Self-assembling peptide nanostructures on aligned poly(lactide-co-glycolide) nanofibers for the functional regeneration of sciatic nerve

Innovative spiral nerve conduits: Addressing nutrient transport and cellular activity for critical-sized nerve defects

Large-gap nerve defects require nerve guide conduits (NGCs) for complete regeneration and muscle innervation. Many NGCs have been developed using various scaffold designs and tissue engineering strategies to promote axon regeneration. Still, most are tubular with inadequate pore sizes and lack surface cues for nutrient transport, cell attachment, and tissue infiltration. This study developed a porous spiral NGC to address these issues using a 3D-printed thermoplastic polyurethane (TPU) fiber lattice. The lattice was functionalized with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) electrospun aligned (aPHBV) and randomly (rPHBV) oriented nanofibers to enhance cellular activity. TPU lattices were made with 25 %, 35 %, and 50 % infill densities to create scaffolds with varied mechanical compliance. The fabricated TPU/PHBV spiral conduits had significantly higher surface areas (25 % TPU/PHBV: 698.97 mm2, 35 % TPU/PHBV: 500.06 mm2, 50 % TPU/PHBV: 327.61 mm2) compared to commercially available nerve conduits like Neurolac™ (205.26 mm2). Aligned PHBV nanofibers showed excellent Schwann cell (RSC96) adhesion, proliferation, and neurogenic gene expression for all infill densities. Spiral TPU/PHBV conduits with 25 % and 35 % infill densities exhibited Young's modulus values comparable to Neurotube® and ultimate tensile strength like acellular cadaveric human nerves. A 10 mm sciatic nerve defect in Wistar rats treated with TPU/aPHBV NGCs demonstrated muscle innervation and axon healing comparable to autografts over 4 months, as evaluated by gait analysis, functional recovery, and histology. The TPU/PHBV NGC developed in this study shows promise as a treatment for large-gap nerve defects.

Unveiling the molecular blueprint of SKP-SCs-mediated tissue engineering-enhanced neuroregeneration

Peripheral nerve injury poses a significant challenge to the nervous system's regenerative capacity. We previously described a novel approach to construct a chitosan/silk fibroin nerve graft with skin-derived precursor-induced Schwann cells (SKP-SCs). This graft has been shown to promote sciatic nerve regeneration and functional restoration to a level comparable to that achieved by autologous nerve grafts, as evidenced by behavioral, histological, and electrophysiological assessments. However, the underlying molecular mechanisms based on SKP-SCs mediated tissue engineering-aid regeneration remain elusive. In the present work, we systematically identified gene modules associated with the differentiation of SKPs into SCs by employing weighted gene co-expression network analysis (WGCNA). By integrating transcriptomic data from the regenerated nerve segment, we constructed a network that delineated the molecular signatures of TENG aid neuroregeneration. Subsequent quantitative PCR (qPCR) validation was performed to substantiate the WGCNA findings. Our WGCNA approach revealed a robust molecular landscape, highlighting hub genes pivotal for tissue engineering-aid regeneration. Notably, the upregulation of specific genes was observed to coincide with the acquisition of SC characteristics. The qPCR validation confirmed the expression patterns of these genes, underscoring their role in promoting neuroregeneration. The current study harnesses the power of WGCNA to elucidate the molecular blueprint governing tissue engineering-aid regeneration. The identified gene modules and validated targets offer novel insights into the cellular and molecular underpinnings of tissue engineering-augmented neuroregeneration. These findings pave the way for developing targeted therapeutics and advanced tissue engineering grafts to enhance peripheral nerve repair.

