A team of researchers from China and Singapore has designed an implantable miniaturized sensor capable of conducting wireless ultrasonic monitoring of signals within the human skull.

In the clinical monitoring of physiological indicators like intracranial pressure, the use of conventional wired sensors demands surgical implantation. Additionally, the wireless sensors currently available are relatively large, requiring minimally invasive surgery.

The researchers from Huazhong University of Science and Technology (HUST) and Nanyang Technological University developed a hydrogel cube sensor, measuring just 2 millimeters in size, which can be implanted into the intracranial space using a puncture needle.

Upon injection, the hydrogel deforms in response to physiological environmental changes, which results in shifts of the peak frequency of the reflected ultrasound waves. These shifts can be non-invasively measured wirelessly by an external ultrasound probe, according to the study published on Wednesday in the journal Nature.

The sensor is capable of independently measuring intracranial pressure, temperature, pH, and flow rate, with a detection depth reaching up to 10 centimeters.

The hydrogel maintains its stability for a period of three to four weeks, subsequently starting to degrade around the fifth week, and is nearly completely decomposed within 18 weeks, causing no systemic immune responses in rats.

Animal experiments on pigs have demonstrated that the sensor exhibits excellent sensing capabilities, comparable to those of conventional non-resorbable wired clinical benchmarks, according to the study.

"Our ultrasonic sensing technology is versatile and can be adapted for use beyond the brain," said Zang Jianfeng, one of the corresponding authors of the paper from the HUST.