New nerve regeneration strategy combining laminin-coated chitosan conduits and stem cell therapy

Comparative gene expression analysis of stemness between periodontal ligament and umbilical cord tissues in humans

Background/purpose

Due to their regenerative potential, periodontal ligament (PDL) and umbilical cord (UBC) tissues are an attractive potential mesenchymal stem cells (MSCs) source. This study compared the expression patterns of genes related to stemness between fresh PDL and UBC tissues.

Materials and methods

PDL tissues were collected from 38 permanent premolars extracted for orthodontic purposes, and UBC tissues were obtained from three newborns. Each sample was immediately frozen to prevent RNA degradation. cDNA microarray analysis, quantitative real-time polymerase chain reaction (PCR), and immunohistochemical staining were performed. Gene expression patterns associated with dental stemness (DS) and induced pluripotent stemness (iPS) were compared between PDL and UBC tissues.

Results

In the cDNA microarray analyses, the expressions of most iPS genes were greater in the PDL than in the UBC. Meanwhile, the expressions of most DS genes were greater in the UBC than in the PDL. Quantitative real-time PCR analyses showed that the expression levels of matrix metallopeptidase 13 (MMP13), ADAM metallopeptidase domain 22 (ADAM22), vascular cell adhesion protein 1 (VCAM1), and kruppel-like factor 4 (KLF4) genes were greater in the PDL than in the UBC, while the expressions of melanoma cell adhesion molecule (MCAM) and activated leukocyte cell adhesion molecule (ALCAM) were greater in the UBC than in the PDL.

Conclusion

These results suggest that UBC and PDL tissues showed slightly different expression patterns of genes related to stemness, which warrants further investigation to use these tissues for future regeneration and implantation therapies.

Multifaceted polymeric nerve guidance conduits with distinctive double-layered architecture and plasma-induced inner chemistry gradient for the repair of critical-sized defects

Despite tissue engineering advances, current nerve guidance conduits (NGCs) are still failing in repairing critical-sized defects. This study aims, therefore, at tackling large nerve gaps (2 cm) by designing NGCs possessing refined physicochemical properties enhancing the activity of Schwann cells (SCs) that support nerve regeneration over long distances. As such, a combinatorial strategy adopting novel plasma-induced surface chemistry and architectural heterogeneity was considered. A mechanically suitable copolymer (Polyactive®) was electrospun to produce nanofibrous NGCs mimicking the extracellular matrix. An innovative seamless double-layered architecture consisting of an inner wall comprised of bundles of aligned fibers with intercalated random fibers and an outer wall fully composed of random fibers was conceived to synergistically provide cell guidance cues and sufficient nutrient inflow. NGCs were subjected to argon plasma treatments using a dielectric barrier discharge (DBD) and a plasma jet (PJ). Surface chemical changes were examined by advanced X-ray photoelectron spectroscopy (XPS) micro-mappings. The DBD homogeneously increased the surface oxygen content from 17 % to 28 % on the inner wall. The PJ created a gradient chemistry throughout the inner wall with an oxygen content gradually increasing from 21 % to 30 %. In vitro studies revealed enhanced primary SC adhesion, elongation and proliferation on plasma-treated NGCs. A cell gradient was observed on the PJ-treated NGCs thus underlining the favorable oxygen gradient in promoting cell chemotaxis. A gradual change from circular to highly elongated SC morphologies mimicking the bands of Büngner was visualized along the gradient. Overall, plasma-treated NGCs are promising candidates paving the way towards critical nerve gap repair.

Repairing sciatic nerve injury with self-assembling peptide nanofiber scaffold-containing chitosan conduit

Background

An increasing number of nerve guide scaffolds have been used to replace the “gold-standard” autologous nerve graft for repairing peripheral nerve defects, but nerve regeneration is usually far from complete.

Methods

Here, we designed and prepared two functionalized self-assembling peptides (SAP) with the IKVAV and KLT sequences, which were derived from the combination of laminin and VEGF, respectively. Their mixtures were also obtained to combine the effects of neuroprotective and neurotrophic and proangiogenic factors.

Results

The beneficial effect of peptide gels on nerve regeneration was evaluated in vitro using Schwann cells (SCs). As a useful intraluminal filling, a three-dimensional (3D) functionalized self-assembling peptide (SAP) nanofiber hydrogel was formed in the hollow lumen of chitosan conduits under physiological conditions. In vivo, the combination of the two functionalized SAP gels containing a chitosan nerve conduit significantly accelerated nerve healing and enhanced morphological repair.

Conclusion

Based on the current findings, the combined application of two functionalized SAP gels with chitosan nerve conduit is a promising therapy for the engineering of peripheral nerve regeneration.

Effects of 17-β-estradiol released from shape-memory terpolymer rods on sciatic nerve regeneration after injury and repair with chitosan nerve conduit in female rats

The aim of this study was to assess 17-β-estradiol (E2) influence on sciatic nerve regeneration after injury followed by a repair with chitosan conduit in ovariectomized female rats. The study was performed in 2 groups (n = 16) of rats: OVChit - after excision of a fragment of the sciatic nerve, a chitosan conduit was implanted; OVChitE10 group - additionally to chitosan conduit, shape-memory terpolymer rods based on poly(L-lactide-co-glycolide- co-trimethylene carbonate) releasing 17-β-estradiol for 20 weeks were implanted. The mean number of regenerating axons and mean fiber area were significantly greater in 17-β-estradiol-treated animals. In this group, the infiltrate of leukocytes was diminished. The presence of 17-β-estradiol receptors alpha and beta in motoneurons in the spinal cord were discovered. This may indicate the location where 17-β-estradiol affects the regeneration of the injured nerve. Estradiol released from the terpolymer rods for 20 weeks could enhance, to some extent, sciatic nerve regeneration after injury, and diminish the inflammatory reaction. In the future, 17-β-estradiol entrapped in terpolymer rods could be used in the repair of injured peripheral nerves, but there is a need for further studies.

Preparation and mechanical optimization of a two-layer silk/magnesium wires braided porous artificial nerve guidance conduit

Peripheral nerve injures have long been a tricky problem in surgery and a feasible treatment is the transplantation of nerve guidance conduits (NGCs). This study presents a two-layer composite NGC with fair mechanical properties and good biocompatibility. The inner layer was made of degummed silk yarns/magnesium wires using braiding technology, and the outer layer was made from mixed solution of silk fibroin/chitosan (SF/CS) using freeze-drying treatment. Orthogonal experimental design was applied to rationally design the braided structural layer and obtain the optimal combination of technical process parameters. Meanwhile, the SF/CS porous outer layer was optimized from three concentrations of SF/CS solution. In vitro and in vivo study suggested that the textile-forming scaffold exhibited good biocompatibility and no toxicity. During 4 weeks' degradation, the skeleton of conduits retained its shape, and magnesium ions released from degraded magnesium wires contributed to sustainable release and uniform dispersion, proliferation and adhesion of Schwann cells, indicating potential approach in the development of NGCs.