Synergic effects of core-shell nanospheres and magnetic field for sciatic nerve regeneration in decellularized artery conduits with Schwann cells

Numerous conduits have been developed to improve peripheral nerve regeneration. However, challenges remain, including remote control of conduit function, and programmed cell behaviors like orientation. We synthesized Fe3O4-MnO2@Zirconium-based Metal-organic frameworks@Retinoic acid (FMZMR) core-shell and assessed their impact on Schwann cell function and behavior within conduits made from decellularized human umbilical arteries (DHUCA) under magnetic field (MF). FMZMR core-shell, featuring a spherical porous structure and catalytic properties, effectively scavenges radicals and facilitates controlled drug release under MF. The histology of the DHUCA indicates effective decellularization with adequate tensile strength and Young's modulus for sciatic nerve regeneration. In-vitro results demonstrate that FMZMR core-shell is biocompatible and promotes Schwann cell proliferation through remotely controlled drug release. Furthermore, its synergy with MF enhances cell orientation and increases neurite length by ~ 1.93-fold. Functional and histological evaluations indicate that the FMZMR core-shell combined with MF promotes nerve regeneration, decreases muscle atrophy, and enhances new neuron growth and myelin formation, without negatively affecting vital tissues. This study suggests that the synergistic effect of FMZMR core-shell with MF can alleviate some of the treatment challenges.

Fabrication of Anatomically Equivalent Pectin-Based Multifilament Nerve Conduits

Reuniting denuded nerve ends after a long segmental peripheral nerve defect is challenging due to delayed axonal regeneration and incomplete, nonspecific reinnervation, as conventional hollow nerve guides fail to ensure proper fascicular complementation and obstruct axonal guidance across the defects. This study focuses on fabricating multifilament conduits using a plant-derived anionic polysaccharide, pectin, where the abundant availability of carboxylate (COO-) functional groups in pectin facilitates instantaneous sol-gel transition upon interaction with divalent cations. Despite their advantages, pectin hydrogels encounter structural instability under physiological conditions. Hence, pectin is conjugated with light-sensitive methacrylate residues (49.8% methacrylation) to overcome these issues, enabling the fabrication of dual cross-linked multifilament nerve conduits through an ionic interaction-driven, template-free 3D wet writing process, followed by photo-cross-linking at 525 nm. The anatomical equivalence including peri-, epi-, and endoneurium structures of the customized multifilament conduits was confirmed through scanning electron micrographs and micro-CT analysis of rat and goat sciatic nerve tissues. Furthermore, the fabricated multifilament nerve conduits demonstrated cytocompatibility and promoted the expression of neuron-specific intermediate filament protein (NF-200) in PC12 cells and neurite outgrowth of 16.90 ± 1.82 μm on day 14. Micro-CT imaging of an anastomosed native goat sciatic nerve with an 8-filament conduit demonstrated precise fascicular complementation in an ex vivo interpositional goat model. This approach not only eliminates the need for a suture-intensive ligation process but also highlights the customizability of multifilament conduits to meet patient- and injury-specific needs.

Efficacy of 3D printed anatomically equivalent thermoplastic polyurethane guide conduits in promoting the regeneration of critical-sized peripheral nerve defects

Three-dimensional (3D) printing is an emerging tool for creating patient-specific tissue constructs analogous to the native tissue microarchitecture. In this study, anatomically equivalent 3D nerve conduits were developed using thermoplastic polyurethane (TPU) by combining reverse engineering and material extrusion (i.e. fused deposition modeling) technique. Printing parameters were optimized to fabricate nerve-equivalent TPU constructs. The TPU constructs printed with different infill densities supported the adhesion, proliferation, and gene expression of neuronal cells. Subcutaneous implantation of the TPU constructs for three months in rats showed neovascularization with negligible local tissue inflammatory reactions and was classified as a non-irritant biomaterial as per ISO 10993-6. To performin vivoefficacy studies, nerve conduits equivalent to rat's sciatic nerve were fabricated and bridged in a 10 mm sciatic nerve transection model. After four months of implantation, the sensorimotor function and histological assessments revealed that the 3D printed TPU conduits promoted the regeneration in critical-sized peripheral nerve defects equivalent to autografts. This study proved that TPU-based 3D printed nerve guidance conduits can be created to replicate the complicated features of natural nerves that can promote the regeneration of peripheral nerve defects and also show the potential to be extended to several other tissues for regenerative medicine applications.

