Cellular and Transcriptional Response of Human Astrocytes to Hybrid Protein Materials

Collagen is a major component of the tissue matrix, and soybean can regulate the tissue immune response. Both materials have been used to fabricate biomaterials for tissue repair. In this study, adult and fetal human astrocytes were grown in a soy protein isolate (SPI)-collagen hybrid gel or on the surface of a cross-linked SPI-collagen membrane. Hybrid materials reduced the cell proliferation rate compared to materials generated by collagen alone. However, the hybrid materials did not significantly change the cell motility compared to the control collagen material. RNA-sequencing (RNA-Seq) analysis showed downregulated genes in the cell cycle pathway, including CCNA2, CCNB1, CCNB2, CCND1, CCND2, and CDK1, which may explain lower cell proliferation in the hybrid material. This study also revealed the downregulation of genes encoding extracellular matrix (ECM) components, including HSPG2, LUM, SDC2, COL4A1, COL4A5, COL4A6, and FN1, as well as genes encoding chemokines, including CCL2, CXCL1, CXCL2, CX3CL1, CXCL3, and LIF, for adult human astrocytes grown on the hybrid membrane compared with those grown on the control collagen membrane. The study explored the cellular and transcriptional responses of human astrocytes to the hybrid material and indicated a potential beneficial function of the material in the application of neural repair.

Delayed inhibition of collagen deposition by targeting bone morphogenetic protein 1 promotes recovery after spinal cord injury

Fibrotic scars appear after spinal cord injury (SCI) and are mainly composed of fibroblasts and excess extracellular matrix (ECM), including different types of collagen. The temporal and spatial distribution and role of excess collagens and ECM after SCI are not yet fully understood. Here, we identified that the procollagen type I C-terminal propeptide (PICP), a marker of collagen type I deposition, and bone morphogenetic protein 1 (BMP1), a secreted procollagen c-proteinase (PCP) for type I collagen maturation, were significantly elevatedin cerebrospinal fluid of patients with SCI compared with healthy controls, and were associated with spinal cord compression and neurological symptoms. We revealed the deposition of type I collagen in the area damaged by SCI in mice and confirmed that BMP1 was the only expressed PCP and induced collagen deposition. Furthermore, transforming growth factor-β (TGF-β), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) can activate the expression of BMP1. However, inhibition of BMP1 at the acute phase eliminated fibrotic scars in the damaged area and inhibited activation and enrichment of astrocytes, which made the damage difficult to repair and increased hematoma. Unexpectedly, knockdown of Bmp1 by adeno-associated virus or the inhibition of BMP1 biological function by specific inhibitors and monoclonal antibodies at different time points after injury led to distinct therapeutic effects. Only delayed inhibition of BMP1 improved axonal regeneration and myelin repair at the subacute stage post-injury, and led to the recovery of motor function, suggesting that scarring had a dual effect. Early inhibition of the scarring was not conducive to limiting inflammation, while excessive scar formation inhibited the growth of axons. After SCI, the collagen deposition indicators increased in both human cerebrospinal fluid and mouse spinal cord. Therefore, suppression of BMP1 during the subacute phase improves nerve function after SCI and is a potential target for scar reduction.

Recent advances in nanotherapeutic strategies for spinal cord injury repair

Spinal cord injury (SCI) is a devastating and complicated condition with no cure available. The initial mechanical trauma is followed by a secondary injury characterized by inflammatory cell infiltration and inhibitory glial scar formation. Due to the limitations posed by the blood-spinal cord barrier, systemic delivery of therapeutics is challenging. Recent development of various nanoscale strategies provides exciting and promising new means of treating SCI by crossing the blood-spinal cord barrier and delivering therapeutics. As such, we discuss different nanomaterial fabrication methods and provide an overview of recent studies where nanomaterials were developed to modulate inflammatory signals, target inhibitory factors in the lesion, and promote axonal regeneration after SCI. We also review emerging areas of research such as optogenetics, immunotherapy and CRISPR-mediated genome editing where nanomaterials can provide synergistic effects in developing novel SCI therapy regimens, as well as current efforts and barriers to clinical translation of nanomaterials.

