Assessing the combination of magnetic field stimulation, iron oxide nanoparticles, and aligned electrospun fibers for promoting neurite outgrowth from dorsal root ganglia in vitro

Palliative effect of rotating magnetic field on glucocorticoid-induced osteonecrosis of the femoral head in rats by regulating osteoblast differentiation

With the substantial increase in the overuse of glucocorticoids (GCs) in clinical medicine, the prevalence of glucocorticoid-induced osteonecrosis of the femoral head (GC-ONFH) continues to rise in recent years. However, the optimal treatment for GC-ONFH remains elusive. Rotating magnetic field (RMF), considered as a non-invasive, safe and effective approach, has been proved to have multiple beneficial biological effects including improving bone diseases. To verify the effects of RMF on GC-ONFH, a lipopolysaccharide (LPS) and methylprednisolone (MPS)-induced invivo rat model, and an MPS-induced invitro cell model have been employed. The results demonstrate that RMF alleviated bone mineral loss and femoral head collapse in GC-ONFH rats. Meanwhile, RMF reduced serum lipid levels, attenuated cystic lesions, raised the expression of anti-apoptotic proteins and osteoprotegerin (OPG), while suppressed the expression of pro-apoptotic proteins and nuclear factor receptor activator-κB (RANK) in GC-ONFH rats. Besides, RMF also facilitated the generation of ALP, attenuated apoptosis and inhibits the expression of pro-apoptotic proteins, facilitated the expression of OPG, and inhibited the expression of RANK in MPS-stimulated MC3T3-E1 cells. Thus, this study indicates that RMF can improve GC-ONFH in rat and cell models, suggesting that RMF have the potential in the treatment of clinical GC-ONFH.

Current multi-scale biomaterials for tissue regeneration following spinal cord injury

Spinal cord injury (SCI) may cause loss of motor and sensory function, autonomic dysfunction, and thus disrupt the quality of life of patients, leading to severe disability and significant psychological, social, and economic burden. At present, existing therapy for SCI have limited ability to promote neural function recovery, and there is an urgent need to develop innovative regenerative approaches to repair SCI. Biomaterials have become a promising strategy to promote the regeneration and repair of damaged nerve tissue after SCI. Biomaterials can provide support for nerve tissue by filling cavities, and improve local inflammatory responses and reshape extracellular matrix structures through unique biochemical properties to create the optimal microenvironment at the SCI site, thereby promoting neurogenesis and reconnecting damaged spinal cord tissue. Considering the importance of biomaterials in repairing SCI, this article reviews the latest progress of multi-scale biomaterials in SCI treatment and tissue regeneration, and evaluates the relevant technologies for manufacturing biomaterials.

Delivery of TGFβ3 from Magnetically Responsive Coaxial Fibers Reduces Spinal Cord Astrocyte Reactivity In Vitro

A spinal cord injury (SCI) compresses the spinal cord, killing neurons and glia at the injury site and resulting in prolonged inflammation and scarring that prevents regeneration. Astrocytes, the main glia in the spinal cord, become reactive following SCI and contribute to adverse outcomes. The anti-inflammatory cytokine transforming growth factor beta 3 (TGFβ3) has been shown to mitigate astrocyte reactivity; however, the effects of prolonged TGFβ3 exposure on reactive astrocyte phenotype have not yet been explored. This study investigates whether magnetic core-shell electrospun fibers can be used to alter the release rate of TGFβ3 using externally applied magnetic fields, with the eventual application of tailored drug delivery based on SCI severity. Magnetic core-shell fibers are fabricated by incorporating superparamagnetic iron oxide nanoparticles (SPIONs) into the shell and TGFβ3 into the core solution for coaxial electrospinning. Magnetic field stimulation increased the release rate of TGFβ3 from the fibers by 25% over 7 days and released TGFβ3 reduced gene expression of key astrocyte reactivity markers by at least twofold. This is the first study to magnetically deliver bioactive proteins from magnetic fibers and to assess the effect of sustained release of TGFβ3 on reactive astrocyte phenotype.

