Personalized Artificial Tibia Bone Structure Design and Processing Based on Laser Powder Bed Fusion

Round 1

Reviewer 1 Report

There are some specific comments need to be considered in the revised manuscript:

1. In abstract, authors reported the optimal laser process parameters are determined to print the porous parts. Revise the abstract that include what methodology adopted to derive the optimal process parameters. It would be better to specifically highlight what are the optimal parameters and their quantitative values.
2. The introduction session needs to be well reorganized. In the introduction section, the authors mentioned the existence of previous studies. What is the current problem? However, no proper justification has been given for selection of stainless steel 316L material. Why you selected only one powder element (i.e., stainless steel 316L) why not 2 or more elements.
3. In page 4, authors mentioned the main parameters (laser wavelength is 1075nm; spot diameter is 70-100μm; maximum molding size is 250mm×250mm×300mm; molding layer thickness is 20-100μm; scanning speed is 5-7000m/s). What was the operating values during the experiments (i.e., scanning speed 7 m/s, layer thickness of 20 μm).
4. The authors need to provide the references for most of the equations drawn from literatures, or in any form. Say Example Equation 3.1, 3.3 – 3.10, and so on through out the paper.
5. Authors used many assumptions such as, “Assuming that the irradiated powder is a uniformly absorbing scattering medium, the radiation transfer equation”, Assuming that only conductive heat transfer occurs between powders, This article assumes that the molten pool flow is Newtonian incompressible laminar flow, and does not consider the thermal expansion caused by the liquid phase of 316L stainless steel, Assuming a linear relationship between the surface tension coefficient and temperature, Assuming that the recoil pressure is a normal impulse applied to the surface, “It can be assumed that the material is isotropic”. How can you justify those assumptions can be met in practical experiments.
6. The dimensions of pores play very important role in tensile test results. Authors are requested to provide those details.
7. Authors need to correlate the numerical simulation with experimental results just before the conclusion section.

Author Response

Dear Editors and Referees,

     Thanks for your letter and for the referees’ comments concerning our manuscript entitled “Personalized Artificial Tibia Design and Processing Method Based on SLM” (Manuscript ID: machines-1601453). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied these comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the manuscript and uploaded as a “Supporting Information for Review Only” file. The responds to the editor and reviewers#1’ comments and the main corrections in the paper are as following:

Response: We express sincere thanks to the reviewer for the positive evaluation of our work. The reviewer’s questions and suggestions are very helpful for improving the quality of our manuscript. In the following, we revised the manuscript according to the reviewer’s comments and responded one by one.

Comment 1: In abstract, authors reported the optimal laser process parameters are determined to print the porous parts. Revise the abstract that include what methodology adopted to derive the optimal process parameters. It would be better to specifically highlight what are the optimal parameters and their quantitative values.

Response: Thanks for the reviewer’s comment. In the abstract, the description of the main methods and key parameters of the experiment is too general. In the resubmitted manuscript, the method of how to determine the optimal laser parameters and the final specific optimal parameters have been added.

Comment 2: The introduction session needs to be well reorganized. In the introduction section, the authors mentioned the existence of previous studies. What is the current problem? However, no proper justification has been given for selection of stainless steel 316L material. Why you selected only one powder element (i.e., stainless steel 316L) why not 2 or more elements.

Response: Thanks for the reviewer’s comment. An introduction to stainless steel 316L and research content have been added to the revised manuscript. This paper mainly explores under what laser parameters can obtain good quality porous stainless steel 316L parts and study the material properties of porous stainless steel 316L parts, not to study which material or which material ratio can obtain the best material properties. Therefore, only stainless steel 316L material is selected in this article.

Comment 3: In page 4, authors mentioned the main parameters (laser wavelength is 1075nm; spot diameter is 70-100μm; maximum molding size is 250mm×250mm×300mm; molding layer thickness is 20-100μm; scanning speed is 5-7000m/s). What was the operating values during the experiments (i.e., scanning speed 7 m/s, layer thickness of 20 μm).

