The successful delivery of a specified mass of inhaled medication to target regions of the human lungs is a complex phenomenon involving several mechanistic obstacles. The optimal combination of particle size and shape, efficient release from the inhaler, and transport through the device and upper airway - all while accounting for realistic breathing patterns - is difficult to replicate during product development. As standard testing methods often exhibit significant limitations, new methodologies are being proposed.

Nikolaos Petrakis was tasked with evaluating these standard methods, identifying their weaknesses, and comparing them with alternative approaches to inhaler testing. Over the course of his study, he successfully fulfilled all the core objectives. He consulted on his progress regularly and effectively integrated feedback throughout the process. Furthermore, his collaborative skills were demonstrated through his successful teamwork with fellow student Htet Aung Latt.

From a supervisory perspective, I witnessed substantial growth in Nikolaos’s capabilities, with the quality of his work increasing steadily throughout the academic year. While he showed reasonable improvement, I did expect a higher degree of initiative and self-reliance; these factors ultimately placed some limitations on the final results. Specifically, some challenges addressed in his conclusions - such as the influence of filter types - could have been investigated more thoroughly within the scope of the thesis.

Nonetheless, given that the overall volume of experimental work exceeded the standard expectations for a bachelor’s thesis, I evaluate this work with a grade of B.

This Master thesis focuses on experimental methods for testing devices used for inhaled drug delivery. The thesis is divided into a theoretical and an experimental part. The theoretical section provides a useful overview of inhalation devices, aerosol transport, and standard testing methods, while the experimental section applies several approaches to evaluate particle size distribution and regional deposition. The thesis is generally well structured and easy to read. The chapters follow a logical sequence, and the topic is relevant for aerosol and inhalation research. However, the clarity of the text would be improved if all abbreviations were explained at their first occurrence in the main text, not only in the list of abbreviations. The thesis also contains some grammatical and typographical errors, such as instances where values and units are on separate lines, but these do not significantly reduce its comprehensibility. A strength of the work is the broad experimental effort. The student used several measurement techniques and tested multiple configurations, demonstrating good practical ability and familiarity with aerosol measurement methods. However, the large number of tested variants also led to limited repeatability. Some configurations were measured only once, which weakens the statistical reliability of the results. Therefore, some apparent differences between configurations may fall within experimental uncertainty or standard deviation. Another limitation is the uncertainty related to the recovery of material from outlet filters and other components. This issue should be discussed in more detail, especially because it directly affects the calculated deposition fractions and overall mass balance.

Despite these limitations, the thesis provides useful experimental data and forms a good basis for further work. The student demonstrated the ability to work with complex experimental setups and interpret aerosol measurements. In my opinion, the objectives of the thesis were fulfilled, and I recommend the thesis for defense. Topics for thesis defence:

1. On page 20, the author states that the Mass Median Aerodynamic Diameter (MMAD) corresponds to the diameter at which 50% of the particles are smaller and 50% are larger. This definition is not correct. What is the MMAD, and what is the Count Median Aerodynamic Diameter (CMAD)? Compare these two quantities and explain why the distinction is important for pharmaceutical aerosols.
2. The MMAD and FPF values measured with the NGI and ACI for the same nebulizer were different. What factors could explain these differences? In particular, could the use of different flow rates in combination with specific connectors have influenced the results?
3. Why does the pharmacopoeia recommend cooling cascade impactors to about 5°C when testing nebulized aerosols? What is the driving force for droplet evaporation, and could such conditions also enhance hygroscopic growth or condensation?