Advances in Bioresorbable Triboelectric Nanogenerators

Abstract

With the growing demand for next-generation health care, the integration of electronic components into implantable medical devices (IMDs) has become a vital factor in achieving sophisticated healthcare functionalities such as electrophysiological monitoring and electroceuticals worldwide. However, these devices confront technological challenges concerning a noninvasive power supply and biosafe device removal. Addressing these challenges is crucial to ensure continuous operation and patient comfort and minimize the physical and economic burden on the patient and the healthcare system. This Review highlights the promising capabilities of bioresorbable triboelectric nanogenerators (B-TENGs) as temporary self-clearing power sources and self-powered IMDs. First, we present an overview of and progress in bioresorbable triboelectric energy harvesting devices, focusing on their working principles, materials development, and biodegradation mechanisms. Next, we examine the current state of on-demand transient implants and their biomedical applications. Finally, we address the current challenges and future perspectives of B-TENGs, aimed at expanding their technological scope and developing innovative solutions. This Review discusses advancements in materials science, chemistry, and microfabrication that can advance the scope of energy solutions available for IMDs. These innovations can potentially change the current health paradigm, contribute to enhanced longevity, and reshape the healthcare landscape soon.

Figure 1

Overview of B-TENGs as an advanced energy solution for transient IMDs. (A) Schematic representation of B-TENGs in terms of their energy conversion, typical structure, and biomedical applications. (B) Profiles of the mass and performance of B-TENGs through passive and active operations for comparison of their working principles. (C) Conventional IMDs categorized according to power consumption and implant duration, illustrating the current state of powering capabilities of B-TENGs.

Figure 2

Power generation mechanism and target energy of B-TENGs. (A) Schematic of the triboelectric effect and overlapped electron cloud model. Reproduced with permission from ref (148). Copyright 2020 Wiley-VCH. (B) Working principle diagram of B-TENGs. (C) Ambient energy sources with a wide frequency range used for triboelectric energy harvesting. Reproduced with permission from refs (138), (165), (164), (154), and (139), respectively. Copyright 2019 American Association for the Advancement of Science. Copyright 2018 American Association for the Advancement of Science. Copyright 2018 Nature Publishing Group under the terms of the Creative Commons Attribution 4.0. (https://creativecommons.org/licenses/by/4.0/). Copyright 2021 American Association for the Advancement of Science. Copyright 2021 Nature Publishing Group under the terms of the Creative Commons Attribution 4.0 (http://creativecommons.org/licenses/by/4.0/).

Figure 3

Service lifetime and biodegradation processes of B-TENGs. (A) Schematic illustration of the biodegradation mechanism; each step illustrates the mechanical/chemical dissolution processes along with the functioning and disappearance times after device transplantation. (B) Categorized diagram of bioresorbable materials along with their degradation rates. (C) Plot of the diffusion rate for degradation factors and the degradation rate for bioresorbable B-TENG materials. Encapsulation layers and inner active layers are illustrated to provide the required properties in the suggested methodologies.

Figure 4

Representative bioresorbable polymers and their chemical structures. Bioresorbable polymers can be categorized into NBPs and SBPs.