Fibroadhesive scarring of grafted collagen scaffolds interferes with implant-host neural tissue integration and bridging in experimental spinal cord injury

Severe traumatic spinal cord injury (SCI) results in a devastating and permanent loss of function, and is currently an incurable condition. It is generally accepted that future intervention strategies will require combinational approaches, including bioengineered scaffolds, to support axon growth across tissue scarring and cystic cavitation. Previously, we demonstrated that implantation of a microporous type-I collagen scaffold into an experimental model of SCI was capable of supporting functional recovery in the absence of extensive implant–host neural tissue integration. Here, we demonstrate the reactive host cellular responses that may be detrimental to neural tissue integration after implantation of collagen scaffolds into unilateral resection injuries of the adult rat spinal cord. Immunohistochemistry demonstrated scattered fibroblast-like cell infiltration throughout the scaffolds as well as the presence of variable layers of densely packed cells, the fine processes of which extended along the graft–host interface. Few reactive astroglial or regenerating axonal profiles could be seen traversing this layer. Such encapsulation-type behaviour around bioengineered scaffolds impedes the integration of host neural tissues and reduces the intended bridging role of the implant. Characterization of the cellular and molecular mechanisms underpinning this behaviour will be pivotal in the future design of collagen-based bridging scaffolds intended for regenerative medicine.

Transplantation of neural scaffolds consisting of dermal fibroblast-reprogrammed neurons and 3D silk fibrous materials promotes the repair of spinal cord injury

Neural scaffolds consisting of dermal fibroblast-reprogrammed neurons and 3D silk fibrous materials promote repair of spinal cord injury.

The combination of induced pluripotent stem cells and bioscaffolds holds promise for spinal cord regeneration

Spinal cord injuries (SCIs) are debilitating conditions for which no effective treatment currently exists. The damage of neural tissue causes disruption of neural tracts and neuron loss in the spinal cord. Stem cell replacement offers a solution for SCI treatment by providing a source of therapeutic cells for neural function restoration. Induced pluripotent stem cells (iPSCs) have been investigated as a potential type of stem cell for such therapies. Transplantation of iPSCs has been shown to be effective in restoring function after SCIs in animal models while they circumvent ethical and immunological concerns produced by other stem cell types. Another approach for the treatment of SCI involves the graft of a bioscaffold at the site of injury to create a microenvironment that enhances cellular viability and guides the growing axons. Studies suggest that a combination of these two treatment methods could have a synergistic effect on functional recovery post-neural injury. While much progress has been made, more research is needed before clinical trials are possible. This review highlights recent advancements using iPSCs and bioscaffolds for treatment of SCI.

3D printed biofunctionalized scaffolds for microfracture repair of cartilage defects

While articular cartilage defects affect millions of people worldwide from adolescents to adults, the repair of articular cartilage defects still remains challenging due to the limited endogenous regeneration of the tissue and poor integration with implants. In this study, we developed a 3D-printed scaffold functionalized with aggrecan that supports the cellular fraction of bone marrow released from microfracture, a widely used clinical procedure, and demonstrated tremendous improvement of regenerated cartilage tissue quality and joint function in a lapine model. Optical coherence tomography (OCT) revealed doubled thickness of the regenerated cartilage tissue in the group treated with our aggrecan functionalized scaffold compared to standard microfracture treatment. H&E staining showed 366 ± 95 chondrocytes present in the unit area of cartilage layer with the support of bioactive scaffold, while conventional microfracture group showed only 112 ± 26 chondrocytes. The expression of type II collagen appeared almost 10 times higher with our approach compared to normal microfracture, indicating the potential to overcome the fibro-cartilage formation associated with the current microfracture approach. The therapeutic effect was also evaluated at joint function level. The mobility was evaluated using a modified Basso, Beattie and Bresnahan (BBB) scale. While the defect control group showed no movement improvement over the course of study, all experimental groups showed a trend of increasing scores over time. The present work developed an effective method to regenerate critical articular defects by combining a 3D-printed therapeutic scaffold with the microfracture surgical procedure. This biofunctionalized acellular scaffold has great potential to be applied as a supplement for traditional microfracture to improve the quality of cartilage regeneration in a cost and labor effective way.