Response: Thanks for the reviewer’s comment. We have added specific experimental parameters in the revised manuscript.

Comment 4: The authors need to provide the references for most of the equations drawn from literatures, or in any form. Say Example Equation 3.1, 3.3 – 3.10, and so on through out the paper.

Response: Thanks for the reviewer’s comment. We have added specific reference formulas in the revised manuscript.

Comment 5: Authors used many assumptions such as, “Assuming that the irradiated powder is a uniformly absorbing scattering medium, the radiation transfer equation”, Assuming that only conductive heat transfer occurs between powders, This article assumes that the molten pool flow is Newtonian incompressible laminar flow, and does not consider the thermal expansion caused by the liquid phase of 316L stainless steel, Assuming a linear relationship between the surface tension coefficient and temperature, Assuming that the recoil pressure is a normal impulse applied to the surface, “It can be assumed that the material is isotropic”. How can you justify those assumptions can be met in practical experiments.

Response: Thanks for the reviewer’s comment. It is undeniable that these assumptions are difficult to be fully satisfied in actual experiments, and only as close as possible. The first thing to be sure is that these assumptions will have an impact on the simulation structure and experimental results, but according to previous articles, it can be understood that these impressions are not the main factors, and the optimal laser parameters and porous stainless steel 316L explored in this experiment are not the main factors. The material properties have little impact, and do not affect the trend and analysis conclusions. At the same time, the content of these assumptions is more complex. Appropriate qualitative assumptions can simplify the mathematical model and simulation model, and can ensure the accuracy of the experimental results.

Comment 6: The dimensions of pores play very important role in tensile test results. Authors are requested to provide those details.

Response: Thanks for the reviewer’s comment. We have added porosity parameters for stainless steel 316L used in tensile tests in revised manuscript

Comment 7: Authors need to correlate the numerical simulation with experimental results just before the conclusion section.

Response: Thanks for the reviewer’s comment. We have added some analysis between numerical simulations and experimental results in the revised manuscript.

We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the corrections will meet with approval.

Once again, thank you very much for your comments and suggestions.

We look forward to your information about our revised papers and thank you for your good comments.   

Yours sincerely,

   All the authors of paper

Edited paper has been uploaded .please see the attachment.

Reviewer 2 Report

Author Response

Dear Editors and Referees,

Thanks for your letter and for the referees’ comments concerning our manuscript entitled “Personalized Artificial Tibia Design and Processing Method Based on SLM” (Manuscript ID: machines-1601453). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied these comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the manuscript and uploaded as a “Supporting Information for Review Only” file. The responds to the editor and reviewers#2’ comments and the main corrections in the paper are as following:

Reviewer #2

We express sincere thanks to the reviewer for the positive evaluation of our work. The reviewer’s questions and suggestions are very helpful for improving the quality of our manuscript. In the following, we revised the manuscript according to the reviewer’s comments and responded one by one.

Comment: The work is highly original and the methodology used has remarkable clinical applicability. But it has serious problems of style, grammatical punctuation and order. Style: continuously mixes present and past in the material and methods and results sections (eg line 136 "...equipment used...." line 138 "The main parameters are as follows:"). It is advised to rewrite everything in the past tense. In lines 37 and 38, "my country" is spoken in the first person, but the article is signed by 7 authors. Grammatical punctuation: There are numerous punctuation errors (Ex. Line 20 "...reconstructed; The...", line 22 "...structure. a laser...", line 35 "...; These bone.. ." Organization: The introduction is too long. In my opinion, all the text from lines 78 to 102 could be left out as discussion. On the other hand, in the material and methods there are phrases that do correspond to the introduction (eg lines 131-135). It is difficult to understand that the methodology of the reconstruction of the tibia is found in the results section. The conclusions are also vague and too long.

