Scaffolds For Nerve Regeneration Research Articles

Comprehensive Development of a Cellulose Acetate and Soy Protein-Based Scaffold for Nerve Regeneration.

The elaboration of biocompatible nerve guide conduits (NGCs) has been studied in recent years as a treatment for total nerve rupture lesions (axonotmesis). Different natural polymers have been used in these studies, including cellulose associated with soy protein. The purpose of this report was to describe manufacturing NGCs suitable for nerve regeneration using the method of dip coating and evaporation of solvent with cellulose acetate (CA) functionalized with soy protein acid hydrolysate (SPAH). The manufacturing method and bacterial control precautions for the CA/SPAH NGCs were described. The structure of the NGCs was analyzed under a scanning electron microscope (SEM); porosity was analyzed with a degassing method using a porosimeter. Schwann cell (SCL 4.1/F7) biocompatibility of cell-seeded nerve guide conduits was evaluated with the MTT assay. The method employed allowed an easy elaboration and customization of NGCs, free of bacteria, with pores in the internal surface, and the uniform wall thickness allowed manipulation, which showed flexibility; additionally, the sample was suturable. The NGCs showed initial biocompatibility with Schwann cells, revealing cells adhered to the NGC structure after 5 days. The fabricated CA/SPAH NGCs showed adequate features to be used for peripheral nerve regeneration studies. Future reports are necessary to discuss the ideal concentration of CA and SPAH and the mechanical and physicochemical properties of this biomaterial.

Regulating Schwann cells and endothelial cells by YIGSR functionalized porous chitosan scaffolds for nerve regeneration

Numerous artificial nerve implants for repair of peripheral nerve injury has been developed while their performance still needs to be further improved. In this study, the Tyr-Ile-Gly-Ser-Arg (YIGSR, YR) functionalized porous chitosan scaffolds were prepared by freeze-drying technique and surface biomodification for simultaneous regulation of Schwann cells (SCs) and endothelial cells (ECs), which play important role in nerve regeneration. The physicochemical properties were characterized, including morphology, composition, wettability, mechanical properties, porosity, etc. The culture of SCs and ECs were used to evaluate the pro-neural and endothelial cell growth effects of the grafts, as well as the constitutive relationship between YR-regulated SCs and ECs. Then, the mechanisms involved were explored using molecular biology experiments. The results showed that the YR-grafted chitosan scaffolds could be successfully prepared with aggregated dopamine and YR particles on the surface of the scaffolds. The scaffolds showed a uniform porous structure, YR grafting decreased the porosity of the scaffolds but increased the mechanical properties of the scaffolds, and YR displayed a relatively stable release behavior. Further on, all YR-grafted scaffolds were proven no cytotoxicity and significantly promoted the proliferation and spreading of SCs and ECs, up-regulated the gene expression of Tumor Necrosis Factor-alpha (TNF-α) and Recombinant Contactin 2 (Cntn2), and facilitated the release of growth factors such as brain derived neurotrophic factor (BDNF), nerve growth factor (NGF), and vascular endothelial growth factor (VEGF). Thus, this YR-functionalized scaffold is expected to simultaneously promote both neuronal cell growth and vascularization in peripheral nerve regeneration. This study provides a strategy for the development of biofunctionalized nerve grafts.

Coaxial 3D printing of hierarchical structured hydrogel scaffolds for on-demand repair of spinal cord injury.

