Microchannels are the essential elements in animals, plants, and various artificial devices such as soft robotics, wearable sensors, and organs-on-a-chip. However, three-dimensional (3D) microchannels with complex geometry and a high aspect ratio remain challenging to generate by conventional methods such as soft lithography, template dissolution, and matrix swollen processes, although they are widespread in nature. Here, we propose a simple and solvent-free fabrication method capable of producing monolithic microchannels with complex 3D structures, long length, and small diameter. A soft template and a peeling-dominant template removal process are introduced to the demoulding process, which is referred to as soft demoulding here. In combination with thermal drawing technology, microchannels with a small diameter (10 µm), a high aspect ratio (6000, length-to-diameter), and intricate 3D geometries are generated. We demonstrate the vast applicability and significant impact of this technology in multiple scenarios, including soft robotics, wearable sensors, soft antennas, and artificial vessels.
Compared to many rigid robots, emerging soft robots possess higher adaptability and safety owing to their compliance, [1,2] making them a promising solution for human-robot interaction, [3,4] manipulation, [5,6] and search and rescue. [7] Instead of only having one state (soft or rigid) in a robot, many scenarios necessitate both soft and rigid properties. For example, when picking an item of varying softness, shape, and weight using various motions, such as grasping and fiddling, a packaging robot should be rigid enough to grasp heavy items but soft enough to grasp fragile or irregular items while also being capable of quickly switching between these two states. [2,8,9] While exploring dangerous and confined environments (e.g., post-earthquake rescue and industrial pipeline inspection), the robot should be sufficiently compliant to adapt to the cluttered environment and rigid to transport a large gap. [10,11] Moreover, if a robot approaches a rugged surface with a heavy payload, it should be sufficiently compliant to move on the surface and rigid to support the payload. [12,13] To circumvent this problem, researchers attempted to integrate rigid and soft robots. One approach is to convert a robot from a rigid to a soft state and vice versa, which requires a variable-stiffness mechanism. This mechanism has been widely used in wearable robots, [14] manipulators, [7,15] and continuum
Soft shells are ubiquitous in soft devices, e.g., soft robots, wearable sensors, and soft medial replicas. However, previous widely accepted methods, such as mold casting, dip coating, and additive manufacturing, are limited to thick shells due to the mold assembly and the large friction during demolding, long processing time for mold dissolution, and poor scalability, respectively. Here, a facile, robust, and scalable manufacturing technique, named flow casting, to create soft shells with complex geometries and multifunctionalities is proposed. The method involves a flow‐governed layer casting process and a peel‐dominated demolding process. A one‐dimensional soft shell is first made with controllable thicknesses (100–400 µm) and fabricated various soft shells of intricate geometries, including three‐branched, circular‐shaped, and exquisite microstructures such as papillae and microgrooves on curved surfaces, with the resolution of feature sizes on the order of 100 µm. Furthermore, the versatility of this method is demonstrated with a 3D vascular phantom model for a magnetic robot transporting, microstructured cubic sleeves for enhancing the grasping ability of rigid grippers, and a stretchable optical waveguide capable of color changing by external mechanical stimuli.
Stimuli perception enables animals and robots to interact with unknown environments safely and predictably. For the sensing of soft robotics and wearable devices, although electronic skins have already been widely accepted and studied, their planar geometries are not applicable for multi‐direction volume sensing. Herein, the innervation of sensing microchannel networks into elastic matrices to mimic the exteroception and proprioception of the human bodies is employed. Soft actuators with interlaced actuating and sensing microchannels resembling the distribution of muscle fiber and proprioceptors are fabricated and the internal stimuli perception of deformation configurations (bending, elongating, and bending directions) and magnitudes (bending angle and elongation) of the soft actuators are demonstrated. It is also demonstrated that a soft cubic sensor containing 3D microchannels (diameter: 400 µm) is capable of identifying 3D external stimuli, including force types (pressing, squeezing, shearing, and twisting) and real‐time directions by measuring the resistance variation, and its application in the virtual reality field is exhibited.
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