Fabrication of Chitosan/Polypyrrole‐coated poly(L‐lactic acid)/Polycaprolactone aligned fibre films for enhancement of neural cell compatibility and neurite growth

Biomaterials for neuroengineering: applications and challenges

Neurological injuries and diseases are a leading cause of disability worldwide, underscoring the urgent need for effective therapies. Neural regaining and enhancement therapies are seen as the most promising strategies for restoring neural function, offering hope for individuals affected by these conditions. Despite their promise, the path from animal research to clinical application is fraught with challenges. Neuroengineering, particularly through the use of biomaterials, has emerged as a key field that is paving the way for innovative solutions to these challenges. It seeks to understand and treat neurological disorders, unravel the nature of consciousness, and explore the mechanisms of memory and the brain's relationship with behavior, offering solutions for neural tissue engineering, neural interfaces and targeted drug delivery systems. These biomaterials, including both natural and synthetic types, are designed to replicate the cellular environment of the brain, thereby facilitating neural repair. This review aims to provide a comprehensive overview for biomaterials in neuroengineering, highlighting their application in neural functional regaining and enhancement across both basic research and clinical practice. It covers recent developments in biomaterial-based products, including 2D to 3D bioprinted scaffolds for cell and organoid culture, brain-on-a-chip systems, biomimetic electrodes and brain-computer interfaces. It also explores artificial synapses and neural networks, discussing their applications in modeling neural microenvironments for repair and regeneration, neural modulation and manipulation and the integration of traditional Chinese medicine. This review serves as a comprehensive guide to the role of biomaterials in advancing neuroengineering solutions, providing insights into the ongoing efforts to bridge the gap between innovation and clinical application.

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.

Advances in Material-Assisted Electromagnetic Neural Stimulation

Bioelectricity plays a crucial role in organisms, being closely connected to neural activity and physiological processes. Disruptions in the nervous system can lead to chaotic ionic currents at the injured site, causing disturbances in the local cellular microenvironment, impairing biological pathways, and resulting in a loss of neural functions. Electromagnetic stimulation has the ability to generate internal currents, which can be utilized to counter tissue damage and aid in the restoration of movement in paralyzed limbs. By incorporating implanted materials, electromagnetic stimulation can be targeted more accurately, thereby significantly improving the effectiveness and safety of such interventions. Currently, there have been significant advancements in the development of numerous promising electromagnetic stimulation strategies with diverse materials. This review provides a comprehensive summary of the fundamental theories, neural stimulation modulating materials, material application strategies, and pre-clinical therapeutic effects associated with electromagnetic stimulation for neural repair. It offers a thorough analysis of current techniques that employ materials to enhance electromagnetic stimulation, as well as potential therapeutic strategies for future applications.

Oriented polyaniline/poly-l-lactic acid/gelatin nanofiber scaffolds promote outgrowth of spiral ganglion neurons

Sensorineural hearing loss (SNHL) is caused by the loss of sensory hair cells (HCs) and/or connected spiral ganglion neurons (SGNs). The current clinical conventional treatment for SNHL is cochlear implantation (CI). The principle of CI is to bypass degenerated auditory HCs and directly electrically stimulate SGNs to restore hearing. However, the effectiveness of CI is limited when SGNs are severely damaged. In the present study, oriented nanofiber scaffolds were fabricated using electrospinning technology to mimic the SGN spatial microenvironment in the inner ear. Meanwhile, different proportions of polyaniline (PANI), poly-l-lactide (PLLA), gelatin (Gel) were composited to mimic the composition and mechanical properties of auditory basement membrane. The effects of oriented PANI/PLLA/Gel biomimetic nanofiber scaffolds for neurite outgrowth were analyzed. The results showed the SGNs grew in an orientation along the fiber direction, and the length of the protrusions increased significantly on PANI/PLLA/Gel scaffold groups. The 2% PANI/PLLA/Gel group showed best effects for promoting SGN adhesion and nerve fiber extension. In conclusion, the biomimetic oriented nanofiber scaffolds can simulate the microenvironment of SGNs as well as promote neurite outgrowth in vitro, which may provide a feasible research idea for SGN regeneration and even therapeutic treatments of SNHL in future.

