Development of Nanofiber Sponges-Containing Nerve Guidance Conduit for Peripheral Nerve Regeneration in Vivo

IKVAV functionalized oriented PCL/Fe3O4 scaffolds for magnetically modulating DRG growth behavior

The re-bridging of the deficient nerve is the main problem to be solved after the functional impairment of the peripheral nerve. In this study, a directionally aligned polycaprolactone/triiron tetraoxide (PCL/Fe3O4) fiber scaffolds were firstly prepared by electrospinning technique, and further then grafted with IKVAV peptide for regulating DRG growth and axon extension in peripheral nerve regeneration. The results showed that oriented aligned magnetic PCL/Fe3O4 composite scaffolds were successfully prepared by electrospinning technique and possessed good mechanical properties and magnetic responsiveness. The PCL/Fe3O4 scaffolds containing different Fe3O4 concentrations were free of cytotoxicity, indicating the good biocompatibility and low cytotoxicity of the scaffolds. The IKVAV-functionalized PCL/Fe3O4 scaffolds were able to guide and promote the directional extension of axons, the application of external magnetic field and the grafting of IKVAV peptides significantly further promoted the growth of DRGs and axons. The ELISA test results showed that the AP-10 F group scaffolds promoted the secretion of nerve growth factor (NGF) from DRG under a static magnetic field (SMF), thus promoting the growth and extension of axons. Importantly, the IKVAV-functionalized PCL/Fe3O4 scaffolds could significantly up-regulate the expression of Cntn2, PCNA, Sox10 and Isca1 genes related to adhesion, proliferation and magnetic receptor function under the stimulation of SMF. Therefore, IKVAV-functionalized PCL/Fe3O4 composite oriented scaffolds have potential applications in neural tissue engineering.

Strategies to enhance the ability of nerve guidance conduits to promote directional nerve growth

Severely damaged peripheral nerves will regenerate incompletely due to lack of directionality in their regeneration, leading to loss of nerve function. To address this problem, various nerve guidance conduits (NGCs) have been developed to provide guidance for nerve repair. However, their clinical application is still limited, mainly because its effect in promoting nerve repair is not as good as autologous nerve transplantation. Therefore, it is necessary to enhance the ability of NGCs to promote directional nerve growth. Strategies include preparing various directional structures on NGCs to provide contact guidance, and loading various substances on them to provide electrical stimulation or neurotrophic factor concentration gradient to provide directional physical or biological signals.

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

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

Human umbilical cord mesenchymal stem cell-derived exosomes loaded into a composite conduit promote functional recovery after peripheral nerve injury in rats

Complete transverse injury of peripheral nerves is challenging to treat. Exosomes secreted by human umbilical cord mesenchymal stem cells are considered to play an important role in intercellular communication and regulate tissue regeneration. In previous studies, a collagen/hyaluronic acid sponge was shown to provide a suitable regeneration environment for Schwann cell proliferation and to promote axonal regeneration. This three-dimensional (3D) composite conduit contains a collagen/hyaluronic acid inner sponge enclosed in an electrospun hollow poly (lactic-co-glycolic acid) tube. However, whether there is a synergy between the 3D composite conduit and exosomes in the repair of peripheral nerve injury remains unknown. In this study, we tested a comprehensive strategy for repairing long-gap (10 mm) peripheral nerve injury that combined the 3D composite conduit with human umbilical cord mesenchymal stem cell-derived exosomes. Repair effectiveness was evaluated by sciatic functional index, sciatic nerve compound muscle action potential recording, recovery of muscle mass, measuring the cross-sectional area of the muscle fiber, Masson trichrome staining, and transmission electron microscopy of the regenerated nerve in rats. The results showed that transplantation of the 3D composite conduit loaded with human umbilical cord mesenchymal stem cell-derived exosomes promoted peripheral nerve regeneration and restoration of motor function, similar to autograft transplantation. More CD31-positive endothelial cells were observed in the regenerated nerve after transplantation of the loaded conduit than after transplantation of the conduit without exosomes, which may have contributed to the observed increase in axon regeneration and distal nerve reconnection. Therefore, the use of a 3D composite conduit loaded with human umbilical cord mesenchymal stem cell-derived exosomes represents a promising cell-free therapeutic option for the treatment of peripheral nerve injury.

Beyond the limiting gap length: peripheral nerve regeneration through implantable nerve guidance conduits

Peripheral nerve damage results in the loss of sensorimotor and autonomic functions, which is a significant burden to patients. Furthermore, nerve injuries greater than the limiting gap length require surgical repair. Although autografts are the preferred clinical choice, their usage is impeded by their limited availability, dimensional mismatch, and the sacrifice of another functional donor nerve. Accordingly, nerve guidance conduits, which are tubular scaffolds engineered to provide a biomimetic environment for nerve regeneration, have emerged as alternatives to autografts. Consequently, a few nerve guidance conduits have received clinical approval for the repair of short-mid nerve gaps but failed to regenerate limiting gap damage, which represents the bottleneck of this technology. Thus, it is still necessary to optimize the morphology and constituent materials of conduits. This review summarizes the recent advances in nerve conduit technology. Several manufacturing techniques and conduit designs are discussed, with emphasis on the structural improvement of simple hollow tubes, additive manufacturing techniques, and decellularized grafts. The main objective of this review is to provide a critical overview of nerve guidance conduit technology to support regeneration in long nerve defects, promote future developments, and speed up its clinical translation as a reliable alternative to autografts.

Silk fibroin-derived electrospun materials for biomedical applications: A review

Electrospinning is a versatile technique for fabricating polymeric fibers with diameters ranging from micro- to nanoscale, exhibiting multiple morphologies and arrangements. By combining silk fibroin (SF) with synthetic and/or natural polymers, electrospun materials with outstanding biological, chemical, electrical, physical, mechanical, and optical properties can be achieved, fulfilling the evolving biomedical demands. This review highlights the remarkable versatility of SF-derived electrospun materials, specifically focusing on their application in tissue regeneration (including cartilage, cornea, nerves, blood vessels, bones, and skin), disease treatment (such as cancer and diabetes), and the development of controlled drug delivery systems. Additionally, we explore the potential future trends in utilizing these nanofibrous materials for creating intelligent biomaterials, incorporating biosensors and wearable sensors for monitoring human health, and also discuss the bottlenecks for its widespread use. This comprehensive overview illuminates the significant impact and exciting prospects of SF-derived electrospun materials in advancing biomedical research and applications.