Magnetic fibrin nanofiber hydrogel delivering iron oxide magnetic nanoparticles promotes peripheral nerve regeneration

Peripheral nerve injury is a debilitating condition that have a profound impact on the overall quality of an individual's life. The repair of peripheral nerve defects continues to present significant challenges in the field. Iron oxide magnetic nanoparticles (IONPs) have been recognized as potent nanotools for promoting the regeneration of peripheral nerves due to their capability as biological carriers and their ability to template the hydrogel structure under an external magnetic field. This research used a fibrin nanofiber hydrogel loaded with IONPs (IONPs/fibrin) to promote the regeneration of peripheral nerves in rats. In vitro examination of PC12 cells on various concentrations of IONPs/fibrin hydrogels revealed a remarkable increase in NGF and VEGF expression at 2% IONPs concentration. The biocompatibility and degradation of 2% IONPs/fibrin hydrogel were assessed using the in vivo imaging system, demonstrating subcutaneous degradation within a week without immediate inflammation. Bridging a 10-mm sciatic nerve gap in Sprague Dawley rats with 2% IONPs/fibrin hydrogel led to satisfactory morphological recovery of myelinated nerve fibers. And motor functional recovery in the 2% IONPs/fibrin group was comparable to autografts at 6, 9 and 12 weeks postoperatively. Hence, the composite fibrin hydrogel incorporating 2% IONPs exhibits potential for peripheral nerve regeneration.

IKVAV functionalized oriented PCL/Fe3O4 scaffolds for magnetically modulating DRG growth behavior

The re-bridging of the deficient nerve is the main problem to be solved after the functional impairment of the peripheral nerve. In this study, a directionally aligned polycaprolactone/triiron tetraoxide (PCL/Fe3O4) fiber scaffolds were firstly prepared by electrospinning technique, and further then grafted with IKVAV peptide for regulating DRG growth and axon extension in peripheral nerve regeneration. The results showed that oriented aligned magnetic PCL/Fe3O4 composite scaffolds were successfully prepared by electrospinning technique and possessed good mechanical properties and magnetic responsiveness. The PCL/Fe3O4 scaffolds containing different Fe3O4 concentrations were free of cytotoxicity, indicating the good biocompatibility and low cytotoxicity of the scaffolds. The IKVAV-functionalized PCL/Fe3O4 scaffolds were able to guide and promote the directional extension of axons, the application of external magnetic field and the grafting of IKVAV peptides significantly further promoted the growth of DRGs and axons. The ELISA test results showed that the AP-10 F group scaffolds promoted the secretion of nerve growth factor (NGF) from DRG under a static magnetic field (SMF), thus promoting the growth and extension of axons. Importantly, the IKVAV-functionalized PCL/Fe3O4 scaffolds could significantly up-regulate the expression of Cntn2, PCNA, Sox10 and Isca1 genes related to adhesion, proliferation and magnetic receptor function under the stimulation of SMF. Therefore, IKVAV-functionalized PCL/Fe3O4 composite oriented scaffolds have potential applications in neural tissue engineering.

Revealing an important role of piezoelectric polymers in nervous-tissue regeneration: A review

Nerve injuries pose a drastic threat to nerve mobility and sensitivity and lead to permanent dysfunction due to low regenerative capacity of mature neurons. The electrical stimuli that can be provided by electroactive materials are some of the most effective tools for the formation of soft tissues, including nerves. Electric output can provide a distinctly favorable bioelectrical microenvironment, which is especially relevant for the nervous system. Piezoelectric biomaterials have attracted attention in the field of neural tissue engineering owing to their biocompatibility and ability to generate piezoelectric surface charges. In this review, an outlook of the most recent achievements in the field of piezoelectric biomaterials is described with an emphasis on piezoelectric polymers for neural tissue engineering. First, general recommendations for the design of an optimal nerve scaffold are discussed. Then, specific mechanisms determining nerve regeneration via piezoelectric stimulation are considered. Activation of piezoelectric responses via natural body movements, ultrasound, and magnetic fillers is also examined. The use of magnetoelectric materials in combination with alternating magnetic fields is thought to be the most promising due to controllable reproducible cyclic deformations and deep tissue permeation by magnetic fields without tissue heating. In vitro and in vivo applications of nerve guidance scaffolds and conduits made of various piezopolymers are reviewed too. Finally, challenges and prospective research directions regarding piezoelectric biomaterials promoting nerve regeneration are discussed. Thus, the most relevant scientific findings and strategies in neural tissue engineering are described here, and this review may serve as a guideline both for researchers and clinicians.

