Self-Assembled Artificial Nanocilia Actuators

Multifunctional Magnetic Muscles for Soft Robotics

Despite recent advancements, artificial muscles have not yet been able to strike the right balance between exceptional mechanical properties and dexterous actuation abilities that are found in biological systems. Here, we present an artificial magnetic muscle that exhibits multiple remarkable mechanical properties and demonstrates comprehensive actuating performance, surpassing those of biological muscles. This artificial muscle utilizes a composite configuration, integrating a phase-change polymer and ferromagnetic particles, enabling active control over mechanical properties and complex actuating motions through remote laser heating and magnetic field manipulation. Consequently, the magnetic composite muscle can dynamically adjust its stiffness as needed, achieving a switching ratio exceeding 2.7 × 10³. This remarkable adaptability facilitates substantial load-bearing capacity, with specific load capacities of up to 1000 and 3690 for tensile and compressive stresses, respectively. Moreover, it demonstrates reversible extension, contraction, bending, and twisting, with stretchability exceeding 800%. We leverage these distinctive attributes to showcase the versatility of this composite muscle as a soft continuum robotic manipulator. It adeptly executes various programmable responses and performs complex tasks while minimizing mechanical vibrations. Furthermore, we demonstrate that this composite muscle excels across multiple mechanical and actuation aspects compared to existing actuators.

Artificial-goosebump-driven microactuation

Microactuators provide controllable driving forces for precise positioning, manipulation and operation at the microscale. Development of microactuators using active materials is often hampered by their fabrication complexity and limited motion at small scales. Here we report light-fuelled artificial goosebumps to actuate passive microstructures, inspired by the natural reaction of hair bristling (piloerection) on biological skin. We use light-responsive liquid crystal elastomers as the responsive artificial skin to move three-dimensionally printed passive polymer microstructures. When exposed to a programmable femtosecond laser, the liquid crystal elastomer skin generates localized artificial goosebumps, resulting in precise actuation of the surrounding microstructures. Such microactuation can tilt micro-mirrors for the controlled manipulation of light reflection and disassemble capillary-force-induced self-assembled microstructures globally and locally. We demonstrate the potential application of the proposed microactuation system for information storage. This methodology provides precise, localized and controllable manipulation of microstructures, opening new possibilities for the development of programmable micromachines.

Dual-Stimuli Cooperative Responsive Hydrogel Microactuators Via Two-Photon Lithography

With the development of bionics as well as materials science, intelligent soft actuators have shown promising applications in many fields such as soft robotics, sensing, and remote manipulation. Microfabrication technologies have enabled the reduction of the size of responsive soft actuators to the micron level. However, it is still challenging to construct microscale actuators capable of responding to different external stimuli in complex and diverse conditions. Here, this work demonstrates a dual-stimuli cooperative responsive hydrogel microactuator by asymmetric fabrication via femtosecond laser direct writing. The dual response of the hydrogel microstructure is achieved by employing responsive hydrogel with functional monomer 2-(dimethylamino)ethyl methacrylate. Raman spectra of the hydrogel microstructures suggest that the pH and temperature response of the hydrogel is generated by the changes in tertiary amine groups and hydrogen bonds, respectively. The asymmetric hydrogel microstructures show opposite bending direction when being heated to high temperature or exposed to acid solution, and can independently accomplish the grasp of polystyrene microspheres. Moreover, this work depicts the cooperative response of the hydrogel microactuator to pH and temperature at the same time. The dual-stimuli cooperative responsive hydrogel microactuators will provide a strategy for designing and fabricating controllable microscale actuators with promising applications in microrobotics and microfluidics.

Nanoparticles with transformable physicochemical properties for overcoming biological barriers

In recent years, tremendous progress has been made in the development of nanomedicines for advanced therapeutics, yet their unsatisfactory targeting ability hinders the further application of nanomedicines. Nanomaterials undergo a series of processes, from intravenous injection to precise delivery at target sites. Each process faces different or even contradictory requirements for nanoparticles to pass through biological barriers. To overcome biological barriers, researchers have been developing nanomedicines with transformable physicochemical properties in recent years. Physicochemical transformability enables nanomedicines to responsively switch their physicochemical properties, including size, shape, surface charge, etc., thus enabling them to cross a series of biological barriers and achieve maximum delivery efficiency. In this review, we summarize recent developments in nanomedicines with transformable physicochemical properties. First, the biological dilemmas faced by nanomedicines are analyzed. Furthermore, the design and synthesis of nanomaterials with transformable physicochemical properties in terms of size, charge, and shape are summarized. Other switchable physicochemical parameters such as mobility, roughness and mechanical properties, which have been sought after most recently, are also discussed. Finally, the prospects and challenges for nanomedicines with transformable physicochemical properties are highlighted.