Figure 5

Bioresorbable polymers for B-TENGs. (A) Schematic representation of B-TENGs composed of various NBPs, including field emission scanning electron microscope (FE-SEM) images and the atomic force microscopy (AFM) topology to demonstrate the nanostructured surface morphology of the NBP triboelectric layer (lower and upper scale bars are 5 and 1 μm, respectively). (B) In vitro biodegradation (scale bars are 5 mm) and (C) working principle and output power of B-TENGs using five different NBPs. (A–C) Reproduced with permission from ref (208). Copyright 2018 Wiley-VCH. (D) Structure of the B-TENG using calcium alginate films. (E) Weight loss of a calcium alginate film via in vitro biodegradation in water at room temperature. (D and E) Reproduced with permission from ref (195). Copyright 2018 Royal Society of Chemistry. (F) 3D printing process of CNTs@SF core–sheath fiber-based smart patterns to fabricate electronic textiles capable of triboelectric energy harvesting. Reproduced with permission from ref (233). Copyright 2019 Elsevier. (G) Illustration of a contact-separation mode B-TENG using nanostructured SBPs, including FE-SEM images and the AFM topology of the SBP triboelectric layer. (H) Output currents of B-TENGs with different SBP triboelectric pairs. (I) Triboelectric series of SBPs using polyimide (Kapton) as a reference. (J) In vitro biodegradation of a B-TENG encapsulated by PLGA in PBS (pH = 7.4, 37 °C, scale bars are 10 mm). (H–J) Reproduced with permission from ref (124). Copyright 2016 American Association for the Advancement of Science under the terms of the Creative Commons Attribution 4.0 (https://creativecommons.org/licenses/by/4.0/). (K) Structure and dimensions of a breathable B-TENG based on electrospun PLGA, PLA, and Ag NWs. (L) FE-SEM images of the surface morphology of PLGA and PLA nanofibers (scale bars 10 and 2 μm, respectively). (M) Sequential photographs of the in vitro biodegradation of PVA, Ag NWs/PVA, and PLGA/Ag NWs/PVA nanofiber films in PBS at 37 °C. (K–M) Reproduced with permission from ref (52). Copyright 2020 American Association for the Advancement of Science under the terms of the Creative Commons Attribution 4.0 (https://creativecommons.org/licenses/by/4.0/).

Figure 6

Triboelectric charge densities and degradation rates of NBPs and SBPs.

Figure 7

Macroscopic degradation mechanisms. (A) Bulk degradation process with a diffusion coefficient higher than the reaction rate. (B) FE-SEM images of bioresorbable polyesters before and after bulk degradation: PLGA, 33 d in PBS (pH = 7.4) at 37 °C. Reproduced with permission from ref (290). Copyright 2016 Springer Nature. (C) FE-SEM images of bioresorbable polyesters before and after bulk degradation: PCL, 20 h in PBS (pH = 7.2) containing 18 U·mL^–1 lipase at 45 °C. Reproduced with permission from ref (133). Copyright 2020 Springer Nature. (D) Surface erosion process with a diffusion coefficient lower than the reaction rate. (E) FE-SEM images of bioresorbable Fe–Mn alloys before and after surface erosion (three months in Hank’s solution at 37 °C). Reproduced with permission from ref (291). Copyright 2010 Elsevier. Profiles of mass, molecular weight, and mechanical strength of polymers during (F) bulk degradation and (G) surface erosion. Reproduced with permission from ref (292). Copyright 2008 Elsevier. (H) Theoretical plot of the erosion number for the hydrolysis of polymers, ε, depending on water diffusivity inside the polymer, D_eff, the dimensions of the polymer matrix, L, and the polymer bond reactivity, λ. (I) Critical thickness, L_critical, the threshold that a polymer specimen must exceed to undergo surface erosion. (H and I) Reproduced with permission from ref (174). Copyright 2002 Elsevier. (J) Mass profiles of surface-eroding polymers with different volume-to-surface area ratios during degradation. Reproduced with permission from ref (178). Copyright 2020 MDPI under the terms of the Creative Commons Attribution 4.0 (https://creativecommons.org/licenses/by/4.0/).

Figure 8

Chemical biodegradation mechanisms, including hydrolysis, oxidation, and enzymatic processes.

Figure 9

Material-based factors that affect the rate of hydrolysis of polyesters. (A) Diagram of the material properties that influence polyester hydrolysis. (B) Illustration of restricted water diffusion due to high crystallinity. (C) Hydrophobicity decreases water diffusion and the degradation rate. (D) Polymer architectures to modulate biodegradation performance via crystallinity and hydrophobicity. (A–D) Reproduced with permission from ref. Copyright 2018 American Chemical Society. Sequential photographs showing (E) bulk biodegradation and (F) surface erosion of POC due to low and high cross-linking ratios, respectively (in PBS (pH = 7.4) at 37 °C). (E and F) Reproduced with permission from ref (230). Copyright 2022 American Chemical Society. FE-SEM images of the surface and core of (G) PHA and (H) a PHA–PLLA polymer blend to demonstrate the influence of hydrophobicity on biodegradation behavior. (G and H) Reproduced with permission from ref (309). Copyright 2006 Elsevier.