Advances in Large Gap Peripheral Nerve Injury Repair and Regeneration with Bridging Nerve Guidance Conduits

Peripheral nerve injury is a common complication of accidents and diseases. The traditional autologous nerve graft approach remains the gold standard for the treatment of nerve injuries. While sources of autologous nerve grafts are very limited and difficult to obtain. Nerve guidance conduits are widely used in the treatment of peripheral nerve injuries as an alternative to nerve autografts and allografts. However, the development of nerve conduits does not meet the needs of large gap peripheral nerve injury. Functional nerve conduits can provide a good microenvironment for axon elongation and myelin regeneration. Herein, the manufacturing methods and different design types of functional bridging nerve conduits for nerve conduits combined with electrical or magnetic stimulation and loaded with Schwann cells, etc., are summarized. It summarizes the literature and finds that the technical solutions of functional nerve conduits with electrical stimulation, magnetic stimulation and nerve conduits combined with Schwann cells can be used as effective strategies for bridging large gap nerve injury and provide an effective way for the study of large gap nerve injury repair. In addition, functional nerve conduits provide a new way to construct delivery systems for drugs and growth factors in vivo.

Fabrication of Multi-Channel Nerve Guidance Conduits Containing Schwann Cells Based on Multi-Material 3D Bioprinting

Nerve guidance conduits (NGCs) are an essential solution for peripheral nerve repair and regeneration in tissue engineering and medicine. However, the ability of current NGCs is limited to repairing longer nerve gap (i.e., >20 mm) because it cannot meet the following two conditions simultaneously: (1) directional guidance of the axial high-density channels and (2) regenerative stimulation of the extracellular matrix secreted by Schwann cells (SCs). Therefore, we propose a multi-material 3D bioprinting process to fabricate multi-channel nerve guide conduits (MNGCs) containing SCs. In the article, cell-laden methacrylate gelatin (GelMA) was used as the bulk material of MNGCs. To improve the printing accuracy of the axial channels and the survival rate of SCs, we systematically optimized the printing temperature parameter based on hydrogel printability analysis. The multi-material bioprinting technology was used to realize the alternate printing of supporting gelatin and cell-laden GelMA. Then, the high-accuracy channels were fabricated through the UV cross-linking of GelMA and the dissolving technique of gelatin. The SCs distributed around the channels with a high survival rate, and the cell survival rate maintained above 90%. In general, the study on multi-material 3D printing was carried out from the fabricating technology and material analysis, which will provide a potential solution for the fabrication of MNGCs containing SCs.

Defect-Rich SnO2 Nanofiber as an Oxygen-Defect-Driven Photoenergy Shield against UV Light Cell Damage

Usually, most studies focus on toxic gas and photosensors by using electrospinning and metal oxide polycrystalline SnO2 nanofibers (PNFs), while fewer studies discuss cell-material interactions and photoelectric effect. In this work, the controllable surface morphology and oxygen defect (VO) structure properties were provided to show the opportunity of metal oxide PNFs to convert photoenergy into bio-energy for bio-material applications. Using the photobiomodulation effect of defect-rich polycrystalline SnO2 nanofibers (PNFs) is the main idea to modulate the cell-material interactions, such as adhesion, growth direction, and reactive oxygen species (ROS) density. The VO structures, including out-of-plane oxygen defects (op-VO), bridge oxygen defects (b-VO), and in-plane oxygen defects (ip-VO), were studied using synchrotron analysis to investigate the electron transfer between the VO structures and conduction bands. These intragrain VO structures can be treated as generation-recombination centers, which can convert various photoenergies (365-520 nm) into different current levels that form distinct surface potential levels; this is referred to as the photoelectric effect. PNF conductivity was enhanced 53.6-fold by enlarging the grain size (410 nm2) by increasing the annealing temperature, which can improve the photoelectric effect. In vitro removal of reactive oxygen species (ROS) can be achieved by using the photoelectric effect of PNFs. Also, the viability and shape of human bone marrow mesenchymal stem cells (hMSCs-BM) were also influenced significantly by the photobiomodulation effect. The cell damage and survival rate can be prevented and enhanced by using PNFs; metal oxide nanofibers are no longer only environmental sensors but can also be a bio-material to convert the photoenergy into bio-energy for biomedical science applications.

Advances in Biomimetic Nerve Guidance Conduits for Peripheral Nerve Regeneration

Injuries to the peripheral nervous system are a common clinical issue, causing dysfunctions of the motor and sensory systems. Surgical interventions such as nerve autografting are necessary to repair damaged nerves. Even with autografting, i.e., the gold standard, malfunctioning and mismatches between the injured and donor nerves often lead to unwanted failure. Thus, there is an urgent need for a new intervention in clinical practice to achieve full functional recovery. Nerve guidance conduits (NGCs), providing physicochemical cues to guide neural regeneration, have great potential for the clinical regeneration of peripheral nerves. Typically, NGCs are tubular structures with various configurations to create a microenvironment that induces the oriented and accelerated growth of axons and promotes neuron cell migration and tissue maturation within the injured tissue. Once the native neural environment is better understood, ideal NGCs should maximally recapitulate those key physiological attributes for better neural regeneration. Indeed, NGC design has evolved from solely physical guidance to biochemical stimulation. NGC fabrication requires fundamental considerations of distinct nerve structures, the associated extracellular compositions (extracellular matrices, growth factors, and cytokines), cellular components, and advanced fabrication technologies that can mimic the structure and morphology of native extracellular matrices. Thus, this review mainly summarizes the recent advances in the state-of-the-art NGCs in terms of biomaterial innovations, structural design, and advanced fabrication technologies and provides an in-depth discussion of cellular responses (adhesion, spreading, and alignment) to such biomimetic cues for neural regeneration and repair.

