Finite Element Analysis in the Balancing Phase for an Open Source Transfemoral Prosthesis with Magneto-Rheological Damper

Round 1

Reviewer 1 Report

The authors did finite element simulation for the stress analysis of a transfemoral prosthesis. However, in current form, the manuscript lacks novelty to warrant publication. 

1. Suggest the authors to highlight the differences between their work and existing literature. Are there new contributions in the simulations?

2. For the testing, individual components are tested. How are these correlated to the performance of the whole prothesis? 

3. Any standard test used for the testing? 

Author Response

Response to reviewers “Finite Element Analysis in the Balancing Phase for an Open Source Transfemoral Prosthesis with Magneto-rheological Damper”

We would like to thank the anonymous reviewers for the valuable suggestions which improve the overall quality and understanding of the paper for any reader.

We have prepared a point-by-point response to the reviewer. Additionally, and for clarity, we have added a marked copy and a clean copy (inventions-2102838 MARKED.docx  and inventions-2102838 CLEAN.docx respectively). The marked version contains changes made with MS-Changes tool, whereas the clean version contains added and already deleted passages. We broke down the answers to the reviewer's concerns in different points as follows.

REV 1

The authors did finite element simulation for the stress analysis of a transfemoral prosthesis. However, in current form, the manuscript lacks novelty to warrant publication. 

1. Suggest the authors to highlight the differences between their work and existing literature. Are there new contributions in the simulations?

We did not find a detailed simulation study for a lower limb prosthesis that included fatigue behavior. With that in mind, we performed a life prediction for the prosthesis as a contribution. Moreover, we show how easy it is to 3D manufacture the foot combining the strength of a carbon composite and the almost-freeform fabrication capabilities of Additive Manufacturing. The last paragraph of the introduction was modified to reflect that. In addition, the inclusion of the MR damper helps to dissipate energy, thus transferring less force to the patient.

Finally, we include blueprints on the web version so anyone can reproduce a tested design.

2. For the testing, individual components are tested. How are these correlated to the performance of the whole prothesis? 

The performance of the prosthesis as a whole was not tested. The computational cost was extremely expensive when we tried to run it. We approached the problem by applying the maximum force on each component, which we believe is the most critical scenario.

3. Any standard test used for the testing? 

Yes, testing for the housing shell fiberglass composite was inspired in ASTM D638 – IV “Standard Test Method For Tensile Properties Of Plastics” We would like to direct the reviewer to section 3.1. We added the description of the standard to better reflect that.

We thank reviewer number 1 for the time dedicated to read the manuscript and the valuable feedback

Reviewer 2 Report

The manuscript 'Finite Element Analysis in the Balancing Phase for an Open Source Transfemoral Prosthesis with Magneto-rheological Damper' is very well written on an interesting subject. 

So, it would be advisable to publish it after the following minor advisors:

1. In line 69 after the word 'nodes' a dot is needed instead of a comma 

2. The parameter of Vi on equation 2 was not described 

3. The graphs in figure 4 has very small size, please resize them. 

4. The 5a graph is dull, please corrected it.

5. The future prospects are not presented, please add a sentence at the end of the manuscript. 

Author Response

Response to reviewers “Finite Element Analysis in the Balancing Phase for an Open Source Transfemoral Prosthesis with Magneto-rheological Damper”

We would like to thank the anonymous reviewers for the valuable suggestions which improve the overall quality and understanding of the paper for any reader.

We have prepared a point-by-point response to the reviewer. Additionally, and for clarity, we have added a marked copy and a clean copy (inventions-2102838 MARKED.docx  and inventions-2102838 CLEAN.docx respectively). The marked version contains changes made with MS-Changes tool, whereas the clean version contains added and already deleted passages. We broke down the answers to the reviewer's concerns in different points as follows.

The manuscript 'Finite Element Analysis in the Balancing Phase for an Open Source Transfemoral Prosthesis with Magneto-rheological Damper' is very well written on an interesting subject. 

So, it would be advisable to publish it after the following minor advisors:

1. In line 69 after the word 'nodes' a dot is needed instead of a comma 

In line 69 (page 2) we neither see a comma nor the need for a period. Perhaps the during the change of format the problem was corrected.

