On the Use of Computational Fluid Dynamics (CFD) Modelling to Design Improved Dry Powder Inhalers.

PURPOSE: Computational Fluid Dynamics (CFD) simulations are performed to investigate the impact of adding a grid to a two-inlet dry powder inhaler (DPI). The purpose of the paper is to show the importance of the correct choice of closure model and modeling approach, as well as to perform validation against particle dispersion data obtained from in-vitro studies and flow velocity data obtained from particle image velocimetry (PIV) experiments. METHODS: CFD simulations are performed using the Ansys Fluent 2020R1 software package. Two RANS turbulence models (realisable k - ε and k - ω SST) and the Stress Blended Eddy Simulation (SBES) models are considered. Lagrangian particle tracking for both carrier and fine particles is also performed. RESULTS: Excellent comparison with the PIV data is found for the SBES approach and the particle tracking data are consistent with the dispersion results, given the simplicity of the assumptions made. CONCLUSIONS: This work shows the importance of selecting the correct turbulence modelling approach and boundary conditions to obtain good agreement with PIV data for the flow-field exiting the device. With this validated, the model can be used with much higher confidence to explore the fluid and particle dynamics within the device.

Insights into Spray Development from Metered-Dose Inhalers Through Quantitative X-ray Radiography.

PURPOSE: Typical methods to study pMDI sprays employ particle sizing or visible light diagnostics, which suffer in regions of high spray density. X-ray techniques can be applied to pharmaceutical sprays to obtain information unattainable by conventional particle sizing and light-based techniques. METHODS: We present a technique for obtaining quantitative measurements of spray density in pMDI sprays. A monochromatic focused X-ray beam was used to perform quantitative radiography measurements in the near-nozzle region and plume of HFA-propelled sprays. RESULTS: Measurements were obtained with a temporal resolution of 0.184 ms and spatial resolution of 5 µm. Steady flow conditions were reached after around 30 ms for the formulations examined with the spray device used. Spray evolution was affected by the inclusion of ethanol in the formulation and unaffected by the inclusion of 0.1% drug by weight. Estimation of the nozzle exit density showed that vapour is likely to dominate the flow leaving the inhaler nozzle during steady flow. CONCLUSIONS: Quantitative measurements in pMDI sprays allow the determination of nozzle exit conditions that are difficult to obtain experimentally by other means. Measurements of these nozzle exit conditions can improve understanding of the atomization mechanisms responsible for pMDI spray droplet and particle formation.

A novel high-speed imaging technique to predict the macroscopic spray characteristics of solution based pressurised metered dose inhalers.

PURPOSE: Non-volatile agents such as glycerol are being introduced into solution-based pMDI formulations in order to control mean precipitant droplet size. To assess their biopharmaceutical efficacy, both microscopic and macroscopic characteristics of the plume must be known, including the effects of external factors such as the flow generated by the patient's inhalation. We test the hypothesis that the macroscopic properties (e.g. spray geometry) of a pMDI spray can be predicted using a self-similarity model, avoiding the need for repeated testing. METHODS: Glycerol-containing and glycerol-free pMDI formulations with matched mass median aerodynamic diameters are investigated. High-speed schlieren imaging is used to extract time-resolved velocity, penetration and spreading angle measurements of the pMDI spray plume. The experimental data are used to validate the analytical model. RESULTS: The pMDI spray develops in a manner characteristic of a fully-developed steady turbulent jet, supporting the hypothesis. Equivalent glycerol-containing and non glycerol-containing formulations exhibit similar non-dimensional growth rates and follow a self-similar scaling behaviour over a range of physiologically relevant co-flow rates. CONCLUSIONS: Using the proposed model, the mean leading edge penetration, velocity and spreading rate of a pMDI spray may be estimated a priori for any co-flow conditions. The effects of different formulations are captured in two scaling constants. This allows formulators to predict the effects of variation between pMDIs without the need for repeated testing. Ultimately, this approach will allow pharmaceutical scientists to rapidly test a number of variables during pMDI development.

A counter-swirl design concept for dry powder inhalers.

