Aligned Nanofibers from Polypyrrole/Graphene as Electrodes for Regeneration of Optic Nerve via Electrical Stimulation

Advances in nanomedicine for retinal drug delivery: overcoming barriers and enhancing therapeutic outcomes

Nanomedicine offers a promising avenue for improving retinal drug delivery, effectively addressing challenges associated with ocular diseases like age-related macular degeneration and diabetic retinopathy. Nanoparticles, with their submicron size and customisable surface properties, enable enhanced permeability and retention within retinal tissues, supporting sustained drug release and minimising systemic side effects. Nanostructured scaffolds further provide a supportive environment for retinal cell growth and tissue regeneration, crucial for treating degenerative conditions. Additionally, advanced nanodevices facilitate real-time monitoring and controlled drug release, marking significant progress in retinal therapy. This study reviews recent advancements in nanomedicine for retinal drug delivery, critically analysing design innovations, therapeutic benefits, and limitations of these systems. By advancing nanotechnology integration in ocular therapies, this field holds strong potential for overcoming current barriers, ultimately improving patient outcomes and quality of life.

Bioactive Inorganic Materials for Innervated Multi-Tissue Regeneration

Tissue engineering aims to repair damaged tissues with physiological functions recovery. Although several therapeutic strategies are there for tissue regeneration, the functional recovery of regenerated tissues still poses significant challenges due to the lack of concerns of tissue innervation. Design rationale of multifunctional biomaterials with both tissue-induction and neural induction activities shows great potential for functional tissue regeneration. Recently, the research and application of inorganic biomaterials attracts increasing attention in innervated multi-tissue regeneration, such as central nerves, bone, and skin, because of its superior tunable chemical composition, topographical structures, and physiochemical properties. More importantly, inorganic biomaterials are easily combined with other organic materials, biological factors, and external stimuli to enhance their therapeutic effects. This review presents a comprehensive overview of recent advancements of inorganic biomaterials for innervated multi-tissue regeneration. It begins with introducing classification and properties of typical inorganic biomaterials and design rationale of inorganic-based material composites. Then, recent progresses of inorganic biomaterials in regenerating various nerves and nerve-innervated tissues with functional recovery are systematically reviewed. Finally, the existing challenges and future perspectives are proposed. This review may pave the way for the direction of inorganic biomaterials and offers a new strategy for tissue regeneration in combination of innervation.

Gradient conducting polymer surfaces with netrin-1-conjugation promote axon guidance and neuron transmission of human iPSC-derived retinal ganglion cells

Major advances have been made in utilizing human-induced pluripotent stem cells (hiPSCs) for regenerative medicine. Nevertheless, the delivery and integration of hiPSCs into target tissues remain significant challenges, particularly in the context of retinal ganglion cell (RGC) restoration. In this study, we introduce a promising avenue for providing directional guidance to regenerated cells in the retina. First, we developed a technique for construction of gradient interfaces based on functionalized conductive polymers, which could be applied with various functionalized ehthylenedioxythiophene (EDOT) monomers. Using a tree-shaped channel encapsulated with a thin PDMS and a specially designed electrochemical chamber, gradient flow generation could be converted into a functionalized-PEDOT gradient film by cyclic voltammetry. The characteristics of the successfully fabricated gradient flow and surface were analyzed using fluorescent labels, time of flight secondary ion mass spectrometry (TOF-SIMS), and X-ray photoelectron spectroscopy (XPS). Remarkably, hiPSC-RGCs seeded on PEDOT exhibited improvements in neurite outgrowth, axon guidance and neuronal electrophysiology measurements. These results suggest that our novel gradient PEDOT may be used with hiPSC-based technologies as a potential biomedical engineering scaffold for functional restoration of RGCs in retinal degenerative diseases and optic neuropathies.

Tissue engineering strategies for ocular regeneration; from bench to the bedside

Millions globally suffer from visual impairment, complicating the management of eye diseases due to various ocular barriers. The eye's complex structure and the limitations of existing treatments have spurred interest in tissue engineering (TE) as a solution. This approach offers new functionalities and improves therapeutic outcomes over traditional drug delivery methods, creating opportunities for treating various eye disorders, from corneal injuries to retinal degeneration. In our review of recent articles concerning the use of scaffolds for eye repair, we categorized scaffolds employed in eye TE from recent studies into four types based on tissue characteristics: natural, synthetic, biohybrid, and decellularized tissue. Additionally, we gathered data on the cell types and animal models associated with each scaffold. This allowed us to gather valuable insights into the benefits and drawbacks of each material. Our research elucidates that, in comparison to conventional treatment modalities, scaffolds in TE emulate the extracellular matrix (ECM) of the eye and facilitate cell proliferation and tissue regeneration. These scaffolds can be precisely tailored to incorporate growth factors that augment the healing process while also providing considerable advantages such as bacterial inhibition, biocompatibility, and enhanced durability. However, they also have drawbacks, such as potential immune responses, poor tissue integration, complex and costly manufacturing, and inconsistent degradation rates that can affect their effectiveness. In this review, we provide an overview of the present condition of eye regenerative treatments, assess notable preclinical and clinical research endeavors, contemplate the obstacles encountered, and speculate on potential advancements in the upcoming decade.

Recent advances in the treatment and delivery system of diabetic retinopathy

Diabetic retinopathy (DR) is a highly tissue-specific neurovascular complication of type 1 and type 2 diabetes mellitus and is among the leading causes of blindness worldwide. Pathophysiological changes in DR encompass neurodegeneration, inflammation, and oxidative stress. Current treatments for DR, including anti-vascular endothelial growth factor, steroids, laser photocoagulation, and vitrectomy have limitations and adverse reactions, necessitating the exploration of novel treatment strategies. This review aims to summarize the current pathophysiology, therapeutic approaches, and available drug-delivery methods for treating DR, and discuss their respective development potentials. Recent research indicates the efficacy of novel receptor inhibitors and agonists, such as aldose reductase inhibitors, angiotensin-converting enzyme inhibitors, peroxisome proliferator-activated receptor alpha agonists, and novel drugs in delaying DR. Furthermore, with continuous advancements in nanotechnology, a new form of drug delivery has been developed that can address certain limitations of clinical drug therapy, such as low solubility and poor penetration. This review serves as a theoretical foundation for future research on DR treatment. While highlighting promising therapeutic targets, it underscores the need for continuous exploration to enhance our understanding of DR pathogenesis. The limitations of current treatments and the potential for future advancements emphasize the importance of ongoing research in this field.

