Functional Gait Evaluation of Collagen Chitosan Nerve Guides for Sciatic Nerve Repair

Laminin-modified gellan gum hydrogels loaded with the nerve growth factor to enhance the proliferation and differentiation of neuronal stem cells

The reconstruction of peripheral nerves has lately received great attention as many patients suffer from peripheral nerve injury every year around the world. However, the damage to human nerve cells has different degrees of irreversibility due to a slow growth speed and low adhesion with the surrounding tissues. In an effort to overcome this challenge, we applied novel laminin (LN)-modified thiolated gellan gum (TGG) and loaded the nerve growth factor (NGF) as a tissue engineering scaffold for facilitating neuronal stem cell proliferation via a synergy effect for the ERK–MAPK pathway. TGG was characterized by ¹H NMR spectroscopy and scanning electron microscopy, and its rheological behavior was also studied. The NGF release curve fitted the Korsmeyer–Peppas model and belonged to a Fickian diffusion-controlled release mechanism. The neuronal stem cells from newborn SD rats could adhere tightly and proliferate at a relatively rapid speed, showing excellent biocompatibility and the ability to promote growth in the modified TGG. LN and NGF could decrease the apoptosis effects of neuronal stem cells, as shown via the flow cytometry results. In a three-dimensional culture environment, LN and NGF could facilitate neuronal stem cells to differentiate into neurons, as proved by immunofluorescence, q-PCR, and western blot analyses. Therefore, the rational design of the TGG gel loaded with NGF has promising applications in the reconstruction of peripheral nerves.

Laminin-modified thiolated gellan gum and loaded with the nerve growth factor in facilitateding neuronal stem cell proliferation and differentiation.

A Reliable Stem Cell Carrier: An Experimental Study in Wistar Rats

INTRODUCTION

Treatments based on cell biology need reliable and precise carriers for reaching the desired targets. For that reason, a PDO-based cell carrier was idealized, with the purpose of carrying stem cells to distant sites at room temperature.

MATERIALS AND METHODS

Three modalities of the same carrier were evaluated: one containing undifferentiated human dental pulp stem cells (DPSCs); one loaded with stem cells induced to neurogenic differentiation (DPSCNs); and one without cells (Blank). The carriers were implanted in sciatic nerve gaps in 48 Wistar rats that were divided in three groups. Two other rats were included in a SHAM control group. Immunohistochemical, histological and clinical analyses were performed in two, four, six and eight weeks of time.

RESULTS

Efficacy of human stem cell transportation at room temperature to rats was attested. Moreover, it was possible to confirm that those cells show tropism for inflamed environments and are also prone to induction of neurogenesis in the first two weeks, vanishing after that period.

CONCLUSION

Clinical evaluation of the animals' gait recovery shows a promising perspective of success with the inclusion of stem cell-loaded PDO tubes in nerve gaps, which may be positively compared to previously published studies.

NO LEVEL ASSIGNED

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The role of peripheral nerve ECM components in the tissue engineering nerve construction

The extracellular matrix (ECM) is the naturally occurring substrate that provides a support structure and an attachment site for cells. It also produces a biological signal, which plays an important role in and has significant impact on cell adhesion, migration, proliferation, differentiation, and gene expression. Peripheral nerve repair is a complicated process involving Schwann cell proliferation and migration, 'bands of Büngner' formation, and newborn nerve extension. In the ECM of peripheral nerves, macromolecules are deposited among cells; these constitute the microenvironment of Schwann cell growth. Such macromolecules include collagen (I, III, IV, V), laminin, fibronectin, chondroitin sulfate proteoglycans (CSPGs), and other nerve factors. Collagen, the main component of ECM, provides structural support and guides newborn neurofilament extension. Laminin, fibronectin, CSPGs, and neurotrophic factors, are promoters or inhibitors, playing different roles in nerve repair after injury. By a chemical decellularization process, acellular nerve allografting eliminates the antigens responsible for allograft rejection and maintains most of the ECM components, which can effectively guide and enhance nerve regeneration. Thus, the composition and features of peripheral nerve ECM suggest its superiority as nerve repair material. This review focuses on the structure, function, and application in the tissue engineering nerve construction of the peripheral nerve ECM components.

The use of chitosan-based scaffolds to enhance regeneration in the nervous system

Various biomaterials have been proposed to build up scaffolds for promoting neural repair. Among them, chitosan, a derivative of chitin, has been raising more and more interest among basic and clinical scientists. A number of studies with neuronal and glial cell cultures have shown that this biomaterial has biomimetic properties, which make it a good candidate for developing innovative devices for neural repair. Yet, in vivo experimental studies have shown that chitosan can be successfully used to create scaffolds that promote regeneration both in the central and in the peripheral nervous system. In this review, the relevant literature on the use of chitosan in the nervous tissue, either alone or in combination with other components, is overviewed. Altogether, the promising in vitro and in vivo experimental results make it possible to foresee that time for clinical trials with chitosan-based nerve regeneration-promoting devices is approaching quickly.

Sciatic nerve regeneration by cocultured Schwann cells and stem cells on microporous nerve conduits

Cell transplantation is a useful therapy for treating peripheral nerve injuries. The clinical use of Schwann cells (SCs), however, is limited because of their limited availability. An emerging solution to promote nerve regeneration is to apply injured nerves with stem cells derived from various tissues. In this study, different types of allogeneic cells including SCs, adipose-derived adult stem cells (ASCs), dental pulp stem cells (DPSCs), and the combination of SCs with ASCs or DPSCs were seeded on nerve conduits to test their efficacy in repairing a 15-mm-long critical gap defect of rat sciatic nerve. The regeneration capacity and functional recovery were evaluated by the histological staining, electrophysiology, walking track, and functional gait analysis after 8 weeks of implantation. An in vitro study was also performed to verify if the combination of cells led to synergistic neurotrophic effects (NGF, BDNF, and GDNF). Experimental rats receiving conduits seeded with a combination of SCs and ASCs had the greatest functional recovery, as evaluated by the walking track, functional gait, nerve conduction velocity (NCV), and histological analysis. Conduits seeded with cells were always superior to the blank conduits without cells. Regarding NCV and the number of blood vessels, conduits seeded with SCs and DPSCs exhibited better values than those seeded with DPSCs only. Results from the in vitro study confirmed the synergistic NGF production from the coculture of SCs and ASCs. It was concluded that coculture of SCs with ASCs or DPSCs in a conduit promoted peripheral nerve regeneration over a critical gap defect.

Recellularized nerve allografts with differentiated mesenchymal stem cells promote peripheral nerve regeneration

Chemical-extracted acellular nerve allografting, containing the natural nerve structure and elementary nerve extracellular matrix (ECM), has been used for peripheral nerve-defect treatment experimentally and clinically. However, functional outcome with acellular nerve allografting decreases with increased size of gap in nerve defects. Cell-based therapy is a good strategy for repairing long nerve defects. Bone-marrow-derived mesenchymal stem cells (BMSCs) and adipose-derived mesenchymal stem cells (ADSCs) can be induced to differentiate into cells with Schwann cell-like properties (BMSC-SCs or ADSC-SCs), which have myelin-forming ability in vitro and secrete trophic nerve growth factors. Here, we aimed to determine whether BMSC-SCs or ADSC-SCs are a promising cell type for enriching acellular grafts in nerve repair. We evaluated axonal regeneration distance by immunofluorescence staining after 2-week implantation. We used functional and histomorphometric analysis to evaluate 3-month regeneration of the novel cell-supplemented tissue-engineered nerve graft used to bridge a 15-mm-long sciatic nerve gap in rats. Introducing BMSC-SCs or ADSC-SCs to the acellular nerve graft promoted sciatic nerve regeneration and functional recovery. Nerve regeneration with BMSC-SCs or ADSC-SCs was comparable to that with autografting and Schwann cells alone and better than that with acellular nerve allografting alone. Differentiated bone-marrow-or adipose-derived MSCs may be a promising cell source for tissue-engineered nerve grafts and promote functional recovery after peripheral nerve injury.

Sciatic nerve regeneration by microporous nerve conduits seeded with glial cell line-derived neurotrophic factor or brain-derived neurotrophic factor gene transfected neural stem cells

Neurotrophic factors such as the glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) promote nerve cell survival and regeneration, but their efficacy in repairing a longer gap defect of rat sciatic nerve (15 mm) has not been established. In this study, two recombinant mammalian vectors containing either rat GDNF gene or BDNF gene were constructed and each was transfected into neural stem cells (NSCs). It was found that the transfection of GDNF or BDNF gene into NSCs led to significantly enhanced expression of GDNF or BDNF mRNA. The amount of GDNF or BDNF protein secreted from the transfected NSCs showed a 3.3-fold or 2.5-fold increase than that from nontransfected NSCs, respectively. The regeneration capacity of rat sciatic nerve in a poly(D,L-lactide) conduit seeded with GDNF or BDNF-transfected NSCs was evaluated by the histology, functional gait, and electrophysiology after 8 weeks of implantation. It was observed that the degree of myelination and the size of regenerated tissue in the conduits seeded with GDNF- and BDNF-transfected NSCs were higher than those seeded with the nontransfected NSCs. Conduits seeded with GDNF-transfected NSCs had the greatest number of blood vessels. The functional recovery assessed by the functional gait and electrophysiology was significantly improved for conduits seeded with GDNF or BDNF-transfected NSCs. It was concluded that the genetically modified NSCs may have potential applications in promoting nerve regeneration and functional recovery.

Ciliary neurotrophic factor-coated polylactic-polyglycolic acid chitosan nerve conduit promotes peripheral nerve regeneration in canine tibial nerve defect repair

A variety of nerve conduits incorporated with chemical and biological factors have been developed to further stimulate nerve regeneration. Although most of the nerve guides in studies are basically limited to bridge a short gap of nerve defect in rat models, it is vital to evaluate effects of conduits on nerve regeneration over distance greater than 20 mm, or more clinically relevant nerve gap lengths in higher mammals. In this study, a poly(lactide-co-glycolide) (PLGA) nerve conduit, treated with pulsed plasma and coated with ciliary neurotrophic factor (CNTF) as well as chitosan, was used to repair 25-mm-long canine tibial nerve defects in eighteen cross-bred dogs. The canines were randomly divided into three groups (n = 6), a 25-mm segment of the tibial nerve was removed and replaced by a PLGA/chitosan-CNTF nerve conduit, PLGA/chitosan conduit and autologous nerve grafts were performed as the control. The results were evaluated by general observation, electromyogram testing, S-100 histological immunostaining, and image analysis at 3 months after operation. The histological results demonstrated that the PLGA/chitosan-CNTF conduits and PLGA/chitosan conduits were capable of leading the damaged axons through the lesioned area. Through the comparison of the three groups, the results in PLGA/chitosan-CNTF conduits group were better than that of PLGA/chitosan conduits group, while they were similar to autologous nerve grafts group. Therefore, CNTF-coated PLGA/chitosan nerve conduits could be an alternative artificial nerve conduit for nerve regeneration.

Construction of tissue engineered nerve grafts and their application in peripheral nerve regeneration

Surgical repair of severe peripheral nerve injuries represents not only a pressing medical need, but also a great clinical challenge. Autologous nerve grafting remains a golden standard for bridging an extended gap in transected nerves. The formidable limitations related to this approach, however, have evoked the development of tissue engineered nerve grafts as a promising alternative to autologous nerve grafts. A tissue engineered nerve graft is typically constructed through a combination of a neural scaffold and a variety of cellular and molecular components. The initial and basic structure of the neural scaffold that serves to provide mechanical guidance and optimal environment for nerve regeneration was a single hollow nerve guidance conduit. Later there have been several improvements to the basic structure, especially introduction of physical fillers into the lumen of a hollow nerve guidance conduit. Up to now, a diverse array of biomaterials, either of natural or of synthetic origin, together with well-defined fabrication techniques, has been employed to prepare neural scaffolds with different structures and properties. Meanwhile different types of support cells and/or growth factors have been incorporated into the neural scaffold, producing unique biochemical effects on nerve regeneration and function restoration. This review attempts to summarize different nerve grafts used for peripheral nerve repair, to highlight various basic components of tissue engineered nerve grafts in terms of their structures, features, and nerve regeneration-promoting actions, and finally to discuss current clinical applications and future perspectives of tissue engineered nerve grafts.

In vivo study of novel nanofibrous intra-luminal guidance channels to promote nerve regeneration

A novel nanofibrous construct for promoting peripheral nerve repair was fabricated and tested in a rat sciatic nerve defect model. The conduit is made out of bilayered nanofibrous membranes with the nanofibers longitudinally aligned in the lumen and randomly oriented on the outer surface. The intra-luminal guidance channel is made out of aligned nanofibrous yarns. In addition, biomolecules such as laminin and nerve growth factor were incorporated in the nanofibrous nerve construct to determine their efficacy in in vivo nerve regeneration. Muscle reinnervation, withdrawal reflex latency, histological, axon density and electrophysiology tests were carried out to compare the efficacy of nanofibrous constructs with an autograft. Our study showed mixed results when comparing the artificial constructs with an autograft. In some cases, the nanofibrous conduit with aligned nanofibrous yarn as an intra-luminal guidance channel performs better than the autograft in muscle reinnervation and withdrawal reflex latency tests. However, the axon density count is highest in the autograft at mid-graft. Functional recovery was improved with the use of the nerve construct which suggested that this nerve implant has the potential for clinical usage in reconstructing peripheral nerve defects.

Chapter 9: Artificial scaffolds for peripheral nerve reconstruction

Posttraumatic peripheral nerve repair is one of the major challenges in restorative medicine and microsurgery. Despite the recent progresses in the field of tissue engineering, functional recovery after severe nerve lesions is generally partial and unsatisfactory. Autograft is still the best method to treat peripheral nerve lesions, although it has several drawbacks and does not allow complete functional recovery. Full recovery of nerve functionality could ideally be achieved by proper guiding axon regeneration toward the original target tissues, through the use of purposely engineered artificial nerve guidance channels (NGCs). In the last decade, artificial NGCs have been produced using a variety of both natural and synthetic, biodegradable and nonbiodegradable polymers. Several techniques have been developed to obtain porous and nonporous NGCs and to realize and incorporate bioactive fillers for NGCs. Some of the developed products have been approved for clinical applications. Many other NGC typologies have been object of interest and are currently under investigation. The current trend of nerve tissue engineering is the realization of biomimetic NGCs, providing chemotactic, topological, and haptotactic signalling to cells, respectively by surface functionalization with cell binding domains, the use of internal-oriented matrices/fibres and the sustained release of neurotrophic factors. The present contribution provides a balanced integration of the most recent achievements of tissue engineering in the field of peripheral nerve repair. By an accurate evaluation of the status of research, the review delineates the most promising directions to which research should address for consistent progress in the field of peripheral nerve repair.