Injectable Composite Systems of Gellan Gum:Alginate Microparticles in Pluronic Hydrogels for Bioactive Cargo Controlled Delivery: Optimization of Hydrogel Composition based on Rheological Behavior

Round 1

Reviewer 1 Report

This manuscript by Carrêlo et al. reports an interesting study into potential drug delivery systems based on polysaccharide microparticles in pluronic gels.  The work demonstrated that the transition temperature from an injectable solution to a gel could be controlled, depending on the pluronic formulation used and the concentrations of microparticles included.

I have only a few comments regarding the scientific or technical content:

1) P1: The authors should specify what the abbreviation 'PLGA' means, please.

2) P2: It would be very helpful to explain what is the difference between these two Pluronic materials, please.  For example, is the difference in molecular weight or ratios of lengths of PEO and PPO segments?

3) P6: The authors stated that G" > G', even though the formulations were gels above Tp.  Did this observation relate to the frequency at which the cross-over from G">G' to G"<G' occurred, please?  A section of frequency sweeps appears later in the manuscript.  It would be useful to refer forward to that at this point.

4) The observation of G" above G' for a gel does seem rather surprising.  I suggest the authors should discuss that in more detail, please.

5) P8: The horizontal dashed lines in Fig. 3 are explained in the text, on page 8.  I suggest it would be useful to add that information to the caption of Fig. 3, please.

6) P10:  Again, it appears to be surprising that a 20 % w/w polymer solution should show Newtonian viscosity behaviour.  Some further comments would be useful, please.  E.g. were the pluronic chains entangled/overlapped at that concentration?  (That might be estimated from the rheology or if the intrinsic viscosities or hydrodynamic radii of the pluronics were known.)

7) P11: In discussing the degradation of the gels (i.e. faster than some previously published reports) have the effects of PBS on the GG/Alg microparticles been considered?   If the microparticles raised the Ti, but the PBS caused them to degrade faster, could the resulting decrease in Ti explain the faster degradation of the hydrogels?

Can the authors comment, please?

8) P13: It would be useful to see how well the models for MB release fitted the experimental data, please.


In my opinion, the manuscript is generally well written, although I noted a few examples of typographic errors.  Examples and my suggested corrections are listed below:

P1) '...a Pluronic aqueous solutions...' (...Pluronic aqueous solutions...)

P3: 'Fours replicas were used...' (Four replicas...'

P5: 'Also, the interaction of the carboxylic groups of alginate and gellan gum with the ether groups of Pluronic.'  (This is not a sentence - there is no verb.  I suggest: 'Also, changes in Ti may have been due to interaction of the carboxylic groups.....')

P9: '...the 18:2 ratio begun the transition...' (...began the transition...)

P14: '...did not altered the...' (...did not alter...)

There also appears to be a technical issue with the manuscript; e.g. see the start of section 3.1 and elsewhere: 'Error! Reference source not found.'

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The analyzed manuscript proves a continuous search on the part of the authors, to find the best drug delivery system formulations using such thermosensitive biopolymers, which gel in situ, and which achieve the most controlled release of the active principle. The analyzed article has a logical, fluent development and mostly includes a study of pre-formulation and formulation for such cargo-type systems, for transport and monitorized delivery of medicines. A drug substance model was used. From the analysis of the manuscript, I can make the following observations:

 1. The introduction must be completed with adequate bibliographic data and references, news about Gellan gum - the advantages and disadvantages of its use, especially in combination with alginates.

2. Bibliographic references are not visible in the text, error fields appear!

3. It is important to coherently explain the choice of each type of biopolymer, considering the authors' experience and previous research.

4. The title of the article must be self-explanatory, and not contain abbreviations of polymers or other materials used, even if they are later explained in the text. A slight modification of the title would be appropriate.

5. The Conclusions chapter must be carefully structured so as not to repeat the discussion of the results, but to present the extent to which the working hypotheses that were the basis of the presented experimental studies were fulfilled and to what extent. The authors should also include a continuation of the studies, as they presented, but more clearly, since an optimization was attempted, but only from a rheological point of view.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Gellan gum/alginate microparticles in Pluronic hydrogels were investigated for sol-gel transition temperatures, rheological properties, and in vitro release of methylene blue as a model drug.  Generally the experimental was properly design and data presentations are clear.  Many grammatical errors should be corrected.  Specific comments:

1.      Page 1: “bioactive glass injectable hydrogel”.  What was bioactive glass?

2.      Page 2 paragraph 4: “which has been previously optimized”.  Please cite a reference.  “Following, in vitro drug delivery…”  Was “Following” correct word here?

3.      Section 2.5: Was degradation correct here?  What was mechanism for Pluronic degradation?  Was it a chemical degradation or a dissolving/mixing process when Pluronic hydrogel in a dialysis membrane was introduced into PBS?

4.      Page 4 paragraph 1: “Within a donor recipient made form a permeable membrane”.  It is a confusing sentence. 

5.      “Error! Reference source not found” appear many times throughout the manuscript for review.  Please check.

6.      Section 3.1: as the ratio of Pluronic F127 and F68 had an effect on sol-gel transition temperature.  It would be better to add mechanistic discussions on why the ratio can have the effect and what differences between these two grades can contribute to the effect.  

7.      Page 9 last paragraph:  As observed in the temperature ramps (Figure 3).  Should it be Figure 2?

8.      Section 3.5:  Is degradation correct term?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors provided an improved version.

The manuscript has been sufficiently improved to warrant publication. 

Reviewer 3 Report

n/a