Biodegradable magnesium wire promotes regeneration of compressed sciatic nerves

Fabrication of GDNF-Gel/HA-Mg nerve conduit and its role in repairing peripheral nerve defects

Background

Magnesium (Mg) and its alloys are receiving increasing attention in peripheral nerve regeneration, but they were limited due to the low corrosion resistance and rapid degradation. In this study, GDNF-Gel/HA-Mg was prepared and its value in peripheral nerve defects repairment was explored both in vitro and in vivo.

Methods

A hydroxyapatite (HA) coating was first applied to the pure Mg surface, followed by the formation of gelatin methacrylate (GelMA) loaded with glial cell-derived neurotrophic factor (GDNF) on the HA-coated Mg surface. GDNF-Gel/HA-Mg corrosion resistance was explored. The effect of GDNF-Gel/HA-Mg conduit on Schwann cell proliferation and migration abilities were investigated. And sciatic nerve defects models were established to explored the role of GDNF-Gel/HA-Mg conduit in peripheral nerve defects repairment.

Findings

The electrochemical, immersion, and hydrogen evolution experiments indicated that the corrosion resistance in phosphate buffer saline (PBS) of pure Mg was significantly improved by the GDNF-Gel/HA coating. Cell cycle, Cell Count Kit-8 (CCK-8), and clone formation assays indicated that GDNF-Gel/HA-Mg promoted the proliferation of Schwann cells. Scratch and Transwell assay results demonstrated that GDNF-Gel/HA-Mg promoted Schwann cell migration ability dose-dependently. GDNF-Gel/HA-Mg was found to enhance the secretion of nerve growth factor (NGF) and the expression of p75NTR. Flow cytometry results showed that GDNF-Gel/HA-Mg could reduce H2O2-induced oxidative stress and Schwann cell apoptosis. GDNF-Gel/HA-Mg inhibited M1 macrophage polarization while facilitated M2 macrophage polarization in a concentration-dependent manner. The in vivo studies demonstrated that GDNF-Gel/HA-Mg conduit could significantly promote the regeneration and myelination of sciatic nerve, as well as the recovery of denervated gastrocnemius atrophy.

Interpretation

The GDNF-Gel/HA-Mg conduit prepared in this study exhibited good hydrophilicity and corrosion resistance and greatly enhanced the proliferation, migration, and invasion abilities of Schwann cells, as well as peripheral nerve regeneration.

The Impact of Chronic Magnesium Deficiency on Excitable Tissues-Translational Aspects

Neuromuscular excitability is a vital body function, and Mg2+ is an essential regulatory cation for the function of excitable membranes. Loss of Mg2+ homeostasis disturbs fluxes of other cations across cell membranes, leading to pathophysiological electrogenesis, which can eventually cause vital threat to the patient. Chronic subclinical Mg2+ deficiency is an increasingly prevalent condition in the general population. It is associated with an elevated risk of cardiovascular, respiratory and neurological conditions and an increased mortality. Magnesium favours bronchodilation (by antagonizing Ca2+ channels on airway smooth muscle and inhibiting the release of endogenous bronchoconstrictors). Magnesium exerts antihypertensive effects by reducing peripheral vascular resistance (increasing endothelial NO and PgI2 release and inhibiting Ca2+ influx into vascular smooth muscle). Magnesium deficiency disturbs heart impulse generation and propagation by prolonging cell depolarization (due to Na+/K+ pump and Kir channel dysfunction) and dysregulating cardiac gap junctions, causing arrhythmias, while prolonged diastolic Ca2+ release (through leaky RyRs) disturbs cardiac excitation-contraction coupling, compromising diastolic relaxation and systolic contraction. In the brain, Mg2+ regulates the function of ion channels and neurotransmitters (blocks voltage-gated Ca2+ channel-mediated transmitter release, antagonizes NMDARs, activates GABAARs, suppresses nAChR ion current and modulates gap junction channels) and blocks ACh release at neuromuscular junctions. Magnesium exerts multiple therapeutic neuroactive effects (antiepileptic, antimigraine, analgesic, neuroprotective, antidepressant, anxiolytic, etc.). This review focuses on the effects of Mg2+ on excitable tissues in health and disease. As a natural membrane stabilizer, Mg2+ opposes the development of many conditions of hyperexcitability. Its beneficial recompensation and supplementation help treat hyperexcitability and should therefore be considered wherever needed.