Polypyrrole-based structures for activation of cellular functions under electrical stimulation

Polypyrrole (Ppy) is an electroconductive polymer used in various applications, including in vitro experiments with cell cultures under electrical stimulation (ES). Ppy can be applied in various forms and most importantly, it is biocompatible with cells. Ppy specifically directs ES to cells, which makes Ppy a potential polymer for the development of novel technologies for targeted tissue regeneration. The high potential of ES in combination with different Ppy-based systems, such as hydrogels, scaffolds, or Ppy-layers is advantageous to stimulate cellular differentiation towards neurogenic, cardiac, muscle, and osteogenic lineages. Different in-house devices and the principles of ES application used to stimulate cellular functions are reviewed and summarized. The focus of this review is to observe the most relevant studies and their in-house techniques regarding the application of Ppy-based materials for the use of bone, neural, cardiac, and muscle tissue regeneration under ES. Different types of Ppy materials, such as Ppy particles, layers/films, membranes, and 3D-shaped synthetic and natural scaffolds, as well as combining Ppy with different active molecules are reviewed.

Conducting polymer-based scaffolds for neuronal tissue engineering

Neuronal tissue engineering has immense potential for treating neurological disorders and facilitating nerve regeneration. Conducting polymers (CPs) have emerged as a promising class of materials owing to their unique electrical conductivity and biocompatibility. CPs, such as poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3-hexylthiophene) (P3HT), polypyrrole (PPy), and polyaniline (PANi), have been extensively explored for their ability to provide electrical cues to neural cells. These polymers are widely used in various forms, including porous scaffolds, hydrogels, and nanofibers, and offer an ideal platform for promoting cell adhesion, differentiation, and axonal outgrowth. CP-based scaffolds can also serve as drug delivery systems, enabling localized and controlled release of neurotrophic factors and therapeutic agents to enhance neural regeneration and repair. CP-based scaffolds have demonstrated improved neural regeneration, both in vitro and in vivo, for treating spinal cord and peripheral nerve injuries. In this review, we discuss synthesis and scaffold processing methods for CPs and their applications in neuronal tissue regeneration. We focused on a detailed literature review of the central and peripheral nervous systems.

The Alphabet of Nanostructured Polypyrrole

This review is devoted to polypyrrole and its morphology, which governs the electroactivity of the material. The macroscopic properties of the material are strictly relevant to microscopic ordering observed at the local level. During the synthesis, various (nano)morphologies can be produced. The formation of the ordered structure is dictated by the ability of the local forces and effects to induce restraints that help shape the structure. This review covers the aspects of morphology and roughness and their impact on the final properties of the modified electrode activity in selected applications.

Electric field bridging-effect in electrified microfibrils' scaffolds

Introduction: The use of biocompatible scaffolds combined with the implantation of neural stem cells, is increasingly being investigated to promote the regeneration of damaged neural tissue, for instance, after a Spinal Cord Injury (SCI). In particular, aligned Polylactic Acid (PLA) microfibrils' scaffolds are capable of supporting cells, promoting their survival and guiding their differentiation in neural lineage to repair the lesion. Despite its biocompatible nature, PLA is an electrically insulating material and thus it could be detrimental for increasingly common scaffolds' electric functionalization, aimed at accelerating the cellular processes. In this context, the European RISEUP project aims to combine high intense microseconds pulses and DC stimulation with neurogenesis, supported by a PLA microfibrils' scaffold. Methods: In this paper a numerical study on the effect of microfibrils' scaffolds on the E-field distribution, in planar interdigitated electrodes, is presented. Realistic microfibrils' 3D CAD models have been built to carry out a numerical dosimetry study, through Comsol Multiphysics software. Results: Under a voltage of 10 V, microfibrils redistribute the E-field values focalizing the field streamlines in the spaces between the fibers, allowing the field to pass and reach maximum values up to 100 kV/m and values comparable with the bare electrodes' device (without fibers). Discussion: Globally the median E-field inside the scaffolded electrodes is the 90% of the nominal field, allowing an adequate cells' exposure.