A combined experimental and computational framework to evaluate the behavior of therapeutic cells for peripheral nerve regeneration

Recent studies have explored the potential of tissue‐mimetic scaffolds in encouraging nerve regeneration. One of the major determinants of the regenerative success of cellular nerve repair constructs (NRCs) is the local microenvironment, particularly native low oxygen conditions which can affect implanted cell survival and functional performance. In vivo, cells reside in a range of environmental conditions due to the spatial gradients of nutrient concentrations that are established. Here we evaluate in vitro the differences in cellular behavior that such conditions induce, including key biological features such as oxygen metabolism, glucose consumption, cell death, and vascular endothelial growth factor secretion. Experimental measurements are used to devise and parameterize a mathematical model that describes the behavior of the cells. The proposed model effectively describes the interactions between cells and their microenvironment and could in the future be extended, allowing researchers to compare the behavior of different therapeutic cells. Such a combinatorial approach could be used to accelerate the clinical translation of NRCs by identifying which critical design features should be optimized when fabricating engineered nerve repair conduits.

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

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

Effects of chitosan and platelet-rich plasma on facial nerve regeneration in an animal model

PURPOSE

There is still no widely-accepted local agent proven to be effective in nerve regeneration. We aimed to investigate the effects of chitosan gel and platelet-rich plasma MATERIALS AND METHODS: Electrophysiological measurements were performed before and immediately after injury. The injured nerves were covered with spongostan impregnated with the following agents: Group 1 (Control Group): Saline at a dose of 50 µl; Group 2: Chitosan (CHT) at a dose of 50 µl; Group 3: PRP at a dose of 50 ml; and Group 4: a solution of CHT with PRP (1:1). The final measurements were performed after 3 weeks and the injured nerve of each rat was removed.

RESULTS

There were statistically-significant differences between the groups regarding the measurements of the after-treatment values of stimulus threshold (p < 0.05). The best improvement in electrophysiological measurement and histopathological evaluation was found in Group 4 (CHT-PRP).

CONCLUSION

Chitosan gel has a positive effect on nerve healing and applying it along with PRP can enhance the effect of chitosan.

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

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

Three-Dimensional Engineered Peripheral Nerve: Toward a New Era of Patient-Specific Nerve Repair Solutions

Reconstruction of peripheral nerve injuries (PNIs) with substance loss remains challenging because of limited treatment solutions and unsatisfactory patient outcomes. Currently, nerve autografting is the first-line management choice for bridging critical-sized nerve defects. The procedure, however, is often complicated by donor site morbidity and paucity of nerve tissue, raising a quest for better alternatives. The application of other treatment surrogates, such as nerve guides, remains questionable, and it is inefficient in irreducible nerve gaps. More importantly, these strategies lack customization for personalized patient therapy, which is a significant drawback of these nerve repair options. This negatively impacts the fascicle-to-fascicle regeneration process, critical to restoring the physiological axonal pathway of the disrupted nerve. Recently, the use of additive manufacturing (AM) technologies has offered major advancements to the bioengineering solutions for PNI therapy. These techniques aim at reinstating the native nerve fascicle pathway using biomimetic approaches, thereby augmenting end-organ innervation. AM-based approaches, such as three-dimensional (3D) bioprinting, are capable of biofabricating 3D-engineered nerve graft scaffolds in a patient-specific manner with high precision. Moreover, realistic in vitro models of peripheral nerve tissues that represent the physiologically and functionally relevant environment of human organs could also be developed. However, the technology is still nascent and faces major translational hurdles. In this review, we spotlighted the clinical burden of PNIs and most up-to-date treatment to address nerve gaps. Next, a summarized illustration of the nerve ultrastructure that guides research solutions is discussed. This is followed by a contrast of the existing bioengineering strategies used to repair peripheral nerve discontinuities. In addition, we elaborated on the most recent advances in 3D printing and biofabrication applications in peripheral nerve modeling and engineering. Finally, the major challenges that limit the evolution of the field along with their possible solutions are also critically analyzed.

Thermosensitive quaternized chitosan hydrogel scaffolds promote neural differentiation in bone marrow mesenchymal stem cells and functional recovery in a rat spinal cord injury model

A thermosensitive quaternary ammonium chloride chitosan/β-glycerophosphate (HACC/β-GP) hydrogel scaffold combined with bone marrow mesenchymal stem cells (BMSCs) transfected with an adenovirus containing the glial cell-derived neurotrophic factor (GDNF) gene (Ad-rGDNF) was applied to spinal cord injury (SCI) repair. The BMSCs from rats were transfected with Ad-rGDNF, resulting in the expression of GDNF mRNA in the BMSCs increasing and their spontaneous differentiation into neural-like cells expressing neural markers such as NF-200 and GFAP. After incubation with HACC/β-GP hydrogel scaffolds for 2 weeks, neuronal differentiation of the BMSCs was confirmed using immunofluorescence (IF), and the expression of GDNF by the BMSCs was detected by Western blot at different time points. MTT assay and scanning electron microscopy confirmed that the HACC scaffold provides a non-cytotoxic microenvironment that supports cell adhesion and growth. Rats with SCI were treated with BMSCs, BMSCs carried by the HACC/β-GP hydrogel (HACC/BMSCs), Ad-rGDNF-BMSCs, or Ad-rGDNF-BMSCs carried by the hydrogel (HACC/GDNF-BMSCs). Animals were sacrificed at 2, 4, and 6 weeks of treatment. IF staining and Western blot were performed to detect the expression of NeuN, NF-200, GFAP, CS56, and Bax in the lesion sites of the injured spinal cord. Upon treatment with HACC/BMSCs, NF200 and GFAP were upregulated but CS56 and Bax were downregulated in the SCI lesion site. Furthermore, transplantation of HACC/GDNF-BMSCs into an SCI rat model significantly improved BBB scores and regeneration of the spinal cord. Thus, HACC/β-GP hydrogel scaffolds show promise for functional recovery in spinal cord injury patients.

