Comparing a Fixed and Freely Rotating Capsule in a Dry Powder Inhaler Under Realistic Breathing Conditions.

PURPOSE: To investigate the performance of a capsule-based dry powder inhaler (DPI) under two device configurations - free-axis and fixed-axis capsule rotation - across steady-state and transient inhalation profiles. METHOD: Two new research-based transparent capsule-based DPI were developed-one with a fixed capsule rotational axis and another with a floating capsule configuration. High-speed imaging was used to capture capsule motion, and the effects of flow regimes (laminar, transient, and turbulent), capsule rotation, and breathing profiles on capsule RPM, wall collisions, and powder retention were analyzed. CONCLUSIONS: Fixed-axis rotation significantly outperformed free-axis rotation (~ 6 × higher RPM and lower powder retention). Higher flow rates and faster-accelerating transient profiles increased RPM and collision frequency, enhancing drug release. Fixing the rotational axis of the capsule had the greatest benefit for the slow inhalation profile. The findings offer key insights for the design of future capsule-based DPIs.