Electroactive scaffolds of biodegradable polyurethane/polydopamine-functionalized graphene oxide regulating the inflammatory response and revitalizing the axonal growth cone for peripheral nerve regeneration

Long-gap peripheral nerve injury remains a major challenge in regenerative medicine and results in permanent sensory and motor dysfunction. Nerve guidance scaffolds (NGSs) are known as a promising alternative to autologous nerve grafting. The latter, the current "gold standard" in clinical practice, is frequently constrained by the limited availability of sources and the inevitable damage to the donor area. Given the electrophysiological properties of nerves, electroactive biomaterials are being intensively investigated in nerve tissue engineering. In this study, we engineered a conductive NGS compounded of biodegradable waterborne polyurethane (WPU) and polydopamine-reduced graphene oxide (pGO) for repairing impaired peripheral nerves. The incorporation of pGO at the optimal concentration (3 wt%) promoted in vitro spreading of Schwann cells (SCs) with high expression of the proliferation marker S100 protein. In an in vivo study of sciatic nerve transection injury, WPU/pGO NGSs were found to regulate the immune microenvironment by activating macrophage M2 polarization and upregulate growth-associated protein 43 (GAP43) to facilitate axonal elongation. Histological and motor function analysis demonstrated that WPU/pGO NGSs had a neuroprosthetic effect close to that of an autograft, which significantly promoted the regeneration of myelinated axons, reduced gastrocnemius atrophy, and enhanced hindlimb motor function. These findings together suggested that electroactive WPU/pGO NGSs may represent a safe and effective strategy to manage large nerve defects.

Nerve ECM and PLA-PCL based electrospun bilayer nerve conduit for nerve regeneration

Introduction: The porcine nerve-derived extracellular matrix (ECM) fabricated as films has good performance in peripheral nerve regeneration. However, when constructed as conduits to bridge nerve defects, ECM lacks sufficient mechanical strength. Methods: In this study, a novel electrospun bilayer-structured nerve conduit (BNC) with outer poly (L-lactic acid-co-ε-caprolactone) (PLA-PCL) and inner ECM was fabricated for nerve regeneration. The composition, structure, and mechanical strength of BNC were characterized. Then BNC biosafety was evaluated by cytotoxicity, subcutaneous implantation, and cell affinity tests. Furthermore, BNC was used to bridge 10-mm rat sciatic nerve defect, and nerve functional recovery was assessed by walking track, electrophysiology, and histomorphology analyses. Results: Our results demonstrate that BNC has a network of nanofibers and retains some bioactive molecules, including collagen I, collagen IV, laminin, fibronectin, glycosaminoglycans, nerve growth factor, and brain-derived neurotrophic factor. Biomechanical analysis proves that PLA-PCL improves the BNC mechanical properties, compared with single ECM conduit (ENC). The functional evaluation of in vivo results indicated that BNC is more effective in nerve regeneration than PLA-PCL conduit or ENC. Discussion: In conclusion, BNC not only retains the good biocompatibility and bioactivity of ECM, but also obtains the appropriate mechanical strength from PLA-PCL, which has great potential for clinical repair of nerve defects.

3D Gelatin Microsphere Scaffolds Promote Functional Recovery after Spinal Cord Hemisection in Rats

Spinal cord injury (SCI) damages signal connections and conductions, with the result that neuronal circuits are disrupted leading to neural dysfunctions. Such injuries represent a serious and relatively common central nervous system condition and current treatments have limited success in the reconstruction of nerve connections in injured areas, especially where sizeable gaps are present. Biomaterial scaffolds have become an effective alternative to nerve transplantation in filling these gaps and provide the foundation for simulating the 3D structure of solid organs. However, there remain some limitations with the application of 3D bioprinting for preparation of biomaterial scaffolds. Here, the approach in constructing and testing mini-tissue building blocks and self-assembly, solid 3D gelatin microsphere (GM) scaffolds with multiple voids as based on the convenient preparation of gelatin microspheres by microfluidic devices is described. These 3D GM scaffolds demonstrate suitable biocompatibility, biodegradation, porosity, low preparation costs, and relative ease of production. Moreover, 3D GM scaffolds can effectively bridge injury gaps, establish nerve connections and signal transductions, mitigate inflammatory microenvironments, and reduce glial scar formation. Accordingly, these 3D GM scaffolds can serve as a novel and effective bridging method to promote nerve regeneration and reconstruction and thus recovery of nerve function after SCI.

Advancement of Electrospun Nerve Conduit for Peripheral Nerve Regeneration: A Systematic Review (2016-2021)

Peripheral nerve injury (PNI) is a worldwide problem which hugely affects the quality of patients' life. Nerve conduits are now the alternative for treatment of PNI to mimic the gold standard, autologous nerve graft. In that case, with the advantages of electrospun micro- or nano-fibers nerve conduit, the peripheral nerve growth can be escalated, in a better way. In this systematic review, we focused on 39 preclinical studies of electrospun nerve conduit, which include the in vitro and in vivo evaluation from animal peripheral nerve defect models, to provide an update on the progress of the development of electrospun nerve conduit over the last 5 years (2016-2021). The physical characteristics, biocompatibility, functional and morphological outcomes of nerve conduits from different studies would be compared, to give a better strategy for treatment of PNI.

Acellular nerve xenografts based on supercritical extraction technology for repairing long-distance sciatic nerve defects in rats

Compared to conventional artificial nerve guide conduits (NGCs) prepared using natural polymers or synthetic polymers, acellular nerve grafts (ACNGs) derived from natural nerves with eliminated immune components have natural bionic advantages in composition and structure that polymer materials do not have. To further optimize the repair effect of ACNGs, in this study, we used a composite technology based on supercritical carbon dioxide (scCO₂) extraction to process the peripheral nerve of a large mammal, the Yorkshire pig, and obtained an innovative Acellular nerve xenografts (ANXs, namely, CD + scCO₂ NG). After scCO₂ extraction, the fat and DNA content in CD + scCO₂ NG has been removed to the greatest extent, which can better supported cell adhesion and proliferation, inducing an extremely weak inflammatory response. Interestingly, the protein in the CD + scCO₂ NG was primarily involved in signaling pathways related to axon guidance. Moreover, compared with the pure chemical decellularized nerve graft (CD NG), the DRG axons grew naturally on the CD + scCO₂ NG membrane and extended long distances. In vivo studies further revealed that the regenerated nerve axons had basically crossed the CD + scCO₂ NG 3 weeks after surgery. 12 weeks after surgery, CD + scCO2 NG was similar to autologous nerves in improving the quality of nerve regeneration, target muscle morphology and motor function recovery and was significantly better than hollow NGCs and CD NG. Therefore, we believe that the fully decellularized and fat-free porcine ACNGs may be the most promising “bridge” for repairing human nerve defects at this stage and for some time to come.

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The native adipose tissue inside acellular nerve xenografts hinders regenerated nerve fibers.

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Environmentally friendly scCO2 extraction has natural advantages in reducing fat content.

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Natural three-dimensional nerve basement membrane tube structure guides regenerating axons.

