The idea for this work comes from a video about the snake shedding process; the snake sheds by contracting its muscle and gradually moves out of its old skin (see Fig. 1). The same situation also occurs when eating crayfish. The whole soft tails could be extracted from their shells intact and easily due to the elastic bodies. Moreover, the shells retain their original geometries and delicate features. Inspired by these phenomena and after receiving positive feedback from my advisor Prof. Hongqiang Wang, we tried employing this concept of embedding soft templates into matrices and removing them for channel generation.
Figure 1. Snake shedding process (left) and a shed snake skin (right).
The material choice for the soft template is also an interesting process. The first material we tried is an elastic filament from elastic cords, which are always used in clothing and are composed of multistrand elastic filaments. When embedding this filament into a PDMS matrix, we found that the interface between the filament and matrix remained an uncured layer. After we extracted the filament, the surface was always sticky. We cleaned the filament repeatedly, but it didn’t work. Then, we considered whether we could take advantage of this uncured phenomenon for channel generation. Well, we found that a paper was already published based on this phenomenon for microchannel fabrication soon. Later, we changed the matrix material by choosing a polyurethane elastomer (Vytaflex 30), and we succussed fabricating microchannels in the polyurethane elastomer and a UV-curable resin (Fig. 2). But another question appeared: we could not tube the diameter or geometries of soft templates since the elastic filament is commercially available, limiting the design flexibility for soft templates. One day, I saw my colleague using a hot glue gun for gluing, and a thin glue filament could be generated on their tips after removing the glue gun from dispensing plots. Inspired by this phenomenon, a sliding stage and a needle tip were employed to generate a controllable and thin filament. In addition, much more complex filament patterns were generated by direct drawing, postprocessing, and assembly, and the corresponding microchannel patterns were also fabricated.
Figure 2. The microchannels fabricated by elastic filaments from elastic cords.
The application part is the most struggling but worthwhile. The demonstrations are straightforward to present the traits of our soft demoulding technology, and we brainstormed for demonstration designing (Fig. 3). The complexity and high aspect ratio of microchannels were presented by the soft worm robot containing a plectoneme microchannel, and the soft tendril robot containing helical microchannel with the aspect ratio over 1600. In addition, solvent-free is one important feature of the fabrication process, which is applicable for biomedical applications. Therefore, to broaden our application region and prove the versatility of soft demoulding, we collaborated with Prof. Qin from Tsinghua Shenzhen International Graduate School to fabricate artificial vascular models based on soft demoulding. We just spent a half day imparting our soft demoulding technology to the Collaborators in Tsinghua, presenting our simple fabrication method.
Figure 3. The applications of soft demoulding.
Our work paves an easy path to more topologically complex scalable microchannels. We believe that more possibilities of soft demoulding are still untapped. We hold an open mind to discussing this work and seek collaborations worldwide.
For more details, please see the recent article published in Nature Communications:https://doi.org/10.1038/s41467-022-32859-z
For more information about Prof. Wang’s research, please visit the following website:https://wanglab.mee.sustech.edu.cn/