Peer review of: Asymmetric elastoplasticity of stacked graphene assembly actualizes programmable untethered s  (2020)

Reviewers' Comments: 
 
Reviewer #1: 
Remarks to the Author: 
please see attached in step 4 
[Comment from the Editor: Please see attached Pdf] 
 

Manuscript: NCOMMS-20-06504 
Type: Article 
Title: Asymmetric elastoplasticity of stacked graphene assembly actualizes programmable 
untethered soft robotics 
Authors: Shuai Wang, Yang Gao, Anran Wei, Peng Xiao, Yun Liang, Wei Lu, Chinyin Chen, 
Chi Zhang, Guilin Yang, Haimin Yao, Tao Chen 
 
Summary: The authors use the Langmuir-Blodgett method to deposit graphene layers on 
polyethylene. These SGA-PE layers exhibit morphing behaviors if exposed to temperature 
(~50*C). The tempering (heat treatment under pressure) of SGA-PE layers enable new types of 
morphing behaviors. Previously, SGA-PE layers flattened at room temperature and deformed at 
increased temperatures; in this work, after tempering, SGA-PE layers deform at room 
temperatures and flatten at increased temperatures. This work essentially improves on the types 
of folding mechanisms that are possible with graphene coated polymers. 
 
I recommend that this paper should be considered for publication after major revisions (i.e. 
restructuring and rewriting of the manuscript, additional demonstrations that indicate the benefits 
of this material (using tempering) relative to those that exist, and a study on actuation cycles and 
material fatigue). The authors dilute the novelty of their work by showing demonstrations of 
mechanisms that have been previously reported (which they missed citing [1]). They fail to 
effectively extract the novelty of their work, that is, the use of tempering on SGA/PE bilayers for 
the creation of new types of actuation modes; in the current state, the manuscript is difficult to 
follow and many of their demonstrations do not support the narrative of their work. 
 
Major Issues: 

•  Given the title of the manuscript, this work insufficiently addresses the field of soft 

robotics. If these actuators are meant to be used for robotics applications, we will also 
need to know more details about their performance such as the number of actuation 
cycles before they experience material fatigue. Please include an extensive study on the 
actuators.  How much force are the actuators capable of exerting? What is your success 
rate of building them? Do 10 out of 10 actuators work? The authors also talked about 
cost-effectiveness without addressing what that actually means (in $). How expensive is a 
single actuator (material cost and time to fabricate a single device (trained/untrained 
students)? What keeps the SGA and PE layers attached to each other (van der Waals 
forces)? How robust are your actuators (could you step onto them and would they still 
work)? 

•  The authors spend significant amount of text on explaining and demonstrating SGA/PE 

layers without heat tempering (artificial mimosa, sit-up robot), however, this does not 
seem the novelty of their work. The layering of graphene onto polyethylene has 
essentially been done before and its response to heat (light) documented (see reference 
[1]). The authors missed citing key literature. By doing so, the entire manuscript becomes 
very difficult to comprehend since the novelty of their work is diluted amongst existing 
approaches. This manuscript must be rewritten solely focusing on heat tempering with 
only a brief introduction to SGA/PE bilayers (unless the authors believe their SGA/PE 

layering is more advantageous (for soft robotics) if compared to existing work, which 
they have to prove). 

 
 
Minor Issues: 
•  Figure 1 is confusing; E) the authors mention that heat deforms the bilayer to its flat state, 
however, they indicate a barely unrolled device in the figure. Does your tempered device 
fully unroll? G) The artificial mimosa and sit-up robot don’t take advantage of the 
constrained tempering, hence, dilute the work. These demonstrations should be taken out 
and replaced by new experiments that take advantage of the novelty of this work, that is, 
the heat tempering of SGA/PE bilayers. 

•  Subfigures 3A and 3B are inconsistent; the right part of Figure 3B should also indicate 

experimental data instead of schematics. 

•  Figure 5 shows the temperature-induced self-folding. This work has essentially been done 

before. If you want to include it, tell us how it is different to existing work [1]. Maybe 
you could show how the entire cube collapses when applying heat? Can you think of 
applications where this is actually useful? G) Why is the lasering done sequentially (one 
edge at the time)? It seems like the laser should program the material all at once when it 
is sandwiched (constrained) between the tempering layers. 
 

General Comments: 

•  The novelty of your work has to be clearly stated in light of existing literature. What 

makes your work novel? In which matrix (e.g. actuation speed?) does your work 
outperform existing approaches? Why should anyone care about this (in the soft robotics 
community)? Maybe because the results are easy to reproduce, and the actuators are low-
cost and reliable? 

References: 
1.  Xu, Weinan et al., Ultrathin thermoresponsive self-folding 3D graphene, Science advances, 
3(10), 2017 

Reviewer #2: 
Remarks to the Author: 
The authors prepared a bilayer film of SGA/PE which exhibits swift morphing behavior in response 
to the variation of the surrounding temperature. The manuscript should be revised before 
acceptance. The detailed comments are as follow: 
1. The as-prepared bi-material film shows bending and coiling behavior in response to the external 
temperature variation. The conditions for bending or coiling need to be clarified. Is the size of film 
the most important factor affecting actuation performance? Are there other factors? 
2. P4 line 115, is the graphene reduced graphene oxide or CVD based graphene? If the graphene 
used here is home-synthesized, the preparation method needs to be provided. 
3. Could you show the DSC curves of PE and SGA/PE film, which are important for understanding 
the mechanism of the morphing behavior of the film? 
4. The sizes of the SGA/PE film in Fig.3 and in Fig. 8 are different. Could the author show the 
influence of size and the ratio of SGA and PE on the morphing behavior? 
5. The film showed inconsistent colors in different figures, e.g. gray appearance in Fig. 2B, Fig. 3A, 
Fig, 3B, while black color in Fig. 3E, Fig. 5G, Fig. 6). What is cause for this difference? 
6. Why does the graphene layer, instead of the PE layer, swell with laser writing in Figure 5G 
7. The author said: “as-prepared SGA/PE bilayer is pre-treated with a heating and a subsequent 
cooling process (similar to the tempering process in metallurgy) in a constrained space.” An as-
prepared flat SGA/PE strip is sandwiched by two pieces of glass slide to suppress the possible 
bending deformation. 
Glass slide can only constrain the film in the vertical direction. What may happen if the film 
deformation is constrained in both vertical and parallel directions? 
8. Do IR light and laser illumination cause difference temperatures of the film? Does the 
illumination time affect the temperature of the film? 
9. How is the structural stability of the bi-layer film, e.g, does delamination or exfoliation occur 
during the deformation? 
 
 
 
Reviewer #3: 
Remarks to the Author: 
In this work, the authors report the graphene/polyethylene based bimorph soft actuators and 
demonstrate their applications in 3D reconfiguration and rolling motors. The working mechanism 
(i.e., thermal and photothermal actuation) is already well known and extensively demonstrated in 
other research papers. It is not new to make soft actuators that can bend toward the material with 
a higher coefficient of thermal expansion by introducing thermal stress (Adv. Mater. 2015, 27, 
7867-7873). Also, the correlation between the so-called asymmetric elastoplasticity and the 
actuator performance is too speculative. Thus, I do not suggest the publication of the manuscript 
in Nature Communications.