CFD simulation of porous microsphere particles in the airways of pulmonary fibrosis

Prediction of Transport and Deposition of Porous Particles in the Respiratory System Using Eulerian-Lagrangian Approach

Deep lung delivery is crucial for respiratory disease treatment. Although nano and submicron particles exhibited a good deposition efficiency in deep regions of the lung, powder nonuniformity and particle agglomeration reduce their efficiency. Inhalation of porous particles (PPs) can overcome the mentioned challenges due to their larger size and low-density. The present study numerically investigates the deposition and penetration efficiency of orally inhaled PPs. A revised drag coefficient was implemented for PP transport. A realistic mouth-throat to the fifth generation of the lung was reconstructed from CT-scan images. A dilute suspension of uniformly distributed particles was considered at three inhalation flow rates (15, 30, and 45 L/min). Governing equations of the flow field and particle transport are solved using an Eulerian-Lagrangian approach. The results demonstrate that inhaling PPs significantly reduces the total and regional deposition of particles. There was also a critical porosity value under moderate and high inhalation flow rates for large PPs. Below this critical value, PP deposition efficiency substantially decreases. Additionally, it was also found that under low inhalation flow rates, the impact of porosity value is negligible. Almost 95% of the PPs penetrate the lower branches. These findings provide particle engineers and pharmaceutics with profound insight into developing novel inhalation techniques and drug delivery methods for deep lung delivery.

Modeling Realistic Geometries in Human Intrathoracic Airways

Geometrical models of the airways offer a comprehensive perspective on the complex interplay between lung structure and function. Originating from mathematical frameworks, these models have evolved to include detailed lung imagery, a crucial enhancement that aids in the early detection of morphological changes in the airways, which are often the first indicators of diseases. The accurate representation of airway geometry is crucial in research areas such as biomechanical modeling, acoustics, and particle deposition prediction. This review chronicles the evolution of these models, from their inception in the 1960s based on ideal mathematical constructs, to the introduction of advanced imaging techniques like computerized tomography (CT) and, to a lesser degree, magnetic resonance imaging (MRI). The advent of these techniques, coupled with the surge in data processing capabilities, has revolutionized the anatomical modeling of the bronchial tree. The limitations and challenges in both mathematical and image-based modeling are discussed, along with their applications. The foundation of image-based modeling is discussed, and recent segmentation strategies from CT and MRI scans and their clinical implications are also examined. By providing a chronological review of these models, this work offers insights into the evolution and potential future of airway geometry modeling, setting the stage for advancements in diagnosing and treating lung diseases. This review offers a novel perspective by highlighting how advancements in imaging techniques and data processing capabilities have significantly enhanced the accuracy and applicability of airway geometry models in both clinical and research settings. These advancements provide unique opportunities for developing patient-specific models.

Impact of the diseased lung microenvironment on the in vivo fate of inhaled particles

Inhalation drug delivery is superior for local lung disease therapy. However, there are several unique absorption barriers for inhaled drugs to overcome, including limited drug deposition at the target site, mucociliary clearance, pulmonary macrophage phagocytosis, and systemic exposure. Moreover, the respiratory disease state can affect or even destroy the physiology of the lung, thus influencing the in vivo fate of inhaled particles compared with that in healthy lungs. Nevertheless, limited information is available on this effect. Thus, in this review, we present pathological changes of the lung microenvironment under varied respiratory diseases and their influence on the in vivo fate of inhaled particles; such insights could provide a basis for rational inhalation particle design based on specific disease states.

