Thermally Degradable Water Diffusion Barrier Assembled by Gelatin and Beeswax toward Edible Electronics.

Making ingestible devices edible facilitates diagnosis and therapy inside the body without the risk of retention; however, food materials are generally soft, absorb water molecules, and are not suitable for electronic devices. Here, we fabricated an edible water diffusion barrier film made by gelatin-beeswax composites for the encapsulation of transient electronics. Hydrophobic beeswax and hydrophilic gelatin are inherently difficult to mix; therefore, we created an emulsion simply by raising the temperature high enough to melt the materials and vigorous stirring them. As they cool, the beeswax with a relatively high solidification temperature aggregates and forms microspheres, which increases the gelatin gel's viscoelasticity and immobilizes the emulsion structure in the film. The thermoresponsive gelatin imparts degradability to the barrier and its stickiness also enables transfer of metal patterned electronics. Furthermore, we designed an edible resonator on the film and demonstrated its operation in an abdominal phantom environment; the resonator was made to be degradable in a warm aqueous solution by optimizing the composition ratio of the gelatin and beeswax. Our findings provide insight into criteria for making transient electronics on hydrophilic substrates with hydrophobic water diffusion barriers. This proof-of-concept study expands the potential of operating edible electronics in aqueous environments in harmony with the human body and nature.

Calcium Alginate as an Active Device Component for Light-Triggered Degradation of 2D MoS2-Based Transient Electronics.

Transient electronics technology has enabled the programmed disintegration of functional devices, paving the way for environmentally sustainable management of electronic wastes as well as facilitating the exploration of novel device concepts. While a variety of inorganic and/or organic materials have been employed as media to introduce transient characteristics in electronic devices, they have been mainly limited to function as passive device components. Herein, we report that calcium (Ca) alginate, a natural biopolymer, exhibits multifunctionalities of introducing light-triggered transient characteristics as well as constituting active components in electronic devices integrated with two-dimensional (2D) molybdenum disulfide (MoS2) layers. Ca2+ ions-based alginate electrolyte films are prepared through hydrolysis reactions and are subsequently incorporated with riboflavin, a natural photosensitizer, for the light-driven dissolution of 2D MoS2 layers. The alginate films exhibit strain-sensitive triboelectricity, confirming the presence of abundant mobile Ca2+ ions, which enables them to be active components of 2D MoS2 field-effect transistors (FETs) functioning as electrolyte top-gates. The alginate-integrated 2D MoS2 FETs display intriguing transient characteristics of spontaneous degradation upon ultraviolet-to-visible light illumination as well as water exposure. Such transient characteristics are demonstrated even in ambient conditions with natural sunlight, highlighting the versatility of the developed approach. This study emphasizes a relatively unexplored aspect of combining naturally abundant polymers with emerging near atom-thickness semiconductors toward realizing unconventional and transformative device functionalities.

Silicon-based transient electronics: principles, devices and applications.

Recent advances in materials science, device designs and advanced fabrication technologies have enabled the rapid development of transient electronics, which represents a class of devices or systems that their functionalities and constitutions can be partially/completely degraded via chemical reaction or physical disintegration over a stable operation. Therefore, numerous potentials, including zero/reduced waste electronics, bioresorbable electronic implants, hardware security, and others, are expected. In particular, transient electronics with biocompatible and bioresorbable properties could completely eliminate the secondary retrieval surgical procedure after their in-body operation, thus offering significant potentials for biomedical applications. In terms of material strategies for the manufacturing of transient electronics, silicon nanomembranes (SiNMs) are of great interest because of their good physical/chemical properties, modest mechanical flexibility (depending on their dimensions), robust and outstanding device performances, and state-of-the-art manufacturing technologies. As a result, continuous efforts have been made to develop silicon-based transient electronics, mainly focusing on designing manufacturing strategies, fabricating various devices with different functionalities, investigating degradation or failure mechanisms, and exploring their applications. In this review, we will summarize the recent progresses of silicon-based transient electronics, with an emphasis on the manufacturing of SiNMs, devices, as well as their applications. After a brief introduction, strategies and basics for utilizing SiNMs for transient electronics will be discussed. Then, various silicon-based transient electronic devices with different functionalities are described. After that, several examples regarding on the applications, with an emphasis on the biomedical engineering, of silicon-based transient electronics are presented. Finally, summary and perspectives on transient electronics are exhibited.

