Characterization of Microarchitectures, Stiffness and Strength of Human Trabecular Bone Using Micro-Computed Tomography (Micro-CT) Scans

Round 1

Reviewer 1 Report

I have found the manuscript original in what concerns 3D additive printing. and image analysis of human femoral trabecular bone.

At the same time, I do not understand why similar results for the human tibia are absent.

In both cases, the authors provided a lot of experimental data concerning the mechanical properties of bone tissue, but without a minimal interpretation of the results.

In my opinion, such interesting results should be interpreted within a certain model or be used to elaborate a mechanical model of investigated tissue.

Moreover, uniaxial stress provides data concerning a single direction. It would be more interesting if the cubic samples would use three more samples to investigate the uniaxial stress following three reciprocal orthogonal directions. Even so, the experimental values of Modulus SI
and Yield Strength showed great variations. This peculiarity should be discussed and eventually explained.

Therefore, the 3D microtomography seems from my point of view OK, but the section devoted to mechanical properties should be thoroughtly revised.

Comments for author File: Comments.pdf

Author Response

We thank the reviewer for the detailed comments. 

Reviewer #1     There are minimal interpretations of the results  We have rearranged our results adding statistical analysis of the results. The average and standard deviation were added to all tabulated data. Explanations are given for all observations. Moreover, microarchitecture parameters: trabecular thickness and spacing have demonstrated a significant degree of parametric variability. Presented histograms associated with the micro-CT analyzed data  fit Gaussian functions.  All tables have been formatted with the standard ones.

Author Response File: Author Response.pdf

Reviewer 2 Report

October, 28^th 2022

The authors underline the importance of X-ray computed tomographic microscopy (micro-CT) for accurate characterization of geometry, microarchitecture, and stiffness properties of bones, using on samples collected from selected cadavers of different age, gender, and race.

Major comments:

1.     Line 86: the 22 specimens from the 73M are equally subdivided in cylindrical and cubic specimens? This aspect is not clear even after in line 143.

 2.     Line 222: the authors wrote “Note that the predicted range of bone elastic modulus values obtained from the gray scale analysis of micro-CT scans of cylindrical bone sample, CY#1, is very close to average values reported using compression testing (Table 2).” This sentence is not so clear because in table 2 there is only one value, while in fig.10 there are 11 values and no mean or most frequent one, therefore the sentence is not adequately supported by numbers expressed.

 3.     Since 22 specimens from 73M and 4 specimens from 21M have been analyzed by microCT, why the bone properties have not been reconstructed for all specimens and correlated to the actual data measured by ex vivo testing in order to draw more solid conclusions about the possibility to estimate bone strength from microCT scans data? Without this analysis the study is definitely incomplete.

 Minor comments:

 4.     Line 60: “Published results of investigations conducted using X-ray computed tomographic microscopy …” there are no references concerning this statement

 5.     Table 2: (Max) and (Min) in the yield strength column might be confusing, I suggest to remove them

 6.     Fig 8 and 9: the unit of measure is missing beside reconstructed images and histograms.

 7.     Fig 10: the column with letter ν what does it refer to? The letter “ν” is never mentioned in the text.

Overall and final opinion of the Reviewer:

The target underlined in the abstract by the authors (<<These properties are crucial for designing and building optimized implants for joint and dental reconstruction applications>>) would be fulfilled if the analyses were complete and the reconstructions were obtained for all specimens. But this is not the case (see comment n. 3), so the manuscript needs further major additions before it can be published.

 

Author Response

We thank the reviewer for the insightful and instructive comments. 

Reviewer #2     Please pay little attention: Bone density referes to average bone which inlued voids or only to the bone tissue itself excepting voids.   It is obvious from discussion of micro-CT results and Figure 7 that it is only for bone cell density and does not include the voids.    Please provide the same data as for the femoral condyle. Use the same type of table, i. e. Sample #, Modulus SI (MP), Yeld strength (MP) and Yeld strain. Otherwise it is difficult to compare the two types of samples. In this paper we never had intention to compare properties of the femoral condyle with that of the tibia of another cadaver. We did mechanical tests on 22 samples collected from a 72 years old male cadaver to confirm heterogeneity of trabecular bone material and to demonstrate that even for samples obtained from the same cadaver, stiffness and strength can vary significantly.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Please mark with red ink al changes you have done in the revised version.

It is very tedious to compare sentences by sentence both versions.

At the same time, I never remarked you have included the uncertainties as I have asked.  

Until I will receive the revised version with the changes you have done marked with red ink, I can't make any recommendations. 

Author Response

Cover Letter Responding to Reviewers Evaluation

Major Concerns Raised by the Reviewers

There are two major concerns raised by both reviewers that need to be addressed and satisfactory explanation should be given.

Major concern #1: Regarding, why we did not report and compare micro-CT microscale properties and microarchitecture features of the femoral condyle with that of the tibia of another cadaver.

Major concern #2: Authors provided a lot of experimental data concerning the mechanical properties and microarchitectures of bone tissues, but with only minimal interpretation of these results.

Authors Explanation for Major concern #1 : The present work aims to assess and experimentally verify the use of micro-CT for accurate characterization of geometry, microarchitecture, and stiffness properties of bones to validate its use for designing and building medical devices and implants. In this paper we never had intension to compare microscale properties of femoral condyle with that of tibia of another cadaver. There are no direct benefits of such comparison for supporting the aim of the present paper. Otherwise, we would have need for unlimited samples from different cadavers and extracted from spine, hip, shoulder, foot, human jaws, etc. The present work introduces evaluation methods and experimental verification of the use of micro-CT for accurate characterization of geometry, microarchitecture, and stiffness properties of bones. These properties are crucial for designing and building optimized implants for joint and dental reconstruction. We did mechanical tests on 22 samples collected from 72 years old male cadaver to only confirm heterogeneity of trabecular bone material and to demonstrate that even for samples obtained from the same cadaver, stiffness and strength can vary significantly.  However, it was suggested in the present paper’s conclusions that micro-CT could be used on samples collected from selected cadavers of different ages, genders, and race groups to form a database that could be used for providing useful microarchitecture information for design of medical devices and implants. We emphasized these facts in the newly modified introduction and conclusions of the present paper.

Authors Explanation for Major concern #2: We have rearranged our results adding statistical analysis of the results. The average and standard deviation were added to all tabulated data. Explanations are given for all observations. Moreover, microarchitecture parameters: trabecular thickness and spacing have demonstrated a significant degree of parametric variability. These results are discussed and explanations are given in the newly modified paper in the discussion section. Our discussion indicated that probabilistic analyses of micro-CT data could take into account the reported variabilities. They can aid in generating the required lattice structures for optimum implant designs that match closely patient bones and hence can overcome most of the issues related to aseptic loosening phenomenon and premature failure of the treated joints.

Author Response File: Author Response.pdf

Reviewer 2 Report

The rebuttal letter should contain point-by-point responses to each reviewer's comments.

Round 3

Reviewer 1 Report

The rebuttal letter should contain point-by-point responses to each reviewer's comments.

Round 4

Reviewer 1 Report

The revised version is significantly improved but remains the problem of significant digits. Until the authors do not correct this issue, I can't recommend the manuscript be accepted.

All my remarks are on the attached file.

Comments for author File: Comments.pdf