Microfabrication Bonding Process Optimization for a 3D Multi-Layer PDMS Suspended Microfluidics

Round 1

Reviewer 1 Report

This manuscript presents the optimization of a multi-layer microfluidic system made of Polydimethylsiloxane (PDMS) and fabricated through soft lithography. Several critical issues need to be improved before the acceptance of this manuscript.

The following points need to be addressed and improved:

1. The title should be reviewed/improved. Please explain the meaning of “suspended microfluidics” ? Improvements should be made on the title.
2. The authors should clarify in the introduction the importance and applications (not only by the authors but also from other researchers) of the 3D multi-layer PDMS suspended microfluidics.
3. The main aim of this manuscript is the optimization of a multi-layer microfluidic device made of PDMS. However, at the literature review/introduction there is no detailed information about the advantages and applications of PDMS in microfluidics and other related fields. In order to broaden the introduction and to increase the attraction of this manuscript by the scientific committee working with PDMS, improvements should be made on this point. The following recent papers may help to improve the quality of this manuscript regarding the advantages of the PDMS and applications not only in microfluidics but also in other fields: https://doi.org/10.3390/jfb13010002 ; https://doi.org/10.1016/j.bprint.2022.e00202 ; 
4. Soft lithography is a well known method to fabricate PDMS microfluidic devices. Hence, the authors should remove figure 1 or move it to the fabrication section.
5. In page 3, line 81, please revise this sentence.
6. Figure 2 should be improved, i. e., the authors should include the main dimensions.
7. Figure 5a) should be improved. It is difficult to see the “pouring PDMS on the mold”.
8. In page 9, more detailed information should be included about the bonding process such as temperature and time and also adhesion tests performed at the different ratios/conditions.
9. Figure 10 should be improved, i. e., the authors should clarify in the figure where is the “three microchannels and nozzle layers”
10. In page 10, line 240, please revise this sentence.
11. Figure 11 should be significantly improved, i. e., the authors should clarify the detailed part of the device in order to understand the performed experiment. It is extremely difficult to understand experimental validation of the SPMF. A schematic diagram should be made to improve our understanding. Please show us, clearly, where is the tip and what is the tip deplection ? Significant improvements should be made on this point.
12. The results from table 2 should be from some reference, please include them. What about the temperature ? Please also correct the representation of Celsius along the manuscript.
13. At the conclusions section, what is the meaning of “a static flow rate”. Is this correct ?

Author Response

Dear Reviewer,

Thanks for your comments. Enclosed you can find our replies and edited manuscript based on your comments.

Best regards,

Author Response File: Author Response.docx

Reviewer 2 Report

Packirisamy and collegues report on a method to produce 3D microfluidic devices in PDMS. The authors follow an approach, in which they stack and bond PDMS layers with discrete channel structures. The authors discuss how alignment can be improved, trapped air be excluded and how to obtain tightly bonded PDMS layers. The authors display the applicability and the limits of their technique by producing an unsupported 3D channel in PDMS, which is flexible to move. By deflecting a laser from the suspended PDMS channel to a photodiode. The suspended PDMS channel acts like the cantilever of an AFM and the pressure oscullation evoked by a perestaltic pump can be followed. Also changes in salinity, density etc. can be monitored using this technique.

The paper is well written and the method and the examples are well presented.

I have the feeling that the authors shouldcompare their method with other technqiques that haven been employed to produce 3D microfluidics. (e.g. https://doi.org/10.1039/C4LC00320A, https://doi.org/10.1021/acsami.5b03969, https://doi.org/10.3390/polym11111887) In this sense, the authors ignore alternative powerful techniques. However, with their technique, where the authors gain 3D freedom of design in a PDMS material, certainly has its advantages.

I support publication of this work in Applied Sciences. 

Author Response

Dear Reviewer,

Thanks for your comments. Enclosed you can find our replies and edited manuscript based on your comments.

Best regards,

Author Response File: Author Response.docx

Reviewer 3 Report

The article is well done and well treated in detail, the authors could cite this articles as a way to build an alternative microfluidic system  and manipulation  in liquid media directly into a microfluidic channel,at the lab-on-a-chip scale.

1)ACS Appl. Mater. Interfaces 2017, 9, 19, 16488–16494

2) RSC Advances 4(6):2851 , 2014

 

Author Response

Dear Reviewer,

Thanks for your comments. Enclosed you can find our replies and edited manuscript based on your comments.

Best regards,

Author Response File: Author Response.docx

Reviewer 4 Report

Rewrite the manuscript's abstract. Background, objective, material and method, results, and conclusion should all be presented in abstract. Lines 9–15 (before during microfluidic systems) seem to be irrelevant and should be removed.

The introduction section is long. Don't go into too much detail about the fabrication. Instead, focus on the SPMF3 and the challenges that come with making it.

There are numerous repeats and intermixed material and method, introduction and result sections. There should be proper material and method, results, and discussion parts for clear presentation.

It's important to break each of these parts into subsections, each of which should focus on a single thing that happened or looked at.

The observations and data that back up the hypothesis should be clearly shown in the results.

Can the authors offer images of several samples to show how the particle stickiness issue was overcome by diluting the microparticle solution with TWEEN20 and 206?

Similarly, how would you confirm the temperature change effect?

Furthermore, the writing is weak. There are several formatting mistakes, such as unnecessary spaces, a lack of full stops, grammatical errors, and lines 79, 81, and 240 and many more.

Please provide additional references, most of the sentences even some paragraphs lack references.

The figure labeling is incomplete, with missing alphabets.

Author Response

Dear Reviewer,

Thanks for your comments. Enclosed you can find our replies and edited manuscript based on your comments.

Best regards,

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have responded to most of my queries satisfactorily and the paper has benefited from all the changes made in the various sections of the manuscript.

Reviewer 4 Report

I believe the manuscript has already been sufficiently improved to warrant publication in Applied Sciences