In Vitro Electrochemical Corrosion Assessment of Magnesium Nanocomposites Reinforced with Samarium(III) Oxide and Silicon Dioxide Nanoparticles

Round 1

Reviewer 1 Report

According to definition used in corrosion science and corrosion technology, corrosion is undesired phenomenon. Magnesium implants, however, should completely dissolve in bodily fluids directly after bone fusion. In this context implant dissolving is a highly desirable, if necessary, phenomenon. Therefore, it cannot be called corrosion. An appropriate comment on this matter should be announced in the introduction. I suggest use the term “implant dissolution” (or decay) in place of corrosion. In further parts of my review I use the word corrosion (of Mg implant) in quotation marks.

What do Authors mean telling “improved corrosion properties”, “superior corrosion resistance” or “deteriorated corrosion results” (lines 60, 65, 77  90 and other places)? Superior corrosion behavior - slow or fast "corrosion"?

Line 105 - Authors describe the composite synthesis route as „hybrid microwave sintering, followed by hot extrusion, as described by Kujur et al [22]. Unfortunately, the Ref. [22] isn’t an article of Kujur but the paper of  Evans, titled: Past, Present, and Possible Future Clinical Applications of the Lanthanides. In Biochemistry of the Lanthanides; Springer: 1990; pp. 391-425. (34 pages).

In my opinion, much more details relating sample fabrication is necessary in „Methods” chapter, including shape and dimensions of reinforcement particles (spheres, needles, fibers?) and homogenization details. Authors write  „success in fabrication” but don't talk about specific procedures.  

Lines 71/72: „For implants use, however, RE elements carry the risk of toxicity which limits their percentages in the used alloys”. This sentence should be developed.  What doses of magnesium, REs and SiO₂ in the body are becoming dangerous for humans? How much does the average magnesium implant mass? How long does bone fusion take and how long does the implant dissolve in bodily fluid? In what form do the oxide phases (Sm₂O₃ and SiO₂) remain in the body after “corrosion”? These pieces of information are absolutely necessary for the readers.

Sub-chapter 2.3. „Electrochemical corrosion tests” – Authors write: „although immersion test data would have been beneficial to determine  the corrosion rates…” and, then, they indicate advantages of polarization- and impedance techniques. In this article, any immersion mass-loss tests are completely omitted, to the detriment of the entire study. The electrochemical tests are described superficially, without going into the mechanisms of the processes. The impedance / polarization data are determined using a computer program (electrochemical station software) without in-depth discussion. At this point a number of questions and doubts arise:

1.       Which solution agent plays the role of “corrosion” depolarizer? (oxygen, hydrogen ion?)
2.    Why Tafel slopes of partial electrode processes are so large (about 0.3 and 0.4 V/dec)?
3.      Which is the role of reinforcement phases in view of local corrosion phenomena (possibility of pitting and stress corrosion cracking, especially at evolution of large amounts of hydrogen gas)?
4.    Why there is so large difference (17 x) in “corrosion” rates of pure Mg and high purity Mg?
5. Other comments:            

1. Title:  why Samarium “oxide” (Sm₂O₃) and silicon “dioxide” (SiO₂). Maybe it would be better, samarium (III) oxide ?
2. Line 176: symbols in Eq.2 are a little bizzare or even eccentric (mass-, mol-, volume fractions should be generally symbolized by x_i, atomic mass (or better: molar mass) by M_i (but not a_i,) etc.
3.  What does it HEPES mean? (Tab.1) – its concentration is defined unintelligibly.
4.  Line 176: “n_i is the valence electrons of each element” (?? it sounds ambiguously!)      
5. Table 2: Which was the polymorfic variety of SiO₂ (quartz, crystobalit, etc?) 

In spite of my criticism, the topic of the paper is interesting and of high importance. However, the article, as it stands, has too many weaknesses for me to recommend it for publication. Therefore, major revision of the manuscript is necessary, according to comments provided.

