Design-Optimization of Dry Powder Inhalers: Selecting an Objective Function

Thomas Kopsch, Digby Symons, Darragh Murnane

In passive dry powder inhalers (DPIs) drug is often stored in blisters incorporated in the device. The patient
inhales through the device, forcing an airstream through the blister. Drug is entrained into the airstream for
delivery to the lung. The entrainment and dispersion of drug depend on internal inhaler geometry. Relevant
design features include the air path in the device and the blister. Two objectives were considered: A) DPI dose
emission that is independent of the inhalation profile, such that the emitted dose reaches similar lung regions
when two patients inhale with different inhalation profiles; B) Targeting of the emitted drug to specific pulmonary
airways for therapeutic applications. For example, for some medical applications a ‘bolus’ delivery is desired, i.e.
most of the drug should leave at a particular instant. We present an optimisation approach for DPI design for
these objectives through simulation of dose emission using computational fluid dynamics (CFD). We demonstrate
the approach by computationally optimizing a simple 2D DPI. The geometry considered is a blister where air
enters through one hole, entrains drug, and exits through another hole. Three parameters characterised the
geometry: the separation of the holes, s; the width of the outlet hole, d1; and the width of the inlet hole, d2. A
gradient descent method was used to vary these parameters to optimise the DPI. Through the CFD studies a DPI
air path geometry was optimised to achieve an ideal ‘early bolus’ drug delivery that was independent of the
inhalation profile.

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