Influence of Magnesium Degradation on Schwannoma Cell Responses to Nerve Injury Using an In Vitro Injury Model

Nerve guidance conduits for peripheral nerve injuries can be improved using bioactive materials such as magnesium (Mg) and its alloys, which could provide both structural and trophic support. Therefore, we investigated whether exposure to Mg and Mg-1.6wt%Li thin films (Mg/Mg-1.6Li) would alter acute Schwann cell responses to injury. Using the RT4-D6P2T Schwannoma cell line (SCs), we tested extracts from freeze-killed cells (FKC) and nerves (FKN) as in vitro injury stimulants. Both FKC and FKN induced SC release of the macrophage chemoattractant protein 1 (MCP-1), a marker of the repair SC phenotype after injury. Next, FKC-stimulated cells exposed to Mg/Mg-1.6Li reduced MCP-1 release by 30%, suggesting that these materials could have anti-inflammatory effects. Exposing FKC-treated cells to Mg/Mg-1.6Li reduced the gene expression of the nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF), and myelin protein zero (MPZ), but not the p75 neurotrophin receptor. In the absence of FKC, Mg/Mg-1.6Li treatment increased the expression of NGF, p75, and MPZ, which can be beneficial to nerve regeneration. Thus, the presence of Mg can differentially alter SCs, depending on the microenvironment. These results demonstrate the applicability of this in vitro nerve injury model, and that Mg has wide-ranging effects on the repair SC phenotype.

The GDNF-gel/HA-Mg conduit promotes the repair of peripheral nerve defects by regulating PPAR-γ/RhoA/ROCK signaling pathway

Magnesium (Mg)-based conduits have gained more attention in repairing peripheral nerve defects. However, they are limited due to poor corrosion resistance and rapid degradation rate. To tackle this issue, glial cell line-derived neurotrophic factor (GDNF)- Gelatin methacryloyl (Gel)/hydroxylapatite (HA)-Mg nerve conduit was developed and implanted in sciatic nerve defect model in Sprague-Dawley (SD) rats. The sciatic functional index measurement showed that the GDNF-Gel/HA-Mg nerve conduit effectively promoted the recovery of sciatic nerve function. The pathological examination results showed that there were more regenerated nerve tissues in GDNF-Gel/HA-Mg group, with a higher number of regenerating axons, and the thickness of the myelin sheath was significantly larger than that of control group (NC group). Immunofluorescence results revealed that the GDNF-Gel/HA-Mg conduit significantly promoted the expression of genes associated with nerve repair. RNA-seq and molecular test results indicated that GDNF-Gel/HA-Mg might be involved in the repair of peripheral nerve defects by regulating PPAR-γ/RhoA/ROCK signaling pathway. Biological sciences; Neuroscience; Molecular neuroscience; Techniques in neuroscience.

Cell-Laden Scaffolds for Vascular-Innervated Bone Regeneration

For regeneration of highly vascularized and innervated tissues, like bone, simultaneous ingrowth of blood vessels and nerves is essential but largely neglected. To address this issue, a "pre-angiogenic" cell-laden scaffold with durable angiogenic functions is prepared according to the bioactivities of silicate bioceramics and the instructive effects of vascular cells on neurogenesis and bone repair. Compared with traditional cell-free scaffolds, the prepared cell-laden scaffolds printed with active cells and bioactive inks can support long-term cell survival and growth for three weeks. The long-lived scaffolds exhibited durable angiogenic capability both in vitro and in vivo. The pre-angiogenic scaffolds can induce the neurogenetic differentiation of neural cells and the osteogenic differentiation of mesenchymal stem cells by the synergistic effects of released bioactive ions and the ability of vascular cells to attract neurons. The enhanced bone regeneration with both vascularization and innervation is attributed to these physiological functions of the pre-angiogenic cell-laden scaffolds, which is defined as "vascular-innervated" bone regeneration. It is suggested that the concept of "vascular-innervated scaffolds" may represent the future direction of biomaterials for complex tissue/organ regeneration.