Controlling the Spatiotemporal Release of Nerve Growth Factor by Chitosan/Polycaprolactone Conduits for Use in Peripheral Nerve Regeneration

Tubular polymeric structures have been recognized in the treatment of peripheral nerves as comparable to autologous grafting. The best therapeutic outcomes are obtained with conduits releasing therapeutic molecules. In this study, a new approach for the incorporation of biologically active agent-loaded microspheres into the structure of chitosan/polycaprolactone conduits was developed. The support of a polycaprolactone helix formed by 3D melt extrusion was coated with dopamine in order to adsorb nerve growth factor-loaded microspheres. The complex analysis of the influence of process factors on the coverage efficiency of polycaprolactone helix by nerve grow factor-loaded microspheres was analyzed. Thus, the PCL helix characterized with the highest adsorption of microspheres was subjected to nerve growth factor release studies, and finally incorporated into chitosan hydrogel deposit through the process of electrophoretic deposition. It was demonstrated by chemical and physical tests that the chitosan/polycaprolactone conduit meets the requirements imposed on peripheral nerve implants, particularly mimicking mechanical properties of surrounding soft tissue. Moreover, the conduit may support regrowing nerves for a prolonged period, as its structure and integrity persist upon incubation in lysozyme-contained PBS solution up to 28 days at body temperature. In vitro cytocompatibility toward mHippoE-18 embryonic hippocampal cells of the chitosan/polycaprolactone conduit was proven. Most importantly, the developed conduits stimulate axonal growth and support monocyte activation, the latter is advantageous especially at early stages of nerve regeneration. It was demonstrated that, through the described approach for controlling spatiotemporal release of nerve growth factors, these biocompatible structures adjusted to the specific peripheral nerve injury case can be manufactured.

Biocompatible Polyurethane Conduit Grafted with Vascular Endothelial Growth Factor-Loaded Hydrogel Repairs the Peripheral Nerve Defect in Rats

Artificial nerve guidance conduits (NGCs) can be potentially used to address the problems of peripheral nerve defects. The biomaterial polyurethane (PU) has already been used to construct NGCs. However, the use of a combination of PU-based NGCs and other bioactive cues, such as extracellular matrix proteins and growth factors, has not been reported yet. A PU conduit grafted with a vascular endothelial growth factor (VEGF)-loaded hydrogel (abbreviated as PU/Gel/VEGF conduit) is fabricated. The leachate generated during the use of the PU/Gel/VEGF conduit could facilitate the proliferation, migration, and expression of the neural marker S100β in RSC96 cells (in vitro). The walking track and target muscle are analyzed, and it is observed that PU/Gel/VEGF conduits promote the functional recovery of the injured side. Various histological staining analyses are carried out, and the results reveal that the PU/Gel/VEGF conduit effectively improves the extent of nerve regeneration achieved. The number of blood vessels developed during the regeneration of the axons in the PU/Gel/VEGF group (attributable to the pro-angiogenic effect of the functional NGC) is higher than the number of blood vessels developed in the PU/Gel conduit. Overall, the results indicate that PU/Gel/VEGF conduits could promote the process of peripheral nerve regeneration.

In Situ Fabrication of Nerve Growth Factor Encapsulated Chitosan Nanoparticles in Oxidized Bacterial Nanocellulose for Rat Sciatic Nerve Regeneration

Autograft is currently the gold standard in the clinical treatment of peripheral nerve injury (PNI), which, however, is limited by the availability of a donor nerve and secondary injuries. Nerve guidance conduits (NGC) provide a suitable microenvironment to promote the regeneration of injured nerves, which could be the substitutes for autografts. In this study, nerve growth factor (NGF) encapsulated chitosan nanoparticles (CSNPs) were first constructed in situ in an oxidized bacterial cellulose (OBC) conduit using the ion gel method after the introduction of a CS/NGF solution under pressure to enable a sustainable release of NGF. A novel NGF@CSNPs/OBC nanocomposite with antibacterial activity, biodegradability, and porous microstructure was successfully developed. In vitro experiments showed that the nanocomposite promoted the adhesion and proliferation of Schwann cells. When the nanocomposite was applied as NGC to repair the sciatic nerve defect of rats, a successful repair of the 10 mm nerve defect was observed after 4 weeks. At week 9, the diameter, morphology, histology, and functional recovery of the regenerated nerve was comparable to the autografts, indicating that the NGC effectively promoted the regeneration and function recovery of the nerve. In summary, the NGF@CSNPs/OBC as a novel NGC provides great potential in the treatment of PNI.

Converging 3D Printing and Electrospinning: Effect of Poly(l-lactide)/Gelatin Based Short Nanofibers Aerogels on Tracheal Regeneration

Recently, various tissue engineering based strategies have been pursued for the regeneration of tracheal tissues. However, previously developed tracheal scaffolds do not accurately mimic the microstructure and mechanical behavior of the native trachea, which restrict their clinical translation. Here, tracheal scaffolds are fabricated by using 3D printing and short nanofibers (SF) dispersion of poly(l-lactide)/gelatin (0.5-1.5 wt%) to afford tracheal constructs. The results display that the scaffolds containing 1.0 wt % of SF exhibit low density, good water absorption capacity, reasonable degradation rate, and stable mechanical properties, which were comparable to the native trachea. Moreover, the designed scaffolds possess good biocompatibility and promote the growth and infiltration of chondrocytes in vitro. The biocompatibility of tracheal scaffolds is further assessed after subcutaneous implantation in mice for up to 4 and 8 weeks. Histological assessment of tracheal constructs explanted at week 4 shows that scaffolds can maintain their structural integrity and support the formation of neo-vessels. Furthermore, cell-scaffold constructs gradually form cartilage-like tissues, which mature with time. Collectively, these engineered tracheal scaffolds not only possess appropriate mechanical properties to afford a stabilized structure but also a biomimetic extracellular matrix-like structure to accomplish tissue regeneration, which may have broad implications for tracheal regeneration.

