Numerical and Experimental Investigation on Key Parameters of the Respimat^® Spray Inhaler

Round 1

Reviewer 1 Report

An interesting paper developing a novel aerosal spray - it was not clear to me in the methods what fluid was used to generate the aerosol this will impact on the findings. Have they used a range of fluids / drugs It also appears that the number of repeat tests for each variable was only 3 . This needs to be highlighted as a limitation. The effect of each of the variables on the droplet diameter suggests the droplets are all > 10 um yet the introudction states < 5.8

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments

• There is very little information on the spray pattern. The authors can probably substantiate the atomization process occurring while using the inhaler device.
• The reviewer notes that the D90 is quite close to 9 µm. Isn’t that a too large diameter for an inhalation therapy device especially for lung treatment?
• What kind of distribution for the particle-size with the specific inhaler under study? Is it log-normal or some other?
• Can the authors give the probability density function? What is the geometric standard deviation
• From this information can the authors derive the main processes at play in the atomization of the drug
• What is the velocity at nozzle exit? What is the velocity when the drops reach a stable state?
• Do the simulations giving the spray angle correspond to actual measurements? If not what are the reasons
• Among the parameters investigated numerically, there is no comment on the impaction force. Doesn’t it play an important role?
• Probably one key question to be addressed here is how much of the inhaled medicine that is droplet mass fraction, travels where in the body and in how much time. The authors perform a number of simulations giving the particle size distribution but there are not many hints as to what this brings the efficiency of the device. Can the authors elaborate more on that?
• Presently the conclusions are too much focussed on a single device and do not give enough insight neither on the processes at play nor on the advantages bought by the simulations to results already obtained with experiments. By doing some complementary analysis and fully addressing the comments put forward in this review, the authors should be able to give more insight and improve the overall quality of their paper.
• The references are very much limited in their scope with many of the articles pointing towards this specific inhaler. There has been a lot of excellent work performed lately on pressurized metered dose inhalers and the reviewer emphasizes particularly two references which may be of some great utility for the authors:
  1. Experimental and Numerical Study of Inhaler Spray Characterization (Size Distributions and Velocity). Thesis at Carleton University, Ottawa, Canada (2018).
  2. Numerical evaluation of spray position for improved nasal drug delivery, Nature Scientific Report by Basu et al. (2020).

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

No further comments