Photosensitive and Conductive Hydrogel Induced Innerved Bone Regeneration for Infected Bone Defect Repair

Repairing infected bone defects is a challenge in the field of orthopedics because of the limited self-healing capacity of bone tissue and the susceptibility of refractory materials to bacterial activity. Innervation is the initiating factor for bone regeneration and plays a key regulatory role in subsequent vascularization, ossification, and mineralization processes. Infection leads to necrosis of local nerve fibers, impeding the repair of infected bone defects. Herein, a biomaterial that can induce skeletal-associated neural network reconstruction and bone regeneration with high antibacterial activity is proposed for the treatment of infected bone defects. A photosensitive conductive hydrogel is prepared by incorporating magnesium-modified black phosphorus (BP@Mg) into gelatin methacrylate (GelMA). The near-infrared irradiation-based photothermal and photodynamic treatment of black phosphorus endows it with strong antibacterial activity, improving the inflammatory microenvironment and reducing bacteria-induced bone tissue damage. The conductive nanosheets and bioactive ions released from BP@Mg synergistically improve the migration and secretion of Schwann cells, promote neurite outgrowth, and facilitate innerved bone regeneration. In an infected skull defect model, the GelMA-BP@Mg hydrogel shows efficient antibacterial activity and promotes bone and CGRP⁺ nerve fiber regeneration. The phototherapy conductive hydrogel provides a novel strategy based on skeletal-associated innervation for infected bone defect repair.

A review of the diet, nutrients, and supplementation potential for the outcome augmentation in surgical treatment of peripheral nerve injuries

OBJECTIVE

Although the studies have shown the beneficial effects of diet, nutrition, and supplementation as an independent treatment modality, their roles are underestimated in the treatment of peripheral nerve injuries. This is in great part due to the development of efficient nerve repair techniques, combined with physical treatment and stimulation. To achieve the best possible functional recovery diet, nutrition, and supplementation should be implemented within a multidisciplinary approach. The aim of the study is to provide insight into the potentially beneficial effects of diet, nutrients, and supplementation, in the limitation of nerve damage and augmentation of the functional recovery after surgery in a review of human and animal studies.

METHODS

The data relating to the diet, nutrients, and supplementation effects on peripheral nerve injuries and their treatment was extracted from the previously published literature.

RESULTS

General balanced diet as well as obesity influence the initial nerve features prior to the injury. In the period following the injury, neuroprotective agents demonstrated beneficial effects prior to surgery, and immediately after the injury, while those potentiating nerve regeneration may be used after the surgical repair to complement the physical treatment and stimulation for improved functional recovery.

CONCLUSIONS

Standardized diet, nutrition, and supplementation recommendations and protocols may be of great importance for better nerve regeneration and functional recovery as a part of the multidisciplinary approach to achieve the best possible results in surgically treated patients with peripheral nerve injuries in the future.

Development of degradable magnesium-based metal implants and their function in promoting bone metabolism (A review)

Background

Use of degradable magnesium (Mg)-based metal implants in orthopaedic surgeries can avoid drawbacks associated with subsequent removal of the non-degradable metallic implants, reducing cost and trauma of patients. Although Mg has been applied in the clinic for orthopaedic treatment, the use of Mg-based metal implants is largely in the research phase. But its application is potentially beneficial in this context as it has been shown that Mg can promote osteogenesis and inhibit osteoclast activity.

Methods

A systematic literature search about “degradable magnesium (Mg)-based metal implants” was performed in PubMed and Web of Science. Meanwhile, relevant findings have been reviewed and quoted.

