Assistance for Predicting Deposition of Tranilast Dry Powder in Pulmonary Airways by Computational Fluid Dynamics

The impact of actuator nozzle and surroundings condition on drug delivery using pressurized-metered dose inhalers

The most commonly used method to deliver aerosolized drugs to the lung is with pressurized metered-dose inhalers (pMDIs). The spray actuator is a critical component of pMDI, since it controls the atomization process by forming aerosol plumes and determining droplet size distribution. Through computational fluid dynamics (CFD) simulations, this study investigated the effect of two different nozzle types (single conventional and twin nozzles) on drug deposition in the mouth-throat (MT) region. We also studied the behavior of aerosol plumes in both an open-air environment and the MT geometry. Our study revealed that spray aerosol generated in an unconfined, open-air environment with no airflow behaves distinctly from spray introduced into the MT geometry in the presence of airflow. In addition, the actuator structure significantly impacts the device's efficacy. In the real MT model, we found that the twin nozzle increases drug deposition in the MT region, and its higher aerosol velocity negatively affects its efficiency.

Dry Powder Formulations for Inhalation Require a Smaller Aerodynamic Diameter for Usage at High Altitude

BACKGROUND

High Altitude Pulmonary Edema (HAPE) seriously threatens the health of people at high altitudes. There are drug treatments for HAPE, and dry powder formulations (DPFs) represent a rapid and accessible delivery vehicle for these drugs. However, there are presently no reports on the inhalability of DPFs in low-pressure environments. Given the reduced atmospheric pressure typical at high altitudes, conventional DPFs might not be suitable for inhalation. Therefore, it is necessary to elucidate the deposition behaviors of dry powder in the respiratory tract at low pressure, as well as to improve their pulmonary deposition efficiency via adjustments to their formulation and design.

METHODS

The effect of air pressure, inspiratory velocity, and particle properties (such as size, density, and aerodynamic diameter) on pulmonary deposition of DPFs was calculated by a computational fluid dynamics (CFD)-coupled discrete phase model. DPFs of various aerodynamic diameters were prepared by spray drying, and the inhalability of these DPFs in a low-pressure environment was evaluated in mice. Finally, a mouse model of HAPE was established, and the treatment of HAPE by nifedipine-loaded DPFs with small aerodynamic diameter was validated.

RESULTS

CFD results showed that low pressure decreased the deposition of DPFs in the lungs. At 0.5 standard atmosphere, DPFs with aerodynamic diameter of ∼2.0 μm could not enter the lower respiratory tract; however, a decrease in the physical diameter, density, and, consequently, the aerodynamic diameter of the DPFs was able to enhance pulmonary deposition of these powders. To validate the CFD results, three kinds of dry powder with aerodynamic diameters of 0.66, 0.98, and 2.00 μm were prepared by spray drying. Powders with smaller aerodynamic diameter could be inhaled into the lungs of mice more effectively, and, consequently could ameliorate the progression of HAPE more effectively than conventional powders. These results were consistent with the CFD results.

CONCLUSIONS

Low atmospheric pressure can prevent the pulmonary deposition of DPFs at high altitudes. Compared with conventional DPFs, powders with smaller aerodynamic diameter can be effectively inhaled at these pressures and thus might be more suitable for the treatment the HAPE.

Non-spherical drug particle deposition in human airway using computational fluid dynamics and discrete element method

Currently, the air pollution and the respiratory disease problems that affect human health are increasing rapidly. Hence, there is attention for trend prediction of the located deposition of inhaled particles. In this study, Weibel's based human airway model (G0-G5) was employed. The computational fluid dynamics and discrete element method (CFD-DEM) simulation was successfully validated by comparison to the previous research studies. The CFD-DEM achieves a better balance between numerical accuracy and computational requirement when comparing with the other methods. Then, the model was used to analyze the non-spherical drug transport with different drug particle sizes, shapes, density, and concentrations. The results found that all the studied factors affected the drug deposition and particle out-mass percentage except the drug concentration. The drug deposition was increased with the increasing of particle size and particle density due to the influence of particle inertia. The Tomahawk-shaped drug deposited easier than the cylindrical drug shape because of the different drag behavior. For the effect of airway geometries, G0 was the maximum deposited zone and G3 was the minimum deposited zone. The boundary layer was found around bifurcation due to the shear force at the wall. Finally, the knowledge can give an essential recommendation for curing patients with pharmaceutical aerosol. The design suggestion of a proper drug delivery device can be summarized.

Effect of Particle-Wall Interaction and Particle Shape on Particle Deposition Behavior in Human Respiratory System

Dry powder inhalation (DPI) has attracted much attention as a treatment for respiratory diseases owing to the large effective absorption area in a human respiratory system. Understanding the drug particle motion in the respiratory system and the deposition behavior is necessary to improve the efficiency of DPI. We conducted computer simulations using a model coupling a discrete element method and a computational fluid dynamics method (DEM-CFD) to evaluate the particle deposition in human respiratory system. A simple artificial respiratory model was developed, which numerically investigated the effect of particle properties and inhalation patterns on the particle deposition behavior. The DEM-CFD simulations demonstrated that the smaller- and lower-density particles showed higher reachability into the simple respiratory model, and the particle arrival ratio to the deep region strongly depended on the aerodynamic diameter. The particle arrival ratio can be described as an exponential function of the aerodynamic diameter. Furthermore, the exponential relationship between the particle reachability into the depth of the simple respiratory model and the aerodynamic diameter predicted the particle aerodynamic diameter based on the required reachability. The particle shape also had an impact on the particle deposition behavior. The rod-like particles with a larger aspect ratio indicated higher reachability into the depth of the simple respiratory model. This was attributed to the high velocity motion of the particles whose long axis was in the direction of the deep region.