3D Printed Stem‐Cell Derived Neural Progenitors Generate Spinal Cord Scaffolds

A bioengineered spinal cord is fabricated via extrusion‐based multimaterial 3D bioprinting, in which clusters of induced pluripotent stem cell (iPSC)‐derived spinal neuronal progenitor cells (sNPCs) and oligodendrocyte progenitor cells (OPCs) are placed in precise positions within 3D printed biocompatible scaffolds during assembly. The location of a cluster of cells, of a single type or multiple types, is controlled using a point‐dispensing printing method with a 200 µm center‐to‐center spacing within 150 µm wide channels. The bioprinted sNPCs differentiate and extend axons throughout microscale scaffold channels, and the activity of these neuronal networks is confirmed by physiological spontaneous calcium flux studies. Successful bioprinting of OPCs in combination with sNPCs demonstrates a multicellular neural tissue engineering approach, where the ability to direct the patterning and combination of transplanted neuronal and glial cells can be beneficial in rebuilding functional axonal connections across areas of central nervous system (CNS) tissue damage. This platform can be used to prepare novel biomimetic, hydrogel‐based scaffolds modeling complex CNS tissue architecture in vitro and harnessed to develop new clinical approaches to treat neurological diseases, including spinal cord injury.     

Training Neural Stem Cells on Functional Collagen Scaffolds for Severe Spinal Cord Injury Repair

Neural stem cells (NSCs) transplantation is regarded as a promising therapeutic strategy to treat severe spinal cord injury (SCI) by compensating the neuronal loss. However, significant challenges including long‐term survival, directed neuronal differentiation, and functional integration of the transplanted NSCs and their progenies within the host spinal cord are yet to be solved. In this study, NSCs are trained on differently modified collagen scaffolds to increase their neuronal differentiation rate when cultured under the simulated SCI microenvironment. Then, a functional scaffold is screened out, on which the cultured NSCs show high neuronal differentiation rate and generate both sensory and motor mature neurons. Subsequently, that NSC seeded functional scaffold is transplanted into a rat severe SCI model. The results show that higher endogenous neurogenesis efficiency as well as in vivo survival and neuronal differentiation rate of the grafted NSCs are observed. Moreover, both sensory and motor neurons are found to be differentiated from the grafted NSCs in the lesion site and those newly generated neurons can functionally interact with each other and the host neurons. Taken together, the in vitro training systems for modulating the differentiation profiles of NSCs are instructive and exhibit strong potentials for SCI treatments.     

Two-Dimensional-Germanium Phosphide-Reinforced Conductive and Biodegradable Hydrogel Scaffolds Enhance Spinal Cord Injury Repair

Developing biodegradable conductive hydrogels is of great importance for the repair of electroactive tissues, such as myocardium, skeletal muscle, and nerves. However, conventional conductive phase incorporation in composite hydrogels, such as polypyrrole, polyaniline, carbon nanotubes, graphene, and gold nanowires, which are non-degradable materials, will exist in the body as foreign matter. Herein, an injectable hydrogel based on the integration of conductive and biodegradable germanium phosphide (GeP) nanosheets into an adhesive hyaluronic acid-graft-dopamine (HA-DA) hydrogel matrix is explored, and the successful application of this biohybrid hydrogel in spinal cord injury (SCI) repair is demonstrated. The incorporation of polydopamine (PDA)-modified GeP nanosheets (GeP@PDA) into HA-DA hydrogel matrix significantly improves the conductivity of HA-DA/GeP@PDA hydrogels. The conductive HA-DA/GeP@PDA hydrogels can accelerate the differentiation of neural stem cells (NSC) into neurons in vitro. In a rat SCI complete transection model, the in vivo implanted HA-DA/GeP@PDA hydrogel is found to improve the recovery of locomotor function significantly. The immunohistofluorescence investigation suggests that the HA-DA/GeP@PDA hydrogels promote immune regulation, endogenous angiogenesis, and endogenous NSC neurogenesis in the lesion area. The strategy of integrating conductive and biodegradable GeP nanomaterials into an injectable hydrogel provides new insight into designing advanced biomaterials for SCI repair.     