Results

In this review, we summarize the latest developments in Mg-based metal implants and their role in bone regeneration. We also review the various molecular mechanisms by which Mg ions regulate bone metabolic processes, including osteogenesis, osteoclast activity, angiogenesis, immunity, and neurology. Finally, we discuss the remaining research challenges and opportunities for Mg-based implants and their applications.

Conclusion

Currently, establishment of the in vitro and in vivo biological evaluation systems and phenotypic modification improvement of Mg-based implants are still needed. Clarifying the functions of Mg-based metal implants in promoting bone metabolism is beneficial for their clinical application.

The Translational potential of this article

All current reviews on Mg-based implants are mainly concerned with the improvement of Mg alloy properties or the progress of applications. However, there are few reviews that provides a systematic narrative on the effect of Mg on bone metabolism. This review summarized the latest developments in Mg-based metal implants and various molecular mechanisms of Mg ions regulating bone metabolism, which is beneficial to further promote the translation of Mg based implants in the clinic and is able to provide a strong basis for the clinical application of Mg based implants.

Magnesium-Encapsulated Injectable Hydrogel and 3D-Engineered Polycaprolactone Conduit Facilitate Peripheral Nerve Regeneration

Peripheral nerve injury is a challenging orthopedic condition that can be treated by autograft transplantation, a gold standard treatment in the current clinical setting. Nevertheless, limited availability of autografts and potential morbidities in donors hampers its widespread application. Bioactive scaffold-based tissue engineering is a promising strategy to promote nerve regeneration. Additionally, magnesium (Mg) ions enhance nerve regeneration; however, an effectively controlled delivery vehicle is necessary to optimize their in vivo therapeutic effects. Herein, a bisphosphonate-based injectable hydrogel exhibiting sustained Mg2+ delivery for peripheral nerve regeneration is developed. It is observed that Mg2+ promoted neurite outgrowth in a concentration-dependent manner by activating the PI3K/Akt signaling pathway and Sema5b. Moreover, implantation of polycaprolactone (PCL) conduits filled with Mg2+ -releasing hydrogel in 10 mm nerve defects in rats significantly enhanced axon regeneration and remyelination at 12 weeks post-operation compared to the controls (blank conduits or conduits filled with Mg2+ -absent hydrogel). Functional recovery analysis reveals enhanced reinnervation in the animals treated with the Mg2+ -releasing hydrogel compared to that in the control groups. In summary, the Mg2+ -releasing hydrogel combined with the 3D-engineered PCL conduit promotes peripheral nerve regeneration and functional recovery. Thus, a new strategy to facilitate the repair of challenging peripheral nerve injuries is proposed.

Magnesium Promotes the Regeneration of the Peripheral Nerve

Peripheral nerve injury is a common complication in trauma, and regeneration and function recovery are clinical challenges. It is indispensable to find a suitable material to promote peripheral nerve regeneration due to the limited capacity of peripheral nerve regeneration, which is not an easy task to design a material with good biocompatibility, appropriate degradability. Magnesium has captured increasing attention during the past years as suitable materials. However, there are little types of research on magnesium promoting peripheral nerve regeneration. In this review, we conclude the possible mechanism of magnesium ion promoting peripheral nerve regeneration and the properties and application of different kinds of magnesium-based biomaterials, such as magnesium filaments, magnesium alloys, and others, in which we found some shortcomings and challenges. So, magnesium can promote peripheral nerve regeneration with both challenge and potential.

The Role of Dietary Nutrients in Peripheral Nerve Regeneration

Peripheral nerves are highly susceptible to injuries induced from everyday activities such as falling or work and sport accidents as well as more severe incidents such as car and motorcycle accidents. Many efforts have been made to improve nerve regeneration, but a satisfactory outcome is still unachieved, highlighting the need for easy to apply supportive strategies for stimulating nerve growth and functional recovery. Recent focus has been made on the effect of the consumed diet and its relation to healthy and well-functioning body systems. Normally, a balanced, healthy daily diet should provide our body with all the needed nutritional elements for maintaining correct function. The health of the central and peripheral nervous system is largely dependent on balanced nutrients supply. While already addressed in many reviews with different focus, we comprehensively review here the possible role of different nutrients in maintaining a healthy peripheral nervous system and their possible role in supporting the process of peripheral nerve regeneration. In fact, many dietary supplements have already demonstrated an important role in peripheral nerve development and regeneration; thus, a tailored dietary plan supplied to a patient following nerve injury could play a non-negotiable role in accelerating and promoting the process of nerve regeneration.

