Stiffness Characterization of Healthy and Deficient Tracheal Cartilage Segments using Micromachined Piezoresistive Force Sensor

Tracheal malformations such as incomplete/absent tracheal rings induce flaccidity in the tissue causing stenosis in the central airway. The short- and long-segmental deficient rings compromise the rigidity of the airway channel leading to collapse. The anomaly can be of varying length, occur in the cervical, middle, or distal region with varying degrees of obstruction. Despite the conservative treatment and interventional procedures, caseloads with restenosis remain high. Quantifying the local tissue mechanical property can directly measure the segment heath and aid in staging the disease. This work discusses the fabrication of a MEMS-based piezoresistive force sensor designed for sheep tracheal tissue mechanical characterization. The sensor with 2mm squared diaphragm, and 30µm membrane thickness has a linear working range between 10–120 mN with a sensitivity of 0.21 mV/ (V mN) and less than 1% hysteresis under normal loads. The compressive load-unload test was performed at 50 µm/s strain rate up to maximum stress of 85mN on PDMS (10% crosslinker concentration), excised sheep tracheal tissue and the malacic model. The difference in stiffness of healthy tracheal tissue over the malacic model, evaluated using the hysteresis data, was statistically significant with
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p-value 1e-3. The sensor demonstrates its potential to be integrated into diagnostic tools facilitating preoperative clinical evaluation.