A swirling airflow is incorporated in several dry powder inhalers (DPIs) for effective powder de-agglomeration. This commonly requires the use of a flow-straightening grid in the DPI to reduce drug deposition loss caused by large lateral spreading of the emerging aerosol. Here, we propose a novel grid-free DPI design concept that improves the aerosol flow characteristics and reduces the aforementioned drug loss. The basis of this design is the implementation of a secondary airflow that swirls in the opposite direction (counter-swirl) to that of a primary swirling airflow. In-vitro deposition, computational fluid dynamics simulations and particle image velocimetry measurements are used to evaluate the counter-swirl DPI aerosol performance and flow characteristics. In comparison with a baseline-DPI that has only a primary swirling airflow, the counter-swirl DPI has 20% less deposition of the emitted drug dose in the induction port and pre-separator of a next generation impactor (NGI). This occurs as a result of the lower flow-swirl generated from the counter-swirl DPI which eliminates the axial reverse flow outside of the mouthpiece and substantially reduces lateral spreading in the exiting aerosol. Modifications to the counter-swirl DPI design were made to prevent drug loss from the secondary airflow tangential inlets, which involved the addition of wall perforations in the tangential inlets and the separation of the primary and secondary swirling airflows by an annular channel. These modified DPI devices were successful in that aspect but had higher flow-swirl than that in the counter-swirl DPI and thus had higher drug mass retained in the device and deposited in the induction port and pre-separator of the NGI. The fine particle fraction in the aerosols generated from all the counter-swirl-based DPIs and the baseline-DPI are found to be statistically similar to each other.

Glycolysis as key regulatory step in FSH-induced rat Sertoli cell proliferation: Role of the mTORC1 pathway.

The definitive number of Sertoli cells (SCs), achieved during the proliferative periods, defines the spermatogenic capacity in adulthood. It is recognized that FSH is the main mitogen targeting SC and that it exerts its action, at least partly, through the activation of the PI3K/Akt/mTORC1 pathway. mTORC1 controls a large number of cellular functions, including glycolysis and cell proliferation. Interestingly, recent evidence revealed that the glycolytic flux might modulate mTORC1 activity and, consequently, cell cycle progression. Although mature SC metabolism has been thoroughly studied, several aspects of metabolism regulation in proliferating SC are still to be elucidated. The objective of this study was to explore whether aerobic glycolysis is regulated by FSH through mTORC1 pathway in proliferating SC, and to assess the involvement of glycolysis in the regulation of SC proliferation. The present study was carried out utilizing 8-day-old rat SC cultures. The results obtained show that FSH enhances glycolytic flux through the induction of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) and lactate dehydrogenase A (LDHA) in an mTORC1 dependent manner. In addition, PFKFB3 and LDH inhibitors prevent FSH from activating mTORC1 and stimulating SC proliferation and glycolysis, presumably through mTORC1 pathway inhibition. In summary, FSH simultaneously regulates SC proliferation and glycolysis in an mTORC1 dependent manner, and glycolysis seems to cooperate with FSH in the stimulation of both cellular functions through the modulation of the same signalling pathway. Therefore, a positive feedback between the mTORC1 pathway and glycolysis triggered by FSH is hypothesized.

Advances in soft mist inhalers.

INTRODUCTION: Soft mist inhalers (SMIs) are propellant-free inhalers that utilize mechanical power to deliver single or multiple doses of inhalable drug aerosols in the form of a slow mist to patients. Compared to traditional inhalers, SMIs allow for a longer and slower release of aerosol with a smaller ballistic effect, leading to a limited loss in the oropharyngeal area, whilst requiring little coordination of actuation and inhalation by patients. Currently, the Respimat® is the only commercially available SMI, with several others in different stages of preclinical and clinical development. AREAS COVERED: The primary purpose of this review is to critically assess recent advances in SMIs for the delivery of inhaled therapeutics. EXPERT OPINION: Advanced particle formulations, such as nanoparticles which target specific areas of the lung, Biologics, such as vaccines, proteins, and antibodies (which are sensitive to aerosolization), are expected to be generally delivered by SMIs. Furthermore, repurposed drugs are expected to constitute a large share of future formulations to be delivered by SMIs. SMIs can also be employed for the delivery of formulations that target systemic diseases. Finally, digitalizing SMIs would improve patient adherence and provide clinicians with fundamental insights into patients' treatment progress.

Unraveling the Kinematics of Sperm Motion by Reconstructing the Flagellar Wave Motion in 3D.