Figure 10

Environment-based factors and surface properties for the biodegradation of polymers. (A) pH circumstances in gastrointestinal organs of the human body. Reproduced with permission from ref (178). Copyright 2020 MDPI under the terms of the Creative Commons Attribution 4.0 (https://creativecommons.org/licenses/by/4.0/). (B) Acid- and (C) base-catalyzed hydrolysis of polyesters. (D) Illustration of the influence of surface morphology on biodegradation performance. (E) FE-SEM images of a PLA solid film and a PLA porous scaffold before and after degradation in water at 60 °C for 14 d. (F) Mass profile of a PLA film vs hydrolysis time depending on the pore size. (E and F) Reproduced with permission from ref (179). Copyright 2011 American Chemical Society. (G) Schematic of how surface coating suppresses water diffusion and the adhesion of proteins and microsomes. (H) Schematic representation of nonmodified and zwitterionic polymer-coated beads, demonstrating antifouling methods against biotinylated serum proteins. Reproduced with permission from ref (180). Copyright 2018 American Chemical Society. (I) Super hydrophobicity was achieved by incorporating GOgODA nanosheets (NSs) into PLA aimed at a decrease in weight loss rate and moisture permeability. Reproduced with permission from ref (313). Copyright 2017 Royal Society of Chemistry.

Figure 11

Mechanisms of metal biodegradation. (A) Environment-specific biodegradation processes of metals based on their reaction with body fluid. Reproduced with permission from ref (317). Copyright 2019 Elsevier. (B) Specific biodegradation processes of metals based on their reaction with body fluids. Reproduced with permission from ref (283) Copyright 2018 Elsevier under the terms of the Creative Commons Attribution 4.0 (https://creativecommons.org/licenses/by/4.0/). (C) Macroscopic observation of Mo degradation in a Kokubo SBF solution at 37 °C. Reproduced with permission from ref (285). Copyright 2020 Elsevier. (D) Optical micrographs of degraded pure Fe and Fe-based alloys after implantation into a growing rat skeleton. Reproduced with permission from ref (318). Copyright 2014 Elsevier. (E) Cell viability test according to the biodegradation of Mg and alloys to examine cytotoxicity and biocompatibility. Reproduced with permission from ref (282). Copyright 2016 PLOS under the terms of the Creative Commons Attribution 4.0 (https://creativecommons.org/licenses/by/4.0/).

Figure 12

Ultrasound-triggered on-demand transience in B-TENGs and polymers. (A) Mechanism of triggered biodegradation by intensified acoustic pressure in the micropores of a PHBV encapsulation layer. (B) Photographs of degrading PHBV and PHBV/PEG films over time. (A and B) Reproduced with permission from ref (58). Copyright 2022 American Association for the Advancement of Science. (C) Structural design of an on-demand B-TENG for bacterial inactivation and (D) improved biodegradation rate of its constituent membranes by applying high-intensity ultrasounds (HIU). (C and D) Reproduced with permission from ref (117). Copyright 2023 Wiley-VCH under the terms of the Creative Commons Attribution 4.0 (https://creativecommons.org/licenses/by/4.0/). (E) Self-clearance mechanism of an alginate hydrogel-TiO₂ NPs composite. Reproduced with permission from ref (329). Copyright 2022 American Chemical Society. (F) Degradation mechanisms of mechanically gated degradable polymers and decrease in molecular weight when subjected to sonication. Reproduced with permission from ref (339). Copyright 2020 American Chemical Society.

Figure 13

Thermally triggered transience. (A) Diagram of the strategies employed to implement thermally responsive degradation and (B) review of triggering temperature and time of thermoresponsive polymers compared to the threshold curve for human skin thermal injury. (C) Photothermally tunable degradation of a PLA-based B-TENG using laser treatment. Reproduced with permission from ref (137). Copyright 2016 PLOS under the terms of the Creative Commons Attribution License. (D) Photothermally tunable degradation of a chitosan-based B-TENG using laser treatment. Reproduced with permission from ref (122). Copyright 2018 Wiley-VCH.

