Design of a Metered-Dose Inhaler Actuated by Shape Memory Alloy

Abstract

The global prevalence of asthma and chronic obstructive pulmonary disease (COPD) is on the order of hundreds of millions of individuals. The most common treatment approach is to take a self-administered inhaled medication. This study focuses on pressurized metered-dose inhalers (MDIs) where, unfortunately, rates of mishandling and misuse are extremely high and lead to improper treatment. One significant challenge results from the timing miscoordination of the medicine dispersion and inhalation breath. To address this, this study demonstrates the feasibility of automating the timing of the medicine dispersion by integrating a shape memory alloy (SMA) actuator and a differential pressure sensor into the casing of a traditional MDI. The approach is to measure the vacuum pressure created by an inspiratory breath, evaluate criteria indicating an acceptable breath, and if those criteria are met, heat the SMA actuator to depress the cartridge and disperse medicine. To meet actuation requirements and reliably depress the inhaler cartridge, two concepts for configuring an SMA wire were designed and compared with respect to complexity, actuation timing, and energy consumption. The proposed concept was able to disperse medicine in 263 ms, averaged over 100 actuations on a single battery charge, facilitating the early dispersion of medicine during an inhalation breath. By describing the design process of an SMA-actuated MDI that does not result in a significant increase of its weight or size, this study provides a practical technological approach for reducing the improper treatment of asthma and COPD due to timing miscoordination.