Wireless metamaterial medical implant

Abstract

A self-powering medical implant and sensor ("medical implant / sensor") for electronic-free wireless transmission of data sensed by the medical implant / sensor, comprising an active mechanical metamaterial, comprising first and second electrically conductive components disposed relative to each other to act as opposite electrodes to induce contact electrification; wherein the first and second electrically conductive components, along with a dielectric component serving as a skeleton of the active mechanical metamaterial, form a lattice of snapping curved semicircular-shaped segments, wherein each of the snapping curved semicircular-shaped segments has an elastic snap-through instability mechanism; and wherein the lattice of snapping curved semicircular-shaped segments comprises periodic repeatable parallel rows of the snapping curved semicircular-shaped segments.

Description

WIRELESS METAMATERIAL MEDICAL IMPLANTRELATED APPLICATION

[0001] This application claims priority benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 63 / 688,604 filed August 29, 2024, the contents of which are herein incorporated by reference.STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under 2235494 awarded by the National Science Foundation. The government has certain rights in the invention.FIELD OF THE DISCLOSURETechnical field

[0003] The present disclosure generally relates to the field of wireless medical implant devices comprising metamaterials and methods for making and using the same.Background

[0004] Smart wireless implants have emerged as a progressive advancement in modern healthcare. They enable continuous monitoring of a spectrum of physiological signals. These implantable devices possess the potential to fundamentally transform patient care via enabling the continuous acquisition of data and facilitating timely medical interventions. Meanwhile, force sensing plays a pivotal role in the realm of smart implants. This process encompasses applications such as intraocular pressure monitoring, assessment of joint biomechanics, and stabilization of orthopedic implants. However, the conventional methods for acquiring force sensing data from smart implants (e.g., LC resonant, magnetic soft material, electromagnetic (EM) waves) require various bulky modules for signal generation, power supply, signal modulation, and transmission. The utilization of external electronics or batteries in biomedical implants proves impractical due to limitations in their operational lifespan, size, and associated chemical risks. Many of the existing smart implants utilize radio-frequency identification (RFID) technology for sensor interrogation, which encounters significant limitations within tissue environments. These wireless implants are primarily passive devices, incapable of continuously recording the data unless exposed to an inductive energy source. They areoften designed to capture momentary changes in strain levels, offering only a single snapshot in time. While more recent self-powered sensor-data loggers (e.g., piezo-floating-gate (PFG) and Fowler-Nordheim (FN) data loggers) provide partial solutions to these challenges, they remain electronic modules that require additional RFID or ultrasound connectivity to transmit the stored data. Consequently, there is a growing demand for wireless force sensing techniques implants characterized by their compact form, self-powered operation, and precise data transmission.

[0005] Over the past decades, researchers have dedicated substantial efforts to the development of smart biomaterials capable of replicating properties found in human tissues. Initially, the focus was primarily on enhancing the mechanical performance of these biomaterials. Subsequently, the concept of mechanical metamaterials, artificial structures endowed with specific properties not encountered in nature, was introduced to augment mechanical, physical, and biological characteristics. For instance, Zadpoor et al. highlighted the potential of their proposed mechanical metamaterials in tissue replacement, thereby facilitating tissue regeneration. Prior multifunctional metamaterial implantable devices could sense spine forces, harvest energy from spine motion and monitor the bone healing progress. However, a significant research gap exists regarding the establishment of a wireless communication paradigm for retrieving the biological data collected by such systems. Such an advancement would greatly enhance the suitability of these materials for various biomedical applications.

[0006] Wireless force sensing in smart implants enables real-time monitoring of mechanical forces and facilitates dynamic adjustments to optimize implant functionality in-situ. This capability enhances the precision of diagnostics and treatment leading to superior surgical outcomes. Despite significant advancements in wireless smart implants over the last two decades, current implantable devices still operate passively and require additional electronic modules for wireless transmission of the stored biological data. To address these challenges, the present disclosure is directed to an innovative wireless force sensing paradigm for implantable systems through the integration of mechanical metamaterials and nano energy harvesting technologies. Composite mechanical metamaterial implants of the present disclosure are preferably capable of serving as all-in-one wireless force sensing units, incorporating functions for powergeneration, sensing and transmission. In this alternative communication approach, the electrical signals harvested by the implants from mechanical stimuli are utilized directly for the wireless transmission of the sensed data. Experimental and theoretical studies have demonstrated the wireless detection of the generated strain-induced polarization electric field using electrodes. The feasibility of the wireless force sensing approach of the present disclosure is evaluated through a proof-of-concept orthopedic implant in the form of a total knee replacement (TKR). The wireless, electronic-free metamaterial implants of the present disclosure with a power output as low as 0.1 pW enable direct, self-powered wireless communication during force sensing across air, simulated body fluid and animal tissue. The functionality of the implants of the present disclosure has been validated through a series of experiments conducted on an ex vivo human cadaver knee specimen. Furthermore, the effect of electrode size and placement on the strength of the received signals from wireless, electronic-free metamaterial implants of the present disclosure was examined. The present disclosure is directed to a diverse array of mechanically-tunable implants capable of precise force measurements and wireless real-time data transmission, all without relying on any external antennas, power sources, or telemetry systems.

[0007] The present disclosure introduces a new concept based on Maxwell's displacement current to realize wireless communication directly using mechanical metamaterial implants. Metamaterial orthopedic implants of the present disclosure can harvest energy from body motions and use the generated electrical signal for “direct, wireless and electronic-free” transmission of the sensed data, without relying on additional electronics. Experimental studies on the metamaterial implants of the present disclosure were conducted under various loading conditions to evaluate the communication capabilities of such all-in-one wireless metamaterial implants. Theoretical models were used to characterize the strain-induced polarization electric field generated by the metamaterial implants of the present disclosure across different media. The functionality of the metamaterial implants of the present disclosure was further studied through a series of experiments conducted using a human cadaver knee specimen. Personalized electronic-free wireless metamaterial implants of the present disclosure are capable of accurately measuring the forces and wirelessly transmitting real-time data.BRIEF SUMMARY OF THE DISCLOSURE

[0008] In a preferred aspect, the present disclosure comprises a self-powering medical implant and sensor (“medical implant / sensor”) for electronic-free wireless transmission of data sensed by the medical implant / sensor, comprising an active mechanical metamaterial, comprising first and second electrically conductive components disposed relative to each other to act as opposite electrodes to induce contact electrification; wherein the first and second electrically conductive components, along with a dielectric component serving as a skeleton of the active mechanical metamaterial, form a lattice of snapping curved semicircular-shaped segments, wherein each of the snapping curved semicircular-shaped segments has an elastic snap-through instability mechanism; and wherein the lattice of snapping curved semicircular-shaped segments comprises periodic repeatable parallel rows of the snapping curved semicircular-shaped segments.

