A robust and low cost ionic liquid based strain sensor is fabricated for high strain measurements in biomedical applications (up to 40 % and higher). A tubular 5 mm long silicone microchannel with an inner diameter of 310 µm and an outer diameter of 650 µm is filled with an ionic liquid. Three ionic liquids have been investigated: 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide, ethylammonium nitrate and cholinium ethanoate. When the channel is axially stretched, geometrical deformations change the electrical impedance of the liquid channel. The sensors display a linear response and low hysteresis with an average gauge factors of 1.99 for strains up to 40 %. Additionally, to fix the sensor by surgical stitching to soft biological tissue, a sensor with tube clamps consisting of photopatternable SU-8 epoxy-based resin is proposed.

The aim of this study is to investigate the intravascular application of a micro-electro-mechanical system (MEMS) pressure sensor to directly measure the hemodynamic characteristics of a ventricular assist device (VAD). A bio- and hemo-compatible packaging strategy is implemented, based on a ceramic thick film process. A commercial sub-millimeter piezoresistive sensor is attached to an alumina substrate, and a double coating of polydimethylsiloxane (PDMS) and parylene-C is applied. The final size of the packaged device is 2.6 mm by 3.6 mm by 1.8 mm. A prototype electronic circuit for conditioning and read-out of the pressure signal is developed, satisfying the VAD-specific requirements of low power consumption (less than 14.5 mW in continuous mode) and small form factor. The packaged sensor has been submitted to extensive in vitro tests. The device displayed a temperature-independent sensitivity (12 μV/V/mmHg) and good in vitro stability when exposed to the continuous flow of saline solution (less than 0.05 mmHg/day drift after 50 h). During in vivo validation, the transducer has been successfully used to record the arterial pressure waveform of a female sheep. A small, intravascular sensor to continuously register the blood pressure at the inflow and the outflow of a VAD is developed and successfully validated in vivo.

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