Figure 14

Thermoresponsive transient electronics. (A) Thermally degradable inductors based on gelatin–chitosan hydrogel films. Reproduced with permission from ref (203). Copyright 2022 American Chemical Society. (B) Temperature-dependent transience originating from the LCST behavior of a Ag NW/methylcellulose composite. Reproduced with permission from ref (342). Copyright 2017 American Chemical Society. (C) Schematic diagram of the phase transition via LCST behavior. (D) Thermally triggered transience using a wax-encapsulated acid. Reproduced with permission from ref (61) Copyright 2015 Wiley-VCH. (E) Wireless transient microfluidic system with a heat-expandable polymer for controlled release. Reproduced with permission from ref (343). Copyright 2015 Wiley-VCH.

Figure 15

Light-triggered transient electronics. (A) Photographs of photoresponsive transient electronics based on MBTT/cPPA films and schematic diagrams of working mechanisms. Reproduced with permission from ref (56). Copyright 2014 Wiley-VCH. (B) Photographs of a hydrogel that transitions from gel to sol by UV light, optical microscopy images of a Mg electrode that consequently undergoes hydrolysis, and schematics of the working mechanisms. Reproduced with permission from ref (70). Copyright 2018 American Chemical Society.

Figure 16

Representative strategies to develop large power output bioresorbable triboelectric materials.

Figure 17

Development of high-charge polymers to achieve large power output B-TENGs. (A) Schematics of chemical structures and 3D networks of a chitosan–citric acid (CC) polymeric composite. (B) Photograph of a transparent and flexible CC-TENG. (C) Comparison of the output current density of CC-TENGs based on CC-1 and CC-4 composites. (D) Changes in the output current density of CC-TENGs at different chitosan/citric acid ratios. (A–D) Reproduced with permission from ref (360) Copyright 2019 Wiley-VCH under the terms of the Creative Commons Attribution 4.0 (https://creativecommons.org/licenses/by/4.0/). (E) Optical microscopy and SEM images of chitosan-based composite membranes with different nature-derived additives, demonstrating their transparency and changes in surface morphology. (F) Electrical output current of chitosan-based TENGs along with the type of additives incorporated. (E and F) Reproduced with permission from ref (122). Copyright 2018 Wiley-VCH. (G) 3D network of nature-driven ϰ-carrageenan–agar composites. (H) Kelvin probe force microscopy (KPFM) measurement showing an increase in surface potentials of composite films. (G and H) Reproduced with permission from ref (118). Copyright 2022 Elsevier. (I) Schematics and SEM images of cellulose-loaded PVA film (CPF) containing microcrystalline cellulose (MCC) particles and a PVA matrix polymer. (J) Output currents of B-TENGs based on bare PVA, CPF, and microarchitectured CPF (MACPF) that demonstrate highly improved performance. (I and J) Reproduced with permission from ref (371). Copyright 2019 Elsevier. (K) Enhanced output voltages of partially bioresorbable TENGs based on chemically functionalized cellulose nanofibrils (CNF) with nitro and methyl functional groups. Reproduced with permission from ref (202). Copyright 2017 Wiley-VCH.