Biosafety and biodegradation studies of AZ31B magnesium alloy carotid artery stent in vitro and in vivo

Biosafety of AZ31B magnesium (Mg) alloy and the effect of its degradation products on tissues, organs, and whole systems are highly needed to be evaluated before clinical application. This study serves a wide variety of safety evaluations of biodegradable AZ31B alloy on nerve cells. As a result of this in vitro study, the maximum aluminum (Al) ion and Mg ion concentrations in the medium were estimated to be 22 μmol/L and 2.75 mmol/L, respectively, during degradation. In addition, the corresponding cell mortality was observed to be 36% and lower than 5% according to the resistance curves of the cell to Mg and Al ions. Furthermore, the maximum Al ion and Mg ion concentrations in serum and cerebrospinal fluid were detected to be 26.1 μmol/L and 1.2 mmol/L, respectively, for 5 months implantation. Combining the result of in vivo dialysis with the result of ion tolerance assay experiments, the actual death rate of nerve cells is estimated between 4 and 10% in vivo, which is lower than the result of in vitro cytotoxicity evaluation. Moreover, no psychomotor disability during clinical studies is observed. Consequently, stent made of AZ31B alloy with surface treatment is feasible for carotid artery stenosis, and it is safe in terms of cell viability on the nervous system.

In vivo evaluation of bending strengths and degradation rates of different magnesium pin designs for oral stapler

Magnesium alloys have been potential biodegradable implants in the areas of bone, cardiovascular system, gastrointestinal tract, and so on. The purpose of this study is to evaluate Mg-2Zn alloy degradation as a potential suture material. The study included Sprague-Dawley (SD) rats in vivo. In 24 male SD rats, tests in the leg muscle were conducted using traditional surgical incision and insertion of magnesium alloys of different designs into the tissue. The material degradation topography, elemental composition, and strength of the pins were analyzed. This paper explores magnesium pins with different cross-sectional shapes and diameters to establish a suitable pin diameter and shape for use as an oral stapler, which must have a good balance of degradation rate and strength. The results showed there were good bending strengths over different degradation periods in groups with diameters of 0.8 mm and 0.5 mm, and no significantly different bending strength between the groups of triangle and round cross-section shapes with same diameter of 0.3 mm, although the degradation rate still needs to be improved.

Down-Regulated Expression of Magnesium Transporter Genes Following a High Magnesium Diet Attenuates Sciatic Nerve Crush Injury

BACKGROUND

Magnesium supplementation has potential for use in nerve regeneration. The expression of some magnesium transporter genes is reflective of the intracellular magnesium levels.

OBJECTIVE

To assess the expression of various magnesium transporter genes as they relate to neurological alterations in a sciatic nerve injury model.

METHODS

Sciatic nerve injury was induced in rats, which were then fed either basal or high magnesium diets. Magnesium concentrations and 5 magnesium transporter genes (SLC41A1, MAGT1, CNNM2, TRPM6, and TRPM7) were measured in the tissue samples.

RESULTS

The high magnesium diet attenuated cytoskeletal loss in a dose-dependent manner in isolated nerve explants. The high magnesium diet augmented nerve regeneration and led to the restoration of nerve structure, increased S-100, and neurofilaments. This increased regeneration was consistent with the improvement of neurobehavioral and electrophysiological assessment. The denervated muscle morphology was restored with the high magnesium diet, and that was also highly correlated with the increased expression of desmin and acetylcholine receptors in denervated muscle. The plasma magnesium levels were significantly elevated after the animals consumed a high magnesium diet and were reciprocally related to the down-regulation of CNNM2, MagT1, and SCL41A1 in the blood monocytes, nerves, and muscle tissues of the nerve crush injury model.