Advanced Hollow Cathode Discharge Plasma Treatment of Unique Bilayered Fibrous Nerve Guidance Conduits for Enhanced/Oriented Neurite Outgrowth

Despite all recent progresses in nerve tissue engineering, critical-sized nerve defects are still extremely challenging to repair. Therefore, this study targets the bridging of critical nerve defects and promoting an oriented neuronal outgrowth by engineering innovative nerve guidance conduits (NGCs) synergistically possessing exclusive topographical, chemical, and mechanical cues. To do so, a mechanically adequate mixture of polycaprolactone (PCL) and polylactic-co-glycolic acid (PLGA) was first carefully selected as base material to electrospin nanofibrous NGCs simulating the extracellular matrix. The electrospinning process was performed using a newly designed 2-pole air gap collector that leads to a one-step deposition of seamless NGCs having a bilayered architecture with an inner wall composed of highly aligned fibers and an outer wall consisting of randomly oriented fibers. This architecture is envisaged to afford guidance cues for the extension of long neurites on the underlying inner fiber alignment and to concurrently provide a sufficient nutrient supply through the pores of the outer random fibers. The surface chemistry of the NGCs was then modified making use of a hollow cathode discharge (HCD) plasma reactor purposely designed to allow an effective penetration of the reactive species into the NGCs to eventually treat their inner wall. X-ray photoelectron spectroscopy (XPS) results have indeed revealed a successful O2 plasma modification of the inner wall that exhibited a significantly increased oxygen content (24 → 28%), which led to an enhanced surface wettability. The treatment increased the surface nanoroughness of the fibers forming the NGCs as a result of an etching effect. This effect reduced the ultimate tensile strength of the NGCs while preserving their high flexibility. Finally, pheochromocytoma (PC12) cells were cultured on the NGCs to monitor their ability to extend neurites which is the base of a good nerve regeneration. In addition to remarkably improved cell adhesion and proliferation on the plasma-treated NGCs, an outstanding neural differentiation occurred. In fact, PC12 cells seeded on the treated samples extended numerous long neurites eventually establishing a neural network-like morphology with an overall neurite direction following the alignment of the underlying fibers. Overall, PCL/PLGA NGCs electrospun using the 2-pole air gap collector and O2 plasma-treated using an HCD reactor are promising candidates toward a full repair of critical nerve damage.

Magnetoactive Composite Conduits Based on Poly(3-hydroxybutyrate) and Magnetite Nanoparticles for Repair of Peripheral Nerve Injury

Peripheral nerve injury poses a threat to the mobility and sensitivity of a nerve, thereby leading to permanent function loss due to the low regenerative capacity of mature neurons. To date, the most widely clinically applied approach to bridging nerve injuries is autologous nerve grafting, which faces challenges such as donor site morbidity, donor shortages, and the necessity of a second surgery. An effective therapeutic strategy is urgently needed worldwide to overcome the current limitations. Herein, a magnetic nerve guidance conduit (NGC) based on biocompatible biodegradable poly(3-hydroxybutyrate) (PHB) and 8 wt % of magnetite nanoparticles modified by citric acid (Fe3O4-CA) was fabricated by electrospinning. The crystalline structure of NGCs was studied by X-ray diffraction, which indicated an enlarged β-phase of PHB in the composite conduit compared to a pure PHB conduit. Tensile tests revealed greater ductility of PHB/Fe3O4-CA: the composite conduit has Young's modulus of 221 ± 52 MPa and an elongation at break of 28.6 ± 2.9%, comparable to clinical materials. Saturation magnetization (σs) of Fe3O4-CA and PHB/Fe3O4-CA is 61.88 ± 0.29 and 7.44 ± 0.07 emu/g, respectively. The water contact angle of the PHB/Fe3O4-CA conduit is lower as compared to pure PHB, while surface free energy (σ) is significantly higher, which was attributed to higher surface roughness and an amorphous phase as well as possible PHB/Fe3O4-CA interface interactions. In vitro, the conduits supported the proliferation of rat mesenchymal stem cells (rMSCs) and SH-SY5Y cells in a low-frequency magnetic field (0.67 Hz, 68 mT). In vivo, the conduits were used to bridge damaged sciatic nerves in rats; pure PHB and composite PHB/Fe3O4-CA conduits did not cause acute inflammation and performed a barrier function, which promotes nerve regeneration. Thus, these conduits are promising as implants for the regeneration of peripheral nerves.

