Electrodes for interfacing implantable electronics and neural tissue are of great importance to gain a better understanding of the nervous system and to help people suffering from impaired body functions due to nerve lesions or lost organ functionality. In particular, neurostimulation techniques for bioelectronic medicine rely on the development of mechanically and electrochemically stable electrodes. While contemporary electrodes are based mainly on metals, new materials are being designed to enhance the mechanical and electrochemical properties of the interface. In this work, a nerve interface based on carbon nanotubes (CNTs) embedded in polydimethylsiloxane (PDMS) is fabricated and investigated. The fabrication process relies on the selective vacuum filtration of CNT suspensions through a printed wax pattern. The mechanical and electrochemical stability of the nerve interface was validated by 10 000 stretching cycles up to 20% strain and >4 × 106 biphasic stimulation pulses with 32 μC cm−2 per phase. The feedline resistance and electrode impedance showed only minor alterations after the stress tests. The functionality of the nerve interface was demonstrated by successful stimulation of the central nerve cord of a horse leech applying stimulation conditions within the water window of the CNT/PDMS electrodes. This work shows the practical usability of CNT/PDMS composites as electrodes and feedlines in peripheral nerve interfaces for future neuroprosthetic devices.

Peripheral nerve interfacing (PNI) has a high clinical potential for treating various diseases, such as obesity or diabetes. However, currently existing electrodes present challenges to the interfacing procedure, which limit their clinical application, in particular, when targeting small peripheral nerves (<200 µm). To improve the electrode handling and implantation, a nerve interface that can fold itself to a cuff around a small nerve, triggered by the body moisture during insertion, is fabricated. This folding is achieved by printing a bilayer of a flexible polyurethane printing resin and a highly swelling sodium acrylate hydrogel using photopolymerization. When immersed in an aqueous liquid, the hydrogel swells and folds the electrode softly around the nerve. Furthermore, the electrodes are robust, can be stretched (>20%), and bent to facilitate the implantation due to the use of soft and stretchable printing resins as substrates and a microcracked gold film as conductive layer. The straightforward implantation and extraction of the electrode as well as stimulation and recording capabilities on a small peripheral nerve in vivo are demonstrated. It is believed that such simple and robust to use self‐folding electrodes will pave the way for bringing PNI to a broader clinical application.

Superabsorbent polymers are materials that exhibit a high swelling behavior in liquids and can hold the absorbed liquid even against externally applied pressure. They are commercially used, for example, in baby diapers, fake snow, or swellable children's toys. Most commercially available superabsorbent polymers are based on polymerized and crosslinked sodium acrylate. Here, a material formulation to create 3D objects using stereolithographic printing of sodium acrylate is demonstrated. The material shows typical superabsorbent properties that cannot be reached with conventional 3D printing materials. The printed structures swell strongly (up to 20 times in weight) in aqueous environments and still show 65% of the swelling under an external load of 100 kPa. This swelling can be used for 3D printed parts that can automatically change their size or shape when exposed to water. To show the versatility of this approach, selected structures are 3D printed, including a ship and a medical stent. Also the applicability of actuation by printing a structure is demonstrated, which deforms to a self‐closing container upon exposure to water.

Interfacing with the peripheral nervous system is a powerful method for diagnosing and treating several diseases, such as drug‐resistant epilepsy and depression. In most clinical applications, large nerves such as the vagus and the hypoglossal nerve are targeted. Large nerves carry multiple nerve fibers, and maintaining selectivity of a specific target response demands complex stimulation strategies. As the large trunks bifurcate toward their distal ends, their diameter and number of comprised fibers reduce. Consequently, interfacing small nerves can provide increased fiber selectivity. However, their small size presents challenges to the fabrication and implantation of suitable electrodes due to their fragility and constrained environments. Here, a cuff electrode that combines two‐photon stereolithography and 3D inkjet printing techniques for the selective interfacing of small nerves in vivo is introduced. The device is easy to implant, and its size can be tailored for specific nerve dimensions. Its capability to record and selectively stimulate is demonstrated by targeting a locust's hind leg nerve.

An increasing demand for bioelectronics that interface with living systems has driven the development of materials to resolve mismatches between electronic devices and biological tissues. So far, a variety of different polymers have been used as substrates for bioelectronics. Especially, biopolymers have been investigated as next-generation materials for bioelectronics because they possess interesting characteristics such as high biocompatibility, biodegradability, and sustainability. However, their range of applications has been restricted due to the limited compatibility of classical fabrication methods with such biopolymers. Here, we introduce a fabrication process for thin and large-area films of chitosan nanofibers (CSNFs) integrated with conductive materials. To this end, we pattern carbon nanotubes (CNTs), silver nanowires, and poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) by a facile filtration process that uses polyimide masks fabricated via laser ablation. This method yields feedlines of conductive material on nanofiber paper and demonstrates compatibility with conjugated and high-aspect-ratio materials. Furthermore, we fabricate a CNT neural interface electrode by taking advantage of this fabrication process and demonstrate peripheral nerve stimulation to the rapid extensor nerve of a live locust. The presented method might pave the way for future bioelectronic devices based on biopolymer nanofibers.