Reduced graphene oxide-coated electrospun fibre: effect of orientation, coverage and electrical stimulation on Schwann cells behavior

Electrically conductive coatings in tissue engineering

Recent interest in tissue engineering (TE) has focused on electrically conductive biomaterials. This has been inspired by the characteristics of the cells' microenvironment where signalling is supported by electrical stimulation. Numerous studies have demonstrated the positive influence of electrical stimulation on cell excitation to proliferate, differentiate, and deposit extracellular matrix. Even without external electrical stimulation, research shows that electrically active scaffolds can improve tissue regeneration capacity. Tissues like bone, muscle, and neural contain electrically excitable cells that respond to electrical cues provided by implanted biomaterials. To introduce an electrical pathway, TE scaffolds can incorporate conductive polymers, metallic nanoparticles, and ceramic nanostructures. However, these materials often do not meet implantation criteria, such as maintaining mechanical durability and degradation characteristics, making them unsuitable as scaffold matrices. Instead, depositing conductive layers on TE scaffolds has shown promise as an efficient alternative to creating electrically conductive structures. A stratified scaffold with an electroactive surface synergistically excites the cells through active top-pathway, with/without electrical stimulation, providing an ideal matrix for cell growth, proliferation, and tissue deposition. Additionally, these conductive coatings can be enriched with bioactive or pharmaceutical components to enhance the scaffold's biomedical performance. This review covers recent developments in electrically active biomedical coatings for TE. The physicochemical and biological properties of conductive coating materials, including polymers (polypyrrole, polyaniline and PEDOT:PSS), metallic nanoparticles (gold, silver) and inorganic (ceramic) particles (carbon nanotubes, graphene-based materials and Mxenes) are examined. Each section explores the conductive coatings' deposition techniques, deposition parameters, conductivity ranges, deposit morphology, cell responses, and toxicity levels in detail. Furthermore, the applications of these conductive layers, primarily in bone, muscle, and neural TE are considered, and findings from in vitro and in vivo investigations are presented. STATEMENT OF SIGNIFICANCE: Tissue engineering (TE) scaffolds are crucial for human tissue replacement and acceleration of healing. Neural, muscle, bone, and skin tissues have electrically excitable cells, and their regeneration can be enhanced by electrically conductive scaffolds. However, standalone conductive materials often fall short for TE applications. An effective approach involves coating scaffolds with a conductive layer, finely tuning surface properties while leveraging the scaffold's innate biological and physical support. Further enhancement is achieved by modifying the conductive layer with pharmaceutical components. This review explores the under-reviewed topic of conductive coatings in tissue engineering, introducing conductive biomaterial coatings and analyzing their biological interactions. It provides insights into enhancing scaffold functionality for tissue regeneration, bridging a critical gap in current literature.

Recent advances in enhances peripheral nerve orientation: the synergy of micro or nano patterns with therapeutic tactics

Several studies suggest that topographical patterns influence nerve cell fate. Efforts have been made to improve nerve cell functionality through this approach, focusing on therapeutic strategies that enhance nerve cell function and support structures. However, inadequate nerve cell orientation can impede long-term efficiency, affecting nerve tissue repair. Therefore, enhancing neurites/axons directional growth and cell orientation is crucial for better therapeutic outcomes, reducing nerve coiling, and ensuring accurate nerve fiber connections. Conflicting results exist regarding the effects of micro- or nano-patterns on nerve cell migration, directional growth, immunogenic response, and angiogenesis, complicating their clinical use. Nevertheless, advances in lithography, electrospinning, casting, and molding techniques to intentionally control the fate and neuronal cells orientation are being explored to rapidly and sustainably improve nerve tissue efficiency. It appears that this can be accomplished by combining micro- and nano-patterns with nanomaterials, biological gradients, and electrical stimulation. Despite promising outcomes, the unclear mechanism of action, the presence of growth cones in various directions, and the restriction of outcomes to morphological and functional nerve cell markers have presented challenges in utilizing this method. This review seeks to clarify how micro- or nano-patterns affect nerve cell morphology and function, highlighting the potential benefits of cell orientation, especially in combined approaches.