2. The parameter of Vi on equation 2 was not described 

Thank you for pointing that out. It was added to the manuscript

3. The graphs in figure 4 has very small size, please resize them.

Thank you. The graph has been improved

4. The 5a graph is dull, please corrected it.

Thank you. The graph has been improved

5. The future prospects are not presented, please add a sentence at the end of the manuscript. 

Thank you. The following paragraph was added “Finally, in this version, the housing shell was manufactured as a laminated composite. With 3D printers becoming even more popular, cheaper, and able to print in larger formats, the housing shell could be manufactured in a 3D composite printer. This possibility would make it easier to change the small radii where the highest stress concentration occurs, hence improving the life of the prosthesis.”

Reviewer 3 Report

The paper “Finite Element Analysis in the Balancing Phase for an Open Source Transfemoral Prosthesis with Magneto-rheological Damper” presents a finite element simulation for the stress analysis of a transfemoral prosthesis with damping for a 100 kg person in the balancing phase. Overall, a positive recommendation can be provided after reviewing some comments highlighted below.

Comments:

1.      A graphical abstract would add interest to catch the eye

2.      Please introduce clearly the novelty of the paper in one sentence and include it in the introduction

3.      A nice overview of the literature has been done but adding some references on the use of simulation and modelling to improve parts with 3D printing technologies will enrich the introduction, such as:

·        https://doi.org/10.3390/polym14112177

·        https://doi.org/10.1007/978-3-031-05230-9_24

·        https://doi.org/10.1089/3dp.2021.0008

4.      When including equations or Figures there has been a problem with the journal's template. The justification of the paragraphs is incorrect.

5.      Figures 5 could be of better quality (labels are difficult to read).

6.      The conclusions could be enriched and presented in bullet format.

7.      I think it would be interesting to consider possible points of improvement of the design as future lines in the conclusions.

As a summary and having to account that the research is useful as a practical guidance to both the academic community and industry thus, I believe the draft should be a paper for the journal if minor changes are made.

Happy Holidays and New Year.

Author Response

Response to reviewers “Finite Element Analysis in the Balancing Phase for an Open Source Transfemoral Prosthesis with Magneto-rheological Damper”

We would like to thank the anonymous reviewers for the valuable suggestions which improve the overall quality and understanding of the paper for any reader.

We have prepared a point-by-point response to the reviewer. Additionally, and for clarity, we have added a marked copy and a clean copy (inventions-2102838 MARKED.docx  and inventions-2102838 CLEAN.docx respectively). The marked version contains changes made with MS-Changes tool, whereas the clean version contains added and already deleted passages. We broke down the answers to the reviewer's concerns in different points as follows.

The paper “Finite Element Analysis in the Balancing Phase for an Open Source Transfemoral Prosthesis with Magneto-rheological Damper” presents a finite element simulation for the stress analysis of a transfemoral prosthesis with damping for a 100 kg person in the balancing phase. Overall, a positive recommendation can be provided after reviewing some comments highlighted below.

Comments:

1. A graphical abstract would add interest to catch the eye

Thank you. A graphical abstract was added

2. Please introduce clearly the novelty of the paper in one sentence and include it in the introduction.

We did not find a detailed simulation study for a lower limb prosthesis that included fatigue behavior. With that in mind, we performed a life prediction for the prosthesis as a contribution. Moreover, we show how easy it is to 3D manufacture the foot combining the strength of a carbon composite and the almost-freeform fabrication capabilities of Additive Manufacturing. The last paragraph of the introduction was modified to reflect that. In addition, the inclusion of the MR damper helps to dissipate energy, thus transferring less force to the patient. Finally, we include blueprints on the web version so anyone can reproduce a tested design.

3. A nice overview of the literature has been done but adding some references on the use of simulation and modelling to improve parts with 3D printing technologies will enrich the introduction, such as:

• https://doi.org/10.3390/polym14112177
• https://doi.org/10.1007/978-3-031-05230-9_24
• https://doi.org/10.1089/3dp.2021.0008

Thank you. The references have been included along the paper

4. When including equations or Figures there has been a problem with the journal's template. The justification of the paragraphs is incorrect.

