Studies of the Crystallization and Dissolution of Individual Suspended Sodium Chloride Aerosol Particles.

Aerosols transform between physical phases, as they respond to variations in environmental conditions. There are many industries that depend on these dynamic processes of crystallization and dissolution. Here, a single particle technique (an electrodynamic balance) is used to explore the crystallization and dissolution dynamics of a model system, sodium chloride. The physical and environmental factors that influence the dynamics of crystal formation from a saline droplet (whose initial radius is ∼25 µm) and the kinetics of water adsorption onto dried particles are examined. The drying relative humidity (RH) is shown to impact the physical properties of the dried particle. When a saline droplet is injected into an airflow at an RH close to the efflorescence RH (ERH, 45%), an individual single crystal forms. By contrast, when a compositionally equivalent saline droplet is injected into dry air (RH ∼ 0%), a salt crystal made of multiple crystalline particles is formed. Subsequent to crystallization, the crystal shape, morphology, and surface area were all found to affect the dissolution dynamics of the dried particle. Additionally, we report that the difference between the deliquesce RH and environmental RH significantly impacts the dissolution time scale.

Assessing Aerosol Performance of a Dry Powder Carrier Formulation with Increasing Doses Using a Novel Inhaler.

This study aims to investigate the implications of loaded formulation mass on aerosol performance using a reservoir novel dry powder inhaler containing a custom dosing cup to deliver carrier-based formulation to the lungs. A 3D printed dosing cup with volume size of 133.04 mm3 was manufactured to allow for the progressive loading of different carrier formulation masses of 1% beclomethasone dipropionate BDP (w/w) formulation (10 to 60 mg, with increments of 10 mg), in a novel customizable DPI device. Scanning electron micrographs were used to investigate BDP detachment from carrier particles post-aerosolisation and particle deposition on the USP induction port. The subsequent aerosol performance analysis was performed using the next generation impactor (NGI). Incrementally increasing the loading mass to 60 mg led to decreases in BDP detachment from carrier particles, resulting in significant decreases in aerosol performance. Increases in loading dose mass led to progressively decreased detachment of BDP from the carrier and the overall aerosol performance in comparison to the initial mass of 10 mg. These results are likely to be due to a decrease in void volume within the dosing cup with increased loading mass leading to altered airflow, decreased impaction forces and the possibility of a significant quantity of large carrier particles introducing a 'sweeping' effect on the inhaler inner surface. This study has shown that despite the decreased BDP detachment from the carrier and decreased aerosol performance, the dose delivered to the lung still increased due to the higher loaded dose.

High-Speed Laser Image Analysis of Plume Angles for Pressurised Metered Dose Inhalers: The Effect of Nozzle Geometry.

The aim of this study is to investigate aerosol plume geometries of pressurised metered dose inhalers (pMDIs) using a high-speed laser image system with different actuator nozzle materials and designs. Actuators made from aluminium, PET and PTFE were manufactured with four different nozzle designs: cone, flat, curved cone and curved flat. Plume angles and spans generated using the designed actuator nozzles with four solution-based pMDI formulations were imaged using Oxford Lasers EnVision system and analysed using EnVision Patternate software. Reduced plume angles for all actuator materials and nozzle designs were observed with pMDI formulations containing drug with high co-solvent concentration (ethanol) due to the reduced vapour pressure. Significantly higher plume angles were observed with the PTFE flat nozzle across all formulations, which could be a result of the nozzle geometry and material's hydrophobicity. The plume geometry of pMDI aerosols can be influenced by the vapour pressure of the formulation, nozzle geometries and actuator material physiochemical properties.

The effect of actuator nozzle designs on the electrostatic charge generated in pressurised metered dose inhaler aerosols.

PURPOSE: To investigate the influence of different actuator nozzle designs on aerosol electrostatic charges and aerosol performances for pressurised metered dose inhalers (pMDIs). METHODS: Four actuator nozzle designs (flat, curved flat, cone and curved cone) were manufactured using insulating thermoplastics (PET and PTFE) and conducting metal (aluminium) materials. Aerosol electrostatic profiles of solution pMDI formulations containing propellant HFA 134a with different ethanol concentration and/or model drug beclomethasone dipropionate (BDP) were studied using a modified electrical low-pressure impactor (ELPI) for all actuator designs and materials. The mass of the deposited drug was analysed using high performance liquid chromatography (HPLC). RESULTS: Both curved nozzle designs for insulating PET and PTFE actuators significantly influenced aerosol electrostatics and aerosol performance compared with conducting aluminium actuator, where reversed charge polarity and higher throat deposition were observed with pMDI formulation containing BDP. Results are likely due to the changes in plume geometry caused by the curved edge nozzle designs and the bipolar charging nature of insulating materials. CONCLUSIONS: This study demonstrated that actuator nozzle designs could significantly influence the electrostatic charges profiles and aerosol drug deposition pattern of pMDI aerosols, especially when using insulating thermoplastic materials where bipolar charging is more dominant.

