The Contribution of Different Formulation Components on the Aerosol Charge in Carrier-Based Dry Powder Inhaler Systems

Discrete Element Method Evaluation of Triboelectric Charging Due to Powder Handling in the Capsule of a DPI

The generation and accumulation of an electrostatic charge from handling pharmaceutical powders is a well-known phenomenon, given the insulating nature of most APIs (Active Pharmaceutical Ingredients) and excipients. In capsule-based DPIs (Dry Powder Inhalers), the formulation is stored in a gelatine capsule placed in the inhaler just before inhalation. The action of capsule filling, as well as tumbling or vibration effects during the capsule life cycle, implies a consistent amount of particle-particle and particle-wall contacts. A significant contact-induced electrostatic charging can then take place, potentially affecting the inhaler's efficiency. DEM (Discrete Element Method) simulations were performed on a carrier-based DPI formulation (salbutamol-lactose) to evaluate such effects. After performing a comparison with the experimental data on a carrier-only system under similar conditions, a detailed analysis was conducted on two carrier-API configurations with different API loadings per carrier particle. The charge acquired by the two solid phases was tracked in both the initial particle settling and the capsule shaking process. Alternating positive-negative charging was observed. Particle charging was then investigated in relation to the collision statistics, tracking the particle-particle and particle-wall events for the carrier and API. Finally, an analysis of the relative importance of electrostatic, cohesive/adhesive, and inertial forces allowed the importance of each term in determining the trajectory of the powder particles to be estimated.

Characterization of dry powder inhaler performance through experimental methods

Experimental methods provide means for the quality control of existing DPIs and for exploring the influence of formulation and device parameters well in advance of clinical trials for novel devices and formulations. In this review, we examine the state of the art of in vitro testing of DPIs, with a focus primarily on the development of accurate in vitro-in vivo correlations. Aspects of compendial testing are discussed, followed by the influence of flow profiles on DPI performance, the characterization of extrathoracic deposition using mouth-throat geometries, and the characterization of regional thoracic deposition. Additional experimental methods that can inform the timing of bolus delivery, the influence of environmental conditions, and the development of electrostatic charge on aerosolized DPI powders are reviewed. We conclude with perspectives on current in vitro methods and identify potential areas for future investigation, including the estimation of variability in deposition, better characterization of existing compendial methods, optimization of formulation and device design to bypass extrathoracic deposition, and the use of novel tracheobronchial filters that aim to provide more clinically relevant measures of performance directly from in vitro testing.

Addressing the Need for Controls on Particle Bounce and Re-entrainment in the Cascade Impactor and for the Mitigation of Electrostatic Charge for Aerodynamic Particle Size Assessment of Orally Inhaled Products: an Assessment by the International Consortium on Regulation and Science (IPAC-RS)

Multi-stage cascade impactors (CI) are accepted for the determination of metrics of the drug mass aerodynamic particle size distributions (APSD) of aerosols emitted from orally inhaled products (OIPs). This is particularly important for products where the drug to excipient ratio or particle density may not be the same in each aerodynamic size fraction; examples of such products are carrier-containing dry powder inhalers (DPIs) and suspension pressurized metered-dose inhalers (pMDIs). CI measurements have been used as the "gold standard" for acceptance of alternative methods of APSD assessment, such as laser diffraction for nebulized solutions. Although these apparatus are labor-intensive, they are accepted in regulatory submissions and quality control assessments because the mass of active pharmaceutical ingredient(s) in the aerosol can be quantified by chemical assay and measured particle size is based on the aerodynamic diameter scale that is predictive of deposition in the respiratory tract. Two of the most important factors that modify the ideal operation of an impactor are "particle bounce," that is often accompanied by re-entrainment in the air flow passing the stage of interest, and electrostatic charge acquired by the particles during the preparation and aerosolization of the formulation when the inhaler is actuated. This article reviews how both factors can lead to biased APSD measurements, focusing on measurements involving pMDIs and DPIs, where these sources of error are most likely to be encountered. Recommendations are provided for the mitigation of both factors to assist the practitioner of these measurements.