[0009] In another preferred aspect of a self-powering medical implant / sensor of the present disclosure, the first electrically conductive component comprises a first electrically conductive lattice and the second electrically conductive component comprises a second electrically conductive lattice.

[0010] In yet another preferred aspect of a self-powering medical implant / sensor of the present disclosure, the dielectric component comprises first and second outer dielectric layers and an inner dielectric layer- disposed between the first and second outer dielectric layers.

[0011] In another preferred aspect of a self-powering medical implant / sensor of the present disclosure, the medical implant / sensor comprises a spacer for a total knee replacement prosthetic, wherein the spacer is disposed between a femoral component and a tibial component of the total knee replacement prosthetic.

[0012] In an additional preferred aspect, the self-powering medical implant / sensor of the present disclosure further comprises an external receiving electrode for receiving wireless electric signals generated by the medical implant / sensor.

[0013] In another preferred aspect of a self-powering medical implant / sensor of the present disclosure, the first and second electrically conductive components comprise polylactic acid (PLA) containing carbon black and the dielectric component comprises thermoplastic polyurethane (TPU).

[0014] In yet another preferred aspect of a self-powering medical implant / sensor of the present disclosure, the first and second electrically conductive lattices comprise polylactic acid (PLA) containing carbon black and each of the first and second outer dielectric layers and the inner dielectric layer comprises thermoplastic polyurethane (TPU).

[0015] In another preferred aspect of a self-powering medical implant / sensor of the present disclosure, the first and second electrically conductive components and the dielectric component each comprises one or more of a biocompatible material and a bioresorbable material.

[0016] In another preferred aspect of a self-powering medical implant / sensor of the present disclosure, the first and second electrically conductive components are embedded in the dielectric component.

[0017] In a further preferred aspect of a self-powering medical implant / sensor of the present disclosure, a structure of the self-powering medical implant / sensor forms a composite matrix of the electrically conductive components and the dielectric component in a periodic manner.

[0018] In another preferred aspect of a self-powering medical implant / sensor of the present disclosure, each of the snapping curved semicircular-shaped segments comprises a portion of each of the first electrically conductive component, the second electrically conductive component and the dielectric component.

[0019] In another preferred aspect, the present disclosure comprises a self-powering medical implant and sensor (“medical implant / sensor”) for electronic-free wireless transmission of data sensed by the medical implant / sensor, comprising a triboelectric nanogenerator (TENG); and an external receiving electrode for receiving wireless electric signals generated by the TENG.

[0020] In another preferred aspect of a self-powering medical implant / sensor of the present disclosure, the TENG comprises a spacer for a total knee replacement (TKR) prosthetic (“TKR Prosthetic”), wherein the spacer is disposed between a femoral component and a tibial component of the TKR prosthetic.

[0021] In yet an additional preferred aspect, the present disclosure comprises a total knee replacement (TKR) prosthetic (“TKR Prosthetic”) for electronic-free wireless transmission of data sensed by the TKR Prosthetic, comprising a self-powering spacer comprising an active mechanical metamaterial, comprising first and second electrically conductive components disposed relative to each other to act as opposite electrodes toinduce contact electrification; wherein the first and second electrically conductive components, along with a dielectric component serving as a skeleton of the active mechanical metamaterial, form a lattice of snapping curved semicircular-shaped segments, wherein each of the snapping curved semicircular-shaped segments has an elastic snap-through instability mechanism; and wherein the lattice of snapping curved semicircularshaped segments comprises periodic repeatable parallel rows of the snapping curved semicircular-shaped segments; wherein the self-powering spacer is disposed between a femoral component and a tibial component of the TKR prosthetic.

[0022] In another preferred aspect of a TKR prosthetic of the present disclosure, the first electrically conductive component comprises a first electrically conductive lattice and the second electrically conductive component comprises a second electrically conductive lattice.

[0023] In yet another preferred aspect of a TKR prosthetic of the present disclosure, the dielectric component comprises first and second outer dielectric layers and an inner dielectric layer disposed between the first and second outer dielectric layers.

[0024] In yet an additional preferred aspect, the TKR prosthetic of the present disclosure further comprises an external receiving electrode for receiving wireless electric signals generated by the self-powering spacer.

[0025] In yet another preferred aspect of a TKR prosthetic of the present disclosure, the first and second electrically conductive components are embedded in the dielectric component.

[0026] In a further preferred aspect of a TKR prosthetic of the present disclosure, a structure of the selfpowering spacer forms a composite matrix of the electrically conductive components and the dielectric component in a periodic manner.

[0027] In yet another preferred aspect of a TKR prosthetic of the present disclosure, each of the snapping curved semicircular-shaped segments comprises a portion of each of the first electrically conductive component, the second electrically conductive component and the dielectric component.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] For the present disclosure to be easily understood and readily practiced, the present disclosure will now be described for purposes of illustration and not limitation in connection with the following figures, wherein:

[0029] FIG. 1(a) shows schematics of a wireless metamaterial system of the present disclosure composed of rationally designed conductive and dielectric lattices. This multi -material composite metamaterial induces contact-electrification under mechanical triggering. The generated signal is proportional to the applied force. The strain-induced Maxwell's displacement current generated by the wireless metamaterial lattice enables wireless transmission of the sensed signal through various media without any antenna and power supply;

[0030] FIG. 1(b) shows a working principle for wireless communication with wireless metamaterial lattice as a capacitance model;

[0031] FIG. 1(c) shows schematics and dimensions of a mechanically-tunable wireless metamaterial TKR implant 10 of the present disclosure capable of self-powering through knee loads, measuring forces, and wirelessly transmitting real-time data, without relying on any battery-powered telemetry system or external antennas;

[0032] FIG. 2(a) shows a 3D printed wireless metamaterial TKR implant and test setup of the present disclosure;

[0033] FIG. 2(b) shows stress-strain curves used to determine the elastic modulus of a wireless metamaterial TKR implant of the present disclosure;

[0034] FIG. 2(c) shows electrical signals generated by a wireless metamaterial TKR implant of the present disclosure (in blue) and received by the electrode of the present disclosure (in red) in air under uniaxial loading at 1 Hz;

[0035] FIG. 2(d) shows electrical signals generated by a wireless metamaterial TKR implant of the present disclosure (in blue) and received by the electrode of the present disclosure (in red) in air under uniaxial loading at 3 Hz;

[0036] FIG. 2(e) shows electrical signals generated by a wireless metamaterial TKR implant of the present disclosure (in blue) and received by the electrode of the present disclosure (in red) in air under uniaxial loading at 5 Hz;

[0037] FIG. 2(f) shows electrical signals generated by a wireless metamaterial TKR implant of the present disclosure (in blue) and received by the electrode of the present disclosure (in red) in air under varus loading;

[0038] FIG. 2(g) shows electrical signals generated by a wireless metamaterial TKR implant of the present disclosure (in blue) and received by the electrode of the present disclosure (in red) in air at 25° internal rotation;

