Electronics with shape actuation for minimally invasive spinal cord stimulation

Soft neural interface with color adjusted PDMS encapsulation layer for spinal cord stimulation

BACKGROUND

Spinal cord stimulation (SCS) plays a crucial role in treating various neurological diseases. Utilizing soft spinal cord electrodes in SCS allows for a better fit with the physiological structure of the spinal cord and reduces tissue damage. Polydimethylsiloxane (PDMS) has emerged as an ideal material for soft bioelectronics. However, micromachining soft PDMS bioelectronics devices with low thermal effects and high uniformity remains challenging.

NEW METHOD

Here, we demonstrated a fully laser-micromachined soft neural interface for SCS. The native and color adjusted PDMS with variable absorbance characteristics were investigated in laser processing. In addition, we systematically evaluated the impact of electrode sizes on the electrochemical performance of neural interface. By fitting the equivalent circuit model, the electrochemical process of neural interface was revealed and the performance of the electrode was evaluated. The biocompatibility of color adjusted PDMS was confirmed by cytotoxicity assays. Finally, we validated the neural interface in mice.

RESULTS

Color adjusted PDMS has good biocompatibility and can significantly reduce the damage caused by thermal effects, enhancing the electrochemical performance of bioelectronic devices. The soft neural interface with color adjusted PDMS encapsulation layer can activate the motor function safely.

COMPARISON WITH EXISTING METHODS

The fully laser-micromachined soft neural interface was proposed for the first time. Compared with existing methods, this method showed low thermal effects, high uniformity, and could be easily scaled up.

CONCLUSIONS

The fully laser-micromachined soft neural interface device with color adjusted PDMS encapsulation layer shows great promise for applications in SCS.

Fabrication of thin-film electrodes and organic electrochemical transistors for neural implants

Bioelectronic medicine, which involves the delivery of electrical stimulation via implantable electrodes, is poised to advance the treatment of neurological conditions. However, current hand-made devices are bulky, invasive and lack specificity. Thin-film neurotechnology devices can overcome these disadvantages. With a typical thickness in the range of micrometers, thin-film devices demonstrate high conformability, stretchability, are minimally invasive and can be fabricated using traditional lithography techniques. Despite their potential, variability and unreliability in fabrication processes hinder their wider utilization. Here, we detail a fabrication method for thin-film poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) electrodes and organic electrochemical transistors. The use of organic materials makes these devices particularly well suited for bioelectronic medicine applications as they show superior mechanical and electrical matching of biological tissues compared with devices made of inorganic materials. The procedure details the entire process, including mask design, the fabrication through three photolithography stages, the integration with larger-scale electronics, implantation procedures and the expected electrical characterization metrics. The nanofabrication protocol requires at least 3 d and is suitable for those familiar with lithographic fabrication procedures. The surgery requires up to 10 h and is suitable for those familiar with in vivo implantation procedures.

Cylindrical vs Paddle Leads in Spinal Cord Stimulation for the Long-term Treatment of Chronic Pain: A Systematic Review and Meta-analysis

OBJECTIVES

This systematic review compares the long-term efficacy of cylindrical-lead spinal cord stimulation (CL-SCS) vs paddle-lead spinal cord stimulation (Paddle-SCS) for chronic pain management.

MATERIALS AND METHODS

We included prospective and retrospective studies with at least ten patients reporting on the efficacy of either lead type. Primary outcomes were pain score reduction (measured by the visual analog scale [VAS] and numeric rating scale [NRS]) and 50% pain relief after at least 12 months. Secondary outcomes included functional disability and complications, such as lead migration and infection rates. Meta-analyses compared effect sizes, while meta-regression and subgroup analyses addressed heterogeneity.

RESULTS

A total of 96 studies, comprising 7726 patients, met the inclusion criteria. Paddle-SCS demonstrated superior pain reduction, with a standardized mean difference (SMD) of 5.37 (95% CI [5.35, 5.38]) compared with CL-SCS, which had an SMD of 4.09 (95% CI [4.08, 4.10]) on the VAS. However, CL-SCS outperformed Paddle-SCS on the NRS, with SMDs of 4.39 vs 2.35, respectively. For 50% pain relief, Paddle-SCS had a success rate of 41.4%, as opposed to 35.4% for CL-SCS. Paddle-SCS showed a lower migration rate (4.3% vs 7.2% for CL-SCS) but higher infection rates (5.0% vs 3.3%).

CONCLUSIONS

Paddle-SCS offers superior pain reduction (as measured by the VAS) and a lower migration rate, but a higher infection risk compared with CL-SCS. CL-SCS showed better outcomes as measured by the NRS. The choice between Paddle-SCS and CL-SCS should be individualized according to patient-specific factors and treatment goals. Further research with rigorous study designs is needed to provide clearer comparisons between these interventions.

Endocisternal interfaces for minimally invasive neural stimulation and recording of the brain and spinal cord

Minimally invasive neural interfaces can be used to diagnose, manage and treat many disorders, with reduced risks of surgical complications. However, endovascular probes lack access to key cortical, subcortical and spinal targets, and are not typically explantable after endothelialization. Here we report the development and testing, in sheep, of endocisternal neural interfaces that approach brain and spinal cord targets through inner and outer spaces filled with cerebrospinal fluid. Thus, the interfaces gain access to the entire brain convexity, to deep brain structures within the ventricles and to the spinal cord from the spinal subarachnoid space. We combined an endocisternal neural interface with wireless miniature magnetoelectrically powered bioelectronics so that it can be freely navigated percutaneously from the spinal space to the cranial subarachnoid space, and from the cranial subarachnoid space to the ventricles. In sheep, we show recording and stimulation functions, as well as repositioning of the flexible electrodes and explantation of the interface after chronic implantation. Minimally invasive endocisternal bioelectronics may enable chronic and transient therapies, particularly for stroke rehabilitation and epilepsy monitoring.

Biological and hardware-related spinal cord stimulation complications and their management: A single-center retrospective analysis of the implantation of nonrechargeable implantable pulse generators in different pain conditions

Background

We present our experience with spinal cord stimulation (SCS) for patients suffering from different pain conditions who subsequently developed hardware-related complications after SCS surgery. The SCS hardware-related complications may compromise the continuous SCS therapy due to partial or total hardware removal. Such situations should be avoided, and possible predisposing factors for their development should be minimized. The present study aimed to evaluate the frequency of hardware-related complications and their proper neurosurgical management.

Methods

The study is designed as a retrospective analysis of all hardware-related complications of SCS procedures for pain patients who underwent the implantation of the nonrechargeable PrimeAdvanced™ SureScan™ magnetic resonance imaging (MRI) neurostimulator (Medtronic, Minneapolis, United States). This neurostimulator allows patients safe access to MRI scans anywhere on the body. The PrimeAdvanced™ SureScan™ MRI neurostimulator can deliver stimulation through one or more leads in the epidural space. From December 2017 to December 2021, 20 patients with SCS implantations and a minimum postoperative follow-up of 3 months were included. All patients were operated on using identical surgical and intraprocedural techniques. The same SCS hardware was implanted (nonrechargeable PrimeAdvanced™ SureScan™ MRI neurostimulator) in all patients. We examined numerous preoperative variables (i.e., sex, age at surgery, diabetes, body mass index, and type of pain syndrome) to detect any correlation between them and the incidence of postoperative hardware-related complications.

Results

Among 20 patients, 8 (40%) patients were affected by hardware-related complications. The most common complications were skin erosion found in 5 patients (25%) and incorrect functioning of the implantable pulse generator (IPG) affecting 2 patients (10%). There were 1 case of an IPG migration (5%) and 1 hardware infection (5%) due to a staphylococcal wound. A total number of 16 revision surgeries were performed to manage all hardware-related complications in these patients adequately. Most of the patients (5 of them) were troubled by more than one hardware-related complication episode. Three patients had 3 revision surgeries, 2 patients had 2 revision surgeries, and 3 patients had 1 revision surgery. Among 8 patients with complications, 3 patients had no further continuation of SCS therapy due to hardware-related complications. Among these 3 patients who stopped their SCS therapy, 1 patient had 3 hardware-related episodes, and the remaining 2 patients were troubled by two hardware-related episodes before discontinuation of SCS therapy.

Conclusion

Our results indicate that patients treated by the SCS technique are at higher risk for the development of skin-related complications, especially skin erosions and less common skin infections, notably in cases when large (high profile) IPGs are utilized. The use of smaller IPGs could reduce the number of these biological as well as hardware-related complications and associated revision surgeries.

Wearable and Implantable Soft Robots

Soft robotics presents innovative solutions across different scales. The flexibility and mechanical characteristics of soft robots make them particularly appealing for wearable and implantable applications. The scale and level of invasiveness required for soft robots depend on the extent of human interaction. This review provides a comprehensive overview of wearable and implantable soft robots, including applications in rehabilitation, assistance, organ simulation, surgical tools, and therapy. We discuss challenges such as the complexity of fabrication processes, the integration of responsive materials, and the need for robust control strategies, while focusing on advances in materials, actuation and sensing mechanisms, and fabrication techniques. Finally, we discuss the future outlook, highlighting key challenges and proposing potential solutions.

Thin-film implants for bioelectronic medicine

This article is based on the MRS Mid-Career Researcher Award "for outstanding contributions to the fundamentals and development of organic electronic materials and their application in biology and medicine" presentation given by George G. Malliaras, University of Cambridge, at the 2023 MRS Spring Meeting in San Francisco, Calif.Bioelectronic medicine offers a revolutionary approach to treating disease by stimulating the body with electricity. While current devices show safety and efficacy, limitations, including bulkiness, invasiveness, and scalability, hinder their wider application. Thin-film implants promise to overcome these limitations. Made using microfabrication technologies, these implants conform better to neural tissues, reduce tissue damage and foreign body response, and provide high-density, multimodal interfaces with the body. This article explores how thin-film implants using organic materials and novel designs may contribute to disease management, intraoperative monitoring, and brain mapping applications. Additionally, the technical challenges to be addressed for this technology to succeed are discussed.

Graphical abstract

Bioelectronics for electrical stimulation: materials, devices and biomedical applications

Bioelectronics is a hot research topic, yet an important tool, as it facilitates the creation of advanced medical devices that interact with biological systems to effectively diagnose, monitor and treat a broad spectrum of health conditions. Electrical stimulation (ES) is a pivotal technique in bioelectronics, offering a precise, non-pharmacological means to modulate and control biological processes across molecular, cellular, tissue, and organ levels. This method holds the potential to restore or enhance physiological functions compromised by diseases or injuries by integrating sophisticated electrical signals, device interfaces, and designs tailored to specific biological mechanisms. This review explains the mechanisms by which ES influences cellular behaviors, introduces the essential stimulation principles, discusses the performance requirements for optimal ES systems, and highlights the representative applications. From this review, we can realize the potential of ES based bioelectronics in therapy, regenerative medicine and rehabilitation engineering technologies, ranging from tissue engineering to neurological technologies, and the modulation of cardiovascular and cognitive functions. This review underscores the versatility of ES in various biomedical contexts and emphasizes the need to adapt to complex biological and clinical landscapes it addresses.

Origami-inspired soft fluidic actuation for minimally invasive large-area electrocorticography

Electrocorticography is an established neural interfacing technique wherein an array of electrodes enables large-area recording from the cortical surface. Electrocorticography is commonly used for seizure mapping however the implantation of large-area electrocorticography arrays is a highly invasive procedure, requiring a craniotomy larger than the implant area to place the device. In this work, flexible thin-film electrode arrays are combined with concepts from soft robotics, to realize a large-area electrocorticography device that can change shape via integrated fluidic actuators. We show that the 32-electrode device can be packaged using origami-inspired folding into a compressed state and implanted through a small burr-hole craniotomy, then expanded on the surface of the brain for large-area cortical coverage. The implantation, expansion, and recording functionality of the device is confirmed in-vitro and in porcine in-vivo models. The integration of shape actuation into neural implants provides a clinically viable pathway to realize large-area neural interfaces via minimally invasive surgical techniques.

Skin-inspired, sensory robots for electronic implants

Drawing inspiration from cohesive integration of skeletal muscles and sensory skins in vertebrate animals, we present a design strategy of soft robots, primarily consisting of an electronic skin (e-skin) and an artificial muscle. These robots integrate multifunctional sensing and on-demand actuation into a biocompatible platform using an in-situ solution-based method. They feature biomimetic designs that enable adaptive motions and stress-free contact with tissues, supported by a battery-free wireless module for untethered operation. Demonstrations range from a robotic cuff for detecting blood pressure, to a robotic gripper for tracking bladder volume, an ingestible robot for pH sensing and on-site drug delivery, and a robotic patch for quantifying cardiac function and delivering electrotherapy, highlighting the application versatilities and potentials of the bio-inspired soft robots. Our designs establish a universal strategy with a broad range of sensing and responsive materials, to form integrated soft robots for medical technology and beyond.

A biodegradable and flexible neural interface for transdermal optoelectronic modulation and regeneration of peripheral nerves

Optoelectronic neural interfaces can leverage the photovoltaic effect to convert light into electrical current, inducing charge redistribution and enabling nerve stimulation. This method offers a non-genetic and remote approach for neuromodulation. Developing biodegradable and efficient optoelectronic neural interfaces is important for achieving transdermal stimulation while minimizing infection risks associated with device retrieval, thereby maximizing therapeutic outcomes. We propose a biodegradable, flexible, and miniaturized silicon-based neural interface capable of transdermal optoelectronic stimulation for neural modulation and nerve regeneration. Enhancing the device interface with thin-film molybdenum significantly improves the efficacy of neural stimulation. Our study demonstrates successful activation of the sciatic nerve in rodents and the facial nerve in rabbits. Moreover, transdermal optoelectronic stimulation accelerates the functional recovery of injured facial nerves.

Flexible circumferential bioelectronics to enable 360-degree recording and stimulation of the spinal cord

The spinal cord is crucial for transmitting motor and sensory information between the brain and peripheral systems. Spinal cord injuries can lead to severe consequences, including paralysis and autonomic dysfunction. We introduce thin-film, flexible electronics for circumferential interfacing with the spinal cord. This method enables simultaneous recording and stimulation of dorsal, lateral, and ventral tracts with a single device. Our findings include successful motor and sensory signal capture and elicitation in anesthetized rats, a proof-of-concept closed-loop system for bridging complete spinal cord injuries, and device safety verification in freely moving rodents. Moreover, we demonstrate potential for human application through a cadaver model. This method sees a clear route to the clinic by using materials and surgical practices that mitigate risk during implantation and preserve cord integrity.

There and Back Again: Building Systems That Integrate, Interface, and Interact with the Human Body

Since Dr. Theodor Schwann posed the extension of Cell Theory to mammals in 1839, scientists have dreamt up ways to interface with and influence the cells. Recently, considerable ground in this area is gained, particularly in the scope of bioelectronics. New advances in this area have provided with a means to record electrical activity from cells, examining neural firing or epithelial barrier integrity, and stimulate cells through applied electrical fields. Many of these applications utilize invasive implantation systems to perform this interaction in close proximity to the cells in question. Traditionally, the body's immune system fights back against these systems through the foreign body response, limiting the efficacy of long-term interactions. New technologies in tissue engineering, biomaterials science, and bioelectronics offer the potential to circumvent the foreign body response and create stable long-term biological interfaces. Looking ahead, the next advancements in the biomedical sciences can truly integrate, interface, and interact with the human body.

Minimally invasive power sources for implantable electronics

As implantable medical electronics (IMEs) developed for healthcare monitoring and biomedical therapy are extensively explored and deployed clinically, the demand for non-invasive implantable biomedical electronics is rapidly surging. Current rigid and bulky implantable microelectronic power sources are prone to immune rejection and incision, or cannot provide enough energy for long-term use, which greatly limits the development of miniaturized implantable medical devices. Herein, a comprehensive review of the historical development of IMEs and the applicable miniaturized power sources along with their advantages and limitations is given. Despite recent advances in microfabrication techniques, biocompatible materials have facilitated the development of IMEs system toward non-invasive, ultra-flexible, bioresorbable, wireless and multifunctional, progress in the development of minimally invasive power sources in implantable systems has remained limited. Here three promising minimally invasive power sources summarized, including energy storage devices (biodegradable primary batteries, rechargeable batteries and supercapacitors), human body energy harvesters (nanogenerators and biofuel cells) and wireless power transfer (far-field radiofrequency radiation, near-field wireless power transfer, ultrasonic and photovoltaic power transfer). The energy storage and energy harvesting mechanism, configurational design, material selection, output power and in vivo applications are also discussed. It is expected to give a comprehensive understanding of the minimally invasive power sources driven IMEs system for painless health monitoring and biomedical therapy with long-term stable functions.

Shape-changing electrode array for minimally invasive large-scale intracranial brain activity mapping

Large-scale brain activity mapping is important for understanding the neural basis of behaviour. Electrocorticograms (ECoGs) have high spatiotemporal resolution, bandwidth, and signal quality. However, the invasiveness and surgical risks of electrode array implantation limit its application scope. We developed an ultrathin, flexible shape-changing electrode array (SCEA) for large-scale ECoG mapping with minimal invasiveness. SCEAs were inserted into cortical surfaces in compressed states through small openings in the skull or dura and fully expanded to cover large cortical areas. MRI and histological studies on rats proved the minimal invasiveness of the implantation process and the high chronic biocompatibility of the SCEAs. High-quality micro-ECoG activities mapped with SCEAs from male rodent brains during seizures and canine brains during the emergence period revealed the spatiotemporal organization of different brain states with resolution and bandwidth that cannot be achieved using existing noninvasive techniques. The biocompatibility and ability to map large-scale physiological and pathological cortical activities with high spatiotemporal resolution, bandwidth, and signal quality in a minimally invasive manner offer SCEAs as a superior tool for applications ranging from fundamental brain research to brain-machine interfaces.

Soft touchless sensors and touchless sensing for soft robots

Soft robots are characterized by their mechanical compliance, making them well-suited for various bio-inspired applications. However, the challenge of preserving their flexibility during deployment has necessitated using soft sensors which can enhance their mobility, energy efficiency, and spatial adaptability. Through emulating the structure, strategies, and working principles of human senses, soft robots can detect stimuli without direct contact with soft touchless sensors and tactile stimuli. This has resulted in noteworthy progress within the field of soft robotics. Nevertheless, soft, touchless sensors offer the advantage of non-invasive sensing and gripping without the drawbacks linked to physical contact. Consequently, the popularity of soft touchless sensors has grown in recent years, as they facilitate intuitive and safe interactions with humans, other robots, and the surrounding environment. This review explores the emerging confluence of touchless sensing and soft robotics, outlining a roadmap for deployable soft robots to achieve human-level dexterity.

Water-Responsive 3D Electronics for Smart Biological Interfaces

Three-dimensional (3D) electronic systems with their potential for enhanced functionalities often require complex fabrication processes. This paper presents a water-based, stimuli-responsive approach for creating self-assembled 3D electronic systems, particularly suited for biorelated applications. We utilize laser scribing to programmatically shape a water-responsive bilayer, resulting in smart 3D electronic substrates. Control over the deformation direction, actuation time, and surface curvature of rolling structures is achieved by adjusting laser-scribing parameters, as validated through experiments and numerical simulations. Additionally, self-locking structures maintain the integrity of the 3D systems. This methodology enables the implementation of spiral twining electrodes for electrophysiological signal monitoring in plants. Furthermore, the integration of self-rolling electrodes onto peripheral nerves in a rodent model allows for stimulation and recording of in vivo neural activities with excellent biocompatibility. These innovations provide viable paths to next-generation 3D biointegrated electronic systems for life science studies and medical applications.

Skin-inspired, sensory robots for electronic implants

Living organisms with motor and sensor units integrated seamlessly demonstrate effective adaptation to dynamically changing environments. Drawing inspiration from cohesive integration of skeletal muscles and sensory skins in these organisms, we present a design strategy of soft robots, primarily consisting of an electronic skin (e-skin) and an artificial muscle, that naturally couples multifunctional sensing and on-demand actuation in a biocompatible platform. We introduce an in situ solution-based method to create an e-skin layer with diverse sensing materials (e.g., silver nanowires, reduced graphene oxide, MXene, and conductive polymers) incorporated within a polymer matrix (e.g., polyimide), imitating complex skin receptors to perceive various stimuli. Biomimicry designs (e.g., starfish and chiral seedpods) of the robots enable various motions (e.g., bending, expanding, and twisting) on demand and realize good fixation and stress-free contact with tissues. Furthermore, integration of a battery-free wireless module into these robots enables operation and communication without tethering, thus enhancing the safety and biocompatibility as minimally invasive implants. Demonstrations range from a robotic cuff encircling a blood vessel for detecting blood pressure, to a robotic gripper holding onto a bladder for tracking bladder volume, an ingestible robot residing inside stomach for pH sensing and on-site drug delivery, and a robotic patch wrapping onto a beating heart for quantifying cardiac contractility, temperature and applying cardiac pacing, highlighting the application versatilities and potentials of the nature-inspired soft robots. Our designs establish a universal strategy with a broad range of sensing and responsive materials, to form integrated soft robots for medical technology and beyond.

Laminin-coated electronic scaffolds with vascular topography for tracking and promoting the migration of brain cells after injury

In the adult brain, neural stem cells are largely restricted into spatially discrete neurogenic niches, and hence areas of neuron loss during neurodegenerative disease or following a stroke or traumatic brain injury do not typically repopulate spontaneously. Moreover, understanding neural activity accompanying the neural repair process is hindered by a lack of minimally invasive devices for the chronic measurement of the electrophysiological dynamics in damaged brain tissue. Here we show that 32 individually addressable platinum microelectrodes integrated into laminin-coated branched polymer scaffolds stereotaxically injected to span a hydrogel-filled cortical lesion and deeper regions in the brains of mice promote neural regeneration while allowing for the tracking of migrating host brain cells into the lesion. Chronic measurements of single-unit activity and neural-circuit analyses revealed the establishment of spiking activity in new neurons in the lesion and their functional connections with neurons deeper in the brain. Electronic implants mimicking the topographical and surface properties of brain vasculature may aid the stimulation and tracking of neural-circuit restoration following injury.

Minimally-Invasive and In-Vivo Hydrogel Patterning Method for In Situ Fabrication of Implantable Hydrogel Devices

Despite advances in a wide range of device applications of hydrogels, including implantable ones, a method for deploying patterned hydrogel devices into the body in a minimally-invasive manner is not available yet. However, in situ patterning of the hydrogel in vivo has an obvious advantage, by which incision surgery for implantation of the hydrogel device can be avoided. Here, a minimally-invasive and in vivo hydrogel patterning method for in situ fabrication of implantable hydrogel devices is presented. The sequential application of injectable hydrogels and enzymes, with assistance of minimally-invasive surgical instruments, enables the in vivo and in situ hydrogel patterning. This patterning method can be achieved by adopting an appropriate combination of the sacrificial mold hydrogel and the frame hydrogel, in consideration of unique material properties of the hydrogels such as high softness, facile mass transfer, biocompatibility, and diverse crosslinking mechanisms. In vivo and in situ patterning of the hydrogels functionalized with nanomaterials is also demonstrated to fabricate the wireless heater and tissue scaffold, showcasing broad applicability of the patterning method.

A flexible omnidirectional rotating magnetic array for MRI-safe transdermal wireless energy harvesting through flexible electronics

Magnetic resonance imaging (MRI)-safe implantable wireless energy harvester offers substantial benefits to patients suffering from brain disorders, hearing impairment, and arrhythmias. However, rigid magnets in cutting-edge systems with limited numbers of rotation axis impose high risk of device dislodgement and magnet failure. Here, a flexible omnidirectional rotating magnetic array (FORMA) and a flexible MRI-safe implantable wireless energy-harvesting system have been developed. Miniaturized flexible magnetic balls 1 millimeter in diameter achieved by molding three-dimensional printed templates can rotate freely in elastomer cavities and supply a magnetic force of 2.14 Newtons at a distance of 1 millimeter between an implantable receiver and a wearable transceiver. The system can work stably under an acceleration of 9g and obtain a power output of 15.62 decibel milliwatts at a transmission frequency of 8 megahertz. The development of the FORMA may lead to life-long flexible and batteryless implantable systems and offers the potential to promote techniques for monitoring and treating acute and chronic diseases.

Neurotechnology for Pain

Neurotechnologies for treating pain rely on electrical stimulation of the central or peripheral nervous system to disrupt or block pain signaling and have been commercialized to treat a variety of pain conditions. While their adoption is accelerating, neurotechnologies are still frequently viewed as a last resort, after many other treatment options have been explored. We review the pain conditions commonly treated with electrical stimulation, as well as the specific neurotechnologies used for treating those conditions. We identify barriers to adoption, including a limited understanding of mechanisms of action, inconsistent efficacy across patients, and challenges related to selectivity of stimulation and off-target side effects. We describe design improvements that have recently been implemented, as well as some cutting-edge technologies that may address the limitations of existing neurotechnologies. Addressing these challenges will accelerate adoption and change neurotechnologies from last-line to first-line treatments for people living with chronic pain.

Deployment of an electrocorticography system with a soft robotic actuator

Electrocorticography (ECoG) is a minimally invasive approach frequently used clinically to map epileptogenic regions of the brain and facilitate lesion resection surgery and increasingly explored in brain-machine interface applications. Current devices display limitations that require trade-offs among cortical surface coverage, spatial electrode resolution, aesthetic, and risk consequences and often limit the use of the mapping technology to the operating room. In this work, we report on a scalable technique for the fabrication of large-area soft robotic electrode arrays and their deployment on the cortex through a square-centimeter burr hole using a pressure-driven actuation mechanism called eversion. The deployable system consists of up to six prefolded soft legs, and it is placed subdurally on the cortex using an aqueous pressurized solution and secured to the pedestal on the rim of the small craniotomy. Each leg contains soft, microfabricated electrodes and strain sensors for real-time deployment monitoring. In a proof-of-concept acute surgery, a soft robotic electrode array was successfully deployed on the cortex of a minipig to record sensory cortical activity. This soft robotic neurotechnology opens promising avenues for minimally invasive cortical surgery and applications related to neurological disorders such as motor and sensory deficits.

Accessing the brain with soft deployable electrocorticography arrays

Soft robotics facilitates the deployment of large radial electrode arrays on the brain cortex through small craniotomies.

4D-Printed Soft and Stretchable Self-Folding Cuff Electrodes for Small-Nerve Interfacing

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.

Fluidic enabled bioelectronic implants: opportunities and challenges

Bioelectronic implants are increasingly facilitating novel strategies for clinical diagnosis and treatment. The integration of fluidic technologies into such implants enables new complementary routes for sensing and therapy alongside electrical interaction. Indeed, these two technologies, electrical and fluidic, can work synergistically in a bioelectronics implant towards the fabrication of a complete therapeutic platform. In this perspective article, the leading applications of fluidic enabled bioelectronic implants are highlighted and methods of operation and material choices are discussed. Furthermore, a forward-looking perspective is offered on emerging opportunities as well as critical materials and technological challenges.

X-Ray Markers for Thin Film Implants

Implantable electronic medical devices are used in functional mapping of the brain before surgery and to deliver neuromodulation for the treatment of neurological and neuropsychiatric disorders. Their electrode arrays are assembled by hand, and this leads to bulky form factors with limited flexibility and low electrode counts. Thin film implants, made using microfabrication techniques, are emerging as an attractive alternative, as they offer dramatically improved conformability and enable high density recording and stimulation. A major limitation of these devices, however, is that they are invisible to fluoroscopy, the most common method used to monitor the insertion of implantable electrodes. Here, the development of mechanically flexible X-ray markers using bismuth- and barium-infused elastomers is reported. Their X-ray attenuation properties in human cadavers are explored and it is shown that they are biocompatible in cell cultures. It is further shown that they do not distort magnetic resonance imaging images and their integration with thin film implants is demonstrated. This work removes a key barrier for the adoption of thin film implants in brain mapping and in neuromodulation.

Materials for Implantable Surface Electrode Arrays: Current Status and Future Directions

Surface electrode arrays are mainly fabricated from rigid or elastic materials, and precisely manipulated ductile metal films, which offer limited stretchability. However, the living tissues to which they are applied are nonlinear viscoelastic materials, which can undergo significant mechanical deformation in dynamic biological environments. Further, the same arrays and compositions are often repurposed for vastly different tissues rather than optimizing the materials and mechanical properties of the implant for the target application. By first characterizing the desired biological environment, and then designing a technology for a particular organ, surface electrode arrays may be more conformable, and offer better interfaces to tissues while causing less damage. Here, the various materials used in each component of a surface electrode array are first reviewed, and then electrically active implants in three specific biological systems, the nervous system, the muscular system, and skin, are described. Finally, the fabrication of next-generation surface arrays that overcome current limitations is discussed.

Analysis of the Therapeutic Effect and Prognostic Factors of 126 Patients With Hypertensive Cerebral Hemorrhage Treated by Soft-Channel Minimally Invasive Puncture and Drainage

Background

Surgery is the main method for the clinical treatment of hypertensive cerebral hemorrhage. Traditional craniotomy faces the disadvantages of the long operation time, easy to cause secondary injury to patients during the operation, and prone to infection after the operation, which is not conducive to the rehabilitation of patients. At present, it is urgent to find a surgical scheme, which can clear hematoma in time, protect brain tissue, and effectively reduce surgical trauma in the clinic.

