Biologically Safe, Degradable Self-Destruction System for On-Demand, Programmable Transient Electronics

Wireless Battery-free and Fully Implantable Organ Interfaces

Advances in soft materials, miniaturized electronics, sensors, stimulators, radios, and battery-free power supplies are resulting in a new generation of fully implantable organ interfaces that leverage volumetric reduction and soft mechanics by eliminating electrochemical power storage. This device class offers the ability to provide high-fidelity readouts of physiological processes, enables stimulation, and allows control over organs to realize new therapeutic and diagnostic paradigms. Driven by seamless integration with connected infrastructure, these devices enable personalized digital medicine. Key to advances are carefully designed material, electrophysical, electrochemical, and electromagnetic systems that form implantables with mechanical properties closely matched to the target organ to deliver functionality that supports high-fidelity sensors and stimulators. The elimination of electrochemical power supplies enables control over device operation, anywhere from acute, to lifetimes matching the target subject with physical dimensions that supports imperceptible operation. This review provides a comprehensive overview of the basic building blocks of battery-free organ interfaces and related topics such as implantation, delivery, sterilization, and user acceptance. State of the art examples categorized by organ system and an outlook of interconnection and advanced strategies for computation leveraging the consistent power influx to elevate functionality of this device class over current battery-powered strategies is highlighted.

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.

Resorbable barrier polymers for flexible bioelectronics

Resorbable, implantable bioelectronic devices are emerging as powerful tools to reliably monitor critical physiological parameters in real time over extended periods. While degradable magnesium-based electronics have pioneered this effort, relatively short functional lifetimes have slowed clinical translation. Barrier films that are both flexible and resorbable over predictable timelines would enable tunability in device lifetime and expand the viability of these devices. Herein, we present a library of stereocontrolled succinate-based copolyesters which leverage copolymer composition and processing method to afford tunability over thermomechanical, crystalline, and barrier properties. One copolymer composition within this library has extended the functional lifetime of transient bioelectronic prototypes over existing systems by several weeks-representing a considerable step towards translational devices.

Mechanochromism and Strain-Induced Crystallization in Thiol-yne-Derived Stereoelastomers

Most elastomers undergo strain-induced crystallization (SIC) under tension; as individual chains are held rigidly in a fixed position by an applied strain, their alignment along the strain field results in a shift from strain-hardening (SH) to SIC. A similar degree of stretching is associated with the tension necessary to accelerate mechanically coupled, covalent chemical responses of mechanophores in overstretched chains, raising the possibility of an interplay between the macroscopic response of SIC and the molecular response of mechanophore activation. Here, thiol-yne-derived stereoelastomers doped covalently with a dipropiolate-derivatized spiropyran (SP) mechanophore (0.25-0.38 mol%) are reported. The material properties of SP-containing films are consistent with undoped controls, indicating that the SP is a reporter of the mechanical state of the polymer. Uniaxial tensile tests reveal correlations between mechanochromism and SIC, which are strain-rate-dependent. When mechanochromic films are stretched slowly to the point of mechanophore activation, the covalently tethered mechanophore remains trapped in a force-activated state, even after the applied stress is removed. Mechanophore reversion kinetics correlate with the applied strain rate, resulting in highly tunable decoloration rates. Because these polymers are not covalently crosslinked, they are recyclable by melt-pressing into new films, increasing their potential range of strain-sensing, morphology-sensing, and shape-memory applications.

Ultra-stretchable and biodegradable elastomers for soft, transient electronics

As rubber-like elastomers have led to scientific breakthroughs in soft, stretchable characteristics-based wearable, implantable electronic devices or relevant research fields, developments of degradable elastomers with comparable mechanical properties could bring similar technological innovations in transient, bioresorbable electronics or expansion into unexplored areas. Here, we introduce ultra-stretchable, biodegradable elastomers capable of stretching up to ~1600% with outstanding properties in toughness, tear-tolerance, and storage stability, all of which are validated by comprehensive mechanical and biochemical studies. The facile formation of thin films enables the integration of almost any type of electronic device with tunable, suitable adhesive strengths. Conductive elastomers tolerant/sensitive to mechanical deformations highlight possibilities for versatile monitoring/sensing components, particularly the strain-tolerant composites retain high levels of conductivities even under tensile strains of ~550%. Demonstrations of soft electronic grippers and transient, suture-free cardiac jackets could be the cornerstone for sophisticated, multifunctional biodegradable electronics in the fields of soft robots and biomedical implants.

Pathway of transient electronics towards connected biomedical applications

Transient electronic devices have shown promising applications in hardware security and medical implants with diagnosing therapeutics capabilities since their inception. Control of the device transience allows the device to "dissolve at will" after its functional operation, leading to the development of on-demand transient electronics. This review discusses the recent developments and advantages of triggering strategies (e.g., electrical, thermal, ultrasound, and optical) for controlling the degradation of on-demand transient electronics. We also summarize bioresorbable sensors for medical diagnoses, including representative applications in electrophysiology and neurochemical sensing. Along with the profound advancements in medical diagnosis, the commencement of therapeutic systems such as electrical stimulation and drug delivery for the biomedical or medical implant community has also been discussed. However, implementing a transient electronic system in real healthcare infrastructure is still in its infancy. Many critical challenges still need to be addressed, including strategies to decouple multimodal sensing signals, dissolution selectivity in the presence of multiple stimuli, and a complete sensing-stimulation closed-loop system. Therefore, the review discusses future opportunities in transient decoupling sensors and robust transient devices, which are selective to a particular stimulus and act as hardware-based passwords. Recent advancements in closed-loop controller-enabled electronics have also been analyzed for future opportunities of using data-driven artificial intelligence-powered controllers in fully closed-loop transient systems.

Biodegradable, three-dimensional colorimetric fliers for environmental monitoring

Recently reported winged microelectronic systems offer passive flight mechanisms as a dispersal strategy for purposes in environmental monitoring, population surveillance, pathogen tracking, and other applications. Initial studies indicate potential for technologies of this type, but advances in structural and responsive materials and in aerodynamically optimized geometries are necessary to improve the functionality and expand the modes of operation. Here, we introduce environmentally degradable materials as the basis of 3D fliers that allow remote, colorimetric assessments of multiple environmental parameters-pH, heavy metal concentrations, and ultraviolet exposure, along with humidity levels and temperature. Experimental and theoretical investigations of the aerodynamics of these systems reveal design considerations that include not only the geometries of the structures but also their mass distributions across a range of bioinspired designs. Preliminary field studies that rely on drones for deployment and for remote colorimetric analysis by machine learning interpretation of digital images illustrate scenarios for practical use.

Factors Controlling Degradation of Biologically Relevant Synthetic Polymers in Solution and Solid State

The field of biodegradable synthetic polymers, which is central for regenerative engineering and drug delivery applications, encompasses a multitude of hydrolytically sensitive macromolecular structures and diverse processing approaches. The ideal degradation behavior for a specific life science application must comply with a set of requirements, which include a clinically relevant kinetic profile, adequate biocompatibility, benign degradation products, and controlled structural evolution. Although significant advances have been made in tailoring materials characteristics to satisfy these requirements, the impacts of autocatalytic reactions and microenvironments are often overlooked resulting in uncontrollable and unpredictable outcomes. Therefore, roles of surface versus bulk erosion, in situ microenvironment, and autocatalytic mechanisms should be understood to enable rational design of degradable systems. In an attempt to individually evaluate the physical state and form factors influencing autocatalytic hydrolysis of degradable polymers, this Review follows a hierarchical analysis that starts with hydrolytic degradation of water-soluble polymers before building up to 2D-like materials, such as ultrathin coatings and capsules, and then to solid-state degradation. We argue that chemical reactivity largely governs solution degradation while diffusivity and geometry control the degradation of bulk materials, with thin "2D" materials remaining largely unexplored. Following this classification, this Review explores techniques to analyze degradation in vitro and in vivo and summarizes recent advances toward understanding degradation behavior for traditional and innovative polymer systems. Finally, we highlight challenges encountered in analytical methodology and standardization of results and provide perspective on the future trends in the development of biodegradable polymers.

Thermally Degradable Inductors with Water-Resistant Metal Leaf/Oleogel Wires and Gelatin/Chitosan Hydrogel Films

Ingestible electronics monitor biometric information from outside the body. Making them with harmless or digestible materials will contribute to further reducing the burden on the patient's oral intake. Here, considering that the inductive part plays an important role in communications, we demonstrate a degradable inductor fabricated with harmless substances. Such a transient component must meet conflicting requirements for both operation and disassembly. Therefore, we integrated a substrate made of gelatin, a thermally degradable material, and a precision coil pattern made of edible gold or silver leaf. However, gelatin itself lost its initial shape easily due to quick sol-gel changes in physiological conditions. Thus, we managed the gelatin's thermal responsiveness by using a tangle of gelatin/chitosan gel networks and genipin, an organic cross-linking agent, and gained insights into the criteria for developing transient devices with thermo-degradability. In addition, to compensate for the lack of water resistance and low conductivity of thin metal foils, we propose a laminated structure with oleogel (beeswax/olive oil). LCR resonance circuits, by connecting a commercial capacitor to the coil, worked wirelessly in the megahertz band and gradually degraded in a warm-water environment. The presented organic electronics will contribute to the future development of transient wireless communications for implantable and ingestible medical devices or environmental sensors with natural and harmless ingredients.