization, an array of analytical techniques is employed. Specifically, UV-vis absorption and fluorescence spectroscopy, steady-state photolysis, stability experiments, fluorescence quenching experiments, cyclic voltammetry, and electron spin resonance spin trapping (ESR-ST) experiments, collectively contribute to a comprehensive understanding of the photochemical mechanisms. Photoinitiation capacities of these systems are determined using real-time Fourier transformed infrared spectroscopy (RT-FTIR). Of particular interest is the revelation that, owing to the superior initiation ability of these dyes, high-resolution 3D patterns can be manufactured by direct laser write (DLW) technology and 3D printing. This underscores the efficient initiation of free radical polymerization processes by the newly developed dyes under both artificial and natural light sources, presenting an avenue for energy-saving, and environmentally friendly polymerization conditions.

Individual and collective manipulation of multifunctional bimodal droplets in three dimensions

Spatiotemporally controllable droplet manipulation is vital across numerous applications, particularly in miniature droplet robots known for their exceptional deformability. Despite notable advancements, current droplet control methods are predominantly limited to two-dimensional (2D) deformation and motion of an individual droplet, with minimal exploration of 3D manipulation and collective droplet behaviors. Here, we introduce a bimodal actuation strategy, merging magnetic and optical fields, for remote and programmable 3D guidance of individual ferrofluidic droplets and droplet collectives. The magnetic field induces a magnetic dipole force, prompting the formation of droplet collectives. Simultaneously, the optical field triggers isothermal changes in interfacial tension through Marangoni flows, enhancing buoyancy and facilitating 3D movements of individual and collective droplets. Moreover, these droplets can function autonomously as soft robots, capable of transporting objects. Alternatively, when combined with a hydrogel shell, they assemble into jellyfish-like robots, driven by sunlight. These findings present an efficient strategy for droplet manipulation, broadening the capabilities of droplet-based robotics.

Multimodal Soft Robotic Actuation and Locomotion

Diverse and adaptable modes of complex motion observed at different scales in living creatures are challenging to reproduce in robotic systems. Achieving dexterous movement in conventional robots can be difficult due to the many limitations of applying rigid materials. Robots based on soft materials are inherently deformable, compliant, adaptable, and adjustable, making soft robotics conducive to creating machines with complicated actuation and motion gaits. This review examines the mechanisms and modalities of actuation deformation in materials that respond to various stimuli. Then, strategies based on composite materials are considered to build toward actuators that combine multiple actuation modes for sophisticated movements. Examples across literature illustrate the development of soft actuators as free-moving, entirely soft-bodied robots with multiple locomotion gaits via careful manipulation of external stimuli. The review further highlights how the application of soft functional materials into robots with rigid components further enhances their locomotive abilities. Finally, taking advantage of the shape-morphing properties of soft materials, reconfigurable soft robots have shown the capacity for adaptive gaits that enable transition across environments with different locomotive modes for optimal efficiency. Overall, soft materials enable varied multimodal motion in actuators and robots, positioning soft robotics to make real-world applications for intricate and challenging tasks.

Bioinspired Surfaces Derived from Acoustic Waves for On-Demand Droplet Manipulations

The controllable manipulation and transfer of droplets are fundamental in a wide range of chemical reactions and even life processes. Herein, we present a novel, universal, and straightforward acoustic approach to fabricating biomimetic surfaces for on-demand droplet manipulations like many natural creatures. Based on the capillary waves induced by surface acoustic waves, various polymer films could be deformed into pre-designed structures, such as parallel grooves and grid-like patterns. These structured and functionalized surfaces exhibit impressive ability in droplet transportation and water collection, respectively. Besides these static surfaces, the tunability of acoustics could also endow polymer surfaces with dynamic controllability for droplet manipulations, including programming wettability, mitigating droplet evaporation, and accelerating chemical reactions. Our approach is capable of achieving universal surface manufacturing and droplet manipulation simultaneously, which simplifies the fabrication process and eliminates the need for additional chemical modifications. Thus, we believe that our acoustic-derived surfaces and technologies could provide a unique perspective for various applications, including microreactor integration, biochemical reaction control, tissue engineering, and so on.

Combined three dimensional locomotion and deformation of functional ferrofluidic robots

Magnetic microrobots possess remarkable potential for targeted applications in the medical field, primarily due to their non-invasive, controllable properties. These unique qualities have garnered increased attention and fascination among researchers. However, these robotic systems do face challenges such as limited deformation capabilities and difficulties navigating confined spaces. Recently, researchers have turned their attention towards magnetic droplet robots, which are notable for their superior deformability, controllability, and potential for a range of applications such as automated virus detection and targeted drug delivery. Despite these advantages, the majority of current research is constrained to two-dimensional deformation and motion, thereby limiting their broader functionality. In response to these limitations, this study proposes innovative strategies for controlling deformation and achieving a three-dimensional (3D) trajectory in ferrofluidic robots. These strategies leverage a custom-designed eight-axis electromagnetic coil and a sliding mode controller. The implementation of these methods exhibits the potential of ferrofluidic robots in diverse applications, including microfluidic pump systems, 3D micromanipulation, and selective vascular occlusion. In essence, this study aims to broaden the capabilities of ferrofluidic robots, thereby enhancing their applicability across a multitude of fields such as medicine, micromanipulation, bioengineering, and more by maximizing the potential of these intricate robotic systems.