Biodegradable Mg-Mo2C MXene Air Batteries for Transient Energy Storage.

Primary batteries are the fundamental power sources in small electronic gadgets and bio/ecoresorbable batteries. They are fabricated from benign and biodegradable materials and are of interest in environmental sensing and implants because of their low toxicity toward the environment and human body during decomposition. However, current bio/ecoresorbable batteries suffer from low operating voltages and output powers because of the occurrence of undesired hydrogen evolution reactions (HERs) at cathodes. Herein, Mo2C MXene was used as a cathode to achieve high operating voltage and areal power. Mo2C provides energy barriers for HERs in alkaline solutions, and such barriers suppress HERs and allow the oxygen reduction reaction to dominate at the cathode. The fabricated battery exhibits an operating voltage and areal power of 1.4 V and 0.92 mW cm-2, respectively. Degradation tests show that the full cell completely degrades within 123 days, leaving only Mo fragments from the electrode and biodegradable encapsulation. This study provides insights into bio/ecoresorbable batteries with high power and operating voltage, which can be used for environmental sensing.

Transient N-GQDs/PVA nanocomposite thin film for memristor application.

In recent years quantum dot (QDs) based resistive switching devices(memristors) have gained a lot of attention. Here we report the resistive switching behavior of nitrogen-doped graphene quantum dots/Polyvinyl alcohol (N-GQDs/PVA) degradable nanocomposite thin film with different weight percentages (wt.%) of N-GQDs. The memristor device was fabricated by a simple spin coating technique. It was found that 1 wt% N-GQDs/PVA device shows a prominent resistive switching phenomenon with good cyclic stability, high on/off ratio of ~102and retention time of ∼104s. From a detailed experimental study of band structure, we conclude that memristive behavior originates from the space charge controlled conduction (SCLC) mechanism. Further transient property of built memristive device was studied. Within three minutes of being submerged in distilled water, the fabricated memory device was destroyed. This phenomenon facilitates the usage of fabricated memristor devices to develop memory devices for military and security purposes.

Highly Elastic, Bioresorbable Polymeric Materials for Stretchable, Transient Electronic Systems.

Substrates or encapsulants in soft and stretchable formats are key components for transient, bioresorbable electronic systems; however, elastomeric polymers with desired mechanical and biochemical properties are very limited compared to non-transient counterparts. Here, we introduce a bioresorbable elastomer, poly(glycolide-co-ε-caprolactone) (PGCL), that contains excellent material properties including high elongation-at-break (< 1300%), resilience and toughness, and tunable dissolution behaviors. Exploitation of PGCLs as polymer matrices, in combination with conducing polymers, yields stretchable, conductive composites for degradable interconnects, sensors, and actuators, which can reliably function under external strains. Integration of device components with wireless modules demonstrates elastic, transient electronic suture system with on-demand drug delivery for rapid recovery of post-surgical wounds in soft, time-dynamic tissues.

Ultrathin, Transferred Layers of Silicon Oxynitrides as Tunable Biofluid Barriers for Bioresorbable Electronic Systems.

Bio/ecoresorbable electronic systems create unique opportunities in implantable medical devices that serve a need over a finite time period and then disappear naturally to eliminate the need for extraction surgeries. A critical challenge in the development of this type of technology is in materials that can serve as thin, stable barriers to surrounding ground water or biofluids, yet ultimately dissolve completely to benign end products. This paper describes a class of inorganic material (silicon oxynitride, SiON) that can be formed in thin films by plasma-enhanced chemical vapor deposition for this purpose. In vitro studies suggest that SiON and its dissolution products are biocompatible, indicating the potential for its use in implantable devices. A facile process to fabricate flexible, wafer-scale multilayer films bypasses limitations associated with the mechanical fragility of inorganic thin films. Systematic computational, analytical, and experimental studies highlight the essential materials aspects. Demonstrations in wireless light-emitting diodes both in vitro and in vivo illustrate the practical use of these materials strategies. The ability to select degradation rates and water permeability through fine tuning of chemical compositions and thicknesses provides the opportunity to obtain a range of functional lifetimes to meet different application requirements.