Three-dimensional aligned nanofibers-hydrogel scaffold for controlled non-viral drug/gene delivery to direct axon regeneration in spinal cord injury treatment

Spinal cord injuries (SCI) often lead to persistent neurological dysfunction due to failure in axon regeneration. Unfortunately, currently established treatments, such as direct drug administration, do not effectively treat SCI due to rapid drug clearance from our bodies. Here, we introduce a three-dimensional aligned nanofibers-hydrogel scaffold as a bio-functionalized platform to provide sustained non-viral delivery of proteins and nucleic acid therapeutics (small non-coding RNAs), along with synergistic contact guidance for nerve injury treatment. A hemi-incision model at cervical level 5 in the rat spinal cord was chosen to evaluate the efficacy of this scaffold design. Specifically, aligned axon regeneration was observed as early as one week post-injury. In addition, no excessive inflammatory response and scar tissue formation was triggered. Taken together, our results demonstrate the potential of our scaffold for neural tissue engineering applications.

Biocompatibility of reduced graphene oxide nanoscaffolds following acute spinal cord injury in rats

Background:

Graphene has unique electrical, physical, and chemical properties that may have great potential as a bioscaffold for neuronal regeneration after spinal cord injury. These nanoscaffolds have previously been shown to be biocompatible in vitro; in the present study, we wished to evaluate its biocompatibility in an in vivo spinal cord injury model.

Methods:

Graphene nanoscaffolds were prepared by the mild chemical reduction of graphene oxide. Twenty Wistar rats (19 male and 1 female) underwent hemispinal cord transection at approximately the T2 level. To bridge the lesion, graphene nanoscaffolds with a hydrogel were implanted immediately after spinal cord transection. Control animals were treated with hydrogel matrix alone. Histologic evaluation was performed 3 months after the spinal cord transection to assess in vivo biocompatibility of graphene and to measure the ingrowth of tissue elements adjacent to the graphene nanoscaffold.

Results:

The graphene nanoscaffolds adhered well to the spinal cord tissue. There was no area of pseudocyst around the scaffolds suggestive of cytotoxicity. Instead, histological evaluation showed an ingrowth of connective tissue elements, blood vessels, neurofilaments, and Schwann cells around the graphene nanoscaffolds.

Conclusions:

Graphene is a nanomaterial that is biocompatible with neurons and may have significant biomedical application. It may provide a scaffold for the ingrowth of regenerating axons after spinal cord injury.

A novel composite type I collagen scaffold with micropatterned porosity regulates the entrance of phagocytes in a severe model of spinal cord injury

Traumatic spinal cord injury (SCI) is a damage to the spinal cord that results in loss or impaired motor and/or sensory function. SCI is a sudden and unexpected event characterized by high morbidity and mortality rate during both acute and chronic stages, and it can be devastating in human, social and economical terms. Despite significant progresses in the clinical management of SCI, there remain no effective treatments to improve neurological outcomes. Among experimental strategies, bioengineered scaffolds have the potential to support and guide injured axons contributing to neural repair. The major aim of this study was to investigate a novel composite type I collagen scaffold with micropatterned porosity in a rodent model of severe spinal cord injury. After segment resection of the thoracic spinal cord we implanted the scaffold in female Sprague-Dawley rats. Controls were injured without receiving implantation. Behavioral analysis of the locomotor performance was monitored up to 55 days postinjury. Two months after injury histopathological analysis were performed to evaluate the extent of scar and demyelination, the presence of connective tissue and axonal regrowth through the scaffold and to evaluate inflammatory cell infiltration at the injured site. We provided evidence that the new collagen scaffold was well integrated with the host tissue, slightly ameliorated locomotor function, and limited the robust recruitment of the inflammatory cells at the injury site during both the acute and chronic stage in spinal cord injured rats. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1040-1053, 2017.

Regeneration strategies after the adult mammalian central nervous system injury-biomaterials

The central nervous system (CNS) has very restricted intrinsic regeneration ability under the injury or disease condition. Innovative repair strategies, therefore, are urgently needed to facilitate tissue regeneration and functional recovery. The published tissue repair/regeneration strategies, such as cell and/or drug delivery, has been demonstrated to have some therapeutic effects on experimental animal models, but can hardly find clinical applications due to such methods as the extremely low survival rate of transplanted cells, difficulty in integrating with the host or restriction of blood–brain barriers to administration patterns. Using biomaterials can not only increase the survival rate of grafts and their integration with the host in the injured CNS area, but also sustainably deliver bioproducts to the local injured area, thus improving the microenvironment in that area. This review mainly introduces the advances of various strategies concerning facilitating CNS regeneration.

