Magnetoelastic wireless sensing of tissue growth for self-expanding biliary stents

Tissue growth in biliary stents causes a loss of patency after only 2-12 months in 50% of cases, leading to complications such as jaundice or cholangitis. We report micro-machined resonant magnetoelastic sensors for monitoring tissue growth on biliary stents and an appropriate transmit/receive coil configuration for these sensors. An 8 mm diameter stainless steel mesh that was used as a self-expanding stent had a 33% recovery expansion in the absence of loading. Paraffin mass loads up to 251 mg simulated tissue growth on 37.5x2 mm², 28 mum thick sensors. A resonant frequency shift from 57.85 kHz to 22.35 kHz was observed. Varying the local viscosity over the range of healthy and diseased bile gave a shift of 1 kHz. The sensor response without mounting in the stent was negligibly different.