Mechanical and Fatigue Behavior of Cellular Structure Ti-6Al-4V Alloy Femoral Stems: A Finite Element Analysis

Round 1

Reviewer 1 Report

Dear author you have done a nice work

In the mean time I have some coments:

• First of all please enhance the quality of figures and tables. it is hard to see the details
• The figures are to small
• You must explain more crearly your work. It is full of colour but difficult to follow.

Author Response

• The figures are to small
• Authors: This has been corrected
•  
• You must explain more clearly your work. It is full of colour but difficult to follow.
• Authors: This has been corrected and Enhanced

Reviewer 2 Report

Dear Authors,

In my opinion, the work is an important contribution to the development of new metrics for medical applications. The use of FEA as a tool to assess the strength of titanium composite design options has demonstrated the flexibility in the selection of design parameters for developing femoral stems.
There are no conceptual concerns on my part.
There is a need for correct formatting of the article according to the template (tables, illustrations, bibliography).

 

Author Response

There is a need for correct formatting of the article according to the template (tables, illustrations, bibliography). 

Authors response: This has been updated in the manuscript

Reviewer 3 Report

Dear authors,

The reviewed work: Mechanical and Fatigue Behaviour of Cellular Structure Ti-6Al-4V Alloy Femoral Stems: A Finite Element Analysis by N.F. Al Zoubi et al. (applsci-1625027) concerns the development of a lightweight bone endoprosthesis project with better functional properties. The variable load associated with human movement is one of the main causes of implant failure or rejection by the body. The cause of this condition appears to be the improperly selected stiffness of the prosthesis stem in relation to the bone. I consider the concept of making them through 3D printing with a porous pin structure right. The subject of the article therefore concerns issues that are very important for a human being, and the ways of its implementation should be considered very modern and up-to-date.

The research carried out and presented is very interesting, but unfortunately it is limited only to the numerical analysis of the phenomenon. Their lack of physical verification. The description of the experiment is too complex and leads to problems with understanding. The results obtained are widely presented, and sometimes even too detailed, which also does not improve the ease of reading. On the other hand, there are no results that would allow you to relate your project to the current state of knowledge (e.g. solid stems). There is also a clear lack of analyzes that generalize the obtained results.

I also recommend making the following corrections:

Page 2

• Section S.1 - … to 1,537,422 in 2050 with annual growth rate … - Why such precise data, since we are only 2022;
• S.2 - …significantly reduce the stress shielding - incorrect stylistic construction, the sentence suggests a reduction and deterioration of the material properties;
• Chapters are incorrect throughout the article, due to converting word file to pdf;
• S.4 - In this section, various essential aspects … - the content of this section is trivial and can be omitted;

Page 3

• S.1 - Square pores microstructure … - no explanation for this choice;

- … porosities ranging from 10% to 90% … - at such a value it would not be appropriate to speak of an openwork structure, not a porous one;

• pattern numbering errors, correct throughout the article;
• Table 1 - the porosity values given in the table are inconsistent with the further content, e.g., with 37, 49, 55, 59 [%];

Page 4

• Figure 1

- illegible descriptions on diagrams;

- stress-strain - do you mean “engineering strain – stress”;

- use different symbols and colors for each curve;

- the legend is illegible and too complicated;

- the strain axis has titles incorrectly written;

 - which means notation “Strain (mm/mm);

• S. 2 - The designed porous cellular structures … and added to the stems design groups. –

- It is not clear what variants were created based on the 30, 50 and 70% porosity!;

- What are the structures D5, D10, and D15;

- The fifteen designs were integrated… - This finding suggests that another 15 structures were created;

- The stem–bone assembly was fixed into cylindrical shape epoxy… - I don't understand again, are they numerical or physical simulations? How does epoxy affect the joint and system stiffness? Or is it negligible?

- Generally - this entire paragraph is very vague and requires detailed elaboration.

Page 5 and next

• Figure 2, 4, 7, 8 - These are examples of a lack of adequate rethinking of how to present them. They have the same content and as such are too detailed. For example, one should leave one example graph or not, and add a basic graph summarizing this issue for the entirety of the research variants carried out. The results and drawings can be included in the supplement to the article.
• Fig. 2 - Problem again. We have 3 porosities, and 4 are shown in the figure. Additionally, they are not ordered in terms of increasing porosity. Lack of clarity about D markings ... No dimensions, What are L1, L2, L3? L2 is confused with the symbol in formula (1).
• Fig. 4 - The drawing is illegible. It is better to show selected cases and discuss the rest in the text or in a graph.
• Fig. 7 and 8 - Too much information, no summary study available. Not understanding in the figure what the D1-15 projects are;

Page 6

• S.1 - A more detailed description is needed to explain why P1 and P2 were added to P0 (what were their values).
• S.2 - The assembly was meshed with a mesh size of 3 mm using C3D10 quadratic tetrahedral elements, which was used based on a previous sensitivity study - Does it mean that the FEM model had a mesh size of 3 mm? How does this relate to the size of the pore cell? What does "C3D10" mean?