Micropatterned shape-memory polymer substrate containing hydrogen bonds creates a long-term dynamic microenvironment for regulating nerve-cell fate

Peripheral nerve injuries (PNIs) caused by mechanical contusion are frequently encountered in clinical practice, using nerve guidance conduits (NGCs) is now a promising therapy. An NGC creates a microenvironment for cell growth and differentiation, thus understanding physical and biochemical cues that can affect nerve-cell fate is a prerequisite for rationally designing NGCs. However, most of the previous works were focused on some static cues, the dynamic nature of the nerve microenvironment has not yet been well captured. Herein, we develop a micropatterned shape-memory polymer as a programmable substrate for providing a dynamic cue for nerve-cell growth. The shape-memory properties enable temporal programming of the substrate, and a dynamic microenvironment is created during standard cell culturing at 37 °C. Unlike most of the biomedical shape-memory polymers that recover rapidly at 37 °C, the proposed substrate shows a slow recovery process lasting 3-4 days and creates a long-term dynamic microenvironment. Results demonstrate that the vertically programmed substrates provide the most suitable dynamic microenvironment for PC12 cells as both the differentiation and maturity are promoted. Overall, this work provides a strategy for creating a long-term dynamic microenvironment for regulating nerve-cell fate and will inspire the rational design of NGCs for the treatment of PNIs.

Sea Cucumber-Inspired Microneedle Nerve Guidance Conduit for Synergistically Inhibiting Muscle Atrophy and Promoting Nerve Regeneration

Muscle atrophy resulting from peripheral nerve injury (PNI) poses a threat to a patient's mobility and sensitivity. However, an effective method to inhibit muscle atrophy following PNI remains elusive. Drawing inspiration from the sea cucumber, we have integrated microneedles (MNs) and microchannel technology into nerve guidance conduits (NGCs) to develop bionic microneedle NGCs (MNGCs) that emulate the structure and piezoelectric function of sea cucumbers. Morphologically, MNGCs feature an outer surface with outward-pointing needle tips capable of applying electrical stimulation to denervated muscles. Simultaneously, the interior contains microchannels designed to guide the migration of Schwann cells (SCs). Physiologically, the incorporation of conductive reduced graphene oxide and piezoelectric zinc oxide nanoparticles into the polycaprolactone scaffold enhances conductivity and piezoelectric properties, facilitating SCs' migration, myelin regeneration, axon growth, and the restoration of neuromuscular function. These combined effects ultimately lead to the inhibition of muscle atrophy and the restoration of nerve function. Consequently, the concept of the synergistic effect of inhibiting muscle atrophy and promoting nerve regeneration has the capacity to transform the traditional approach to PNI repair and find broad applications in PNI repair.

Electrical aligned polyurethane nerve guidance conduit modulates macrophage polarization and facilitates immunoregulatory peripheral nerve regeneration

Biomaterials can modulate the local immune microenvironments to promote peripheral nerve regeneration. Inspired by the spatial orderly distribution and endogenous electric field of nerve fibers, we aimed to investigate the synergistic effects of electrical and topological cues on immune microenvironments of peripheral nerve regeneration. Nerve guidance conduits (NGCs) with aligned electrospun nanofibers were fabricated using a polyurethane copolymer containing a conductive aniline trimer and degradable L-lysine (PUAT). In vitro experiments showed that the aligned PUAT (A-PUAT) membranes promoted the recruitment of macrophages and induced their polarization towards the pro-healing M2 phenotype, which subsequently facilitated the migration and myelination of Schwann cells. Furthermore, NGCs fabricated from A-PUAT increased the proportion of pro-healing macrophages and improved peripheral nerve regeneration in a rat model of sciatic nerve injury. In conclusion, this study demonstrated the potential application of NGCs in peripheral nerve regeneration from an immunomodulatory perspective and revealed A-PUAT as a clinically-actionable strategy for peripheral nerve injury.