Figure 18

NP-embedded composites for large power output. (A) Photograph and (B) SEM images of a cellulose aerogel film containing BTO NPs. (C) Dielectric constants of C/BT-1,3,5 and pure cellulose and (D) improved electrical output voltage of the cellulose aerogel/BTO-based TENG. (A–D) Reproduced with permission from ref (199). Copyright 2020 Wiley-VCH. (E) Schematic illustrations of PCL/GO-based B-TENGs. (F) SEM image of a PCL fibrous membrane with 4% GO. (G) Improved output current of PCL/GO−based TENGs owing to the presence of GO NPs. (E–G) Reproduced with permission from ref (145). Copyright 2019 Elsevier. (H) Schematic illustration of a cellulose acetate/nano-Al₂O₃ (CA/Al₂O₃) nanocomposite-based TENG. (I) Short-circuit charge transfer and output voltage of a CA/Al₂O₃ nanocomposite-based TENG at different Al₂O₃ nanofiller contents. (H and I) Reproduced with permission from ref (374). Copyright 2020 American Chemical Society. (J) Schematic illustration of a TENG based on a cellulose filter paper (CFP)-Ti_0.8O₂ NSs composite. (K) Increase in the output current density of a CFP composite-based TENG through the addition of Ti_0.8O₂ NSs. (J and K) Reproduced with permission from ref (200). Copyright 2020 Wiley-VCH.

Figure 19

Ion-doped polymers for large power output. (A) Schematic illustration of the triboelectric charge transfer between bare PVA and PVA-based solid polymer electrolytes (SPEs). (B) Surface potentials of ion-doped PVA-based SPEs ddepending on salts and concentration, measured by KPFM. (C) Energy band diagrams presenting electron transfer between bare PVA and PVA:CaCl₂ SPE during a triboelectric event. (A–C) Reproduced with permission from ref (225). Copyright 2017 Wiley-VCH. (D) Output voltages and (E) charge densities of PVA−MClx SPEs-based TENGs. (F) KPFM measurement for PVA−LiCl SPEs to identify their CPDs at different LiCl concentrations. (F) KPFM images of PVA-LiCl SPEs with different LiCl concentrations. (D–F) Reproduced with permission from ref (226). Copyright 2019 Elsevier. (G) Photographs of microstructured ion-doped starch films. (H) Chemical network of a starch:CaCl₂ composite polymer. (I) Output current densities of starch:CaCl₂-based TENGs at different concentrations of CaCl₂. (G–I) Reproduced with permission from ref (380). Copyright 2019 Elsevier.

Figure 20

Bioresorbable polymers with nanostructured surfaces for large power output B-TENGs. (A) Schematic illustration of an arch-shaped silk B-TENG with an electrospun silk fibroin (SF) membrane. (B) FE-SEM image of an electrospun silk membrane. (C) Peak voltages of partially bioresorbable TENGs based on electrospun silk and cast silk membranes. (A–C) Reproduced with permission from ref (209). Copyright 2016 Wiley-VCH. (D) Top-view SEM images of a rough gelatin membrane cast on sandpaper and an electrospun PLA membrane. (E) Schematics of B-TENGs (red, smooth/rough gelatin film; blue, smooth/electrospun PLA membrane) and (F) their short-circuit output current density resulting from contact and separation between different membrane pairs. (D–F) Reproduced with permission from ref (51). Copyright 2018 Elsevier. (G) Photograph, (H) SEM image, and (I) AFM topology of an ICP plasma-etched PLA/PLGA film. (J) Plot of the 100% increase in the output current of a B-TENG based on a PLA/PLGA film upon plasma etching-induced nanostructuring. (G–J) Reproduced with permission from ref (388). Copyright 2020 Wiley-VCH.

Figure 21

Surface functionalization for large power output bioresorbable tribo-materials. (A) Schematic illustration of the surface functionalization process to prepare fluoroalkylated siloxane-grafted fabric (F-fabric) and cyanoalkylated siloxane-grafted fabric (CN-fabric). (B) XPS spectra of F-cotton. (C) Output currents of natural textile TENGs (N-TENGs) based on surface-functionalized cotton and silk fabrics. (A–C) Reproduced with permission from ref (361). Copyright 2021 Royal Society of Chemistry. (D) Schematic illustrations of the grafting process of fluorinated group to functionalize fish gelatin (FG) films. (E) Structure of a fully sustainable fish gelatin (FSFG)-TENG. (F) XPS spectra and (G) contact angles of fluorinated FG (F-FG), dopamine-doped FG (D-FG), and FG. (H) V_OC and (I) I_SC of the TENGs based on the F-FG film paired with cotton, Al, cellulose, Cu, and D-FG. (D–I) Reproduced with permission from ref (394). Copyright 2021 Elsevier.