Spinal Cord Implant Studies

A loaded probe technique was used to measure the current density distribution resulting from application of electrical current to the spinal cords of live anesthetized stumptail macaque monkeys and fresh human cadaver spinal cords via the electrode arrays of four commercially available spinal implant systems used for management of intractable pain.     

Nanofibrous Patches for Spinal Cord Regeneration

The difficulty in spinal cord regeneration is related to the inhibitory factors for axon growth and the lack of appropriate axon guidance in the lesion region. Here scaffolds are developed with aligned nanofibers for nerve guidance and drug delivery in the spinal cord. Blended polymers including poly(L ‐lactic acid) (PLLA) and poly(lactide‐co‐glycolide) (PLGA) are used to electrospin nanofibrous scaffolds with a two‐layer structure: aligned nanofibers in the inner layer and random nanofibers in the outer layer. Rolipram, a small molecule that can enhance cAMP (cyclic adenosine monophosphate) activity in neurons and suppress inflammatory responses, is immobilized onto nanofibers. To test the therapeutic effects of nanofibrous scaffolds, the nanofibrous scaffolds loaded with rolipram are used to bridge the hemisection lesion in 8‐week old athymic rats. The scaffolds with rolipram increase axon growth through the scaffolds and in the lesion, promote angiogenesis through the scaffold, and decrease the population of astrocytes and chondroitin sulfate proteoglycans in the lesion. Locomotor scale rating analysis shows that the scaffolds with rolipram significantly improved hindlimb function after 3 weeks. This study demonstrates that nanofibrous scaffolds offer a valuable platform for drug delivery for spinal cord regeneration.     

Multifunctional Hydroxyapatite Nanobelt Haystacks Integrated Neural Stem Cell Spheroid for Rapid Spinal Cord Injury Repair

Due to the unwarranted lifespan and differentiation, applying neural stem cells (NSCs) in spinal cord injury (SCI) remains challenging. In this study, 3D bioactive hydroxyapatite (HAp) nanobelt haystack-mouse NSC (mNSC) hybrid spheroids are customized in which the specific nanobelt haystack framework provided the structural function of hypoxia alleviation in the spherical core and biological process of neural differentiation promotion. Commodified with superparamagnetic ferroferric oxide (Fe₃O₄) nanoparticles and a polydopamine (PDA) coating, the HAp nanobelts are endowed with magnetic field-driven properties and enhanced cell-nanobelt adhesion. The engineered bioresponsive 3D nanobelt haystack-mNSC hybrid spheroids effectively repair SCI in vivo, showing new potential for stem cell therapy by incorporating nanomaterials in 3D culture based on cell-material interactions.     

Bioinspired Hydrogel Electrospun Fibers for Spinal Cord Regeneration

Fully simulating the components and microstructures of soft tissue is a challenge for its functional regeneration. A new aligned hydrogel microfiber scaffold for spinal cord regeneration is constructed with photocrosslinked gelatin methacryloyl (GelMA) and electrospinning technology. The directional porous hydrogel fibrous scaffold consistent with nerve axons is vital to guide cell migration and axon extension. The GelMA hydrogel electrospun fibers soak up water more than six times their weight, with a lower Young's modulus, providing a favorable survival and metabolic environment for neuronal cells. GelMA fibers further demonstrate higher antinestin, anti‐Tuj‐1, antisynaptophysin, and anti‐CD31 gene expression in neural stem cells, neuronal cells, synapses, and vascular endothelial cells, respectively. In contrast, anti‐GFAP and anti‐CS56 labeled astrocytes and glial scars of GelMA fibers are shown to be present in a lesser extent compared with gelatin fibers. The soft bionic scaffold constructed with electrospun GelMA hydrogel fibers not only facilitates the migration of neural stem cells and induces their differentiation into neuronal cells, but also inhibits the glial scar formation and promotes angiogenesis. Moreover, the scaffold with a high degree of elasticity can resist deformation without the protection of a bony spinal canal. The bioinspired aligned hydrogel microfiber proves to be efficient and versatile in triggering functional regeneration of the spinal cord.     

Neural Interface Devices: Spinal Cord Stimulation Technology

This review of spinal cord stimulation (SCS) and its technology begins with an overview of the history and background of electroanalgesia, from the use of electric fish in ancient times through the development of the first SCS devices. Discussion of the clinical goals of SCS as a treatment for neuropathic and ischemic pain includes accepted and emerging indications and focuses on various aspects of the technical goal of appropriate paresthesia coverage. While acknowledging that much remains to be discovered about the mechanisms of action of SCS, the review describes what is known about its neurochemical effects and summarizes the results of experimental and clinical studies that seek to illuminate why SCS is effective. After noting the importance and development of computer modeling studies that indicate ways to improve delivery of the electrical pulses, the review covers the advantages of various types of SCS electrodes and power generators and the use of computerized methods to optimize SCS therapy in individual patients and to provide information about the clinical performance of various types of equipment. Finally, this paper identifies important design issues and options as well as the challenges posed by various failure modes, by environmental and medical precautions, and by cost effectiveness and patient access issues.     

Spinal Cord Injury Detection and Monitoring Using Spectral Coherence

In this paper, spectral coherence (SC) is used to study the somatosensory evoked potential (SEP) signals in rodent model before and after spinal cord injury (SCI). The SC technique is complemented with the Basso, Beattie, and Bresnahan (BBB) behavior analysis method to help us assess the status of the motor recovery. SC can be used to follow the effects of SCI without any preinjury baseline information. In this study, adult female Fischer rats received contusion injury at T8 level with varying impact heights using the standard New York University impactor. The results show that the average SC between forelimb and hindlimb SEP signals before injury was relatively high ( ges0.7). Following injury, the SC between the forelimb and hindlimb SEP signals dropped to various levels (les0.7) corresponding to the severity of SCI. The SC analysis gave normalized quantifiable results for the evaluation of SCI and recovery thereafter using the forelimb signals as an effective control, without the need of any baseline data. This technique solves the problems associated with the commonly used time-domain analysis like the need of a trained neurophysiologist to interpret the data and the need for baseline data. We believe that both SC and BBB may provide a comprehensive and complementary picture of the health status of the spinal cord after injury. The presented method is applicable to SCIs not affecting the forelimb SEP signals.     

X-Ray Reconstruction of the Spinal Cord, Using Bone Suppression

In this paper, a new method is developed for obtaining an X-ray reconstruction of the soft tissue detail of the spinal canal. By removing the dominant effects of the bony vertebral body within the projection actual clinical data, higher quality images of the residual soft tissues components can be reconstructed. The intent is a direct visualization of the spinal cord without the need for water-soluble contrast (e.g., Metrizamide) to be installed through a lumbar or cervical puncture. This technique for bone suppression also has potential for improving visualization of the interior of the mastoid cavities in the head.     

Role of Trichocytic Keratins in Anti-Neuroinflammatory Effects After Spinal Cord Injury

Shifting microglia/macrophages to M2 anti-inflammatory phenotype is considered a pivotal therapeutic target for spinal cord injury (SCI). Keratin extracted from human hair exhibits anti-inflammatory properties. However, the differences among the 17 types of human hair keratins and their mechanisms of anti-inflammation remain poorly understood. In this study, the anti-inflammatory activity of 17 human hair keratins using a recombinant synthesis approach is explored. Distinct activities of microglia/macrophage phenotype modulation of 17 keratins are found through qRT-PCR analysis, and recombinant keratin 33A (RK33A) and RK35 display superior anti-inflammatory efficiency compared to other keratins. Immunofluorescence and flow cytometry reveals a significant effect of RK33A on the regulation of microglia/macrophages into an anti-inflammatory M2 phenotype. Subsequently, recombinant keratin 33A nanofiber (RKNF33A) is fabricated to evaluate its in vivo anti-inflammatory and nerve regeneration properties using the rat T9 spinal cord lateral hemisection model. The optimized keratin-based nanofiber shows outstanding performance in enhancing M2 polarization, reducing glial scarring, promoting nerve regeneration, and improving locomotor function recovery in SCI rats. Moreover, it is preliminarily found that RK33A regulates M2 microglia/macrophage polarization by upregulating the PI3K/AKT/mTOR signaling pathway. Together, this study reveals that trichocytic keratins exhibit distinct anti-inflammatory properties, providing a prospective treatment for SCI by modulating microglia/macrophage polarization.     

