Release of Aloe vera Extracts from Therapeutic Lenses
Round 1
Reviewer 1 Report
This article is concerned about the delivery of aloe vera extracts from different therapeutic contact lenses. The premise is valid, especially due to the projected deterioration of global eye health over the next few decades; new solutions are always of interest. The results demonstrated that the ionic hydrogel lens delivered more of the aloe vera extract, and over a longer time, compared to the non-ionic hydrogel lens. This suggests that delivering the therapeutic benefits of aloe vera is best done using an ionic hydrogel lens.
However, there are some significant issues with the design/justification of the study;
1) Why was the study conducted without including silicone hydrogels (e.g. a Lotrafilcon A lens)? Without sufficient reasons to exclude silicone hydrogels I would recommend adding this data to the study to increase the articles strength and validity.
2) Lines 208-2012 I do not entirely agree with this justification. There was no measure of how much Aloesin was absorbed by each lens, therefore we do not know how much was remaining in each lens (although it was clear the ionic lens released more). The results could be interpreted that the ionic lens absorbed more Aloesin, therefore was able to released more. Can the authors clarify this point further?
More general comments;
3) The graphs are generally hard to read, and in some cases without a labelled axis. Ensuring the graphs are clear will help the reader greatly.
4) Polishing the text is required; e.g a typo in line 146, "from" not "form". Lines 163/164 and more or less the same as lines 169/170; this can be simplified. I recommend rereading throughly to minimise these sorts of errors.
5) Please ensure up to date references are used. For example one paper is from the 1970's, which is perhaps used much older contact lens technology compared with today. With 27 references, it might be worthwhile to add several more.
Author Response
Dear Editor:
thank you for your letter stating that our manuscript entitles: “Release of Aloe Vera Extracts from Therapeutic Lenses” should be acceptable for publication in Applied Sciences pending major revisions.
Accordingly, we prepared a revised version of the manuscript acknowledging Referees’ and Editor’s comments as below specified:
Reviewer 1:
COMMENT 1. Why was the study conducted without including silicone hydrogels (e.g. a Lotrafilcon A lens)?
ANSWER 1. We agree with the reviewer that testing silicone hydrogel would be of interest. However, it has been already a considerable effort to test 3 different lens types and there is no chance to set up a further experiment in short time. We have already planned to set up in the next future a research program focused on silicone hydrogel lens as compared to other lens. The novelty of the herein presented study is not to test every lens type but to present, for the first time in our knowledge, an experimental procedure able to quantify aloe release from therapeutic lenses.
COMMENT 2. Lines 208-212 I do not entirely agree with this justification. There was no measure of how much Aloesin was absorbed by each lens, therefore we do not know how much was remaining in each lens (although it was clear the ionic lens released more.
ANSWER 2. We agree with this comment. Accordingly, we now state that this is only a hypothesis. Furthermore the suggested comment was added in the text (lines 206-212).
COMMENT 3. The results could be interpreted that the ionic lens absorbed more Aloesin, therefore was able to released more. Can the authors clarify this point further?
ANSWER 3. Ionic lenses can adsorb a thicker layer of protein than nonionic lenses, with the former adsorbing primarily lysozyme [Sack RA, Jones B, Antignani A, Libow R, Harvey H. Specificity and biological activity of the protein deposited on the hydrogel surface. Relationship of polymer structure to biofilm formation. Invest Ophthalmol Vis Sci 1987; 28: 842– 9]. Hydrogel lenses with higher water content adsorb larger amounts of protein [Baines MG, Cai F, Backman HA. Adsorption and removal of protein bound to hydrogel contact lenses. Optom Vis Sci 1990; 67: 807– 10]. Hydrogel materials were the most common lens materials for decades, until the recent successful development of truly complex soft lenses.
COMMENT 4. The graphs are generally hard to read, and in some cases without a labelled axis
ANSWER 4. Figures have been reformatted and axis labels added.
COMMENT 5. Polishing the text is required; e.g a typo in line 146, "from" not "form". Lines 163/164 and more or less the same as lines 169/170; this can be simplified.
ANSWER 5. The text has been corrected as suggested.
COMMENT 6. Please ensure up to date references are used
ANSWER 6. Citations on the text has been changed and corrected.
Citation 3. Is changed with:
Omali N.B.; Subbaraman L.N; Coles-Brennan C.; Fadli Z.; Jones L.W.Biological and Clinical Implications of Lysozyme Deposition on Soft Contact Lenses. Optom Vis Sci. 2015;92:750-7.
Citation 5. Is changed with:
Teichroeb J.H.; Forrest J.A.; Ngai V.; Martin J.W.; Jones L.; Medley J. Imaging protein deposits on contact lens materials. Optom Vis Sci. 2008;85:1151-64
Citation 8. Is changed with:
Lim CHL.; Stapleton F.; Mehta JS. Review of Contact Lens-Related Complications. Eye Contact Lens. 2018;44:S1-S10.
Citation 23. Is changed with:
Grzech A.; Misiuk-Hojło M. The meaning of oxygen permeability in different materials for optimalization of contact lenses function. Polim Med. 2007;37:67-71.
