Abstract
A safe and affordable ingestible thermometer measuring core body temperature has the potential to become a future healthcare device for versatile applications in daily life. In this study, we developed an ingestible thermometer charged by a gastric acid battery. The device can operate in bowels by using the charged energy in multilayer ceramic capacitors as a storage capacitor. Adopting this strategy for energy storage solves the issues related to a conventional button battery: risk of injury to the digestive tract, bad disposability, and degradation. Additionally, to make it easy to assemble a coil antenna and electrical circuits in the device automatically, we developed a fabrication process based on a vertical stacking process of printed circuit boards with coil patterns. The dimensions of the prototyped device were smaller than those of existing ingestible thermometers. In an experiment involving a dog, we successfully recorded the temperature in the digestive tract for 24 h in cycles of approximately 10 or 20 min, using a rectal thermometer and an existing ingestible thermometer as references. The temperature variations in time among our device, rectal thermometer, and existing ingestible thermometer were almost parallel. The recording ability of the core body temperature using our device has the potential to measure basal body temperature during sleep, the circadian rhythm, and fever type easily and robustly in daily life. Our ingestible thermometer is a step toward the development of sensors that can be swallowed for preventive medicine and health promotion.
Highlights
Vital sensing or monitoring in daily life has prospects in promoting health and detecting diseases at an early stage
We successfully developed a fabrication process that makes it easy to integrate a coil antenna into an ingestible thermometer. We demonstrated that this thermometer based on gastric acid power generation can measure the core body temperature of a living animal for a long time
In this study, we prototyped an ingestible thermometer with a built-in coil antenna, whose operation energy is charged by a gastric acid battery
Summary
Vital sensing or monitoring in daily life has prospects in promoting health and detecting diseases at an early stage. In previous studies, we developed a core-body thermometer based on gastric acid power generation even after the device has passed through the stomach, as shown in Fig. 1 [33]–[35]. The gastric acid power generation charges electrical energy into a storage capacitor, which is safer than a button battery, in the device. This concept reduces the environmental burden of disposing of the device after use. An 11.3-MHz carrier frequency generated by a crystal oscillator was used because such a relatively low radio-frequency carrier should have a well-balanced performance between biological permeability and efficiency as a limited-size transmission antenna in the ingestible device This contributes to ensuring safety in the human body and reducing energy consumption in telecommunications. A synergy effect of elimination of a button battery, use of custom IC and adapt of the sophisticated assemble process considerably contributed to the miniaturization
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