Controlling the droplet size of formulations nebulized by vibrating-membrane technology

Low-dose intrapulmonary drug delivery device for studies on next-generation therapeutics in mice

Although nebulizers have been developed for delivery of small molecules in human patients, no tunable device has been purpose-built for targeted delivery of modern large molecule and temperature-sensitive therapeutics to mice. Mice are used most of all species in biomedical research and have the highest number of induced models for human-relevant diseases and transgene models. Regulatory approval of large molecule therapeutics, including antibody therapies and modified RNA highlight the need for quantifiable dose delivery in mice to model human delivery, proof-of-concept studies, efficacy, and dose-response. To this end, we developed and characterized a tunable nebulization system composed of an ultrasonic transducer equipped with a mesh nebulizer fitted with a silicone restrictor plate modification to control the nebulization rate. We have identified the elements of design that influence the most critical factors to targeted delivery to the deep lungs of BALB/c mice. By comparing an in silico model of the mouse lung with experimental data, we were able to optimize and confirm the targeted delivery of over 99% of the initial volume to the deep portions of the mouse lung. The resulting nebulizer system provides targeted lung delivery efficiency far exceeding conventional nebulizers preventing waste of expensive biologics and large molecules during proof-of-concept and pre-clinical experiments involving mice. (Word Count =207).

Liposomal form of erlotinib for local inhalation administration and efficiency of its transport to the lungs

This contribution is focused on the preparation of a liposomal drug delivery system of erlotinib resisting the nebulization process that could be used for local treatment of non-small-cell lung cancer. Liposomes with different compositions were formulated to reveal their influence on the encapsulation efficiency of erlotinib. An encapsulation efficiency higher than 98 % was achieved for all vesicles containing phosphatidic acid (d ≈ 100 nm, ζ = - 43 mV) even in the presence of polyethylene glycol (d ≈ 150 nm, ζ = - 17 mV) which decreased this value in all other formulas. The three most promising formulations were nebulized by two air-jet and two vibrating mesh nebulizers, and the aerosol deposition in lungs was calculated by tools of computational fluid and particle mechanics. According to the numerical simulations and measurements of liposomal stability, air-jet nebulizers generated larger portion of the aerosol able to penetrate deeper into the lungs, but the delivery is likely to be more efficient when the formulation is administered by Aerogen Solo vibrating mesh nebulizer because of a higher portion of intact vesicles after the nebulization. The leakage of encapsulated drug from liposomes nebulized by this nebulizer was lower than 2 % for all chosen vesicles.

Improvement of Pulmonary Photodynamic Therapy: Nebulisation of Curcumin-Loaded Tetraether Liposomes

Lung cancer is one of the most common causes for a high number of cancer related mortalities worldwide. Therefore, it is important to improve the therapy by finding new targets and developing convenient therapies. One of these novel non-invasive strategies is the combination of pulmonary delivered tetraether liposomes and photodynamic therapy. In this study, liposomal model formulations containing the photosensitiser curcumin were nebulised via two different technologies, vibrating-mesh nebulisation and air-jet nebulisation, and compared with each other. Particle size and ζ-potential of the liposomes were investigated using dynamic light scattering and laser Doppler anemometry, respectively. Furthermore, atomic force microscopy and transmission electron microscopy were used to determine the morphological characteristics. Using a twin glass impinger, suitable aerodynamic properties were observed, with the fine particle fraction of the aerosols being ≤62.7 ± 1.6%. In vitro irradiation experiments on lung carcinoma cells (A549) revealed an excellent cytotoxic response of the nebulised liposomes in which the stabilisation of the lipid bilayer was the determining factor. Internalisation of nebulised curcumin-loaded liposomes was visualised utilising confocal laser scanning microscopy. Based on these results, the pulmonary application of curcumin-loaded tetraether liposomes can be considered as a promising approach for the photodynamic therapy against lung cancer.

In Vitro Evaluation of a Vibrating-Mesh Nebulizer Repeatedly Use over 28 Days

This in vitro study evaluates the performance of a disposable vibrating-mesh nebulizer when used for 28 days. A lung model was used to simulate the breathing pattern of an adult with chronic obstructive pulmonary disease. The vibrating-mesh nebulizer was used for three treatments/day over 28 days without cleaning after each test. Results showed that the inhaled drug dose was similar during four weeks of use (p = 0.157), with 16.73 ± 4.46% at baseline and 15.29 ± 2.45%, 16.21 ± 2.21%, 17.56 ± 1.98%, and 17.13 ± 1.81%, after the first, second, third, and fourth weeks, respectively. The particle size distribution, residual drug volume, and nebulization time remained similar across four weeks of use (p = 0.110, p = 0.763, and p = 0.573, respectively). Mesh was inspected using optical microscopy and showed that approximately 50% of mesh pores were obscured after 84 runs, and light penetration through the aperture plate was significantly reduced after the 21st use (p < 0.001) with no correlation to nebulizer performance. We conclude that the vibrating-mesh nebulizer delivered doses of salbutamol solution effectively over four weeks without cleaning after each use even though the patency and clarity of the aperture plate were reduced by the first week of use.