Hereditary Optic Neuropathies: A Systematic Review on the Interplay between Biomaterials and Induced Pluripotent Stem Cells

Hereditary optic neuropathies (HONs) such as dominant optic atrophy (DOA) and Leber Hereditary Optic Neuropathy (LHON) are mitochondrial diseases characterized by a degenerative loss of retinal ganglion cells (RGCs) and are a cause of blindness worldwide. To date, there are only limited disease-modifying treatments for these disorders. The discovery of induced pluripotent stem cell (iPSC) technology has opened several promising opportunities in the field of HON research and the search for therapeutic approaches. This systematic review is focused on the two most frequent HONs (LHON and DOA) and on the recent studies related to the application of human iPSC technology in combination with biomaterials technology for their potential use in the development of RGC replacement therapies with the final aim of the improvement or even the restoration of the vision of HON patients. To this purpose, the combination of natural and synthetic biomaterials modified with peptides, neurotrophic factors, and other low- to medium-molecular weight compounds, mimicking the ocular extracellular matrices, with human iPSC or iPSC-derived cell retinal progenitors holds enormous potential to be exploited in the near future for the generation of transplantable RGC populations.

Advances in Conductive Hydrogel for Spinal Cord Injury Repair and Regeneration

Spinal cord injury (SCI) treatment represents a major challenge in clinical practice. In recent years, the rapid development of neural tissue engineering technology has provided a new therapeutic approach for spinal cord injury repair. Implanting functionalized electroconductive hydrogels (ECH) in the injury area has been shown to promote axonal regeneration and facilitate the generation of neuronal circuits by reshaping the microenvironment of SCI. ECH not only facilitate intercellular electrical signaling but, when combined with electrical stimulation, enable the transmission of electrical signals to electroactive tissue and activate bioelectric signaling pathways, thereby promoting neural tissue repair. Therefore, the implantation of ECH into damaged tissues can effectively restore physiological functions related to electrical conduction. This article focuses on the dynamic pathophysiological changes in the SCI microenvironment and discusses the mechanisms of electrical stimulation/signal in the process of SCI repair. By examining electrical activity during nerve repair, we provide insights into the mechanisms behind electrical stimulation and signaling during SCI repair. We classify conductive biomaterials, and offer an overview of the current applications and research progress of conductive hydrogels in spinal cord repair and regeneration, aiming to provide a reference for future explorations and developments in spinal cord regeneration strategies.

Electrical, Electromagnetic, Ultrasound Wave Therapies, and Electronic Implants for Neuronal Rejuvenation, Neuroprotection, Axonal Regeneration, and IOP Reduction

The peripheral nervous system (PNS) of mammals and nervous systems of lower organisms possess significant regenerative potential. In contrast, although neural plasticity can provide some compensation, the central nervous system (CNS) neurons and nerves of adult mammals generally fail to regenerate after an injury or damage. However, use of diverse electrical, electromagnetic and sonographic energy waves are illuminating novel ways to stimulate neuronal differentiation, proliferation, neurite growth, and axonal elongation/regeneration leading to various levels of functional recovery in animals and humans afflicted with disorders of the CNS, PNS, retina, and optic nerve. Tools such as acupuncture, electroacupuncture, electroshock therapy, electrical stimulation, transcranial magnetic stimulation, red light therapy, and low-intensity pulsed ultrasound therapy are demonstrating efficacy in treating many different maladies. These include wound healing, partial recovery from motor dysfunctions, recovery from ischemic/reperfusion insults and CNS and ocular remyelination, retinal ganglion cell (RGC) rejuvenation, and RGC axonal regeneration. Neural rejuvenation and axonal growth/regeneration processes involve activation or intensifying of the intrinsic bioelectric waves (action potentials) that exist in every neuronal circuit of the body. In addition, reparative factors released at the nerve terminals and via neuronal dendrites (transmitter substances), extracellular vesicles containing microRNAs and neurotrophins, and intercellular communication occurring via nanotubes aid in reestablishing lost or damaged connections between the traumatized tissues and the PNS and CNS. Many other beneficial effects of the aforementioned treatment paradigms are mediated via gene expression alterations such as downregulation of inflammatory and death-signal genes and upregulation of neuroprotective and cytoprotective genes. These varied techniques and technologies will be described and discussed covering cell-based and animal model-based studies. Data from clinical applications and linkage to human ocular diseases will also be discussed where relevant translational research has been reported.

Next-Generation Nanomedicine Approaches for the Management of Retinal Diseases

Retinal diseases are one of the leading causes of blindness globally. The mainstay treatments for these blinding diseases are laser photocoagulation, vitrectomy, and repeated intravitreal injections of anti-vascular endothelial growth factor (VEGF) or steroids. Unfortunately, these therapies are associated with ocular complications like inflammation, elevated intraocular pressure, retinal detachment, endophthalmitis, and vitreous hemorrhage. Recent advances in nanomedicine seek to curtail these limitations, overcoming ocular barriers by developing non-invasive or minimally invasive delivery modalities. These modalities include delivering therapeutics to specific cellular targets in the retina, providing sustained delivery of drugs to avoid repeated intravitreal injections, and acting as a scaffold for neural tissue regeneration. These next-generation nanomedicine approaches could potentially revolutionize the treatment landscape of retinal diseases. This review describes the availability and limitations of current treatment strategies and highlights insights into the advancement of future approaches using next-generation nanomedicines to manage retinal diseases.

Synthesis and application of polypyrrole nanofibers: a review

State-of-the-art polypyrrole nanofiber-based nanoarchitectonics can be generally fabricated by electrospinning, interfacial polymerization and reactive template methods. Even though analogous nanofiber morphologies and nanofibrous network architectures can be obtained by these methods, the structural details and structural complexities may alter significantly as different synthesis methods are applied. For the electrospinning technique, on one hand, nanofibers can be directly obtained by spinning polypyrrole-containing dope solutions; on the other, the electrospun nanofiber mats can be used as templates to direct the nanofiber formation; a two-step fabrication process, including the electrospinning of polymer nanofiber mats and deposition of polypyrrole on the polymer nanofibers' surface, is generally employed. By tuning the electrospinning parameters, the composition, diameter, morphology, and alignment of the as-obtained electrospun nanofiber mat can be effectively controlled, which may allow the fabrication of polypyrrole nanofibers with sophisticated nanostructures and nanoarchitectures. Interfacial polymerization is capable of generating polypyrrole nanofibers without templates. It is speculated that the protonation and re-orientation of polypyrrole at the oil-water interface may decoil the polymer chains and transform them into more extended conformations, while the charged polymer chains more easily diffuse into the water phase and form a stable dispersion. Different from electrospinning, the reactive templates may drive the formation of polypyrrole nanofibers through either redox or protonation mechanisms. Nanofibers with different curvatures, compositions, and architectures can be obtained by using different types of reactive template in a simple, fast, environment-friendly and one-step manner. A wide range of applications have been demonstrated by the polypyrrole nanofiber-based nanoarchitectonics, including cell culture, tissue engineering, neural stimulation, energy storage, and organic electronics.