Response: Thanks for the reviewer’s comment. The style, grammar, punctuation, order, etc. of the relevant paragraphs of the article have been revised and self-checked in the resubmitted manuscript. At the same time, the experimental content, process and results of the predecessors in the introduction are summarized and simplified. At the same time, the conclusion part has been revised.

We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the corrections will meet with approval.

Once again, thank you very much for your comments and suggestions.

We look forward to your information about our revised papers and thank you for your good comments.   

Yours sincerely,

Youping Gong

Reviewer 3 Report

The SLM Additive manufacturing process is adopted in this work to print personalized bone implants. The authors have adopted heat transfer-based analysis and simulation to select the optimal process parameters. Despite the efforts of the authors, this reviewer has the following critical concerns about the manuscript:  

1. Although the authors have put effort into the manuscript, the presented work and its individual steps do not appear to be novel or new in any form, i.e., there are many studies in the literature adopting the heat transfer models in SLM for identifying optimal process parameters and for printing customized implants with acceptable performance. The authors should highlight what is different or new in their work compared to the literature. It is also not clear whether any of the heat-transfer models or details in chapter 3 are contributions of authors or are just directly extracted from the literature and adopted for simulation purposes.
2. In 4.1, the authors mention that "After comprehensively considering the pore size, porosity, equivalent elastic modulus, SLM molding constraint and tensile strength, the regular octahedron structure with square cell body unit side length a = 1.2 mm and pillar diameter d = 0.35 mm is selected as the best parameter for the design of porous structure of tibial implant. ". What comprehensive analysis? no information on the reasoning behind this design is presented. 

Author Response

Dear Editors and Referees,

Thanks for your letter and for the referees’ comments concerning our manuscript entitled “Personalized Artificial Tibia Design and Processing Method Based on SLM” (Manuscript ID: machines-1601453). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied these comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the manuscript and uploaded as a “Supporting Information for Review Only” file. The responds to the editor and reviewers#3’ comments and the main corrections in the paper are as following:

Reviewer #3

We express sincere thanks to the reviewer for the positive evaluation of our work. The reviewer’s questions and suggestions are very helpful for improving the quality of our manuscript. In the following, we revised the manuscript according to the reviewer’s comments and responded one by one.

Comment 1: Although the authors have put effort into the manuscript, the presented work and its individual steps do not appear to be novel or new in any form, i.e., there are many studies in the literature adopting the heat transfer models in SLM for identifying optimal process parameters and for printing customized implants with acceptable performance. The authors should highlight what is different or new in their work compared to the literature. It is also not clear whether any of the heat-transfer models or details in chapter 3 are contributions of authors or are just directly extracted from the literature and adopted for simulation purposes.

Response: Thanks for the reviewer’s comment. There is no significant difference between the method of determining the optimal parameters and the previous methods, mainly through the method of controlling variables to determine the optimal process parameters. However, the model established before the simulation is more comprehensive. For the entire SLM molding process, the heat source model, the reflection model of the laser between the metal powders, the heat transfer model between the metal particles, the molten pool model of the metal powder, and the model of the hole in the molding are established respectively. The heat transfer model of the heat inside the porous part when the part is used. The heat transfer model inside the porous part is a new model established after improving the heat transfer model of the composite material. In this paper, since the inside of the porous material is not a solid material, but air, Therefore, the heat transfer model of porous materials established in this paper is based on the heat transfer model between solid and gas. At the same time, due to the large number of pores in the porous model, the heat transfer does not end at one time. There are certain differences and innovations in the model, which are supplemented here in the revised manuscript for this model.

Comment 2: In 4.1, the authors mention that "After comprehensively considering the pore size, porosity, equivalent elastic modulus, SLM molding constraint and tensile strength, the regular octahedron structure with square cell body unit side length a = 1.2 mm and pillar diameter d = 0.35 mm is selected as the best parameter for the design of porous structure of tibial implant. ". What comprehensive analysis? no information on the reasoning behind this design is presented.

