Review Reports

Round 1

Reviewer 1 Report

 

Report on „Preparation of fractured nanoquartz: surface features and cell membrane damage“ by Bellomo et al.

 

This manuscript explores the impact of fracturing on the toxicity of quartz. Although the impact of fracturing on cytotoxicity and membrane damage has been published previously by the authors, this new study warrants publication in IJMS.  Here, the conditions for fracturing are systematically altered in a top-down milling approach using different times and speed to produce quartz samples of different sizes. Specifically, the as synthesized micro-sized quartz is reduced in size down to the nanoscale to address the impact of nanoquartz, which exists also in natural quartz after mechanical processing, on biomembranes. The phys-chem properties of such samples include assessment of the agglomeration state, EM analysis of the amorphous and crystal structure and surface analysis of silanol groups with a focus on nearly free silanols (NFS). As the nanoquartz samples strongly agglomerate due to electrostatic interactions and can also not be disagglomerated in various media, the bioavailability upon inhalation is most likely also limited. Actually, this aspect could be further discussed in the manuscript.

Also the aspect of the relatively high energy input due to ball milling should be discussed in the context of real world applications of mechanical processing of quartz.

 

Interestingly, the membranolytic activity correlates with the amount of NFS, however is not directly linked to the specific surface area of the samples. A model is put forward to explain these results. Particles with a lower diameter have a reduced contact area and at the same time also a reduced weight thus limiting their impact on the membrane. At the same time, the density of NFS positively correlates with membrane rupture. Certainly, this model needs to be followed up in future in in vitro and in vivo studies and will be quite important to understand the various detrimental effects of quartz, which is still a very important topic in occupational health science.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The presented manuscript studies the products of grinding synthetic quartz obtained by hydrothermal synthesis from "sodium metasilicate pentahydrate" aqueous solution. Research methods: SEM, TEM, IR, XRD, DCS, DLS, BET. In general, the work is not bad. However, the reviewer's task is to find places that need to be changed in order to improve the quality of the manuscript.

 

1. It seems that the authors are hiding something:

A) In the Materials and Methods section, there is not a word about the origin of sodium metasilicate pentahydrate. On the market, this product can be bought with varying degrees of purity.

B) No full IR spectrum (4000-400 cm-1) (preferably without CaF2). One might think that there are some peaks that the authors do not want to show to readers.

C) There is no description of how self-supporting pellets were obtained (weight, size, pressure, temperature, press-form).

 

2. Why do all sections have a digital designation 1., and subsections 1.1.?

 

3. The abstract (Line 27) says: “Membranolytic nanoquartz for toxicological investigations was obtained”. In addition, in the conclusion (Lines 501-503) it is written: “Our quartz nanoparticles showed dimensional and adhesion properties which can be compatible with the quartz nanoparticles that are generated in standard workplace operations”. It turns out that one could simply take “the quartz nanoparticles that are generated in standard workplace operations” and carry out “the toxicological assessment” with these quartz nanoparticles. It seems that the authors are confused.

 

 

4. Lines 45-47: Written: "This newly formed layer is subjected to chemical and structural rearranging, in a dynamic process of surface reconstruction that generates silanols (≡Si‒OH) and siloxanes (≡Si‒O‒Si≡) upon reaction with molecular water. I agree that silanols are formed upon reaction with molecular water. But the siloxanes are present in the bulk structure. What is the water here?

 

5. Lines 147-148: Written: ZrO₂ balls (diameter = 2 mm, mass = 41 mg). You don't even need a calculator. Count the volume of the ball: (4/3)pr³ = 4.1 mm³. Hence the specific gravity is 10. That's a bit too much for ZrO₂!

 

6. The text (Lines 243-257) has nothing to do with the results of the peer-reviewed work. It could have been placed in the Introduction section.

 

7. Lines 258-259: Written: "We prepared nanoquartz (gQ-n) starting from a high-pure synthetic as-grown quartz (gQ, 99.9% SiO₂), micrometric in size." Q: How was it determined that "as-grown quartz" is 99.9% SiO₂?

 

8. Quartz is the name of one of the possible structures of SiO2. Can a gQ-n3 sample containing 40% amorphous phase be called quartz? Maybe a more accurate title would be Post-Quartz Phase in Silica after Ball Milling?

 

9. By the way, when reading the manuscript sequentially, the question arises - how do the authors distinguish between "an amorphous surface layer" (Line 293) and "amorphous particles" (Lines 330-331)? And only after the description of TEM studies, this issue becomes clear. It is necessary to state the results in such a way that this question does not arise.

 

10. Lines 366-368: Written: "High-resolution image of one nanometric quartz particle (D) highlights crystalline core, with several diffraction planes visible, and the amorphous outer layer (highlighted by the asterisk) formed during high energy milling." Why did the authors decide that in Fig. 6D shows one particle?

 

11. In Fig. 6, the scale bar should be placed in image.

 

12. It seems to me that Figure S3 should be moved to the manuscript.

 

13. Lines 405-407: Written: “FE-SEM analysis on filtered gQ-n3 (Figure 7E-F) clearly evidence the presence of primary silica nanoparticles particles (diameter of ca. 20-40 nm), and small clusters in the 100-200 nm range". After such a discovery, it is urgent to move on to the study of filtered gQ-n3 by the TEM method in order to study the structure of a single nanoparticle. But for some reason this was not done.

 

14. It seems to me that it is misleading to explain the activity of silica by the presence of a small number of NFS on their surface. It follows from the IR spectra that these groups do not participate in hydrogen bonds. Hence, these are isolated groups. Why can't a hydroxyl group approach NFS within a reaction distance, while complex biological objects can? References to published works are not convincing here.

 

15. Finally, if we assume that the studied quartz particles do not have pores, then from the SSA values the average particle size (a) can be estimated {a = 6/(ρˑSSA), where ρ is the specific gravity}. For the gQ-n3 sample (SSA = 55 m²/g) a = 42 nm.

 

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx