Stimulation and Repair of Peripheral Nerves Using Bioadhesive Graft-Antenna

Effect of Brief Electrical Stimulation on Cell Biomechanics in Hereditary Sensory Neuropathy

SH-SY5Y neuroblastoma cells are widely used to model neurodegenerative disorders like Alzheimer's, Parkinson's, Huntington's, and Hereditary Sensory Neuropathy type 1A (HSN-1A), a peripheral nerve condition causing axon degeneration and sensory loss. A cell model of HSN-1A is developed by overexpressing wild-type and mutant SPTLC1 genes (C133W, C133Y, V144D). Cells are cultured on plastic and gold substrates, with brief electrical stimulation applied to the gold-grown cells. Atomic force microscopy (AFM) is used to measure Young's modulus, indentation, and energy dissipation. Finite Element Method and non-linear modeling validate the results. In the absence of stimulation, mutant cells show lower stiffness compared to non-transfected cells, indicating a direct biomechanical impact of the mutations. Brief electrical stimulation significantly increases the stiffness of mutant cells, particularly in C133W (99%), C133Y (100%), and V144D (111%) variants, despite the mutations. Energy dissipation of stimulated V144D cells decreases to levels comparable to untreated non-transfected cells. The simulations support the AFM measurements, demonstrating that brief electrical stimulation can partially reverse the biomechanical effects of gene mutations.

A Systematic Review to Compare Electrical, Magnetic, and Optogenetic Stimulation for Peripheral Nerve Repair

The purpose of this systematic review was to assess the currently available evidence for the use of external stimulation to modulate neural activity and promote peripheral nerve regeneration. The most common external stimulations are electrical stimulation (ES), optogenetic stimulation (OS), and magnetic stimulation (MS). Understanding the comparative effectiveness of these stimulation methods is pivotal in advancing therapeutic interventions for peripheral nerve injuries. This systematic review focused on these three external stimulation modalities as potential strategies to enhance peripheral nerve repair (PNR). We used the Preferred Reporting Items for Systematic Reviews and Meta-Analyses framework to systematically evaluate and compare the efficiency of ES, OS, and MS in PNR. The review included studies published between 2018 and 2023 using ES, OS, or MS for PNR focused on enhancing recovery of peripheral nerve injuries in rodent models identified through PubMed and Google Scholar. The search strategies and inclusion criteria identified 19 studies (13 ES, 4 OS, and 2 MS) for detailed analysis, focusing on critical parameters such as functional recovery, histological outcomes, and electrophysiological data. Although ES demonstrated a consistent improvement in all the analyses, high-frequency repetitive MS (HFr-MS) emerged as a promising modality. HFr-MS demonstrated accelerated PNR, as histological and electrophysiological evidence indicated. In contrast, OS exhibited superior functional recovery outcomes. Notable limitations include constrained MS and OS data sets and the challenge of comparing relative improvements because of methodological diversity in evaluation techniques. Our findings underscore the potential of HFr-MS and OS in PNR while emphasizing the critical need for standardized testing protocols to facilitate meaningful cross-study comparisons. External stimulations have the potential to improve functional recovery in patients with nerve injury.

Advancements in stimulation therapies for peripheral nerve regeneration

Soft-tissue injuries affecting muscles, nerves, vasculature, tendons, and ligaments often diminish the quality of life due to pain, loss of function, and financial burdens. Both natural healing and surgical interventions can result in scarring, which potentially may impede functional recovery and lead to persistent pain. Scar tissue, characterized by a highly disorganized fibrotic extracellular matrix, may serve as a physical barrier to regeneration and drug delivery. While approaches such as drugs, biomaterials, cells, external stimulation, and other physical forces show promise in mitigating scarring and promoting regenerative healing, their implementation remains limited and challenging. Ultrasound, laser, electrical, and magnetic forms of external stimulation have been utilized to promote soft tissue as well as neural tissue regeneration. After stimulation, neural tissues experience increased proliferation of Schwann cells, secretion of neurotropic factors, production of myelin, and growth of vasculature, all aimed at supporting axon regeneration and innervation. Yet, the outcomes of healing vary depending on the pathophysiology of the damaged nerve, the timing of stimulation following injury, and the specific parameters of stimulation employed. Increased treatment intensity and duration have been noted to hinder the healing process by inducing tissue damage. These stimulation modalities, either alone or in combination with nerve guidance conduits and scaffolds, have been demonstrated to promote healing. However, the literature currently lacks a detailed understanding of the stimulation parameters used for nerve healing applications. In this article, we aim to address this gap by summarizing existing reports and providing an overview of stimulation parameters alongside their associated healing outcomes.