The Effect of Active Pharmaceutical Ingredients on Aerosol Electrostatic Charges from Pressurized Metered Dose Inhalers.

PURPOSE: This study investigated the effect of different active pharmaceutical ingredients (API) on aerosol electrostatic charges and aerosol performances for pressurized metered dose inhalers (pMDIs), using both insulating and conducting actuators. METHODS: Five solution-based pMDIs containing different API ingredients including: beclomethasone dipropionate (BDP), budesonide (BUD), flunisolide (FS), salbutamol base (SB) and ipratropium bromide (IPBr) were prepared using pressure filling technique. Actuator blocks made from nylon, polytetrafluoroethylene (PTFE) and aluminium were manufactured with 0.3 mm nominal orifice diameter and cone nozzle shape. Aerosol electrostatics for each pMDI formulation and actuator were evaluated using the electrical low-pressure impactor (ELPI) and drug depositions were analysed using high performance liquid chromatography (HPLC). RESULTS: All three actuator materials showed the same net charge trend across the five active drug ingredients, with BDP, BUD and FS showing positive net charges for both nylon and PTFE actuators, respectively. While SB and IPBr had significantly negative net charges across the three different actuators, which correlates to the ionic functional groups present on the drug molecule structures. CONCLUSIONS: The API present in a pMDI has a dominant effect on the electrostatic properties of the formulation, overcoming the charge effect arising from the actuator materials. Results have shown that the electrostatic charges for a solution-based pMDI could be related to the interactions of the chemical ingredients and change in the work function for the overall formulation.

The influence of actuator materials and nozzle designs on electrostatic charge of pressurised metered dose inhaler (pMDI) formulations.

PURPOSE: To investigate the influence of different actuator materials and nozzle designs on the electrostatic charge properties of a series of solution metered dose inhaler (pMDI) aerosols. METHODS: Actuators were manufactured with flat and cone nozzle designs using five different materials from the triboelectric series (Nylon, Polyethylene terephthalate, Polyethylene-High density, Polypropylene copolymer and Polytetrafluoroethylene). The electrostatic charge profiles of pMDI containing beclomethasone dipropionate (BDP) as model drug in HFA-134a propellant, with different concentrations of ethanol were studied. Electrostatic measurements were taken using a modified electrical low-pressure impactor (ELPI) and the deposited drug mass assayed chemically using HPLC. RESULTS: The charge profiles of HFA 134a alone have shown strong electronegativity with all actuator materials and nozzle designs, at an average of -1531.34 pC ± 377.34. The presence of co-solvent ethanol significantly reduced the negative charge magnitude. BDP reduced the suppressing effect of ethanol on the negative charging of the propellant. For all tested formulations, the flat nozzle design showed no significant differences in net charge between different actuator materials, whereas the charge profiles of cone designs followed the triboelectric series. CONCLUSION: The electrostatic charging profiles from a solution pMDI containing BDP and ethanol can be significantly influenced by the actuator material, nozzle design and formulation components. Ethanol concentration appears to have the most significant impact. Furthermore, BDP interactions with ethanol and HFA have an influence on the electrostatic charge of aerosols. By choosing different combinations of actuator materials and orifice design, the fine particle fractions of formulations can be altered.

Effect of Dosing Cup Size on the Aerosol Performance of High-Dose Carrier-Based Formulations in a Novel Dry Powder Inhaler.

This study investigated how varying the dosing cup size of a novel reservoir dry powder inhaler (DPI) affects the detachment of a micronized active pharmaceutical ingredient from larger carrier particles, and the aerosol performance of a DPI carrier formulation. Three different-sized dosing cups were designed: 3D printed with cup volumes of 16.26 mm3, 55.99 mm3, and 133.04 mm3, and tested with five different carrier type formulations with beclomethasone dipropionate (BDP) concentrations between 1% and 30% (w/w). The morphology of the BDP attached to the carrier was investigated using scanning electron microscopy and the aerosol performance using the Next Generation Impactor. Increasing the volume of the dosing cup led to a reduction of BDP deposition in the Next Generation Impactor preseparator, and an increase in BDP detachment from the carrier was observed, leading to increased aerosol performance. The decreased amount of BDP attached to carrier after aerosolization was attributed to the increased dosing cup void volume. This may enable greater particle-particle and particle-wall collisions, with greater BDP detachment from the carrier and deagglomeration of smaller agglomerates. The dosing cup volume was observed to have significant influence on particle dispersion and the overall aerosol performance of a DPI.