Thank you. It looks like when the draft was changed into the journal´s template by the editorial office, some misalignment was introduced. We corrected that issue.

5. Figures 5 could be of better quality (labels are difficult to read).

Thank you. Figures have been enhanced

6. The conclusions could be enriched and presented in bullet format.

We believe the journal´s guidelines require conclusions as indented text and not as bullets. However, we have updated the conclusion to reflect the inclusion of blueprints and possible improvements.

7. I think it would be interesting to consider possible points of improvement of the design as future lines in the conclusions.

Thank you. The following paragraph has added “Finally, in this version, the housing shell was manufactured as a laminated composite. With 3D printers becoming even more popular, cheaper, and able to print in larger formats, the housing shell could be manufactured in a 3D composite printer. This possibility would make it easier to change the small radii where the highest stress concentration occurs, hence improving the life of the prosthesis.”

As a summary and having to account that the research is useful as a practical guidance to both the academic community and industry thus, I believe the draft should be a paper for the journal if minor changes are made.

Happy Holidays and New Year.

We thank the reviewer for the valuable insights and time spent reading the paper. We wish you a happy new year as well.

Round 2

Reviewer 1 Report

The authors did a finite element analysis for the prosthesis fabricated by additive manufacturing. While the manuscript is generally well executed, there are several issues that should be addressed before further consideration for publication.

1. The authors planned to only customise the socket using additive manufacturing. In this case, will the FEM done on the individual component be representative of the end use application/design?

2. As additive manufacturing comprises of several techniques, the part properties differ due to the processing techniques used. In addition, the processing conditions, eg. part orientation, affect the properties as well. Any consideration and discussion for this? 

3. Will the customised part be produced by reverse engineering? Any discussion on how the accuracy of the fabricated part can deviate from the FEM model?

Author Response

Response to “Finite Element Analysis in the Balancing Phase for an Open Source Transfemoral Prosthesis with Magneto-rheological Damper”

We would like to thank the editor and reviewers for their valuable time spent reading and making valuable suggestions to improve the overall quality of the manuscript. We hope the answers clarify the editor and reviewer´s concerns. The response is organized by answering each reviewer's concerns individually, and they are placed right underneath each question

Rev 1.

1. The authors planned to only customise the socket using additive manufacturing. In this case, will the FEM done on the individual component be representative of the end use application/design?

Thank you for the observation. The socket is the adapter between the prosthesis and the remaining limb. So, it needs to be customized depending on each patient´s needs. Whether it is fabricated via AM or not, is up to the final user.

2. As additive manufacturing comprises of several techniques, the part properties differ due to the processing techniques used. In addition, the processing conditions, eg. part orientation, affect the properties as well. Any consideration and discussion for this? 

Thank you for the observation. Yes, indeed, the mechanical performance of AM parts is heavily dependent on printing direction, cellular infill, and volume fiber fraction, among other factors. As a matter of fact, references [11], [33], and [34] discuss and present how mechanical properties are affected by said variables. As supplementary material, we included the *.STL files for the parts so anyone can fabricate them as designed. We changed lines 86 and 461 to reflect that inclusion. We also added the printing parameters on the blueprints for the prosthetic foot, as follows:

Printed on Markforged Two ®

Matrix: Onyx ®

Reinforcement: carbon fiber

Infill: 100% solid

Fiber orientation: concentric

Fiber volume fraction: 32%

Finally, we added a cautionaty note on the conclusions as suggested by the reviewer, “As with any design, geometric or shape deviation from initial specifications may induce unwanted results, the prosthetic foot also has to be built following printing direction, cel-lular infill, volume fiber fraction, among other factors choices as described on the blue-prints.”

3. Will the customised part be produced by reverse engineering? Any discussion on how the accuracy of the fabricated part can deviate from the FEM model?

Thank you for the observation. We did not perform a sensitivity analysis for geometric deviation. However, the stresses should increase in the case of a reduction of dimensions by say a manufacture defect. However, the high safety values should guarantee the prosthesis´ safety performance.

We thank reviewer 1 for the valuable suggestions and time reading the manuscript.

Round 3

Reviewer 1 Report

NA