Aligned Electroactive Electrospun Fibrous Scaffolds for Peripheral Nerve Regeneration

Effective repair and functional recovery of large peripheral nerve deficits are urgent clinical needs. A biofunctional electroactive scaffold typically acts as a "bridge" for the repair of large nerve defects. In this study, we constructed a biomimetic piezoelectric and conductive aligned polypyrrole (PPy)/polydopamine (PDA)/poly-l-lactic acid (PLLA) electrospun fibrous scaffold to improve the hydrophilicity and cellular compatibility of PLLA and restore the weakened piezoelectric effect of PDA, which is beneficial in promoting Schwann cell differentiation and dorsal root ganglion neuronal extension and alignment. The aligned PPy/PDA/PLLA fibrous scaffold bridged the sciatic nerve of Sprague-Dawley rats with a 10 mm deficit, prevented autotomy, and promoted nerve regeneration and functional recovery, thereby activating the calcium and AMP-activated protein kinase signaling pathways. Therefore, electroactive fibrous scaffolds exhibit great potential for neural tissue regeneration.

Enhanced neural differentiation by applying electrical stimulation utilizing conductive and antioxidant alginate-polypyrrole/poly-l-lysine hydrogels

The challenge of restoration from neurodegenerative disorder requires effective solutions. To enhance the healing efficiencies, scaffolds with antioxidant activities, electroconductivity, and versatile features to encourage neuronal differentiation are potentially useful. Herein, polypyrrole-alginate (Alg-PPy) copolymer was used to design antioxidant and electroconductive hydrogels through the chemical oxidation radical polymerization method. The hydrogels have antioxidant effects to combat oxidative stress in nerve damage thanks to the introduction of PPy. Additionally, poly-l-lysine (PLL) provided these hydrogels with a great differentiation ability of stem cells. The morphology, porosity, swelling ratio, antioxidant activity, rheological behavior, and conductive characteristics of these hydrogels were precisely adjusted by altering the amount of PPy. Characterization of hydrogels showed appropriate electrical conductivity and antioxidant activity for neural tissue applications. Cytocompatibility, live/dead assays, and Annexin V/PI staining by flow cytometry using P19 cells confirmed the excellent cytocompatibility and cell protective effect under ROS microenvironment of these hydrogels in both normal and oxidative conditions. The neural marker investigation in the induction of electrical impulses was assessed through RT-PCR and immunofluorescence assay, demonstrating the differentiation of P19 cells to neurons cultured in these scaffolds. In summary, the antioxidant and electroconductive Alg-PPy/PLL hydrogels demonstrated excellent potential as promising scaffolds for treating neurodegenerative disorders.

Effects of ceramic additives and bioactive coatings on the degradation of polylactic acid-based bone scaffolds under hydrolytic conditions

Polylactic acid (PLA) has been extensively used for the manufacturing of scaffolds in bone tissue engineering applications. Due to the low hydrophilicity and the acidic degradation process of this biomaterial, different strategies have been proposed to increase the biofunctionality of the support structure. The use of ceramic particles is a generally preferred option to increase the osteoconductivity of the base material, while acting as buffers to maintain the pH level of the surroundings tissues. Surface modification is another approach to overcome the limitations of PLA for tissue engineering applications. In this work, the degradation profile of 3D-printed PLA scaffolds containing beta-tricalcium phosphate (β-TCP) and calcium carbonate (CaCO3 ) particles has been studied under hydrolytic conditions. Composite samples treated with plasma and coated with Aloe vera extracts were also studied to evaluate the effect of this surface modification method. The characterization of the 3D structures included its morphological, calorimetric and mechanical evaluation. According to the results obtained, the proposed composite scaffolds allowed an adequate maintenance of the pH level of the surrounding medium, with no effects observed on the morphology and mechanical properties of these structures. Hence, these samples showed potential to be further investigated as candidates for bone tissue regeneration.

Electrical stimulation: Effective cue to direct osteogenic differentiation of mesenchymal stem cells?

Mesenchymal stem cells (MSCs) play a major role in bone tissue engineering (BTE) thanks to their capacity for osteogenic differentiation and being easily available. In vivo, MSCs are exposed to an electroactive microenvironment in the bone niche, which has piezoelectric properties. The correlation between the electrically active milieu and bone's ability to adapt to mechanical stress and self-regenerate has led to using electrical stimulation (ES) as physical cue to direct MSCs differentiation towards the osteogenic lineage in BTE. This review summarizes the different techniques to electrically stimulate MSCs to induce their osteoblastogenesis in vitro, including general electrical stimulation and substrate mediated stimulation by means of conductive or piezoelectric cell culture supports. Several aspects are covered, including stimulation parameters, treatment times and cell culture media to summarize the best conditions for inducing MSCs osteogenic commitment by electrical stimulation, from a critical point of view. Electrical stimulation activates different signaling pathways, including bone morphogenetic protein (BMP) Smad-dependent or independent, regulated by mitogen activated protein kinases (MAPK), extracellular signal-regulated kinases (ERK) and p38. The roles of voltage gate calcium channels (VGCC) and integrins are also highlighted according to their application technique and parameters, mainly converging in the expression of RUNX2, the master regulator of the osteogenic differentiation pathway. Despite the evident lack of homogeneity in the approaches used, the ever-increasing scientific evidence confirms ES potential as an osteoinductive cue, mimicking aspects of the in vivo microenvironment and moving one step forward to the translation of this approach into clinic.

Electrical Stimulation Increases Axonal Growth from Dorsal Root Ganglia Co-Cultured with Schwann Cells in Highly Aligned PLA-PPy-Au Microfiber Substrates

Nerve regeneration is a slow process that needs to be guided for distances greater than 5 mm. For this reason, different strategies are being studied to guide axonal growth and accelerate the axonal growth rate. In this study, we employ an electroconductive fibrillar substrate that is able to topographically guide axonal growth while accelerating the axonal growth rate when subjected to an exogenous electric field. Dorsal root ganglia were seeded in co-culture with Schwann cells on a substrate of polylactic acid microfibers coated with the electroconductive polymer polypyrrole, adding gold microfibers to increase its electrical conductivity. The substrate is capable of guiding axonal growth in a highly aligned manner and, when subjected to an electrical stimulation, an improvement in axonal growth is observed. As a result, an increase in the maximum length of the axons of 19.2% and an increase in the area occupied by the axons of 40% were obtained. In addition, an upregulation of the genes related to axon guidance, axogenesis, Schwann cells, proliferation and neurotrophins was observed for the electrically stimulated group. Therefore, our device is a good candidate for nerve regeneration therapies.

Design and Fabrication of Nanofibrous Dura Mater with Antifibrosis and Neuroprotection Effects on SH-SY5Y Cells

The development and treatment of some diseases, such as large-area cerebral infarction, cerebral hemorrhage, brain tumor, and craniocerebral trauma, which may involve the injury of the dura mater, elicit the need to repair this membrane by dural grafts. However, common dural grafts tend to result in dural adhesions and scar tissue and have no further neuroprotective effects. In order to reduce or avoid the complications of dural repair, we used PLGA, tetramethylpyrazine, and chitosan as raw materials to prepare a nanofibrous dura mater (NDM) with excellent biocompatibility and adequate mechanical characteristics, which can play a neuroprotective role and have an antifibrotic effect. We fabricated PLGA NDM by electrospinning, and then chitosan was grafted on the nanofibrous dura mater by the EDC-NHS cross-linking method to obtain PLGA/CS NDM. Then, we also prepared PLGA/TMP/CS NDM by coaxial electrospinning. Our study shows that the PLGA/TMP/CS NDM can inhibit the excessive proliferation of fibroblasts, as well as provide a sustained protective effect on the SH-SY5Y cells treated with oxygen-glucose deprivation/reperfusion (OGD/R). In conclusion, our study may provide a new alternative to dural grafts in undesirable cases of dural injuries.