Citation 24. Is changed with:
Gu X.J.; Liu X.; Chen Y.Y.; Zhao Y., Xu M., Han X.J.; Liu Q.; Yi J.L.; Li J.M.
Involvement of NADPH oxidases in alkali burn-induced corneal injury. Int J Mol Med. 2016;38:75-82.
Citation 26. Is changed with :
Chigbu DI. The pathophysiology of ocular allergy: a review.Cont Lens Anterior Eye. 2009 ;32:3-15.
Reviewer 2 Report
The release kinetics of Aloe vera extract (AE) and of one of its bioactive compounds (aloesin) is studied after the Aloe vera extract is soaked into hydrogel contact lens (HL). This goal is relevant and well motivated with the fact that hydrogel contact lens are commonly used for therapeutic applications. However a common complication associated with HCL extended wear is microbial infection and inflammation. These can be prevented by AE, which is well known to be rich with antimicrobial, antioxidant and bioactive compounds. Two HCL are probed in the study (1) Contaflex 75% (C75) (Contamac) non-ionic hydrogel lenses and (2) G72 HW (Benz Research & Development) ionic hydrogel lenses. The AE release is followed by the absorbtion at 230 nm and aloesin release is monitored by LC -MS, and its activity is quantified by Nanodrop spectrophotometer. The measurements are performed at the relevant time points of 30 minutes, 60 minutes, 2 hours , 6 hours and 24 hours. The methodology is described well and allows for reproducibility in independent laboratories. The main conclusion of the study is that the release of AE and of aleosin is significantly higher from the ionic hydrogel compared to the non-ionic sample.
The major point to address is the technical presentation of the results both in graphical format and also in terms of description of the results
- Purely technical comment is the quality of the figures- Figs. 2 to 5 appear blurred, with very low size of the values on the axes (particularly the plots on the bottom rows).
- Comment to Fig. 2 and Fig. 5- please describe on the axes and also in the captions what is measured on the x and y-axis. Is it in arbitrary units, non-dimensional, or other and what it actually measures. It is possible to extract the information from the main text, although it is also not too detailed and most importantly figures should be clear, of good visual content and taken together with the captions- self-explanatory.
- Fig. 2, bottom row- why the data are fitted with linear equation. It is obviously not the right choice and his should be probably revealed by analysis of residuals. It appears that power/hyperbolic equation might provide a far better fit. The low R2 value for non-ionic lens does not “indicates that the release of extract form non-ionic lens is minimal” but simply that it is not the right model to fit the data.
- Fig. 5- here linear fits appear more reasonable. However if we look on the graph at the upper row it is evident that at each time point the aloesin peak area is higher for ionic HL compared to non-ionic HL. If this is so then why son the bottom row some of the values at the y-axis for non-ionic lens at least visually appear higher than some of the data points for ionic lens (which correspond to a higher peak area). Once again the visual quality of the figure needs strong improvement.
- The Discussion will benefit from enhancement. It is stated that “Aloesin remains passively trapped in the non-ionic lens and the release is therefore less and decrease over time. Conversely, in the ionic lens, the negative charge rejects the aloesin making it possible its release continuous and steady increasing release to the outside in the medium. Therefore, the release is greater and more prolonged over time from ionic as compared to non ionic lens.” Can you extend a bit this part by reporting data if such are available in the literature on the microstructure of the hydrogels- surface roughness, pore size etc. Alternatively please extend the paragraph by brief description on the choice of methodologies and equations, their advantages and disadvantages etc. Other option is to discuss on the chemical nature of the molecules in AE- their charge, size, hidrophilicity to lipophilicity balance etc. so that the findings of the study to be put into the context of the chemical nature of thelens material and of the loaded substance.
Author Response
Reviewer 2:
COMMENT 1. Purely technical comment is the quality of the figures- Figs. 2 to 5 appear blurred, with very low size of the values on the axes (particularly the plots on the bottom rows.
ANSWER 1. Figures quality have been improved as suggested.
COMMENT 2. Comment to Fig. 2 and Fig. 5- please describe on the axes and also in the captions what is measured on the x and y-axis.
ANSWER 2. Figures captions axes have been described.
COMMENT 3. Fig. 2, bottom row- why the data are fitted with linear equation
ANSWER 3. This is a Spearm linear regression analysis whose (angular coefficient) is calculated using linear regression. We tested other regression models (polynomial, log, etc., not shown) but the two models having the best fit to the data were the linear and log regression model. In the Figure 2 the linear regression analysis in the upper panel and the log regression equation model is represented in the lower panel.
COMMENT 4. The low R2 value for non-ionic lens does not “indicates that the release of extract form non-ionic lens is minimal” but simply that it is not the right model to fit the data.
ANSWER 4.
Logarithmic regression model was those best fitting the data as compared to other models. Furthermore, the comparison was made between lenses using the same linear regression models. Accordingly, the observed difference is related to the lens and not to the type of the regression model adopted.