Multichannel Conduits with Fascicular Complementation: Significance in Long Segmental Peripheral Nerve Injury

Despite the advances in tissue engineering approaches, reconstruction of long segmental peripheral nerve defects remains unsatisfactory. Although autologous grafts with proper fascicular complementation have shown meaningful functional recovery according to the Medical Research Council Classification (MRCC), the lack of donor nerve for such larger defect sizes (>30 mm) has been a serious clinical issue. Further clinical use of hollow nerve conduits is limited to bridging smaller segmental defects of denuded nerve ends (<30 mm). Recently, bioinspired multichannel nerve guidance conduits (NGCs) gained attention as autograft substitutes as they mimic the fascicular connective tissue microarchitecture in promoting aligned axonal outgrowth with desirable innervation for complete sensory and motor function restoration. This review outlines the hierarchical organization of nerve bundles and their significance in the sensory and motor functions of peripheral nerves. This review also emphasizes the major challenges in addressing the longer nerve defects with the role of fascicular arrangement in the multichannel nerve guidance conduits and the need for fascicular matching to accomplish complete functional restoration, especially in treating long segmental nerve defects. Further, currently available fabrication strategies in developing multichannel nerve conduits and their inconsistency in existing preclinical outcomes captured in this review would seed a new process in designing an ideal larger nerve conduit for peripheral nerve repair.

Oriented Graphene Oxide Scaffold Promotes Nerve Regeneration in vitro and in vivo

Background

Treating peripheral nerve injuries (PNI) with defects remains challenging in clinical practice. The commercial conduits have shown suboptimal nerve regeneration and functional recovery due to their basic tubular design without electroactive and oriented topographical cues.

Purpose

To develop a new scaffold with oriented microstructure and electroactive Graphene oxide (GO) and investigate its' therapeutic effect on nerve regeneration in vitro and in vivo.

Methods

This study employed a straightforward approach to co-spin PCL and GO, yielding an oriented hybrid nanofibrous scaffold known as the O-GO/PCL scaffold. The physical and chemical properties of nanofibrous scaffold were tested by scanning electron microscopy (SEM), transmission electron microscope (TEM), tensile test and so on. Primary Schwann cells (SCs) and dorsal root ganglia (DRG) were used to investigate the impact of the newly developed scaffolds on the biological behavior of neural cells in vitro. Transcriptome sequencing (mRNA-seq) was employed to probe the underlying mechanisms of the synergistic effect of electroactive GO and longitudinal topographic guidance on nerve regeneration. Furthermore, the developed O-GO/PCL scaffold was utilized to bridge a 10-mm sciatic nerve defect in rat, aiming to investigate its therapeutic potential for peripheral nerve regeneration in vivo.

Results and discussion

The SEM and TEM revealed that the newly developed O-GO/PCL scaffold showed longitudinally oriented microstructure and GO particles were homogenously and uniformly distributed inside the nanofibers. Primary SCs were utilized to assess the biocompatibility of the GO-based scaffold, revealing that negligible cytotoxicity when GO concentration does not exceed 0.5%. In vitro analysis of nerve regeneration demonstrated that axons in the O-GO/PCL group exhibited an average length of 1054.88 ± 161.32 µm, significant longer than those in the other groups (P < 0.05). Moreover, mRNA sequencing results suggested that the O-GO/PCL scaffold could enhance nerve regeneration by upregulating genes associated with neural regeneration, encompassing ion transport, axon guidance and cell-cell interactions. Most importantly, we employed the O-GO/PCL scaffold to repair a 10-mm sciatic nerve defect in rat, resulting in augmented nerve regeneration, myelination, and functional recovery.

Conclusion

The O-GO/PCL scaffold with oriented microstructure and electroactive GO represents a promising heral nerve reconstruction.