Engineering Tissues of the Central Nervous System: Interfacing Conductive Biomaterials with Neural Stem/Progenitor Cells

Conductive biomaterials provide an important control for engineering neural tissues, where electrical stimulation can potentially direct neural stem/progenitor cell (NS/PC) maturation into functional neuronal networks. It is anticipated that stem cell-based therapies to repair damaged central nervous system (CNS) tissues and ex vivo, "tissue chip" models of the CNS and its pathologies will each benefit from the development of biocompatible, biodegradable, and conductive biomaterials. Here, technological advances in conductive biomaterials are reviewed over the past two decades that may facilitate the development of engineered tissues with integrated physiological and electrical functionalities. First, one briefly introduces NS/PCs of the CNS. Then, the significance of incorporating microenvironmental cues, to which NS/PCs are naturally programmed to respond, into biomaterial scaffolds is discussed with a focus on electrical cues. Next, practical design considerations for conductive biomaterials are discussed followed by a review of studies evaluating how conductive biomaterials can be engineered to control NS/PC behavior by mimicking specific functionalities in the CNS microenvironment. Finally, steps researchers can take to move NS/PC-interfacing, conductive materials closer to clinical translation are discussed.

Regenerative rehabilitation with conductive biomaterials for spinal cord injury

The individual approaches of regenerative medicine efforts alone and rehabilitation efforts alone have not yet fully restored function after severe spinal cord injury (SCI). Regenerative rehabilitation may be leveraged to promote regeneration of the spinal cord tissue, and promote reorganization of the regenerated neural pathways and intact spinal circuits for better functional recovery for SCI. Conductive biomaterials may be a linchpin that empowers the synergy between regenerative medicine and rehabilitation approaches, as electrical stimulation applied to the spinal cord could facilitate neural reorganization. In this review, we discuss current regenerative medicine approaches in clinical trials and the rehabilitation, or neuromodulation, approaches for SCI, along with their respective translational limitations. Furthermore, we review the translational potential, in a surgical context, of conductive biomaterials (e.g., conductive polymers, carbon-based materials, metallic nanoparticle-based materials) as they pertain to SCI. While pre-formed scaffolds may be difficult to translate to human contusion SCIs, injectable composites that contain blended conductive components and can form within the injury may be more translational. However, given that there are currently no in vivo SCI studies that evaluated conductive materials combined with rehabilitation approaches, we discuss several limitations of conductive biomaterials, including demonstrating safety and efficacy, that will need to be addressed in the future for conductive biomaterials to become SCI therapeutics. Even so, the use of conductive biomaterials creates a synergistic opportunity to merge the fields of regenerative medicine and rehabilitation and redefine what regenerative rehabilitation means for the spinal cord. STATEMENT OF SIGNIFICANCE: For spinal cord injury (SCI), the individual approaches of regenerative medicine and rehabilitation are insufficient to fully restore functional recovery; however, the goal of regenerative rehabilitation is to combine these two disparate fields to maximize the functional outcomes. Concepts similar to regenerative rehabilitation for SCI have been discussed in several reviews, but for the first time, this review considers how conductive biomaterials may synergize the two approaches. We cover current regenerative medicine and rehabilitation approaches for SCI, and the translational advantages and disadvantages, in a surgical context, of conductive biomaterials used in biomedical applications that may be additionally applied to SCI. Furthermore, we identify the current limitations and translational challenges for conductive biomaterials before they may become therapeutics for SCI.

Nerve guidance conduit development for primary treatment of peripheral nerve transection injuries: A commercial perspective

Commercial nerve guidance conduits (NGCs) for repair of peripheral nerve discontinuities are of little use in gaps larger than 30 mm, and for smaller gaps they often fail to compete with the autografts that they are designed to replace. While recent research to develop new technologies for use in NGCs has produced many advanced designs with seemingly positive functional outcomes in animal models, these advances have not been translated into viable clinical products. While there have been many detailed reviews of the technologies available for creating NGCs, none of these have focussed on the requirements of the commercialisation process which are vital to ensure the translation of a technology from bench to clinic. Consideration of the factors essential for commercial viability, including regulatory clearance, reimbursement processes, manufacturability and scale up, and quality management early in the design process is vital in giving new technologies the best chance at achieving real-world impact. Here we have attempted to summarise the major components to consider during the development of emerging NGC technologies as a guide for those looking to develop new technology in this domain. We also examine a selection of the latest academic developments from the viewpoint of clinical translation, and discuss areas where we believe further work would be most likely to bring new NGC technologies to the clinic. STATEMENT OF SIGNIFICANCE: NGCs for peripheral nerve repairs represent an adaptable foundation with potential to incorporate modifications to improve nerve regeneration outcomes. In this review we outline the regulatory processes that functionally distinct NGCs may need to address and explore new modifications and the complications that may need to be addressed during the translation process from bench to clinic.