Materials and Methods

The case database of our hospital was consulted, and the clinical data of patients with hypertensive intracerebral hemorrhage (HICH) treated with soft channel minimally invasive puncture and drainage from February 2018 to October 2021 were retrospectively analyzed. Patients were evaluated for efficacy, and the changes in serum C-reactive protein (CRP), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), homocysteine (Hcy), endothelin (ET), and vasopressin (AVP) levels before surgery, 3 days after surgery, and 7 days after surgery were analyzed. Clinical data were collected and Logistic regression was used to analyze the prognostic factors.

Results

Finally, according to the inclusion and exclusion criteria, 126 patients were selected as the research object. Among them, there were 24 cases (19.05%) of recovery, 47 cases (37.30%) of markedly effective, 34 cases (26.98%) of effective, 11 cases (8.73%) of ineffective, and 10 cases (7.94%) of death. The total effective rate was 83.33%. The hematoma was basically removed in 116 cases (92.06%). The average evacuation time of hematoma was (7.82 ± 1.63) days. Post-operative intracranial infection occurred in 2 cases (1.59%) and post-operative rebleeding occurred in 5 cases (3.97%). The average hospital stay was (34.16 ± 16.59) days. Serum CRP, TNF-α, IL-6, Hcy, ET, and AVP levels of all patients on the third and seventh days after surgery were lower than those before surgery, and those on the seventh day after surgery were lower than those on the third day after surgery (p < 0.05). The differences in pre-operative Glasgow Coma Scale (GCS) score, bleeding volume, ventricular rupture, complicated cerebral hernia, and attack time to surgery between the good prognosis group and the bad prognosis group were statistically significant (p < 0.05). Pre-operative GCS score, bleeding volume, ventricular rupture, complicated cerebral hernia, and onset time to surgery were all independent factors that affect the prognosis of patients (p < 0.05).

Conclusion

Soft-channel minimally invasive puncture and drainage treatment of HICH has a significant effect, which is conducive to the complete removal of hematoma, reducing hospitalization time, while adjusting the balance and stability of various cytokines, and improving patient prognosis. Pre-operative GCS score, bleeding volume, rupture into the ventricle, complicated cerebral hernia, and time from onset to operation are all independent factors that affect the prognosis of patients.

Flexible Electronics and Devices as Human-Machine Interfaces for Medical Robotics

Medical robots are invaluable players in non-pharmaceutical treatment of disabilities. Particularly, using prosthetic and rehabilitation devices with human-machine interfaces can greatly improve the quality of life for impaired patients. In recent years, flexible electronic interfaces and soft robotics have attracted tremendous attention in this field due to their high biocompatibility, functionality, conformability, and low-cost. Flexible human-machine interfaces on soft robotics will make a promising alternative to conventional rigid devices, which can potentially revolutionize the paradigm and future direction of medical robotics in terms of rehabilitation feedback and user experience. In this review, the fundamental components of the materials, structures, and mechanisms in flexible human-machine interfaces are summarized by recent and renowned applications in five primary areas: physical and chemical sensing, physiological recording, information processing and communication, soft robotic actuation, and feedback stimulation. This review further concludes by discussing the outlook and current challenges of these technologies as a human-machine interface in medical robotics.

Spinal cord bioelectronic interfaces: opportunities in neural recording and clinical challenges

Bioelectronic stimulation of the spinal cord has demonstrated significant progress in restoration of motor function in spinal cord injury (SCI). The proximal, uninjured spinal cord presents a viable target for the recording and generation of control signals to drive targeted stimulation. Signals have been directly recorded from the spinal cord in behaving animals and correlated with limb kinematics. Advances in flexible materials, electrode impedance and signal analysis will allow SCR to be used in next-generation neuroprosthetics. In this review, we summarize the technological advances enabling progress in SCR and describe systematically the clinical challenges facing spinal cord bioelectronic interfaces and potential solutions, from device manufacture, surgical implantation to chronic effects of foreign body reaction and stress-strain mismatches between electrodes and neural tissue. Finally, we establish our vision of bi-directional closed-loop spinal cord bioelectronic bypass interfaces that enable the communication of disrupted sensory signals and restoration of motor function in SCI.