[0039] FIG. 2(h) shows power- voltage-current curve output of a wireless metamaterial TKR implant of the present disclosure;

[0040] FIG. 2(i) shows low-cycle fatigue test results for a wireless metamaterial TKR implant of the present disclosure showing the variations of the signal delivery ratios over time;

[0041] FIG. 3(a)-FIG.3(m) shows experimental and theoretical evaluation of the wireless force sensing capability of a wireless metamaterial TKR implant of the present disclosure, wherein:

[0042] FIG. 3(a) shows an experimental test setup for a wireless metamaterial TKR implant of the present disclosure using porcine tissue;

[0043] FIG. 3(b) shows a 3D view of the simplified schematic of the formulated wireless transmission in the experiments with a wireless metamaterial TKR implant of the present disclosure;

[0044] FIG. 3(c) shows a top view of the simplified schematic of the formulated wireless transmission in the experiments with a wireless metamaterial TKR implant of the present disclosure;

[0045] FIG. 3(d) shows transmitted (in blue) and received (in red) electrical signals measured during the experiments and predicted using a wireless metamaterial TKR implant of the present disclosure in air;

[0046] FIG. 3(e) shows transmitted (in blue) and received (in red) electrical signals measured during the experiments and predicted using a wireless metamaterial TKR implant of the present disclosure in porcine tissue;

[0047] FIG. 3(f) shows transmitted (in blue) and received (in red) electrical signals measured during the experiments and predicted using a wireless metamaterial TKR implant of the present disclosure in SBF;

[0048] FIG. 3(g) shows signal delivery ratios in air, porcine tissue and SBF in a wireless metamaterial TKR implant of the present disclosure;

[0049] FIG. 3(h) shows transmitted (in blue) and received (in red) electrical signals generated by a damaged wireless metamaterial TKR implant of the present disclosure in air under uniaxial loading;

[0050] FIG. 3(i) shows transmitted (in blue) and received (in red) electrical signals generated by an intact wireless metamaterial TKR implant of the present disclosure in air under uniaxial loading; a

[0051] FIG. 3(j) shows a human cadaver knee before and after instrumentation with components of a wireless metamaterial TKR implant of the present disclosure;

[0052] FIG. 3(k) shows an experimental test setup of a wireless metamaterial TKR implant of the present disclosure using the cadaver knee and copper electrodes with varying surface areas;

[0053] FIG. 3(1) shows transmitted electrical signals (in blue), received electrical signals (in red) and signal delivery ratios (in black) for the 1 cm2, 4 cm2, 9 cm2, and 16 cm2electrodes placed at a fixed distance of 5 cm from a wireless metamaterial TKR implant of the present disclosure on the back side of a cadaver knee;

[0054] FIG. 3(m) shows transmitted electrical signals (in blue), received electrical signals (in red) and signal delivery ratios (in black) for the reference 9 cm2electrode positioned at distances of 0 cm, 2 cm, 5 cm, 10 cm, and 20 cm from a wireless metamaterial TKR implant of the present disclosure on the back side of a cadaver knee;

[0055] FIG. 4(a) illustrates an evolution of smart implants equipped with force sensing, demonstrating key studies conducted in this field, functionalities of the implants and their power demand, plus a vision for the future application of wireless force sensing approach in medical implants of the present disclosure;

[0056] FIG. 4(b) shows a schematic of a smart, stand-alone metamaterial cardiovascular stent of the present disclosure with wireless integration functionality for continuous monitoring of local hemodynamic changes upon a restenosis condition where the stent generates electrical signals in response to periodic deformations caused by the dilations of the artery;

[0057] FIG. 4(c) shows that a commercially-available smartphone-connectable ECG recorder can detect the bursts of electrical energy released by the stent of FIG. 4(b); and

[0058] FIG. 4(d) shows that the stent of FIG. 4(b) can be fine-tuned for optimal performance, aiming to produce electrical signals of greater magnitude than the heart's intrinsic electrical signals, such that they can tall waves in one of the chest (precordial) leads and such signals will correspond to various luminal renarrowing rates and can thus be used for accurate in-stent restenosis assessments.DETAILED DESCRIPTION

[0059] In the following detailed description, reference is made to the accompanying examples and figures that form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the inventive subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice them, and it is to be understood that other embodiments may be utilized and that structural or logical changes may be made without departing from the scope of the inventive subject matter. Such embodiments of the inventive subject matter may be referred to, individually and / or collectively, herein by the term "disclosure" merely for convenience and without intending to voluntarily limit the scope of this application to any single inventive concept if more than one is in fact disclosed.

[0060] The following description is, therefore, not to be taken in a limited sense, and the scope of the inventive subject matter is defined by the appended claims and their equivalents.

[0061] As shown in FIG. 1, the a preferred self-powering medical implant and sensor 10 (“medical implant / sensor”) for electronic-free wireless transmission of data sensed by the medical implant / sensor 10 of the present disclosure, comprises an active mechanical metamaterial 12, comprising first and second electrically conductive components 14, 16 disposed relative to each other to act as opposite electrodes to induce contact electrification; wherein the first and second electrically conductive components 14, 16, along with a dielectric component 18 serving as a skeleton 19 of the active mechanical metamaterial 12, form a lattice 20 of snapping curved semicircular-shaped segments 22, wherein each of the snapping curved semicircular-shaped segments 22 has an elastic snap-through instability mechanism; andwherein the lattice 20 of snapping curved semicircular-shaped segments 22 comprises periodic repeatable parallel rows 24 of the snapping curved semicircular-shaped segments 22.

[0062] A preferred self-powering medical implant / sensor 10 of the present disclosure may also have a first electrically conductive component 14 that comprises a first electrically conductive lattice 30 and a second electrically conductive component 16 comprising a second electrically conductive lattice 32.

[0063] The dielectric component 18 preferably may comprise first and second outer dielectric layers 34, 36 and an inner dielectric layer 35 disposed between the first and second outer dielectric layers 34, 36.

[0064] In another preferred embodiment, self-powering medical implant / sensor 10 may further comprise a spacer 40 for a total knee replacement prosthetic 42. Spacer 40 is preferably disposed between a femoral component 44 and a tibial component 46 of the total knee replacement prosthetic 42.

[0065] Additionally, self-powering medical implant / sensor 10 may preferably comprise an external receiving electrode 50 for receiving wireless electric signals generated by the medical implant / sensor 10.

[0066] Further, the first and second electrically conductive components 14, 16 of the self-powering medical implant / sensor 10 preferably comprise polylactic acid (PLA) containing carbon black and the dielectric component 18 comprises thermoplastic polyurethane (TPU). Preferably, the first and second electrically conductive lattices 30, 32 of the self-powering medical implant / sensor 10 comprise polylactic acid (PLA) containing carbon black and each of the first and second outer dielectric layers 34, 36 and the inner dielectric layer 35 comprises thermoplastic polyurethane (TPU). Additionally, first and second electrically conductive components 14, 16 and the dielectric component 18 of self-powering medical implant / sensor 10 are preferably fabricated using a wide range of biocompatible and / or bioresorbable materials. Preferably, the first and second electrically conductive components 14, 16 of the self-powering medical implant / sensor 10 are embedded in the dielectric component 18.