Rapid Soft Material Actuation Through Droplet Evaporation

Soft material actuation is a promising field that can potentially solve several limitations of traditional robotic systems. These systems comprise soft and flexible materials to achieve high degrees of freedom and compliance with their surroundings. One method to actuate such structures is to vaporize liquid that is embedded inside the soft material. The soft elastomers are inflated since the generated vapor occupies a much larger volume after phase transformation. The simplest and widely used design to vaporize such liquids is installing a heating element near the liquid. Heating the system beyond the boiling point rapidly boils the liquid and deforms the structure. However, this technique possesses several limitations, such as the heating element must be in the liquid's vicinity, and boiling the liquid requires high temperatures. In addition, embedding a small amount of liquid for faster boiling prevents the use of valves to exhaust the vapor. Instead, the structure is slowly cooled until it returns to its original position. In this study, these limitations are addressed by combining heating with vibrating mesh atomization. The atomizer disperses the liquid into small droplets, which vaporize much faster as compared with simply heating the bulk liquid. Actuation through vibrating mesh atomization was first characterized and compared with other techniques. Then, the introduced method was used to demonstrate cyclic actuation, and a bistable structure was designed and fabricated to demonstrate gripping motion.

Polymer-coated aperture plates for tailored atomization processes

There is a significant industrial demand for minimizing the size of droplets for various technical applications. Herein, conformal polymer coatings were used to decrease the orifice dimensions of aperture plates to almost any desired dimension. The generated droplet size revealed a relevant impact on the final dried particle size in a spray-drying process. Likewise, the smaller droplets generated resulted in an improved lung deposition following inhalation. Overall, the current results help increase the understanding on how to manipulate the size distribution of droplets produced by actuated aperture plates, especially in the sub-10 μm range.

Stability of Polymer Coatings on Nebulizer Membranes During Aerosol Generation

The dimensions of orifices found in aperture plates used for nebulization can be modified by thin polymer coatings with the aim to control the size distribution of the generated aerosol droplets. However, the stability of such polymer coatings on the surface of nebulizer membranes during aerosol generation has not been elucidated. Nebulizer membranes made of stainless steel were covered with a thin film of poly(chloro-p-xylylene) (~1 μm) in the presence or absence of a silane-based adhesion promoter. Thereby, the orifice cross-sections of the nebulizer membrane were reduced by ~50%, accompanied by a remarkable decline in droplet size. Upon continuous nebulization of aqueous test liquids, the droplet size generated by the nonconditioned (no silane), poly(chloro-p-xylylene)-coated membranes reverted to that of the uncoated nebulizer membrane within ~5 min. By contrast, no such rapid return of droplet size to "baseline" values was noticed for the silane-conditioned, poly(chloro-p-xylylene)-coated counterparts. Scanning electron microscopy exhibited significant polymer detachment from the orifices of the nonconditioned (no silane) membranes and thus confirmed the findings from laser diffraction. Overall, silane-based adhesion promoters can increase the persistence of poly(chloro-p-xylylene) coatings on nebulizer membranes during aerosol generation.

A comprehensive screening platform for aerosolizable protein formulations for intranasal and pulmonary drug delivery

Aerosolized administration of biopharmaceuticals to the airways is a promising route for nasal and pulmonary drug delivery, but - in contrast to small molecules - little is known about the effects of aerosolization on safety and efficacy of biopharmaceuticals. Proteins are sensitive against aerosolization-associated shear stress. Tailored formulations can shield proteins and enhance permeation, but formulation development requires extensive screening approaches. Thus, the aim of this study was to develop a cell-based in vitro technology platform that includes screening of protein quality after aerosolization and transepithelial permeation. For efficient screening, a previously published aerosolization-surrogate assay was used in a design of experiments approach to screen suitable formulations for an IgG and its antigen-binding fragment (Fab) as exemplary biopharmaceuticals. Efficient, dose-controlled aerosol-cell delivery was performed with the ALICE-CLOUD system containing RPMI 2650 epithelial cells at the air-liquid interface. We could demonstrate that our technology platform allows for rapid and efficient screening of formulations consisting of different excipients (here: arginine, cyclodextrin, polysorbate, sorbitol, and trehalose) to minimize aerosolization-induced protein aggregation and maximize permeation through an in vitro epithelial cell barrier. Formulations reduced aggregation of native Fab and IgG relative to vehicle up to 50% and enhanced transepithelial permeation rate up to 2.8-fold.