Nerve conduits constructed by electrospun P(LLA-CL) nanofibers and PLLA nanofiber yarns

Nerve conduits constructed by PLLA nanofiber yarns could facilitate the proliferation, spreading, and migration of SC cells.

Repair of injured spinal cord using biomaterial scaffolds and stem cells

The loss of neurons and degeneration of axons after spinal cord injury result in the loss of sensory and motor functions. A bridging biomaterial construct that allows the axons to grow through has been investigated for the repair of injured spinal cord. Due to the hostility of the microenvironment in the lesion, multiple conditions need to be fulfilled to achieve improved functional recovery. A scaffold has been applied to bridge the gap of the lesion as contact guidance for axonal growth and to act as a vehicle to deliver stem cells in order to modify the microenvironment. Stem cells may improve functional recovery of the injured spinal cord by providing trophic support or directly replacing neurons and their support cells. Neural stem cells and mesenchymal stem cells have been seeded into biomaterial scaffolds and investigated for spinal cord regeneration. Both natural and synthetic biomaterials have increased stem cell survival in vivo by providing the cells with a controlled microenvironment in which cell growth and differentiation are facilitated. This optimal multi‒disciplinary approach of combining biomaterials, stem cells, and biomolecules offers a promising treatment for the injured spinal cord.

Presence of trans-synaptic neurons derived from olfactory mucosa transplanted after spinal cord injury

STUDY DESIGN

Using biotinylated dextran amine (BDA) and wheat germ agglutinin (WGA) tracers, we measured the effectiveness of olfactory mucosa (OM) transplantation as a scaffold in a rat model of chronic spinal cord injury (SCI).

OBJECTIVE

We examined whether OM transplantation for chronic SCI in rats results in reconstruction of neuronal pathways by both regeneration of the remaining axons and supply of OM-derived trans-synaptic neurons.

SUMMARY OF BACKGROUND DATA

OM is one of the ideal scaffolds for axonal regeneration after chronic SCI.

METHODS

Rats received a mild contusion at vertebral level T6-T7. Two weeks after SCI, enhanced green fluorescent protein rat-derived OM, respiratory mucosa, and phosphate-buffered saline were transplanted into each group of SCI rats. Ten weeks after SCI, BDA was injected into the right sensorimotor cortex. Eleven weeks after SCI, WGA was injected into the L1-L2 posterior column to label the corticospinal tract retrogradely and trans-synaptically. Twelve weeks after SCI, rats were killed and their spinal cords were divided into cervical (area a), thoracic-injured (area b), and lower thoracic portions (area c). Immunohistochemically, sections of area (b) were evaluated by counting cells positive for enhanced green fluorescent protein, 4',6-diamidino-2-phenylindole, WGA, and BDA (OM and respiratory mucosa groups). Axonal regenerations were estimated by counting WGA- and BDA-positive dots in transverse sections of area (a) and area (c).

RESULTS

Compared with respiratory mucosa and phosphate-buffered saline transplantation, OM transplantation increased the number of WGA-positive dots in area (a), and the number of BDA-positive dots in area (c) was more after OM transplantation than after phosphate-buffered saline transplantation. Furthermore, the number of quadruple-positive cells in area (b) was much higher after OM transplantation.

CONCLUSION

Our results provide both indirect and direct evidence for the presence of trans-synaptic neurons. OM transplantation in rats with chronic SCI resulted in reconstruction of neural pathways by both providing trans-synaptic neurons and supporting regeneration of remaining axons. The olfactory mucosa is thought to be an efficacious scaffold to produce the relay neuron in chronic spinal cord injury.

Biologic scaffold for CNS repair

Injury to the CNS typically results in significant morbidity and endogenous repair mechanisms are limited in their ability to restore fully functional CNS tissue. Biologic scaffolds composed of individual purified components have been shown to facilitate functional tissue reconstruction following CNS injury. Extracellular matrix scaffolds derived from mammalian tissues retain a number of bioactive molecules and their ability for CNS repair has recently been recognized. In addition, novel biomaterials for dural mater repairs are of clinical interest as the dura provides barrier function and maintains homeostasis to CNS. The present article describes the application of regenerative medicine principles to the CNS tissues and dural mater repair. While many approaches have been exploring the use of cells and/or therapeutic molecules, the strategies described herein focus upon the use of extracellular matrix scaffolds derived from mammalian tissues that are free of cells and exogenous factors.

