Properties of Titanium Oxide Coating on MgZn Alloy by Magnetron Sputtering for Stent Application

Round 1

Reviewer 1 Report

The reviewed article titled " Properties of titanium oxide coating on Mg alloy by magnetron sputtering for stent application" is focused on the preparation of corrosion resistant and biocompatible inorganic coating for implantable magnesium alloys. The manuscript construction is correct. The research methodology is rather correct. The results are presented in a clear way, but their analysis needs some improvements. The English need to be revised by a native speaker.

I have objections to the title. First, its current version is ungrammatical. Second, in my opinion, it should be more specified. I suggest changing the phrase "Mg alloy" to "MgZn alloy" since this specific material was used as a substrate for the coating, and this phrase is mainly used in the paper.

Some crucial remarks are listed below:

1. I agree that one of the main challenges in the use of magnesium alloys in a physiological environment is to overcome its poor corrosion resistance. Of course, titanium dioxide is a very good material for corrosion protection. However, I wonder if this choice is good in the case of bioabsorbable substrates, here magnesium alloys, for stents. If such a bioabsorbable material (MgZn alloy) is coated by a non-bioabsorbable material (TiO₂ coating) it ceases to be bioresorbable. I am not sure if this is in line with the current stent research trend. Please comment it.
2. In the Abstract Authors write: "The surface features were characterized using scanning electron microscope (SEM), atomic force microscope (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and contact angle goniometer." In my opinion here the methods/techniques should be mentioned instead of instruments.: (…)scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and contact angle method".
3. Section 2.2. Characterizations – here instruments should be listed: microscope, spectroscope, diffractometer, instead of names of techniques
4. Figure 1b presents the SEM cross-section of the coating. The authors stated that this coating is 400nm thick, and that’s all. There is no information in the text about the interlayer visible in the SEM image between the substrate and the coating. Please comment it and add appropriate information in the text.
5. It is well known that samples coated with TiO₂ show bioactivity and, when immersed in SBF solution, they cover with an apatite layer. The authors should compare the corrosion characteristics of the materials before immersion in SBF solution. In my opinion, performing corrosion tests only for samples after 14 days of immersion in SBF provides only part of the information about the corrosion properties of the tested systems.
6. Do Authors performed analysis (XRD, XPS, etc) of the deposits visible on the TiO₂-coated sample after 14 days after immersion in SBF? 400nm thick TiO₂ layer should block corrosion processes of magnesium substrate if this coating is compact/dense of course. I suppose that this deposit is an apatite-like layer.
7. Page 6 line 173 – "The E_corr of the MgZn sample increased from −1.65 V to −1.70 V after TiO2 coating deposited." The authors put wrong values of E_corr, it should be "(…) from -1.70V to -1.65V (…)"

Minor remarks:

Page 6 line 156 – Please, do not use the term "electrochemical technology", it can be "technique" or "measurement" instead of "technology".

There are many grammar errors in the text

Author Response

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Reviewer 2 Report

The study mentioned in the manuscript is of great importance. The authors have done good work on to the development and characterization of titanium oxide coating on Mg alloy by 3 magnetron sputtering for stent application. Still I suggest that the authors can take care of the following issues before resubmitting the manuscript:

1. The authors did not mention any statistical analysis at all. It is unclear how many samples of each batch has been created and characterized.
2. Figure 5: Comparing (a) and (b), TiO₂ coated substrates still absorbs good amount of platelets. Can the authors may provide a quantitative comparison? I mean, what is the percentage reduction of platelets in the coated substrates?
3. Lines 225-227: The author should check whether the sentence ‘Generally, the smaller the…………….adhesion [27] is technically and grammatically correct.
4. It has been observed that cells adhesion improved a lot on the TiO2 coated MgZn substrates which exhibit greater contact angle (~80^o). Authors may need to examine whether the further increase in contact angle or hydrophobic substrates can provide even better cell adhesion.
5. Figure 6: no cells are shown in (a) at all. Can the authors provide a better resolution image of figure 6(b)? Moreover, figure 6 is the SEM image of cells on the substrates after 1 day of seeding. The author may provide similar SEM images after 3 days of seeding. After 3 days, both the number and morphology of the cells are expected to be improved.
6. Lines 244-254: Findings 2 in Conclusion may be rewritten as ‘the surface of TiO2 coated sample was less corroded more slightly than that of the substrate’

Comments for author File: Comments.pdf

Author Response

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Reviewer 3 Report

Comments on the paper:

The manuscript titled: "Properties of titanium oxide coating on Mg alloy by magnetron sputtering for stent application" is very interesting paper and worth of publication. I kindly suggest some additional explanations and corrections to make paper ready for publication.

1) In the "Introduction" it is stated that magnesium alloy is an excellent biological material for bioapsorbable implant, but its rapid and inhomogeneous corrosion in the physiological environment makes it often unsuitable for medical applications. In order to solve this problem, surface modification is carried out to improve their mechanical stability. In some cases, the implant should only remain in place for a limited period of time in the patient, followed by controlled degradation. The authors employed titanium dioxide as protection layer stated that it is chemically stable, but what is misunderstanding for me is whether the authors want it to be a degradable implant in a relatively short limited time or a long-term implant ?

2) In line 85, "Then, the appearance and corrosion products were analyzed by SEM and XRD", "and" should be replaced by "of"

3) Regarding the Figure 1, the SEM image of bare MgZn sample would be very useful to compare with the SEM image of TiO₂ coated MgZn sample. It can be more clearly seen what are the changes of the surface upon coating by titanium oxide.

4) In Figure 1, in Figure caption "...of the titanium oxide coating." should be replaced by " "...of the titanium oxide coated MgZn alloy."

4) In line 145, please insert that a noisy pattern proves the amorphous structure of the coating.

5) In Figure 4, in Figure caption "The corrosion morphologies of... " please insert that those are the SEM images.

6) Why didn′t author investigate corrosion behavior of bare and TiO₂ coated MgZn alloy immediately after sample preparation, and compare these findings with those after 14 days? It would be useful to have starting information and again after 14 days?

Author Response

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Round 2

Reviewer 1 Report

The manuscript has only been partially corrected, the answer to some of my comments (points: 2, 3, 4, 5) is insufficient. 

Please see the details in the attachment - my re-comments are in dark blue.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx