Evaluation of the Physico-mechanical Properties and Electrostatic Charging Behavior of Different Capsule Types for Inhalation Under Distinct Environmental Conditions

Abstract

Capsule-based dry powder inhaler (DPI) products can be influenced by a multitude of interacting factors, including electrostatic charging. Tribo-charging is a process of charge transfer impacted by various factors, i.e., material surface characteristics, mechanical properties, processing parameters and environmental conditions. Consequently, this work aimed to assess how the charging behavior of capsules intended for inhalation might be influenced by environmental conditions. Capsules having different chemical compositions (gelatin and hydroxypropyl methylcellulose (HPMC)) and distinct inherent characteristics from manufacturing (thermally and cold-gelled) were exposed to various environmental conditions (11%, 22% and 51% RH). Their resulting properties were characterized and tribo-charging behavior was measured against stainless steel and PVC. It was observed that all capsule materials tended to charge to a higher extent when in contact with PVC. The tribo-charging of the thermally gelled HPMC capsules (Vcaps ® Plus) was more similar to the gelatin capsules (Quali-G™-I) than to their HPMC cold-gelled counterparts (Quali-V ®-I). The sorption of water by the capsules at different relative humidities notably impacted their properties and tribo-charging behavior. Different interactions between the tested materials and water molecules were identified and are proposed to be the driver of distinct charging behaviors. Finally, we showed that depending on the capsule types, distinct environmental conditions are necessary to mitigate charging and assure optimal behavior of the capsules.

Assessment of Tribo-charging and Continuous Feeding Performance of Direct Compression Grades of Isomalt and Mannitol Powders

“…The effect of different mechanical properties of the two powders (i.e., G721 undergoing a brittle-plastic whereas P200SD a brittle deformation) [12] on the mode of contact and thus their overall tribo-electrification [54,55] cannot be ruled out.…”

Understanding the Importance of Capsules in Dry Powder Inhalers

“…The different interactions between the capsule materials and water molecules entrapped in the shell were identified as being responsible for differing charging behaviors. Finally, it was shown that, depending on the capsule types, distinct environmental conditions were necessary to mitigate charging and assure optimal behavior of the capsules [39].…”

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

“…In some cases, experimental studies that focused on the tribocharging phenomenon [ 7 , 8 , 9 , 10 , 11 ] reported somewhat conflicting results, even in the polarity of the reported charge, calling for additional investigations at small scales. The charge polarity of lactose particles (a widely used carrier and excipient) depends on the chosen inhaler [ 8 ], on the material of the containing capsule [ 12 ], and even on their manufacturing process; for example, milled lactose tends to charge positively, while sieved lactose tends to charge negatively [ 8 ]. Salbutamol sulphate (a commonly used API in inhalation formulations) tends to acquire a positive charge if it is amorphous and a negative charge if it is in its crystalline form [ 11 ].…”