Magnetic Microsphere Scaffold-Based Soft Microbots for Targeted Mesenchymal Stem Cell Delivery

A soft microbot assembled from individual magnetic microsphere scaffold (MMS) beads carrying mesenchymal stem cells (MSC) is navigated under magnetic actuation, where an oscillating field induces mechanical flexion to propel the microbot toward the target site. A seven-bead microbot attained a top translational speed of 205.6 µm s-1 (0.068 body length s-1 ) under 10 mT and 2 Hz field oscillation. The shallow flexion angle (10-24.5°) allows precision movements required to navigate narrow spaces. Upon arrival at the target site, the MMS beads unload their MSC cargo following exposure to a phosphate-buffered saline (PBS) solution, mimicking the extracellular fluid's sodium concentration. The released stem cells have excellent viability and vitality, promoting rapid healing (i.e., 83.2% vs 49%) in a scratch-wound assay. When paired with minimally invasive surgical methods, such as laparoscopy and endoscopic surgery, the microbot can provide precise stem cell delivery to hard-to-reach injury sites in the body to promote healing. Moreover, the microbot is designed to be highly versatile, with individual MMS beads customizable for cargoes of live cells, biomolecules, bionanomaterials, and pharmaceutical compounds for various therapeutic requirements.

Bioinspired Wire-on-Pillar Magneto-Responsive Superhydrophobic Arrays

Versatile surfaces demonstrating multiple interfacial functionalities are highly demanded as a surface typically serves various duties and faces multiple challenges in real practice. However, such versatile surfaces are rarely reported mainly due to the challenges in integrating multiple structural characteristics. Here, by mimicking lotus leaves, butterfly wing, and respiratory cilia, we develop a surface termed wire-on-pillar magneto-responsive superhydrophobic arrays (WP-MRSA), which possess interfacial properties of structural superhydrophobicity, anisotropicity, stimuli responsiveness, and flexibility. By combining soft lithography and self-alignment of iron-laden aerosols under a magnetic field, iron-laden wires are planted atop prefabricated pillar arrays, resulting in well-ordered, sparse, high-aspect-ratio, flexible, and superhydrophobic wires, which largely deflect in response to a magnetic field. This unique integration of structural properties and configurations enables various functionalities, such as on-demand control of droplet impact dynamics, real-time regulation of surface lateral adhesion force, fast removal and sorting of objects, and precise manipulation of droplets for selective reactions. Those functionalities benefit various applications especially droplet-based microfluidics and active self-cleaning surfaces.

3D Printable Self-Adhesive and Self-Healing Ionotronic Hydrogels for Wearable Healthcare Devices

Ionotronic hydrogels have attracted significant attention in emerging fields such as wearable devices, flexible electronics, and energy devices. To date, the design of multifunctional ionotronic hydrogels with strong interfacial adhesion, rapid self-healing, three-dimensional (3D) printing processability, and high conductivity are key requirements for future wearable devices. Herein, we report the rational design and facile synthesis of 3D printable, self-adhesive, self-healing, and conductive ionotronic hydrogels based on the synergistic dual reversible interactions of poly(vinyl alcohol), borax, pectin, and tannic acid. Multifunctional ionotronic hydrogels exhibit strong adhesion to various substrates with different roughness and chemical components, including porcine skin, glass, nitrile gloves, and plastics (normal adhesion strength of 55 kPa on the skin). In addition, the ionotronic hydrogels exhibit intrinsic ionic conductivity imparting strain-sensing properties with a gauge factor of 2.5 up to a wide detection range of approximately 2000%, as well as improved self-healing behavior. Based on these multifunctional properties, we further demonstrate the use of ionotronic hydrogels in the 3D printing process for implementing complex patterns as wearable strain sensors for human motion detection. This study is expected to provide a new avenue for the design of multifunctional ionotronic hydrogels, enabling their potential applications in wearable healthcare devices.

Magnetoresponsive Artificial Cilia Self-Assembled with Magnetic Micro/Nanoparticles

Biological cilia have exquisitely organized dynamic ultrafine structures with submicron diameters and exceptional aspect ratios, which are self-assembled with ciliary proteins. However, the construction of artificial cilia with size and dynamic functions comparable to biological cilia remains highly challenging. Here, we propose a self-assembly technique that generates magnetoresponsive artificial cilia with a highly ordered 3D structural arrangement using vapor-phase magnetic particles of varying sizes and shapes. We demonstrate that both monodispersed Fe₃O₄ nanoparticles and Fe microparticles can be assembled layer-by-layer vertically in patterned magnetic fields, generating both "nanoscale" or "microscale" artificial cilia, respectively. The resulting cilia display several structural features, such as diameters of single particle resolution, controllable diameters and lengths spanning from nanometers to micrometers, and accurate positioning. We further demonstrate that both the magnetic nanocilia and microcilia can dynamically and immediately actuate in response to modulated magnetic fields while providing different stroke ranges and actuation torques. Our strategy provides new possibilities for constructing artificial nano- and microcilia with controlled 3D morphology and dynamic field responsiveness using magnetic particles of varied sizes and shapes.