Home System concept “Self-aware” and self-powered metamaterial implants

“Self-aware” and self-powered metamaterial implants

June 03, 2022

(Spotlight on Nanowerk) Medical research is rapidly moving towards a future where smart medical implants can continuously monitor their condition inside the body and autonomously respond to changes such as, for example, infection by releasing anti-inflammatory agents. Some examples that researchers have already demonstrated are sensors that can be placed under the skin to measure blood glucose levels, hormone levels, pH, and various other physical parameters; the use of polypyrrole films as electrically driven drug delivery devices on implant surfaces to improve bone implants; electronic sensors under the skin to monitor blood flow; and pressure sensors to improve medical implants.

Intrinsic diagnostic functionality is the missing component of nearly every implant available today. Where smart implants have been demonstrated, they often rely on power sources such as batteries, capacitors, or external telemetry systems.

Currently, two major challenges limit the wider application of smart implants in daily clinical practice. The first challenge is the size of these implants for sensor integration. For example, imagine the difficulties associated with integrating multiple circuit boards for sensing, energy storage, and wireless communications into the small area of ​​a miniaturized stent. The second challenge is the lack of scalable and intelligent biomaterials to fabricate these devices.

Some studies have attempted to address these issues separately. But until now, no research team has addressed all of these issues comprehensively by designing a multi-functional implant that can diagnose healing progression, is capable of self-powering, and can be tuned to deliver almost any desired mechanical performance.

A potential solution to all of these challenges is to use the implant matrix as a means of active sensing and energy harvesting. This eliminates the need to figure out how to fit large circuits or power sources into the small device area of ​​an implant.

write in Advanced functional materials (“Patient-Specific Self-Powered Metamaterial Implants for Detecting Bone Healing Progress”), researchers now offer the first smart orthopedic implant with diagnostic and energy harvesting capabilities.

This multi-functional, mechanically adjustable metamaterial implant can sense and harvest energy from body movements.

“Our concept is clinically meaningful because these implants allow surgeons to directly and accurately assess bone healing progress,” Amir H. Alavi, assistant professor in the University of Pittsburgh’s Department of Bioengineering, told Nanowerk. “These features have the potential to eliminate the need for radiographic imaging techniques, which are typically expensive and expose patients to significant radiation.”

In what could be a game-changer, these implants use only their constituent components to achieve these advanced features – they require no external power source or bulky electronics. Additionally, implants can be 3D printed and customized for each patient based on clinical requirements and anatomical matching.

“We rely on the rational design of the microlayers of the implants to integrate advanced functionalities into their matrix,” explains Alavi. “Think about the fact that you can use our technology to literally turn any implantable device into a sensor and nanogenerator by manipulating their geometric designs. There are tons of biocompatible material options that can be used with this technology.”

This manufacturing technique relies primarily on the team’s patented meta-tribomaterial technology. This technology deals with the rational design of multiple layers of triboelectric auxetic microstructures with multi-stable/self-recovery hook-up segments.

The beauty of this concept is that the same design works at both the nanoscale and the macroscale simply by adapting the design geometry.

Building on their recent study of meta-tribomaterial sensors and nanogenerators (“Self-aware materials form the basis of living structures”), the team uses different rationally designed triboelectric auxetic microstructures to construct the implant.

The entire structure of the implant serves as an energy harvesting medium as well as an active sensing system.

Vision of the proposed research showing a self-aware metamaterial implant that can be used for reliable determination of spinal fusion development after surgery directly at the intervertebral level. a) A multifunctional nanogenerator interbody fusion cage with self-recovery, self-sensing and energy harvesting features implanted during spinal fusion surgery. b) Composition of a self-aware cage implant. The implant generates electrical signals due to micro-movements of the spine using its built-in contact electrification mechanism. The signal can be used for detection and energy harvesting purposes. c) Physical mechanisms of contact electrification integrated in self-aware implants. d) Recorded data will be retrieved using an FDA compliant portable ultrasound system. This figure shows a Clarius C3 HD3 ultrasound system. e) The sensor output signals represent different healing stages and can be correlated with changes in FSU stiffness due to the healing process. (reproduced with permission from Wiley-VCH Verlag) (click image to enlarge)

According to the team, orthopedic implants seem to be the most immediate field of application for this technology since the implants require mechanical vibrations to harvest the energy necessary for their self-powering.

Therefore, they are highlighting the underlying characteristics and mechanisms of their proposed technology by creating a prototype proof-of-concept spinal fusion cage that harvests energy from spinal micro-movements. The electrical signal generated is then used for diagnostic purposes.

As shown in the figure above, the self-aware metamaterial fusion cage can detect different levels of spinal fusion through continuous stability and load-sharing measurements directly at the intervertebral disc space. These features allow physicians to assess fusion progression without the need for radiographic imaging.

Other medical fields can also benefit from this technology. For example, the same approach could be used to design smart heart stents with energy sensing and harvesting capabilities.

Gloved hand holding a multi-functional nanogenerator interbody cage with self-recovery, self-sensing and energy-harvesting functionality Close-up of a multi-functional nanogenerator interbody cage with self-recovery, self-sensing and energy-harvesting functionality. (Image courtesy of the researchers)

Researchers have previously tested these spinal implants using synthetic spine and human cadaver spine models. Their next step is to study their performance live use large animal models to establish a preclinical basis prior to human clinical trial.

“Under loading conditions similar to those of the human lumbar spine, our fusion cage prototype can generate voltage and current values ​​equal to 9.2 V and 4.9 nA, respectively,” says Alavi. “A series of fatigue tests using the synthetic spine model revealed that the modulus of elasticity of the cage decreases from 1.76 to 1.4 MPa after 40,000 loading cycles. The results imply the need to develop more robust manufacturing and calibration methods for the long-term performance of the implants live.”

Currently, the main challenge is the wireless interrogation of the data measured by the implants and the team is exploring viable solutions to deal with this problem. For example, they worked closely with collaborators at the University of Washington to couple electrical signals generated by self-aware implants with ultra-low-power wireless data-logging technologies to create fully self-powered. Of course, implant interrogation can also be easily performed via simpler passive strategies such as existing RFID telemetry systems.

fusion cage implant prototypes The team demonstrated a wide range of patient-specific and use-specific fusion cage implant prototypes. (Image courtesy of the researchers)

Over time, researchers envision creating nano, micro, meso and macro scale 3D implants with their technology.

“We are confident that our concept can push the boundaries of many existing medical implant technologies,” concludes Alavi. “The reason is that it allows us to create implants that can perform sensing, energy harvesting and information processing using their own matrix.”

Michael is the author of three Royal Society of Chemistry books: Nano-Society: Pushing the Boundaries of Technology, Nanotechnology: The Future is Tiny and Nanoengineering: The Skills and Tools Making Technology Invisible Copyright ©


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