Fig. 6: Injectable bioelectronic platforms with sensing and stimulating functions.

a A graphical illustration describing the injection process of a hydrogel-based nanocomposite carrying various nanoparticles, including PLGA-drug NPs (Nanoparticles) and FIONs (Ferrimagnetic iron oxide nanocubes). Reproduced with permission from ref. ²⁰². b Intracortical hydrogel nanocomposite-mediated penetrative drug transport to deep brain tumors. (i) Illustration of drug diffusion into deep brain tumors enabled by magnetically triggered mild hyperthermia. (ii) Hydrogel nanocomposite injection. (iii) Hydrogel nanocomposite biodegradation process. Reproduced with permission from ref. ²⁰³. c Illustration of bidirectional electrophysiological interfacing facilitated by injectable tissue-interfacing prostheses composed of conductive hydrogels (IT-IC hydrogel). The hydrogel fills injured muscle or nerve sites, restoring tissue continuity and enabling neuromuscular signal transmission (red box). It forms a bioelectronic bridge (blue box) that allows bidirectional electrical signal transfer between muscles and peripheral nerves. This system integrates robotic assistance to enable real-time neuromuscular monitoring, facilitate targeted electrical stimulation, and support adaptive rehabilitation for enhanced functional recovery. Reproduced with permission from ref. ²⁰⁴. d (i) A composite material comprising a prepolymer carrier and conductive filler is injected near a target nerve, curing in place to establish an electrically conductive interface. (ii) Application of an injectable composite electrode in swine models, enabling stimulation of single or multiple nerves, including parallel nerve bundles and neural plexuses. Syringe-based delivery facilitated nerve cuff formation (1–3 mm diameter) and targeted encapsulation within the nerve sheath, utilizing its structure as a natural mold for uniform distribution. Reproduced with permission from ref. ²⁰⁵. e (i) Injectable deployment of elastin–gelatin–carbon nanotubes 20 (EGCx, where x is the concentration of carbon nanotubes (CNTs) in mg ml⁻¹) scaffolds utilizing its water-activated shape-memory properties. The EGC20 cardiac patch was delivered onto a porcine heart via a commercial catheter under thoracoscopic guidance. (ii) Schematic representation of the minimally invasive catheter-based injection of the prefabricated EGC20 scaffold (top) and the thoracoscopic view of the surgical site projected onto a monitor (bottom). (iii) In vivo catheter-based delivery of the EGC20 scaffold onto a porcine heart, illustrating the sequential process of insertion, ejection, saline application, and shape recovery. Reproduced with permission from ref. ²⁰⁶. f (i) Conceptual schematic of an injectable mesh cardiac patch for atrial fibrillation treatment. (ii) Illustration showing the endoscope-assisted injection of the mesh patch into a living animal. (iii) Mesh patch deployment process, including injection from a glass tube, release, and shape recovery on the heart tissue surface. Reproduced with permission from ref. ²⁰⁷. g (i) Schematic illustration of injectable electronics, highlighting the overall mesh structure with red-orange lines and indicating supporting and passivating polymer mesh layers. Yellow lines depict metal interconnects between I/O pads and recording devices. (ii) Illustration of the stereotaxic-guided in vivo injection of mesh electronics into a mouse brain. (iii) Optical image of the injection process in an anesthetized mouse. Reproduced with permission from ref. ²⁰⁸. h (i) Photograph of a mouse immediately after the injection of mesh electronics. The inset illustrates the noncoaxial intravitreal injection targeting the RGC layer. Yellow dots represent multiplexed recording electrodes. (ii) In vivo through-lens fundus images of the same mouse eye, recorded at days 0 and 14 post-injection. Reproduced with permission from ref. ²⁰⁹. i (i) Illustration detailing the syringe-based injection process of electrode arrays and their subsequent unfolding in the subdural space, with through-hole sizes typically in the millimeter range. (ii) Schematic of a syringe-injectable electronic device preloaded in a glass syringe with a buffer solution such as PBS or artificial cerebrospinal fluid. Air pressure from a dispenser expels the buffer solution, allowing the fluid flow to carry the device through the syringe tip. Scanning electron microscopy (SEM) image of the fabricated sensor section of the injectable electrode array. Reproduced with permission from ref. ²¹⁰. j (i) Conceptual schematic of a biodegradable electronic tent introduced into the intracranial space via a minimally invasive device. The inset provides an X-ray image of the device post-deployment. (ii) Sequential images illustrating the deployment process in a simulated structure. Reproduced with permission from ref. ²¹¹. k Photographic top-view images of the soft ECoG array prototype: (i) in a folded configuration and (ii) in its fully expanded state. (iii) Cross-sectional schematic illustrating the inner chamber containing aqueous solution. (iv) Post-placement image of the ECoG system on the brain (left) and a photograph of the extracted brain showing the electrode array positioned on the contralateral hemisphere (right). Reproduced with permission from ref. ²¹². l Conceptual illustration of minimally invasive ECoG (MI-ECoG): (i) A folded ECoG device implanted onto the cortical surface through a burr-hole craniotomy. (ii) Controlled expansion via fluidic actuation for large-area cortical signal acquisition. (iii) A top-down view showing the MI-ECoG unfolding inside a brain phantom model, driven by syringe-applied air pressure. (iv) X-ray images demonstrating the device’s expansion process, with white boxes indicating its structure before, during, and after deployment. Reproduced with permission from ref. ²¹³. m (i) Conceptual illustration of shape-adaptive electrode arrays (SCEAs) engineered for minimally invasive implantation and large-area intracranial neural recording. The inset presents an image of an epidurally implanted SCEA in a rat brain, delivered via a minimally invasive surgical procedure. The skull was subsequently removed to provide a clear view of the implanted array. (ii) Optical images showing the SCEA in both its compressed and fully deployed states. Reproduced with permission from ref. ²¹⁴. n (i) Conceptual schematic showing the adhesive implantation of the bioadhesive pacing lead onto the epicardium, highlighting its capabilities for sensing, stimulation, controlled detachment via reservoir-injected fluid, and subsequent retrieval. (ii) Image of an ex vivo porcine heart (400 g) being lifted by the attached bioadhesive pacing lead. (iii) Sequential images displaying the bioadhesive pacing lead affixed to a porcine heart (top) and the heart post-detachment (bottom). Reproduced with permission from ref. 215.