Biodegradable polyurethane nerve guide conduits with different moduli influence axon regeneration in transected peripheral nerve injury

Nerve guide conduits (NGCs) can replace autogenous nerve grafting in the treatment of peripheral nerve system (PNS) injury. However, the modulus of polyurethane NGCs that affects the outcome of PNS repair has been rarely elucidated in vivo. In this study, we developed biodegradable waterborne polyurethane (BWPU) NGCs with an outer BWPU membrane and an inner three-dimensional scaffold structure. The mechanical properties of BWPU NGCs can be modified by adjusting the molar content of polyethylene glycol (PEG) in the soft segments within the BWPU. Two types of BWPU NGCs with different moduli were prepared, containing 17% and 25% PEG in BWPU (termed as BWPU 17 NGCs and BWPU 25 NGCs, respectively). In rat sciatic nerves with 10-mm transected injury, mechanically stronger BWPU 17 NGCs exhibited superior nerve repair, which was similar to that obtained by the current gold standard autograft implantation, whereas weaker BWPU 25 NGCs displayed an unsatisfactory effect. Histological results revealed that both BWPU NGCs had anti-inflammatory effects and altered the activation state of macrophages to M2 phenotypes to enhance PNS regeneration. The analysis of growth-associated protein 43 expression, which regulates axon growth, revealed that the mechanical properties of BWPU NGCs influence the outcome of PNS regeneration by affecting the formation and extension of axons. These findings suggest that the mechanical properties of NGCs could play a key role in regulating PNS repair and should be considered in future biomaterial NGC designs.

Nerve Guidance Conduits with Hierarchical Anisotropic Architecture for Peripheral Nerve Regeneration

Nerve guidance conduits with multifunctional features could offer microenvironments for improved nerve regeneration and functional recovery. However, the challenge remains to optimize multiple cues in nerve conduit systems due to the interplay of these factors during fabrication. Here, a modular assembly for the fabrication of nerve conduits is utilized to address the goal of incorporating multifunctional guidance cues for nerve regeneration. Silk-based hollow conduits with suitable size and mechanical properties, along with silk nanofiber fillers with tunable hierarchical anisotropic architectures and microporous structures, are developed and assembled into conduits. These conduits supported improves nerve regeneration in terms of cell proliferation (Schwann and PC12 cells) and growth factor secretion (BDNF, brain-derived neurotrophic factor) in vitro, and the in vivo repair and functional recovery of rat sciatic nerve defects. Nerve regeneration using these new conduit designs is comparable to autografts, providing a path towards future clinical impact.

Recent advances in PLGA-based biomaterials for bone tissue regeneration

Bone regeneration is an interdisciplinary complex lesson, including but not limited to materials science, biomechanics, immunology, and biology. Having witnessed impressive progress in the past decades in the development of bone substitutes; however, it must be said that the most suitable biomaterial for bone regeneration remains an area of intense debate. Since its discovery, poly (lactic-co-glycolic acid) (PLGA) has been widely used in bone tissue engineering due to its good biocompatibility and adjustable biodegradability. This review systematically covers the past and the most recent advances in developing PLGA-based bone regeneration materials. Taking the different application forms of PLGA-based materials as the starting point, we describe each form's specific application and its corresponding advantages and disadvantages with many examples. We focus on the progress of electrospun nanofibrous scaffolds, three-dimensional (3D) printed scaffolds, microspheres/nanoparticles, hydrogels, multiphasic scaffolds, and stents prepared by other traditional and emerging methods. Finally, we briefly discuss the current limitations and future directions of PLGA-based bone repair materials. STATEMENT OF SIGNIFICANCE: As a key synthetic biopolymer in bone tissue engineering application, the progress of PLGA-based bone substitute is impressive. In this review, we summarized the past and the most recent advances in the development of PLGA-based bone regeneration materials. According to the typical application forms and corresponding crafts of PLGA-based substitutes, we described the development of electrospinning nanofibrous scaffolds, 3D printed scaffolds, microspheres/nanoparticles, hydrogels, multiphasic scaffolds and scaffolds fabricated by other manufacturing process. Finally, we briefly discussed the current limitations and proposed the newly strategy for the design and fabrication of PLGA-based bone materials or devices.

Fabrication and in vitro evaluation of 3D composite scaffold based on collagen/hyaluronic acid sponge and electrospun polycaprolactone nanofibers for peripheral nerve regeneration

Replacement of peripheral nerve autografts with tissue engineered nerve grafts will potentially resolve the lack of nerve tissue especially in patients with severe concomitant soft tissue injuries. This study attempted to fabricate a tissue engineered nerve graft composed of electrospun PCL conduit filled with collagen-hyaluronic acid (COL-HA) sponge with different COL-HA weight ratios including 100:0, 98:2, 95:5 and 90:10. The effect of HA addition on the sponge porosity, mechanical properties, water absorption and degradation rate was assessed. A good cohesion between the electrospun PCL nanofibers and COL-HA sponges were seen in all sponges with different HA contents. Mechanical properties of PCL nanofibrous layer were similar to the rat sciatic nerve; the ultimate tensile strength was 2.23 ± 0.35 MPa at the elongation of 35%. Additionally, Schwann cell proliferation and morphology on three dimensional (3D) composite scaffold were evaluated by using MTT and SEM assays, respectively. Rising the HA content resulted in higher water absorption as well as greater pore size and porosity, while a decrease in Schwann cell proliferation compared to pure collagen sponge, although reduction in cell proliferation was not statistically significant. The lower Schwann cell proliferation on the COL-HA was attributed to the greater degradation rate and pore size of the COL-HA sponges. Also, dorsal root ganglion assay showed that the engineered 3D construct significantly increases axon growth. Taken together, these results suggest that the fabricated 3D composite scaffold provide a permissive environment for Schwann cells proliferation and maturation and can encourage axon growth.

Electrofabrication of flexible and mechanically strong tubular chitosan implants for peripheral nerve regeneration

The development of peripheral nerve tissue engineering requires a safe and reliable methodology to construct biodegradable conduits. Herein, a new type of chitosan-based nerve-guide hydrogel conduit (CNHC) with enhanced mechanical flexibility in the wet state was fabricated using a one-step electrofabrication technology. The formation of the chitosan conduit is a physical process which can be conducted in a mild water phase without toxic crosslinks. The current density during electrofabrication has a profound effect on the physical and structural properties of the conduits. Cytocompatibility results indicate that the CNHC can promote cell proliferation and adhesion. Functional and histological tests indicate that the CNHC has the ability to guide the growth of axons through the conduit to reach a distal stump, which is closely similar to the autograft group. Overall, the results of this study demonstrate that the CNHCs from electrofabrication have a great potential in peripheral nerve regeneration.