[0067] In a further embodiment, a structure of the self-powering medical implant / sensor 10 preferably forms a composite matrix 52 of the electrically conductive components 14, 16 and the dielectric component 18 in a periodic manner.

[0068] In yet another preferred embodiment, each of the snapping curved semicircular-shaped segments 22 of the self-powering medical implant / sensor 10 preferably comprises a portion of each of the first electrically conductive component 14, the second electrically conductive component 16 and the dielectric component 18.

[0069] In a further preferred embodiment, a self-powering medical implant and sensor 10 (“medical implant / sensor”) for electronic-free wireless transmission of data sensed by the medical implant / sensor 10, comprises a triboelectric nanogenerator (TENG) 60; and an external receiving electrode 50 for receiving wireless electric signals generated by the TENG 60. Preferably, TENG 60 comprises a spacer 40 for a total knee replacement (TKR) prosthetic (“TKR Prosthetic”) 42, wherein spacer 40 is disposed between a femoral component 44 and a tibial component 46 of the TKR prosthetic 42.

[0070] In an additional preferred embodiment, the total knee replacement (TKR) prosthetic (“TKR Prosthetic”) 42 for electronic-free wireless transmission of data sensed by the TKR Prosthetic 42, comprises a self-powering spacer 40 comprising an active mechanical metamaterial 12, comprising first and second electrically conductive components 14, 16 disposed relative to each other to act as opposite electrodes to induce contact electrification. Preferably, the first and second electrically conductive components 14, 16, along with a dielectric component 18 serving as a skeleton 19 of the active mechanical metamaterial 12, form a lattice 20 of snapping curved semicircular-shaped segments 22. Additionally, each of the snapping curved semicircular-shaped segments 22 preferably has an elastic snap-through instability mechanism and the lattice 20 of snapping curved semicircular-shaped segments 22 comprises periodic repeatable parallel rows 24 of the snapping curved semicircular-shaped segments 22. Also, the self-powering spacer 40 is preferably disposed between a femoral component 44 and a tibial component 46 of the TKR prosthetic 42. Here, the first electrically conductive component 14 of the TKR Prosthetic 42 preferably comprises a first electrically conductive lattice 30 and the second electrically conductive component 16 preferably comprises a second electrically conductive lattice 32. Also, the dielectric component 18 of the TKR Prosthetic 42 preferably comprises first and second outer dielectric layers 34, 36 and an inner dielectric layer 35 disposed between the first and second outer dielectric layers 34, 36. TKR Prosthetic 42 preferably may further comprise an external receiving electrode 50 for receiving wireless electric signals generated by the self-powering spacer 40. First and second electrically conductive components 14, 16 of TKR Prosthetic 42 preferably comprises poly lactic acid (PL A) containing carbon black and the dielectric component 18 preferably comprises thermoplastic polyurethane (TPU). First and second electrically conductive components 14, 16 and the dielectric component 18 of TKR Prosthetic 42 preferably may be fabricated using a wide range of biocompatible and bioresorbable materials. First and second electrically conductive lattices 30, 32 preferably comprise polylactic acid (PLA) containing carbon black and each of the first and second outer dielectric layers 34, 36 and the inner dielectric layer 35 preferably comprise thermoplastic polyurethane (TPU). In the TKR Prosthetic 42 the first and second electrically conductive components 14, 16 are preferably embedded in the dielectric component 18. Additionally, a preferred structure of the self-powering spacer 40 of the TKR Prosthetic 42 forms a composite matrix 52 of the electrically conductive components 14, 16 and the dielectric component 18 in a periodic manner. Also, each of the snapping curved semicircularshaped segments 22 of the TKR Prosthetic 42 preferably comprises a portion of each of the first electrically conductive component 14, the second electrically conductive component 16 and the dielectric component 18.

[0071] Incorporating additional electronics, wiring, and power supply resources poses significant challenges in reducing the size of conventional force sensors for medical implants. Departing from the passive wireless implants developed over the last 40 years, the present disclosure is directed to an innovative signal transmission mechanism for wireless force sensing. The metamaterial implants of the present disclosure transform medical implants into entirely self-contained units capable of wirelessly transmitting the sensed data. This is achieved by integrating mechanical metamaterials with nano energy harvesting technologies to create a composite biomateriaL These composite material systems are constructed from a combination of conductive and dielectric lattices, specifically designed to induce triboelectrification. This allows them to function as triboelectric nanogenerators (TENGs) when subjected to applied forces. While previous devices explored the versatility of a metamaterial platform for creating scalable structural systems with sensing capabilities, the present disclosure is directed to solving the distinct, longstanding challenge in the biomedical field of providing direct wireless, electronic-free interrogation of implants. More specifically, the present disclosure is directed to composite mechanical metamaterial implants that enable the wirelesstransmission of self-generated electrical signals without the need for integrated electronics and external power sources. As shown in FIG. 1, the self-powering wireless capability of the metamaterial implants 10 of the present disclosure enables miniaturization of such implants by eliminating the requirement for external power sources, extra electronics, or large antennas. FIG. 1(a) shows the schematics of conductive and dielectric lattices forming a wireless mechanical metamaterial lattice with wireless communication functionality of the present disclosure. Upon mechanical triggering, contact-electrification occurs within such metamaterial lattice, leading to the generation of an electric signal proportional to the applied force. The strain-induced signal produced by the lattice can then be detected by an electrode wirelessly.

[0072] Characterizing wireless transmission of the strain-induced signals generated by the wireless metamaterial systems of the present disclosure revolves around the utilization of Maxwell's displacement current to formulate wireless transmission of the measured force signals. This concept can be elucidated using a capacitance model, as shown in FIG. 1(b). The analysis of electric field propagation is approached by considering the displacement current, akin to the principles governing TENG. In this model, the transmitting and receiving electrodes serve as the positive and negative terminals of a capacitor, while the intervening medium acts as the dielectric. Under the influence of the electric field (E), the dielectric becomes polarized, generating a polarization electric field (P). This polarization electric field arises from the juxtaposition of negative and positive polarization charges. The resulting combined electric field (Ez) can be quantified relative to E by defining the relative permittivity (Er):£r =E / E' (1)The relationship between polarization charge (Q') and the charge (Q) on the transmitting electrode can be defined as:

[0073] Owing to the attenuation of the electric field during propagation through the medium, the charge received (Q") at the receiving electrode is less than Q'. The Gauss’s law of Maxwell’s equations gives the relationship between the electric displacement vector D and distribution of free charges in space p as:V • D = p.D can be expressed as: D = e0E + Pwhere D signifies the electric displacement vector, £0is the permittivity in a vacuum, and P represents the medium polarization vector, respectively. In practical scenarios, polarization can also result from the strain field, which emerges due to surface contact-electrification (e.g., triboelectric effect) and is independent of the presence of an electric field. To incorporate the influence of contact-electrification-induced electrostatic charges into Maxwell's equations, Wang introduced an additional term (Ps) that represents the polarization arising from the relative movement of the charged dielectric media, the final displacement vector is given in Eq. (5):D = +p+ Ps

[0074] In Eq. (5), polarization vector P arises from the impact of an external electric field, while Pspredominantly emerges from the presence of surface charges that are independent of the electric field's d existence. The displacement current observed in TENG is given by Ps- Based on these explanations, the strain-induced polarization term, i.e. Ps, preferably can be employed to develop a current transport equation for wireless metamaterial systems, thereby enabling wireless transmission functionality.