Electroactive Smart Materials for Neural Tissue Regeneration

Repair in the human nervous system is a complex and intertwined process that offers significant challenges to its study and comprehension. Taking advantage of the progress in fields such as tissue engineering and regenerative medicine, the scientific community has witnessed a strong increase of biomaterial-based approaches for neural tissue regenerative therapies. Electroactive materials, increasingly being used as sensors and actuators, also find application in neurosciences due to their ability to deliver electrical signals to the cells and tissues. The use of electrical signals for repairing impaired neural tissue therefore presents an interesting and innovative approach to bridge the gap between fundamental research and clinical applications in the next few years. In this review, first a general overview of electroactive materials, their historical origin, and characteristics are presented. Then a comprehensive view of the applications of electroactive smart materials for neural tissue regeneration is presented, with particular focus on the context of spinal cord injury and brain repair. Finally, the major challenges of the field are discussed and the main challenges for the near future presented. Overall, it is concluded that electroactive smart materials play an ever-increasing role in neural tissue regeneration, appearing as potentially valuable biomaterials for regenerative purposes.

Mussel-inspired ultra-stretchable, universally sticky, and highly conductive nanocomposite hydrogels

Developing ultra-stretchable, universally sticky, and highly conductive nanocomposite hydrogels without doping agents and nanoparticle-aggregation is still a challenge. Herein, doping-free and nanoparticle-aggregation-inhibited hydrogels composed of Fe3+, dopamine (DA), pyrrole (Py) and polyacrylic acid (PAA) were prepared. Polypyrrole-polydopamine (PPy-PDA)/PAA hydrogels were quickly formed due to the abundant ionic bonds and physical cross-linking under the addition of Fe3+. Moreover, the H+ ions of the carboxylic acid groups on the PAA polymer chain helped to improve the conductivity of the hydrogels. Surprisingly, the multi-functional hydrogels received a high stretchability of 1900%, a tissue-like elastic modulus of 22 kPa, an adhesive strength of 2125.9 J m-2, and a high conductivity of 0.39 S m-1. Besides, the PPy-PDA/PAA hydrogels showed good antioxidant activity, biocompatibility and tissue repairing behavior. In short, the prepared multi-functional hydrogels have potential to address the human clinical problem of tissue repair and regeneration.

Boron nitride nanotube scaffolds: emergence of a new era in regenerative medicine

Tissue engineering scaffolds have transformed from passive geometrical supports for cell adhesion, extension and proliferation to active, dynamic systems that can in addition, trigger functional maturation of the cells in response to external stimuli. Such 'smart' scaffolds require the incorporation of active response elements that can respond to internal or external stimuli. One of the key elements that direct the cell fate processes is mechanical stress. Different cells respond to various types and magnitudes of mechanical stresses. The incorporation of a pressure-sensitive element in the tissue engineering scaffold therefore, will aid in tuning the cell response to the desired levels. Boron nitride nanotubes (BNNTs) are analogous to carbon nanotubes and have attracted considerable attention due to their unique amalgamation of chemical inertness, piezoelectric property, biocompatibility and, thermal and mechanical stability. Incorporation of BNNTs in scaffolds confers them with piezoelectric property that can be used to stimulate the cells seeded on them. Biorecognition and solubilization of BNNTs can be engineered through surface functionalization with different biomolecules. Over the years, the importance of BNNT has grown in the realm of healthcare nanotechnology. This review discusses the salient properties of BNNTs, the influence of functionalization on theirin vitroandin vivobiocompatibility, and the uniqueness of BNNT-incorporated tissue engineering scaffolds.