Application of Conductive Hydrogels on Spinal Cord Injury Repair: A Review

Spinal cord injury (SCI) causes severe motor or sensory damage that leads to long-term disabilities due to disruption of electrical conduction in neuronal pathways. Despite current clinical therapies being used to limit the propagation of cell or tissue damage, the need for neuroregenerative therapies remains. Conductive hydrogels have been considered a promising neuroregenerative therapy due to their ability to provide a pro-regenerative microenvironment and flexible structure, which conforms to a complex SCI lesion. Furthermore, their conductivity can be utilized for noninvasive electrical signaling in dictating neuronal cell behavior. However, the ability of hydrogels to guide directional axon growth to reach the distal end for complete nerve reconnection remains a critical challenge. In this Review, we highlight recent advances in conductive hydrogels, including the incorporation of conductive materials, fabrication techniques, and cross-linking interactions. We also discuss important characteristics for designing conductive hydrogels for directional growth and regenerative therapy. We propose insights into electrical conductivity properties in a hydrogel that could be implemented as guidance for directional cell growth for SCI applications. Specifically, we highlight the practical implications of recent findings in the field, including the potential for conductive hydrogels to be used in clinical applications. We conclude that conductive hydrogels are a promising neuroregenerative therapy for SCI and that further research is needed to optimize their design and application.

Nanofibers in Ocular Drug Targeting and Tissue Engineering: Their Importance, Advantages, Advances, and Future Perspectives

Nanofibers are frequently encountered in daily life as a modern material with a wide range of applications. The important advantages of production techniques, such as being easy, cost effective, and industrially applicable are important factors in the preference for nanofibers. Nanofibers, which have a broad scope of use in the field of health, are preferred both in drug delivery systems and tissue engineering. Due to the biocompatible materials used in their construction, they are also frequently preferred in ocular applications. The fact that they have a long drug release time as a drug delivery system and have been used in corneal tissue studies, which have been successfully developed in tissue engineering, stand out as important advantages of nanofibers. This review examines nanofibers, their production techniques and general information, nanofiber-based ocular drug delivery systems, and tissue engineering concepts in detail.

A Polypyrrole-Polycarbonate Polyurethane Elastomer Alleviates Cardiac Arrhythmias via Improving Bio-Conductivity

Myocardial fibrosis, resulting from myocardial infarction (MI), significantly alters cardiac electrophysiological properties. As fibrotic scar tissue forms, its resistance to incoming action potentials increases, leading to cardiac arrhythmia, and eventually sudden cardiac death or heart failure. Biomaterials are gaining increasing attention as an approach for addressing post-MI arrhythmias. The current study investigates the hypothesis that a bio-conductive epicardial patch can electrically synchronize isolated cardiomyocytes in vitro and rescue arrhythmic hearts in vivo. A new conceived biocompatible, conductive, and elastic polyurethane composite bio-membrane, referred to as polypyrrole-polycarbonate polyurethane (PPy-PCNU), is developed, in which solid-state conductive PPy nanoparticles are distributed throughout an electrospun aliphatic PCNU nanofiber patch in a controlled manner. Compared to PCNU alone, the resulting biocompatible patch demonstrates up to six times less impedance, with no conductivity loss over time, as well as being able to influence cellular alignment. Furthermore, PPy-PCNU promotes synchronous contraction of isolated neonatal rat cardiomyocytes and alleviates atrial fibrillation in rat hearts upon epicardial implantation. Taken together, epicardially-implanted PPy-PCNU could potentially serve as a novel alternative approach for the treatment of cardiac arrhythmias.

Applications of Graphene in Five Senses, Nervous System, and Artificial Muscles

Graphene remains of great interest in biomedical applications because of biocompatibility. Diseases relating to human senses interfere with life satisfaction and happiness. Therefore, the restoration by artificial organs or sensory devices may bring a bright future by the recovery of senses in patients. In this review, we update the most recent progress in graphene based sensors for mimicking human senses such as artificial retina for image sensors, artificial eardrums, gas sensors, chemical sensors, and tactile sensors. The brain-like processors are discussed based on conventional transistors as well as memristor related neuromorphic computing. The brain-machine interface is introduced for providing a single pathway. Besides, the artificial muscles based on graphene are summarized in the means of actuators in order to react to the physical world. Future opportunities remain for elevating the performances of human-like sensors and their clinical applications.

Soft Fiber Electronics Based on Semiconducting Polymer

Fibers, originating from nature and mastered by human, have woven their way throughout the entire history of human civilization. Recent developments in semiconducting polymer materials have further endowed fibers and textiles with various electronic functions, which are attractive in applications such as information interfacing, personalized medicine, and clean energy. Owing to their ability to be easily integrated into daily life, soft fiber electronics based on semiconducting polymers have gained popularity recently for wearable and implantable applications. Herein, we present a review of the previous and current progress in semiconducting polymer-based fiber electronics, particularly focusing on smart-wearable and implantable areas. First, we provide a brief overview of semiconducting polymers from the viewpoint of materials based on the basic concepts and functionality requirements of different devices. Then we analyze the existing applications and associated devices such as information interfaces, healthcare and medicine, and energy conversion and storage. The working principle and performance of semiconducting polymer-based fiber devices are summarized. Furthermore, we focus on the fabrication techniques of fiber devices. Based on the continuous fabrication of one-dimensional fiber and yarn, we introduce two- and three-dimensional fabric fabricating methods. Finally, we review challenges and relevant perspectives and potential solutions to address the related problems.

Recent advancements in polymeric nanofibers for ophthalmic drug delivery and ophthalmic tissue engineering

Nanofibers due to their unique properties such as high surface-to-volume ratio, porous structure, mechanical strength, flexibility and their resemblance to the extracellular matrix, have been researched extensively in the field of ocular drug delivery and tissue engineering. Further, different modifications considering the formulation and process parameters have been carried out to alter the drug release profile and its interaction with the surrounding biological environment. Electrospinning is the most commonly used technique for preparing nanofibers with industrial scalability. Advanced techniques such as co-axial electrospinning and combined system such as embedding nanoparticles in nanofiber provide an alternative approach to enhance the performance of the scaffold. Electrospun nanofibers offers a matrix like structure for cell regeneration. Nanofibers have been used for ocular delivery of various drugs like antibiotics, anti-inflammatory and various proteins. In addition, lens-coated medical devices provide new insights into the clinical use of nanofibers. Through fabricating the nanofibers researchers have overcome the issues of low bioavailability and compatibility with ocular tissue. Therefore, nanofibers have great potential in ocular drug delivery and tissue engineering and have the capacity to revolutionize these therapeutic areas in the field of ophthalmology. This review is mainly focused on the recent advances in the preparation of nanofibers and their applications in ocular drug delivery and tissue engineering. The authors have attempted to emphasize the processing challenges and future perspectives along with an overview of the safety and toxicity aspects of nanofibers.

Promotion of right ventricular outflow tract reconstruction using a novel cardiac patch incorporated with hypoxia-pretreated urine-derived stem cells

Approximately 25% of patients with congenital heart disease require implantation of patches to repair. However, most of the currently available patches are made of inert materials with unmatched electrical conductivity and mechanical properties, which may lead to an increased risk for arrhythmia and heart failure. In this study, we have developed a novel Polyurethane/Small intestinal submucosa patch (PSP) with mechanical and electrical properties similar to those of the native myocardial tissue, and assessed its feasibility for the reconstruction of right ventricular outflow tract. A right ventricular outflow tract reconstruction model was constructed in 40 rabbits. Compared with commercially available bovine pericardium patch, the PSP patch has shown better histocompatibility and biodegradability, in addition with significantly improved cardiac function. To tackle the significant fibrosis and relatively poor vascularization during tissue remodeling, we have further developed a bioactive patch by incorporating the PSP composites with urine-derived stem cells (USCs) which were pretreated with hypoxia. The results showed that the hypoxia-pretreated bioactive patch could significantly inhibit fibrosis and promote vascularization and muscularization, resulting in better right heart function. Our findings suggested that the PSP patch combined with hypoxia-pretreated USCs may provide a better strategy for the treatment of congenital heart disease.

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A novel cardiac patch (PSP) with mechanical and electrical properties similar to native myocardium.

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PSP patch improved cardiac function in right ventricular outflow tract reconstruction model.

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Hypoxia pretreated USCs combined PSP patch promoted vascularization and inhibited fibrosis.

Recent advances and challenges in graphene-based nanocomposite scaffolds for tissue engineering application

Graphene-based nanocomposites have recently attracted increasing attention in tissue engineering because of their extraordinary features. These biocompatible substances, in the presence of an apt microenvironment, can stimulate and sustain the growth and differentiation of stem cells into different lineages. This review discusses the characteristics of graphene and its derivatives, such as their excellent electrical signal transduction, carrier mobility, outstanding mechanical strength with improving surface characteristics, self-lubrication, antiwear properties, enormous specific surface area, and ease of functional group modification. Moreover, safety issues in the application of graphene and its derivatives in terms of biocompatibility, toxicity, and interaction with immune cells are discussed. We also describe the applicability of graphene-based nanocomposites in tissue healing and organ regeneration, particularly in the bone, cartilage, teeth, neurons, heart, skeletal muscle, and skin. The impacts of special textural and structural characteristics of graphene-based nanomaterials on the regeneration of various tissues are highlighted. Finally, the present review gives some hints on future research for the transformation of these exciting materials in clinical studies.

The Efficient Regeneration of Corneal Nerves via Tunable Transmembrane Signaling Channels Using a Transparent Graphene-Based Corneal Stimulation Electrode

The efficient regeneration of corneal nerves is of limited success in the field of ophthalmology. This work reports the use of a non-invasive electrical stimulation technique that uses a transparent graphene-based corneal stimulation electrode and that can achieve efficient regeneration of corneal nerves. The corneal stimulation electrode is prepared using electroactive nitrogen-containing conducting polymers such as polyaniline functionalized graphene (PAG). This composite can carry a high capacitive current. It can be used to tune transmembrane signaling pathways including calcium channels and the MAPK signaling pathway. Tuning can lead to the efficient regeneration of corneal damaged nerves after the surgery of laser in-situ keratomileusis (LASIK). The composite and its application reported have the potential to provide a new way to treat nerve-related injuries.

Integrated osteochondral differentiation of mesenchymal stem cells on biomimetic nanofibrous mats with cell adhesion-generated piezopotential gradients

Biomimetic piezoelectric scaffolds provide a noninvasive method for in vivo cell regulation and tissue regeneration. Herein, considering the gradually varied piezoelectric properties of native cartilage and bone tissues, we fabricated biomimetic electrospun poly(L-lactic acid) (PLLA) nanofibrous mats with gradient piezoelectric properties to induce the integrated osteochondral differentiation of rat mesenchymal stem cells (MSCs). Nanofibrous mats are polarized under electric fields with linear variation of strength to generate gradient piezoelectricity, and cell adhesion-derived contraction forces could produce gradient piezoelectric potential on the scaffolds. Our results demonstrated that the piezoelectric potential could positively modulate cell adhesion, intracellular calcium transients, Ca²⁺ binding proteins, and differentiation-related genes. In addition, the differentiation of MSCs into osteogenic and chondrogenic lineages was integrated on a single scaffold at different areas with relatively high and low piezoelectricity values, respectively. The continuous gradient scaffold exhibited the potential to provide a smooth transition between the cartilage and bone, offering new insights to probe the regeneration mechanisms of the osteochondral tissue in a single scaffold and inspiring a future efficient and rational design of piezoelectric smart biomaterials for tissue engineering.

A Microfluidic Eye Facsimile System to Examine the Migration of Stem-like Cells

Millions of adults are affected by progressive vision loss worldwide. The rising incidence of retinal diseases can be attributed to damage or degeneration of neurons that convert light into electrical signals for vision. Contemporary cell replacement therapies have transplanted stem and progenitor-like cells (SCs) into adult retinal tissue to replace damaged neurons and restore the visual neural network. However, the inability of SCs to migrate to targeted areas remains a fundamental challenge. Current bioengineering projects aim to integrate microfluidic technologies with organotypic cultures to examine SC behaviors within biomimetic environments. The application of neural phantoms, or eye facsimiles, in such systems will greatly aid the study of SC migratory behaviors in 3D. This project developed a bioengineering system, called the μ-Eye, to stimulate and examine the migration of retinal SCs within eye facsimiles using external chemical and electrical stimuli. Results illustrate that the imposed fields stimulated large, directional SC migration into eye facsimiles, and that electro-chemotactic stimuli produced significantly larger increases in cell migration than the individual stimuli combined. These findings highlight the significance of microfluidic systems in the development of approaches that apply external fields for neural repair and promote migration-targeted strategies for retinal cell replacement therapy.