Mesenchymal stem cell treatment for peripheral nerve injury: a narrative review

Peripheral nerve injuries occur as the result of sudden trauma and lead to reduced quality of life. The peripheral nervous system has an inherent capability to regenerate axons. However, peripheral nerve regeneration following injury is generally slow and incomplete that results in poor functional outcomes such as muscle atrophy. Although conventional surgical procedures for peripheral nerve injuries present many benefits, there are still several limitations including scarring, difficult accessibility to donor nerve, neuroma formation and a need to sacrifice the autologous nerve. For many years, other therapeutic approaches for peripheral nerve injuries have been explored, the most notable being the replacement of Schwann cells, the glial cells responsible for clearing out debris from the site of injury. Introducing cultured Schwann cells to the injured sites showed great benefits in promoting axonal regeneration and functional recovery. However, there are limited sources of Schwann cells for extraction and difficulties in culturing Schwann cells in vitro. Therefore, novel therapeutic avenues that offer maximum benefits for the treatment of peripheral nerve injuries should be investigated. This review focused on strategies using mesenchymal stem cells to promote peripheral nerve regeneration including exosomes of mesenchymal stem cells, nerve engineering using the nerve guidance conduits containing mesenchymal stem cells, and genetically engineered mesenchymal stem cells. We present the current progress of mesenchymal stem cell treatment of peripheral nerve injuries.

Review of Integrin-Targeting Biomaterials in Tissue Engineering

The ability to direct cell behavior has been central to the success of numerous therapeutics to regenerate tissue or facilitate device integration. Biomaterial scientists are challenged to understand and modulate the interactions of biomaterials with biological systems in order to achieve effective tissue repair. One key area of research investigates the use of extracellular matrix-derived ligands to target specific integrin interactions and induce cellular responses, such as increased cell migration, proliferation, and differentiation of mesenchymal stem cells. These integrin-targeting proteins and peptides have been implemented in a variety of different polymeric scaffolds and devices to enhance tissue regeneration and integration. This review first presents an overview of integrin-mediated cellular processes that have been identified in angiogenesis, wound healing, and bone regeneration. Then, research utilizing biomaterials are highlighted with integrin-targeting motifs as a means to direct these cellular processes to enhance tissue regeneration. In addition to providing improved materials for tissue repair and device integration, these innovative biomaterials provide new tools to probe the complex processes of tissue remodeling in order to enhance the rational design of biomaterial scaffolds and guide tissue regeneration strategies.

Chitosan Hydrogel Enhances the Therapeutic Efficacy of Bone Marrow-Derived Mesenchymal Stem Cells for Myocardial Infarction by Alleviating Vascular Endothelial Cell Pyroptosis

Supplemental Digital Content is Available in the Text.

Myocardial infarction (MI) is one of the higher mortality rates, and current treatment can only delay the progression of the disease. Experiments have shown that cell therapy could improve cardiac function and mesenchymal stem cells (MSCs)-based therapies provide a great promising approach in the treatment of MI. However, low cell survival and engraftment restricts the successful application of MSCs for treating MI. Here, we explored whether co-transplantation of a chitosan (CS) thermosensitive hydrogel with bone marrow-derived MSCs (BMSCs) could optimize and maximize the therapeutic of BMSCs in a mouse model of MI. The fate of transplanted BMSCs was monitored by bioluminescence imaging, and the recovery of cardiac function was detected by echocardiogram. Our results proved that CS hydrogel enhanced the BMSCs' survival and the recovery of cardiac function by protecting the vascular endothelial cells. Further studies revealed that the increased number of vascular endothelial cells was due to the fact that transplanted BMSCs inhibited the inflammatory response and alleviated the pyroptosis of vascular endothelial cells. In conclusions, CS hydrogel improved the engraftment of transplanted BMSCs, ameliorated inflammatory responses, and further promoted functional recovery of heart by alleviating vascular endothelial cell pyroptosis.

Additive-lathe 3D bioprinting of bilayered nerve conduits incorporated with supportive cells

Nerve conduits have been identified as one of the most promising treatments for peripheral nerve injuries, yet it remains unsolved how to develop ideal nerve conduits with both appropriate biological and mechanical properties. Existing nerve conduits must make trade-offs between mechanical strength and biocompatibility. Here, we propose a multi-nozzle additive-lathe 3D bioprinting technology to fabricate a bilayered nerve conduit. The materials for printing consisted of gelatin methacrylate (GelMA)-based inner layer, which was cellularized with bone marrow mesenchymal stem cells (BMSCs) and GelMA/poly(ethylene glycol) diacrylate (PEGDA)-based outer layer. The high viability and extensive morphological spreading of BMSCs encapsulated in the inner layer was achieved by adjusting the degree of methacryloyl substitution and the concentration of GelMA. Strong mechanical performance of the outer layer was obtained by the addition of PEGDA. The performance of the bilayered nerve conduits was assessed using in vitro culture of PC12 cells. The cell density of PC12 cells attached to cellularized bilayered nerve conduits was more than 4 times of that on acellular bilayered nerve conduits. The proliferation rate of PC12 cells attached to cellularized bilayered nerve conduits was over 9 times higher than that on acellular bilayered nerve conduits. These results demonstrate the additive-lathe 3D bioprinting of BMSCs embedded bilayered nerve conduits holds great potential in facilitating peripheral nerve repair.

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A multi-nozzle additive-lathe 3D bioprinting technology is developed to fabricate a bilayered nerve conduit.

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The outer layer of nerve conduit provide a strong mechanical property and the inner layer has a good biocompatibility.

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Bone marrow mesenchymal stem cells (BMSCs) are incorporated in the inner layer of nerve conduit using bioprinting.

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In vitro culture of PC12 cells demonstrates the neuron outgrowth is significantly improved in BMSCs embedded nerve conduits.

Brain Derived Neurotrophic Factor and Glial Cell Line-Derived Neurotrophic Factor-Transfected Bone Mesenchymal Stem Cells for the Repair of Periphery Nerve Injury

Peripheral nerve injury is a common clinical neurological disease. In our previous study, highly oriented poly (L-lactic acid) (PLLA)/soy protein isolate (SPI) nanofiber nerve conduits were constructed and exhibited a certain repair capacity for peripheral nerve injury. In order to further improve their nerve repairing efficiency, the bone mesenchymal stem cells (BMSCs) overexpressing brain derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) were introduced into the conduits as seed cells and then were used to repair the 10-mm sciatic nerve defects in rats. The nerve repair efficiency of the functional nerve conduits was evaluated by gait experiment, electrophysiological test, and a series of assays such as hemotoxylin-eosin (HE) staining, immunofluorescence staining, toluidine blue (TB) staining, transmission electron microscopy (TEM) observation of regenerated nerve and Masson's trichrome staining of gastrocnemius muscle. The results showed that the conduits containing BMSCs overexpressing BDNF and GDNF double-factors group had better nerve repairing efficiency than blank BMSCs and single BDNF or GDNF factor groups, and superior to autografts group in some aspects. These data demonstrated that BDNF and GDNF produced by BMSCs could synergistically promote peripheral nerve repair. This study shed a new light on the conduits and stem cells-based peripheral nerve repair.