Soft, Long-Lived, Bioresorbable Electronic Surgical Mesh with Wireless Pressure Monitor and On-Demand Drug Delivery.

Current research in the area of surgical mesh implants is somewhat limited to traditional designs and synthesis of various mesh materials, whereas meshes with multiple functions may be an effective approach to address long-standing challenges including postoperative complications. Herein, a bioresorbable electronic surgical mesh is presented that offers high mechanical strength over extended timeframes, wireless post-operative pressure monitoring, and on-demand drug delivery for the restoration of tissue structure and function. The study of materials and mesh layouts provides a wide range of tunability of mechanical and biochemical properties. Dissolvable dielectric composite with porous structure in a pyramidal shape enhances sensitivity of a wireless capacitive pressure sensor, and resistive microheaters integrated with inductive coils provide thermo-responsive drug delivery system for an antibacterial agent. In vivo evaluations demonstrate reliable, long-lived operation, and effective treatment for abdominal hernia defects, by clear evidence of suppressed complications such as adhesion formation and infections.

Micropatterned Elastomeric Composites for Encapsulation of Transient Electronics.

Although biodegradable, transient electronic devices must dissolve or decompose via environmental factors, an effective waterproofing or encapsulation system is essential for reliable, durable operation for a desired period of time. Existing protection approaches use multiple or alternate layers of electrically inactive organic/inorganic elements combined with polymers; however, their high mechanical stiffness is not suitable for soft, time-dynamic biological tissues/skins/organs. Here, we introduce a stretchable, bioresorbable encapsulant using nanoparticle-incorporated elastomeric composites with modifications of surface morphology. Nature-inspired micropatterns reduce the diffusion area for water molecules, and embedded nanoparticles impede water permeation, which synergistically enhances the water-barrier performance. Empirical and theoretical evaluations validate the encapsulation mechanisms under strains. Demonstration of a soft, degradable shield with an optical component under a biological solution highlights the potential applicability of the proposed encapsulation strategy.

On-Demand Transient Paper Substrate for Selective Disposability of Thin-Film Electronic Devices.

This study demonstrates a novel approach to creating a thin-film electronic device that offers selective or complete disposability only in on-demand conditions while maintaining stable operation reliability during everyday use. The approach involves a transient paper substrate, combined with phase change encapsulation and highly bendable planarization materials, achieved through a simple solution process. The substrate used in this study offers a smooth surface morphology that enables the creation of stable multilayers for thin-film electronic devices. It also exhibits superior waterproof properties, which allows the proof-of-concept organic light-emitting device to function even when submerged in water. Additionally, the substrate provides controlled surface roughness under repeated bending, demonstrating reliable folding stability for 1000 cycles at 10 mm of curvature. Furthermore, a specific component of the electronic device can be selectively made to malfunction through predetermined voltage input, and the entire device can be fully disposed of via Joule-heating-induced combustion.

Bioderived Ionic Liquids with Alkaline Metal Ions for Transient Ionics.

Choline lactate, an ionic liquid composed of bioderived materials, offers an opportunity to develop biodegradable electrochemical devices. Although ionic liquids possess large potential windows, high conductivity, and are nonvolatile, they do not exhibit electrochemical characteristics such as intercalation pseudocapacitance, redox pseudocapacitance, and electrochromism. Herein, bioderived ionic liquids are developed, including metal ions, Li, Na, and Ca, to yield ionic liquid with electrochemical behavior. Differential scanning calorimetry results reveal that the ionic liquids remained in liquid state from 230.42 to 373.15 K. The conductivities of the ionic liquids with metal are lower than those of the pristine ionic liquid, whereas the capacitance change negligibly. A protocol of the Organization for Economic Co-operation and Development 301C modified MITI test (I) confirms that the pristine ionic liquid and ionic liquids with metal are readily biodegradable. Additionally, an ionic gel comprising the ionic liquid and poly(vinyl alcohol) is biodegradable. An electrochromic device is developed using an ionic liquid containing Li ions. The device successfully changes color at -2.5 V, demonstrating the intercalation of Li ions into the WO3 crystal. The results suggest that the electrochemically active ionic liquids have potential for the development of environmentally benign devices, sustainable electronics, and bioresorbable/implantable devices.