Towards the translation of electroconductive organic materials for regeneration of neural tissues

Carbon-based conductive and electroactive materials (e.g., derivatives of graphene, fullerenes, polypyrrole, polythiophene, polyaniline) have been studied since the 1970s for use in a broad range of applications. These materials have electrical properties comparable to those of commonly used metals, while providing other benefits such as flexibility in processing and modification with biologics (e.g., cells, biomolecules), to yield electroactive materials with biomimetic mechanical and chemical properties. In this review, we focus on the uses of these electroconductive materials in the context of the central and peripheral nervous system, specifically recent studies in the peripheral nerve, spinal cord, brain, eye, and ear. We also highlight in vivo studies and clinical trials, as well as a snapshot of emerging classes of electroconductive materials (e.g., biodegradable materials). We believe such specialized electrically conductive biomaterials will clinically impact the field of tissue regeneration in the foreseeable future. STATEMENT OF SIGNIFICANCE: This review addresses the use of conductive and electroactive materials for neural tissue regeneration, which is of significant interest to a broad readership, and of particular relevance to the growing community of scientists, engineers and clinicians in academia and industry who develop novel medical devices for tissue engineering and regenerative medicine. The review covers the materials that may be employed (primarily focusing on derivatives of fullerenes, graphene and conjugated polymers) and techniques used to analyze materials composed thereof, followed by sections on the application of these materials to nervous tissues (i.e., peripheral nerve, spinal cord, brain, optical, and auditory tissues) throughout the body.

Electrospun conductive nanofiber yarns for accelerating mesenchymal stem cells differentiation and maturation into Schwann cell-like cells under a combination of electrical stimulation and chemical induction

Development of multifunctional tube-filling materials is required to improve the performances of the existing nerve guidance conduits (NGCs) in the repair of long-gap peripheral nerve (PN) injuries. In this study, composite nanofiber yarns (NYs) based on poly(p-dioxanone) (PPDO) biopolymer and different concentrations of carbon nanotubes (CNTs) were manufactured by utilizing a modified electrospinning apparatus. We confirmed the successful incorporation of CNTs into the PPDO nanofibers of as-fabricated composite NYs. The PPDO/CNT NYs exhibited similar morphology and structure in comparison with pure PPDO NYs. However, the PPDO/CNT NYs showed obviously enhanced mechanical properties and electrical conductivity compared to PPDO NYs. The biological tests revealed that the addition of CNTs had no negative effects on the cell growth, and proliferation of rabbit Schwann cells (rSCs), but it better maintained the phenotype of rSCs. We also demonstrated that the electrical stimulation (ES) significantly enhanced the differentiation capability of human adipose-derived mesenchymal stem cells (hADMSCs) into SC-like cells (SCLCs) on the PPDO/CNT NYs. More importantly, a unique combination of ES and chemical induction was found to further enhance the maturation of hADMSC-SCLCs on the PPDO/CNT NYs by notably upregulating the expression levels of SC myelination-associated gene markers and increasing the growth factor secretion. Overall, this study showed that our electrically conductive PPDO/CNT composite NYs could provide a beneficial microenvironment for various cell activities, making them an attractive candidate as NGC-infilling substrates for PN regeneration applications. STATEMENT OF SIGNIFICANCE: The morphology, microstructure, and bioelectrical properties of conductive PPDO/CNT NYs have been explored for guiding or controlling cell behaviors. The PPDO/CNT NYs exhibited improved mechanical properties and increased electrical conductivity compared to the CNT-free PPDO NYs. They also presented an obviously enhanced biocompatibility by effectively maintaining the phenotype of rSCs. In addition, when hADMSCs were seeded and cultured on the conductive PPDO/CNT NYs, CI was demonstrated to promote the SC-related growth factor secretion of hADMSCs, and ES was demonstrated to improve the phenotypic maturation of hADMSCs into myelinating SCLCs. Moreover, the combination of CI and ES was found to further synergistically enhance the maturation of hADMSC-SCLCs. The achievement of conductive PPDO/CNT NYs shows potential for application as NGC-infilling substrates for PN regeneration.

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.

Organic Bioelectronics for In Vitro Systems

Bioelectronics have made strides in improving clinical diagnostics and precision medicine. The potential of bioelectronics for bidirectional interfacing with biology through continuous, label-free monitoring on one side and precise control of biological activity on the other has extended their application scope to in vitro systems. The advent of microfluidics and the considerable advances in reliability and complexity of in vitro models promise to eventually significantly reduce or replace animal studies, currently the gold standard in drug discovery and toxicology testing. Bioelectronics are anticipated to play a major role in this transition offering a much needed technology to push forward the drug discovery paradigm. Organic electronic materials, notably conjugated polymers, having demonstrated technological maturity in fields such as solar cells and light emitting diodes given their outstanding characteristics and versatility in processing, are the obvious route forward for bioelectronics due to their biomimetic nature, among other merits. This review highlights the advances in conjugated polymers for interfacing with biological tissue in vitro, aiming ultimately to develop next generation in vitro systems. We showcase in vitro interfacing across multiple length scales, involving biological models of varying complexity, from cell components to complex 3D cell cultures. The state of the art, the possibilities, and the challenges of conjugated polymers toward clinical translation of in vitro systems are also discussed throughout.

Conductive conduit based on electrospun poly (l-lactide-co-D, l-lactide) nanofibers containing 4-aminopyridine-loaded molecularly imprinted poly (methacrylic acid) nanoparticles used for peripheral nerve regeneration

Using biocompatible polymer nanofibrous conduits with a controlled drug delivery have attracted much attention for peripheral nerve regeneration. This work was aimed at preparing electrospun poly (l-lactide-co-D, l-lactide) (PLDLLA) containing multi-walled carbon nanotubes (MWCNTs) and 4-aminopyridine (4-AP)-loaded molecularly imprinted nanoparticles (MIP_4-AP) as well as evaluating their performance in in vitro and in vivo assessments. After synthesis of MIP_4-AP based on poly (methacrylic acid) with imprinting factor of 1.78, it was incorporated into the PLDLLA/MWCNTs nanofibers to optimize. By adjusting the process variables, the average diameter and electrical conductivity of the nanofibrous sample were 92 nm and 2870 × 10^-7 S cm^-1, respectively. Afterward, 4-AP release of the optimum sample showed the presence of MIP_4-AP leading to initial burst release decrease and plateau level postpone up to 96 h. Moreover, the culture results of PC12 as neuroblastoma cell line on optimal PLDLLA/MWCNTs/MIP_4-AP nanofibrous sample revealed the highest cell proliferation without cytotoxicity compared to neat nanofibers. Eventually, the animal model experiment exhibited that the conductive conduit based on the optimum sample was able to repair the rat's sciatic nerve after four weeks in accordance with sciatic function index and histological studies.