BDNF-Gene Transfected Schwann Cell-Assisted Axonal Extension and Sprouting on New PLA-PPy Microfiber Substrates

The work here reported analyzes the effect of increased efficiency of brain-derived neurotrophic factor (BDNF) production by electroporated Schwann cells (SCs) on the axonal extension in a coculture system on a biomaterial platform that can be of interest for the treatment of injuries of the nervous system, both central and peripheral. Rat SCs are electrotransfected with a plasmid coding for the BDNF protein in order to achieve an increased expression and release of this protein into the culture medium of the cells, performing the best balance between the level of transfection and the number of living cells. Gene-transfected SCs show an about 100-fold increase in the release of BDNF into the culture medium, compared to nonelectroporated SCs. Cocultivation of electroporated SCs with rat dorsal root ganglia (DRG) is performed on highly aligned substrates of polylactic acid (PLA) microfibers coated with the electroconductive polymer polypyrrol (PPy). The coculture of DRG with electrotransfected SCs increase both the axonal extension and the axonal sprouting from DRG neurons compared to the coculture of DRG with nonelectroporated SCs. Therefore, the use of PLA-PPy highly aligned microfiber substrates preseeded with electrotransfected SCs with an increased BDNF secretion is capable of both guiding and accelerating axonal growth.

Effects of surface condition of conductive electrospun nanofiber mats on cell behavior for nerve tissue engineering

Electrospun nanofibrous scaffold is a promising implant for peripheral nerve regeneration. Herein, to investigate the effect of surface morphological features and electrical properties of scaffolds on nerve cell behavior, we modified electrospun cellulose (EC) fibrous mats with four kind of soluble conductive polymers derivates (poly (N-(methacryl ethyl) pyrrole) (PMAEPy), poly (N-(2-hydroxyethyl) pyrrole) (PHEPy), poly (3-(Ethoxycarbonyl) thiophene) (P3ECT) and poly (3-thiophenethanol) (P3TE)) by an in-situ polymerization method. The morphological characterization showed that conductive polymers formed aggregated nanoparticles and coatings on the EC nanofibers with the increased fiber diameter further affected the surface properties. Compared with pure EC scaffold, more PC12 cells were adhered and grown on modified mats, with more integral and clearer cell morphology. The results of protein adsorption study indicated that modified EC mats could provide more protein adsorption site due to their characteristic surface morphology, which is beneficial to cell adhesion and growth. The results in this study suggested that these conductive polymers modified scaffolds with special surface morphology have potential applications in neural tissue engineering.

Graphene oxide-composited chitosan scaffold contributes to functional recovery of injured spinal cord in rats

The study illustrates that graphene oxide nanosheets can endow materials with continuous electrical conductivity for up to 4 weeks. Conductive nerve scaffolds can bridge a sciatic nerve injury and guide the growth of neurons; however, whether the scaffolds can be used for the repair of spinal cord nerve injuries remains to be explored. In this study, a conductive graphene oxide composited chitosan scaffold was fabricated by genipin crosslinking and lyophilization. The prepared chitosan-graphene oxide scaffold presented a porous structure with an inner diameter of 18–87 μm, and a conductivity that reached 2.83 mS/cm because of good distribution of the graphene oxide nanosheets, which could be degraded by peroxidase. The chitosan-graphene oxide scaffold was transplanted into a T9 total resected rat spinal cord. The results show that the chitosan-graphene oxide scaffold induces nerve cells to grow into the pores between chitosan molecular chains, inducing angiogenesis in regenerated tissue, and promote neuron migration and neural tissue regeneration in the pores of the scaffold, thereby promoting the repair of damaged nerve tissue. The behavioral and electrophysiological results suggest that the chitosan-graphene oxide scaffold could significantly restore the neurological function of rats. Moreover, the functional recovery of rats treated with chitosan-graphene oxide scaffold was better than that treated with chitosan scaffold. The results show that graphene oxide could have a positive role in the recovery of neurological function after spinal cord injury by promoting the degradation of the scaffold, adhesion, and migration of nerve cells to the scaffold. This study was approved by the Ethics Committee of Animal Research at the First Affiliated Hospital of Third Military Medical University (Army Medical University) (approval No. AMUWEC20191327) on August 30, 2019.

