Tangentially Active Polymers in Cylindrical Channels

1) Interesting paper, very thorough in the data analysis and gathering
2) New nontrivial results in the field of active polymers under confinement

1) Figures can be improved, they are at times hard to read and interpret
2) I have a number of points that need to be addressed

This is an interesting paper. The authors consider the problem of a tangentially driven active polymer under cylindrical confinement.
They study the system under three different degrees of confinement for for two strength of the active forces. They also map their system to that of a single Brownian active particle and study structural and dynamic properties of the system.
They find a couple of intriguing results that are notable and worth of publication, including
1) The way active polymers accumulate on the confining surface, is quite different than how single particles behave near them.

2) This papaer show how the blob scaling used for passive polymers breaks down
for tangential active polymers, and that radius of the channel is not a fundamental length scale of this problem.

1) The conclusions could be written more clearly.

2) What is the interaction between the beads defining the channel and the monomers?

3) In Figure 2 it would be very useful to mark in the horizontal axis at which size N, the passive radius of gyration of the polymer becomes comparable to the degree of confinement, just to have a sense of the degree of confinement the reference passive system would be experiencing.

3) The authors say
“Indeed, here \nu is reminiscent of the passive exponent under confinement (\nu =1); however, as the tangential activity tends to shrink the polymer chains, the final outcome results from their interplay.”
The \nu=1 is only true under very strong confinement. For a passive polymer under weak confinement (small N) that should be ~0.6. I am not sure the authors are in the limit of very strong confinement, as even for the longest polymer discussed in Fig2 (N=200) I would expect a radius of gyration of the order of ~ 15
This is confusing. I get that the activity reduce the power law dependence of Re, I am not sure the reference limit is correct here.

4) 
Put more ticks in the x axis in Figure 3.
The saturation of the red-points in the two figures does not seem to happen at the same value of N as discussed in the paper. Add horizontal lines (or colored dots on the y-axis) to indicate the size of the confinement (R).

4) In discussing Fig. 4 the authors say:
“We observe that, in some regimes of confinement and activity, sufficiently small active polymers behave as their passive counterpart (gray line)”
There is no gray line in the figure (should that be black?).

5) The authors say:
“More importantly, given this rescaling, the reported data do not collapse on a single universal curve.” However the data in Fig.4 (b) seems to suggest that they do in the large Pe limit.
What am I missing? That seems like a pretty good collapse to me, it does not follow the passive prediction, but the data seem to collapse into a master curve nonetheless.

Ask for minor revision

1 - An interesting problem in the physics of active matter systems
2- Very clean and carefully done numerical simulations
3- Extensive and careful analysis of the results

1 - Limited relevance to biological systems
2- A bit artificial model of activity

Overall, this is quite interesting and carefully done numerical work with good comparison to theory. The problem is of interest to the community working on active matter systems, in particular those working on problems that go beyond simple active agent models. The model is, however, a bit artificial in terms of the way the activity is introduced - most biological filaments involve some molecular motor that acts to slide pairs of filaments against each other. So, it is not clear how relevant the results would be to biology.

I am also wondering how sensitive are the results on the way the confinement is implemented. At present, the authors use a set of fixed beads which might introduce roughness to the wall. Implementing the actual confinement constraint is conceptually not hard, but might be technically challenging in LAMMPS. Could they please comment?

1 - Please add legends to most figures
2 - Please comment in the caption of Fig. 4 about the solid black line
3- Please make notation consistent between that main text and the SI (e.g. vectors in the main text are shown in bold, and in SI they have overhead arrows).
4 - Full-line equations are part of the text and should include proper punctuation.
5- The last paragraph in Conclusions is highly speculative and vague. Please either remove it or make it more precise.
6 - Please be consistent with the space between a word and the citation that follows it.

Publish (easily meets expectations and criteria for this Journal; among top 50%)

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Publish (easily meets expectations and criteria for this Journal; among top 50%)