Emulsion Electrospinning of Polytetrafluoroethylene (PTFE) Nanofibrous Membranes for High-Performance Triboelectric Nanogenerators

Electrospinning is a simple, versatile technique for fabricating fibrous nanomaterials with the desirable features of extremely high porosities and large surface areas. Using emulsion electrospinning, polytetrafluoroethylene/polyethene oxide (PTFE/PEO) membranes were fabricated, followed by a sintering process to obtain pure PTFE fibrous membranes, which were further utilized against a polyamide 6 (PA6) membrane for vertical contact-mode triboelectric nanogenerators (TENGs). Electrostatic force microscopy (EFM) measurements of the sintered electrospun PTFE membranes revealed the presence of both positive and negative surface charges owing to the transfer of positive charge from PEO which was further corroborated by FTIR measurements. To enhance the ensuing triboelectric surface charge, a facile negative charge-injection process was carried out onto the electrospun (ES) PTFE subsequently. The fabricated TENG gave a stabilized peak-to-peak open-circuit voltage (V_oc) of up to ∼900 V, a short-circuit current density (J_sc) of ∼20 mA m^-2, and a corresponding charge density of ∼149 μC m^-2, which are ∼12, 14, and 11 times higher than the corresponding values prior to the ion-injection treatment. This increase in the surface charge density is caused by the inversion of positive surface charges with the simultaneous increase in the negative surface charge on the PTFE surface, which was confirmed by using EFM measurements. The negative charge injection led to an enhanced power output density of ∼9 W m^-2 with high stability as confirmed from the continuous operation of the ion-injected PTFE/PA6 TENG for 30 000 operation cycles, without any significant reduction in the output. The work thus introduces a relatively simple, cost-effective, and environmentally friendly technique for fabricating fibrous fluoropolymer polymer membranes with high thermal/chemical resistance in TENG field and a direct ion-injection method which is able to dramatically improve the surface negative charge density of the PTFE fibrous membranes.

The use of a quartz crystal microbalance as an analytical tool to monitor particle/surface and particle/particle interactions under dry ambient and pressurized conditions: a study using common inhaler components

Metered dose inhalers (MDI) and multidose powder inhalers (MPDI) are commonly used for the treatment of chronic obstructive pulmonary diseases and asthma. Currently, analytical tools to monitor particle/particle and particle/surface interaction within MDI and MPDI at the macro-scale do not exist. A simple tool capable of measuring such interactions would ultimately enable quality control of MDI and MDPI, producing remarkable benefits for the pharmaceutical industry and the users of inhalers. In this paper, we have investigated whether a quartz crystal microbalance (QCM) could become such a tool. A QCM was used to measure particle/particle and particle/surface interactions on the macroscale, by additions of small amounts of MDPI components, in the powder form into a gas stream. The subsequent interactions with materials on the surface of the QCM sensor were analyzed. Following this, the sensor was used to measure fluticasone propionate, a typical MDI active ingredient, in a pressurized gas system to assess its interactions with different surfaces under conditions mimicking the manufacturing process. In both types of experiments the QCM was capable of discriminating interactions of different components and surfaces. The results have demonstrated that the QCM is a suitable platform for monitoring macro-scale interactions and could possibly become a tool for quality control of inhalers.

Empirical modeling of the fine particle fraction for carrier-based pulmonary delivery formulations

In vitro study of the deposition of drug particles is commonly used during development of formulations for pulmonary delivery. The assay is demanding, complex, and depends on: properties of the drug and carrier particles, including size, surface characteristics, and shape; interactions between the drug and carrier particles and assay conditions, including flow rate, type of inhaler, and impactor. The aerodynamic properties of an aerosol are measured in vitro using impactors and in most cases are presented as the fine particle fraction, which is a mass percentage of drug particles with an aerodynamic diameter below 5 μm. In the present study, a model in the form of a mathematical equation was developed for prediction of the fine particle fraction. The feature selection was performed using the R-environment package "fscaret". The input vector was reduced from a total of 135 independent variables to 28. During the modeling stage, techniques like artificial neural networks, genetic programming, rule-based systems, and fuzzy logic systems were used. The 10-fold cross-validation technique was used to assess the generalization ability of the models created. The model obtained had good predictive ability, which was confirmed by a root-mean-square error and normalized root-mean-square error of 4.9 and 11%, respectively. Moreover, validation of the model using external experimental data was performed, and resulted in a root-mean-square error and normalized root-mean-square error of 3.8 and 8.6%, respectively.

Electrostatics in pharmaceutical aerosols for inhalation

Electrostatics continues to play an important role in pharmaceutical aerosols for inhalation. Despite its ubiquitous nature, the charging process is complex and not well understood. Nonetheless, significant advances in the past few years continue to improve understanding and lead to better control of electrostatics. The purpose of this critical review is to present an overview of the literature, with an emphasis on how electrostatic charge can be useful in improving pulmonary drug delivery.