Page 7

• Table 3 - Where did the P0 values come from and on what basis?
• S.1 - Von Misses is a surname and is spelled in capital letters.

- I do not understand why the division into Figures 4 and 7, 8 and 9 was written. What is this for? Any understatement?

Page 8

• stress ratios equal 0.1 and 1.0… - And the system overload?

Page 11

• … ten increments at the stem head - Does this mean that the load was increased by leaps and bounds? Nothing was said about this in the description of the experiment.
• … Jette et al. Model results… - There is no information about what results were used for the comparisons;

Page 12

• … found to be less than bulk stem one… - What does it mean? Anyway, the whole sentence is too complicated and unclear. The entire paragraph contains a lot of detail with too modest comments and references to the relevant drawings.

Page 14

• S.1 and 2 - This part of the text is true, but to simplify it: a lot of words, little specificity.

Page 16

• Conclusion - …D1, D2 … - Can't it be written more clearly (less complicated) which models have worked and which have not?

Author Response

Their lack of physical verification.

Authors response: Conducting computational analysis is an accepted norm in this field of study. The authors have published many works in this field through computational analysis, some are in the references section of this manuscript. Besides conducting experimental is not easy task. Actually the in-vitro testing is more limited than computational model due to the complexity of human join and gait to be mimicked exactly in experiments. It is more easier to mimic this in computational analysis and at a much lover cost.

The description of the experiment is too complex and leads to problems with understanding.

Authors response: Due to the nature of the problem and the design approach, the approach presented is rather complex. the authors have tried their very best to easy the reading. Similar work by the authors have been published in this journal. NF Al Zoubi, F Tarlochan, H Mehboob, F Jarrar. Design of Titanium Alloy Femoral Stem Cellular Structure for Stress Shielding and Stem Stability: Computational Analysis. Applied Sciences 12 (3), 1548, 2022

On the other hand, there are no results that would allow you to relate your project to the current state of knowledge (e.g. solid stems). 

Authors response: The performance of solid stems is well established along with he draw backs. Some of this have been discussed in the literature. the authors are more concern is proposing new solutions to reduce stress shielding experience by solid stems. 

Page 2

• Section S.1 - … to 1,537,422 in 2050 with annual growth rate … - Why such precise data, since we are only 2022;
• Authors response: these are expected data based on “projections of hip arthroplasty in OECD countries up to 2050” reference number 15 and 16. This calculation was done based on the current growth rate of around 1.7% (based on the previous history before 2020) and the reported THA in 2020 which was 930575. the expected number of THA at any future year can be calculated using the following formula (THA_n =930575*1.017ⁿ ). Where n is the number of future years (n=30, for the expected figure in 2050). Noting that the provided figure was taken from the AJRR annual report of 2020.

• S.2 - …significantly reduce the stress shielding - incorrect stylistic construction, the sentence suggests a reduction and deterioration of the material properties;
• Authors response: the significant reduction in stress shielding suggested in reference to the stress shielding related to  bulk /dense stem
• Chapters are incorrect throughout the article, due to converting word file to pdf;
• Authors response: chapter’s numbering is corrected.

Page 3

• S.1 - Square pores microstructure … - no explanation for this choice;
• Authors response: justification added under section 2.1.1
• … porosities ranging from 10% to 90% … - at such a value it would not be appropriate to speak of an openwork structure, not a porous one;
• Authors response: this range of porous structure need to be studied in order to be able to design functionally graded porous structures in the radial direction.
• pattern numbering errors, correct throughout the article;
• Authors response: This has been corrected.
• Table 1 - the porosity values given in the table are inconsistent with the further content, e.g., with 37, 49, 55, 59 [%];
• Authors response: these are additional porosities added to achieve the required average porosities of 30 %, 50% and 70%, table 1 is updated accordingly.