After spinal cord injury (SCI), endogenous neural stem cells (NSCs) near the damaged site are activated, but few NSCs migrate to the injury epicenter and differentiate into neurons because of the harsh microenvironment. It has demonstrated that implantation of hydrogel scaffold loaded with multiple cues can enhance the function of endogenous NSCs. However, programming different cues on request remains a great challenge. Herein, a time-programmed linear hierarchical structure scaffold is developed for spinal cord injury recovery. The scaffold is obtained through coaxial 3D printing by encapsulating a dual-network hydrogel (composed of hyaluronic acid derivatives and N-cadherin modified sodium alginate, inner layer) into a temperature responsive gelatin/cellulose nanofiber hydrogel (Gel/CNF, outer layer). The reactive species scavenger, metalloporphyrin, loaded in the outer layer is released rapidly by the degradation of Gel/CNF, inhibiting the initial oxidative stress at lesion site to protect endogenous NSCs; while the inner hydrogel with appropriate mechanical support, linear topology structure and bioactive cues facilitates the migration and neuronal differentiation of NSCs at the later stage of SCI treatment, thereby promoting motor functional restorations in SCI rats. This study offers an innovative strategy for fabrication of multifunctional nerve regeneration scaffold, which has potential for clinical treatment of SCI. STATEMENT OF SIGNIFICANCE: Two major challenges facing the recovery from spinal cord injury (SCI) are the low viability of endogenous neural stem cells (NSCs) within the damaged microenvironment, as well as the difficulty of neuronal regeneration at the injured site. To address these issues, a spinal cord-like coaxial scaffold was fabricated with free radical scavenging agent metalloporphyrin Mn (III) tetrakis (4-benzoic acid) porphyrin and chemokine N-cadherin. The scaffold was constructed by 3D bioprinting for time-programmed protection and modulation of NSCs to effectively repair SCI. This 3D coaxially bioprinted biomimetic construct enables multi-factor on-demand repair and may be a promising therapeutic strategy for SCI.

The Impact of the Molecular Weight of Degradation Products with Silicon from Porous Chitosan-Siloxane Hybrids on Neuronal Cell Behavior.

Silicon (Si) is an essential trace element in the human body and it exists in connective tissue as aqueous orthosilicic acid. Porous chitosan-3-glycidoxypropyltrimethoxysilane (GPTMS) hybrids can regenerate nerve tissue and recover sensor and motor functions. However, the structures and roles of the degradation products with Si extracted from the hybrids in nerve regeneration are not clear. In this study, we prepared porous chitosan-GPTMS hybrids with different amounts of GPTMS to amino groups of chitosan (chitosan:GPTMS = 1:0.5 and 1:1 molar ratios). The structures of the degradation products with Si from the hybrids were examined using time-of-flight mass spectrometry, and biological assessments were conducted in order to evaluate their potential use in the preparation of devices for nerve repair. Glial and motor cell lines and ex vivo explants of dorsal root ganglia were used in this study for evaluating their behavior in the presence of the different degradation products with Si. The structure of the degradation products with Si depended on the starting composition. The results showed that glial cell proliferation was lower in the medium with the higher-molecular-weight degradation products with Si. Moreover, motor cell line differentiation and the neurite outgrowth of dorsal root ganglion explants were improved with the lower-molecular-weight degradation products with Si. The results obtained could be useful for designing a new nerve regeneration scaffold including silicon components.

Polyhydroxybutyrate (PHB) Scaffolds for Peripheral Nerve Regeneration: A Systematic Review of Animal Models.