Ultrathin, Soft, Bioresorbable Organic Electrochemical Transistors for Transient Spatiotemporal Mapping of Brain Activity.

A critical challenge lies in the development of the next-generation neural interface, in mechanically tissue-compatible fashion, that offer accurate, transient recording electrophysiological (EP) information and autonomous degradation after stable operation. Here, an ultrathin, lightweight, soft and multichannel neural interface is presented based on organic-electrochemical-transistor-(OECT)-based network, with capabilities of continuous high-fidelity mapping of neural signals and biosafety active degrading after performing functions. Such platform yields a high spatiotemporal resolution of 1.42 ms and 20 µm, with signal-to-noise ratio up to ≈37 dB. The implantable OECT arrays can well establish stable functional neural interfaces, designed as fully biodegradable electronic platforms in vivo. Demonstrated applications of such OECT implants include real-time monitoring of electrical activities from the cortical surface of rats under various conditions (e.g., narcosis, epileptic seizure, and electric stimuli) and electrocorticography mapping from 100 channels. This technology offers general applicability in neural interfaces, with great potential utility in treatment/diagnosis of neurological disorders.

Vitamin C-Induced Enhanced Performance of PEDOT:PSS Thin Films for Eco-Friendly Transient Thermoelectrics.

Conjugated polymer-based energy-harvesting devices hold distinctive advantages in terms of low toxicity, high flexibility, and capability of large-area integration at low cost for sustainable development. An organic thermoelectric (OTE) device has been considered one of the promising energy-harvesting candidates in recent years because it can efficiently convert low-temperature waste heat into electricity over its inorganic counterparts. However, a cruel irony is that environmentally toxic solvents and acids are utilized for fabrication and performance improvement of the OTE devices, retarding the development and use of genuinely green energy-harvesting. Here, we present eco-friendly, non-toxic strategies for a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based high-performance OTE device by incorporating a nature-abundant material, vitamin C (VC), as an additive. We found that the intrinsic polar nature and reducing ability of VC induce synergy effects of microstructure alignment with PSS removal and dedoping of PEDOT, leading to simultaneous enhancement of the electrical conductivity (>400 S cm-1) and the Seebeck coefficient (>30 µV K-1) and a resultant high thermoelectric power factor of 51.8 µW m-1 K-2. In addition, inspired by the eco-friendly fabrication process, we further demonstrated a transient OTE device, which can be fully degraded with naturally occurring substances, by fabricating it on a bio-based cellulose acetate substrate. We believe that our eco-friendly strategies from fabrication to disposal of the OTE can be applied to the development of high-performance, wearable, and bio-compatible OTE devices with minimal waste and further trigger the research on genuinely green thermal energy harvesting.

A Transient Pseudo-Capacitor Using a Bioderived Ionic Liquid with Na Ions.

A pseudo-capacitor with transient behavior is applied in implantable, disposable, and bioresorbable devices, incorporating an Na ion-doped bioderived ionic liquid, molybdenum trioxide (MoO3 )-covered molybdenum foil, and silk sheet as the electrolyte, electrode, and separator, respectively. Sodium lactate is dissolved in choline lactate as a source of Na ions. The Experimental results reveal that the Na ions are intercalated into the van der Waals gaps in MoO3 , and the pseudo-capacitor shows an areal capacitance (1.5 mF cm-2 ) that is three times larger than that without the Na ion. The fast ion diffusion of the electrolyte and the low resistance of the MoO3 and Mo interface result in an equivalent series resistance of 96 Ω. A cycle test indicates that the pseudo-capacitor exhibited a high capacitance retention of 82.8% after 10 000 cycles. The transient behavior is confirmed by the dissolution of the pseudo-capacitor into phosphate-buffered saline solution after 101 days. Potential applications of transient pseudo-capacitors include electronics without the need for device retrieval after use, including smart agriculture, implantable, and wearable devices.