Perspectives on the Novel Multifunctional Nerve Guidance Conduits: From Specific Regenerative Procedures to Motor Function Rebuilding

Peripheral nerve injury potentially destroys the quality of life by inducing functional movement disorders and sensory capacity loss, which results in severe disability and substantial psychological, social, and financial burdens. Autologous nerve grafting has been commonly used as treatment in the clinic; however, its rare donor availability limits its application. A series of artificial nerve guidance conduits (NGCs) with advanced architectures are also proposed to promote injured peripheral nerve regeneration, which is a complicated process from axon sprouting to targeted muscle reinnervation. Therefore, exploring the interactions between sophisticated NGC complexes and versatile cells during each process including axon sprouting, Schwann cell dedifferentiation, nerve myelination, and muscle reinnervation is necessary. This review highlights the contribution of functional NGCs and the influence of microscale biomaterial architecture on biological processes of nerve repair. Progressive NGCs with chemical molecule induction, heterogenous topographical morphology, electroactive, anisotropic assembly microstructure, and self-powered electroactive and magnetic-sensitive NGCs are also collected, and they are expected to be pioneering features in future multifunctional and effective NGCs.

Reduced Graphene Oxide Fibers Combined with Electrical Stimulation Promote Peripheral Nerve Regeneration

Background

The treatment of long-gap peripheral nerve injury (PNI) is still a substantial clinical problem. Graphene-based scaffolds possess extracellular matrix (ECM) characteristic and can conduct electrical signals, therefore have been investigated for repairing PNI. Combined with electrical stimulation (ES), a well performance should be expected. We aimed to determine the effects of reduced graphene oxide fibers (rGOFs) combined with ES on PNI repair in vivo.

Methods

rGOFs were prepared by one-step dimensionally confined hydrothermal strategy (DCH). Surface characteristics, chemical compositions, electrical and mechanical properties of the samples were characterized. The biocompatibility of the rGOFs were systematically explored both in vitro and in vivo. Total of 54 Sprague-Dawley (SD) rats were randomized into 6 experimental groups: a silicone conduit (S), S+ES, S+rGOFs-filled conduit (SGC), SGC+ES, nerve autograft, and sham groups for a 10-mm sciatic defect. Functional and histological recovery of the regenerated sciatic nerve at 12 weeks after surgery in each group of SD rats were evaluated.

Results

rGOFs exhibited aligned micro- and nano-channels with excellent mechanical and electrical properties. They are biocompatible in vitro and in vivo. All 6 groups exhibited PNI repair outcomes in view of neurological and morphological recovery. The SGC+ES group achieved similar therapeutic effects as nerve autograft group (P > 0.05), significantly outperformed other treatment groups. Immunohistochemical analysis showed that the expression of proteins related to axonal regeneration and angiogenesis were relatively higher in the SGC+ES.

Conclusion

The rGOFs had good biocompatibility combined with excellent electrical and mechanical properties. Combined with ES, the rGOFs provided superior motor nerve recovery for a 10-mm nerve gap in a murine acute transection injury model, indicating its excellent repairing ability. That the similar therapeutic effects as autologous nerve transplantation make us believe this method is a promising way to treat peripheral nerve defects, which is expected to guide clinical practice in the future.

Influence of Graphene-Based Nanocomposites in Neurogenesis and Neuritogenesis: A Brief Summary

Graphene is a prospective candidate for various biomedical applications, including drug transporters, bioimaging agents, and scaffolds for tissue engineering, thanks to its superior electrical conductivity and biocompatibility. The clinical issue of nerve regeneration and rehabilitation still has a major influence on people's lives. Nanomaterials based on graphene have been exploited extensively to promote nerve cell differentiation and proliferation. Their high electrical conductivity and mechanical robustness make them appropriate for nerve tissue engineering. Combining graphene with other substances, such as biopolymers, may transmit biochemical signals that support brain cell division, proliferation, and regeneration. The utilization of nanocomposites based on graphene in neurogenesis and neuritogenesis is the primary emphasis of this review. Here are some examples of the many synthetic strategies used. For neuritogenesis and neurogenesis, it has also been explored to combine electrical stimulation with graphene-based materials.