Author Response

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Reviewer 2 Report

Thank you for the opportunity to review the article entitled In vitro Electrochemical Corrosion Assessment of Magnesium Nanocomposites Reinforced with samarium Oxide and silicon dioxide Nanoparticles.  The article is interesting, however, it contains a few minor bugs that need to be corrected before further editing. Detailed comments are presented below.

1. The authors should describe the parameters of the SEM measurement in more detail and provide more information about the manufacturer of the SEM microscope.
2. Line 148 Is HCO3- , should be HCO₃^-.
3. Table 1. Is Na₂S_o4, should be Na₂SO₄.
4. Equations 1-3 are disproportionately larger than the rest of the text.
5. Figure 2. SEM parameters should be placed in the Methods section, not under the micrographs. Only the scale should remain with the micrographs.
6. Figure 3. I suggest enlarging both graphs, because the text under the axes is not legible. Moreover, the axes should have their own captions (e.g. sample symbol, microhardness with the unit in parentheses).
7. Numerical results in tables should include standard deviations (if possible).

Author Response

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Reviewer 3 Report

1. Figure 8, there is no error bar, please add it and data number and the analysis of significant difference, including figure 3.
2. Table 4, there is HP-Mg and pure Mg, should cite the literatures. It would be better to mention their ingredients.
3. It would be better to indicate the nanoparticles by arrows in Figure 2.
4. Figure 8, "corrosion rate", isn't it the corrosion resistance?
5. Please polish the sentences and words.
6. "3.1. SEM investigation", it would be better to show the SEM images of localized agglomeration of nanocomposite in the Mg alloys with higher-content nanocomposite, to prove the higher localized agglomeration of nanocomposites would result in the higher corrosion rate. 
7. "Conclusion" "These pure magnesium samples was manufactured using.......to make the nanocomposites", here, "make the nanocomposites" should be "Mg alloys with nanocomposites", right?
8. The authors prepared the Mg-Sm2O3 and Mg-SiO2 for future biodegradable materials, i am curious whether the authors consider the biocompatibility of Sm2O3 and SiO2 nanoparticles and biodegradability, and the metabolism of nanoparticles in vivo?

Author Response

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Round 2

Reviewer 1 Report

Authors have some problems with fundamentals of chemistry and electrochemistry and they highly complicate simple questions.

Conversion of corrosion rate expressed in [mA/cm2] into [mm/y] is very simple but the Authors make the problem unnecessarily bizarre. One can get an impression that Equations (1) – (3) are introduced only with the intention to improve the “scientific image” of the paper. In principle, notation of Eqs 1 - 3 is clumsy and full of inconsistency. Authors’ narration (“corrosion rate was then measured using Faraday’s law”, “n is the valence electrons of each elemens” (and in many other places) testifies to their very low experience in corrosion.

The mentioned conversion can be applicable to the alloy whose atoms oxidize and enter test solution in the form of adequate cations. Unfortunately, particles of reinforcing phases (Sm2O3 and SiO2) do not oxidize, so the Equation (1) is not relevant here. The additional explanations in lines 200 and 201 are naive, completely unnecessary and should be removed. Concentration of HEPES is still defined incomprehensively. That’s true, Authors cite the reference [37] (Oyane) in the Table caption but earlier (lines 169 and 170) they cite the paper of Oyane as Ref.[25]. Nevertheless, even the authors of Ref.[25] made an obvious mistake, then it shouldn’t be duplicated anymore.

Some of other rebuttals are also not satisfactory to me.

In conclusion, I believe that the changes introduced by the Authors did not improve the quality of the article. For this reason, I cannot recommend its publication.

Author Response

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Reviewer 2 Report

All my comments have been taken into account. I recommend publishing this article.

Author Response

The authors would like to thank the reviewer for their thoughtful review.

Reviewer 3 Report

I agree to accept in present form.