Engineering the Physical Microenvironment into Neural Organoids for Neurogenesis and Neurodevelopment

Understanding the signals from the physical microenvironment is critical for deciphering the processes of neurogenesis and neurodevelopment. The discovery of how surrounding physical signals shape human developing neurons is hindered by the bottleneck of conventional cell culture and animal models. Notwithstanding neural organoids provide a promising platform for recapitulating human neurogenesis and neurodevelopment, building neuronal physical microenvironment that accurately mimics the native neurophysical features is largely ignored in current organoid technologies. Here, it is discussed how the physical microenvironment modulates critical events during the periods of neurogenesis and neurodevelopment, such as neural stem cell fates, neural tube closure, neuronal migration, axonal guidance, optic cup formation, and cortical folding. Although animal models are widely used to investigate the impacts of physical factors on neurodevelopment and neuropathy, the important roles of human stem cell-derived neural organoids in this field are particularly highlighted. Considering the great promise of human organoids, building neural organoid microenvironments with mechanical forces, electrophysiological microsystems, and light manipulation will help to fully understand the physical cues in neurodevelopmental processes. Neural organoids combined with cutting-edge techniques, such as advanced atomic force microscopes, microrobots, and structural color biomaterials might promote the development of neural organoid-based research and neuroscience.

Recent trends in preparation and biomedical applications of iron oxide nanoparticles

The iron oxide nanoparticles (IONPs), possessing both magnetic behavior and semiconductor property, have been extensively used in multifunctional biomedical fields due to their biocompatible, biodegradable and low toxicity, such as anticancer, antibacterial, cell labelling activities. Nevertheless, there are few IONPs in clinical use at present. Some IONPs approved for clinical use have been withdrawn due to insufficient understanding of its biomedical applications. Therefore, a systematic summary of IONPs' preparation and biomedical applications is crucial for the next step of entering clinical practice from experimental stage. This review summarized the existing research in the past decade on the biological interaction of IONPs with animal/cells models, and their clinical applications in human. This review aims to provide cutting-edge knowledge involved with IONPs' biological effects in vivo and in vitro, and improve their smarter design and application in biomedical research and clinic trials.

Static Magnetic Field Reduces Intracellular ROS Levels and Protects Cells Against Peroxide-Induced Damage: Suggested Roles for Catalase

A feature in neurodegenerative disorders is the loss of neurons, caused by several factors including oxidative stress induced by reactive oxygen species (ROS). In this work, static magnetic field (SMF) was applied in vitro to evaluate its effect on the viability, proliferation, and migration of human neuroblastoma SH-SY5Y cells, and on the toxicity induced by hydrogen peroxide (H2O2), tert-butyl hydroperoxide (tBHP), H2O2/sodium azide (NaN3) and photosensitized oxidations by photodynamic therapy (PDT) photosensitizers. The SMF increased almost twofold the cell expression of the proliferation biomarker Ki-67 compared to control cells after 7 days of exposure. Exposure to SMF accelerated the wound healing of scratched cell monolayers and significantly reduced the H2O2-induced and the tBHP-induced cell deaths. Interestingly, SMF was able to revert the effects of NaN3 (a catalase inhibitor), suggesting an increased activity of catalase under the influence of the magnetic field. In agreement with this hypothesis, SMF significantly reduced the oxidation of DCF-H2, indicating a lower level of intracellular ROS. When the redox imbalance was triggered through photosensitized oxidation, no protection was observed. This observation aligns with the proposed role of catalase in cellular proctetion under SMF.  Exposition to SMF should be further validated in vitro and in vivo as a potential therapeutic approach for neurodegenerative disorders.

Iron oxide nanoparticle-based nanocomposites in biomedical application

Iron-oxide-based biomagnetic nanocomposites, recognized for their significant properties, have been utilized in MRI and cancer treatment for several decades. The expansion of clinical applications is limited by the occurrence of adverse effects. These limitations are largely attributed to suboptimal material design, resulting in agglomeration, reduced magnetic relaxivity, and inadequate functionality. To address these challenges, various synthesis methods and modification strategies have been used to tailor the size, shape, and properties of iron oxide nanoparticle (FeONP)-based nanocomposites. The resulting modified nanocomposites exhibit significant potential for application in diagnostic, therapeutic, and theranostic contexts, including MRI, drug delivery, and anticancer and antimicrobial activity. Yet, their biosafety profile must be rigorously evaluated. Such efforts will facilitate the broader clinical translation of FeONP-based nanocomposites in biomedical applications.