Photolithography-Based Microfabrication of Biodegradable Flexible and Stretchable Sensors.

Biodegradable sensors based on integrating conductive layers with polymeric materials in flexible and stretchable forms have been established. However, the lack of a generalized microfabrication method results in large-sized, low spatial density, and low device yield compared to the silicon-based devices manufactured via batch-compatible microfabrication processes. Here, a batch fabrication-compatible photolithography-based microfabrication approach for biodegradable and highly miniaturized essential sensor components is presented on flexible and stretchable substrates. Up to 1600 devices are fabricated within a 1 cm2 footprint and then the functionality of various biodegradable passive electrical components, mechanical sensors, and chemical sensors is demonstrated on flexible and stretchable substrates. The results are highly repeatable and consistent, proving the proposed method's high device yield and high-density potential. This simple, innovative, and robust fabrication recipe allows complete freedom over the applicability of various biodegradable materials with different properties toward the unique application of interests. The process offers a route to utilize standard micro-fabrication procedures toward scalable fabrication of highly miniaturized flexible and stretchable transient sensors and electronics.

Water-Soluble Polythiophene-Conjugated Polyelectrolyte-Based Memristors for Transient Electronics.

The key to protect sensitive information stored in electronic memory devices from disclosure is to develop transient electronic devices that are capable of being destroyed quickly in an emergency. By using a highly water-soluble polythiophene-conjugated polyelectrolyte PTT-NMI+Br- as an active material, which was synthesized by the reaction of poly[thiophene-alt-4,4-bis(6-bromohexyl)-4H-cyclopenta(1,2-b:5,4-b')dithiophene] with N-methylimidazole, a flexible electronic device, Al/PTT-NMI+Br-/ITO-coated PET (ITO: indium tin oxide; PET: polyethylene terephthalate), is successfully fabricated. This device shows a typical nonvolatile rewritable resistive random access memory (RRAM) effect at a sweep voltage range of ±3 V and a history-dependent memristive switching performance at a small sweep voltage range of ±1 V. Both the learning/memorizing functions and the synaptic potentiation/depression of biological systems have been emulated. The switching mechanism for the PTT-NMI+Br--based electronic device may be highly associated with ion migration under bias. Once water is added to this device, it will be destructed rapidly within 20 s due to the dissolution of the active layer. This device is not only a typical transient device but can also be used for constructing conventional memristors with long-term stability after electronic packaging. Furthermore, the soluble active layer in the device can be easily recycled from its aqueous solution and reused for fabricating new transient memristors. This work offers a train of new thoughts for designing and constructing a neuromorphic computing system that can be quickly destroyed with water in the near future.

Transient Elastomers with High Dielectric Permittivity for Actuators, Sensors, and Beyond.

Dielectric elastomers (DEs) are key materials in actuators, sensors, energy harvesters, and stretchable electronics. These devices find applications in important emerging fields such as personalized medicine, renewable energy, and soft robotics. However, even after years of research, it is still a great challenge to achieve DEs with increased dielectric permittivity and fast recovery of initial shape when subjected to mechanical and electrical stress. Additionally, high dielectric permittivity elastomers that show reliable performance but disintegrate under normal environmental conditions are not known. Here, we show that polysiloxanes modified with amide groups give elastomers with a dielectric permittivity of 21, which is 7 times higher than regular silicone rubber, a strain at break that can reach 150%, and a mechanical loss factor tan δ below 0.05 at low frequencies. Actuators constructed from these elastomers respond to a low electric field of 6.2 V µm-1, giving reliable lateral actuation of 4% for more than 30 000 cycles at 5 Hz. One survived 450 000 cycles at 10 Hz and 3.6 V µm-1. The best actuator shows 10% lateral strain at 7.5 V µm-1. Capacitive sensors offer a more than a 6-fold increase in sensitivity compared to standard silicone elastomers. The disintegrated material can be re-cross-linked when heated to elevated temperatures. In the future, our material could be used as dielectric in transient actuators, sensors, security devices, and disposable electronic patches for health monitoring.