Self-assembling peptide RADA16: a promising scaffold for tissue engineering and regenerative medicine

RADA16 is a peptide-based biomaterial whose acidic aqueous solution spontaneously forms an extracellular matrix-like 3D structure within seconds upon contact with physiological pH body fluids. Meanwhile, its good biocompatibility, low immunogenicity, nontoxic degradation products and ease of modification make it an ideal scaffold for tissue engineering. RADA16 is a good delivery vehicle for cells, drugs and factors. Its shear thinning and thixotropic properties allow it to fill tissue voids by injection and not to swell. However, the weaker mechanical properties and poor hydrophilicity are troubling limitations of RADA16. To compensate for this limitation, various functional groups and polymers have been designed to modify RADA16, thus contributing to its scope and progress in the field of tissue engineering.

Additive manufacturing of peripheral nerve conduits - Fabrication methods, design considerations and clinical challenges

Tissue-engineered nerve guidance conduits (NGCs) are a viable clinical alternative to autografts and allografts and have been widely used to treat peripheral nerve injuries (PNIs). Although these NGCs are successful to some extent, they cannot aid in native regeneration by improving native-equivalent neural innervation or regrowth. Further, NGCs exhibit longer recovery period and high cost limiting their clinical applications. Additive manufacturing (AM) could be an alternative to the existing drawbacks of the conventional NGCs fabrication methods. The emergence of the AM technique has offered ease for developing personalized three-dimensional (3D) neural constructs with intricate features and higher accuracy on a larger scale, replicating the native feature of nerve tissue. This review introduces the structural organization of peripheral nerves, the classification of PNI, and limitations in clinical and conventional nerve scaffold fabrication strategies. The principles and advantages of AM-based techniques, including the combinatorial approaches utilized for manufacturing 3D nerve conduits, are briefly summarized. This review also outlines the crucial parameters, such as the choice of printable biomaterials, 3D microstructural design/model, conductivity, permeability, degradation, mechanical property, and sterilization required to fabricate large-scale additive-manufactured NGCs successfully. Finally, the challenges and future directions toward fabricating the 3D-printed/bioprinted NGCs for clinical translation are also discussed.

Schwann cell-matrix coated PCL-MWCNT multifunctional nanofibrous scaffolds for neural regeneration

Nerve tissue engineering aims to create scaffolds that promote nerve regeneration in the damaged peripheral nervous system. However, there remain some challenges in the construction of scaffolds in terms of mechanical properties and cellular behaviour. The present work aims to develop multifunctional implantable nanofibrous scaffolds for nerve regeneration. Using electrospinning, nanofibrous neat polycaprolactone (PCL) and PCL/multiwalled carbon nanotubes (PCL-MWCNT) composite scaffolds were prepared in random and aligned morphology. Schwann cells and their secreted biochemical factors are responsible for neuronal survival in the peripheral nervous system. Therefore, the acellular matrix of Schwann cells was spin-coated on the PCL-MWCNT scaffolds to aid nerve regeneration. Physicochemical and mechanical properties, and the in vitro cellular response of the developed nanofibrous were investigated. We observed no significant change in fibre diameter between neat PCL and PCL-MWCNT scaffolds regardless of the morphology. However, the inclusion of MWCNT reduced the mechanical strength of nanocomposite scaffolds compared to neat PCL. In vitro study revealed biocompatibility of the developed scaffolds both with and without an acellular matrix. Gene expression study revealed a significant increase in peripheral myelin protein (PMP22) expression on acellular matrix-coated PCL-MWCNT scaffolds compared to neat PCL counterparts. Overall, the results suggested Schwann cell matrix-coated PCL-MWCNT nanofibers as a promising conduit for peripheral nerve regeneration.