Cellular and Molecular Processes Are Differently Influenced in Primary Neural Cells by Slight Changes in the Physicochemical Properties of Multicore Magnetic Nanoparticles

Herein, we use two exemplary superparamagnetic iron oxide multicore nanoparticles (SPIONs) to illustrate the significant influence of slightly different physicochemical properties on the cellular and molecular processes that define SPION interplay with primary neural cells. Particularly, we have designed two different SPION structures, NFA (i.e., a denser multicore structure accompanied by a slightly less negative surface charge and a higher magnetic response) and NFD (i.e., a larger surface area and more negatively charged), and identified specific biological responses dependent on SPION type, concentration, exposure time, and magnetic actuation. Interestingly, NFA SPIONs display a higher cell uptake, likely driven by their less negative surface and smaller protein corona, more significantly impacting cell viability and complexity. The tight contact of both SPIONs with neural cell membranes results in the significant augmentation of phosphatidylcholine, phosphatidylserine, and sphingomyelin and the reduction of free fatty acids and triacylglycerides for both SPIONs. Nonetheless, NFD induces greater effects on lipids, especially under magnetic actuation, likely indicating a preferential membranal location and/or a tighter interaction with membrane lipids than NFA, in agreement with their lower cell uptake. From a functional perspective, these lipid changes correlate with an increase in plasma membrane fluidity, again larger for more negatively charged nanoparticles (NFD). Finally, the mRNA expression of iron-related genes such as Ireb-2 and Fth-1 remains unaltered, while TfR-1 is only detected in SPION-treated cells. Taken together, these results demonstrate the substantial impact that minor physicochemical differences of nanomaterials may exert in the specific targeting of cellular and molecular processes. A denser multicore structure generated by autoclave-based production is accompanied by a slight difference in surface charge and magnetic properties that become decisive for the biological impact of these SPIONs. Their capacity to markedly modify the lipidic cell content makes them attractive as lipid-targetable nanomedicines.

Advances in biotechnology and clinical therapy in the field of peripheral nerve regeneration based on magnetism

Peripheral nerve injury (PNI) is one of the most common neurological diseases. Recent studies on nerve cells have provided new ideas for the regeneration of peripheral nerves and treatment of physical trauma or degenerative disease-induced loss of sensory and motor neuron functions. Accumulating evidence suggested that magnetic fields might have a significant impact on the growth of nerve cells. Studies have investigated different magnetic field properties (static or pulsed magnetic field) and intensities, various magnetic nanoparticle-encapsulating cytokines based on superparamagnetism, magnetically functionalized nanofibers, and their relevant mechanisms and clinical applications. This review provides an overview of these aspects as well as their future developmental prospects in related fields.

Exploring the Physicochemical, Electroactive, and Biodelivery Properties of Metal Nanoparticles on Peripheral Nerve Regeneration

Despite the advances in the regeneration/rehabilitation field of damaged tissues, the functional recovery of peripheral nerves (PNs), especially in a long gap injury, is considered a great medical challenge. Recent progress in nanomedicine has provided great hope for PN regeneration through the strategy of controlling cell behavior by metal nanoparticles individually or loaded on scaffolds/conduits. Despite the confirmed toxicity of metal nanoparticles due to long-term accumulation in nontarget tissues, they play a role in the damaged PN regeneration based on the topography modification of scaffolds/conduits, enhancing neurotrophic factor secretion, the ion flow improvement, and the regulation of electrical signals. Determining the fate of neural progenitor cells would be a major achievement in PN regeneration, which seems to be achievable by metal nanoparticles through altering cell vital approaches and controlling their functions. Therefore, in this literature, an attempt was made to provide an overview of the effective activities of metal nanoparticles on the PN regeneration, until the vital clues of the PN regeneration and how they are changed by metal nanoparticles are revealed to the researcher.