Simple SummaryCurrently, polymeric biomaterials are the choice for the design of scaffolds for the regeneration of peripheral nerves. Polyhydroxybutyrate (PHB) is a polymer belonging to the class of polyesters that are produced naturally in nature by microorganisms. To gain a better understanding of the efficacy of therapeutic approaches involving PHB scaffolds for peripheral nerve regeneration, we conducted a systematic review of the literature with the aim of discussing the current knowledge of PHB scaffolds applied to nerve regeneration. The use of PHB as a biomaterial to prepare tubular scaffolds for nerve regeneration was shown to be promising. The incorporation of additives appears to be a trend that improves nerve regeneration.In the last two decades, artificial scaffolds for nerve regeneration have been produced using a variety of polymers. Polyhydroxybutyrate (PHB) is a natural polyester that can be easily processed and offer several advantages; hence, the purpose of this review is to provide a better understanding of the efficacy of therapeutic approaches involving PHB scaffolds in promoting peripheral nerve regeneration following nerve dissection in animal models. A systematic literature review was performed following the “Preferred Reporting Items for Systematic Reviews and Meta-Analyses” (PRISMA) criteria. The revised databases were: Pub-Med/MEDLINE, Web of Science, Science Direct, EMBASE, and SCOPUS. Sixteen studies were included in this review. Different animal models and nerves were studied. Extension of nerve gaps reconnected by PHB scaffolds and the time periods of analysis were varied. The additives included in the scaffolds, if any, were growth factors, neurotrophins, other biopolymers, and neural progenitor cells. The analysis of the quality of the studies revealed good quality in general, with some aspects that could be improved. The analysis of the risk of bias revealed several weaknesses in all studies. The use of PHB as a biomaterial to prepare tubular scaffolds for nerve regeneration was shown to be promising. The incorporation of additives appears to be a trend that improves nerve regeneration. One of the main weaknesses of the reviewed articles was the lack of standardized experimentation on animals. It is recommended to follow the currently available guidelines to improve the design, avoid the risk of bias, maximize the quality of studies, and enhance translationality.

Biocompatibility of hydroxyethyl cellulose/glycine/RuO2 composite scaffolds for neural-like cells

Fabrication of scaffolds for nerve regeneration is one of the most challenging topics in regenerative medicine at the moment, which is also interlinked with the development of biocompatible substrates for cells growth. This work is targeted towards the development of green biomaterial composite scaffolds for nerve cell culture applications. Hybrid scaffolds of hydroxyethyl cellulose/glycine (HEC/Gly) composite doped with different concentrations of green ruthenium oxide (RuO2) were synthesized and characterized via a combination of different techniques. X-rays diffraction (XRD) and differential scanning calorimetry (DSC) analyses showed a crystalline nature for all the samples with noticeable decrease in the peak intensity of the fabricated scaffolds as compared to that for pure glycine. Fourier transform infrared spectroscopy (FTIR) tests revealed an increase in the vibrational bands of the synthesized RuO2 containing scaffolds which are related to the functional groups of the natural plant extract (Aspalathuslinearis) used for RuO2 nanoparticles (NPs) synthesis. Scanning electron microscopy (SEM) results revealed a 3D porous structure of the scaffolds with variant features attributed to the concentration of RuO2 NPs in the scaffold. The compressive test results recorded an enhancement in mechanical properties of the fabricated scaffolds (up to 8.55 MPa), proportionally correlated to increasing the RuO2 NPs concentration in HEC/Gly composite scaffold. Our biocompatibility tests revealed that the composite scaffolds doped with 1 and 2 ml of RuO2 demonstrated the highest proliferation percentages (152.2 and 135.6%) compared to control. Finally, the SEM analyses confirmed the impressive cells attachments and differentiation onto the scaffold surfaces as evidenced by the presence of many neuron-like cells with apparent cell bodies and possessing few short neurite-like processes. The presence of RuO2 and glycine was due to their extraordinary biocompatibility due to their cytoprotective and regenerative effects. Therefore, we conclude that these scaffolds are promising for accommodation and growth of neural-like cells.

Gene delivery of chitosan-graft-polyethyleneimine vectors loaded on scaffolds for nerve regeneration

As an important transcription factor, c-Jun could upregulate growth factors expression in Schwann cells (SCs). Arginine-Glycine-Aspartate (RGD)-functionalized chitosan-graft-polyethyleneimine (RCP) gene vectors were prepared through the maleic anhydride & the carbodiimide methods, and electrostatically bound with c-Jun plasmids (pJUN), finally loaded on poly-L-lactic acid/silk fibroin parallel fiber films to fabricate nerve scaffold (RCP/pJUN-PSPF@PGA), which could locally deliver c-Jun plasmids into SCs via the mediation of RGD peptides, and upregulate the expression of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) in SCs. After the scaffold was bridged in sciatic nerve defect, the delivery of c-Jun plasmids from RCP/pJUN-PSPF@PGA facilitated SCs to sustain the expressions of NGF, BDNF and vascular endothelial growth factor in the injury field, promoting myelination, axonal growth and microvascular generation and nerve regeneration, muscle reinnervation and functional recovery. These results suggested that RCP/pDNA-PSPF@PGA, as an effective gene delivery platform, could provide a local gene therapy to improve nerve regeneration.