Electrolyte type and nozzle composition affect the process of vibrating-membrane nebulization

The size of airborne particles determines their deposition pattern within the lungs and therefore, the efficacy of inhalation therapy. The present study analyzed factors affecting liquid atomization performed by vibrating-membrane technology. First, the process of vibrating-membrane nebulization (eFlow®rapid and Aeroneb® Pro) was challenged with numerous inorganic salts and active pharmaceutical ingredients. All investigated samples caused a sigmoidal decrease in aerosol droplet size upon an increase in concentration. Calculated dose-effect curve characteristics (i.e., half maximal effective sample concentration inducing a halfway drop of the droplet size) indicated distinct molar "potency" amongst the utilized samples with respect to generation of "adequate" inhalation aerosols. Second, the employed solvent (aqueous vs. organic) was shown to amplify the electrolyte effect on vibrating-membrane technology (i.e., dose-effect curve characteristics and overall aerosol droplet size). Third, besides the sample and solvent type, the nozzle composition (diverse metal and polymer coatings) induced a strong impact on the current mode of nebulization. Here, coating materials were identified, which necessitated higher and lower electrolyte concentrations in order to decrease the aerosol droplet size in comparable manner to plain nebulizer membranes. Thus, depending on the employed sample type and concentration, solvent and nozzle composition, a delivery of "inadequate" or "adequate" aerosols for inhalation purpose was observed. Overall, the current observations could be used to compile suggestions for the rational design of aerosol formulations and nebulizer devices meeting the specific requirements for successful inhalation therapy.

Aerosol Production by Vibrating Membrane Technology: Analysis of the Electrolyte Effect on Generated Droplet Size and Nebulizer Output Rate

The performance of vibrating membrane technology (i.e., aerosol droplet size and output rate) depends on the specific electrolyte concentration. However, the underlying factors, which determine nebulizer performance, are currently only poorly understood. This study compared the charge of aerosol droplets (Dekati^® BOLAR^™) nebulized with the eFlow^® rapid and the streaming potential (SurPASS^®) forming at the liquid/metal interface. Nebulization of 0.01 mM sodium chloride resulted in a rather large droplet size of >8 μm and an output rate of only ∼0.4 g/min. Increasing the sodium chloride content to 10 mM led to a droplet size of <5 μm and an output rate of ∼1.0 g/min. No significant difference was detected when comparing the net charge-to-mass ratios of generated aerosols. In contrast, the streaming potential (i.e., adversary of droplet detachment) differed remarkably between the 2 electrolyte solutions. The higher salt concentration compensated the electrical potential difference formed at the liquid/metal interface and, thus, caused an increased output rate (and a delivery of smaller aerosol droplets). Overall, this study identified the streaming potential as a significant parameter with impact on vibrating membrane nebulizer performance. The presented results will promote progress in this specific subfield of aerosol drug delivery.

Combinations of colistin solutions and nebulisers for lung infection management in cystic fibrosis patients

In this work different nebulisers were investigated in order to assess their efficiency in combination with colistimethate sodium (CMS) inhalation products. Four nebulisers, namely I-neb(®), Aeroneb(®) Go, eFlow(®)rapid and PARI LC(®) Sprint were studied in terms of delivered dose (DD), drug delivery rate (DDR) and respirable dose (RD) of CMS. The goal was to provide scientific data to physicians for prescribing the most appropriate nebuliser for the CMS specific user. All the apparatuses nebulised ColiFin 1MIU/3 ml solution (80 mg of CMS) with delivered doses between 31% and 41% of the loaded amount. Aeroneb Go showed the longest nebulisation time (more than 20 min). When ColiFin 2 MIU/4 ml was nebulised with eFlow rapid or PARI LC Sprint, the CMS respirable dose was 45.3mg and 39.2mg, in times of 5.6 and 10.8 min, respectively. I-neb, having a medication cup capacity limited to 0.4 ml, loaded with Promixin 0.4 MIU/0.4 ml (32 mg of CMS), provided in a time of 9 min a RD of 21.5mg, a value slightly higher than those obtained by nebulising ColiFin 1 MIU/3 ml with the other nebulisers (range 15.9-17.6 mg). The results illustrate that the clinical outcome depends on the comparative analysis of nebulisation efficiency (respirable dose) and convenience (time), not disregarding the ratios between the amount loaded, delivered and deposited at lung level.