Electrical Stimulation and Conductive Polymers as a Powerful Toolbox for Tailoring Cell Behaviour in vitro

Electrical stimulation (ES) is a well-known method for guiding the behaviour of nerve cells in in vitro systems based on the response of these cells to an electric field. From this perspective, understanding how the electrochemical stimulus can be tuned for the design of a desired cell response is of great importance. Most biomedical studies propose the application of an electrical potential to cell culture arrays while examining the cell response regarding viability, morphology, and gene expression. Conversely, various studies failed to evaluate how the fine physicochemical properties of the materials used for cell culture influence the observed behaviours. Among the various materials used for culturing cells under ES, conductive polymers (CPs) are widely used either in pristine form or in addition to other polymers. CPs themselves do not possess the optimal surface for cell compatibility because of their hydrophobic nature, which leads to poor protein adhesion and, hence, poor bioactivity. Therefore, understanding how to tailor the chemical properties on the material surface will determine the obtention of improved ES platforms. Moreover, the structure of the material, either in a thin film or in porous electrospun scaffolds, also affects the biochemical response and needs to be considered. In this review, we examine how materials based on CPs influence cell behaviour under ES, and we compile the various ES setups and physicochemical properties that affect cell behaviour. This review concerns the culture of various cell types, such as neurons, fibroblasts, osteoblasts, and Schwann cells, and it also covers studies on stem cells prone to ES. To understand the mechanistic behaviour of these devices, we also examine studies presenting a more detailed biomolecular level of interaction. This review aims to guide the design of future ES setups regarding the influence of material properties and electrochemical conditions on the behaviour of in vitro cell studies.

Oxygen content-related DNA damage of graphene oxide on human retinal pigment epithelium cells

Arguments regarding the biocompatibility of graphene-based materials (GBMs) have never ceased. Particularly, the genotoxicity (e.g., DNA damage) of GBMs has been considered the greatest risk to healthy cells. Detailed genotoxicity studies of GBMs are necessary and essential. Herein, we present our recent studies on the genotoxicity of most widely used GBMs such as graphene oxide (GO) and the chemically reduced graphene oxide (RGO) toward human retinal pigment epithelium (RPE) cells. The genotoxicity of GO and RGOs against ARPE-19 (a typical RPE cell line) cells was investigated using the alkaline comet assay, the expression level of phosphorylated p53 determined via Western blots, and the release level of reactive oxygen species (ROS). Our results suggested that both GO and RGOs induced ROS-dependent DNA damage. However, the DNA damage was enhanced following the reduction of the saturated C-O bonds in GO, suggesting that surface oxygen-containing groups played essential roles in the reduced genotoxicity of graphene and had the potential possibility to reduce the toxicity of GBMs via chemical modification.

Progress of Nanotechnology in Diabetic Retinopathy Treatment

Diabetic retinopathy (DR) is a chronic diabetes complication that progressively manifests itself as blurred vision, eye floaters, distorted vision, and even partial or total loss of vision as a result of retinal detachment in severe cases. Clinically, patients who have undergone variations in the microcirculation of the ocular fundus are treated with laser photocoagulation to improve the circulation of retina; but for patients with macular edema, anti-vascular endothelial growth factor (anti-VEGF) drugs are generally injected to eliminate macular edema and improve vision. The worst cases are patients with fundus hemorrhage or proliferative vitreoretinopathy, for whom vitrectomy has been performed. At present, these clinical treatment methods have widely been used, providing satisfactory results. However, considering the low bioavailability and potential side effects of drugs and the inevitable risks in major surgery, DR prevention, and treatment as well as nerve tissue regeneration in the later stage have always been the focus of research. In recent years, nanotechnology has been increasingly applied in the medical field, leading to new ideas for DR treatment. This study aims to systematically review the research progress of nanotechnology in DR treatment.

Optimizing the electrical conductivity of polyacrylonitrile/polyaniline with nickel nanoparticles for the enhanced electrostimulation of Schwann cells proliferation

Tissue engineering scaffolds made of biocompatible polymers are promising alternatives for nerve reparation. For this application, cell proliferation will be speeded up by electrostimulation, which required electrically-conductive materials. Here, a biomimicking scaffold with optimized conductivity was developed from electrospun polyacrylonitrile/electrically-conductive polyaniline (PAN/PANI) nanofibers doped with Ni nanoparticles. PAN/PANI/Ni was biocompatible for Schwann cells and exhibited a suitable tensile strength and wettability for cell proliferation. When compared with unmodified PAN/PANI, the electrical conductivity of PAN/PANI/Ni was 6.4 fold higher. Without electrostimulation, PAN/PANI and PAN/PANI/Ni exhibited similar Schwann cells' proliferation rates. Upon electrostimulation at 100 mV cm^-1 for one hour per day over five days, PAN/PANI/Ni accelerated Schwann cells' proliferation 2.1 times compared to PAN/PANI. These results demonstrate the importance of expanding the electrical conductivity of the tissue engineering scaffold to ensure optimal electrostimulation of nerve cell growth. Additionally, this study describes a straightforward approach to modulate the electrical conductivity of polymeric materials via the addition of Ni nanoparticles that can be applied to different biomimicking scaffolds for nerve healing.

Surface-Functionalized Conducting Nanofibers for Electrically Stimulated Neural Cell Function

Strategies involving the inclusion of cell-instructive chemical and topographical cues to smart biomaterials in combination with a suitable physical stimulus may be beneficial to enhance nerve-regeneration rate. In this regard, we investigated the surface functionalization of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)-based electroconductive electrospun nanofibers coupled with externally applied electrical stimulus for accelerated neuronal growth potential. In addition, the voltage-dependent conductive mechanism of the nanofibers was studied in depth to interlink intrinsic conductive properties with electrically stimulated neuronal expressions. Surface functionalization was accomplished using 3-aminopropyltriethoxysilane (APTES) and 1,6-hexanediamine (HDA) as an alternative to costly biomolecule coating (e.g., collagen) for cell adhesion. The nanofibers were uniform, porous, electrically conductive, mechanically strong, and stable under physiological conditions. Surface amination boosted biocompatibility, 3T3 cell adhesion, and spreading, while the neuronal model rat PC12 cell line showed better differentiation on surface-functionalized mats compared to nonfunctionalized mats. When coupled with electrical stimulation (ES), these mats showed comparable or faster neurite formation and elongation than the collagen-coated mats with no-ES conditions. The findings indicate that surface amination in combination with ES may provide an improved strategy to faster nerve regeneration using MEH-PPV-based neural scaffolds.

Current Advances in 3D Tissue and Organ Reconstruction

Bi-dimensional culture systems have represented the most used method to study cell biology outside the body for over a century. Although they convey useful information, such systems may lose tissue-specific architecture, biomechanical effectors, and biochemical cues deriving from the native extracellular matrix, with significant alterations in several cellular functions and processes. Notably, the introduction of three-dimensional (3D) platforms that are able to re-create in vitro the structures of the native tissue, have overcome some of these issues, since they better mimic the in vivo milieu and reduce the gap between the cell culture ambient and the tissue environment. 3D culture systems are currently used in a broad range of studies, from cancer and stem cell biology, to drug testing and discovery. Here, we describe the mechanisms used by cells to perceive and respond to biomechanical cues and the main signaling pathways involved. We provide an overall perspective of the most recent 3D technologies. Given the breadth of the subject, we concentrate on the use of hydrogels, bioreactors, 3D printing and bioprinting, nanofiber-based scaffolds, and preparation of a decellularized bio-matrix. In addition, we report the possibility to combine the use of 3D cultures with functionalized nanoparticles to obtain highly predictive in vitro models for use in the nanomedicine field.