Functional Imaging of Spinal Cord Electrical Activity From Its Evoked Magnetic Field

This paper investigates dynamic source imaging of the spinal cord electrophysiological activity from its evoked magnetic field by applying the spatial filter version of standardized low-resolution brain electromagnetic tomography (sLORETA). Our computer simulation shows that the sLORETA-based spatial filter can reconstruct the four current sources typically associated with the elicitation of the spinal cord evoked magnetic field (SCEF). The results from animal experiments show that significant changes in the latency and intensity of the reconstructed volume current arise near the location of the artificial incomplete conduction block. The results from the human SCEF show that the SCEF source imaging can visualize the dynamics of the volume currents and other nerve electrical activity propagating along the human spinal cord. These experimental results demonstrate the potential of SCEF source imaging as a future clinical tool for diagnosing cervical spinal cord disorders.     

A 75-ch SQUID Biomagnetometer System for Human Cervical Spinal Cord Evoked Field

A 75-ch SQUID biomagnetometer system for the measurement of the cervical spinal cord evoked magnetic field (SCEF) was developed for the purpose of the noninvasive functional diagnosis of the spinal cord. The sensor array has 25 SQUID vector sensors arranged along the cylindrical surface to fit to the shape of the subject's neck. The magnetic fields, not only in the direction radial to the subject's body surface but also in the tangential direction, are observed in the area of 80 mm times 90 mm at one time. The dewar has a unique shape with a cylindrical main body and a protrusion from its side surface. The sensor array is installed in the protruded part. This design is optimized to detect magnetic signals at the back of the neck of the subject sitting in a reclining position. We applied the developed SQUID system to the cervical SCEF measurement of normal subjects who were given electric pulse stimulation to their median nerves at the wrists. The evoked magnetic signals were successfully detected at the cervixes of all subjects. A characteristic pattern of transition of the SCEF distribution was observed as a reproducible result and the signal components propagating along the spinal cord were found in the time varying SCEF distribution. We expect that the investigation of the propagating signal components would help to establish a noninvasive functional diagnosis of the spinal cord.     

Functional Neuromuscular Stimulation of the Respiratory Muscles for Patients With Spinal Cord Injury

Respiratory complication is a major cause of morbidity and mortality in patients with spinal cord injury (SCI). These complications arise partly due to the loss of supraspinal control over expiratory and/or inspiratory muscles caused by SCI. Functional neuromuscular stimulation of the respiratory muscles has been used to restore inspiratory and respiratory functions to these patients, helping them to reduce the incidence of respiratory complications and to have more normal lives. This paper covers three types of techniques for respiratory muscle stimulation: functional electric stimulation, functional magnetic stimulation, and semiconductor-based microstimulator stimulation. Functional electrical stimulation has been used to restore breathing to patients with spinal cord injury for several decades. It is a mature and reliable technology, and there are several commercial systems available. Functional magnetic stimulation of the respiratory muscles has been demonstrated to be an effective tool for producing cough in patients with SCI for nearly a decade. This is a safe and noninvasive technology that is well tolerated by most subjects. Semiconductor-based microstimulators have been widely publicized in recent years, and several clinical applications have been demonstrated, including the applications for restoring cough and breathing. This technology may eventually play a major role in respiratory muscle pacing.     