Millimetric devices for nerve stimulation: a promising path towards miniaturization

Nerve stimulation is a rapidly developing field, demonstrating positive outcomes across several conditions. Despite potential benefits, current nerve stimulation devices are large, complicated, and are powered via implanted pulse generators. These factors necessitate invasive surgical implantation and limit potential applications. Reducing nerve stimulation devices to millimetric sizes would make these interventions less invasive and facilitate broader therapeutic applications. However, device miniaturization presents a serious engineering challenge. This review presents significant advancements from several groups that have overcome this challenge and developed millimetric-sized nerve stimulation devices. These are based on antennas, mini-coils, magneto-electric and opto-electronic materials, or receive ultrasound power. We highlight key design elements, findings from pilot studies, and present several considerations for future applications of these devices.

Sticky and Strain-Gradient Artificial Epineurium for Sutureless Nerve Repair in Rodents and Nonhuman Primates

The need for the development of soft materials capable of stably adhering to nerve tissues without any suturing followed by additional damages is at the fore at a time when success in postoperative recovery depends largely on the surgical experience and/or specialized microsuturing skills of the surgeon. Despite fully recognizing such prerequisite conditions, designing the materials with robust adhesion to wet nerves as well as acute/chronic anti-inflammation remains to be resolved. Herein, a sticky and strain-gradient artificial epineurium (SSGAE) that overcomes the most critically challenging aspect for realizing sutureless repair of severely injured nerves is presented. In this regard, the SSGAE with a skin-inspired hierarchical structure entailing strain-gradient layers, anisotropic Janus layers including hydrophobic top and hydrophilic bottom surfaces, and synergistic self-healing capabilities enables immediate and stable neurorrhaphy in both rodent and nonhuman primate models, indicating that the bioinspired materials strategy significantly contributes to translational medicine for effective peripheral nerve repair.

Investigation of the mechanisms for wireless nerve stimulation without active electrodes

Electric-field stimulation of neuronal activity can be used to improve the speed of regeneration for severed and damaged nerves. Most techniques, however, require invasive electronic circuitry which can be uncomfortable for the patient and can damage surrounding tissue. A recently suggested technique uses a graft-antenna-a metal ring wrapped around the damaged nerve-powered by an external magnetic stimulation device. This technique requires no electrodes and internal circuitry with leads across the skin boundary or internal power, since all power is provided wirelessly. This paper examines the microscopic basic mechanisms that allow the magnetic stimulation device to cause neural activation via the graft-antenna. A computational model of the system was created and used to find that under magnetic stimulation, diverging electric fields appear at the metal ring's edges. If the magnetic stimulation is sufficient, the gradients of these fields can trigger neural activation in the nerve. In-vivo measurements were also performed on rat sciatic nerves to support the modeling finding that direct contact between the antenna and the nerve ensures neural activation given sufficient magnetic stimulation. Simulations also showed that the presence of a thin gap between the graft-antenna and the nerve does not preclude neural activation but does reduce its efficacy.

A Bioinspired Self-Healing Conductive Hydrogel Promoting Peripheral Nerve Regeneration

The development of self-healing conductive hydrogels is critical in electroactive nerve tissue engineering. Typical conductive materials such as polypyrrole (PPy) are commonly used to fabricate artificial nerve conduits. Moreover, the field of tissue engineering has advanced toward the use of products such as hyaluronic acid (HA) hydrogels. Although HA-modified PPy films are prepared for various biological applications, the cell-matrix interaction mechanisms remain poorly understood; furthermore, there are no reports on HA-modified PPy-injectable self-healing hydrogels for peripheral nerve repair. Therefore, in this study, a self-healing electroconductive hydrogel (HASPy) from HA, cystamine (Cys), and pyrrole-1-propionic acid (Py-COOH), with injectability, biodegradability, biocompatibility, and nerve-regenerative capacity is constructed. The hydrogel directly targets interleukin 17 receptor A (IL-17RA) and promotes the expression of genes and proteins relevant to Schwann cell myelination mainly by activating the interleukin 17 (IL-17) signaling pathway. The hydrogel is injected directly into the rat sciatic nerve-crush injury sites to investigate its capacity for nerve regeneration in vivo and is found to promote functional recovery and remyelination. This study may help in understanding the mechanism of cell-matrix interactions and provide new insights into the potential use of HASPy hydrogel as an advanced scaffold for neural regeneration.

Electrical stimulation for the treatment of spinal cord injuries: A review of the cellular and molecular mechanisms that drive functional improvements

Spinal cord injury (SCI) is a devastating condition that causes severe loss of motor, sensory and autonomic functions. Additionally, many individuals experience chronic neuropathic pain that is often refractory to interventions. While treatment options to improve outcomes for individuals with SCI remain limited, significant research efforts in the field of electrical stimulation have made promising advancements. Epidural electrical stimulation, peripheral nerve stimulation, and functional electrical stimulation have shown promising improvements for individuals with SCI, ranging from complete weight-bearing locomotion to the recovery of sexual function. Despite this, there is a paucity of mechanistic understanding, limiting our ability to optimize stimulation devices and parameters, or utilize combinatorial treatments to maximize efficacy. This review provides a background into SCI pathophysiology and electrical stimulation methods, before exploring cellular and molecular mechanisms suggested in the literature. We highlight several key mechanisms that contribute to functional improvements from electrical stimulation, identify gaps in current knowledge and highlight potential research avenues for future studies.

