Ultrasound‐Powered Implants: A Critical Review of Piezoelectric Material Selection and Applications

Abstract

Ultrasound‐powered implants (UPIs) represent cutting edge power sources for implantable medical devices (IMDs), as their powering strategy allows for extended functional lifetime, decreased size, increased implant depth, and improved biocompatibility. IMDs are limited by their reliance on batteries. While batteries proved a stable power supply, batteries feature relatively large sizes, limited life spans, and toxic material compositions. Accordingly, energy harvesting and wireless power transfer (WPT) strategies are attracting increasing attention by researchers as alternative reliable power sources. Piezoelectric energy scavenging has shown promise for low power applications. However, energy scavenging devices need be located near sources of movement, and the power stream may suffer from occasional interruptions. WPT overcomes such challenges by more stable, on‐demand power to IMDs. Among the various forms of WPT, ultrasound powering offers distinct advantages such as low tissue‐mediated attenuation, a higher approved safe dose (720 mW cm−2), and improved efficiency at smaller device sizes. This study presents and discusses the state‐of‐the‐art in UPIs by reviewing piezoelectric materials and harvesting devices including lead‐based inorganic, lead‐free inorganic, and organic polymers. A comparative discussion is also presented of the functional material properties, architecture, and performance metrics, together with an overview of the applications where UPIs are being deployed.

Osteogenic activity of bone: Novel approach of polyvinylidene fluoride films, marrow blood supply, and ultrasound stimulation

“…In this sense, the use of ultrasound stimulation to improve the piezoelectric PVDF implant performance is an innovation in the field of osteogenic activity of bone. The use of the piezoelectric film implant brings the advantage of wireless connection thus avoiding the use of traditional electrically powered implants which need batteries or external power source; the cantilever beam‐shape gives the implant the capability to work in a low‐frequency environment 36 . In order to improve the implant setup, an aspect to take into account is the mismatch in acoustic impedance between the piezoelectric transducer and the tissue due to differences in acoustic velocity and densities.…”

Soft Implantable Bioelectronics

“…Meanwhile, the long-term, sustainable operation of implantable devices with excellent stability is also associated with their power sources. Among the different methods of power delivery, − the method of supplying power self-harnessed from the dynamic micromotions of tissues inside the human body has recently been highlighted. Such energy harvesting devices can convert the intracorporeal kinetic energy into electrical power, but challenges remain, such as constant power supply and insufficient power generation.…”

An implantable ultrasound-powered device for the treatment of brain cancer using electromagnetic fields

“…Meanwhile, the adoption of wireless power transmission (WPT) eliminates the need for wires (23,24). Ultrasound or acoustic power transfer features significantly higher efficiency than inductive coupling approaches for WPT and is more suitable for implanted biomedical applications (25)(26)(27)(28)(29). Moreover, the low propagation loss of ultrasound leads to an extended penetration depth in the body and reduces unnecessary biological hazards (30).…”