Limitations of high dose carrier based formulations.

PURPOSE: This study was performed to investigate how increasing the active pharmaceutical ingredient (API) content within a formulation affects the dispersion of particles and the aerosol performance efficiency of a carrier based dry powder inhalable (DPI) formulation, using a custom dry powder inhaler (DPI) development rig. METHODS: Five formulations with varying concentrations of API beclomethasone dipropionate (BDP) between 1% and 30% (w/w) were formulated as a multi-component carrier system containing coarse lactose and fine lactose with magnesium stearate. The morphology of the formulation and each component were investigated using scanning electron micrographs while the particle size was measured by laser diffraction. The aerosol performance, in terms of aerodynamic diameter, was assessed using the British pharmacopeia Apparatus E cascade impactor (Next generation impactor). Chemical analysis of the API was observed by high performance liquid chromatography (HPLC). RESULTS: Increasing the concentration of BDP in the blend resulted in increasing numbers and size of individual agglomerates and densely packed BDP multi-layers on the surface of the lactose carrier. BDP present within the multi-layer did not disperse as individual primary particles but as dense agglomerates, which led to a decrease in aerosol performance and increased percentage of BDP deposition within the Apparatus E induction port and pre-separator. CONCLUSION: As the BDP concentration in the blends increases, aerosol performance of the formulation decreases, in an inversely proportional manner. Concurrently, the percentage of API deposition in the induction port and pre-separator could also be linked to the amount of micronized particles (BDP and Micronized composite carrier) present in the formulation. The effect of such dose increase on the behaviour of aerosol dispersion was investigated to gain greater insight in the development and optimisation of higher dosed carrier-based formulations.

Pulmonary aerosol delivery and the importance of growth dynamics.

Aerosols are dynamic systems, responding to variations in the surrounding environmental conditions by changing in size, composition and phase. Although, widely used in inhalation therapies, details of the processes occurring on aerosol generation and during inhalation have received little attention. Instead, research has focused on improvements to the formulation of the drug prior to aerosolization and the resulting clinical efficacy of the treatment. Here, we highlight the processes that occur during aerosol generation and inhalation, affecting aerosol disposition when deposited and, potentially, impacting total and regional doses. In particular, we examine the response of aerosol particles to the humid environment of the respiratory tract, considering both the capacity of particles to grow by absorbing moisture and the timescale for condensation to occur. [Formula: see text].

Experimental and computational study of the effect of breath-actuated mechanism built in the NEXThaler® dry powder inhaler.

The breath-actuated mechanism (BAM) is a mechanical unit included in NEXThaler® with the role of delaying the emission of the drug until the inhalation flow rate of the patient is sufficiently high to detach the drug particles from their carriers. The main objective of this work was to analyse the effect of the presence of BAM on the size distribution of the emitted drug and its airway deposition efficiency and distribution. Study of the hygroscopic growth of the emitted drug particles and its effect on the deposition was another goal of this study. Size distributions of Foster® NEXThaler® drug particles emitted by dry powder inhalers with and without BAM have been measured by a Next Generation Impactor. Three characteristic inhalation profiles of asthmatic patients (low, moderate and high flow rates) were used for both experimental and modelling purposes. Particle hygroscopic growth was determined by a new method, where experimental measurements are combined with simulations. Upper airway and lung deposition fractions were computed assuming 5s and 10s breath-hold times. By the inclusion of BAM the fine particle fraction of the steroid component increased from 24 to 30% to 47-51%, while that of bronchodilator from 25-34% to 52-55%. The predicted upper airway steroid and bronchodilator doses decreased from about 60% to 35-40% due to BAM. At the same time, predicted lung doses increased from about 20%-35% (steroid) and from 22% to 38% (bronchodilator) for the moderate flow profile and from about 25% to 40% (steroid) and from 29% to 47% (bronchodilator) for the high inhalation flow profile. Although BDP and FF upper airway doses decreased by a factor of about two when BAM was present, lung doses of both components were about the same in the BAM and no-BAM configurations at the weakest flow profile. However, lung dose increased by 2-3% even for this profile when hygroscopic growth was taken into account. In conclusion, the NEXThaler® BAM mechanism is a unique feature enabling high emitted fine particle fraction and enhanced drug delivery to the lungs.