Novel inhalation therapy in pulmonary fibrosis: principles, applications and prospects

Pulmonary fibrosis (PF) threatens millions of people worldwide with its irreversible progression. Although the underlying pathogenesis of PF is not fully understood, there is evidence to suggest that the disease can be blocked at various stages. Inhalation therapy has been applied for lung diseases such as asthma and chronic obstructive pulmonary disease, and its application for treating PF is currently under consideration. New techniques in inhalation therapy, such as the application of microparticles and nanoparticles, traditional Chinese medicine monomers, gene therapy, inhibitors, or agonists of signaling pathways, extracellular vesicle interventions, and other specific drugs, are effective in treating PF. However, the safety and effectiveness of these therapeutic techniques are influenced by the properties of inhaled particles, biological and pathological barriers, and the type of inhalation device used. This review provides a comprehensive overview of the pharmacological, pharmaceutical, technical, preclinical, and clinical experimental aspects of novel inhalation therapy for treating PF and focus on therapeutic methods that significantly improve existing technologies or expand the range of drugs that can be administered via inhalation. Although inhalation therapy for PF has some limitations, the advantages are significant, and further research and innovation about new inhalation techniques and drugs are encouraged.

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.

Relaxin-Loaded Inhaled Porous Microspheres Inhibit Idiopathic Pulmonary Fibrosis and Improve Pulmonary Function Post-Bleomycin Challenges

Idiopathic pulmonary fibrosis (IPF) causes worsening pulmonary function, and no effective treatment for the disease etiology is available now. Recombinant Human Relaxin-2 (RLX), a peptide agent with anti-remodeling and anti-fibrotic effects, is a promising biotherapeutic candidate for musculoskeletal fibrosis. However, due to its short circulating half-life, optimal efficacy requires continuous infusion or repeated injections. Here, we developed the porous microspheres loading RLX (RLX@PMs) and evaluated their therapeutic potential on IPF by aerosol inhalation. RLX@PMs have a large geometric diameter as RLX reservoirs for a long-term drug release, but smaller aerodynamic diameter due to their porous structures, which were beneficial for higher deposition in the deeper lungs. The results showed a prolonged release over 24 days, and the released drug maintained its peptide structure and activity. RLX@PMs protected mice from excessive collagen deposition, architectural distortion, and decreased compliance after a single inhalation administration in the bleomycin-induced pulmonary fibrosis model. Moreover, RLX@PMs showed better safety than frequent gavage administration of pirfenidone. We also found RLX-ameliorated human myofibroblast-induced collagen gel contraction and suppressed macrophage polarization to the M2 type, which may be the reason for reversing fibrosis. Hence, RLX@PMs represent a novel strategy for the treatment of IPF and suggest clinical translational potential.

Formulation of Resveratrol-Loaded Polycaprolactone Inhalable Microspheres Using Tween 80 as an Emulsifier: Factorial Design and Optimization

Resveratrol (RSV) is a bioactive phytoconstituent that has potential applications in respiratory diseases. However, poor oral bioavailability is the major hurdle to its clinical use. In the present work, resveratrol-loaded polycaprolactone (PCL) inhalable microspheres (MSs) were formulated to improve their therapeutic potential. The inhalable microspheres were formulated using the emulsion-solvent evaporation method. In this research, inhalable resveratrol microspheres were prepared using Tween 80 in place of polyvinyl alcohol which formed insoluble lumps. A 3² factorial design was applied taking polymer (PCL) and emulsifier (Tween 80) as independent variables and drug loading (DL) and encapsulation efficiency (EE) as dependent variables. The DL and EE of the optimized formulation were found to be 30.6% and 63.84% respectively. The in vitro aerosolization study performed using the Anderson cascade impactor showed that the fine particle fraction (FPF) of optimized resveratrol polycaprolactone microspheres (RSV-PCL-MSs) blended with lactose, and RSV-PCL-MSs were significantly higher than those of the pure drugs. The MMAD_T (theoretical mass median aerodynamic diameter) of optimized RSV-PCL-MSs was found to be 3.25 ± 1.15. The particle size of microspheres was within the inhalable range, i.e., between 1 and 5 µm. The morphological analysis showed spherical-shaped particles with smooth surfaces. The in vitro release study showed sustained drug release from the microspheres for up to 12 h. The study concluded that resveratrol-loaded inhalable microspheres may be an efficient delivery system to treat COPD.