Figure 22

Overview of self-powered bioresorbable IMDs based on B-TENGs.

Figure 23

Physiological sensing using B-TENGs. (A) Expanded structure of an implantable bioresorbable triboelectric sensor (BTS) for cardiovascular postoperative care. (B) Output variation of a BTS implanted in a small animal according to the respiratory event identification. (C) Identification of vascular occlusion events following BTS implantation in a large animal. (A–C) Reproduced with permission from ref (30). Copyright 2021 Wiley-VCH. (D) Working mechanism of TENG-integrated vascular grafts (VG-TENG). (E) Experimental setup images and (F) electrical properties of VG-TENGs under different blood flow conditions. (D–F) Reproduced with permission from ref (127). Copyright 2023 Elsevier. (G) Structure and material design of transient TENG (T²ENGs). (H) Photographs of an implanted T²ENG under the subdermal dorsal region in an in vivo experiment. (I) Electrical output of T²ENG to demonstrate the epilepsy monitoring function. (G–I) Reproduced with permission from ref (128). Copyright 2018 Wiley-VCH.

Figure 24

Electroceuticals using B-TENGs. (A) Schematic illustration of an I-TENG under the skin. (B) Photographs of I-TENGs placed inside a needle. (C) Scratch assay to demonstrate enhanced migration by equivalent electrical stimulation. (A–C) Reproduced with permission from ref (123). Copyright 2023 Wiley-VCH. (D) Overall procedure for rapid wound closure and hemostasis using BA-TENG. (E) Scratch wound healing experiments using BA-TENG. (D and E) Reproduced with permission from ref (125). Copyright 2023 Wiley-VCH. (F) Schematic illustration of electrical stimulation using BN-TENG and of the progress observed after BN-TENG implantation. (G) Pause time between two beating cycles of the cardiomyocyte cluster, according to the stimulation effect of the BN-TENG. (H) Beating rates of different cardiomyocyte clusters according to the stimulation effect of the BN-TENG. (F–H) Reproduced with permission from ref (208). Copyright 2018 Wiley-VCH. (I) Schematic illustration of electrical stimulation using BD-TENG. (J) Neuron cells oriented by the electric field (the yellow arrow represents the direction of the electric field, scale bar is 50 μm). (K) Neuron cell alignment analysis for different cell angles. (I–K) Reproduced with permission from ref (124). Copyright 2016 American Association for the Advancement of Science under the terms of the Creative Commons Attribution 4.0 (https://creativecommons.org/licenses/by/4.0/).

Figure 25

Rehabilitation and antibacterial activity of B-TENGs. (A) Schematic illustration of a FED structure. (B) Fracture healing process. (C) Improvement of mineral density and bending performance through FED electrical stimulation. (A–C) Reproduced with permission from ref (54). Copyright 2021 National Academy of Science. (D) Schematic illustration of a TENG-based tissue battery. (E) Cartilage repair system for electrical stimulation using a TENG-based tissue battery. (F) Flow cytometry results that demonstrate accelerated cartilage repair using a TENG-based tissue battery structure. (D–F) Reproduced with permission from ref (130). Copyright 2023 Elsevier. (G) Schematic illustration of the antibacterial mechanism of an RSSP Patch. (H) In vivo antibacterial inhibition of S. aureus by the RSSP Patch. (collected after 7 d, n = 20, ***p ≤ 0.001). (G and H) Reproduced with permission from ref (131). Copyright 2018 Wiley-VCH. (I) Schematic illustration of IBV-TENG under the surgical site to prevent SSI. (J) Images of viable bacteria (E. coli and S. aureus) and the ex vivo antibacterial effect with/without electrical stimulation using IBV-TENG. (I and J) Reproduced with permission from ref (117). Copyright 2023 Wiley-VCH under the terms of the Creative Commons Attribution 4.0 (https://creativecommons.org/licenses/by/4.0/).

Figure 26

Challenges and required properties of future TENGs for transient electronics and IMDs.