The effect of surface modification of poly-lactide-co-glycolide/carbon nanotube nanofibrous scaffolds by laminin protein on nerve tissue engineering

The presence of biological cues to promote the attachment, proliferation, and differentiation of neuronal cells is important in the process of nerve regeneration. In this study, laminin as a neurite promoting protein, has been used to modify poly-lactide-co-glycolide/carbon nanotube (PLGA/CNT) electrospun nanofibrous scaffolds by means of either mussel-inspired poly(dopamine) (PD) coating or via direct physical adsorption as a simple route for the functionalization of biomaterials. The laminin-modified scaffolds were characterized by a combination of field emission scanning electron microscopy (SEM), X-ray photoelectron spectroscopy, and contact angle measurements. Subsequently, various properties of scaffolds such as degradation time, amount of attached laminin and the rate of CNT release were investigated. The synergistic effect of topographical and biological cues for PC12 cell attachment, proliferation, and differentiation were then studied by SEM and confocal microscopy. The results of degradation study showed that laminin-modified scaffolds were biodegradable with good structural integrity that persisted about 4 weeks. The amount of laminin attached to the PLGA/CNT and PLGA/CNT-PD scaffolds was 3.12 ± 0.6 and 3.04 ± 071 μg per mg of the scaffold, respectively. Although laminin-modified scaffolds could improve cell proliferation identically, neurite extensions on the PLGA/CNT scaffold modified via PD coating (PLGA/CNT-PD-lam scaffold) were significantly longer than those observed on PLGA/CNT scaffold modified via physical adsorption (PLGA/CNT-lam scaffold) and unmodified scaffolds. Together, these results indicated that surface modification via PD coating could be a promising strategy to fabricate biomimetic scaffolds capable of sustaining longer neuronal growth for nerve tissue engineering.

Relevance and Recent Developments of Chitosan in Peripheral Nerve Surgery

Developments in tissue engineering yield biomaterials with different supporting strategies to promote nerve regeneration. One promising material is the naturally occurring chitin derivate chitosan. Chitosan has become increasingly important in various tissue engineering approaches for peripheral nerve reconstruction, as it has demonstrated its potential to interact with regeneration associated cells and the neural microenvironment, leading to improved axonal regeneration and less neuroma formation. Moreover, the physiological properties of its polysaccharide structure provide safe biodegradation behavior in the absence of negative side effects or toxic metabolites. Beneficial interactions with Schwann cells (SC), inducing differentiation of mesenchymal stromal cells to SC-like cells or creating supportive conditions during axonal recovery are only a small part of the effects of chitosan. As a result, an extensive body of literature addresses a variety of experimental strategies for the different types of nerve lesions. The different concepts include chitosan nanofibers, hydrogels, hollow nerve tubes, nerve conduits with an inner chitosan layer as well as hybrid architectures containing collagen or polyglycolic acid nerve conduits. Furthermore, various cell seeding concepts have been introduced in the preclinical setting. First translational concepts with hollow tubes following nerve surgery already transferred the promising experimental approach into clinical practice. However, conclusive analyses of the available data and the proposed impact on the recovery process following nerve surgery are currently lacking. This review aims to give an overview on the physiologic properties of chitosan, to evaluate its effect on peripheral nerve regeneration and discuss the future translation into clinical practice.

Current and novel polymeric biomaterials for neural tissue engineering

The nervous system is a crucial component of the body and damages to this system, either by of injury or disease, can result in serious or potentially lethal consequences. Restoring the damaged nervous system is a great challenge due to the complex physiology system and limited regenerative capacity.Polymers, either synthetic or natural in origin, have been extensively evaluated as a solution for restoring functions in damaged neural tissues. Polymers offer a wide range of versatility, in particular regarding shape and mechanical characteristics, and their biocompatibility is unmatched by other biomaterials, such as metals and ceramics. Several studies have shown that polymers can be shaped into suitable support structures, including nerve conduits, scaffolds, and electrospun matrices, capable of improving the regeneration of damaged neural tissues. In general, natural polymers offer the advantage of better biocompatibility and bioactivity, while synthetic or non-natural polymers have better mechanical properties and structural stability. Often, combinations of the two allow for the development of polymeric conduits able to mimic the native physiological environment of healthy neural tissues and, consequently, regulate cell behaviour and support the regeneration of injured nervous tissues.Currently, most of neural tissue engineering applications are in pre-clinical study, in particular for use in the central nervous system, however collagen polymer conduits aimed at regeneration of peripheral nerves have already been successfully tested in clinical trials.This review highlights different types of natural and synthetic polymers used in neural tissue engineering and their advantages and disadvantages for neural regeneration.

Strategies for Targeted Delivery to the Peripheral Nerve

Delivery of compounds to the peripheral nervous system has the potential to be used as a treatment for a broad range of conditions and applications, including neuropathic pain, regional anesthesia, traumatic nerve injury, and inherited and inflammatory neuropathies. However, efficient delivery of therapeutic doses can be difficult to achieve due to peripheral neuroanatomy and the restrictiveness of the blood-nerve barrier. Depending on the underlying integrity of the blood-nerve barrier in the application at hand, several strategies can be employed to navigate the peripheral nerve architecture and facilitate targeted delivery to the peripheral nerve. This review describes different applications where targeted delivery to the peripheral nervous system is desired, the challenges that the blood-nerve barrier poses in each application, and bioengineering strategies that can facilitate delivery in each application.

Surface functionalization of polyurethane scaffolds mimicking the myocardial microenvironment to support cardiac primitive cells

Scaffolds populated with human cardiac progenitor cells (CPCs) represent a therapeutic opportunity for heart regeneration after myocardial infarction. In this work, square-grid scaffolds are prepared by melt-extrusion additive manufacturing from a polyurethane (PU), further subjected to plasma treatment for acrylic acid surface grafting/polymerization and finally grafted with laminin-1 (PU-LN1) or gelatin (PU-G) by carbodiimide chemistry. LN1 is a cardiac niche extracellular matrix component and plays a key role in heart formation during embryogenesis, while G is a low-cost cell-adhesion protein, here used as a control functionalizing molecule. X-ray photoelectron spectroscopy analysis shows nitrogen percentage increase after functionalization. O1s and C1s core-level spectra and static contact angle measurements show changes associated with successful functionalization. ELISA assay confirms LN1 surface grafting. PU-G and PU-LN1 scaffolds both improve CPC adhesion, but LN1 functionalization is superior in promoting proliferation, protection from apoptosis and expression of differentiation markers for cardiomyocytes, endothelial and smooth muscle cells. PU-LN1 and PU scaffolds are biodegraded into non-cytotoxic residues. Scaffolds subcutaneously implanted in mice evoke weak inflammation and integrate with the host tissue, evidencing a significant blood vessel density around the scaffolds. PU-LN1 scaffolds show their superiority in driving CPC behavior, evidencing their promising role in myocardial regenerative medicine.