Effect of Olibanum Extract/Graphene Oxide on Differentiation of Bone Marrow Mesenchymal Stem Cells into Neuron-Like Cells on Freeze Dried Scaffolds.

One of the challenges in using stem cells to neural repair is to induce their differentiation into neurons and lack of glial formation. Mesenchymal stem cells have revealed great potential for neural reorganization and renewal by taking advantage of differentiation capabilities. Here we explored the potential use of olibanum extract in freeze-dried scaffolds for induction of stem cells differentiation. In this study, gelatin/ collagen/olibanum/ graphene oxide (GEL/COL/OL/GO) freeze-dried scaffolds were synthesized and then adult rat bone marrow mesenchymal stem cells (BMMSCs) were seeded on scaffolds. The viability of cells was evaluated using MTT test on days 1, 3 and 5. The morphology of the cells seeded on scaffolds was studied using SEM and specific protein expression detected by immunohistochemical analysis. Real-time PCR was applied to detect the expression of Chat, Pax6, Hb-9, Nestin, Islet-1, and neurofilament-H (NF-H). The data were analyzed using Tukey test and one-way ANOVA and the means difference was considered significant atP<0.05, P<0.01, and P<0.001. Showed that the pore size is increased in GEL/COL/OL/GO scaffolds compared with GO-free scaffolds and higher attachment and proliferation of BMMSCs on GEL/COL/OL /1.5% GO scaffolds compared to GEL/COL/OL/3% GO scaffolds. The cell viability results after 5 days of incubation showed the significant biocompatibility of GEL/COL/OL /1.5% GO freeze-dried scaffold. The results of immunohistochemicaland PCR analysis revealed positive role of GEL/COL/OL/1.5% GO scaffolds in upregulation of neuron-specific markers. These results reveal the great potential of GEL/COL/OL/GO scaffolds for nerve regeneration. Our data suggested that both OL extract and GO can regulate the MSCs differentiation into neurons.

Multifunctional biomimetic hydrogel based on graphene nanoparticles and sodium alginate for peripheral nerve injury therapy.

Peripheral nerve injury (PNI) caused by injury may influence the patients' lifelong mobility unless there is an appropriate treatment. Tissue engineering has become a hot field to replace traditional autologous nerve transplantation due to its low surgical damage and easy-to-industrial advantages. Graphene (GR) is a kind of carbon nanomaterial with good electrical and mechanical properties that satisfy the demand for a good tissue scaffold for nerve regeneration. Herein, a novel and biosafe hydrogel is fabricated by using graphene and sodium alginate (GR-SA) together. This hydrogel not only can mimic the nerve growth microenvironment but also can promote the expression of neurotrophic substances and growth factors. Additionally, GR-SA hydrogel can significantly reduce inflammatory factors. Moreover, the results of both in vitro and in vivo tests demonstrate that GR-SA hydrogel has a promising prospect in PNI regeneration.

Electrospun Fibers Derived from Peptide Coupled Amphiphilic Copolymers for Dorsal Root Ganglion (DRG) Outgrowth.

