Effect of Crystallinity on Electrostatic Charging in Dry Powder Inhaler Formulations

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.

Large and Tunable Ranking Shift in Triboelectric Series of Polymers by Introducing Phthalazinone Moieties

Regulating the ranking of polymer in triboelectric series over a wide range is of great help for material's selection of triboelectric nanogenerators (TENGs). Herein, fluorinated poly(phthalazinone ether)s (FPPEs) with tunable molecular structure and aggregate structure are synthesized by co-polycondensation, while the large positive ranking shift in the triboelectric series can be achieved by introducing phthalazinone moieties with strong electron donating capability. FPPE-5, which includes abundant phthalazinone moieties, is more positive than all of the previously reported triboelectric polymers. Hence, the regulating range of FPPEs in this work updates a new record in triboelectric series, which is wider than that of previous works. A peculiar crystallization behavior, capable of trapping and storing more electrons, has been observed in FPPE-2 with 25% phthalazinone moieties. Correspondingly, FPPE-2 is more negative than FPPE-1 without a phthalazinone moiety, which is an unexpected shift against the common changing tendency in triboelectric series. With FPPEs films as the probing material, a tactile TENG sensor is applied to enable material identification via electrical signal polarity. Hence, this study demonstrates a strategy to regulate the series of triboelectric polymers by copolymerization using monomers with distinct electrification capabilities, where both the monomer ratio and the peculiar nonlinear behavior can control triboelectric performance.

Insights into the Impact of Nanostructural Properties on Powder Tribocharging: The Case of Milled Salbutamol Sulfate

The impact of the crystallinity of organic solid materials on their tribocharging propensity is well reported. However, no unequivocal explanation about the potential underlying mechanism(s) could be found so far in the literature. This study reports the effect that different degrees of crystalline disorder has on the tribocharging propensity of a small molecular organic material, salbutamol sulfate (SS). Ball-milling was used to induce structural transformations in the crystalline structure of SS. Particles with different nanostructures were produced and analyzed for their solid-state, particle properties, and tribocharging. It was found that differences in the amorphous content among the processed particles and related moisture levels had an impact on powder tribocharging. A correlation between the latter and the nanostructural properties of the particles was also established. The presence of interfaces between nanodomains of different densities and shorter average lengths within the phases seems to lead to a mitigation of charge. This suggests that undetected, subtle nanostructural differences of materials can affect powder handling and processability by altering their tribocharging. The present findings demonstrate the nanostructural implications of powder triboelectrification, which can help toward the rational design of a wide variety of organic solids.

Manufacturing Stable Bacteriophage Powders by Including Buffer System in Formulations and Using Thin Film Freeze-drying Technology

PURPOSE

Bacteriophage (phage) therapy has re-gained attention lately given the ever-increasing prevalence of multi-drug resistance 'super-bugs'. To develop therapeutic phage into clinically usable drug products, the strategy of solidifying phage formulations has been implemented to diversify the dosage forms and to overcome the storage condition limitations for liquid phage formulations.

METHOD

In our work, we hypothesize and tested that an advanced technology, thin film freeze-drying (TFFD), can be used to produce phage containing dry powders without significantly losing phage viability. Here we selected T7 phage as our model phage in a preliminary screening study.

RESULTS

We found that a binary excipient matrix of sucrose and leucine at ratios of 90:10 or 75:25 by weight, protected phage from the stresses encountered during the TFFD process. In addition, we confirmed that incorporating a buffer system in the formulation significantly improved the survival of phage during the initial freezing step and subsequent sublimation step in the solidifying processes. The titer loss of phage in SM buffer (Tris/NaCl/MgSO4) containing formulation was as low as 0.19 log plaque forming units, which indicated that phage function was well preserved after the TFFD process. The presence of buffers markedly reduced the geometric particle sizes as determined by a dry dispersion method using laser diffraction, which indicated that the TFFD phage powder formulations were easily sheared into smaller powder aggregates, an ideal property for facilitating a variety of topical drug delivery routes including pulmonary delivery through dry powder inhalers, nebulization after reconstitution, and intranasal or wound therapy, etc. CONCLUSION: From these findings, we show that introducing buffer system can stabilize phage during dehydration processes, and TFFD, as a novel particle engineering method, can successfully produce phage containing powders that possess the desired properties for bioactivity and potentially for inhalation therapy.

Investigation into powder tribo-charging of pharmaceuticals. Part I: Process-induced charge via twin-screw feeding

Powder feeding is a crucial unit operation in continuous manufacturing (CM) of pharmaceutical products. Twin-screw feeders are typically employed to ensure the accurate mass flow of pharmaceutical materials throughout the production process. Here, contact and separation of particles can give rise to electrostatic charges, affecting feeder performance and final product quality. The knowledge of the material charging tendency would therefore be beneficial for both formulation and process design. At the early stage of product development, only a limited amount of material is available and the propensity of the powders to charge needs to be assessed on lab test equipment, which not necessarily represent the material state during processing. In this study, the tribo-charging behaviour of a set of common pharmaceutical materials (i.e., microcrystalline cellulose, D-mannitol, paracetamol and magnesium stearate) was experimentally evaluated. To this end, powder materials were let to flow over the stainless-steel pipes of the GranuCharge™ instrument. The resulting charge was compared to the one acquired during twin-screw feeding. In both cases, paracetamol exhibited the highest charging tendency followed by D-mannitol and microcrystalline cellulose and last by magnesium stearate. A good correlation was found for charge values obtained for both methods, despite the different tribo-charging mechanisms involved in the two set-ups. However, these differences in experimental set-ups led to diverse magnitudes and, in one case, polarity of charge. Additionally, an extensive material characterization was performed on the selected powders and results were statistically analyzed to identify critical material attributes (CMAs) affecting powder tribo-charging. A strong correlation was obtained between the measured charge and inter-particle friction. This indicated the latter as one of the most influencing material characteristic impacting the powder tribo-charging phenomenon of the selected materials.

Delivery of Dry Powders to the Lungs: Influence of Particle Attributes from a Biological and Technological Point of View

Dry powder inhalers are medical devices used to deliver powder formulations of active pharmaceutical ingredients via oral inhalation to the lungs. Drug particles, from a biological perspective, should reach the targeted site, dissolve and permeate through the epithelial cell layer in order to deliver a therapeutic effect. However, drug particle attributes that lead to a biological activity are not always consistent with the technical requirements necessary for formulation design. For example, small cohesive drug particles may interact with neighbouring particles, resulting in large aggregates or even agglomerates that show poor flowability, solubility and permeability. To circumvent these hurdles, most dry powder inhalers currently on the market are carrier-based formulations. These formulations comprise drug particles, which are blended with larger carrier particles that need to detach again from the carrier during inhalation. Apart from blending process parameters, inhaler type used and patient's inspiratory force, drug detachment strongly depends on the drug and carrier particle characteristics such as size, shape, solid-state and morphology as well as their interdependency. This review discusses critical particle characteristics. We consider size of the drug (1-5 µm in order to reach the lung), solid-state (crystalline to guarantee stability versus amorphous to improve dissolution), shape (spherical drug particles to avoid macrophage clearance) and surface morphology of the carrier (regular shaped smooth or nano-rough carrier surfaces for improved drug detachment.) that need to be considered in dry powder inhaler development taking into account the lung as biological barrier.

Investigation of Electrostatic Behavior of Dry Powder-Inhaled Model Formulations

The accumulation of electrostatic charge on drug particles and excipient powders arising from interparticulate collisions or contacts with other surfaces can lead to agglomeration and adhesion problems during the manufacturing process, filling, and delivery of dry powder inhaler (DPI) formulations. The objective of the study was to investigate the role of triboelectrification to better understand the influence of electrostatic charge on the performance of DPIs with 2 capsule-based dimensionally similar devices constructed with different materials. In addition, strategies to reduce electrostatic charge build up during the manufacturing process, and the processes involved in this phenomenon were investigated. Electrostatic charge measurements showed that there was a significant difference in electrostatic charge generated between tested formulations and devices. This affects particle detachment from carrier and thus significantly impacts aerosol performance. Conditioning fluticasone DPI capsules at defined temperature and humidity conditions reduced electrostatic charges acquired during manufacturing. Conditioning salmeterol DPI capsules at same conditions seemed disadvantageous for their aerosol performance because of increasing capillary forces and solid bridge formation caused by water absorption. Knowledge and understanding of the role of electrostatic forces in influencing DPI formulation performance was increased by these studies.

Tribo-Charging Behaviour of Inhalable Mannitol Blends with Salbutamol Sulphate

PURPOSE

The performance of carrier-based dry powder inhaler (DPI) formulations can be critically impacted by interfacial interactions driven by tribo-electrification. Therefore, the aim of the present work was to understand how distinct API particle characteristics affect the charging behaviour of blends intended for DPI delivery.

METHODS

Salbutamol sulphate (SBS) particles engineered via spray-drying and jet milling were used as model APIs. D-mannitol was selected as a model carrier. The materials were characterized concerning their different particle properties and their charge was analysed alone and in blends before and after flow over a stainless-steel pipe.

RESULTS

The spray-dried SBS (amorphous and spherical) charged positively and to a higher extent than jet milled SBS (crystalline and acicular) that charged negatively and to a lower extent. D-mannitol charged positively and to a higher extent than the APIs. All drug-excipient blends charged negatively and differences were found between the spray-dried and jet milled SBS blends at 2% and 5% drug loads.

CONCLUSIONS

It was demonstrated how distinct solid-states, particle shape, size and morphology as well as different water contents of the different materials can affect tribo-charging. For their binary blends, the amount and nature of fines seem to govern inter-particle contacts critically impacting charge evolution.

Tribo-electric charging and adhesion of cellulose ethers and their mixtures with flurbiprofen

The pervasiveness of tribo-electric charge during pharmaceutical processing can lead to the exacerbation of a range of problems including segregation, content heterogeneity and particle surface adhesion. The excipients, hydroxypropyl methylcellulose (HPMC) and methylcellulose (MC), are often used in drug delivery systems and so it is important to understand the impact of associated factors on their charging and adhesion mechanisms, however, little work has been reported in this area. Such phenomena become more prominent when excipients are introduced to a powder mixture alongside the active pharmaceutical ingredient(s) (APIs) with inter- and intra-particulate interactions giving rise to electrification and surface adhesion of powder particles. The aim of this study was to understand the impact of material attributes (particle size, hydroxypropyl (Hpo) to methoxyl (Meo) ratio and molecular size) on the charging and adhesion characteristics of cellulose ethers. Furthermore, a poorly compactible and highly electrostatically charged drug, flurbiprofen, was used to develop binary powder mixtures having different polymer to drug ratios and the relationship between tribo-electric charging and surface adhesion was studied. Charge was induced on powder particles and measured using a custom built device based on a shaking concept, consisting of a Faraday cup connected to an electrometer. The diversity in physicochemical properties has shown a significant impact on the tribo-electric charging and adhesion behaviour of MC and HPMC. Moreover, the adhesion and electrostatic charge of the API was significantly reduced when MC and HPMC were incorporated and tribo-electric charging showed a linear relationship (R(2)=0.81-0.98) with particle surface adhesion, however, other factors were also involved. It is anticipated that such a reduction in charge and particle surface adhesion would improve flow and compaction properties during processing.