A Review on Microfluidic Platforms Applied to Nerve Regeneration

Round 1

Reviewer 1 Report

The presented paper focuses on the latest achivements in development and fabrication of microfluidic platforms for nerve regeneration. I find this review paper very interesting.  In my opinion, the examples of  microfluidic platforms contained in the manuscript are representative.

However, the paper consists of few grammar  (eg. on p. 5, l. 162, there is "(...) device do not (...)" and should be "(...) device does not (...)", on p. 13, l. 440 there is "(...) platforms have has not (...)" and should be "(...) platforms have not (...)") and editorial errors (eg. Table 2).

The aforementioned errors do not affect the scientific value of the work, but may make it difficult to read. Therefore, the Authors should once more read cerfoully thier paper and correct all grammar, typos and editorial errors. 

Author Response

Dear reviewer

Thank you very much for reviewing the manuscript and your kind opinions.  The response to the comments is in the attachment file.

Wish you have a good day!

Chuankai Dai

Author Response File: Author Response.pdf

Reviewer 2 Report

 The authors introduced the development of microfluidic platforms for neural regeneration studies. The authors reviewed many papers to explain the information of recent advances. However, I think the paper is not organized perfectly to describe the information to potential readers. So, I recommend the authors reorganize the information which the authors gathered well.

1. I recommend the authors to help potential readers navigate the structure of the paper. In the introduction section, there is no guidance to inform the purpose and the logic of the paper. Now the paper is organized to describe the design of microfluidic devices and microfluidic platforms applied to the various fields of neural regeneration. I think it is better for the authors to explain the logic of the paper in the introduction section, and the logic should be mutually exclusive and collectively exhaustive to describe the subject of the paper. Furthermore, the authors should persuade readers why that logic is the best way to describe the subject.
2. The authors mentioned the advances and the limitations in the introduction section and the final section. However, the advances are not revealed well because the authors didn’t explain the traditional methods precisely. Also, the limitations are not described well in the second, third, and fourth sections. I recommend the authors to explain more and tables can be a good tool to compare traditional methods and microfluidic platforms including the limitations of the recent platforms. I think the authors can organize this comparison well because they reviewed well the advantages of the microfluidic platforms to be applied to neurobiology.
3. Table 1 might be improved well by changing the title into properties of different materials to be applied to neurobiology. The authors explained well the advantageous properties of PDMS including convenient fabrication, chemical inert surface, and nontoxicity. But those advantageous properties to be applied to neurobiology are not described well in the paper. 
4. The authors mentioned hydrogels in line 124 – 125. However, hydrogels are too variant to be explained shortly. For example, some hydrogels are hydrophobic but hydrogels are explained as a hydrophilic material in table 1. The authors explained hydrogels as a source to introduce 3D scaffolds regarding the specific purposes. The authors should explain more about this material including the views about the roles of hydrogels in neurobiology applications.
5. In the section ‘2.2 Structures’, the purposes and the advantages of the specific structures are not explained well in the paper. I think it is better to inform more biological scientific backgrounds to readers. For example, the authors should explain the importance of increasing the number of cell types to culture and the role of microchannels where neural cells are cultured or connected. Especially, the purposes and the advantages of the 2D culture structures are not described enough.
6. I am curious if there were specific results that show the advantages of 3D culture structures. Were there any biological experiments to show the difference between 2D and 3D culture structures?
7. In the section ‘3.1 Nerve Repair’, the authors summarized the difficulties of the nerve repair experiments in two processes. However, the following paragraphs are structured in those processes. Especially detecting methods are not described enough in the following paragraphs. I recommend the authors to structure again following the process. Also, I think repairing methods can be added as an additional process to the previous two processes.
8. The subject of the paper is vague for some reasons. For example, figure 4B and figure 5B are figures to explain the fabrication process. However, the paper focuses more on materials, microfluidic structures, and neurobiological applications. 
9. In some figures, the sizes of letters are not readable. For example, I cannot read letters in figure 2G and figure 3C. I think it is better to unify the font sizes in the figures. 
10. There are some minor typo errors. For example, in line 445 – 447, there is no conjunction between two sentences.