Interaction of graphene and WS2 with neutrophils and mesenchymal stem cells: implications for peripheral nerve regeneration

Graphene and bidimensional (2D) materials have been widely used in nerve conduits to boost peripheral nerve regeneration. Nevertheless, the experimental and commercial variability in graphene-based materials generates graphene forms with different structures and properties that can trigger entirely diverse biological responses from all the players involved in nerve repair. Herein, we focus on the graphene and tungsten disulfide (WS2) interaction with non-neuronal cell types involved in nerve tissue regeneration. We synthesize highly crystalline graphene and WS2 with scalable techniques such as thermal decomposition and chemical vapor deposition. The materials were able to trigger the activation of a neutrophil human model promoting Neutrophil Extracellular Traps (NETs) production, particularly under basal conditions, although neutrophils were not able to degrade graphene. Of note is that pristine graphene acts as a repellent for the NET adhesion, a beneficial property for nerve conduit long-term applications. Mesenchymal stem cells (MSCs) have been proposed as a promising strategy for nerve regeneration in combination with a conduit. Thus, the interaction of graphene with MSCs was also investigated, and reduced viability was observed only on specific graphene substrates. Overall, the results confirm the possibility of regulating the cell response by varying graphene properties and selecting the most suitable graphene forms.

Techniques and graft materials for repairing peripheral nerve defects

Peripheral nerve defects refer to damage or destruction occurring in the peripheral nervous system, typically affecting the limbs and face. The current primary approaches to address peripheral nerve defects involve the utilization of autologous nerve transplants or the transplantation of artificial material. Nevertheless, these methods possess certain limitations, such as inadequate availability of donor nerve or unsatisfactory regenerative outcomes post-transplantation. Biomaterials have been extensively studied as an alternative approach to promote the repair of peripheral neve defects. These biomaterials include both natural and synthetic materials. Natural materials consist of collagen, chitosan, and silk, while synthetic materials consist of polyurethane, polylactic acid, and polycaprolactone. Recently, several new neural repair technologies have also been developed, such as nerve regeneration bridging technology, electrical stimulation technology, and stem cell therapy technology. Overall, biomaterials and new neural repair technologies provide new methods and opportunities for repairing peripheral nerve defects. However, these methods still require further research and development to enhance their effectiveness and feasibility.

Graphene oxide-doped chiral dextro-hydrogel promotes peripheral nerve repair through M2 polarization of macrophages

Dextro-chirality is reported to specifically promote the proliferation and survival of neural cells. However, applying this unique performance to nerve repair remains a great challenge. Graphite oxide (GO)-phenylalanine derivative hydrogel system was constructed through doping 5% GO into self-assembly dextro- or levo-hydrogels (named as dextro and levo group, respectively), which exhibited identical physical and chemical properties, cyto-compatibility, and mirror-symmetrical chirality. In vivo experiments using rat sciatic nerve repair models showed that the functional recovery and histological restoration of regenerating nerves in the dextro group were significantly improved, approaching that of autograft implantation. The doped GO promoted M2 polarization of macrophages, increasing the expression of platelet-derived growth factor BB chain and vascular endothelial growth factor, thereby improving angiogenesis in regenerating nerves. A mechanism is proposed for the facilitated nerve repair through the synergistic effect of GO and dextro-hydrogel, involving dextro-chirality selection of neural cells and GO-induced M2 polarization, which promotes microvascular regeneration and myelination. This study showcases the immense potential of chirality in addressing neurological issues by providing a compelling demonstration of the development of effective therapies that leverage the unique matrix chirality selection of nerve cells to promote peripheral nerve regeneration.