Collagen scaffolds modified with collagen-binding bFGF promotes the neural regeneration in a rat hemisected spinal cord injury model

Nerve conduit is one of strategies for spine cord injury (SCI) treatment. Recently, studies showed that biomaterials could guide the neurite growth and promote axon regeneration at the injury site. However, the scaffold by itself was difficult to meet the need of SCI functional recovery. The basic fibroblast growth factor (bFGF) administration significantly promotes functional recovery after organ injuries. Here, using a rat model of T9 hemisected SCI, we aimed at assessing the repair capacity of implantation of collagen scaffold (CS) modified by collagen binding bFGF (CBD-bFGF). The results showed that CS combined with CBD-bFGF treatment improved survival rates after the lateral hemisection SCI. The CS/CBD-bFGF group showed more significant improvements in motor than the simply CS-implanted and untreated control group, when evaluated by the 21-point Basso-Beattie-Bresnahan (BBB) score and footprint analysis. Both hematoxylin and eosin (H&E) and immunohistochemical staining of neurofilament (NF) and glial fibrillary acidic protein (GFAP) demonstrated that fibers were guided to grow through the implants. These findings indicated that administration of CS modified with CBD-bFGF could promote spinal cord regeneration and functional recovery.

Regenerative medicine for the treatment of spinal cord injury: more than just promises?

Spinal cord injury triggers a complex set of events that lead to tissue healing without the restoration of normal function due to the poor regenerative capacity of the spinal cord. Nevertheless, current knowledge about the intrinsic regenerative ability of central nervous system axons, when in a supportive environment, has made the prospect of treating spinal cord injury a reality. Among the range of strategies under investigation, cell-based therapies offer the most promising results, due to the multifactorial roles that these cells can fulfil. However, the best cell source is still a matter of debate, as are clinical issues that include the optimal cell dose as well as the timing and route of administration. In this context, the role of biomaterials is gaining importance. These can not only act as vehicles for the administered cells but also, in the case of chronic lesions, can be used to fill the permanent cyst, thus creating a more favourable and conducive environment for axonal regeneration in addition to serving as local delivery systems of therapeutic agents to improve the regenerative milieu. Some of the candidate molecules for the future are discussed in view of the knowledge derived from studying the mechanisms that facilitate the intrinsic regenerative capacity of central nervous system neurons. The future challenge for the multidisciplinary teams working in the field is to translate the knowledge acquired in basic research into effective combinatorial therapies to be applied in the clinic.

Tissue engineering is a promising method for the repair of spinal cord injuries (Review)

Spinal cord injury (SCI) may lead to a devastating and permanent loss of neurological function, which may place a great economic burden on the family of the patient and society. Methods for reducing the death of neuronal cells, inhibiting immune and inflammatory reactions, and promoting the growth of axons in order to build up synapses with the target cells are the focus of current research. Target cells are located in the damaged spinal cord which create a connect with the scaffold. As tissue engineering technology is developed for use in a variety of different areas, particularly the biomedical field, a clear understanding of the mechanisms of tissue engineering is important. This review establishes how this technology may be used in basic experiments with regard to SCI and considers its potential future clinical use.

The possible influence of varying diameter of aligned electrospun fibers on Schwann cells maturation in culture

The development of Schwann cells, the principal glial cell in the peripheral nervous system, occurs through a series of transitional embryonic and postnatal phases, which are tightly regulated by a number of axonal signals. During the axon ensheathment and myelin growth, the diameter of the axon play an important role in the maturation of Schwann cells. Because of electrospun fibers similar to protein fibers within the native extracellular matrix, the scaffolds are being developed as neural tissue engineering scaffolds. Until now, the correlation between varying diameter of aligned electrospun fibers and Schwann cells maturation has not been investigated. We hypothesize that the different diameter of aligned electrospun fibers may influence the maturation of Schwann cells and may help improve the outcome of cell-based approaches to cure demyelinated lesions or peripheral nerve regeneration.

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.