Nanopatterned Scaffolds for Neural Tissue Engineering and Regenerative Medicine

Biologically inspired approaches employing nanoengineering techniques have been influential in the progress of neural tissue repair and regeneration. Neural tissues are exposed to complex nanoscale environments such as nanofibrils. In this chapter, we summarize representative nanotechniques, such as electrospinning, lithography, and 3D bioprinting, and their use in the design and fabrication of nanopatterned scaffolds for neural tissue engineering and regenerative medicine. Nanotopographical cues in combination with other cues (e.g., chemical cues) are crucial to neural tissue repair and regeneration using cells, including various types of stem cells. Production of biologically inspired nanopatterned scaffolds may encourage the next revolution for studies aiming to advance neural tissue engineering and regenerative medicine.

Three-dimensional imaging and analysis of entire peripheral nerves after repair and reconstruction

BACKGROUND

We wanted to achieve a three-dimensional (3D), non-destructive imaging and automatic post-analysis and evaluation of reconstructed peripheral nerves without involving cutting and staining processes.

NEW METHOD

We used a laboratory-based micro computed tomography system for imaging, as well as a custom analysis protocol. The sample preparation was also adapted in order to achieve 3D images with true micrometer resolution and suitable contrast.

RESULTS

Analysis of the acquired tomograms enabled the quantitative assessment of 3D tissue structures, i.e., surface morphology, nerve fascicles, nerve tissue volume, geometry, and vascular regrowth. The resulting data showed significant differences between operated animals and non-operated controls.

COMPARISON WITH EXISTING METHODS

Our approach avoids the sampling error associated with conventional 2D visualization approaches and holds promise for automation of the analysis of large series of datasets.

CONCLUSIONS

We have presented a potential way for 3D imaging and analysis of entire regenerated nerves non-destructively, paving the way for high-throughput analysis of therapeutic conditions of treating adult nerve injuries.

Polymeric scaffolds for three-dimensional culture of nerve cells: a model of peripheral nerve regeneration

Understanding peripheral nerve repair requires the evaluation of 3D structures that serve as platforms for 3D cell culture. Multiple platforms for 3D cell culture have been developed, mimicking peripheral nerve growth and function, in order to study tissue repair or diseases. To recreate an appropriate 3D environment for peripheral nerve cells, key factors are to be considered including: selection of cells, polymeric biomaterials to be used, and fabrication techniques to shape and form the 3D scaffolds for cellular culture. This review focuses on polymeric 3D platforms used for the development of 3D peripheral nerve cell cultures.

Effects of RPE-conditioned medium on the differentiation of hADSCs into RPE cells, and their proliferation and migration

Age-related macular degeneration (AMD) is associated with the dysfunction and death of the retinal pigment epithelium (RPE). Recently, there has been increasing interest in stem cell-derived RPE cells for cell replacement therapies, such as those for AMD. The present study investigated whether RPE-conditioned medium (RPECM) could promote the differentiation of human adipose tissue-derived mesenchymal stromal cells (hADSCs) into RPE cells, and enhance the proliferation and migration of these cells. Reverse-transcription quantitative polymerase chain reaction analysis demonstrated that RPECM induced hADSCs to differentiate into cells expressing RPE markers, including retinoid isomerohydrolase (RPE65), cytokeratin (CK8) and Bestrophin, which were identified to be significantly upregulated by ~10-fold, 3.5-fold and 2.4-fold, respectively, compared with the control group [hADSCs cultured in ADSC-conditioned medium (ADSCCM)]. The immunocytochemistry and western blot analysis results demonstrated that the protein levels of RPE65, CK8 and Bestrophin were significantly increased in RPECM-treated hADSCs. In addition, Cell Counting Kit-8 analysis demonstrated that RPECM promoted the proliferation of induced cells. RPECM also increased the expression level of the cell proliferative marker Ki-67. Furthermore, to evaluate the migration potential, cell migration assays were performed. These assays demonstrated that following RPECM treatment hADSCs migrated more quickly compared with the control group. The results of the present study suggest that RPECM induces hADSCs to differentiate into RPE cells with higher proliferative and migratory potentials, which may aid in applications for hADSCs in RPE regenerative therapy.

Fabrication and characterization of electrospun laminin-functionalized silk fibroin/poly(ethylene oxide) nanofibrous scaffolds for peripheral nerve regeneration

The peripheral nerve regeneration is still one of the major clinical problems, which has received a great deal of attention. In this study, the electrospun silk fibroin (SF)/poly(ethylene oxide) (PEO) nanofibrous scaffolds were fabricated and functionalized their surfaces with laminin (LN) without chemical linkers for potential use in the peripheral nerve tissue engineering. The morphology, surface chemistry, thermal behavior and wettability of the scaffolds were examined to evaluate their performance by means of scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and water contact angle (WCA) measurements, respectively. The proliferation and viability of Schwann cells onto the surfaces of SF/PEO nanofibrous scaffolds were investigated using SEM and thiazolyl blue (MTT) assay. The results showed an improvement of SF conformation and surface hydrophilicity of SF/PEO nanofibers after methanol and O₂ plasma treatments. The immunostaining observation indicated a continuous coating of LN on the scaffolds. Improving the surface hydrophilicity and LN functionalization significantly increased the cell proliferation and this was more prominent after 5 days of culture time. In conclusion, the obtained results revealed that the electrospun LN-functionalized SF/PEO nanofibrous scaffold could be a promising candidate for peripheral nerve tissue regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1595-1604, 2018.