Functional material-mediated wireless physical stimulation for neuro-modulation and regeneration

Nerve injuries and neurological diseases remain intractable clinical challenges. Despite the advantages of stem cell therapy in treating neurological disorders, uncontrollable cell fates and loss of cell function in vivo are still challenging. Recently, increasing attention has been given to the roles of external physical signals, such as electricity and ultrasound, in regulating stem cell fate as well as activating or inhibiting neuronal activity, which provides new insights for the treatment of neurological disorders. However, direct physical stimulations in vivo are short in accuracy and safety. Functional materials that can absorb energy from a specific physical field exerted in a wireless way and then release another localized physical signal hold great advantages in mediating noninvasive or minimally invasive accurate indirect physical stimulations to promote the therapeutic effect on neurological disorders. In this review, the mechanism by which various physical signals regulate stem cell fate and neuronal activity is summarized. Based on these concepts, the approaches of using functional materials to mediate indirect wireless physical stimulation for neuro-modulation and regeneration are systematically reviewed. We expect that this review will contribute to developing wireless platforms for neural stimulation as an assistance for the treatment of neurological diseases and injuries.

3D printed reduced graphene oxide-GelMA hybrid hydrogel scaffolds for potential neuralized bone regeneration

Peripheral nerves participate in bone growth and repair by secreting neurotransmitters, and enable new bone to possess physiological bone-sensing capability. However, it is difficult to achieve synchronized nerve regeneration during the healing process of large bone defects at present. As a bioactive nanomaterial, reduced graphene oxide (rGO) can promote neuronal differentiation and myelination of Schwann cells (SCs), while enhancing the adhesion and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) through its strong non-covalent binding ability. In this study, 3D printing-based rGO/GelMA hydrogels with enhanced osteogenic and neurogenic dual differentiation were used to simultaneously load SCs and BMSCs. By changing the concentration of rGO(0.03%/0.05%/0.1%), the compressive strength, rheological properties and aperture of the hydrogel can be improved. In vitro, cell live/death staining, phalloidin staining and SEM showed that cells loaded on the hydrogel had a high survival rate (85%) and good adhesion ability. In vivo, we found that the rGO/GelMA hydrogel exhibited the same low inflammatory response compared to the pure-GelMA group and the cell-only group, but surrounded by collagen fibers. Meanwhile, the osteogenic and neural proteins in the rGO/GelMA group were found to be highly expressed in immunohistochemistry and immunofluorescence. In this study, a scaffold material containing double cells was used to promote synergistic regeneration of nerves and bone, providing a promising strategy for the preparation of personalized and functionalized biomimetic bone material.

Polydopamine-Decorated PLCL Conduit to Induce Synergetic Effect of Electrical Stimulation and Topological Morphology for Peripheral Nerve Regeneration

Due to the limited self-repairing capacity after peripheral nerve injuries (PNI), artificial nerve conduits are widely applied to facilitate neural regeneration. Exogenous electrical stimulation (ES) that is carried out by the conductive conduit regulates the biological behavior of Schwann cells (SCs). Meanwhile, a longitudinal surface structure counts to guide axonal growth to accelerate the end-to-end connection. Currently, there are no conduits equipped with both electrical conduction and axon-guiding surface structure. Herein, a biodegradable, conductive poly(l-lactide-co-caprolactone)/graphene (PLCL/GN) composite conduit is designed. The conduit with 20.96 ± 1.26 MPa tensile strength has a micropatterned surface of 20 µm groove fabricated by microimprint technology and self-assembled polydopamine (PDA). In vitro evaluation shows that the conduits with ES effectively stimulate the directional cell migration, adhesion, and elongation, and enhance neuronal expression of SCs. The rat sciatic nerve crush model demonstrates that the conductive micropatterned conduit with ES promotes the growth of myelin sheath, faster nerve regeneration, and 20-fold functional recovery in vivo. These discoveries prove that the PLCL(G)/PDA/GN composite conduit is a promising tool for PNI treatment by providing the functional integration of physical guidance, biomimetic biological regulation, and bioelectrical stimulation, which inspires a novel therapeutic approach for nerve regeneration in the future.