Unidirectional diphenylalanine nanotubes for dynamically guiding neurite outgrowth

Neural networks have been culturedin vitroto investigate brain functions and diseases, clinical treatments for brain damage, and device development. However, it remains challenging to form complex neural network structures with desired orientations and connectionsin vitro. Here, we introduce a dynamic strategy by using diphenylalanine (FF) nanotubes for controlling physical patterns on a substrate to regulate neurite-growth orientation in cultivating neural networks. Parallel FF nanotube patterns guide neurons to develop neurites through the unidirectional FF nanotubes while restricting their polarization direction. Subsequently, the FF nanotubes disassemble and the restriction of neurites disappear, and secondary neurite development of the neural network occurs in other direction. Experiments were conducted that use the hippocampal neurons, and the results demonstrated that the cultured neural networks by using the proposed dynamic approach can form a significant cross-connected structure with substantially more lateral neural connections than static substrates. The proposed dynamic approach for neurite outgrowing enables the construction of oriented innervation and cross-connected neural networksin vitroand may explore the way for the bio-fabrication of highly complex structures in tissue engineering.

Recent advances in PLLA-based biomaterial scaffolds for neural tissue engineering: Fabrication, modification, and applications

Repairing and regenerating injured neural tissue remains a worldwide challenge. Tissue engineering (TE) has been highlighted as a potential solution to provide functional substitutes for damaged organs or tissue. Among the biocompatible and biodegradable materials, poly-L-lactic-acid (PLLA) has been widely investigated in the TE field because of its tunable mechanical properties and tailorable surface functionalization. PLLA-based biomaterials can be engineered as scaffolds that mimic neural tissue extracellular matrix and modulate inflammatory responses. With technological advances, PLLA-based scaffolds can also have well-controlled three-dimensional sizes and structures to facilitate neurite extension. Furthermore, PLLA-based scaffolds have the potential to be used as drug-delivery carriers with controlled release. Moreover, owing to the good piezoelectric properties and capacity to carry conductive polymers, PLLA-based scaffolds can be combined with electrical stimulation to maintain stemness and promote axonal guidance. This mini-review summarizes and discusses the fabrication and modification techniques utilized in the PLLA-based biomaterial scaffolds for neural TE. Recent applications in peripheral nerve and spinal cord regeneration are also presented, and it is hoped that this will guide the future development of more effective and multifunctional PLLA-based nerve scaffolds.

A Strategy for Magnetic and Electric Stimulation to Enhance Proliferation and Differentiation of NPCs Seeded over PLA Electrospun Membranes

Neural progenitor cells (NPCs) have been shown to serve as an efficient therapeutic strategy in different cell therapy approaches, including spinal cord injury treatment. Despite the reported beneficial effects of NPC transplantation, the low survival and differentiation rates constrain important limitations. Herein, a new methodology has been developed to overcome both limitations by applying a combination of wireless electrical and magnetic stimulation to NPCs seeded on aligned poly(lactic acid) nanofibrous scaffolds for in vitro cell conditioning prior transplantation. Two stimulation patterns were tested and compared, continuous (long stimulus applied once a day) and intermittent (short stimulus applied three times a day). The results show that applied continuous stimulation promotes NPC proliferation and preferential differentiation into oligodendrocytic and neuronal lineages. A neural-like phenotypic induction was observed when compared to unstimulated NPCs. In contrast, intermittent stimulation patterns did not affect NPC proliferation and differentiation to oligodendrocytes or astrocytes morphology with a detrimental effect on neuronal differentiation. This study provides a new approach of using a combination of electric and magnetic stimulation to induce proliferation and further neuronal differentiation, which would improve therapy outcomes in disorders such as spinal cord injury.

3D Polycaprolactone/Gelatin-Oriented Electrospun Scaffolds Promote Periodontal Regeneration

Periodontitis is a worldwide chronic inflammatory disease, where surgical treatment still shows an uncertain prognosis. To break through the dilemma of periodontal treatment, we fabricated a three-dimensional (3D) multilayered scaffold by stacking and fixing electrospun polycaprolactone/gelatin (PCL/Gel) fibrous membranes. The biomaterial displayed good hydrophilic and mechanical properties. Besides, we found human periodontal ligament stem cell (hPDLSC) adhesion and proliferation on it. The following scanning electron microscopy (SEM) and cytoskeleton staining results proved the guiding function of fibers to hPDLSCs. Then, we further analyzed periodontal regeneration-related proteins and mRNA expression between groups. In vivo results in a rat acute periodontal defect model confirmed that the topographic cues of materials could directly guide cellular orientation and might provide the prerequisite for further differentiation. In the aligned scaffold group, besides new bone regeneration, we also observed that angular concentrated fiber regeneration in the root surface of the defect is similar to the normal periodontal tissue. To sum up, we have constructed electrospun membrane-based 3D biological scaffolds, which provided a new treatment strategy for patients undergoing periodontal surgery.