Chitosan adhesives with sub-micron structures for photochemical tissue bonding

We describe a method for fabricating biocompatible chitosan-based adhesives with sub-micron structures to enhance tissue bonding. This procedure avoids coating and chemical modification of structures and requires a simple drop-casting step for the adhesive film formation. Chitosan thin films (27±3 μm) were fabricated with sub-micron pillars (rectangular cuboid with height ∼150 nm, square dimension ∼1 μm and pitch ∼2 μm) or holes (diameter ~500 nm or ~1 μm, depth ~100 or 400 nm, pitch of 1 or 2 μm). Polydimethylsiloxane moulds were used as negative templates for the adhesive solution that was cast and then allowed to dry to form thin films. These were applied on bisected rectangular strips of small sheep intestine and photochemically bonded by a green laser (λ= 532 nm, irradiance ∼110 J/cm2). The tissue repair was subsequently measured using a computer-interfaced tensiometer. The mould sub-micron structures were reproduced in the chitosan adhesive with high fidelity. The adhesive with pillars achieved the highest bonding strength (17.1±1.2 kPa) when compared to the adhesive with holes (13.0±1.3 kPa, p<0.0001, one-way ANOVA, n=15). The production of chitosan films with patterned pillars or holes in the sub-micron range was demonstrated, using a polydimethylsiloxane mould and a single drop-casting step. This technique is potentially scalable to produce adhesives of larger surface areas.

The effect of transcranial magnetic stimulation on the recovery of attention and memory impairment following stroke: a systematic review and meta-analysis

BACKGROUND

Previous studies indicated inconsistent results for the treatment effect of repetitive transcranial magnetic stimulation (rTMS) on attention and memory impairment following stroke.

METHODS

Randomized controlled trials (RCTs) on TMS for the treatment of stroke were retrieved from Online databases. Data were analyzed by RevMan 5.3 software.

RESULTS

Ten RCTs performed in China were included, with a total of 591 younger post-stroke patients ranging in age from their 40s to their 60s. The meta-analysis indicated that TMS could significantly improve the recovery of cognitive impairment following a stroke, according to the Montreal Cognitive Assessment (MoCA) score (8 studies, MD = 2.69, 95% CI: 1.44 to 3.95, P < 0.0001), the Rivermead Behavioral Memory Test (RBMT) score (7 studies, MD = 1.74, 95% CI:1.13 to 2.34, P < 0.00001), and the Modified Barthel Index (MBI) for Activities of Daily Living (3 studies, MD = 8.83, 95% CI:5.34 to 12.32, P < 0.00001). Sub-group analysis of MoCA and RBMT suggested that a low-frequency (1 Hz) stimulation exhibited similar effect with a higher-frequency (10 Hz) treatment.

DISCUSSION

TMS might effectively improve the attention and memory impairment of stroke patients without increasing side effects. But this effect needs to be verified by more multi-center, high-quality, large-sample, rigorously designed RCTs.

A Review on the Technological Advances and Future Perspectives of Axon Guidance and Regeneration in Peripheral Nerve Repair

Despite a significant advance in the pathophysiological understanding of peripheral nerve damage, the successful treatment of large nerve defects remains an unmet medical need. In this article, axon growth guidance for peripheral nerve regeneration was systematically reviewed and discussed mainly from the engineering perspective. In addition, the common approaches to surgery, bioengineering approaches to emerging technologies such as optogenetic stimulation and magnetic stimulation for functional recovery were discussed, along with their pros and cons. Additionally, clear future perspectives of axon guidance and nerve regeneration were addressed.

Effective photodynamic treatment of Trichophyton species with Rose Bengal

Photodynamic therapy (PDT) with Rose Bengal has previously achieved eradication of Trichophyton rubrum infections causing toenail onychomycosis; however, its antifungal activity against other clinically relevant dermatophytes has yet to be studied. Here, we test the efficacy of PDT using Rose Bengal (140 μM) and 532 nm irradiation (101 J/cm² ) against Trichophyton mentagrophytes and Trichophyton interdigitale spores, in comparison to T. rubrum. A significant reduction (>99%) of T. mentagrophytes and T. interdigitale was observed, while actual eradication of viable T. rubrum was achieved (99.99%). Laser irradiation alone inhibited growth of T. rubrum (55.2%) and T. mentagrophytes (45.2%) significantly more than T. interdigitale (25.5%) (P = .0086), which may indicate an increased presence of fungal pigments, xanthomegnin and melanin. The findings suggest that Rose Bengal-PDT can act against a broader spectrum of fungal pathogens, and with continued development may be employed in a wider range of clinical antifungal applications.