Page 4

• Figure 1

- illegible descriptions on diagrams; rectified

- stress-strain - do you mean “engineering strain – stress”;

- use different symbols and colors for each curve; 

- the legend is illegible and too complicated; 

- the strain axis has titles incorrectly written;

 - which means notation “Strain (mm/mm); the ratio of the change of the height to the original height of the cube

• Authors response: all the above have been addressed 

• S. 2 - The designed porous cellular structures … and added to the stems design groups. –
• What are the structures D5, D10, and D15; corrected: porous homogeneous structure
• Authors response: This have been addressed in the manuscript
• - The fifteen designs were integrated… - This finding suggests that another 15 structures were created;
• Authors response: This has been corrected in the manuscript  
•  
• The stem–bone assembly was fixed into cylindrical shape epoxy… - I don't understand again, are they numerical or physical simulations? How does epoxy affect the joint and system stiffness? Or is it negligible?
• Authors response: It clearly mentioned that the study is only a numerical simulation, the epoxy used for assembly fixation as per ISO 7206-4 the purpose of using it is to prevent rotation or movement of the stem assembly in any direction and it should not affect the joint and system stiffness.

- Generally - this entire paragraph is very vague and requires detailed elaboration.

• Authors response: This has been updated in the manuscript

Page 5 and next

• Figure 2, 4, 7, 8 - These are examples of a lack of adequate rethinking of how to present them. They have the same content and as such are too detailed. For example, one should leave one example graph or not, and add a basic graph summarizing this issue for the entirety of the research variants carried out. The results and drawings can be included in the supplement to the article.
• Authors response: The authors would prefer this to be part of the main text for completeness of the paper
• Fig. 2 - Problem again. We have 3 porosities, and 4 are shown in the figure. Additionally, they are not ordered in terms of increasing porosity. Lack of clarity about D markings ... No dimensions, What are L1, L2, L3? L2 is confused with the symbol in formula (1).
• Authors response: D , L abbreviations were elaborated in section 2.1.2, the figure is arranged. Formula 1 is related to the porous structure design not to the stem design. Formula 2 is added for calculating the average volumetric porosities.
• Fig. 4 - The drawing is illegible. It is better to show selected cases and discuss the rest in the text or in a graph.
• Authors response: the graph quality is improved
• Fig. 7 and 8 - Too much information, no summary study available. Not understanding in the figure what the D1-15 projects are;
• Authors response: D1- D15 are the designs numbers refer to section 2.1.2, the summary is available in section 3.2.2

Page 6

• S.1 - A more detailed description is needed to explain why P1 and P2 were added to P0 (what were their values).
• Authors response: The values of P0, P1 and  P3 are included in table 3 as mentioned in section 2.1.2
• S.2 - The assembly was meshed with a mesh size of 3 mm using C3D10 quadratic tetrahedral elements, which was used based on a previous sensitivity study - Does it mean that the FEM model had a mesh size of 3 mm? How does this relate to the size of the pore cell? What does "C3D10" mean?
• Authors response: This is related to the finite element model and the mesh size was selected based on sensitivity study, The C3D10 element is a general-purpose tetrahedral element (4 integration points) in ABAQUS software.

Page 7

• Table 3 - Where did the P0 values come from and on what basis?
• Authors response: It is done based on the assumed human bodyweight of 900 N and percent of the body weight (%BW) associated with each walking speed as mentioned in section 2.1.2
• S.1 - Von Misses is a surname and is spelled in capital letters.
• Authors response: This has been Corrected
• I do not understand why the division into Figures 4 and 7, 8 and 9 was written. What is this for? Any understatement?
• Authors response: The divisions were added to the figures to indicate the design number, walking speed, volumetric porosity, and the stem’s radial layers

Page 8

• stress ratios equal 0.1 and 1.0… - And the system overload?
• Authors response: This has been corrected, it’s = 0.1

Page 11

• … ten increments at the stem head - Does this mean that the load was increased by leaps and bounds? Nothing was said about this in the description of the experiment.
• Authors response: The increment size of 300N is added to section 3.2.1
• … Jette et al. Model results… - There is no information about what results were used for the comparisons;
• Authors response: This has been modified in section 3.2.1

Page 12

• … found to be less than bulk stem one… - What does it mean? Anyway, the whole sentence is too complicated and unclear. The entire paragraph contains a lot of detail with too modest comments and references to the relevant drawings.
• Authors response: This has been  corrected

Page 16

• Conclusion - …D1, D2 … - Can't it be written more clearly (less complicated) which models have worked and which have not?
• Authors response: This has been corrected

 

Round 2

Reviewer 3 Report

Dear autors

In my opinion, figures as 2, 4, 7 and 8 contain similar content developed for all the cases considered, which is too detailed an approach. They should be transferred to supplementary materials. However, there is no study presenting the observed trends.

I leave the final decision to allow yours article to published at the discretion of the editor.