Piezoelectric sensors have many applications including as vibration sensors, accelerometers, energy harvesters, and even electronic drum pads. A small piezoelectric film can sense strains on the order of 10^-6 making them highly attractive for devices that require miniaturization without compromising on performance. Canan Dagdeviren and her colleagues at the Massachusetts Institute of Technology and the Harvard Medical School have extended this concept to an ingestible electronic sensor for gastrointestinal (GI) disorders. As described in their article published recently in Nature Biomedical Engineering, the idea is to allow a sensor to measure the expansion and contraction of the stomach or the intestinal wall thereby allowing the physiological states of the GI tract to be monitored. This can tell, for example, if there is more gas in the stomach or if the person is suffering from irritable bowel syndrome. The group has demonstrated the viability of the concept in a balloon filled with water as well as in a pig’s stomach. The results are promising and could one day be extended to humans. What is additionally attractive about using piezoelectric sensors is that they could be modified to generate current from movement, effectively acting as self-charging devices.

The sensor developed includes a group of lead zirconium titanate (PZT) ribbons that are connected in series where each group consists of 10 ribbons in parallel. This structure is covered by several polymer layers which ensure that the toxic fluids of the GI tract do not come in contact with the ceramic. Lead wires of a conductive polymer are connected to a multimeter to monitor the electrical signals from the device.

The first set of experiments was conducted with the sensor attached to the walls of a balloon which was then inflated with water. The sensor responded to the changing curvature of the membrane through variations in signal output. The second set of experiments was performed by placing the sensor in the stomach wall of a pig. As water was infused into the stomach, the voltage output increased from around 10 mV to around 30 mV where it remained until the water was suctioned out. The sensor was shown to be sensitive to lateral motion was well as palpation of the pig demonstrating its efficiency in detecting the motility of the organism, and potentially one day converting this to a self-charging device.

Ghazaleh Haghiashtiani and Michael C. McAlpine at the University of Minnesota have commented in a perspective for Nature Biomedical Engineering that “various aspects of the device could be improved to extend its applicability and efficacy. For instance, from a commercialization perspective, integration of a wireless sensing network into the device to yield an untethered system would facilitate disease monitoring.” They have also suggested that the device could be miniaturized even further so that it could be orally ingested like a pill.

Other researchers in the field have also expressed admiration for the novel design. Luana Persano of the Italian National Research Council said in a communication to MRS, “This generation of devices opens exciting perspectives to monitor the gastrointestinal motility, thus providing new insights into the basic understanding of disorders whose pathogenesis is currently unknown. Next challenges will include extending the use of biodegradable and biocompatible materials to the active piezoelectric component, and allowing the device to dissolve in the body by bioresorption.”

Read the abstract in Nature Biomedical Engineering.