Soft, Soft Robot.

 

I’m going to go out on a limb here and assume that when most of you hear the term “soft robot,” your thoughts immediately go to cuddling with it. Who wouldn’t want a soft, squishy robot to cuddle with? Alas, that isn’t covered in this journal entry from February 2019’s Extreme Mechanics Letters Volume 27 entitled An untethered soft chemo-mechanical robot with composite structure and optimized control written by Liyuan Chen, Weijia Chen, Yaoting Xue,  Jie-Wei Wong, Yiming Liang, Mingqi Zhang, Xiangping Chen, Xunuo Cao, Zhen Zhang, and Tiefeng Li. However, what is covered is an example of a soft robot, which is also referred to as a soft machine. Let’s talk about.

This soft machine draws its design inspiration from natural muscle.  When a muscle flexes, it does so due to the mitochondrion (the “power house” of the muscle cell) reacting to the introduction of fuel, which causes a decomposition process that generates adenosine triphosphate as a form of “catalyst and reactant” process that creates energy for the muscle, leading to it “flexing.” This soft robot uses a similar process where a reaction chamber, which serves as a mitochondrion of sorts, contains a catalyst that, when combined with the reactant, produces a chemical reaction that leads to inflation of the soft chamber, not unlike a muscle. In the instance of the soft robot, the catalyst is manganese dioxide (MnO2), which causes the reactant, hydrogen peroxide (H2O2), to degrade in a manner that produces oxygen by separating it from the hydrogen. The reaction takes place in a small chamber called the soft chemical engine (SCE). When the SCE fills with oxygen, the oxygen moves through a tube into the soft pneumatic chamber (SPC). The SPC is softer material than the SCE, so it gives way to the pressure created by the SCE, causing it to inflate and flex. 

The whole system can be seen in Figure 1 a and b, with more details of the catalyst in Figs. 1 c-e. Fig. 1a  shows a syringe of H2O2 injecting into the reaction chamber, where the composite catalyst is located (this is the SCE), and a tube runs to the SPC, which is the chamber that looks like three white cubicles.  Fig. 1b shows the results of the H2O2/MnO2 reaction, with the SPC inflated.  Fig. 1c shows the MnO2 catalyst plates that are separated and held in place by plates of Dragon Skin 20, which is a soft silicone. Fig. 1d not only gives you an idea of the scale/size of the catalyst, but also shows how squishy the Dragon Skin is, which allows it to be squeezed into place within the reaction chamber, and the spring tension when it is released holds it in place, nice and tight. Fig. 1e is an overhead view of the whole machine. 

Fig. 1. The (a) reference and (b) working states of the SCE. The (c) reference and (d) deformed states of the soft composite catalyst. (catalyst plate: 35 mm x 35 mm x 1.7mm, dragon skin plate: 35 mm x 35 mm 2 x mm). The SPC, The fixed soft composite catalyst and unsealed cubic reaction chamber of wall thickness 4 mm and side length 50 mm.

Different SPC shapes could have significantly different functions, too. For example, check out Fig 1b. And take note of how the SPC is flexing. Using a thicker walled/less stretchable material as the base, this causes the inflated SPC cubes to deform the base convexly,  into an arch. This arch in motion could create a crawling type movement to propel itself. This may not seem like that impressive of a feat, but considering the relative simplicity of this machine along with the fact that no electricity is even involved, this is just the tip of the iceberg for the potential this type of machine presents.

Pretty cool, right? I think so. And this is without even getting into the really deep, technical stuff that you can read more about in the original paper (follow the doi in the citation at the end of the article). My imagination really took hold while thinking about these soft machines and what could be done with them. Kooky sci-fi stuff like automatons could be produced, using these soft machines as their actual muscles, which would give them a lifelike feel. So you could end up with the soft robot cuddle buddy of your dreams after all! I hope you, too, will let your imagination run with this idea, and I hope even more that you share those ideas with someone and that they become a reality one day.  Heck, maybe you could even build your own soft robot in the not-so-distant-future. It’s certainly not out of the question!

Work Cited

Chen, L., Chen, W., Xue, Y., Wong, J.-W., Liang, Y., Zhang, M., Chen, X., Cao, X., Zhang, Z., & Li, T. (2019). An untethered soft chemo-mechanical robot with composite structure and optimized control. Extreme Mechanics Letters, 27(Feb. 2019), 27–33. https://doi.org/10.1016/j.eml.2018.12.001