[0075] The present disclosure demonstrates the viability of a total knee replacement (TKR) implant 10 with wireless force sensing. The technology of the present disclosure is not exclusive to TKR implants but can be adapted for designing any medical implant aligned with the proposed conceptual framework. FIG. 1(c) illustrates the schematics and dimensions of the wireless metamaterial TKR implant 10. We chose TKR implants since they are exposed to significant loading during daily activities like jumping, running, and walking. The TKR surgery numbers are rapidly growing and expected to reach 3.48 million by 2030 in the United States. This surgery is performed to remove damaged cartilage and bone, and to replace the removed part with artificial components (e.g., tibial, femoral or spacers), known as knee implants. The knee implants generate a new surface between tibia and femur. Approximately, 20% of the patients with TKR surgery experience pain and reduced functionality levels after the surgery. A main contributor to the unsatisfied function of TKRs is incorrect ligament balancing, which can accelerate abrasion from unbalanced joint reaction force and increase prosthetic loosening. Although various techniques are used for analyzing postsurgery TKRs kinematics, direct measurement of loads on the TKR implant components is still challenging. These loads can eventually result in implant failure. A better understanding of the loading pattern on kneeimplants can be clinically beneficial to assess the health and functionality of the prosthesis. All of the current smart TKR implants with force-sensing capabilities contain multiple electronic modules and rely on inductive wireless power transfer. Also, the only clinically available smart TKR implant, Persona IQ, launched in 2021 by Zimmer Biomet and Canary Medical, is a tibial stem instrumented with internal motion sensors and battery-powered telemetry modules to collect and transmit kinematic data. Despite the novelty of the Persona IQ implant, it requires a 58 mm long tibial stem extension to house electronics, resulting in additional bone resection and an alteration to the implant orientation.

[0076] A mechanically-tunable TKR implant 10 with the ability to self-power through knee loads, accurately measure forces, and wirelessly transmit real-time data, all without relying on a battery-powered telemetry system, holds the potential for substantial clinical advantages. Herein, wireless metamaterial TKR polymer spacer 40 directly carries the knee load between the tibial component 46 and femoral component 44 and thus can provide objective information about the loading pattern on the implant as shown in FIG. 1(c).Preliminary finite element (FE) simulations were carried out to design the multi-layered metamaterial spacer with an elastic modulus within the range of central region of human medial meniscus (-20-80 kPa). The wireless metamaterial TKR implant 10 was then 3D printed and tested to determine its mechanical and electrical properties. During the tests, implant 10 was placed within a polyacrylonitrile testing bath with a diameter of 15 cm. A conductive copper tape with a width of 5 cm was affixed to the exterior of the bath to serve as the receiving electrode 50. The printed implant 10 and test setup are shown in FIG. 2(a). The elastic modulus was calculated following the procedure explained in the ISO standard 13313:2011 for porous and cellular metals. FIG. 2(b) shows the obtained stress-strain curves for the implant. The slope of the fitted straight lines represents the elastic modulus value (~ 45 kPa). Depending on the clinical requirements, such metamaterial implants can be designed with any desired mechanical properties.

[0077] The TKR implant 10 was initially tested under uniaxial loading conditions at 1, 3, and 5 Hz, corresponding to knee joint loading frequencies during walking and running. Knee joint load ranges from 1.8 times body weight to 8.1 times body weight during daily life activities. To assess the mechanical and electrical performance of the metamaterial spacer, cyclic loading tests were conducted within the range of 0to 350 N (~ 4 times the body weight of a 100 kg person). FIGS. 2(c)-(e) show the electrical signal transmitted by the implant lattice and the received by the electrode in air under uniaxial loading at different frequencies. The typical applied loading cycles at 1 Hz are also illustrated in FIG. 2(c). Typical signals transmitted and received under uniaxial loading at 3 and 5 Hz, respectively, were also investigated. The electric signals are proportional to the applied force, as thoroughly discussed in our prior study. Referring to FIGS. 2(c)-(e), it is evident that both the transmitted voltage signals and their corresponding received signals increase with the rising frequency. Here, “signal delivery ratio” is defined as the ratio of voltage signal received to the signal transmitted. The signal delivery ratios are 0.52, 0.44 and 0.36 at 1, 3 and 5 Hz, respectively. TKR implant 10 was then tested under internal rotation and varus loading conditions at 1 Hz. A 25° internal rotation was taken into consideration. The results are shown in FIG. 2(f) and FIG. 2(g). The signal delivery ratios are 0.61 and 0.39 for the internal rotation and varus loading, respectively.

[0078] The output performance of the wireless metamaterial TKR implant 10 can be determined by measuring open-circuit voltage, current, and power density. The power-voltage-current curve output of the implant is shown in FIG. 2(h). The power output of the implant gradually increases from 0.1 MG to 100 MG, reaching a maximum value of 0.125 pW. The meta-mechatronic systems feature a built-in TENG mechanism 60, thereby providing high voltage and low current. This characteristic can be explained through both physical and mathematical perspectives. Furthermore, low-cycle fatigue tests were conducted to assess the electrical and mechanical performance of TKR implant 10. During the fatigue study, TKR implant 10 underwent 30,000 axial loading cycles at a frequency of 1 Hz with a 350 N axial compression force. FIG. 2(i) shows the fatigue test results. The elastic modulus of TKR implant 10 decreased by approximately 24% to 35.9 kPa after 30,000 loading cycles. The transmitted and received voltage values exhibited a decline from 1.1 V and 0.58 V in the initial 20,000 cycles to 0.87 V and 0.43 V, respectively. The transmitted and received voltage exhibited stability beyond 20,000 cycles. Nevertheless, the signal delivery ratio remained consistently around 0.5. This observed voltage trend reflects changes in both the mechanical and electrical properties of the wireless metamaterial implant 10. The diminishing electrical and mechanical performance under repeated loading cycles is anticipated and warrants careful investigation to establish calibrationparameters for implants. However, the preferred performance for such implants varies case by case, and the target performance need not necessarily prioritize maximum electrical output or mechanical prowess, as it heavily relies on clinical requirements.