The potential for cellular therapy combined with growth factors in spinal cord injury

Any traumatic spinal cord injury (SCI) may cause symptoms ranging from pain to complete loss of motor and sensory functions below the level of the injury. Currently, there are over 2 million SCI patients worldwide. The cost of their necessary continuing care creates a burden for the patient, their families, and society. Presently, few SCI treatments are available and none have facilitated neural regeneration and/or significant functional improvement. Research is being conducted in the following areas: pathophysiology, cellular therapies (Schwann cells, embryonic stem cells, induced pluripotent stem cells, mesenchymal stem cells, olfactory ensheathing cells), growth factors (BDNF), inhibitory molecules (NG2, myelin protein), and combination therapies (cell grafts and neurotrophins, cotransplantation). Results are often limited because of the inhibitory environment created following the injury and the limited regenerative potential of the central nervous system. Therapies that show promise in small animal models may not transfer to nonhuman primates and humans. None of the research has resulted in remarkable improvement, but many areas show promise. Studies have suggested that a combination of therapies may enhance results and may be more effective than a single therapy. This paper reviews and discusses the most promising new SCI research including combination therapies.

Nanofibrous collagen nerve conduits for spinal cord repair

Nerve regeneration in an injured spinal cord is often restricted, contributing to the devastating outcome of neurologic impairment below the site of injury. Although implantation of tissue-engineered scaffolds has evolved as a potential treatment method, the outcomes remain sub-optimal. One possible reason may be the lack of topographical signals from these constructs to provide contact guidance to invading cells or regrowing axons. Nanofibers mimic the natural extracellular matrix architecturally and may therefore promote physiologically relevant cellular phenotypes. In this study, the potential application of electrospun collagen nanofibers (diameter=208.2±90.4 nm) for spinal cord injury (SCI) treatment was evaluated in vitro and in vivo. Primary rat astrocytes and dorsal root ganglias (DRGs) were seeded on collagen-coated glass cover slips (two-dimensional [2D] substrate controls), and randomly oriented or aligned collagen fibers to evaluate scaffold topographical effects on astrocyte behavior and neurite outgrowth, respectively. When cultured on collagen nanofibers, astrocyte proliferation and expression of glial fibrillary acidic protein (GFAP) were suppressed as compared to cells on 2D controls at days 3 (p<0.05) and 7 (p<0.01). Aligned fibers resulted in elongated astrocytes (elongation factor >4, p<0.01) and directed the orientation of neurite outgrowth from DRGs along fiber axes. In the contrast, neurites emanated radially on randomly oriented collagen fibers. By forming collagen scaffolds into spiral tubular structures, we demonstrated the feasibility of using electrospun nanofibers for the treatment of acute SCI using a rat hemi-section model. At days 10 and 30 postimplantation, extensive cellular penetration into the constructs was observed regardless of fiber orientation. However, scaffolds with aligned fibers appeared more structurally intact at day 30. ED1 immunofluorescent staining revealed macrophage invasion by day 10, which decreased significantly by day 30. Neural fiber sprouting as evaluated by neurofilament staining was observed as early as day 10. In addition, GFAP immunostained astrocytes were found only at the boundary of the lesion site, and no astrocyte accumulation was observed in the implantation area at any time point. These findings indicate the feasibility of fabricating 3D spiral constructs using electrospun collagen fibers and demonstrated the potential of these scaffolds for SCI repair.

The reparative response to cross-linked collagen-based scaffolds in a rat spinal cord gap model