Engineering Neural Interfaces for Rehabilitation of Lower Limb Function in Spinal Cord Injured

Recent progress in neural interface technologies and demonstration of direct cortical control of robotic arm or computer cursor for simple movement has generated high expectation of rapid development of cortically controlled neuroprosthetics to improve motor function in subjects with severe neurological deficits. However, several challenging engineering and biological issues remain to be resolved before a practical system can be developed for patients to receive real benefit. The ability of neural systems to adapt to changes and learn new functions should be taken into consideration in the design and development of neuroprosthetics so that the two systems can cooperatively work together to accommodate continued changes (neural degeneration or functional improvement) in a human user. An intelligent neural interface should be able to activate residual function and facilitate adaptation and learning ability of the neural system. Current efforts in developing wireless and networked neural interfaces and utilizing smart materials and sensors will revolutionize the future design of neuroprosthetics and advance the investigation of brain function. This report reviews two recent projects in activating residual neural functions and investigating brain control of lower limb functions.     

Polymer Fiber Probes Enable Optical Control of Spinal Cord and Muscle Function In Vivo

Restoration of motor and sensory functions in paralyzed patients requires the development of tools for simultaneous recording and stimulation of neural activity in the spinal cord. In addition to its complex neurophysiology, the spinal cord presents technical challenges stemming from its flexible fibrous structure and repeated elastic deformation during normal motion. To address these engineering constraints, we developed highly flexible fiber probes, consisting entirely of polymers, for combined optical stimulation and recording of neural activity. The fabricated fiber probes exhibit low‐loss light transmission even under repeated extreme bending deformations. Using our fiber probes, we demonstrate simultaneous recording and optogenetic stimulation of neural activity in the spinal cord of transgenic mice expressing the light sensitive protein channelrhodopsin 2 (ChR2). Furthermore, optical stimulation of the spinal cord with the polymer fiber probes induces on‐demand limb movements that correlate with electromyographical (EMG) activity.     

Characteristics of Somatosensory Evoked Potentials Recorded over the Spinal Cord and Brain of Man

Evoked potentials were recorded from the skin over the lumbar and cervical portions of the spinal cord, and the scalp over the sensory cortex of the brain, using averaging techniques. Responses could be identified over the cauda equina and root entry zone in the lumbar spine to stimulation of the tibial nerve at the popliteal fossa. These responses had characteristics of nerve root and spinal cord events in their thresholds, timing, duration, and refractoriness. Stimulation of the median nerve at the wrist likewise resulted in recognizable responses over root entry portions of the cervical spinal cord. These later waves had a morphology suggestive of components arising from nerve plexus, nerve roots, and spinal cord. Responses recorded over the spinal cord were in the 1-10 ?V amplitude range. Tibial, peroneal and median nerve stimulation were used to elicit 1-20 ?V responses recorded over the cortex, which were found to be sensitive to the site, amplitude, and rate of stimulation.     

激光照射对急性脊髓损伤后脊髓再生的促进作用

建立大鼠皮质脊髓背侧束全横断模型,利用弱激光照射脊髓受损部位的皮肤,观察激光照射对急性脊髓损伤后脊髓再生的促进作用.30只SD大鼠,随机分成对照组和照射组.照射组:急性皮质脊髓背侧束全横断后15 min进行连续14 d采用弱激光照射脊髓受损部位的皮肤.对照组:急性皮质脊髓背侧束全横断后未行弱激光经皮照射治疗.术后两组分别于第3,7,14 d分别取材,用苏木精-伊红染色法(HE)染色和免疫荧光标记染色观察.实验发现,脊髓损伤后14 d,照射组的空洞及瘢痕形成面积小于对照组,有统计学差异(p<0.05);对照神经胶质酸性组蛋白(GFAP)和硫酸软骨素(CS)表达强烈分布紧密,照射组GFAP和CS56表达达微弱且分布稀疏;对照组少量神经微丝蛋白(NF)在损伤区周围,神经生长相关蛋白(GAP43)形态肿大变形分布紊乱,照射组大量成纤维丝状的NF分布在损伤区周围,并与GAP43相伴行.结果表明,脊髓损伤急性期采用弱激光照射脊髓受损部位的皮肤,可减少脊髓损伤后空洞形成,并促进轴突再生.