Abstract
Implantable biosensors were developed for real-time monitoring of pressure and strain in the human body. The sensors, which are wireless and passive, consisted of a soft magnetic material and a permanent magnet. When exposed to a low frequency AC magnetic field, the soft magnetic material generated secondary magnetic fields that also included the higher-order harmonic modes. Parameters of interest were determined by measuring the changes in the pattern of these higher-order harmonic fields, which was achieved by changing the intensity of a DC magnetic field generated by a permanent magnet. The DC magnetic field, or the biasing field, was altered by changing the separation distance between the soft magnetic material and the permanent magnet. For pressure monitoring, the permanent magnet was placed on the membrane of an airtight chamber. Changes in the ambient pressure deflected the membrane, altering the separation distance between the two magnetic elements and thus the higher-order harmonic fields. Similarly, the soft magnetic material and the permanent magnet were separated by a flexible substrate in the stress/strain sensor. Compressive and tensile forces flexed the substrate, changing the separation distance between the two elements and the higher-order harmonic fields. In the current study, both stress/strain and pressure sensors were fabricated and characterized. Good stability, linearity and repeatability of the sensors were demonstrated. This passive and wireless sensor technology may be useful for long term detection of physical quantities within the human body as a part of treatment assessment, disease diagnosis, or detection of biomedical implant failures.
Highlights
Physical parameters such as pressure, stress, strain and fluid flow within the human body are critical indicators for detection of many diseases [1]
The 2nd order harmonic field shifts of the pressure and stress/strain sensors were measured as a function of the separation distance between the biasing and sensing elements, and the results are plotted in Figure 4, where Figure 4a presents the response of the pressure sensor and Figure 4b shows the response of the stress/strain sensor
Pressures vary in different parts of a human body, most of them are under 10 kPa
Summary
Physical parameters such as pressure, stress, strain and fluid flow within the human body are critical indicators for detection of many diseases [1]. Many physical parameters in the human body are measured indirectly via ex vivo methods such as sphygmomanometry and ultrasound techniques. A technique to obtain accurate results is to insert the sensor into the human body via catheter and to perform in vivo measurements. The measurement of biliary pressure, which is critical to diagnose sphincter of Oddi (SO) dysfunction, is currently conducted with SO manometry (SOM) [3] that uses a catheter-tip pressure sensor. The major limitation of using the catheter-based measurement technique is that it often requires the patient to be sedated, which may not reflect the actual conditions during the patient’s daily activities. This may result in poor prognostic and diagnostic outcomes
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