Electrospun Fiber Scaffolds for Engineering Glial Cell Behavior to Promote Neural Regeneration

Electrospinning is a fabrication technique used to produce nano- or micro- diameter fibers to generate biocompatible, biodegradable scaffolds for tissue engineering applications. Electrospun fiber scaffolds are advantageous for neural regeneration because they mimic the structure of the nervous system extracellular matrix and provide contact guidance for regenerating axons. Glia are non-neuronal regulatory cells that maintain homeostasis in the healthy nervous system and regulate regeneration in the injured nervous system. Electrospun fiber scaffolds offer a wide range of characteristics, such as fiber alignment, diameter, surface nanotopography, and surface chemistry that can be engineered to achieve a desired glial cell response to injury. Further, electrospun fibers can be loaded with drugs, nucleic acids, or proteins to provide the local, sustained release of such therapeutics to alter glial cell phenotype to better support regeneration. This review provides the first comprehensive overview of how electrospun fiber alignment, diameter, surface nanotopography, surface functionalization, and therapeutic delivery affect Schwann cells in the peripheral nervous system and astrocytes, oligodendrocytes, and microglia in the central nervous system both in vitro and in vivo. The information presented can be used to design and optimize electrospun fiber scaffolds to target glial cell response to mitigate nervous system injury and improve regeneration.

Biomimetic and hierarchical nerve conduits from multifunctional nanofibers for guided peripheral nerve regeneration

Development of a functional nerve conduit to replace autografts remains a significant challenge particularly considering the compositional complexity and structural hierarchy of native peripheral nerves. In the present study, a multiscale strategy was adopted to fabricate 3D biomimetic nerve conduit from Antheraea pernyi silk fibroin (ApF)/(Poly(L-lactic acid-co-caprolactone)) (PLCL)/graphene oxide (GO) (ApF/PLCL/GO) nanofibers via nanofiber dispersion, template-molding, freeze-drying and crosslinking. The resultant conduits exhibit parallel multichannels (ϕ = 125 µm) surrounded by biomimetic fibrous fragments with tailored degradation rate and improved mechanical properties in comparison with the scaffold without GO. In vitro studies showed that such 3D biomimetic nerve scaffolds had the ability to offer an effective guiding interface for neuronal cell growth. Furthermore, these conduits showed a similarity to autografts in vivo repairing sciatic nerve defects based on a series of analysis (walking track, triceps weight, morphogenesis, vascularization, axonal regrowth and myelination). The conduits almost completely degraded within 12 weeks. These findings demonstrate that the 3D hierarchical nerve guidance conduit (NGC) with fascicle-like structure have great potential for peripheral nerve repair.

Bioinspired Multichannel Nerve Guidance Conduit Based on Shape Memory Nanofibers for Potential Application in Peripheral Nerve Repair

Repairing peripheral nerve injury, especially long-range defects of thick nerves, is a great challenge in the clinic due to their limited regeneration capability. Most FDA-approved nerve guidance conduits with large hollow lumen are only suitable for short lesions, and their effects are unsatisfactory in repairing long gaps of thick nerves. Multichannel nerve guidance conduits have been shown to offer better regeneration of long nerve defects. However, existing approaches of fabricating multichannel nerve conduits are usually complicated and time-consuming. Inspired by the intelligent responsive shaping process of shape memory polymers, in this study, a self-forming multichannel nerve guidance conduit with topographical cues was constructed based on a degradable shape memory PLATMC polymer. With an initial tubular shape obtained by a high-temperature molding process, the electrospun shape memory nanofibrous mat could be temporarily formed into a planar shape for cell loading to realize the uniform distribution of cells. Then triggered by a physical temperature around 37 °C, it could automatically restore its permanent tubular shape to form the multichannel conduit. This multichannel conduit exhibits better performance in terms of cell growth and the repair of rat sciatic nerve defects. These results reveal that self-forming nerve conduits can be realized based on shape memory polymers; thus, the fabricated bioinspired multichannel nerve guidance conduit has great potential in peripheral nerve regeneration.

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.

Synthesis and Evaluation of Cytocompatible Alkyne-Containing Poly(β-amino ester)-Based Hydrogels Functionalized via Click Reaction

Although poly(β-amino esters) (PAEs) have been widely applied in nonviral gene transfection, drug delivery systems, and regenerative medicine, the multifunctional modification of PAEs and bio-orthogonal strategies of PAE-based hydrogel functionalization is still a challenge. Herein, a strategy of poly(β-amino ester)-based hydrogel functionalization was developed via bio-orthogonal reactions in this study. Acrylate-terminated poly(β-amino esters) containing alkyne groups were synthesized by Michael addition reaction. Alkyne groups on poly(β-amino esters) could conjugate bioactive molecules with azide of K(N₃)RGD via copper-catalyzed azide-alkyne cycloaddition, and terminal acrylate groups could in situ polymerize to prepare a hydrogel. A biomimetic peptide K(N₃)RGD functionalized hydrogel was prepared by polymerization of acrylate-terminated poly(β-amino esters) containing conjugated peptide and polyethylene glycol diacrylate (PEGDA). The storage modulus and mechanical properties exhibited an increased trend with the increased concentration; nevertheless, swelling ratio and surface wetting properties demonstrated a decreased tendency by increased concentrations. Cell proliferation and live/dead staining showed that Schwann cells plated on the hydrogel with an elastic modulus of 25.39 KPa are more suitable for proliferation and function exertion of Schwann cells compared with that of 42.11 and 57.86 KPa, and KRGD-conjugated hydrogel could increase the elongation of Schwann cells relative to nonconjugated hydrogels. This azide-alkyne strategy may be a promising candidate for hydrogel functionalization in tissue engineering and other biomedical applications.

3D Reduced Graphene Oxide Scaffolds with a Combinatorial Fibrous-Porous Architecture for Neural Tissue Engineering

Graphene oxide (GO) assists a diverse set of promising routes to build bioactive neural microenvironments by easily interacting with other biomaterials to enhance their bulk features or, alternatively, self-assembling toward the construction of biocompatible systems with specific three-dimensional (3D) geometries. Herein, we first modulate both size and available oxygen groups in GO nanosheets to adjust the physicochemical and biological properties of polycaprolactone-gelatin electrospun nanofibrous systems. The results show that the incorporation of customized GO nanosheets modulates the properties of the nanofibers and, subsequently, markedly influences the viability of neural progenitor cell cultures. Interestingly, the partially reduced GO (rGO) nanosheets with larger dimensions trigger the best cell response, while the rGO nanosheets with smaller size provoke an accentuated decrease in the cytocompatibility of the resulting electrospun meshes. Then, the most auspicious nanofibers are synergistically accommodated onto the surface of 3D-rGO heterogeneous porous networks, giving rise to fibrous-porous combinatorial architectures suitable for enhancing adhesion and differentiation of neural cells. By varying the chemical composition of the nanofibers, it is possible to adapt their performance as physical crosslinkers for the rGO sheets, leading to the modulation of both pore size and structural/mechanical integrity of the scaffold. Importantly, the biocompatibility of the resultant fibrous-porous systems is not compromised after 14 days of cell culture, including standard differentiation patterns of neural progenitor cells. Overall, in light of these in vitro results, the reported scaffolding approach presents not only an indisputable capacity to support highly viable and interconnected neural circuits but also the potential to unlock novel strategies for neural tissue engineering applications.