[0079] Establishing the wireless force sensing and communication framework of the present disclosure requires theoretical characterizing the polarization, Ps, created by the electrostatic surface charges within the wireless metamaterial lattice in different media. To this aim, wireless transmission tests of implant 10 were conducted in air, simulated body fluid (SBF), and porcine, a theoretical model was subsequently developed. The TKR implant 10 was a proof-of-concept prototype and was not optimized for ingress protection. Thus, it was encased within a smaller polyacrylonitrile bath with a diameter of 12.5 cm to prevent contact with SBF and tissue as shown in FIG. 3(a). The tests in air were replicated using such setup. The space between the two testing baths was then filled with SBF and porcine tissue. FIG. 3(b) and FIG. 3(c) present the simplified schematic of the formulated wireless transmission in the experiments. In particular, the TKR implant 10 and receiving electrode 50 form the positive and negative electrodes of capacitor, while the dielectric contains four layers of mediums as shown in FIG. 3(c). The voltage and charge generated by the TKR implant 10 can be determined using the V-Q-x relationship. For TKR implant 10 with a built-in contact-separation modeTENG 60, this is relationship can be expressed as:where, V, Q, £0y, and £rare the output voltage, transferred charge, vacuum permittivity, thickness and relative dielectric constant, respectively. The varying gap distance X(t) is given by the axial displacement d(t). The surface charge density cr is experimentally calibrated as 0.00136 pC / m2. The contact area can be written as:where, ptpresent the curvature radius of semicircular segment and width of dielectric layer of snapping units, respectively. Connecting a load consistence R to the TKR implant 42 to form a circuit, the output voltage can be calculated by the Ohm’s law as:Substituting Eq. (8) into Eq. (6), we have:Solving the differential equation Eq. (9) yields:where, pi denotes the integration constant. Substituting Eq. (11) into Eq. (8) leads to:The boundary conditions of Eq. (9) are given as:pi is determined as 0 according to Eq. (13), and thus, Q(t) and V(t) can be rewritten as:For the open-circuit condition, the load consistence R can be treated as infinity, Therefore, Q (t) and V (t) are:2(0 = o, (16) and aX (t). . . . m)Based on the principle of signal attenuation in the wireless transmission process (as illustrated in FIG.3(c)), Eq. (4) can be formulated as follows:where, Pt(i — 1, 2, 3, 4) presents the polarization electric field in medium i with the presence of electric field E.The Maxwell’s displacement current density can be written as:

[0080] In order to quantitatively analyze the signal attenuation in the wireless transmission process, the external electric field of TKR implant is simplified as the electric field of a uniformly charged spherical shellwith the charge of q and radius of p0. pQis experimentally calibrated as 33 mm. In the vacuum, the electric field strength outside the spherical shell is:where, p (p > p0) denotes the distance from the center of spherical shell. The transmitted voltage T(t) can be regarded as the surface electric potential of spherical shell, and thus, producing:substituting Eq. (21) into Eq. (20), F(p) is rewritten as:PoV(t)E(p) =P2(22)In order to find the combined electric field of E and Pt(i = 1, 2, 3, 4), Eq. (1) can be expressed as: r =£E. 23) where (i — 1, 2, 3, 4) is the relative permittivity of medium i. Thence, the actual electric field strength is modified as:The electric potential difference is defined as the integral of electric field strength over the effective displacement. Consequently, the electric potential difference between the wireless metamaterial TKR implant and receiving electrode is:where yacr, Pinte r and Pexterarethethickness of polyacrylonitrile baths, radius of internal polyacrylonitrile bath and radius of external polyacrylonitrile bath.

[0081] FIG. 3(d) - FIG.3(f) show the transmitted and received voltage values measured during the experiments and those predicted using the theoretical models for the air, tissue and SBF media, respectively. There is an acceptable agreement between the experimental and theoretical results. FIG. 3(g) shows the signal delivery ratios in air, tissue and SBF. The experimental delivery ratios in air, tissue and SBF are 0.55, 0.75 and 0.81, respectively. The delivery ratios estimated using the theoretical model are 0.54, 0.74, 0.74 in the respective media. An important observation from the results is that attenuation of the polarization electricfield generated by the implant 10 is lower in lossy (e.g. salt water, blood, animal tissue) than in lossless (e.g. air, vacuum) media. The ability of the polarization electric field to travel more effectively in lossy (conductive) media compared to lossless (non-conductive) media can be explained by the presence of free charge carriers in the conductive medium. In lossy media, there are mobile charged particles (ions) that can move in response to the applied electric field. These free charge carriers facilitate the transmission of the electric field through the medium, resulting in lower resistance and less dissipation of the signal. In contrast, lossless media like air or vacuum have fewer or no free charge carriers, leading to higher electrical resistance. As the polarization electric field travels through these non-conductive media, it encounters increased resistance, causing more rapid dissipation and attenuation of the signal.

[0082] In addition, the wireless force sensing capability of the TKR implant 10 was evaluated in case of implant failure. To this aim, the intact implant 10 was initially tested under uniaxial loading in air at 1 Hz. The transmitted and received signals for the intact implant 10 are shown in FIG. 3(h). Then, damage was introduced by cutting one of the unit cells of the implant through its width. The damaged implant 10 was tested under uniaxial loading similar to the intact prototype. FIG. 3(i) presents the transmitted and received signals for the damaged implant 10. The transmitted and received signals sharply decrease from 0.77 V and 0.41 V to 0.3 V and 0.15 after introducing the damage, respectively. The signal delivery ratios are 0.53 and 0.51 for the intact and damaged implant 10, respectively. The decrease in the generated voltage is anticipated due to the presence of inactive unit cells that do not contribute to signal generation. Wireless self-sensing using the metamaterial systems has a broader range of applications for monitoring the health of structural systems experiencing multilevel damage states.

[0083] To further validate the functionality of a TKR implant 10, a series of experiments were conducted using a human cadaver knee specimen. An ex vivo knee from a 75-year-old male donor (weight: 81.65 kg, height: 177.8 cm) was obtained with prior institutional ethics committee approval as shown in FIG. 3(j). Using CT scans of the specimen, the geometry of the components of TKR 42 were determined. These patient-specific components were then 3D printed. A series of experimental and FE simulations were carried out to assess the mechanical properties of the TKR implant 10. These measurements yielded the followingvalues for the experimental compressive elastic modulus, torsional modulus and shear modulus of the TKR implant 10: 0.72 MPa, 1.28 MPa and 1.21 MPa, respectively. The implant's elastic modulus matched the target range for the human medial meniscus (20-80 kPa) [35,36], Additionally, the implant 10 has a Poisson’s ratio of 0.1. Materials with a Poisson's ratio between roughly -0.1 and +0.1 are considered near-zero Poisson's ratio materials [42,43], This near-zero Poisson's ratio is a unique feature of mechanical metamaterials, distinguishing them from conventional materials. The results of the experimental and FE simulation demonstrate good agreement between the experiments and numerical simulations.