Electrospun cellulose-based conductive polymer nanofibrous mats: composite scaffolds and their influence on cell behavior with electrical stimulation for nerve tissue engineering

The fabrication of scaffolds with suitable chemical, physical, and electrical properties is critical for nerve cell adhesion and proliferation. Recently, electrical stimulation on conductive polymers has been applied to construct functional nerve cell scaffolds. Herein, we prepared natural polymer (cellulose)/conductive polymer nanofibrous mats, i.e., electrospun cellulose (EC)/poly N-vinylpyrrole (PNVPY) and EC/poly(3-hexylthiophene) (P3HT) through an efficient in situ polymerization method. The surface immobilization was characterized by optical microscopy (OM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, hydrophilicity, porosity, and cyclic voltammetry. The OM and SEM images showed that PNVPY formed polymer coatings and aggregated nanoparticles on the EC nanofibers, while P3HT only produced polymer coatings. Compared with pure EC mats, both the composite mats had increased thickness, higher porosity, and higher conductivity. Also, an increase in hydrophilicity was found for EC/P3HT. In vivo cytocompatibility of the undifferentiated PC12 cells showed that the EC/PNVPY and EC/P3HT scaffolds exhibited favorable cell activity, adhesion, and proliferation. Furthermore, the results of electrical stimulation experiments indicated that the EC/P3HT mats could effectively promote the proliferation of the PC12 cells more than the EC and EC/PNVPY mats. The findings suggest a positive outcome regarding the conductive polymer-modified EC/PNVPY and EC/P3HT nanofibrous mats in neural tissue engineering.

Fabrication of a Highly Conductive Silk Knitted Composite Scaffold by Two-Step Electrostatic Self-Assembly for Potential Peripheral Nerve Regeneration

Peripheral nerve injury is a common serious disease, and the electrical conductivity of nerve scaffolds is of special significance for nerve regeneration. Here, a highly conductive silk knitted composite scaffold was prepared by utilizing hydrogen bonding and electrostatic adsorption between silk amino, graphene (RGO), and polyaniline (PANI). Compared to traditional in situ polymerization of aniline (ANI), the surface of the RGO/PANI/silk conductive knitted scaffold prepared by two-step electrostatic self-assembly had more uniform PANI particles and lower resistance; when GO was 1 g/L and ANI was 0.4, 0.6, or 0.8 mol/L, the RGO/PANI/silk scaffold had better electrical properties when the conductivity was between 0.62 × 10^-3 and 1.72 × 10^-3 S/cm. The scaffolds had good conductive stability under different physical stresses and good mechanical properties, wherein ultimately the strength, elongation at break, and Young's modulus ranges were 28.07-34.97 MPa, 105.91-109.85%, and 10.2-12.48 MPa, respectively, and so they provided good support. Conductive scaffolds had ordered loops, fiber structure, and large pore sizes between 40 and 70 μm. In summary, RGO/PANI/silk scaffold with good conductivity, pore size distribution, mechanical properties, thermal properties had potential applications in the field of peripheral nerve regeneration.

Conductive Electrospun Nanofiber Mats

Conductive nanofiber mats can be used in a broad variety of applications, such as electromagnetic shielding, sensors, multifunctional textile surfaces, organic photovoltaics, or biomedicine. While nanofibers or nanofiber from pure or blended polymers can in many cases unambiguously be prepared by electrospinning, creating conductive nanofibers is often more challenging. Integration of conductive nano-fillers often needs a calcination step to evaporate the non-conductive polymer matrix which is necessary for the electrospinning process, while conductive polymers have often relatively low molecular weights and are hard to dissolve in common solvents, both factors impeding spinning them solely and making a spinning agent necessary. On the other hand, conductive coatings may disturb the desired porous structure and possibly cause problems with biocompatibility or other necessary properties of the original nanofiber mats. Here we give an overview of the most recent developments in the growing field of conductive electrospun nanofiber mats, based on electrospinning blends of spinning agents with conductive polymers or nanoparticles, alternatively applying conductive coatings, and the possible applications of such conductive electrospun nanofiber mats.