Natural microscale vessels ubiquitously exist in animals and plants since they are critical for nutrient transportation and byproduct removal. In recent decades, microchannels have also played an important role in artificial devices, such as sensors, actuators, and medical devices.

With the rapid development of these fields in recent decades, more complex and thinner microchannels are highly desired for devices of higher performance. The conventional fabrication method, soft lithography, is a labor-intensive process, which is applicable for microchannels in 2D geometries with rectangular cross-sections. It becomes inadequate and hinders the further growth of this field. Different solutions, such as template dissolution, matrix swelling, and 3D printing, have been proposed for microchannel generation, but they are confined to simple geometries, rough surfaces, and long durations. Hence, novel techniques that generate complex 3D structured, nontoxic, and slender monolithic microchannels are expected to revolutionize the vast applications where microchannels are indispensable.

Inspired by the tension-induced necking phenomenon during the cold drawing process of the polymeric specimens, Associate Professor Hongqiang Wang’s research group from the Department of Mechanical and Energy Engineering at the Southern University of Science and Technology (SUSTech) proposed a simple and solvent-free fabrication method capable of producing monolithic microchannels with complex 3D structures, long length, and small diameter.

Their paper, entitled  “Self-shrinking soft demoulding for complex high-aspect-ratio microchannels,” was published in Nature Communication, a multidisciplinary journal covering the natural sciences, including physics, chemistry, earth sciences, medicine, and biology.

During the fabrication process, a soft template and a peeling-dominant template removal process are introduced to the demoulding process, named soft demoulding (Fig. 1).

Figure 1. The concept and mechanism of soft demoulding

The soft template and gentle demoulding process are two traits of the soft demoulding technology. This work contrives the soft templates by thermal drawing, i.e., dipping the tip of a thin rod into a polymer melt and then drawing the rod out of the melt. The template structures were generated according to drawing speed, temperature controls, postprocessing, and assembly. These included a straight, taper-shaped, branched, spindle-knotted, helical, plectoneme, conical surface, saddle surface, hyperboloid surface, and tree-like template structures. Based on the researchers’ soft demoulding technology, the corresponding microchannel patterns were generated (Fig. 2). The microchannels created by soft demoulding can be as small as 10 µm in diameter and over 6000 in aspect ratio (length-to-diameter).

Figure 2. Microchannel structures fabricated by soft demoulding

In order to exhibit the traits and advantages of our fabrication method and prove its applicability for versatile applications, Prof. Wang’s team demonstrated the vast applicability and significant impact of this technology in multiple scenarios, such as a worm robot containing a plectoneme microchannel (Video 1), a tendril robot capable of winding with a super-long helical microchannel, a soft mechanically-tunable miniature antenna with a 3D helical microchannel, and artificial vessels with straight and tapered structures capable of transporting nutrition to the surrounding cells (Fig. 3).

Figure 3. Application of soft demoulding (including soft worm robot, soft miniature antenna, a thread-like sensor, and a tapered artificial vessel)

Video 1. Actuation of the soft worm robot

This study introduces a novel methodology of microchannel formation to expand the applications of microchannels in various fields. It paves the path to more topologically complex scalable microchannels. In the future, this technique can vastly impact the research on, e.g., robots, wearable devices, and medical devices, where microchannels are essential, by bringing in more design and fabrication possibilities.

Dongliang Fan, a Ph.D. student in Assoc. Prof. Hongqiang Wang’s research group, is the first author of this paper. Prof. Hongqiang Wang is the first corresponding author, while Prof. Peiwu Qin from Tsinghua Shenzhen International Graduate School (Tsinghua SIGS) is the co-corresponding author. SUSTech is the first affiliation.

This work was supported by the National Natural Science Foundation of China (NSFC), Natural Science Foundation of Guangdong Province, Science, Technology and Innovation Commission of Shenzhen Municipality, Natural Science Foundation of Liaoning Province, and Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou).

Paper link: https://doi.org/10.1038/s41467-022-32859-z

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