Modification Strategies for Ionic Complementary Self-Assembling Peptides: Taking RADA16-I as an Example

Ion-complementary self-assembling peptides have been studied in many fields for their distinct advantages, mainly due to their self-assembly properties. However, their shortcomings, such as insufficient specific activity and poor mechanical properties, also limited their application. For the better and wider application of these promising biomaterials, ion-complementary self-assembling peptides can be modified with their self-assembly properties not being destroyed to the greatest extent. The modification strategies were reviewed by taking RADA16-I as an example. For insufficient specific activity, RADA16-I can be structurally modified with active motifs derived from the active domain of the extracellular matrix or other related active factors. For weak mechanical properties, materials with strong mechanical properties or that can undergo chemical crosslinking were used to mix with RADA16-I to enhance the mechanical properties of RADA16-I. To improve the performance of RADA16-I as drug carriers, appropriate adjustment of the RADA16-I sequence and/or modification of the RADA16-I-related delivery system with polymer materials or specific molecules can be considered to achieve sustained and controlled release of specific drugs or active factors. The modification strategies reviewed in this paper may provide some references for further basic research and clinical application of ion-complementary self-assembling peptides and their derivatives.

Peptide Biomaterials for Tissue Regeneration

Expanding the toolbox of therapeutic materials for soft tissue and organ repair has become a critical component of tissue engineering. While animal- and plant-derived proteins are the foundation for developing biomimetic tissue constructs, using peptides as either constituents or frameworks for the materials has gained increasing momentum in recent years. This mini review discusses recent advances in peptide-based biomaterials' design and application. We also discuss some of the future challenges posed and opportunities opened by peptide-based structures in the field of tissue engineering and regenerative medicine.

Antioxidant for Neurological Diseases and Neurotrauma and Bioengineering Approaches

Antioxidants are a class of molecules with an innate affinity to neutralize reactive oxygen species (ROS), which are known to cause oxidative stress. Oxidative stress has been associated with a wide range of diseases mediated by physiological damage to the cells. ROS play both beneficial and detrimental roles in human physiology depending on their overall concentration. ROS are an inevitable byproduct of the normal functioning of cells, which are produced as a result of the mitochondrial respiration process. Since the establishment of the detrimental effect of oxidative stress in neurological disorders and neurotrauma, there has been growing interest in exploring antioxidants to rescue remaining or surviving cells and reverse the neurological damage. In this review, we present the survey of different antioxidants studied in neurological applications including neurotrauma. We also delve into bioengineering approaches developed to deliver antioxidants to improve their cellular uptake in neurological applications.

Advancing Cell-Instructive Biomaterials Through Increased Understanding of Cell Receptor Spacing and Material Surface Functionalization

Abstract

Regenerative medicine is aimed at restoring normal tissue function and can benefit from the application of tissue engineering and nano-therapeutics. In order for regenerative therapies to be effective, the spatiotemporal integration of tissue-engineered scaffolds by the native tissue, and the binding/release of therapeutic payloads by nano-materials, must be tightly controlled at the nanoscale in order to direct cell fate. However, due to a lack of insight regarding cell–material interactions at the nanoscale and subsequent downstream signaling, the clinical translation of regenerative therapies is limited due to poor material integration, rapid clearance, and complications such as graft-versus-host disease. This review paper is intended to outline our current understanding of cell–material interactions with the aim of highlighting potential areas for knowledge advancement or application in the field of regenerative medicine. This is achieved by reviewing the nanoscale organization of key cell surface receptors, the current techniques used to control the presentation of cell-interactive molecules on material surfaces, and the most advanced techniques for characterizing the interactions that occur between cell surface receptors and materials intended for use in regenerative medicine.

Lay Summary

The combination of biology, chemistry, materials science, and imaging technology affords exciting opportunities to better diagnose and treat a wide range of diseases. Recent advances in imaging technologies have enabled better understanding of the specific interactions that occur between human cells and their immediate surroundings in both health and disease. This biological understanding can be used to design smart therapies and tissue replacements that better mimic native tissue. Here, we discuss the advances in molecular biology and technologies that can be employed to functionalize materials and characterize their interaction with biological entities to facilitate the design of more sophisticated medical therapies.