Developing scaffolds with appropriate mechanical/structural features as well as tunable bioactivities are indispensable in the field of tissue engineering. This study focused on one such attempt to electrospin the copolymer of L-lactic acid (L-LA) and functional monomer (3(S)- [(benzyloxycarbony)methyl]-1,4-dioxane-2,5-dione, BMD) with small peptide modifications for the purpose of neural tissue engineering. Scanning Electron Microscopy (SEM) micrographs showed fabricated electrospun copolymer as porous and uniform nanofibrous materials with diameter in the range of 800–1000 nm. In addition, the modified scaffolds displayed a lower contact angle than poly(L-lactide) (PLLA) indicating higher hydrophilicity. To further incorporate the bioactive functions, the nanofibers were chemically coupled with small peptide (isoleucine-lysine-valine-alanine-valine, IKVAV). The incorporation of IKVAV onto the electrospun fiber was confirmed by X-ray photoelectron spectroscopy (XPS) and such incorporation did not affect the surface morphology or fiber diameters. To demonstrate the potential of applying the designed scaffolds for nerve regeneration, dorsal root ganglion (DRG) neurons were cultured on the nanofibers to examine the impact on neurite outgrowth of DRGs. The results indicated that the fabricated nanofibrous matrix with small peptide might be a potential candidate for neural tissue engineering.

Enhanced neural differentiation of human-induced pluripotent stem cells on aligned laminin-functionalized polyethersulfone nanofibers; a comparison between aligned and random fibers on neurogenesis.

Despite the numerous attempts in nerve tissue engineering, no ideal strategy has been translated into effective therapy for neuronal regeneration yet. Here, we designed a novel nerve regeneration scaffold combining aligned laminin-immobilized polyethersulfone (PES) nanofibers and human-induced pluripotent stem cells (hiPSCs) for transplantation strategies. Aligned and random PES nanofibers were fabricated by electrospinning method with a diameter of 95-500 nm and were then modified with covalent laminin bounding subsequent to O2 plasma treatment. PES-functionalized fibers found to induce a remarkable higher rate of neuronal genes expression as compared to nontreated group. In addition, hiPSCs cultured on aligned pure fibers exhibited the extension of neurites along with fibers direction and an exponentially elevated expression of neuron specific enolase (early neuroectoderm marker), Tuj-1 (axonal marker), and microtubule-associated protein 2 (dendritic marker) in comparison with random pure fibers. The concomitant of increased hydrophilicity and biocompatibility along with exploiting topographical cues and directional guidance make aligned PES-plasma-laminin a versatile scaffold for adhesion, proliferation, spreading, and differentiation of hiPSCs into nerve cells.

Fabrication of a dual-layer cell-laden tubular scaffold for nerve regeneration and bile duct reconstruction

Tubular scaffolds serve as a controllable extracellular environment to guide the repair and regeneration of tissues. But it is still a challenge to achieve both excellent mechanical properties and cell compatibility of artificial scaffolds for long-term structural and biological stability. In this study, a four-step solution casting method was developed to fabricate dual-layer cell-laden tubular scaffolds for nerve and bile duct regeneration. The dual-layer tubular scaffold consisted of a bone marrow mesenchymal stem cells (BMSCs)-laden hydrogel inner layer and an outer layer of gelatin methacrylate (GelMA)/polyethylene glycol diacrylate. While the inner layer had a good biocompatibility, the outer layer had desired mechanical properties. The interfacial toughness, Young’s modulus, maximum tensile strain, and compressive modulus of dual-layer tubular scaffolds were 65 J m−2, 122.37 ± 23.21 kPa, 100.87 ± 40.10%, and 39.14 ± 18.56 N m−1, respectively. More importantly, the fabrication procedure was very cell-friendly, since the BMSC viability encapsulated in the inner layer of 10% (w/v) GelMA reached 94.68 ± 0.43% after 5 d of culture. Then, a preliminary evaluation of the potential application of dual-layer tubular scaffolds as nerve conduits and biliary scaffolds was performed, and demonstrated that the cell-laden dual-layer tubular scaffolds proposed in this work are expected to extend the application of tubular scaffolds in tissue engineering.