Response: Thanks for the reviewer’s comment. In Section 4.1 of the revised manuscript, the parameters of the initially determined four groups of regular octahedral porous structure models and the specific parameters after related calculations and finite element calculations are added, and the reason for choosing "regular octahedral structure with square cell unit side length = 1.2 mm and column diameter d = 0.35 mm" as the optimal design parameters for the porous structure of tibial implant.

We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the corrections will meet with approval.

Once again, thank you very much for your comments and suggestions.

We look forward to your information about our revised papers and thank you for your good comments.   

Yours sincerely,

Youping Gong

Reviewer 4 Report

The paper presents a combination of concepts related to the manufacturing of porous structures via Laser Powder Bed Fusion of stainless steel 316L. Authors need to perform intensive editing work before sending the paper to be considered for publication. It has several flaws that should be addressed:

1. The topic is about tibia bone structure design using AM technologies, but there is a major defect on the main concept. Current implants made with Additive manufacturing do not use stainless steel as the primary material, due to the relative high density and low biocompatibility in comparison to other materials like titanium-niobium alloys. Authors should re-consider their case study focusing in other applications requiring lightweight properties.
2. There is no any mention about the necessity of providing biocompatibility via osseointegration and stress shielding mechanisms/properties. This aspect could receive more interest and more scientific soundness.
3. Quality of figures is very poor and difficult to compare mechanical properties (stress-strain) with those obtained from a literature review and from the bone properties. Also, there is no any discussion about the relevance of the model when compared to cortical/porous bone properties. Authors just generalize properties in the range of 10-40 Gpa of modulus of elasticity which is to broad.
4. SEM images are presented in very poor quality.
5. Literature review is very general, there are several works related to lattice structures in implants which are not being addressed in the manuscript. 
6. Models related to heat conduction problems are adapted from well-known literature and authors are not presenting new approaches to the study of the heat transfer in porous parts (or the originality is not well explained).
7. Laser Powder Bed Fusion is the correct, ASTM-standardized name of the process, not SLM.

Author Response

Dear Editors and Referees,

Thanks for your letter and for the referees’ comments concerning our manuscript entitled “Personalized Artificial Tibia Design and Processing Method Based on SLM” (Manuscript ID: machines-1601453). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied these comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the manuscript and uploaded as a “Supporting Information for Review Only” file. The responds to the editor and reviewers#4’ comments and the main corrections in the paper are as following:

Reviewer #4

We express sincere thanks to the reviewer for the positive evaluation of our work. The reviewer’s questions and suggestions are very helpful for improving the quality of our manuscript. In the following, we revised the manuscript according to the reviewer’s comments and responded one by one.

Comment 1: The topic is about tibia bone structure design using AM technologies, but there is a major defect on the main concept. Current implants made with Additive manufacturing do not use stainless steel as the primary material, due to the relative high density and low biocompatibility in comparison to other materials like titanium-niobium alloys. Authors should re-consider their case study focusing in other applications requiring lightweight properties.

Response: Thanks for the reviewer’s comment. Stainless steel is one of the most widely studied materials in metal additive manufacturing, especially 316L stainless steel has the advantages of high strength, low density, corrosion resistance, and good biocompatibility, and is widely used in medical biological bones. So it can be used to design the tibial bone structure. But as you said, stainless steel 316L has no significant advantages compared to titanium-niobium alloys in some aspects, We are also studying the 3D printing process of porous structure of metals with good biocompatibility, such as titanium alloy and tantalum alloy.

Comment 2: There is no any mention about the necessity of providing biocompatibility via osseointegration and stress shielding mechanisms/properties. This aspect could receive more interest and more scientific soundness.

Response: Added introduction to stress shielding and biocompatibility and the need to address stress shielding and provide biocompatibility in the revised introduction.