Fiber and Electrical Field Alignment Increases BDNF Expression in SH-SY5Y Cells following Electrical Stimulation

The limited expression of neurotrophic factors that can be included in neural tissue engineering scaffolds is insufficient for sustained neural regeneration. A localized and sustained method of introducing neurotrophic factors is required. We describe our attempt at inducing neuroblastoma cells to express trophic factors following electrical stimulation. Human SH-SY5Y neuroblastoma cells, cultured on polycaprolactone electrospun nanofibers, were electrically stimulated using a 100 mV/mm electric field. Nuclear morphology and brain-derived neurotrophic factor (BDNF) expression were analyzed. Cells were classified based on the type of fiber orientation and the alignment of these fibers in relation to the electric field. Nuclear deformation was mainly influenced by fiber orientation rather than the electrical field. Similarly, fiber orientation also induced BDNF expression. Although electrical field alone had no significant effect on BDNF expression, combining fiber orientation with electrical field resulted in BDNF expression in cells that grew on electrospun fibers that were aligned perpendicular to the electrical field.

The impact of physical, biochemical, and electrical signaling on Schwann cell plasticity

Peripheral nervous system (PNS) injuries are an ongoing health care concern. While autografts and allografts are regarded as the current clinical standard for traumatic injury, there are inherent limitations that suggest alternative remedies should be considered for therapeutic purposes. In recent years, nerve guidance conduits (NGCs) have become increasingly popular as surgical repair devices, with a multitude of various natural and synthetic biomaterials offering potential to enhance the design of conduits or supplant existing technologies entirely. From a cellular perspective, it has become increasingly evident that Schwann cells (SCs), the primary glia of the PNS, are a predominant factor mediating nerve regeneration. Thus, the development of severe nerve trauma therapies requires a deep understanding of how SCs interact with their environment, and how SC microenvironmental cues may be engineered to enhance regeneration. Here we review the most recent advancements in biomaterials development and cell stimulation strategies, with a specific focus on how the microenvironment influences the behavior of SCs and can potentially lead to functional repair. We focus on microenvironmental cues that modulate SC morphology, proliferation, migration, and differentiation to alternative phenotypes. Promotion of regenerative phenotypic responses in SCs and other non-neuronal cells that can augment the regenerative capacity of multiple biomaterials is considered along with innovations and technologies for traumatic injury.

The role of mechanobiology on the Schwann cell response: A tissue engineering perspective

Schwann cells (SCs), the glial cells of the peripheral nervous system (PNS), do not only form myelin sheaths thereby insulating the electrical signal propagated by the axons, but also play an essential role in the regeneration of injured axons. SCs are inextricably connected with their extracellular environment and the mechanical stimuli that are received determine their response during development, myelination and injuries. To this end, the mechanobiological response of SCs is being actively researched, as it can determine the suitability of fabricated scaffolds for tissue engineering and regenerative medicine applications. There is growing evidence that SCs are sensitive to changes in the mechanical properties of the surrounding environment (such as the type of material, its elasticity and stiffness), different topographical features provided by the environment, as well as shear stress. In this review, we explore how different mechanical stimuli affect SC behaviour and highlight the importance of exploring many different avenues when designing scaffolds for the repair of PNS injuries.

Conductive biocomposite hydrogels with multiple biophysical cues regulate schwann cell behaviors

Peripheral nerve injuries are serious clinical events, and surgical treatment has certain limitations. Conductive hydrogels are promising biomaterials for neural tissue engineering, as they can enhance the functionality of neurons and Schwann cells (SCs) by mimicking the biophysical and biochemical cues existing in the natural extracellular matrix. It remains unexplored, however, whether there is a connection between the effects of different cues, such as hydrogel elasticity and conductivity, on SC fate. In the present work, we fabricated a series of conductive biocomposite hydrogels with the combination of silk fibroin (SF) and graphene oxide (GO) nanosheets and demonstrated an approach to control hydrogel electrical conductivity, independent of matrix elasticity and polymer concentration. Our results indicated that the soft substrates play a more critical role in SC survival, proliferation, spreading, and gene expression of neurotrophic factors, while the increased conductivity may also be beneficial to SC functional behaviors. These findings may promote the understanding of cell-matrix interactions and provide new insights for the design of neural tissue engineering scaffolds.

