A Coupled Magnetoelastic Strain Sensor Array for Guiding and Monitoring Hernia Repairs

Objective: Ventral hernia repairs using mesh prosthetics suffer from high recurrence rates, with 10%–20% of repairs failing within three years. Uneven distribution of stress within the implanted mesh prosthetic is thought to contribute to the high recurrence rate. We propose a method for providing quantitative guidance and monitoring of hernia repairs using an array of magnetoelastic strain sensors. Methods: The magnetoelastic strain sensors presented here are based on a coupled design to achieve measurements with higher signal-to-noise ratio (SNR). A first magnetoelastic element (the transducer) is bonded to the mesh prosthetic and is characterized by a strain-dependent magnetic field. The resonance frequency of a second magnetoelastic element (the resonator) encased in a rigid casing is biased by the transducer element's magneticity and can be measured noninvasively using an external interrogation coil. The coupled magnetoelastic strain sensors are assembled using a combination of photochemical machining, patterning, and heat sealing. Results: The dynamic range of the coupled sensors can be tuned by altering the transducer geometry. Additional spring elements are integrated onto the transducer element to achieve high dynamic range measurements saturating at 74 millistrains. Conclusion: A coupled magnetoelastic strain sensor combines a transducer with an encased resonator element to measure strain with high SNR on an implantable flexible hernia mesh substrate. Significance: This study provides surgeons and researchers with a clinically relevant tool to quantify the strain distributions within implanted mesh prosthetics, with the ultimate goal of reducing the recurrence rate of ventral hernia repairs.