Insights into the Therapeutic Potential of Heparinized Collagen Scaffolds Loading Human Umbilical Cord Mesenchymal Stem Cells and Nerve Growth Factor for the Repair of Recurrent Laryngeal Nerve Injury

Recurrent laryngeal nerve (RLN) injury can result in unilateral or bilateral vocal cords paralysis, thereby causing a series of complications, such as hoarseness and dyspnea. However, the repair of RLN remains a great challenge in current medicine. This study aimed to develop human umbilical mesenchymal stem cells (HuMSCs) and nerve growth factor (NGF)-loaded heparinized collagen scaffolds (HuMSCs/NGF HC-scaffolds) and evaluate their potential in the repair of RLN injury. HuMSCs/NGF HC-scaffolds were prepared through incorporating HuMSCs and NGF into heparinized collagen scaffolds that were prefabricated by freeze-drying in a template. The resulting scaffolds were characterized by FTIR, SEM, porosity, degradation in vitro, NGF release in vitro and bioactivity. A rabbit RLN injury model was constructed to appraise the performance of HuMSCs/NGF HC-scaffolds for nerve injury repair. Electrophysiology, histomorphology and diagnostic proteins expression for treated nerves were checked after application of various scaffolds. The results showed that the composite scaffolds with HuMSCs and NGF were rather helpful for the repair of broken RLN. The RLN treated with HuMSCs/NGF HC-scaffolds for 8 weeks produced a relatively normal electromyogram, and the levels of calcium-binding protein S100, neurofilament and AchE pertinent to nerve were found to be close to the normal ones but higher than those resulted from other scaffolds. Taken together, HuMSCs/NGF HC-scaffolds exhibited a high score on the nerve injury repair and may be valuable for the remedy of RLN injury.

clickECM: Development of a cell-derived extracellular matrix with azide functionalities

In vitro cultured cells produce a complex extracellular matrix (ECM) that remains intact after decellularization. The biological complexity derived from the variety of distinct ECM molecules makes these matrices ideal candidates for biomaterials. Biomaterials with the ability to guide cell function are a topic of high interest in biomaterial development. However, these matrices lack specific addressable functional groups, which are often required for their use as a biomaterial. Due to the biological complexity of the cell-derived ECM, it is a challenge to incorporate such functional groups without affecting the integrity of the biomolecules within the ECM. The azide-alkyne cycloaddition (click reaction, Huisgen-reaction) is an efficient and specific ligation reaction that is known to be biocompatible when strained alkynes are used to avoid the use of copper (I) as a catalyst. In our work, the ubiquitous modification of a fibroblast cell-derived ECM with azides was achieved through metabolic oligosaccharide engineering by adding the azide-modified monosaccharide Ac₄GalNAz (1,3,4,6-tetra-O-acetyl-N-azidoacetylgalactosamine) to the cell culture medium. The resulting azide-modified network remained intact after removing the cells by lysis and the molecular structure of the ECM proteins was unimpaired after a gentle homogenization process. The biological composition was characterized in order to show that the functionalization does not impair the complexity and integrity of the ECM. The azides within this "clickECM" could be accessed by small molecules (such as an alkyne-modified fluorophore) or by surface-bound cyclooctynes to achieve a covalent coating with clickECM.

STATEMENT OF SIGNIFICANCE

The clickECM was produced by the incorporation of azide-functionalized sugar analogues into the extracellular glycans of fibroblast cell cultures by metabolic oligosaccharide engineering. By introducing these azide groups into the glycan structures, we enabled this cell-derived ECM for bioorthogonal click reactions. Click chemistry provides extremely specific reactions with high efficiency, high selectivity, and high reaction yields. We could show that the azide functionalities within the clickECM are chemically accessible. Based on our here described clickECM technique it will be possible to create and investigate new clickECM materials with tunable bioactive properties and additional functionalities, which offers a promising approach for basic and applied research in the field of biomaterial science, biomedical applications, and tissue engineering.

Chitosan nerve conduits seeded with autologous bone marrow mononuclear cells for 30 mm goat peroneal nerve defect

In the current research, to find if the combination of chitosan nerve conduits seeded with autologous bone marrow mononuclear cells (BM-MNCs) can be used to bridge 30 mm long peroneal nerve defects in goats, 15 animals were separated into BM-MNC group (n = 5), vehicle group (n = 5), and autologous nerve graft group (n = 5). 12 months after the surgery, animals were evaluated by behavioral observation, magnetic resonance imaging tests, histomorphological and electrophysiological analysis. Results revealed that animals in BM-MNC group and autologous nerve graft group achieved fine functional recovery; magnetic resonance imaging tests and histomorphometry analysis showed that the nerve defect was bridged by myelinated nerve axons in those animals. No significant difference was found between the two groups concerning myelinated axon density, axon diameter, myelin sheath thickness and peroneal nerve action potential. Animals in vehicle group failed to achieve significant functional recovery. The results indicated that chitosan nerve conduits seeded with autologous bone marrow mononuclear cells have strong potential in bridging long peripheral nerve defects and could be applied in future clinical trials.

The Horizon of Materiobiology: A Perspective on Material-Guided Cell Behaviors and Tissue Engineering

Although the biological functions of cell and tissue can be regulated by biochemical factors (e.g., growth factors, hormones), the biophysical effects of materials on the regulation of biological activity are receiving more attention. In this Review, we systematically summarize the recent progress on how biomaterials with controllable properties (e.g., compositional/degradable dynamics, mechanical properties, 2D topography, and 3D geometry) can regulate cell behaviors (e.g., cell adhesion, spreading, proliferation, cell alignment, and the differentiation or self-maintenance of stem cells) and tissue/organ functions. How the biophysical features of materials influence tissue/organ regeneration have been elucidated. Current challenges and a perspective on the development of novel materials that can modulate specific biological functions are discussed. The interdependent relationship between biomaterials and biology leads us to propose the concept of "materiobiology", which is a scientific discipline that studies the biological effects of the properties of biomaterials on biological functions at cell, tissue, organ, and the whole organism levels. This Review highlights that it is more important to develop ECM-mimicking biomaterials having a self-regenerative capacity to stimulate tissue regeneration, instead of attempting to recreate the complexity of living tissues or tissue constructs ex vivo. The principles of materiobiology may benefit the development of novel biomaterials providing combinative bioactive cues to activate the migration of stem cells from endogenous reservoirs (i.e., cell niches), stimulate robust and scalable self-healing mechanisms, and unlock the body's innate powers of regeneration.

Zero valent zinc nanoparticles promote neuroglial cell proliferation: A biodegradable and conductive filler candidate for nerve regeneration

Regeneration of nerve, which has limited ability to undergo self-healing, is one of the most challenging areas in the field of tissue engineering. Regarding materials used in neuroregeneration, there is a recent trend toward electrically conductive materials. It has been emphasized that the capacity of conductive materials to regenerate such tissue having limited self-healing ability improves their clinical utility. However, there have been concerns about the safety of materials or fillers used for conductance due to their lack of degradability. Here, we attempt to use poly(Ɛ-caprolactone) (PCL) matrix consisting of varying proportions of zero valent zinc nanoparticles (Zn NPs) via electrospinning. These conductive, biodegradable, and bioactive materials efficiently promoted neuroglial cell proliferation depending on the amount of Zn NPs present in the PCL matrix. Chemical characterizations indicated that the incorporated Zn NPs do not interact with the PCL matrix chemically and that the Zn NPs improved the tensile properties of the PCL matrix. All composites exhibited linear conductivity under in vitro conditions. In vitro cell culture studies were performed to determine the cytotoxicity and proliferative efficiency of materials containing different proportions of Zn NPs. The results were obtained to explore new conductive fillers that can promote tissue regeneration.