Accelerable Self-Sintering of Solvent-Free Molybdenum/Wax Biodegradable Composites for Multimodally Transient Electronics.

Biodegradable conductive composites are key materials or components for printable transient electronics that can be fabricated in a low-cost and high-efficiency manner, thereby boosting their wide applications in biomedical engineering, hardware security, and environmental-friendly electronics. Continuous efforts in this area still lie in the development of strategies for highly conductive, safe, and reliable biodegradable conductive composite materials and devices. This paper introduces molybdenum/wax composites for multimodally printable transient electronics in which multiple transience modes including dissolution-induced degradation and thermally triggered degradation are available. Systematic experiments demonstrate several advantages and unique properties of this material system, including solvent-free fabrication, self-sintering behavior, and long-term and high conductivity via accelerable self-sintering treatment and rehealing capabilities. Notably, the immersion of molybdenum/wax composites in phosphate buffer solution can provide both positive effects (accelerated self-sintering-dominated) and negative effects (degradation-dominated) on their electrical conductivities. Mechanism analyses reveal the basis for balancing the degradation and accelerated self-sintering processes. The presented demonstrations foreshadow opportunities of the developed molybdenum/wax composites in rehealable electronics, on-demand smart transient electronics with multiple transience modes, and many other related unusual applications.

A Transient Supercapacitor with a Water-Dissolvable Ionic Gel for Sustainable Electronics.

We develop an environmentally benign supercapacitor, which decomposes by contact with water, incorporating an ionic liquid, carbon powder, a cellulose separator, and a molybdenum electrode. The ionic liquid is dispersed into a water-dissolvable polymer, poly(vinyl alcohol), to produce a solid electrolyte, so-called ionic gel. A carbon composite mixed with the ionic liquid maintains a gel form. The ionic gel and the carbon composite enable an all-solid-state supercapacitor, which can be charged at a voltage of 1.5 V. The supercapacitor shows areal and volumetric capacitances of 65 mF/cm2 and 2.2 F/cm3, respectively. A cycle test reveals that capacitance retention and Coulombic efficiency are 77 and 90%, respectively. As for the dissolution test, the ionic gel and carbon composite dissolves in phosphate buffer solution in 18 days, and the Mo electrode is able to fully dissolve in 500-588 days. Potential applications of the environmentally benign supercapacitor include smart agriculture by monitoring of soil and disaster prevention by a wireless sensor network without the need for retrieval of devices after use.

Biodegradable Molybdenum (Mo) and Tungsten (W) Devices: One Step Closer towards Fully-Transient Biomedical Implants.

Close monitoring of vital physiological parameters is often key in following the evolution of certain medical conditions (e.g., diabetes, infections, post-operative status or post-traumatic injury). The allocation of trained medical staff and specialized equipment is, therefore, necessary and often translates into a clinical and economic burden on modern healthcare systems. As a growing field, transient electronics may establish fully bioresorbable medical devices capable of remote real-time monitoring of therapeutically relevant parameters. These devices could alert remote medical personnel in case of any anomaly and fully disintegrate in the body without a trace. Unfortunately, the need for a multitude of biodegradable electronic components (power supplies, wires, circuitry) in addition to the electrochemical biosensing interface has halted the arrival of fully bioresorbable electronically active medical devices. In recent years molybdenum (Mo) and tungsten (W) have drawn increasing attention as promising candidates for the fabrication of both energy-powered active (e.g., transistors and integrated circuits) and passive (e.g., resistors and capacitors) biodegradable electronic components. In this review, we discuss the latest Mo and W-based dissolvable devices for potential biomedical applications and how these soluble metals could pave the way towards next-generation fully transient implantable electronic systems.