Polyhydroxybutyrate (PHB) tubular scaffolds for nerve regeneration

Introduction Peripheral nerve injuries remain a challenge in regenerative medicine. Biocompatible polymer tubular nerve guides (GNTs) have been shown to be a promising strategy in the regeneration of total nerve disruption injuries (neurotmesis). The purpose of this systematic literature review was to search and analyze the evidence on the use of the polyhydroxybutyrate (PHB) biopolymer GNT in the regeneration of peripheral nerves in an animal model. Material and method A systematic search was carried out in the search engines: PubMed / MEDLINE, Web of Science, Science Direct, EMBASE and SCOPUS. Using the phrase: (“PHB” OR “P3HB”) AND (“nerve injury” OR “nerve lesion” OR “nerve regeneration”). Between September/2019 and March/2020. In vivo studies with no date limit were considered. Results 193 studies were identified, of which 71 were excluded because they were not related to the topic. Of the remaining 122 studies, 82 were duplicated. Finally, of the remaining 40 studies, 23 were excluded because they were “in vitro” studies and 1 clinical study. Finally 16 studies were reviewed in full text. Conclusions Since the 1990s there have been studies with PHB GNT for nerve injury, primarily in rabbits and rodents. The analysis times and the size of the nerve GAPs do not reveal a standardization. Most of the studies used industrially manufactured PHB sheets. As of 2003, a tendency to include additives (growth factors, neurotrophins and neuroprogenitor cells) to the GNT was noticed. Most of the studies analyzed morphological aspects (macroscopic morphology, histology, immunohistochemistry and ultrastructure), only 3 studies performed functional tests. Overall, the results were positive for the use of GNT made with PHB in animal studies. However, more controlled clinical and functional studies should be performed to confirm the results obtained.

Electrospinning Fabrication and Cytocompatibility Investigation of Nanodiamond Particles-Gelatin Fibrous Tubular Scaffolds for Nerve Regeneration.

This paper reports the electrospinning fabrication of flexible nanostructured tubular scaffolds, based on fish gelatin (FG) and nanodiamond nanoparticles (NDs), and their cytocompatibility with murine neural stem cells. The effects of both nanofiller and protein concentration on the scaffold morphology, aqueous affinity, size modification at rehydration, and degradation are assessed. Our findings indicate that nanostructuring with low amounts of NDs may modify the fiber properties, including a certain regional parallel orientation of fiber segments. NE-4C cells form dense clusters that strongly adhere to the surface of FG50-based scaffolds, while also increasing FG concentration and adding NDs favor cellular infiltration into the flexible fibrous FG70_NDs nanocomposite. This research illustrates the potential of nanostructured NDs-FG fibers as scaffolds for nerve repair and regeneration. We also emphasize the importance of further understanding the effect of the nanofiller-protein interphase on the microstructure and properties of electrospun fibers and on cell-interactivity.

Preparation and characterization of self-electrical stimuli conductive gellan based nano scaffold for nerve regeneration containing chopped short spun nanofibers of PVDF/MCM41 and polyaniline/graphene nanoparticles: Physical, mechanical and morphological studies

Conductive self -electrical stimuli bioactive scaffolds could be used the potential for peripheral nerve regeneration with the maximum efficiency. To produce such conductive self-electrical stimuli bioactive scaffolds, chopped spun piezoelectric nanofibers of polyvinylidene fluoride/mesoporous silica nanoparticle (PVDF/MCM41) are prepared and incorporated in gellan/polyaniline/graphene (gellan/PAG) nanocomposites which have been previously prepared by incorporation of polyaniline/graphene (PAG) nanoparticles in gellan gel at 80 °C. Highly conductive binary doped polyaniline/graphene nanoparticles are prepared by chemical oxidative polymerization of aniline monomer using in-suite precipitation polymerization method in presence of graphene nanoparticles and sodium dodecyl sulfate. All intermediate and final products including spun PVDF/MCM41 nanofibers, PAG nanoparticles, and gellan-gelatin gel scaffolds containing PVDF/MCM41 nano spun fibers and PAG nanoparticles are characterized using different analysis methods. Chemical and structural analyses of PAG nanoparticles and PVDF/MCM41 nanofibers have been done using FTIR and XRD methods. The morphological structure of different samples is investigated using SEM. Morphological investigation and DLS results confirm fabrication of MCM41 nanoparticle with a completely spherical shape and the average size of 50 nm of which have been dispersed in electrospun PVDF nanofibers very well. Also, the preparation of PAG nanoparticle with high conductivity is verified with morphological and conductivity tests. MTT easy and biocompatibility test results indicate potential applicability of the prepared conductive self -stimuli nano-scaffold for nerve regeneration applications.