Author Response

Dear reviewer

Thank you very much for reviewing the manuscript and your kind comments. We really appreciate your detailed constructive suggestions. According to your valuable suggestions, we have modified the manuscript, which is in the attachment.

Wish you have a good day

Chuankai Dai

Author Response File: Author Response.pdf

Reviewer 3 Report

Microfluidic technology has significantly advanced nerve regeneration research over the last decades. In this manuscript, Dai et al., summarized the state-of-art of development and leverage of microfluidic platforms for nerve regeneration research. The scope and depth of this review is comprehensive, yet the manuscript is not well-written. With the other issues listed below being addressed, the reviewer would suggest its publication in Applied Sciences.

1. The definition of complete and incomplete SCI patients is not well given. Line 30 “Among all SCI patients, the incomplete SCI patients account for 65% and the complete SCI patients account for 35%[1].”
2. The discussion on the advantage of thermoplastic materials over PDMS in terms of adsorption and permeation of small molecules is contrary to the current understanding in the community of microfluidics. Researchers are adapting thermoplastic materials over PDMS, since thermoplastic materials would affect the accuracy of drug concentrations due to its low adsorption of hydrophobic molecules. Line 110 “However, thermoplastic materials show less nonspecific adsorption and has greater resistance to permeation of small hydrophobic molecules than PDMS material that makes thermoplastic microfabrication devices unsuitable for some neurobiological experiments with specific requirements.”
3. The reviewer suggest to take the 3D microfluidic culture from Figure 2 and combine with Figure 3.
4. The logic of the section “2.2.2. 3D Culture Structure” is hard to follow.
5. The authors should summarize and discuss the literatures but not just enumerate them. Line 277, “Hosmane, S[55] developed an axonal injury micro-compression device using pneumatic compression. This device enables different degree of deformation of single axon.”
6. The author should use the expression of “et al.,” to limit the list of authors if there are more than three authors. For example, Line 286, Line 291, and Line 295.
7. The reference number of each study should also be given in Table 2.
8. The discussion on the challenges of current microfluidic devices for nerve research is limited and should be expanded.
9. Some typo and grammar errors.

Line 38, “Neuroplasticity lays an important theoretical foundation for the treatment of incomplete SCI, Thus the treatment principle is reactivating the residual neural circuits to modulate the impaired functions of body”.

Line 50, “Microfluidic platform can realize precise spatio-temporal control of cellular microenvironment[4], allow neurobiologists to explore a wide variety of neuronal events such as axon elongation[5, 6], local signaling events[7] and interactions with other cells[8].”

Line 222, “NFGs such as brain-derived”

Line 255, “3.1.2. Microfluidic Platforms for different as injury models”

Line 259, “The common injury models are biochemical injury (hemolytic injury, excitotoxic injury, immunotoxic injury), physical injury (stretch injury, compression injury, incision injury), laser-based injury, vacuum-assisted injury.”

Line 264, “Although there are many method to reproduce tensile/strain injury in organ-type slices such as Morrison, B[50] and Pfister, B. J[51].”

Line 266, “limited by their reproducibility and are difficult to apply to tensile injuries to single isolated axon”

Line 288, “Showed a rise in cytoskeletal and intracellularly transported transcripts under vacuum assistance.”

Line 351, “4. Microfluidic Platforms applied to Axonal guidance”. The authors should keep the capitalization of words in consistent throughout the manuscript.

Line 445, “Second, there are numerous models of nerve injury and repair approaches have been developed, there is not a uniform assessment standard to quantitatively detect and evaluate the efficacy of drugs.”

Author Response

Dear reviewer

Thank you very much for reviewing the manuscript and your kind comments. We really appreciate your detailed constructive suggestions. According to your valuable suggestions, we have modified the manuscript, which is in the attachment.

Wish you have a good day

Chuankai Dai

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have addressed all the concerns.