Microstructure, Mechanical Properties, Degradation Behavior, and Implant Testing of Hot-Rolled Biodegradable ZKX500 Magnesium Alloy

Round 1

Reviewer 1 Report

The authors investigated new type of Mg alloy, ZKX500 Mｇ−Zn-Zr for the biocomatibility,degradation behavior, and efficacy of osteosynthesis in vitro and in vivo. The topic is interesting and most study approach except for in vivo approach look appropriate. However, the results should be more appropriately discussed.
- Concerning Line 44, "The ZKX500 Mg-Zn-Zr alloy can be used to manufacture bone screws for the purpose of clinical applications [7,8].", The Mg alloys tested reference 7 and 8 are likely not exactly same as the materials tested in the present study. The differences of the material components from the previously tested materials must be explained. 
- Materials and Methods section should be divided in each assay. Now the in vitro assay, cell assay and in vivo assay are mixed and difficult to read.
- The medium immersed with ZKX500 specimens for 24 hours were used for cell viability assay. In vitro situation, how long does it take for the tested alloys to be dissolved completely.
- Concerning in vivo assay in minipigs, Wasn't the osteotomy performed before osteosynthesis with MG alloy plates and screws? If not, why wasn't a fracture model used for this kind of study?
- Concerning the results of animal implantation experiment, it was mentioned "they were not gas cavities (line 235)". For this reviewer's eyes, gas-like black spots were observed in the micro-CT images. The gas usually appears during dissolution of the implanted Mg alloys. If the authors believe this tested specimens do not induce any gas during their degradation, how can the degradation behaviour of the tested materials be explained? 

Author Response

Please see attached.

Author Response File: Author Response.docx

Reviewer 2 Report

This is a comprehensive study assessing the material properties of rolled Mg that can be used as a biodegradable implant. This is an emerging field in orthopaedics and one that is certainly needed. I commend the authors on their extensive analyses of material properties; however, I have one big concern, the in vivo study seems incomplete. Just showing micro-CT images is not sufficient. Here, the authors can either delete the in vivo study completely or present more results on histology and the biocompatibility analyses of the material in the animal model. This would significantly strengthen the paper. Moreover, the article has many figures at the moment, I suggest delete some from the main article (for example, data on corrosion or fracture testing) and attach them as supplementary files.

Please see some of my comments below that are somewhat applicable throughout the manuscript.

The article needs to be improved grammatically and figures need to be annotated correctly with consistently described figure legends inserted for each figure.

Overall English needs to be improved.

The acronyms used throughout the study are quite confusing example, difference between F and FH can be easily mixed and misunderstood.

Perhaps, the authors can use the actual name of alloys or think of other acronyms, however, this is just my personal preference.

The authors should also discuss their findings more and compare that to the existing literature. Just 18 articles referenced for such a comprehensive study seems too little.

Comments for author File: Comments.pdf

Author Response

Please see attached.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I do not agree with the author's reply about the animal studies. It cannot be published in its current format. Moreover, the article has not been improved to my satisfaction, the ethical committee approval should be in the main file and not the supplementary file as stated in the document sent. Please include that in the main file.

I am afraid the authors still haven't addressed my comments about the lack of in vivo assessment of results. Just microCT data would not suffice.

Overall, the article still needs to be improved. 

Author Response

We had revised the paper, please see attached.

Author Response File: Author Response.docx