Self-sufficient Electromechanical Implants: Enabling Piezoelectric Functionality for in vivo Devices

Piezoelectric materials exhibit the unique characteristic to develop an electric charge when mechanical pressure is applied to them. This generation of an electric signal is used in a vast range of every-day devices, ranging from pressure sensors in touchpads and cars to vibration damping in planes. Let us assume we could make piezoelectric materials reliably functional within the human body and use the generation of electric signals for medical purposes - electric signals, which are known to improve tissue repair and can be harvested to power implanted electronics or be utilized as sensor signal. This could provide us with a whole new type of medical implants, e.g. as cell stimulating scaffolds for nerve and bone repair or as sensing components in already existing implant materials or drug delivery systems. While a lot is known about how to make a reliable sensor or vibration control device based on a piezoelectric material, very little is known about how these materials interact with and can function within the human body. The environment in the body is determined by various liquids and it is fundamental to understand the processes at the interface between the body liquids and the artificial material to be able to develop a reliable and functional implant. Within EPIC, a novel measurement method will be developed that allows the determination of the piezoelectric functionality within liquid environments mimicking the situation of an implant inside the body. Our first investigations showed that the stability of the functional material within a liquid similar to blood plasma depends on its dielectric properties, especially on the electric charges present on the surface. This indicates a close relationship between the functionality and the long-term stability that is crucial to understand for making safe implants.

Functional biomedical materials that actively communicate with the body, e.g. by monitoring body functions or promoting full body recovery, are highly desirable in terms of patients life quality and health care costs. The main challenge for their realization is the demanding liquid environment inside the body, where they must remain reliably functional without causing harm. Piezoelectric materials generate electric surface potentials when subjected to a mechanical load. Let us assume we could make them reliably functional inside the body and exploit this electromechanical coupling. This would provide us with a whole new aspect of functionality for biomedical implants. We could for the first time realize devices, which self-sufficiently generate electric signals in vivo that can be utilized to improve tissue repair and can be harvested to power implanted electronics. EPIC will contribute to this goal in two ways: it will clarify the functionality of piezoelectrics in a liquid environment by studying the electrostatic interaction of both constituents mimicking chemical and electric conditions of an in vivo scenario. For this, an experimental setup will be developed combining the autonomous electric signal generation of the piezoelectric effect with a contact-less measurement utilizing streaming potentials. Beyond pure functionality, EPIC will map the mechanisms determining the reliability of piezoelectrics by clarifying the origins of chemical degradation at the solid-liquid interface and their impact on piezoelectric functionality. The project is set to demonstrate the potential of the most promising piezoelectric systems for usage in liquid environments and to unfold the relationships between interfacial processes and materials functionality. This will enable application-targeted design of piezoelectric materials and their development into functional and safe biomedical implants.