Graphene-Based Materials Prove to Be a Promising Candidate for Nerve Regeneration Following Peripheral Nerve Injury

Peripheral nerve injury is a common medical condition that has a great impact on patient quality of life. Currently, surgical management is considered to be a gold standard first-line treatment; however, is often not successful and requires further surgical procedures. Commercially available FDA- and CE-approved decellularized nerve conduits offer considerable benefits to patients suffering from a completely transected nerve but they fail to support neural regeneration in gaps > 30 mm. To address this unmet clinical need, current research is focused on biomaterial-based therapies to regenerate dysfunctional neural tissues, specifically damaged peripheral nerve, and spinal cord. Recently, attention has been paid to the capability of graphene-based materials (GBMs) to develop bifunctional scaffolds for promoting nerve regeneration, often via supporting enhanced neural differentiation. The unique features of GBMs have been applied to fabricate an electroactive conductive surface in order to direct stem cells and improve neural proliferation and differentiation. The use of GBMs for nerve tissue engineering (NTE) is considered an emerging technology bringing hope to peripheral nerve injury repair, with some products already in preclinical stages. This review assesses the last six years of research in the field of GBMs application in NTE, focusing on the fabrication and effects of GBMs for neurogenesis in various scaffold forms, including electrospun fibres, films, hydrogels, foams, 3D printing, and bioprinting.

An Update on Graphene-Based Nanomaterials for Neural Growth and Central Nervous System Regeneration

Thanks to their reduced size, great surface area, and capacity to interact with cells and tissues, nanomaterials present some attractive biological and chemical characteristics with potential uses in the field of biomedical applications. In this context, graphene and its chemical derivatives have been extensively used in many biomedical research areas from drug delivery to bioelectronics and tissue engineering. Graphene-based nanomaterials show excellent optical, mechanical, and biological properties. They can be used as a substrate in the field of tissue engineering due to their conductivity, allowing to study, and educate neural connections, and guide neural growth and differentiation; thus, graphene-based nanomaterials represent an emerging aspect in regenerative medicine. Moreover, there is now an urgent need to develop multifunctional and functionalized nanomaterials able to arrive at neuronal cells through the blood-brain barrier, to manage a specific drug delivery system. In this review, we will focus on the recent applications of graphene-based nanomaterials in vitro and in vivo, also combining graphene with other smart materials to achieve the best benefits in the fields of nervous tissue engineering and neural regenerative medicine. We will then highlight the potential use of these graphene-based materials to construct graphene 3D scaffolds able to stimulate neural growth and regeneration in vivo for clinical applications.

Synergic fabrication of pembrolizumab loaded doxorubicin incorporating microbubbles delivery for ultrasound contrast agents mediated anti-proliferation and apoptosis

This study evaluated pembrolizumab-conjugated, doxorubicin (DOX)-loaded microbubbles (PDMs) in combination with ultrasound (US) as molecular imaging agents for early diagnosis of B cell lymphomas, and as a targeted drug delivery system. Pembrolizumab, a monoclonal CD20 antibody, was attached to the surfaces of DOX-loaded microbubbles. PDM binding to B cell lymphoma cells was assessed using immunofluorescence. The cytotoxic effects of PDMs in combination with ultrasound (PDMs + US) were evaluated in vitro in CD20+ and CD20- cell lines, and its antitumor activities were assessed in Raji (CD20+) and Jurkat (CD20-) lymphoma cell-grafted mice. PDMs specifically bound to CD20+ cells in vitro and in vivo. Contrast enhancement was monitored in vivo via US. PDM peak intensities and contrast enhancement durations were higher in Raji than in Jurkat cell-grafted mice (p < 0.05). PDMs + US treatment resulted in improved antitumor effects and reduced systemic toxicity in Raji cell-grafted mice compared with other treatments (p < .05). Our results showed that PDMs + US enhanced tumor targeting, reduced systemic toxicity, and inhibited CD20+ B cell lymphoma growth in vivo. Targeted PDMs could be employed as US molecular imaging agents for early diagnosis, and are an effective targeted drug delivery system in combination with US for CD20+ B cell malignancy treatment.