CNT/Sericin Conductive Nerve Guidance Conduit Promotes Functional Recovery of Transected Peripheral Nerve Injury in a Rat Model

Peripheral nerve injury usually leads to poor outcomes such as painful neuropathies and disabilities. Autogenous nerve grafting is the current gold standard; however, the limited source of a donor nerve remains a problem. Numerous tissue engineering nerve guidance conduits have been developed as substitutes for autografts. However, a few conduits can achieve the reparative effect equivalent to autografts. Here, we report for the development and application of a carbon nanotube (CNT)/sericin nerve conduit with electrical conductivity and suitable mechanical properties for nerve repair. This CNT/sericin conduit possesses favorable properties including biocompatibility, biodegradability, porous microarchitecture, and suitable swelling property. We thus applied this conduit for bridging a 10 mm gap defect of a transected sciatic nerve combined with electrical stimulation (ES) in a rat injury model. By the end of 12 weeks, we observed that the CNT/sericin conduit combined with electrical stimulation could effectively promote both structural repair and functional recovery comparable to those of the autografts, evidenced by the morphological and histological analyses, electrophysiological responses, functional studies, and target muscle reinnervation evaluations. These findings suggest that this electric conductive CNT/sericin conduit combined with electrical stimulation may have the potential to serve as a new alternative for the repair of transected peripheral nerves.

Aligned soy protein isolate-modified poly(L-lactic acid) nanofibrous conduits enhanced peripheral nerve regeneration

OBJECTIVE

Repair and regeneration of peripheral nerve defect by engineered conduits have greatly advanced in the past decades while still facing great challenges.

APPROACH

In this work, we fabricated a new highly oriented poly(L-lactic acid) (PLLA)/soy protein isolate (SPI) nanofibrous conduit (HO-PSNC) for nerve regeneration.

MAIN RESULTS

Firstly, we observed that SPI could efficiently modify PLLA for the electrospinning of PLLA/SPI nanofibers with enhanced physical and biological properties. Incorporation of SPI decreased the fiber diameter and ductility of PLLA/SPI nanofibrous films (PSNFs), improved the tensile strength and surface wettability of PSNFs and increased the in vivo degradability of the PSNFs. When the hybrid ratio of SPI was 20 and 40%, PSNFs could efficiently promote neural cell extension and differentiation in vitro. Based on these data, 20% SPI (PSNF-20) was chosen for further investigation. Next, PSNF-20 with different fiber orientations (random/low orientation, medium, and high orientation, respectively) were developed and used for evaluating neural cell behaviors on the materials. Results revealed that the PSNF-20 with highly oriented nanofibers (HO-PSNF-20) or mediumly oriented nanofibers (MO-PSNF-20) showed a better performance in directing cell extension and enhancing neurite outgrowth. Finally, the highly oriented nanofibers conduits (HO-PSNC-20) were used to bridge sciatic nerve defect in rats with highly oriented PLLA and autografts as controls. HO-PSNC-20 exhibited a significant promotion in nerve regeneration and functional reconstruction comparing to highly oriented PLLA as proven by the evaluations of walking track, electrophysiology, toluidine blue nerve staining, transmission electron microscopy, neural factors staining and qPCR, and gastrocnemius histology.

SIGNIFICANCE

In conclusion, nerve conduit fabricated from aligned electrospinning of SPI-modified PLLA nanofibers is promising for peripheral nerve regeneration.

Combination of electrospinning with other techniques for the fabrication of 3D polymeric and composite nanofibrous scaffolds with improved cellular interactions

The development of three-dimensional (3D) scaffolds with physical and chemical topological cues at the macro-, micro-, and nanometer scale is urgently needed for successful tissue engineering applications. 3D scaffolds can be manufactured by a wide variety of techniques. Electrospinning technology has emerged as a powerful manufacturing technique to produce non-woven nanofibrous scaffolds with very interesting features for tissue engineering products. However, electrospun scaffolds have some inherent limitations that compromise the regeneration of thick and complex tissues. By integrating electrospinning and other fabrication technologies, multifunctional 3D fibrous assemblies with micro/nanotopographical features can be created. The proper combination of techniques leads to materials with nano and macro-structure, allowing an improvement in the biological performance of tissue-engineered constructs. In this review, we focus on the most relevant strategies to produce electrospun polymer/composite scaffolds with 3D architecture. A detailed description of procedures involving physical and chemical agents to create structures with large pores and 3D fiber assemblies is introduced. Finally, characterization and biological assays including in vitro and in vivo studies of structures intended for the regeneration of functional tissues are briefly presented and discussed.

Moving Electrospun Nanofibers and Bioprinted Scaffolds toward Translational Applications

Over the past two decades, electrospun nanofibers have been actively explored for a range of applications, including those related to biomedicine, environmental science, energy harvesting, catalysis, photonics, and electronics. Regarding biomedical applications, one can readily produce nanofiber-based scaffolds with controlled compositions, structures, alignments, and functions by varying the material, design of collector, number of spinnerets, and electrospinning parameters. This report highlights both preclinical and translational applications of electrospun nanofibers and bioprinted constructs presented at the 2019 International Conference on Electrospinning, together with some perspectives on their future development.