Carbon Nanomaterials for Electro-Active Structures: A Review

The use of electrically conductive materials to impart electrical properties to substrates for cell attachment proliferation and differentiation represents an important strategy in the field of tissue engineering. This paper discusses the concept of electro-active structures and their roles in tissue engineering, accelerating cell proliferation and differentiation, consequently leading to tissue regeneration. The most relevant carbon-based materials used to produce electro-active structures are presented, and their main advantages and limitations are discussed in detail. Particular emphasis is put on the electrically conductive property, material synthesis and their applications on tissue engineering. Different technologies, allowing the fabrication of two-dimensional and three-dimensional structures in a controlled way, are also presented. Finally, challenges for future research are highlighted. This review shows that electrical stimulation plays an important role in modulating the growth of different types of cells. As highlighted, carbon nanomaterials, especially graphene and carbon nanotubes, have great potential for fabricating electro-active structures due to their exceptional electrical and surface properties, opening new routes for more efficient tissue engineering approaches.

A universal strategy: Rational construction of noble metal nanoparticle-shell/conducting polymer nanofiber-core electrodes with enhanced electrochemical performances

To address a challenge for decoration of noble metal nanoparticles (NMNPs)-shell on conducting polymer nanofiber (CPNF) electrodes (i.e. NMNP-shell/CPNF-core electrodes) for boosting electrochemical performances, a two-step strategy comprising chemical pre-deposition and electrochemical deposition is designed. The strategy shows a high universality in terms of the diversity of NMNP-shell elements (single-element: AgNP-shell, AuNP-shell, PtNP-shell, PdNP-shell; multi-element: Au/Pt/PdNP-shell) and the independence of conductive substrates of electrodes. The shells are composed of high-density NMNPs and have strong adhesion to CPNF-cores. It is demonstrated that in response to a specific applied electrical stimulus, the resulting low doping level of CPNFs facilitates the generation of high-density nucleation sites (small NMNPs) by chemical pre-deposition (as high capability of electron transfer and low resistance to electron transfer from CP chains to NM ions), which is indispensable for the formation of NMNP-shells on CPNF-cores by electrochemical deposition. The decoration of NMNP-shells can significantly enhance the electrochemical performances of CPNF electrodes. Moreover, the great practicality and reliability of NMNP-shell/CPNF-core electrodes in use as an electrocatalytic platform are confirmed. This universal strategy opens up a new avenue to construct high-dimension shell/core-nanostructured electrodes.

Fabrication of 3D Scaffolds Displaying Biochemical Gradients along Longitudinally Oriented Microchannels for Neural Tissue Engineering

Biochemical and physical guidance cues are both pivotal for axonal guidance and nerve regeneration. However, fabrication of a platform that can integrate biochemical gradients and topographical guidance cues remains challenging, especially in a three-dimensional (3D) scaffold that closely mimics in vivo axonal outgrowth conditions and ready to be used for in vivo nerve repair. In this study, a new method was introduced to construct 3D scaffolds displaying continuous biochemical gradients along longitudinally oriented microchannels by combining the modified 3D printing and directional freezing techniques. Fluorescence analysis and ELISA results demonstrated that a continuous biochemical gradient was formed, and scanning electron microscopy revealed a longitudinally oriented microstructure. Dorsal root ganglia explants seeded on the longitudinal sections of the newly developed scaffold (scaffold with nerve growth factor gradient along oriented microstructure, G-NGF + OS) showed that 81.3 ± 4.5% of neurites oriented within ±10°, 0.3 ± 0.1 of guidance ratio, and 1.5-fold of the average length of neurites on the high-nerve growth factor (NGF) concentration side compared to that on the low-NGF concentration side, which were significantly higher than those in the other groups. In addition, the G-NGF + OS scaffold was used to repair a 15 mm sciatic nerve defect in rats. Immunofluorescence staining, Fluoro-Gold retrograde tracing, and transmission electron microscopy results confirmed that the G-NGF + OS scaffold enhanced nerve regeneration to the distal target and promoted myelination of regenerated axons. More importantly, the sciatic functional index and the von Frey test demonstrated that the G-NGF + OS scaffold accelerated sensory and motor functional recovery. These results provide new insights into the importance of combining topographical guidance cues with bioactive molecule gradient cues for neural tissue engineering. The 3D scaffold displaying biochemical gradients along longitudinally oriented microchannels represents a promising platform for the development of advanced devices for severe nervous system injuries.

Tissue-in-a-Tube: three-dimensional in vitro tissue constructs with integrated multimodal environmental stimulation

Three-dimensional (3D) in vitro tissue models are superior to two-dimensional (2D) cell cultures in replicating natural physiological/pathological conditions by recreating the cellular and cell-matrix interactions more faithfully. Nevertheless, current 3D models lack either the rich multicellular environment or fail to provide appropriate biophysical stimuli both of which are required to properly recapitulate the dynamic in vivo microenvironment of tissues and organs. Here, we describe the rapid construction of multicellular, tubular tissue constructs termed Tissue-in-a-Tube using self-assembly process in tubular molds with the ability to incorporate a variety of biophysical stimuli such as electrical field, mechanical deformation, and shear force of the fluid flow. Unlike other approaches, this method is simple, requires only oxygen permeable silicone tubing that molds the tissue construct and thin stainless-steel pins inserted in it to anchor the construct and could be used to provide electrical and mechanical stimuli, simultaneously. The annular region between the tissue construct and the tubing is used for perfusion. Highly stable, macroscale, and robust constructs anchored to the pins form as a result of self-assembly of the extracellular matrix (ECM) and cells in the bioink that is filled into the tubing. We demonstrate patterning of grafts containing cell types in the constructs in axial and radial modes with clear interface and continuity between the layers. Different environmental factors affecting cell behavior such as compactness of the structure and size of the constructs can be controlled through parameters such as initial cell density, ECM content, tubing size, as well as the distance between anchor pins. Using connectors, network of tubing can be assembled to create complex macrostructured tissues (centimeters length) such as fibers that are bifurcated or columns with different axial thicknesses which can then be used as building blocks for biomimetic constructs or tissue regeneration. The method is versatile and compatible with various cell types including endothelial, epithelial, skeletal muscle cells, osteoblast cells, and neuronal cells. As an example, long mature skeletal muscle and neuronal fibers as well as bone constructs were fabricated with cellular alignment dictated by the applied electrical field. The versatility, speed, and low cost of this method is suited for widespread application in tissue engineering and regenerative medicine.

