With electronic devices such as insulin pumps, pacemakers and implantable hearing aids being increasingly used for medical treatment, a collaborative study at King Abdullah University of Science & Technology (KAUST) and King Saud bin Abdulaziz University for Health Sciences in Saudi Arabia has shown how hydrogels can be used to ultrasonically charge such bioelectronic implants. The breakthrough could significantly reduce the level of invasive surgery required to charge the batteries in these devices.
As described in the journal ACS Nano [Lee et al. ACS Nano (2020) DOI: 10.1021/acsnano.9b08462], the wireless recharging of devices implanted in the body could now be viable as the study demonstrated the remote charging of a battery with the aid of a hydrogel, a soft and biocompatible material able to absorb sound waves as they move through the body. The team combined polyvinyl alcohol with nanosheets of MXene, a transition-metal carbide, nitride or carbonitride, finding the hydrogel, called M-gel, was able to generate electric power under the influence of ultrasound waves. It produced a current when an applied pressure drives the flow of electrical ions in the water, filling the hydrogel – when pressure is due to ultrasound, it results in an electroacoustic phenomenon called streaming vibration potential.
This is the first demonstration that hydrogels can harvest ultrasound energy from common ultrasound probes. The material is cheap to make and the fabrication process straightforward, and new materials and devices could be based on these charging mechanisms, leading to more efficient ultrasound harvesting devices. The concept was shown with a variety of ultrasonic sources, such as standard laboratory ultrasound tips and the ultrasound probes used in hospitals for imaging, and an electrical device buried within several centimeters of beef was quickly charged.
The main application is in the remote charging of implantable devices, as the effectiveness and low cost of the technology means that patients with pacemakers or neurostimulators could avoid having to suffer from invasive surgery to replace batteries, as the implantable devices could be charged remotely with just an ultrasound probe.
The team now hope to implant the device and test its stability and long-term biocompatibility in laboratory animals, as well as check for any possible adverse effects. As Husam Alshareef, the principal investigator of the Functional Nanomaterials and Devices Laboratory at KAUST, where they have been developing MXene hydrogels for sensing and energy applications, told Materials Today, “I believe MXene hydrogels have great potential in several applications. We will continue to develop the materials and fabricate prototype devices with improved performance.”