Humidity affects the morphology of particles emitted from beclomethasone dipropionate pressurized metered dose inhalers.

The effects of propellant type, cosolvent content, and air humidity on the morphology and solid phase of the particles produced from solution pressurized metered dose inhalers containing the corticosteroid beclomethasone dipropionate were investigated. The active ingredient was dissolved in the HFA propellants 134a and 227ea with varying levels of the cosolvent ethanol and filled into pressurized metered dose inhalers. Inhalers were actuated into an evaporation chamber under controlled temperature and humidity conditions and sampled using a single nozzle, single stage inertial impactor. Particle morphology was assessed qualitatively using field emission scanning electron microscopy and focused ion beam-helium ion microscopy. Drug solid phase was assessed using Raman microscopy. The relative humidity of the air during inhaler actuation was found to have a strong effect on the particle morphology, with solid spheroidal particles produced in dry air and highly porous particles produced at higher humidity levels. Air humidification was found to have no effect on the solid phase of the drug particles, which was predominantly amorphous for all tested formulations. A critical level of air relative humidity was required to generate porous particles for each tested formulation. This critical relative humidity was found to depend on the amount of ethanol used in the inhaler, but not on the type of propellant utilized. The results indicate that under the right circumstances water vapor saturation followed by nucleated water condensation or ice deposition occurs during particle formation from evaporating propellant-cosolvent-BDP droplets. This finding reveals the importance of condensed water or ice as a templating agent for porosity when particle formation occurs at saturated conditions, with possible implications on the pharmacokinetics of solution pMDIs and potential applications in particle engineering for drug delivery.

A correlation equation for the mass median aerodynamic diameter of the aerosol emitted by solution metered dose inhalers.

A correlation equation for the mass median aerodynamic diameter (MMAD) of the aerosol emitted by solution metered dose inhalers (MDIs) is presented. A content equivalent diameter is defined and used to describe aerosols generated by evaporating metered dose inhaler sprays. A large set of cascade impaction data is analyzed, and the MMAD and geometric standard deviation is calculated for each datum. Using dimensional analysis, the mass median content equivalent diameter is correlated with formulation variables. Based on this correlation in combination with mass balance considerations and the definition of the aerodynamic diameter, an equation for prediction of the MMAD of an inhaler given the pressure of the propellant in the metering chamber of the MDI valve and the surface tension of the propellant is derived. The accuracy of the correlation equation is verified by comparison with literature results. The equation is applicable to both HFA (hydrofluoroalkane) propellants 134a and 227ea, with varying levels of co-solvent ethanol.

In vitro investigation of the effect of ambient humidity on regional delivered dose with solution and suspension MDIs.

BACKGROUND: Existing literature has shown that high relative humidity (RH) affects in vitro aerosol drug delivery of nebulizer and pressurized metered dose inhaler (pMDI) formulations. The aim of this study is to investigate in vitro mouth-throat deposition and lung delivery of selected solution and suspension pMDI formulations, under a range of RH, temperature, and flow rate conditions. METHODS: The Alberta Idealized Throat was connected to a collection filter and placed in an environmental control chamber. The formulations selected were beclomethasone dipropionate (BDP) in 13% w/w ethanol/1.3% w/w glycerol and HFA-134a propellant solution ("BDP HFA134a"), BDP in 13% w/w ethanol and HFA-227 propellant solution ("BDP HFA227"), and Flixotide Evohaler (fluticasone propionate 250 µg/dose in HFA-134a suspension). Each of these pMDI formulations was dispersed into the mouth-throat and filter assembly in triplicate, according to an experimental matrix consisting of the following conditions: air flow rates of 28.3, 60, and 90 L/min; 0%, 35%, and 80% RH; operating temperatures of 20°C and 40°C. RESULTS: There was a general increase in mouth-throat deposition and corresponding decrease in filter deposition (representing lung dose fraction), with increasing RH for both BDP HFA134a and Flixotide pMDIs. Increasing temperature from 20°C to 40°C resulted in decreased mouth-throat deposition and increased lung dose fraction for the solution pMDIs, but generally no effect for the suspension pMDI. CONCLUSIONS: Not only is the dose delivery of pMDI formulations affected by environmental conditions (in some cases causing up to 50% reduction in lung delivery), but solution and suspension formulations also behave differently in response to these conditions. These results have implications during dosage form design, testing, and for usage patient use.