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.

Physical Stimulation Combined with Biomaterials Promotes Peripheral Nerve Injury Repair

Peripheral nerve injury (PNI) is a clinical problem with high morbidity that can cause severe damage. Surgical suturing or implants are usually required due to the slow speed and numerous factors affecting repair after PNI. An autologous nerve graft is the gold standard for PNI repair among implants. However, there is a potential problem of the functional loss of the donor site. Therefore, tissue-engineered nerve biomaterials are often used to bridge the gap between nerve defects, but the therapeutic effect is insufficient. In order to enhance the repair effect of nerve biomaterials for PNI, researchers are seeking to combine various stimulation elements, such as the addition of biological factors such as nerve growth factors or physical factors such as internal microstructural modifications of catheters and their combined application with physical stimulation therapy. Physical stimulation therapy is safer, is more convenient, and has more practical features than other additive factors. Its feasibility and convenience, when combined with nerve biomaterials, provide broader application prospects for PNI repair, and has therefore become a research hot spot. This paper will review the combined application of physical stimulation and biomaterials in PNI repair in recent years to provide new therapeutic ideas for the future use of physical stimulation in PNI repair.

Light-to-Heat Converting ECM-Mimetic Nanofiber Scaffolds for Neuronal Differentiation and Neurite Outgrowth Guidance

The topological cues of fibrous scaffolds (in particular extracellular matrix (ECM)-mimetic nanofibers) have already proven to be a powerful tool for influencing neuronal morphology and behavior. Remote photothermal optical treatment provides additional opportunities for neuronal activity regulation. A combination of these approaches can provide “smart” 3D scaffolds for efficient axon guidance and neurite growth. In this study we propose two alternative approaches for obtaining biocompatible photothermal scaffolds: surface coating of nylon nanofibers with light-to-heat converting nanoparticles and nanoparticle incorporation inside the fibers. We have determined photoconversion efficiency of fibrous nanomaterials under near infrared (NIR) irradiation, as well as biocompatible photothermal treatment parameters. We also measured photo-induced intracellular heating upon contact of cells with a plasmonic surface. In the absence of NIR stimulation, our fibrous scaffolds with a fiber diameter of 100 nm induced an increase in the proportion of β3-tubulin positive cells, while thermal stimulation of neuroblastoma cells on nanoparticles-decorated scaffolds enhanced neurite outgrowth and promoted neuronal maturation. We demonstrate that contact guidance decorated fibers can stimulate directional growth of processes of differentiated neural cells. We studied the impact of nanoparticles on the surface of ECM-mimetic scaffolds on neurite elongation and axonal branching of rat hippocampal neurons, both as topographic cues and as local heat sources. We show that decorating the surface of nanofibers with nanoparticles does not affect the orientation of neurites, but leads to strong branching, an increase in the number of neurites per cell, and neurite elongation, which is independent of NIR stimulation. The effect of photothermal stimulation is most pronounced when cultivating neurons on nanofibers with incorporated nanoparticles, as compared to nanoparticle-coated fibers. The resulting light-to-heat converting 3D materials can be used as tools for controlled photothermal neuromodulation and as “smart” materials for reconstructive neurosurgery.

Multivariate analysis reveals topography dependent relationships amongst neurite morphological features from dorsal root ganglia neurons

Objective.Nerve guidance scaffolds containing anisotropic architectures provide topographical cues to direct regenerating axons through an injury site to reconnect the proximal and distal end of an injured nerve or spinal cord. Previousin vitrocultures of individual neurons revealed that fiber characteristics such as fiber diameter and inter-fiber spacing alter neurite morphological features, such as total neurite length, the longest single neurite, branching density, and the number of primary neurites. However, the relationships amongst these four neurite morphological features have never been studied on fibrous topographies using multivariate analysis.Approach.In this study, we cultured dissociated dorsal root ganglia on aligned, fibrous scaffolds and flat, isotropic films and evaluated the univariate and multivariate differences amongst these four neurite morphological features.Main results.Univariate analysis showed that fibrous scaffolds increase the length of the longest neurite and decrease branching density compared to film controls. Further, multivariate analysis revealed that, regardless of scaffold type, overall neurite length increases due to a compromise between the longest extending neurite, branching density, and the number of primary neurites. Additionally, multivariate analysis indicated that neurite branching is more independent of the other neurite features when neurons were cultured on films but that branching is strongly related to the other neurite features when cultured on fibers.Significance.These findings are significant as they are the first evidence that aligned topographies affect the relationships between neurite morphological features. This study provides a foundation for analyzing how individual neurite morphology may relate to neural regeneration on a macroscopic scale and provide information that may be used to optimize nerve guidance scaffolds.