[0084] Standard surgical implantation techniques were used by an orthopedic surgeon to insert appropriately sized TKR components of implant 10 into the specimen as shown in FIG. 3(j). The specimen was then mounted in a custom-designed fixture to simulate knee flexion at 1 Hz with a maximum amplitude of 100 N (FIG. 3(k)). The electrode 50 configurations are shown in FIG. 3(j). To investigate the effect of electrode size on the received signals, four copper electrodes with varying surface areas (1 cm2, 4 cm2, 9 cm2, and 16 cm2) were fabricated. These electrodes 50 were then positioned at a fixed distance of 5 cm from the implant 10 on the posterior aspect of the knee. This setup ensured all other parameters remained constant during the experiment. FIG. 3(1) shows the amplitude of the transmitted signals, the received signals, and the signal delivery ratio for the 1 cm2, 4 cm2, 9 cm2, and 16 cm2electrodes. While the transmitted signal remains consistent around 0.35 V ± 10 mV for all electrodes 50 under the same loading condition, the received signal strength significantly increases (205%) as the electrode surface area expands from 1 cm2to 16 cm2. The received signal strength shows a minimal increase between electrodes of 1 cm2and 4 cm2. However, it rises by 42% when comparing the 1 cm2and 9 cm2electrodes. In order to investigate the impact of electrode distance on the signal delivery ratio, the 9 cm2electrode (3 cm x 3 cm) was chosen as the reference electrode. This electrode 50 was positioned at varying distances from the implant (0 cm (not attached to the skin), 2 cm, 5 cm, 10 cm, 20 cm). The results shown in FIG. 3(1) imply that for a constant loading amplitude, the signal delivery ratio exhibits a significant decrease as the electrode is moved away from the implant 10 (adjacent to the skin) to a distance of 5 cm. Thereafter, the ratio stabilizes. Importantly, the received signal remains strong enough for detection at all distances tested. The SNR of the signals wirelessly received atdistances of 0 cm, 2 cm, 5 cm, 10 cm, and 20 cm from the implant was 25.31 dB, 24.28 dB, 22.86 dB, 16.70 dB, and 17.17 dB, respectively.

[0085] An important takeaway from the cadaveric study is the dependence of the received signal on both electrode size, distance and positioning. For consistent wireless force sensing measurements with this technology at the current stage, controlled conditions are necessary. This means using the same type of electrode and maintaining consistent electrode placement relative to the implant for each patient to ensure reliable comparisons with the "reference baseline" voltage signal. Consistent electrode placement refers to maintaining a fixed distance and location (anterior, posterior, or around the knee). The reference baseline voltage signal is the wirelessly received signal measured post-surgery. Subsequent readings for each prescribed motion pattern will be compared to this baseline. This essentially establishes a "relative" monitoring system where each subsequent signal is evaluated against the initial reference baseline. Furthermore, to achieve consistent measurements and facilitate meaningful comparisons, therapists can design a range of flexion and extension knee motions tailored to the patient's specific condition and treatment plan. This leverages the ability of implant 10, as shown in FIG. 2(a)-FIG. 2(i), to generate unique voltage outputs for different loading conditions. By comparing these standardized motions' voltage outputs to the reference baseline, deviations can reveal potential changes in knee biomechanics.

[0086] Over the past six decades, substantial research has been conducted to advance the development of smart orthopedic implants equipped with force-sensing capabilities. FIG. 4(a) shows the evolution of smart implants equipped with force sensing, highlighting key studies conducted in this field. Various types of smart implants investigated are wired, battery-powered wireless, passively-powered wireless, and self-powered wireless equipped with microcontrollers and RFID and ultrasound connectivity. Smart implants incorporating passively-powered wireless capabilities have demonstrated the most enduring success. The majority of studies concentrating on this area were conducted between 2000 and 2015, as indicated by the black circles in FIG. 4(a). More recent studies have explored the concept of harvesting energy from human motion to create self-powered implants (FIG. 4(a), red circles). Nevertheless, these implants still necessitate implantable microcontrollers and additional RFID / ultrasound connectivity for wireless transmission of therecorded data. As existing wireless smart implants utilize different force sensing mechanisms compared to the preferred implants 10 of the present disclosure, direct comparisons require a common metric. Power consumption, as illustrated in FIG. 4(a), serves as a suitable quantitative measure for this purpose. Here, the estimated operational power of these existing implants, including transmission needs, ranges from 1 pW to 10 mW. The TKR implants 10 demonstrate the first generation of implants with direct wireless communication capabilities based on the strain-induced Maxwell's displacement current. In this context, "direct" indicates that the same signal generated by the implant is directly used for wireless communication without relying on additional electronics, external power sources, or data loggers. Although the implant 10 may not necessarily be optimized for maximum power output, it enables mid-range wireless communication in real-time, even with low power output (< 1 pW). The wireless metamaterial implants 10 do not resemble traditional electronic systems; they are biomaterial systems using their fabric for sensing, energy harvesting and wireless transmission. Furthermore, among the existing smart implants, the wireless metamaterial implants 10 are the only class of mechanically tunable implants due to their metamaterial nature. Mechanical tunability in orthopedic implants is crucial for customizing the implant 10 to match individual patient biomechanics, ensuring optimal fit and function. This adaptability also reduces the risk of complications and stress shielding and promotes long-term stability during the healing process.

[0087] The wireless force sensing technology of the present disclosure extends beyond orthopedic and spinal implants due to the scalability of the wireless metamaterial system. Eliminating the need for bulky wireless interrogation circuits can be a breakthrough in developing wireless robotic systems and medical implants. For instance, a wireless metamaterial cardiac stent 80 featuring wireless force sensing capabilities can address a significant challenge associated with integrating electronics into the confined space within an artery. This innovation enables continuous monitoring of local hemodynamic changes, particularly during instances of restenosis (FIG. 4(b)) An all-in-one wireless metamaterial cardiac stent 80 shown in FIG. 4(b) could be designed according to the present disclosure that can measure the radial compressive forces developed inside the stent structure during each arterial pulsation, generating electrical signals in response to periodic deformations caused by the dilations of the artery. Using the principles explained in the presentdisclosure, the generated signal can be detected using any commercially available electrocardiogram (ECG) electrodes or a smartphone-connectable wearable ECG monitors (e.g. Wellue® ECG Recorder) (FIG. 4(c)), The signals will be hypothetically proportional to the radial compressive forces developed inside stent 80 structure during each arterial pulsation and will change upon the onset of in-stent restenosis (FIG. 4(d)). Thus, clinicians / patients could be alerted in real-time to the incidence of tissue or plaque buildup on the inner walls of stent 80, and thereby gain critical information that guides further examination and treatments at an earlier stage.