Regeneration of the peripheral nerve via multifunctional electrospun scaffolds

Over the last two decades, electrospun scaffolds have proved to be advantageous in the field of nerve tissue regeneration by connecting the cavity among the proximal and distal nerve stumps growth cones and leading to functional recovery after injury. Multifunctional nanofibrous structure of these scaffolds provides enormous potential by combining the advantages of nano-scale topography, and biological science. In these structures, selecting the appropriate materials, designing an optimized structure, modifying the surface to enhance biological functions and neurotrophic factors loading, and native cell-like stem cells should be considered as the essential factors. In this systematic review paper, the fabrication methods for the preparation of aligned nanofibrous scaffolds in yarn or conduit architecture are reviewed. Subsequently, the utilized polymeric materials, including natural, synthetic and blend are presented. Finally, their surface modification techniques, as well as, the recent advances and outcomes of the scaffolds, both in vitro and in vivo, are reviewed and discussed.

A scaffold-free Bio 3D nerve conduit for repair of a 10-mm peripheral nerve defect in the rats

INTRODUCTION

A Bio 3D printed nerve conduit was reported to promote nerve regeneration in a 5 mm nerve gap model. The purpose of this study was to fabricate Bio 3D nerve conduits suitable for a 10 mm nerve gap and to evaluate their capacity for nerve regeneration in a rat sciatic nerve defect model.

MATERIALS AND METHODS

Eighteen F344 rats with immune deficiency (9-10 weeks old; weight, 200-250 g) were divided into three groups: a Bio 3D nerve conduit group (Bio 3D, n = 6), a nerve graft group (NG, n = 6), and a silicon tube group (ST, n = 6). A 12-mm Bio 3D nerve conduit or silicon tube was transplanted into the 10-mm defect of the right sciatic nerve. In the nerve graft group, reverse autografting was performed with an excised 10-mm nerve segment. Assessments were performed at 8 weeks after the surgery.

RESULTS

In the region distal to the suture site, the number of myelinated axons in the Bio 3D group were significantly larger compared with the silicon group (2,548 vs. 950, p < .05). The myelinated axon diameter (MAD) and the myelin thickness (MT) of the regenerated axons in the Bio 3D group were significantly larger compared with those of the ST group (MAD: 3.09 vs. 2.36 μm; p < .01; MT: 0.59 vs. 0.40 μm, p < .01).

CONCLUSIONS

This study indicates that a Bio 3D nerve conduit can enhance peripheral nerve regeneration even in a 10 mm nerve defect model.

Synergistic effects of dual-presenting VEGF- and BDNF-mimetic peptide epitopes from self-assembling peptide hydrogels on peripheral nerve regeneration

The crosstalk between vascularization and nerve regeneration in the peripheral nervous system has recently been suggested to play an important role in the treatment of peripheral nerve injury. Regenerative strategies via synergistic delivery of multiple biochemical cues have received growing attention, especially the combination of pro-angiogenic factors and neurotrophic factors. Here we developed a self-assembling peptide nanofiber hydrogel dual-functionalized with vascular endothelial growth factor (VEGF)- and brain-derived neurotrophic factor (BDNF)-mimetic peptide epitopes for peripheral nerve reconstruction. It could simultaneously present VEGF- and BDNF-mimetic peptide epitopes and provides a three-dimensional (3D) neurovascular microenvironment for endothelial cell and neural cell growth. In vitro cellular experiments showed that the functionalized peptide hydrogel scaffold effectively promoted the pro-myelination of Schwann cell, as well as the adhesion and proliferation of endothelial cell compared with scaffolds presenting VEGF- or BDNF-mimetic peptide epitope alone. When implanted in a rat model to bridge a critical-size sciatic nerve gap in vivo, the functionalized peptide hydrogel significantly improved the number of newly formed blood vessels, the density of regenerating axons, the morphometric analysis of the regenerated muscles and the electrophysiological findings, indicating the synergistic effect of the two bioactive motifs on peripheral nerve regeneration. Collectively, constructing an artificial neurovascular microenvironment in the lesion area by using the functionalized self-assembling peptide nanofiber hydrogel may have a great potential for promoting nerve tissue engineering and regeneration in other tissues.