Sperm swim through the female reproductive tract by propagating a 3D flagellar wave that is self-regulatory in nature and driven by dynein motors. Traditional microscopy methods fail to capture the full dynamics of sperm flagellar activity as they only image and analyze sperm motility in 2D. Here, an automated platform to analyze sperm swimming behavior in 3D by using thin-lens approximation and high-speed dark field microscopy to reconstruct the flagellar waveform in 3D is presented. It is found that head-tethered mouse sperm exhibit a rolling beating behavior in 3D with the beating frequency of 6.2 Hz using spectral analysis. The flagellar waveform bends in 3D, particularly in the distal regions, but is only weakly nonplanar and ambidextrous in nature, with the local helicity along the flagellum fluctuating between clockwise and counterclockwise handedness. These findings suggest a nonpersistent flagellar helicity. This method provides new opportunities for the accurate measurement of the full motion of eukaryotic flagella and cilia which is essential for a biophysical understanding of their activation by dynein motors.

Improved Drainage Cannula Design to Reduce Thrombosis in Veno-Arterial Extracorporeal Membrane Oxygenation.

Thrombosis is a potentially life-threatening complication in veno-arterial extracorporeal membrane oxygenation (ECMO) circuits, which may originate from the drainage cannula due to unfavorable blood flow dynamics. This study aims to numerically investigate the effect of cannula design parameters on local fluid dynamics, and thus thrombosis potential, within ECMO drainage cannulas. A control cannula based on the geometry of a 17 Fr Medtronic drainage cannula concentrically placed in an idealized, rigid-walled geometry of the right atrium and superior and inferior vena cava was numerically modeled. Simulated flow dynamics in the control cannula were systematically compared with 10 unique cannula designs which incorporated changes to side hole diameter, the spacing between side holes, and side hole angles. Local blood velocities, maximum wall shear stress (WSS), and blood residence time were used to predict the risk of thrombosis. Numerical results were experimentally validated using particle image velocimetry. The control cannula exhibited low blood velocities (59 mm/s) at the cannula tip, which may promote thrombosis. Through a reduction in the side hole diameter (2 mm), the spacing between the side holes (3 mm) and alteration in the side hole angle (30° relative to the flow direction), WSS was reduced by 52%, and cannula tip blood velocity was increased by 560% compared to the control cannula. This study suggests that simple geometrical changes can significantly alter the risk of thrombosis in ECMO drainage cannulas.

Flagellar energetics from high-resolution imaging of beating patterns in tethered mouse sperm.

We demonstrate a technique for investigating the energetics of flagella or cilia. We record the planar beating of tethered mouse sperm at high resolution. Beating waveforms are reconstructed using proper orthogonal decomposition of the centerline tangent-angle profiles. Energy conservation is employed to obtain the mechanical power exerted by the dynein motors from the observed kinematics. A large proportion of the mechanical power exerted by the dynein motors is dissipated internally by the motors themselves. There could also be significant dissipation within the passive structures of the flagellum. The total internal dissipation is considerably greater than the hydrodynamic dissipation in the aqueous medium outside. The net power input from the dynein motors in sperm from Crisp2-knockout mice is significantly smaller than in wildtype samples, indicating that ion-channel regulation by cysteine-rich secretory proteins controls energy flows powering the axoneme.

In-vitro and particle image velocimetry studies of dry powder inhalers.

Inhalation drug delivery has seen a swift rise in the use of dry powder inhalers (DPIs) to treat chronic respiratory conditions. However, universal adoption of DPIs has been restrained due to their low efficiencies and significant drug losses in the mouth-throat region. Aerosol efficiency of DPIs is closely related to the fluid-dynamics characteristics of the inhalation flow generated from the devices, which in turn are influenced by the device design. In-vitro and particle image velocimetry (PIV) have been used in this study to assess the aerosol performance of a model carrier formulation delivered by DPI devices and to investigate their flow characteristics. Four DPI device models, with modification to their tangential inlets and addition of a grid, have been explored. Similar aerosol performances were observed for all four device models, with FPF larger than 50%, indicating desirable lung deposition. A high swirling and recirculating jet-flow emerging from the mouthpiece of the DPI models without the grid was observed, which contributed to particle deposition in the throat. DPI models where the grid was present showed a straightened outflow without undesired lateral spreading, that reduced particle deposition in the throat and mass retention in the device. These findings demonstrate that PIV measurements strengthen in-vitro evaluation and can be jointly used to develop high-performance DPIs.