Influence of amine-modified poly(vinyl alcohol)s on vibrating-membrane nebulizer performance and lung toxicity

A suitable aerosol droplet size and formulation output rate is essential for the therapy of lung diseases under application of nebulizers. The current study investigated the potential of amine-modified poly(vinyl alcohol)s as excipients for inhalation delivery. A change of conductivity (effective at <0.1mg/ml) and viscosity (effective at >0.1mg/ml) of samples that were supplemented with charge-modified polymers had a significant influence on the generated droplet size (shift from ~8 to ~4 μm) and formulation throughput rate (shift from ~0.2 to ~1.0 g/min), where polymers with a higher amine density (and molecular weight) showed an elevated activity. Biocompatibility assessment of polymers in A549 cells and an isolated lung model resulted in cell lysis and lung edema formation dependent on the type (degree of amine substitution) and dose of polymer applied. Suitable compositions and concentrations of amine-modified poly(vinyl alcohol)s were identified with respect to an optimized nebulizer performance and acceptable biocompatibility. Charge-modified polymers represent novel excipients with potential to improve inhalation therapy.

First Steps to Develop and Validate a CFPD Model in Order to Support the Design of Nose-to-Brain Delivered Biopharmaceuticals

PURPOSE

Aerosol particle deposition in the human nasal cavity is of high interest in particular for intranasal central nervous system (CNS) drug delivery via the olfactory cleft. The objective of this study was the development and comparison of a numerical and experimental model to investigate various parameters for olfactory particle deposition within the complex anatomical nasal geometry.

METHODS

Based on a standardized nasal cavity, a computational fluid and particle dynamics (CFPD) model was developed that enables the variation and optimization of different parameters, which were validated by in vitro experiments using a constructed rapid-prototyped human nose model.

RESULTS

For various flow rates (5 to 40 l/min) and particle sizes (1 to 10 μm), the airflow velocities, the calculated particle airflow patterns and the particle deposition correlated very well with the experiment. Particle deposition was investigated numerically by varying particle sizes at constant flow rate and vice versa assuming the particle size distribution of the used nebulizer.

CONCLUSIONS

The developed CFPD model could be directly translated to the in vitro results. Hence, it can be applied for parameter screening and will contribute to the improvement of aerosol particle deposition at the olfactory cleft for CNS drug delivery in particular for biopharmaceuticals.

Generation of tailored aerosols for inhalative drug delivery employing recent vibrating-mesh nebulizer systems

Direct drug delivery to the lungs is considered the gold standard for the treatment of a variety of respiratory diseases, owing to the increased therapeutic selectivity of the inhalative approach. Airborne formulations with defined size characteristics are required to improve the deposition pattern within the airways. In this respect, different nebulizer systems have been conceived, which has enabled the generation of respirable medicament mists. Here, vibrating-mesh technology revealed significant potential to overcome the main shortcomings associated with ‘traditional’ devices. Tailored orifice dimensions and defined formulation characteristics are of special interest for the generation of suitable aerosol droplets for inhalative purposes. Ongoing developments in device and formulation design will optimize the clinical outcome of inhalative drug delivery under application of vibrating-mesh technology.

Systematic aging of degradable nanosuspension ameliorates vibrating-mesh nebulizer performance

CONTEXT

The process of vibrating-mesh nebulization is affected by sample physicochemical properties. Exemplary, electrolyte supplementation of diverse formulations facilitated the delivery of adequate aerosols for deep lung deposition.

OBJECTIVE

This study addressed the impact of storage conditions of poly(lactide-co-glycolide) nanosuspension on aerosol properties when nebulized by the eFlow®rapid.

MATERIALS AND METHODS

First, purified nanosuspensions were supplemented with electrolytes (i.e. sodium chloride, lactic and glycolic acid). Second, the degradable nanoparticles (NP) were incubated at different temperatures (i.e. 4, 22 and 36 °C) for up to two weeks. The effect of formulation supplementation and storage on aerosol characteristics was studied by laser diffraction and correlated with the sample conductivity.

RESULTS AND DISCUSSION

Nebulization of purified nanosuspensions resulted in droplet diameters of >7.0 µm. However, electrolyte supplementation and storage, which led to an increase in sample conductivity (>10-20 µS/cm), were capable of providing smaller droplet diameters during vibrating-mesh nebulization (≤5.0 µm). No relevant change of NP properties (i.e. size, morphology, remaining mass and molecular weight of the employed polymer) was observed when incubated at 22 °C for two weeks.

CONCLUSION

Sample aging is an alternative to electrolyte supplementation in order to ameliorate the aerosol characteristics of degradable NP formulations when nebulized by vibrating-mesh technology.