Comment 3: Quality of figures is very poor and difficult to compare mechanical properties (stress-strain) with those obtained from a literature review and from the bone properties. Also, there is no any discussion about the relevance of the model when compared to cortical/porous bone properties. Authors just generalize properties in the range of 10-40 Gpa of modulus of elasticity which is to broad.

Response: Thanks for the reviewer’s comment. Bone is generally composed of bone dense and cancellous, and the cancellous area is composed of a large number of bone trabecular structures The outer layer is bone dense, the inner is irregular porous structure, and the porosity gradually decreases inward, showing a gradient change trend. In the article design and 3D printing of interbody fusion cage based on TPMS porous structure introduces a design method of metal porous structure in detail, which mainly focuses on the mechanism and method of how to prepare these metal porous structures, so it is not introduced in detail, which is supplemented in the paper.

Comment 4: SEM images are presented in very poor quality.

Response: Thanks for the reviewer’s comment. The relevant SEM diagrams have been enlarged and retyped in the revised article for the convenience of readers.

Comment 5: Literature review is very general, there are several works related to lattice structures in implants which are not being addressed in the manuscript. 

Response: Thanks for the reviewer’s comment. We edited literature review as reviewers’s advice, we add some references about lattice structures in implants:

[12] Taniguchi N, Fujibayashi S, Takemoto M, et al. Effect of pore size on bone ingrowth into porous titanium implants fabricated by additive manufacturing: An in vivo experiment. Mater Sci Eng C Mater Biol Appl. 2016. 59: 690-701.

[13]Charbonnier, B.; Manassero, M.; Bourguignon, M.; Decambron, A.; El-Hafci, H.; Morin, C.; Leon, D.; Bensidoum, M.; Corsia, S.; Petite, H.; et al. Custom-made macroporous bioceramic implants based on triply-periodic minimal surfaces for bone defects in load-bearing sites. Acta Biomater. 2020, 109, 254-266

Comment 6: Models related to heat conduction problems are adapted from well-known literature and authors are not presenting new approaches to the study of the heat transfer in porous parts (or the originality is not well explained).

Response: Thanks for the reviewer’s comment. The model for heat conduction is quoted from the composite heat transfer model in an article on composite heat transfer. In this paper, since the interior of the porous material is not a solid substance, but air, the heat transfer of the porous material established in this paper is The model is based on the heat transfer model between solid and gas. At the same time, due to the large number of pores in the porous model, the heat transfer does not end at one time, so it is different and innovative compared to the composite heat transfer model of the cited article. It is also supplemented here in the revised manuscript.

Comment 7: Laser Powder Bed Fusion is the correct, ASTM-standardized name of the process, not SLM.

Response: Thanks for the reviewer’s comment. Relevant revisions have been made as requested in the revised article

We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the corrections will meet with approval.

Once again, thank you very much for your comments and suggestions.

We look forward to your information about our revised papers and thank you for your good comments.   

Yours sincerely,

Youping Gong

Round 2

Reviewer 1 Report

Dear Authors, Congratulations for the improvised paper.

Author Response

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Reviewer 2 Report

Author Response

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Reviewer 3 Report

Given the authors' response and after clarifying the contributions, the paper appears to be acceptable for publication. 

Author Response

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Reviewer 4 Report

Authors made significant changes to the manuscript to present it in a better condition to be published. There are still few aspects that could be addressed to increase its scientific soundness:

1. Authors are still naming the process as Selective Laser Melting but this is a commercial name. The correct, standardized name according ASTM standards is laser powder bed fusion. This should be corrected thoroughly in the paper.
2. There is no any discussion on the reason to select that particular lattice structure (cubes). There are other in the literature that have been tested to fabricate orthopedic and surgical implants. See this article: Peto, Marinela, et al. "A Proof of Concept Study of the Mechanical Behavior of Lattice Structures Used to Design a Shoulder Hemi-Prosthesis." Journal of Engineering and Science in Medical Diagnostics and Therapy 4.3 (2021).

Author Response

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Author Response File: Author Response.pdf