COMMENT 5. Fig. 5- here linear fits appear more reasonable. However if we look on the graph at the upper row it is evident that at each time point the aloesin peak area is higher for ionic HL compared to non-ionic HL. If this is so then why son the bottom row some of the values at the y-axis for non-ionic lens at least visually appear higher than some of the data points for ionic lens (which correspond to a higher peak area).
ANSWER 5. This is because the scales of the two graphs are different, i.e. 0-7 for ionic lens (higher data) and 0-4.5 for non ionic lens (lower data). Acknowledging reviewers’ comment, the scales have been normalized (0-7 in both panels).
COMMENT 6. The Discussion will benefit from enhancement. It is stated that “Aloesin remains passively trapped in the non-ionic lens and the release is therefore less and decrease over time. Conversely, in the ionic lens, the negative charge rejects the aloesin making it possible its release continuous and steady increasing release to the outside in the medium. Therefore, the release is greater and more prolonged over time from ionic as compared to non ionic lens.” Can you extend a bit this part by reporting data if such are available in the literature on the microstructure of the hydrogels- surface roughness, pore size etc. Alternatively please extend the paragraph by brief description on the choice of methodologies and equations, their advantages and disadvantages etc.
ANSWER 6. A comment on hydrogel microstructure has been added in the discussion paragraph lines 212-227.
Reviewer 3 Report
Overall, this is not a well-written paper, specially in regard with abstract and introduction. In these sections, work seems to be half-done. Indeed, conclusions shown in the abstract don´t make any sense, but they do at the conclusions section. Further, introduction is based on a series of short sentences without aparent conections each other (no links, no adverbs, no narrative, etc..). Regarding the results, data are poorly presented since figures are insufficiently performed. For instance, figure 1 is just composed of screenshots, showing a bunch of innecesary information for the reader. In Figure 3, it is not able to read anything.
The main concern related to results is that, even although the time course of Aloe vera extarct release from ionic vs non ionic lens is statistically significant, diferences are very small, so that in the clinical practice, both lens may behave similary. On top of that, linear regression is fitted to very few points, which is very risky to come to any conclusion.
Author Response
Reviewer 3:
COMMENT 1. is not a well-written paper, especially in regard with abstract and introduction
ANSWER 1. We accurately revise English language to the best of our efforts.
COMMENT 2. Regarding the results, data are poorly presented since figures are insufficiently performed.
ANSWER 2. Quality of Figures have bene improved and axis labels added.
COMMENT 3.figure 1 is just composed of screenshots, showing a bunch of unnecessary information for the reader.
ANSWER 3. Screenshots were removed and only the equation showing the relationship between 230 nm absorbance and aloesin amounts now remains.
COMMENT 4. In Figure 3, it is not able to read anything.
ANSWER 4. Figure 3 was fully reconstructed.
COMMENT 5. The main concern related to results is that, even although the time course of Aloe vera extarct release from ionic vs non ionic lens is statistically significant, differences are very small, so that in the clinical practice, both lens may behave similary. On top of that, linear regression is fitted to very few points, which is very risky to come to any conclusion.
ANSWER 5. This comments was added to Dicussion (lines 235-236).
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
Firstly, I would like to thank the authors for considering my previous comments, and I appreciate the details and effort that went into revising the manuscript. So I will go through each major point sequentially;
ANSWER 1. We agree with the reviewer that testing silicone hydrogel would be of interest. However, it has been already a considerable effort to test 3 different lens types and there is no chance to set up a further experiment in short time. We have already planned to set up in the next future a research program focused on silicone hydrogel lens as compared to other lens. The novelty of the herein presented study is not to test every lens type but to present, for the first time in our knowledge, an experimental procedure able to quantify aloe release from therapeutic lenses.
Reviewer response;
I appreciate that time was a hinderance in this case. I will be looking forward to seeing future publications including studies with Silicone hydrogel lenses.
ANSWER 2. We agree with this comment. Accordingly, we now state that this is only a hypothesis. Furthermore the suggested comment was added in the text (lines 206-212).
Reviewer response;
This clarification was important and I support the new statement. The additional discussion could also provide future research directions for not only the authors but others in the field.
ANSWER 3. Ionic lenses can adsorb a thicker layer of protein than nonionic lenses, with the former adsorbing primarily lysozyme [Sack RA, Jones B, Antignani A, Libow R, Harvey H. Specificity and biological activity of the protein deposited on the hydrogel surface. Relationship of polymer structure to biofilm formation. Invest Ophthalmol Vis Sci 1987; 28: 842– 9]. Hydrogel lenses with higher water content adsorb larger amounts of protein [Baines MG, Cai F, Backman HA. Adsorption and removal of protein bound to hydrogel contact lenses. Optom Vis Sci 1990; 67: 807– 10]. Hydrogel materials were the most common lens materials for decades, until the recent successful development of truly complex soft lenses.
Reviewer response;
Thank you for the clarification. In the future, this type of discussion could be valuable in supporting the research- especially when more complex hydrogels are subject to investigation. This is something I will keep in mind with my own work.
Reviewer 2 Report
The authors have addressed all my comments and have improved their figures presentation, analysis and discussion well. I recommend publication of the study in its current form.
Reviewer 3 Report
The authors have properly adressed my concerns.