Peptide nanostructures on nanofibers for peripheral nerve regeneration

Self-assembled peptide nanofibrous scaffolds with designer sequences, similar to neurite growth promoting molecules enhance the differentiation of neural stem cells. However, self-assembled peptide nanofibrous scaffolds lack the required mechanical strength to suffice to bridge long critical-sized peripheral nerve defects. Hence, there is a demand for a potential neural substrate, which could be biomimetic coupled with bioactive nanostructures to regrow the denuded axons towards the distal end. In the present study, we developed designer self-assembling peptide-based aligned poly(lactic-co-glycolic acid) (PLGA) nanofibrous scaffolds by simple surface coating of peptides or coelectrospinning. Retention of secondary structures of peptides in peptide-coated and cospun fibers was confirmed by circular dichroism spectroscopy. The rod-like peptide nanostructures enhance the typical bipolar morphology of Schwann cells. Although the peptide-coated PLGA scaffolds exhibited significant increase in Schwann cell proliferation than pristine PLGA and PLGA-peptide cospun scaffolds (p < .05), peptide cospun scaffolds demonstrated better cellular infiltration and significantly higher gene expression of neural cell adhesion molecule, glial fibrillary acidic protein, and peripheral myelin protein22 compared to the pristine PLGA and PLGA-peptide-coated scaffolds. Our results demonstrate the positive effects of aligned peptide coelectrospun scaffolds with biomimetic cell recognition motifs towards functional proliferation of Schwann cells. These scaffolds could subsequently repair peripheral nerve defects by augmenting axonal regeneration and functional nerve recovery.

Application of PLGA/FGF-2 coaxial microfibers in spinal cord tissue engineering: an in vitro and in vivo investigation

Aim: Scaffolds are a promising approach for spinal cord injury (SCI) treatment. FGF-2 is involved in tissue repair but is easily degradable and presents collateral effects in systemic administration. In order to address the stability issue and avoid the systemic effects, FGF-2 was encapsulated into core–shell microfibers by coaxial electrospinning and its in vitro and in vivo potential were studied. Materials & methods: The fibers were characterized by physicochemical and biological parameters. The scaffolds were implanted in a hemisection SCI rat model. Locomotor test was performed weekly for 6 weeks. After this time, histological analyses were performed and expression of nestin and GFAP was quantified by flow cytometry. Results: Electrospinning resulted in uniform microfibers with a core–shell structure, with a sustained liberation of FGF-2 from the fibers. The fibers supported PC12 cells adhesion and proliferation. Implanted scaffolds into SCI promoted locomotor recovery at 28 days after injury and reduced GFAP expression. Conclusion: These results indicate the potential of these microfibers in SCI tissue engineering.

[Formula: see text]

Nanoscaffolds in promoting regeneration of the peripheral nervous system

The ability to surgically repair peripheral nerve injuries is urgently needed. However, traditional tissue engineering techniques, such as autologous nerve transplantation, have some limitations. Therefore, tissue engineered autologous nerve grafts have become a suitable choice for nerve repair. Novel tissue engineering techniques derived from nanostructured conduits have been shown to be superior to other successful functional neurological structures with different scaffolds in terms of providing the required structures and properties. Additionally, different biomaterials and growth factors have been added to nerve scaffolds to produce unique biological effects that promote nerve regeneration and functional recovery. This review summarizes the application of different nanoscaffolds in peripheral nerve repair and further analyzes how the nanoscaffolds promote peripheral nerve regeneration.