Bidirectional Droplet Manipulation on Magnetically Actuated Superhydrophobic Ratchet Surfaces

Droplet manipulation has garnered significant attention in various fields due to its wide range of applications. Among many different methods, magnetic actuation has emerged as a promising approach for remote and instantaneous droplet manipulation. In this study, we present the bidirectional droplet manipulation on a magnetically actuated superhydrophobic ratchet surface. The surface consists of silicon strips anchored on elastomer ridges with superhydrophobic black silicon structures on the top side and magnetic layers on the bottom side. The soft magnetic properties of the strips enable their bidirectional tilting to form a ratchet surface and thus bidirectional droplet manipulation upon varying external magnetic field location and strength. Computational multiphysics models were developed to predict the tilting of the strips, demonstrating the concept of bidirectional tilting along with a tilting angle hysteresis theory. Experimental results confirmed the soft magnetic hysteresis and consequential bidirectional tilting of the strips. The superhydrophobic ratchet surface formed by the tilting strips induced the bidirectional self-propulsion of dispensed droplets through the Laplace pressure gradient, and the horizontal acceleration of the droplets was found to be positively correlated with the tilting angle of the strips. Additionally, a finite element analysis was conducted to identify the critical conditions for dispensed droplet penetration through the gaps between the strips, which hinder the droplet's self-propulsion. The models and findings here provide substantial insights into the design and optimization of magnetically actuated superhydrophobic ratchet surfaces to manipulate droplets in the context of digital microfluidic applications.

Magnetically Enhanced Intracellular Uptake of Superparamagnetic Iron Oxide Nanoparticles for Antitumor Therapy

Superparamagnetic iron oxide nanoparticles (SPIONs) have been widely employed in biomedical fields, including targeted delivery of antitumor therapy. Conventional magnetic tumor targeting has used simple static magnetic fields (SMFs), which cause SPIONs to linearly aggregate into a long chain-like shape. Such agglomeration greatly hinders the intracellular targeting of SPIONs into tumors, thus reducing the therapeutic efficacy. In this study, we investigated the enhancement of the intracellular uptake of SPIONs through the application of rotating magnetic fields (RMFs). Based on the physical principles of SPION chain disassembly, we investigated physical parameters to predict the chain length favorable for intracellular uptake. Our prediction was validated by clear visualization of the intracellular distributions of SPIONs in tumor cells at both cellular and three-dimensional microtissue levels. To identify the potential therapeutic effects of enhanced intracellular uptake, magnetic hyperthermia as antitumor therapy was investigated under varying conditions of magnetic hyperthermia and RMFs. The results showed that enhanced intracellular uptake reduced magnetic hyperthermia time and strength as well as particle concentration. The proposed method will be useful in the development of techniques to determine the optimized physical conditions for the enhanced intracellular uptake of SPIONs in antitumor therapy.

Image-based real-time feedback control of magnetic digital microfluidics by artificial intelligence-empowered rapid object detector for automated in vitro diagnostics

In vitro diagnostics (IVD) plays a critical role in healthcare and public health management. Magnetic digital microfluidics (MDM) perform IVD assays by manipulating droplets on an open substrate with magnetic particles. Automated IVD based on MDM could reduce the risk of accidental exposure to contagious pathogens among healthcare workers. However, it remains challenging to create a fully automated IVD platform based on the MDM technology because of a lack of effective feedback control system to ensure the successful execution of various droplet operations required for IVD. In this work, an artificial intelligence (AI)-empowered MDM platform with image-based real-time feedback control is presented. The AI is trained to recognize droplets and magnetic particles, measure their size, and determine their location and relationship in real time; it shows the ability to rectify failed droplet operations based on the feedback information, a function that is unattainable by conventional MDM platforms, thereby ensuring that the entire IVD process is not interrupted due to the failure of liquid handling. We demonstrate fundamental droplet operations, which include droplet transport, particle extraction, droplet merging and droplet mixing, on the MDM platform and show how the AI rectify failed droplet operations by acting upon the feedback information. Protein quantification and antibiotic resistance detection are performed on this AI-empowered MDM platform, and the results obtained agree well with the benchmarks. We envision that this AI-based feedback approach will be widely adopted not only by MDM but also by other types of digital microfluidic platforms to offer precise and error-free droplet operations for a wide range of automated IVD applications.