Microphysiological Systems: Design, Fabrication, and Applications

Microphysiological systems, including organoids, 3-D printed tissue constructs and organ-on-a-chips (organ chips), are physiologically relevant in vitro models and have experienced explosive growth in the past decades. Different from conventional, tissue culture plastic-based in vitro models or animal models, microphysiological systems recapitulate key microenvironmental characteristics of human organs and mimic their primary functions. The advent of microphysiological systems is attributed to evolving biomaterials, micro-/nanotechnologies and stem cell biology, which enable the precise control over the matrix properties and the interactions between cells, tissues and organs in physiological conditions. As such, microphysiological systems have been developed to model a broad spectrum of organs from microvasculature, eye, to lung and many others to understand human organ development and disease pathology and facilitate drug discovery. Multiorgans-on-a-chip systems have also been developed by integrating multiple associated organ chips in a single platform, which allows to study and employ the organ function in a systematic approach. Here we first discuss the design principles of microphysiological systems with a focus on the anatomy and physiology of organs, and then review the commonly used fabrication techniques and biomaterials for microphysiological systems. Subsequently, we discuss the recent development of microphysiological systems, and provide our perspectives on advancing microphysiological systems for preclinical investigation and drug discovery of human disease.

Controlled Dynamics of Neural Tumor Cells by Templated Liquid Crystalline Polymer Networks

The ability to control the alignment and organization of cell populations has great potential for tissue engineering and regenerative medicine. A variety of approaches such as nano/microtopographical patterning, mechanical loading, and nanocomposite synthesis have been developed to engineer scaffolds able to control cellular properties and behaviors. In this work, a patterned liquid crystal polymer network (LCN) film is synthesized by using a nematic liquid crystal template in which the molecular orientations are predesigned by photopatterning technique. Various configurations of polymer networks such as linear and circular patterns are created. When neural tumor cells are plated onto the templated LCN films, the cell alignment, migration, and proliferation are directed in both linear and curvilinear fashions following the pattern of the aligned polymer chains. A complex LCN pattern with zigzag geometry is also fabricated and found to be capable of controlling cell alignment and collective cellular organization. The demonstrated control of cell dynamics and organization by LCN films with various molecular alignments opens new opportunities to design scaffolds to control cultured cell organization in a manner resembling that found in tissues and to develop novel advanced materials for nerve repair, tissue engineering, and regenerative medicine applications.

Graphene Oxide-Based Nanomaterials: An Insight into Retinal Prosthesis

Retinal prosthesis has recently emerged as a treatment strategy for retinopathies, providing excellent assistance in the treatment of age-related macular degeneration (AMD) and retinitis pigmentosa. The potential application of graphene oxide (GO), a highly biocompatible nanomaterial with superior physicochemical properties, in the fabrication of electrodes for retinal prosthesis, is reviewed in this article. This review integrates insights from biological medicine and nanotechnology, with electronic and electrical engineering technological breakthroughs, and aims to highlight innovative objectives in developing biomedical applications of retinal prosthesis.

Reduced graphene oxide–GelMA–PCL hybrid nanofibers for peripheral nerve regeneration

Graphene oxide is currently used in peripheral nerve engineering but has certain limitations, such as cytotoxicity and lack of electrical conductivity, both of which are crucial in regulating nerve-associated cell behaviors.

A micropatterned conductive electrospun nanofiber mesh combined with electrical stimulation for synergistically enhancing differentiation of rat neural stem cells

The micropatterned conductive nanofiber mesh combined with ES effectively facilitates the differentiation of NSCs into neuron and suppresses the formation of astrocytes.

Current progress in application of polymeric nanofibers to tissue engineering

Tissue engineering uses a combination of cell biology, chemistry, and biomaterials to fabricate three dimensional (3D) tissues that mimic the architecture of extracellular matrix (ECM) comprising diverse interwoven nanofibrous structure. Among several methods for producing nanofibrous scaffolds, electrospinning has gained intense interest because it can make nanofibers with a porous structure and high specific surface area. The processing and solution parameters of electrospinning can considerably affect the assembly and structural morphology of the fabricated nanofibers. Electrospun nanofibers can be made from natural or synthetic polymers and blending them is a straightforward way to tune the functionality of the nanofibers. Furthermore, the electrospun nanofibers can be functionalized with various surface modification strategies. In this review, we highlight the latest achievements in fabricating electrospun nanofibers and describe various ways to modify the surface and structure of scaffolds to promote their functionality. We also summarize the application of advanced polymeric nanofibrous scaffolds in the regeneration of human bone, cartilage, vascular tissues, and tendons/ligaments.

Design of high conductive and piezoelectric poly (3,4-ethylenedioxythiophene)/chitosan nanofibers for enhancing cellular electrical stimulation

Electroactive nanofibrous scaffold is a vital tool for the study of the various biological research fields from bioelectronics to regenerative medicine, which can provide cell preferable 3D nanofiber architecture and programmed electrical signal. However, intrinsic non-biodegradability is a major problem that hinders its widespread application in the clinic. Herein, we designed, synthesized, and characterized shell/core poly (3,4-ethylenedioxythiophene) (PEDOT)/chitosan (CS) nanofibers by combining the electrospinning and recrystallization processes. Upon incorporating a trace amount of PEDOT (1.0 wt%), the resultant PEDOT/CS nanofibers exhibited low interfacial charge transfer impedance, high electrochemical stability, high electrical conductivity (up to 0.1945 S/cm), and ultrasensitive piezoelectric property (output voltage of 22.5 mV by a human hair prodding). With such unique electrical and conductive properties, PEDOT/CS nanofibers were further applied to brain neuroglioma cells (BNCs) to stimulate their adhesion, proliferation, growth, and development under an optimal external electrical stimulation (ES) and a pulse voltage of 400 mV/cm. ES-responsive PEDOT/CS nanofibers indeed promoted BNCs growth and development as indicated by a large number and density of axons. The synergetic interplay between external ES and piezoelectric voltage demonstrates new PEDOT-based nanofibers as implantable electroactive scaffolds for numerous applications in nerve tissue engineering, human health monitoring, brain mantle information extraction, and degradable microelectronic devices.

Advances in electrical and magnetic stimulation on nerve regeneration

Central and peripheral nerve injuries pose a great threat to people. Complications such as inflammation, muscle atrophy, traumatic neuromas and delayed reinnervation can bring huge challenges to clinical practices and barriers to complete nerve regrowth. Physical interventions such as electrical and magnetic stimulation show satisfactory results with varying parameters for acute and chronic nerve damages. The biological basis of electrical and magnetic stimulation mainly relies on protein synthesis, ion channel regulation and growth factor secretion. This review focuses on the various paradigms used in different models of electrical and magnetic stimulation and their regenerative potentials and underlying mechanisms in nerve injuries. The combination of physical stimulation and conductive biomaterial scaffolds displays an infinite potentiality in translational application in nerve regeneration.