Methylcobalamin-Loaded PLCL Conduits Facilitate the Peripheral Nerve Regeneration

The feasible fabrication of nerve guidance conduits (NGCs) with good biological performance is important for translation in clinics. In this study, poly(d,l-lactide-co-caprolactone) (PLCL) films loaded with various amounts (wt; 5%, 15%, 25%) of methylcobalamin (MeCbl) are prepared, and are further rolled and sutured to obtain MeCbl-loaded NGCs. The MeCbl can be released in a sustainable manner up to 21 days. The proliferation and elongation of Schwann cells, and the proliferation of Neuro2a cells are enhanced on these MeCbl-loaded films. The MeCbl-loaded NGCs are implanted into rats to induce the regeneration of 10 mm amputated sciatic nerve defects, showing the ability to facilitate the recovery of motor and sensory function, and to promote myelination in peripheral nerve regeneration. In particular, the 15% MeCbl-loaded PLCL conduit exhibits the most satisfactory recovery of sciatic nerves in rats with the largest diameter and thickest myelinated fibers.

Aligned chitosan nanofiber hydrogel grafted with peptides mimicking bioactive brain-derived neurotrophic factor and vascular endothelial growth factor repair long-distance sciatic nerve defects in rats

Autologous nerve transplantation, which is the gold standard for clinical treatment of peripheral nerve injury, still has many limitations. In this study, aligned chitosan fiber hydrogel (ACG) grafted with a bioactive peptide mixture consisting of RGI (Ac-RGIDKRHWNSQGG) and KLT (Ac-KLTWQELYQLKYKGIGG), designated as ACG-RGI/KLT, was used as nerve conduit filler to repair sciatic nerve defects in rats. Methods: Chitosan nanofiber hydrogel was prepared by a combination of electrospinning and mechanical stretching methods, and was then grafted with RGI and KLT, which are peptides mimicking brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF), respectively. The physicochemical properties of ACG-RGI/KLT were fully characterized. In vitro, the distribution, proliferation, and secretory activity of Schwann cells were analyzed. Next, the in vivo repair potential for 15-mm rat sciatic nerve defects was examined. The recovery of regenerated nerve, muscle, and motor function was evaluated by neuromuscular histology, electrophysiology, and catwalk gait analysis. Results: We first constructed directionally aligned chitosan nanofiber hydrogel grafted with RGI/KLT peptide mixture (ACG-RGI/KLT). ACG-RGI/KLT oriented the Schwann cells, and promoted the proliferation and secretion of neurotrophic factors by Schwann cells. At an early injury stage, ACG-RGI/KLT not only enhanced nerve regeneration, but also promoted vascular penetration. At 12 weeks, ACG-RGI/KLT facilitated nerve regeneration and functional recovery in rats. Conclusions: Aligned chitosan nanofiber hydrogel grafted with RGI/KLT peptide provides an effective means of repairing sciatic nerve defects and shows great potential for clinical application.

Repairing Transected Peripheral Nerve Using a Biomimetic Nerve Guidance Conduit Containing Intraluminal Sponge Fillers

Nerve guide conduits (NGCs) with geometric design have shown significant advantages in guidance of nerve reinnervation across the defect of injured peripheral nerves. It is realized that intraluminal fillers with distinctive structure can effectively provide an inner guidance for sprouting of axons and improve the permeability of NGC. In this work, a poly(lactic-co-glycolic acid) (PLGA) NGC is prepared containing intraluminal sponge fillers (labeled as ISF-NGC) and used for reconstruction of a rat sciatic nerve with a 10 mm gap. For comparison, the same procedure is applied to a single hollow PLGA NGC (labeled as H-NGC) and an autologous nerve. As evidenced by significantly improved nerve morphology and function, the ISF-NGC achieves a superior nerve repair effect over H-NGC, which is comparable to autologous nerve grafting. It is likely that the H-NGC only provides a protected tunnel for nerve fiber regrowth and axonal extension, while ISF-NGC offers an extracellular matrix-mimetic architecture as autograft to provide contact guidance for nerve reinnervation. This newly developed ISF-NGC is a promising candidate to aid nerve reinnervation across longer gaps commonly encountered in clinical cases.

Laminin-Coated Electrospun Regenerated Silk Fibroin Mats Promote Neural Progenitor Cell Proliferation, Differentiation, and Survival in vitro

Neural progenitor cell (NPC) transplantation is a promising technique for central nervous system (CNS) reconstruction and regeneration. Biomaterial scaffolds, frameworks, and platforms can support NPC proliferation and differentiation in vitro as well as serve as a temporary extracellular matrix after transplantation. However, further applications of biomaterials require improved biological attributes. Silk fibroin (SF), which is produced by Bombyx mori, is a widely used and studied protein polymer for biomaterial application. Here, we prepared aligned and random eletrospun regenerated SF (RSF) scaffolds, and evaluated their impact on the growth of NPCs. First, we isolated NPCs and then cultured them on either laminin-coated RSF mats or conventional laminin-coated coverslips for cell assays. We found that aligned and random RSF led to increases in NPC proliferation of 143.8 ± 13.3% and 156.3 ± 14.7%, respectively, compared to controls. Next, we investigated neuron differentiation and found that the aligned and the random RSF led to increases in increase in neuron differentiation of about 93.2 ± 6.4%, and 3167.1 ± 4.8%, respectively, compared to controls. Furthermore, we measured the survival of NPCs and found that RSF promoted NPC survival, and found there was no difference among those three groups. Finally, signaling pathways in cells cultured on RSF mats were studied for their contributions in neural cell differentiation. Our results indicate that RSF mats provide a functional microenvironment and represent a useful scaffold for the development of new strategies in neural engineering research.

Virtually Wall-Less Tubular Sponges as Compartmentalized Reaction Containers

Sponges are open cellular materials with numerous interesting features. However, the potential of compartmentalized sponges has not been explored although many new properties and applications could be envisioned. We found that compartmentalized fibrous ultraporous polymer sponges with superhydrophobic surfaces could be designed as virtually wall-less reaction containers. With this, for example, the efficient removal of CO₂ from water and the controlled mineralization of calcium carbonate are possible. The high porosity (>99%) and superhydrophobicity make these sponges ideal candidates to hold alkanolamine solution for absorbing CO₂ and exchange gas through the walls of the sponges. The tubular sponge exhibits a much higher evaporation rate than a glass tube with the same diameter due to the much larger contact area between water and air. Therefore, the spongy reaction container also possesses a much faster adsorption rate, smaller equilibration time and higher efficiency for CO₂ adsorption than the glass tube container. In addition, these tubular sponges are also utilized to precipitate calcium carbonate by ammonium carbonate decomposition, which can control the deposition rates and products by tailoring the porosity and surface chemistry in the future. These new sponges provide an ideal basis for numerous new applications, for example, as breathable pipe lines for gas-liquid exchange, slag slurry carbonization, humidifier, and blood enricher.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.