Nerve Guidance by a Decellularized Fibroblast Extracellular Matrix

Spinal cord and peripheral nerve injuries require the regeneration of nerve fibers across the lesion site for successful recovery. Providing guidance cues and soluble factors to promote neurite outgrowth and cell survival can enhance repair. The extracellular matrix (ECM) plays a key role in tissue repair by controlling cell adhesion, motility, and growth. In this study, we explored the ability of a mesenchymal ECM to support neurite outgrowth from neurons in the superior cervical ganglia (SCG). Length and morphology of neurites extended on a decellularized fibroblast ECM were compared to those on substrates coated with laminin, a major ECM protein in neural tissue, or fibronectin, the main component of a mesenchymal ECM. Average radial neurite extension was equivalent on laminin and on the decellularized ECM, but contrasted with the shorter, curved neurites observed on the fibronectin substrate. Differences between neurites on fibronectin and on other substrates were confirmed by fast Fourier transform analyses. To control the direction of neurite outgrowth, we developed an ECM with linearly aligned fibril organization by orienting the fibroblasts that deposit the matrix on a polymeric surface micropatterned with a striped chemical interface. Neurites projected from SCGs appeared to reorient in the direction of the pattern. These results highlight the ability of a mesenchymal ECM to enhance neurite extension and to control the directional outgrowth of neurites. This micropatterned decellularized ECM architecture has potential as a regenerative microenvironment for nerve repair.

Multichannel silk protein/laminin grafts for spinal cord injury repair

The physical, chemical, and bioactive cues provided by biomaterials are critical for spinal cord regeneration following injury. In this study, we investigated the bioactivity of a silk-based scaffold for nerve tissue remodeling that featured morphological guidance in the form of ridges as well as bioactive molecules. Multichannel/laminin (LN) silk scaffolds stimulated growth, development, and the extension of primary hippocampal neurons after 7 days of culture in vitro. And then, the multichannel/LN silk scaffolds were implanted into 2-mm-long hemisection defects in Sprague-Dawley rat spinal cords for 70 days to evaluate their bioactivities of spinal cord remolding. Our results demonstrated that animal behavior was significantly improved in the multichannel/LN group, as evaluated by Basso-Beattie-Bresnahan score, whereas the implantation of multichannels and random pores groups resulted in recurring limps. Moreover, histology and immunohistochemical staining revealed an increase in blood vessels and expression of growth associated protein-43 and neurofilament-200 as well as reduced expression of glial fibrillary acidic protein in the multichannel/LN group, which contributed to the rebuilding of spinal cord defects. Thus, multichannel/LN silk scaffolds mediated cell migration, stimulated blood capillary formation, and promoted axonal extension, suggesting the utility of these scaffolds for spinal cord reconstruction. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 3045-3057, 2016.

Facilitation of facial nerve regeneration using chitosan-β-glycerophosphate-nerve growth factor hydrogel

Conclusion C/GP hydrogel was demonstrated to be an ideal drug delivery vehicle and scaffold in the vein conduit. Combined use autologous vein and NGF continuously delivered by C/GP-NGF hydrogel can improve the recovery of facial nerve defects. Objective This study investigated the effects of chitosan-β-glycerophosphate-nerve growth factor (C/GP-NGF) hydrogel combined with autologous vein conduit on the recovery of damaged facial nerve in a rat model. Methods A 5 mm gap in the buccal branch of a rat facial nerve was reconstructed with an autologous vein. Next, C/GP-NGF hydrogel was injected into the vein conduit. In negative control groups, NGF solution or phosphate-buffered saline (PBS) was injected into the vein conduits, respectively. Autologous implantation was used as a positive control group. Vibrissae movement, electrophysiological assessment, and morphological analysis of regenerated nerves were performed to assess nerve regeneration. Results NGF continuously released from C/GP-NGF hydrogel in vitro. The recovery rate of vibrissae movement and the compound muscle action potentials of regenerated facial nerve in the C/GP-NGF group were similar to those in the Auto group, and significantly better than those in the NGF group. Furthermore, larger regenerated axons and thicker myelin sheaths were obtained in the C/GP-NGF group than those in the NGF group.

Gelatin-methacrylamide gel loaded with microspheres to deliver GDNF in bilayer collagen conduit promoting sciatic nerve growth

In this study, we fabricated glial cell-line derived neurotrophic factor (GDNF)-loaded microspheres, then seeded the microspheres in gelatin-methacrylamide hydrogel, which was finally integrated with the commercial bilayer collagen membrane (Bio-Gide^®). The novel composite of nerve conduit was employed to bridge a 10 mm long sciatic nerve defect in a rat. GDNF-loaded gelatin microspheres had a smooth surface with an average diameter of 3.9±1.8 μm. Scanning electron microscopy showed that microspheres were uniformly distributed in both the GelMA gel and the layered structure. Using enzyme-linked immunosorbent assay, in vitro release studies (pH 7.4) of GDNF from microspheres exhibited an initial burst release during the first 3 days (18.0%±1.3%), and then, a prolonged-release profile extended to 32 days. However, in an acidic condition (pH 2.5), the initial release percentage of GDNF was up to 91.2%±0.9% within 4 hours and the cumulative release percentage of GDNF was 99.2%±0.2% at 48 hours. Then the composite conduct was implanted in a 10 mm critical defect gap of sciatic nerve in a rat. We found that the nerve was regenerated in both conduit and autograft (AG) groups. A combination of electrophysiological assessment and histomorphometry analysis of regenerated nerves showed that axonal regeneration and functional recovery in collagen tube filled with GDNF-loaded microspheres (GM + CT) group were similar to AG group (P>0.05). Most myelinated nerves were matured and arranged densely with a uniform structure of myelin in a neat pattern along the long axis in the AG and GM + CT groups, however, regenerated nerve was absent in the BLANK group, left the 10 mm gap empty after resection, and the nerve fiber exhibited a disordered arrangement in the collagen tube group. These results indicated that the hybrid system of bilayer collagen conduit and GDNF-loaded gelatin microspheres combined with gelatin-methacrylamide hydrogels could serve as a new biodegradable artificial nerve guide for nerve tissue engineering.