CONCLUSION

The increased plasma magnesium levels after consuming a high magnesium diet were highly correlated with the down-regulation of magnesium transporter genes in monocytes, nerves, and muscle tissues after sciatic nerve crush injury. The study findings suggest that there are beneficial effects of administering magnesium after a nerve injury.

Molecularly engineered metal-based bioactive soft materials - Neuroactive magnesium ion/polymer hybrids

The development of bioactive soft materials that can guide cell behavior and have biomimetic mechanical properties is an active and challenging topic in regenerative medicine. A common strategy to create a bioactive soft material is the integration of biomacromolecules with polymers. However, limited by their complex structures and sensitivity to temperature and chemicals, it is relatively difficult to maintain the bioactivity of biomacromolecules during their preparation, storage, and application. Here, a new kind of bioactive soft material based on the molecular integration of metal ions and polymers is designed and exemplified by a hybrid of magnesium ion (Mg²⁺) and poly(glycerol-sebacate-maleate) (PGSM-Mg). Mg²⁺ was firmly incorporated into PGSM molecules through a complexation interaction as evidenced by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). The PGSM matrix provided the soft nature and facile processing of the hybrid, which could serve as an injectable material and be fabricated into elastic porous three-dimensional (3D) scaffolds. The Mg²⁺ immobilized in the PGSM chain conferred neuroactivity to the resultant hybrid. PGSM-Mg exhibited adequate biodegradability and a sustained release of Mg²⁺. PGSM-Mg 3D scaffolds promoted the adhesion and proliferation of Schwann cells (SCs) more effectively than poly(lactic-co-glycolic acid) (PLGA) scaffolds. Furthermore, SCs on PGSM-Mg scaffolds expressed significantly more neural specific genes than those on PLGA, PGS, and PGSM, including nerve growth factor (NGF) and neurotrophic factor-3 (NTF3). All these results indicated that Mg²⁺ immobilized through molecular integration could efficiently regulate the bioactivity of polymers. In view of the wide availability, diverse bioactivity, and high stability of metal ions, the strategy of molecular coupling of metal ions and polymers is expected to be a new general approach to construct bioactive soft materials. STATEMENT OF SIGNIFICANCE: Bioactive soft materials are designed on the basis of the molecular integration of metal ions and polymers. Immobilized metal ions offer a new way to endow bioactivity to polymers. Different from biomolecules such as proteins and genes, metal ions are quite stable and can resist harsh processing conditions. Further, the polymeric matrix provides the soft nature and facile processing of the hybrid. Different from stiff metal-containing inorganic materials, the hybrid is a biomimetic soft material and can be readily processed just like its polymer precursor under mild conditions. In view of the diversity of metal ions and polymers, this strategy is expected to be a new powerful and general approach to construct bioactive soft materials for a wide range of biomedical applications.

Effect of chitosan combined with hyaluronate on promoting the recovery of postoperative facial nerve regeneration and function in rabbits

To determine better solutions for postoperative nerve functional recovery, the effects of chitosan and hyaluronate on perineural scar formation and neural function recovery were investigated in 40 rabbits. Rabbits were randomized into 4 groups: A (chitosan), B (chitosan + hyaluronate), C (hyaluronate) and D (control). The rabbits underwent the same parotidectomy surgery, but different materials were used to cover the operated nerves. By evaluating specific indicators, including vibrissae motion tests, neural electrophysiological examinations and extraneural examinations, it was revealed that the amplitude of vibrissae motion of all groups had increased 6 weeks after surgery. The recovery of Group B was superior compared with all other groups at 4 and 12 weeks post-surgery; however no significant differences were detected. Group B exhibited a great number of nerve fibers, thicker myelin sheath and greater nerve conduction velocity. In summary, the use of a chitosan conduit combined with sodium hyaluronate gel may prevent perineural scar formation in facial nerves and promote nerve functional recovery.