Neural tissue engineering: From bioactive scaffolds and in situ monitoring to regeneration

Peripheral nerve injury is a large-scale problem that annually affects more than several millions of people all over the world. It remains a great challenge to effectively repair nerve defects. Tissue engineered nerve guidance conduits (NGCs) provide a promising platform for peripheral nerve repair through the integration of bioactive scaffolds, biological effectors, and cellular components. Herein, we firstly describe the pathogenesis of peripheral nerve injuries at different orders of severity to clarify their microenvironments and discuss the clinical treatment methods and challenges. Then, we discuss the recent progress on the design and construction of NGCs in combination with biological effectors and cellular components for nerve repair. Afterward, we give perspectives on imaging the nerve and/or the conduit to allow for the in situ monitoring of the nerve regeneration process. We also cover the applications of different postoperative intervention treatments, such as electric field, magnetic field, light, and ultrasound, to the well-designed conduit and/or the nerve for improving the repair efficacy. Finally, we explore the prospects of multifunctional platforms to promote the repair of peripheral nerve injury.

Magnetic Nanofibrous Scaffolds Accelerate the Regeneration of Muscle Tissue in Combination with Extra Magnetic Fields

The reversal of loss of the critical size of skeletal muscle is urgently required using biomaterial scaffolds to guide tissue regeneration. In this work, coaxial electrospun magnetic nanofibrous scaffolds were fabricated, with gelatin (Gel) as the shell of the fiber and polyurethane (PU) as the core. Iron oxide nanoparticles (Mag) of 10 nm diameter were added to the shell and core layer. Myoblast cells (C2C12) were cultured on the magnetic scaffolds and exposed to the applied magnetic fields. A mouse model of skeletal muscle injury was used to evaluate the repair guided by the scaffolds under the magnetic fields. It was shown that VEGF secretion and MyoG expression for the myoblast cells grown on the magnetic scaffolds under the magnetic fields were significantly increased, while, the gene expression of Myh4 was up-regulated. Results from an in vivo study indicated that the process of skeletal muscle regeneration in the mouse muscle injury model was accelerated by using the magnetic actuated strategy, which was verified by histochemical analysis, immunofluorescence staining of CD31, electrophysiological measurement and ultrasound imaging. In conclusion, the integration of a magnetic scaffold combined with the extra magnetic fields enhanced myoblast differentiation and VEGF secretion and accelerated the defect repair of skeletal muscle in situ.

Fabrication of a 3D Printed PCL Nerve Guide: In Vitro and In Vivo Testing

Nerve guides are medical devices designed to guide proximal and distal ends of injured peripheral nerves in order to assist regeneration of the damaged nerves. A 3D-printed polycaprolactone (PCL) nerve guide using an aligned gelatin-poly(3-hydroxybutyrate-co-3-hydroxyvalerate) electrospun mat, seeded with PC12 and Schwann cells (SCs) is produced. During characterization with microCT and SEM porosity (55%), pore sizes (675 ± 40 µm), and fiber diameters (382 ± 25 µm) are determined. Electrospun fibers have degree of alignment of 7°, indicating high potential for guidance. On Day 14, PC12 cells migrated from proximal to distal end of nerve guide when SCs are seeded on the guide. After 28 days, over 95% of PC12 are alive and aligned. PC12 cells express early differentiation marker beta-tubulin 10 times more than late marker NeuN. In a 10 mm rat sciatic nerve injury, functional recovery evaluated by using static sciatic index (SSI) is observed in mat-free guides and guides containing mat and SCs. Nerve conduction velocities are also improved in these groups. Histological stainings showed tissue growth around nerve guides with highest new tissue organization being observed with mat and cell-free guides. These suggest 3D-printed PCL nerve guides have significant potential for treatment of peripheral nerve injuries.