Magnetically Actuated Hydrogel Stamping-Assisted Cellular Mechanical Analyzer for Stored Blood Quality Detection

Cellular mechanical property analysis reflecting the physiological and pathological states of cells plays a crucial role in assessing the quality of stored blood. However, its complex equipment needs, operation difficulty, and clogging issues hinder automated and rapid biomechanical testing. Here, we propose a promising biosensor assisted by magnetically actuated hydrogel stamping to fulfill it. The flexible magnetic actuator triggers the collective deformation of multiple cells in the light-cured hydrogel, and it allows for on-demand bioforce stimulation with the advantages of portability, cost-effectiveness, and simplicity of operation. The magnetically manipulated cell deformation processes are captured by the integrated miniaturized optical imaging system, and the cellular mechanical property parameters are extracted from the captured images for real-time analysis and intelligent sensing. In this work, 30 clinical blood samples with different storage durations (<14 days and >14 days) were tested. A deviation of 3.3% in the differentiation of blood storage durations by this system compared to physician annotation demonstrated its feasibility. This system should broaden the application of cellular mechanical assays in diverse clinical settings.

DropLab: an automated magnetic digital microfluidic platform for sample-to-answer point-of-care testing-development and application to quantitative immunodiagnostics

In point-of-care testing (POCT), tests are performed near patients and results are given rapidly for timely clinical decisions. Immunodiagnostic assays are one of the most important analyses for detecting and quantifying protein-based biomarkers. However, existing POCT immunodiagnostics mainly rely on the lateral flow assay (LFA), which has limited sensitivity or quantification capability. Although other immunodiagnostic assays, such as enzyme-linked immunosorbent assays (ELISAs), offer more sensitive and quantitative results, they require complex liquid manipulations that are difficult to implement in POCT settings by conventional means. Here, we show the development of DropLab, an automated sample-in-answer-out POCT immunodiagnostic platform based on magnetic digital microfluidic (MDM) technology. DropLab performs microbead-based ELISA in droplets to offer more sensitive and quantitative testing results. The intricate liquid manipulations required for ELISA are accomplished by controlling droplets with magnetic microbeads using MDM technology, which enables us to achieve full automation and easy operations with DropLab. Four ELISAs (the sample in triplicates and a negative control) can be run in parallel on the thermoformed disposable chip, which greatly improves the throughput and accuracy compared to those of other POCT immunodiagnostic devices. DropLab was validated by measuring two protein targets and one antibody target. The testing results showed that the limit of detection (LOD) of DropLab matched that of the conventional ELISA in a microwell plate. DropLab brings MDM one step closer to being a viable medical technology that is ready for real-world POCT applications.

Biomedical Applications of Microfluidic Devices: A Review

Both passive and active microfluidic chips are used in many biomedical and chemical applications to support fluid mixing, particle manipulations, and signal detection. Passive microfluidic devices are geometry-dependent, and their uses are rather limited. Active microfluidic devices include sensors or detectors that transduce chemical, biological, and physical changes into electrical or optical signals. Also, they are transduction devices that detect biological and chemical changes in biomedical applications, and they are highly versatile microfluidic tools for disease diagnosis and organ modeling. This review provides a comprehensive overview of the significant advances that have been made in the development of microfluidics devices. We will discuss the function of microfluidic devices as micromixers or as sorters of cells and substances (e.g., microfiltration, flow or displacement, and trapping). Microfluidic devices are fabricated using a range of techniques, including molding, etching, three-dimensional printing, and nanofabrication. Their broad utility lies in the detection of diagnostic biomarkers and organ-on-chip approaches that permit disease modeling in cancer, as well as uses in neurological, cardiovascular, hepatic, and pulmonary diseases. Biosensor applications allow for point-of-care testing, using assays based on enzymes, nanozymes, antibodies, or nucleic acids (DNA or RNA). An anticipated development in the field includes the optimization of techniques for the fabrication of microfluidic devices using biocompatible materials. These developments will increase biomedical versatility, reduce diagnostic costs, and accelerate diagnosis time of microfluidics technology.

Kirigami-Inspired Programmable Soft Magnetoresponsive Actuators with Versatile Morphing Modes

Untethered soft magnetoresponsive actuators (SMRAs), which can realize rapid shape transformation, have attracted widespread attention for their strategic applications in exploration, transportation, and minimally invasive medicine. It remains a challenge to fabricate SMRAs with complicated morphing modes (more than bending and folding), limiting their applications to simple shape-morphing and locomotion. Herein, a method integrating the ancient kirigami art and an advanced mechanical assembly method is proposed, which realizes 2D-to-3D and 3D-to-3D complicated shape-morphing and precise magnetization programming through cut-guided deformation. The kirigami-inspired SMRAs exhibit good robustness after actuating more than 10000 times. An integrated finite element analysis method is developed to quantitatively predict the shape transformation of SMRAs under magnetic actuation. By leveraging this method, a set of 3D curved responsive morphologies with programmed Gaussian curvature are fabricated (e.g., ellipsoid and saddle structures), specifically 3D multilayer structures and face-like shapes with different expressions, which are difficult to realize using previous approaches. Furthermore, a bionic-scaled soft crawling robot with significant obstacle surmounting ability is fabricated using the kirigami-inspired method. The ability of the method to achieve programmable SMRAs with versatile morphing modes may broaden its applications in soft robotics, color-switchable devices, and clinical treatments.