Regulating Electrical Cue and Mechanotransduction in Topological Gradient Structure Modulated Piezoelectric Scaffolds to Predict Neural Cell Response

AbstractNeural cells respond to topographical cues with alterations in cell growth and neurite sprouting mediated by changes in cell behavior. The interaction of fiber topography with cell adhesion receptors affects how the cells adhere to the surface of fibers and defines cell fate through alterations in the biochemistry, physiology, and morphology of neural cells. Although previous studies suggest topographical features influence neural cell proliferation and neurite sprouting, only a few studies have attempted to assess the use of both electrical and topological cues in piezoelectric scaffolds for nerve regeneration. In this study, variations in the shape‐modified collectors enable tunable surface topographic constructs, from micropatterns to fiber bundle structure. The crystallinity, chemical composition, and quantitative analysis confirm that the interplay between the topological structures of the fibers and the blending of nanocomposite materials is critical for the formation of the β‐phase. It is found that the topographical features and induced electrical characteristics affect cell growth. Also, the intracellular signaling pathway is induced that can provide clues as to how neural cells respond to the topological gradient structure modulated piezoelectric scaffolds. An analysis of the neuron‐specific cytoskeletal related markers further reveals that the specific topographical features piezoelectric fibrous scaffold reinforces neuron‐specific cytoskeletal proteins and microtubule assembly.

Bioinspired immobilization of carbon nanotubes on scaffolds for nerve regeneration

Carbon nanotubes (CNTs) have different applications in regenerative neurology such as neural signal transfer, nerve tissue engineering and neuroprosthetic devices. Their electrical conductivity and biocompatibility make them appropriate candidates for cell stimulation. This study was conducted to determine whether polydopamine (PD) can immobilize CNTs on the surface of nanofibrous scaffolds. To investigate this, electrospun scaffolds of poly(lactide-co-glycolide) (PLGA) were coated with CNTs both directly and by means of PD. Scanning electron microscopy (SEM), water contact angle measurement and Raman spectroscopy were used to verify the presence of dopamine on the surface of the scaffolds. The presence of PD on the substrate surface decreased the contact angle from 135·92 ± 2 to 82·65 ± 2°. Raman spectroscopy confirmed results by appearance of new peaks at 1350 and 1582 cm−1, which correspond to the aromatic component of PD. Measuring the electrical resistance proved that dopamine could effectively immobilize CNTs on the surface of nanofibers, decreasing the electrical resistance to 5·5 kΩ/square. Likewise, SEM images revealed a change in surface morphology induced by PD coating. Finally, cell viability studies demonstrated that CNT–PD–PLGA had no toxic effect on PC12 cells. The preliminary results were promising, supporting potential application of these materials as conductive scaffolds in nerve cell stimulation.

Enhancement of Schwann Cells Function Using Graphene-Oxide-Modified Nanofiber Scaffolds for Peripheral Nerve Regeneration.

Peripheral nerve regeneration and functional recovery remain a significant clinical challenge. Biomaterials that can regulate biological behavior of Schwann cell (SC) and promote neural cell differentiation are beneficial for nerve regeneration and functional recovery. Graphene oxide (GO), as a bioactive nanomaterial, has attracted great attention in biomedical applications. In this study, the possibility of combining the excellent physicochemical properties of GO with nanofiber to develop a bioactive scaffold for nerve regeneration were explored. Briefly, GO was coated on the ApF/PLCL scaffolds. To demonstrate the potentials of this platform, in vitro and in vivo studies toward nerve regeneration were carried out. In vitro, GO-coated scaffolds could enhance SC biological behaviors including migration, proliferation, and myelination. The secretions from SCs cultured on GO-ApF/PLCL scaffolds could induce PC12 cells differentiation. Furthermore, GO-coated nanofibrous scaffolds proved to up-regulate focal adhesion kinase (FAK) expression of PC12 cell. In vivo, GO-ApF/PLCL nerve conduits could successfully repair a 10 mm sciatic nerve defect. These findings suggest that GO-based scaffolds efficiently modulate cell functions and promote nerve regeneration, indicating their potential for nerve regeneration applications.