[0088] The present disclosure presents electronic-free metamaterial implants 10 for wireless transmission of the sensed data in real-time where the electrical signals harvested by the implants 10 from mechanical stimuli are directly used for wireless transmission of the sensed data, eliminating the need for additional electronics, external power sources, or data loggers. TKR implant 10 was created under the wireless metamaterial paradigm to evaluate the feasibility the instant wireless force sensing approach. The implant 10 was tested under various loading conditions at 1, 3 and 5 Hz to establish its mechanical and electrical properties. The wireless transmission capability of the implant 10 was also tested in air, SBF and porcine tissue. It was found that the wireless metamaterial implant 10 with low power output on the order of 0.1 pW directly enables mid-range wireless communication without an external power source. An acceptable agreement is observed between the experimental and theoretical results. The results imply that the attenuation of the polarization electric field generated by the implant 10 is lower in lossy than in lossless media. This can be regarded as an advantage of using implant 10 in vivo. It is also shown that the wireless metamaterial implants 10 can offer wireless self-sensing capability in case of failure of implant 10.Experimental and numerical simulations were carried out to characterize the mechanical properties of the TKR implant 10. Further validation of the implant 10 was performed using a human cadaver knee specimen. Cadaver studies confirmed the dependence of the wireless signal strength on electrode size and placement. For reliable clinical use, consistent electrode selection and placement relative to the implant 10 were important. This ensures accurate comparisons between the initial baseline signal and subsequentmeasurements during various motions. The implant 10 functions by monitoring signal changes relative to this established baseline.

[0089] Electrical output of implant 10 could potentially be optimized for increasing the wireless transmission range. For instance, using biocompatible materials with high electrical conductivity, such as titanium (electrical conductivity ~ 2.5 x 106S / m), to fabricate the conductive lattice 30, 32 of the implant 10 could substantially increase the generated power. To precisely capture knee joint forces from different directions, the TKR implant 10 can be segmented. Each segment could operate at a unique frequency or generate a distinct power output, allowing for the identification of the force source within the knee.

[0090] In the foregoing Detailed Description, various features are grouped together in a single embodiment to streamline the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the disclosure require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.

Claims

What is claimed is:

1. A self-powering medical implant and sensor (“medical implant / sensor”) for electronic-free wireless transmission of data sensed by the medical implant / sensor, comprising: an active mechanical metamaterial, comprising: first and second electrically conductive components disposed relative to each other to act as opposite electrodes to induce contact electrification; wherein the first and second electrically conductive components, along with a dielectric component serving as a skeleton of the active mechanical metamaterial, form a lattice of snapping curved semicircular-shaped segments, wherein each of the snapping curved semicircular-shaped segments has an elastic snap-through instability mechanism; and wherein the lattice of snapping curved semicircular-shaped segments comprises periodic repeatable parallel rows of the snapping curved semicircular-shaped segments.

2. The self-powering medical implant / sensor of claim 1, wherein the first electrically conductive component comprises a first electrically conductive lattice and the second electrically conductive component comprises a second electrically conductive lattice.

3. The self-powering medical implant / sensor of claim 1, wherein the dielectric component comprises first and second outer dielectric layers and an inner dielectric layer disposed between the first and second outer dielectric layers.

4. The self-powering medical implant / sensor of claim 1, wherein the medical implant / sensor comprises a spacer for a total knee replacement prosthetic, wherein the spacer is disposed between a femoral component and a tibial component of the total knee replacement prosthetic.

5. The self-powering medical implant / sensor of claim 1, further comprising an external receiving electrode for receiving wireless electric signals generated by the medical implant / sensor.

6. The self-powering medical implant / sensor of claim 1, wherein the first and second electrically conductive components comprise polylactic acid (PLA) containing carbon black and the dielectric component comprises thermoplastic polyurethane (TPU).

7. The self-powering medical implant / sensor of claim 2, wherein the first and second electrically conductive lattices comprise poly lactic acid (PLA) containing carbon black and each of the first and second outer dielectric layers and the inner dielectric layer comprises thermoplastic polyurethane (TPU).

8. The self-powering medical implant / sensor of claim 1, wherein the first and second electrically conductive components and the dielectric component each comprises one or more of a biocompatible material and a bioresorbable material.

9. The self-powering medical implant / sensor of claim 1, wherein the first and second electrically conductive components are embedded in the dielectric component.

10. The self-powering medical implant / sensor of claim 1, wherein a structure of the self-powering medical implant / sensor forms a composite matrix of the electrically conductive components and the dielectric component in a periodic manner.

11. The self-powering medical implant / sensor of claim 1, wherein each of the snapping curved semicircular-shaped segments comprises a portion of each of the first electrically conductive component, the second electrically conductive component and the dielectric component.

12. A self-powering medical implant and sensor (“medical implant / sensor”) for electronic-free wireless transmission of data sensed by the medical implant / sensor, comprising: a triboelectric nanogenerator (TENG); and an external receiving electrode for receiving wireless electric signals generated by the TENG.

13. The self-powering medical implant / sensor of claim 12, wherein the TENG comprises a spacer for a total knee replacement (TKR) prosthetic (“TKR Prosthetic”), wherein the spacer is disposed between a femoral component and a tibial component of the TKR prosthetic.

14. A total knee replacement (TKR) prosthetic (“TKR Prosthetic”) for electronic-free wireless transmission of data sensed by the TKR Prosthetic, comprising: a self-powering spacer comprising an active mechanical metamaterial, comprising: first and second electrically conductive components disposed relative to each other to act as opposite electrodes to induce contact electrification: wherein the first and second electrically conductive components, along with a dielectric component serving as a skeleton of the active mechanical metamaterial, form a lattice of snapping curved semicircular-shaped segments, wherein each of the snapping curved semicircular-shaped segments has an elastic snap-through instability mechanism; andwherein the lattice of snapping curved semicircular-shaped segments comprises periodic repeatable parallel rows of the snapping curved semicircular-shaped segments; wherein the self-powering spacer is disposed between a femoral component and a tibial component of the TKR prosthetic.

15. The TKR Prosthetic of claim 14, wherein the first electrically conductive component comprises a first electrically conductive lattice and the second electrically conductive component comprises a second electrically conductive lattice.

16. The TKR Prosthetic of claim 14, wherein the dielectric component comprises first and second outer dielectric layers and an inner dielectric layer disposed between the first and second outer dielectric layers.

17. Tire TKR Prosthetic of claim 14, further comprising an external receiving electrode for receiving wireless electric signals generated by the self-powering spacer.

18. The TKR Prosthetic of claim 14, wherein the first and second electrically conductive components are embedded in the dielectric component.

19. The TKR Prosthetic of claim 14, wherein a structure of the self-powering spacer forms a composite matrix of the electrically conductive components and the dielectric component in a periodic manner.

20. The TKR Prosthetic of claim 14, wherein each of the snapping curved semicircular-shaped segments comprises a portion of each of the first electrically conductive component, the second electrically conductive component and the dielectric component.

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