A Study of the In-Vial Crystallization of Ice in Sucrose–Salt Solutions—An Application for Through-Vial Impedance Spectroscopy (TVIS)
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe work addresses an important challenge in pharmaceutical freeze-drying, non-invasive, real-time monitoring of phase transitions within vials, by proposing TVIS as a sensitive and scalable method. The results are well-presented, and the experimental rationale is convincing. However, the manuscript would benefit from additional clarification and methodological strengthening in several areas.
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Author Response
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Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors reported their development of a non-invasive TVIS method that can determine ice nucleation temperature and average ice growth rate, without altering the intrinsic nucleation kinetics of the system under study.
The authors stated that higher nucleation temperatures favor the formation of fewer, larger ice crystals. How can this be? Higher nucleation temperatures would mean slower cooling because low nucleation temperatures can only be attained by rapid quenching. The growth rate following the nucleation should also be slow at high nucleation temperatures because the driving force (the chemical potential differential between the supercooled water and ice) is smaller. And slow crystal growth would lead to formation of fewer numbers of very large single crystals.
Interfacial capacitance (IC) must be defined much earlier, when it first appears.
Author Response
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Reviewer 3 Report
Comments and Suggestions for AuthorsOverall, the work evaluated is interesting because it concerns a novel technology for application in lyophilization processes in the pharmaceutical industry.
Materials and Methods
In line 136, indicate which parameter corresponds to the value 18.2 MΩ cm.
Results
In Fig. 4 b, is the vial TC 1.63 h or 1.67 h, in accordance with the value in the table inserted in Fig. 3?
In my opinion, parts of Image Analysis Method 1 and 2, which are in Results (lines 249-264 and 293-305), should be moved to materials and methods.
The sentence between lines 280-281 seems incomplete. Please review.
Regarding Fig. 6, page 10. What are the units for the X and Y axes? Does this Fig. 6 correspond to the discussion between lines 267-272? If so, then the following figure 6 on page 11 should be renumbered...
The content between lines 655 and 661 should be at the beginning of the section "Determination of ice nucleation temperature."
characterize the ice formation process in solutions with conductivities that are representative of those one might encounter in an isotonic solution.
• Do you consider the topic original or relevant to the field? Yes Does it address a specific gap in the field? Yes Please also explain why this is/ is not the case. The use of thermocouples inside lyophilization vials for biopharmaceuticals generally results in faster drying. This introduces potential bias into experimental studies, as the sensors may inadvertently alter the process they are intended to monitor. For this reason, several noninvasive online techniques have been developed to monitor product temperature during the lyophilization cycle. Through-vial impedance spectroscopy (TVIS), studied in this article, may be a promising technology to aid in the development process by measuring the in situ behavior of the product formulation. • What does it add to the subject area compared with other published
material? A noninvasive process control technology that can more accurately reproduce the actual conditions of the vials during the freeze-drying process. This can contribute to energy savings and the sustainability of this type of technology.
• What specific improvements should the authors consider regarding the
methodology? No
• Are the conclusions consistent with the evidence and arguments presented
and do they address the main question posed? Yes Please also explain why this is/is not the case. The classical scientific method is followed throughout, since the conclusions drawn between lines 715-729 address the objectives of the work expressed between lines 107-117.
• Are the references appropriate? Yes
• Any additional comments on the tables and figures. Review the figure numbering. Starting with Figure 6, the numbering should be reviewed. In the Results section, the authors should sometimes attempt to summarize the information provided, e.g., by referring to previous publications.
For example, "Qualitative analysis of the TVIS spectra" should be summarized further, otherwise it becomes tedious for the reader. A similar situation applies to the section "The Maxwell-Wagner process of solutions in the liquid state" and "Interfacial capacitance (IC) at the glass surface." and "Quantitative analysis of TVIS spectra".
Author Response
Responses are in the Word document uploaded to the portal
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Authors,
Thank you for your extensive responses to my questions and for including some comments and explanations in the final manuscript. I think this is something different and certainly interesting, with some newer uses of impedance spectroscopy as such. Thank you.