Electron microscopy imaging of proteins on gallium phosphide semiconductor nanowires

We have imaged GaP nanowires (NWs) incubated with human laminin, serum albumin (HSA), and blood plasma using both cryo-transmission electron microscopy and synchrotron based X-ray photoemission electron microscopy. This extensive imaging methodology simultaneously reveals structural, chemical and morphological details of individual nanowires and the adsorbed proteins. We found that the proteins bind to NWs, forming coronas with thicknesses close to the proteins' hydrodynamic diameters. We could directly image how laminin is extending from the NWs, maximizing the number of proteins bound to the NWs. NWs incubated with both laminin and HSA show protein coronas with a similar appearance to NWs incubated with laminin alone, indicating that the presence of HSA does not affect the laminin conformation on the NWs. In blood plasma, an intermediate sized corona around the NWs indicates a corona with a mixture of plasma proteins. The ability to directly visualize proteins on nanostructures in situ holds great promise for assessing the conformation and thickness of the protein corona, which is key to understanding and predicting the properties of engineered nanomaterials in a biological environment.

Neuromuscular Regeneration: Perspective on the Application of Mesenchymal Stem Cells and Their Secretion Products

Mesenchymal stem cells are posing as a promising character in the most recent therapeutic strategies and, since their discovery, extensive knowledge on their features and functions has been gained. In recent years, innovative sources have been disclosed in alternative to the bone marrow, conveying their associated ethical concerns and ease of harvest, such as the umbilical cord tissue and the dental pulp. These are also amenable of cryopreservation and thawing for desired purposes, in benefit of the donor itself or other patients in pressing need. These sources present promising possibilities in becoming useful cell sources for therapeutic applications in the forthcoming years. Effective and potential applications of these cellular-based strategies for the regeneration of peripheral nerve are overviewed, documenting recent advances and identified issues for this research area in the near future. Finally, besides the differentiation capacities attributed to mesenchymal stem cells, advances in the recognition of their effective mode of action in the regenerative theatre have led to a new area of interest: the mesenchymal stem cells' secretome. The paracrine modulatory pathway appears to be a major mechanism by which these are beneficial to nerve regeneration and comprehension on the specific growth factors, cytokine, and extracellular molecules secretion profiles is therefore of great interest.

Utilizing stem cells for three-dimensional neural tissue engineering

Three-dimensional neural tissue engineering has significantly advanced the development of neural disease models and replacement tissues for patients by leveraging the unique capabilities of stem cells.

Biological behavior of mesenchymal stem cells on poly-ε-caprolactone filaments and a strategy for tissue engineering of segments of the peripheral nerves

Introduction

Peripheral nerves may fail to regenerate across tube implants because these lack the microarchitecture of native nerves. Bone marrow mesenchymal stem cells (MSC) secrete soluble factors that improve the regeneration of the peripheral nerves. Also, microstructured poly-caprolactone (PCL) filaments are capable of inducing bands of Büngner and promote regeneration in the peripheral nervous system (PNS). We describe here the interaction between PCL filaments and MSC, aiming to optimize PNS tubular implants.

Methods

MSC were plated on PCL filaments for 48 h and the adhesion profile, viability, proliferation and paracrine capacity were evaluated. Also, Schwann cells were plated on PCL filaments covered with MSC for 24 h to analyze the feasibility of the co-culture system. Moreover, E16 dorsal root ganglia were plated in contact with PCL filaments for 4 days to analyze neurite extension. Right sciatic nerves were exposed and a 10 mm nerve segment was removed. Distal and proximal stumps were reconnected inside a 14-mm polyethylene tube, leaving a gap of approximately 13 mm between the two stumps. Animals then received phosphate-buffered saline 1×, PCL filaments or PCL filaments previously incubated with MSC and, after 12 weeks, functional gait performance and histological analyses were made. Statistical analyses were made using Student’s unpaired t-test, one-way analysis of variance (ANOVA) or two-way ANOVA followed by Bonferroni post-test.

Results

MSC were confined to lateral areas and ridges of PCL filaments, aligning along the longitudinal. MSC showed high viability (90 %), and their proliferation and secretion capabilities were not completely inhibited by the filaments. Schwann cells adhered to filaments plated with MSC, maintaining high viability (90 %). Neurites grew and extended over the surface of PCL filaments, reaching greater distances when over MSC-plated filaments. Axons showed more organized and myelinized fibers and reinnervated significantly more muscle fibers when they were previously implanted with MSC-covered PLC filaments. Moreover, animals with MSC-covered filaments showed increased functional recovery after 12 weeks.

Conclusions

We provide evidence for the interaction among MSC, Schwann cells and PCL filaments, and we also demonstrate that this system can constitute a stable and permissive support for regeneration of segments of the peripheral nerves.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0121-2) contains supplementary material, which is available to authorized users.

Carbon-nanotube-interfaced glass fiber scaffold for regeneration of transected sciatic nerve

Carbon nanotubes (CNTs), with their unique and unprecedented properties, have become very popular for the repair of tissues, particularly for those requiring electrical stimuli. Whilst most reports have demonstrated in vitro neural cell responses of the CNTs, few studies have been performed on the in vivo efficacy of CNT-interfaced biomaterials in the repair and regeneration of neural tissues. Thus, we report here for the first time the in vivo functions of CNT-interfaced nerve conduits in the regeneration of transected rat sciatic nerve. Aminated CNTs were chemically tethered onto the surface of aligned phosphate glass microfibers (PGFs) and CNT-interfaced PGFs (CNT-PGFs) were successfully placed into three-dimensional poly(L/D-lactic acid) (PLDLA) tubes. An in vitro study confirmed that neurites of dorsal root ganglion outgrew actively along the aligned CNT-PGFs and that the CNT interfacing significantly increased the maximal neurite length. Sixteen weeks after implantation of a CNT-PGF nerve conduit into the 10 mm gap of a transected rat sciatic nerve, the number of regenerating axons crossing the scaffold, the cross-sectional area of the re-innervated muscles and the electrophysiological findings were all significantly improved by the interfacing with CNTs. This first in vivo effect of using a CNT-interfaced scaffold in the regeneration process of a transected rat sciatic nerve strongly supports the potential use of CNT-interfaced PGFs at the interface between the nerve conduit and peripheral neural tissues.

Peripheral nerve conduits: technology update

Peripheral nerve injury is a worldwide clinical problem which could lead to loss of neuronal communication along sensory and motor nerves between the central nervous system (CNS) and the peripheral organs and impairs the quality of life of a patient. The primary requirement for the treatment of complete lesions is a tension-free, end-to-end repair. When end-to-end repair is not possible, peripheral nerve grafts or nerve conduits are used. The limited availability of autografts, and drawbacks of the allografts and xenografts like immunological reactions, forced the researchers to investigate and develop alternative approaches, mainly nerve conduits. In this review, recent information on the various types of conduit materials (made of biological and synthetic polymers) and designs (tubular, fibrous, and matrix type) are being presented.