Fabrication of poly (trimethylene carbonate)/reduced graphene oxide-graft-poly (trimethylene carbonate) composite scaffolds for nerve regeneration

One of the key challenges for neural tissue engineering is to exploit functional materials to guide and support nerve regeneration. Currently, reduced graphene oxide (rGO), which is well-known for its unique electrical and mechanical properties, has been incorporated into biocompatible polymers to manufacture functional scaffolds for nerve tissue engineering. However, rGO has poor dispersity in polymer matrix, which limits its further application. Here, we replaced rGO with rGO-graft-PTMC. The rGO-graft-PTMC was firstly prepared by grafting trimethylene carbonate (TMC) oligomers onto rGO. Subsequently, PTMC/rGO-graft-PTMC composite fibrous mats were fabricated by electrospinning of a dispersion of PTMC and rGO-graft-PTMC. The loading of rGO-graft-PTMC could reach up to 6 wt% relative to PTMC. Scanning electron microscopy images showed that the morphologies and average diameters of PTMC/rGO-graft-PTMC composite fibrous mats were affected by the content of rGO-graft-PTMC. Additionally, the incorporation of rGO-graft-PTMC resulted in enhanced thermal stability and hydrophobicity of PTMC fibers. Biological results demonstrated that PC12 cells showed higher cell viability on PTMC/rGO-graft-PTMC fibers of 2.4, 4.0 and 6.0 wt% rGO-graft-PTMC compared to pure PTMC fibers. These results suggest that PTMC/rGO-graft-PTMC composite fibrous structures hold great potential for neural tissue engineering.

Design and fabrication of poly (glycerol sebacate)‐based fibers for neural tissue engineering: Synthesis, electrospinning, and characterization

Poly (glycerol sebacate) (PGS) is a thermoset biodegradable elastomer considered as a promising candidate material for nerve applications. However, PGS synthesis is very time and energy consuming. In this study, the PGS pre‐polymer (pPGS) was synthesized using three synthesis times of 3, 5, and 7 hours at 170°C. Fourier transform infrared (FTIR), nuclear magnetic resonance spectroscopy, X‐ray diffraction analysis, and differential scanning calorimetry thermogram were utilized to study the pPGS behavior. Poly (vinyl alcohol) was used as a carrier to fabricate aligned poly (vinyl alcohol)‐poly (glycerol sebacate) (PVA‐PGS) fibers with various ratios (60:40, 50:50, and 40:60) using electrospinning and crosslinked through the thermal crosslinking method. Morphology of the fibers was studied before and after crosslinking using scanning electron microscopy (SEM). FTIR, mechanical properties in the dry and wet state, water contact angle, in vitro degradation, and water uptake behavior of crosslinked scaffolds were also investigated. 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay, SEM analysis, and 4′, 6‐diamidino‐2‐phenylindole (DAPI) staining were utilized to determine the biocompatibility of scaffolds. The results show the synthesized pPGS in 3 hours at 170°C is the optimized sample in the terms of chemical reaction. All scaffolds have bead‐free and a uniform fiber diameter. The Young's modulus of crosslinked PVA‐PGS (50:50 and 40:60) fibers is shown to be in the expected range for nerve applications. The cell culture studies reveal PVA‐PGS (50:50 and 40:60) fibers could lead to better cell adhesion and proliferation. The results suggest that PVA‐PGS (50:50 and 40:60) is a suitable and promising biodegradable material in the fabrication of scaffolds for nerve regeneration.