In Vitro Investigation of Corrosion Control of Magnesium with Degradable Polycaprolactone Coatings for Cardiovascular Grafts

Round 1

Reviewer 1 Report

The paper describes the influence of the method of magnesium coating with PCL on the corrosion processes of this material in the context of applications in cardiology. The work seems to be very interesting, especially from the point of view of its application. The results are presented in a clear way. The Authors used statistical methods to develop the results. The overall level of work is high.

1.      The paper is well written. However, the authors did not avoid a few mistakes, including spaces in the wrong places (in particular, the temperature values need to be standardized).

2.      The data shown in Table 2 contains the chemical compositions of the fluids included in Table 1. I think that more reasonable is to give firstly Table 2.

3.     Please precise if the immersion and coroosion tests were conducted under the same conditions i.e. temperature, time.

4.     How Authors explain the increased fiber diameter observed in Figure 6? 

5.    The summary is quite general. While the most important conclusions are included, the Authors may consider adding a few sentences to the summary, especially regarding the application issue which were shown in paragraph 4, it would be advisable to briefly describe the advantages of the PCL coatings.

Author Response

Dear Reviewer,

Thank you very much for the helpful and constrictive comments. The paper will gain in precision, clarity, and expressiveness. We have incorporated your comments as follows:

1. We checked and corrected the spacing, especcilally the units. IWe are very glade that you found the misspacing of the temperature.
2. We give the table 2 (composion of the fluids) in the beginning. We put the overview of the experimental design  in the end of the material and methods section.
3. We added a sentence in section 2.5 (PCL fiber degradation) (Line 241) which clarifies the testing temperature. We also put the information about choice of testing periode for magnesium-corrosion  and PCL-degradation in the beginning of Material and Methods section (Line 112). I hope that this has made the approach clearer for the reader. We are very grateful for pointing out this weakness and the lack of this information.
4. We added a senteance that explains the increasing fiber diameter. It's the uptake of water. (Line 495)
5. We added a paragaph describing the special advantages of magnesium/PCL implants for cardiovascular applications (including 3 references that point out the possiblities that come with PCL as material that can be functionalized. (Line 521) We hope to be able to better conclude the thematic and provide the reader with starting points for his or her own research. Thank you very much for this valuable advice.

We wish you very nice new year,

best regards.

Reviewer 2 Report

Please address the comments according the attached file. 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you very much for the helpful and constrictive comments. The paper will gain in precision, clarity, and expressiveness. I have incorporated your comments as follows:

1. We changed the title to your advice: 

In vitro investigation of corrosion control of magnesium with degradable polycaprolactone coatings for cardiovascular grafts

2. We considered your comment to include more numbers in the abstract. Since we only have 200 words, we desided for the mayor massage, and gave the reduction of the corrosion rate caused by the coating. (Line 20)

3. In line 61 (Magnesium corrosion equation) you gave use the hint that the magnesium corrosion is more complex than depicted in our paper. We took your advice to heart and introduced a paragaph and your adviced reference in line 483.

4. The novelty of the paper is discribed starting from line 85. We tried to stress the point that magnesium coating with polymers often only consider the influence of the coationg on the magnesium corrosion rate and not the influence of the magnesium corrosion on the coating degradation.

5. Thank you very much for the comments on the table. We corrected it according to your advice. SEM was defined earlier in the text, but there was a miaaspelling, so it was not fully clear.

6. We didn't conducted electrochemical tests, because electrochemical testing was not implementable in our experimental design. We therefore looked to a variety of other studies on magnesium corrosion that describe hydrogen measurements as an informative method.

7. We measued the mass loss by calculating the emitted hydrogen into the corresponding mass loss of magnesium using equations 3 -5. Thank you for asking this question. We made a misstake in the equation numbers, that we corrected. Additionally, we unified the parameters to clarify for the reader.

8.In figure 4 you suggested SEM pictures. We tried but the changes of dense coating after immersion were much better visible in light microscopic pictures.

9. We put scale bares into the pictures and clarified in the caption by writing (White scale bars = 2mm). Thank you for given this hint.

10. We converted the unit in mm/y in the text to meet the needs for different scienticed of diffrent backgrounds. Thank you for this advice the discription of the results will be more understandable for more people.

11. We provide more information on the peaks in raman in figure 7.

12. Thank you for the hint to the leack of information concerning the choice of the pH 13 in the fiber degradation experiment. We introduced a paragraph in section Material and Methods (Line 106)

13. We introduced a Reference according to your advice.

14. We tried to clearify the stages with stronger adjectives. Thank you for giving this advise.

15. We could not understand your last comment. We assume that it asked for the pull-off test of electrospun fiber coating. This test reaveled that the fibers have no adheasion to the magnesium surface. We tried to stress this point in the text.

Thank you very much again for this valuable advices.

we wish you very nice new year,

best regards.

Round 2

Reviewer 2 Report

Authors addressed many comments. However, in the stages of corrosion, they did not revise any thing, but I recommend to accept the paper.