*Matthew Backfish*, Brandon Davis, Sharath Gopal, Christopher Kovalchick

Delivery, Device and Connected Solutions

Eli Lilly and Company

 

Nitinol has proven to be widely useful in the medical device arena due to its unique shape memory properties and robust biocompatibility, particularly via invasive applications such as stents and localized drug delivery. It is also an attractive basis for drive mechanisms in a range of applications including fluid delivery pumps utilizing electrical actuation due to its temperature characteristics, power efficiency and overall durability. However, the use of nitinol in this area presents unique challenges in coupling the desired electromechanical design with available power budget and the overall durability for the application, including both low- and high-cycle fatigue across the use life of the device. Additionally, the variation in material loading over the life-cycle of the design use given constraints on the wide number of design variables cited introduces transient failure modes that need to be considered.

 

We explore specific challenges of implementing an electromechanical design utilizing nitinol as it relates to device footprint, geometry, boundary conditions, load history, available power, and reliability. Using a specific drug delivery application as the framework for our study, the fixturing and geometry of the nitinol drive system is studied relative to cable and beam loading configuration assumptions. A finite element analysis is conducted to examine failure modes of the nitinol in static loading conditions at varying points over the use life profile. A novel experimental configuration is developed to assess the effect of both repetitive actuation strains and loading over time as a function of the phase transformation properties. The experiment also evaluates low temperature cyclical annealing processes as a pre-treatment and their impact on low- and high-cycle fatigue. Using the analytical, computational and experimental data, an assessment is generated of the overall reliability potential of nitinol in this application along with the effects of varying power budget availability on the loading and cyclic fatigue of the design.


Nitinol as a Drive Mechanism in Drug Delivery Devices

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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