Encapsulation Approaches for In-Stent Wireless Magnetoelastic Sensors

Wireless magnetoelastic sensors offer significant potential for measuring the accumulation of biomass within stents-enabling early detection prior to stent occlusion-but the encapsulation of these sensors remains a critical challenge. The encapsulation must allow the sensors to navigate the curvature and accommodate the contact forces imparted during and after the implantation procedure, while also leaving the sensor open to mechanical interaction with the biomass during the extended period of deployment. This paper is focused on the encapsulation of ribbon-like magnetoelastic sensors (12.5 mm × 1 mm × 60 μm) within plastic biliary stents (inner diameter of 2.54 mm). The compromise between two polymer-based package designs-one mechanically flexible (Type F) and one mechanically stiff (Type S)-is evaluated. The primary advantage of the Type F package is the flexibility during the delivery process while that of the Type S package is in maintaining a strong signal even when the stent is in a curved bile duct. The maximum thicknesses of the Type F and S packages are 0.53 and 0.74 mm, respectively. Mechanical tests show that both types protect the sensors from forces imparted by a standard introducer, and allow the encapsulated sensors to accommodate bending with a radius of curvature as small as 3 cm. The Type F package has also been tested in situ, in the bile duct of a porcine carcass. The signal is measurable with a wireless range of ≈10 cm, at a resonant frequency of 159 kHz and a quality factor of 397.