Prior work demonstrated the improvement of peripheral nerve regeneration in gaps implanted with collagen scaffold-filled collagen tubes, compared with nerve autografts, and the promise of such implants for treating gaps in spinal cord injury (SCI) in rats. The objective of this study was to investigate collagen implants alone and incorporating select therapeutic agents in a 5-mm full-resection gap model in the rat spinal cord. Two studies were performed, one with a 6-week time point and one with a 2-week time point. For the 6-week study the groups included: (1) untreated control, (2) dehydrothermally (DHT)-cross-linked collagen scaffold, (3) DHT-cross-linked collagen scaffold seeded with adult rat neural stem cells (NSCs), and (4) DHT-cross-linked collagen scaffold incorporating plasmid encoding glial cell line-derived neurotropic factor (pGDNF). The 2-week study groups were: (1) nontreated control, (2) DHT-cross-linked collagen scaffold; (3) DHT-cross-linked collagen scaffold containing laminin; and (4) carbodiimide-cross-linked collagen scaffold containing laminin. The tissue filling the defect of all groups at 6 weeks was largely composed of fibrous scar; however, the tissue was generally more favorably aligned with the long axis of the spinal cord in all of the treatment groups, but not in the control group. Quantification of the percentage of animals per group containing cystic cavities in the defect showed a trend toward fewer rats with cysts in the groups in which the scaffolds were implanted compared to control. All of the collagen implants were clearly visible and mostly intact after 2 weeks. A band of fibrous tissue filling the control gaps was not seen in the collagen implant groups. In all of the groups there was a narrowing of the spinal canal within the gap as a result of surrounding soft tissue collapse into the defect. The narrowing of the spinal canal occurred to a greater extent in the control and DHT scaffold alone groups compared to the DHT scaffold/laminin and EDAC scaffold/laminin groups. Collagen biomaterials can be useful in the treatment of SCI to: favorably align the reparative tissue with the long axis of the spinal cord; potentially reduce the formation of fluid-filled cysts; serve as a delivery vehicle for NSCs and the gene for GDNF; and impede the collapse of musculature and connective tissue into the defect.

Bioengineered scaffolds for spinal cord repair

Spinal cord injury can lead to devastating and permanent loss of neurological function, affecting all levels below the site of trauma. Unfortunately, the injured adult mammalian spinal cord displays little regenerative capacity and little functional recovery in large part due to a tissue environment that is nonpermissive for regenerative axon growth. Artificial tissue repair scaffolds may provide a physical guide to allow regenerative axon growth that bridges the lesion cavity and restores functional neural connectivity. By integrating different strategies, including the use of various biomaterials and microstructures as well as incorporation of bioactive molecules and living cells, combined or synergistic effects for spinal cord repair through regenerative axon growth may be achieved. This article briefly reviews the development of bioengineered scaffolds for spinal cord repair, focusing on spinal cord injury and the subsequent cellular response, scaffold materials, fabrication techniques, and current therapeutic strategies. Key issues and challenges are also identified and discussed along with recommendations for future research.

Peripheral nerve repair through multi-luminal biosynthetic implants

Peripheral nerve damage is routinely repaired by autogenic nerve grafting, often leading to less than optimal functional recovery at the expense of healthy donor nerves. Alternative repair strategies use tubular scaffolds to guide the regeneration of damaged nerves, but despite the progress made on improved structural materials for the nerve tubes, functional recovery remains incomplete. We developed a biosynthetic nerve implant (BNI) consisting of a hydrogel-based transparent multichannel scaffold with luminar collagen matrix as a 3-D substrate for nerve repair. Using a rat sciatic nerve injury model we showed axonal regeneration through the BNI to be histologically comparable to the autologous nerve repair. At 10 weeks post-injury, nerve defects repaired with collagen-filled, single lumen tubes formed single nerve cables, while animals that received the multi-luminal BNIs showed multiple nerve cables and the formation of a perineurial-like layer within the available microchannels. Total numbers of myelinated and unmyelinated axons in the BNI were increased 3-fold and 30%, respectively, compared to collagen tubes. The recovery of reflexive movement confirmed the functional regeneration of both motor and sensory neurons. This study supports the use of multi-luminal BNIs as a viable alternative to autografts in the repair of nerve gap injuries.

Peripheral nerve regeneration using autologous porcine skin-derived mesenchymal stem cells

Porcine skin-derived mesenchymal stem cells (pSMSCs) were evaluated on their biological MSC characterizations and differentiation into mesenchymal lineages, along with in vitro and in vivo neural inductions. Isolated pSMSCs showed plate-adherent growth, expression of various MSC-marker proteins and transcriptional factors, and differentiation potential into mesenchymal lineages. Neuron-like cell morphology and various neural markers were highly detected at 6 h and 24 h after in vitro neural induction of pSMSCs, but their neuron-like characteristics disappeared as induction time extended to 48 and 72 h. To evaluate the in vivo peripheral nerve regeneration potential of pSMSCs, a total of 5 × 10(6) autologous pSMSCs labelled with tracking dye, supplemented with fibrin glue scaffold and collagen tubulization, were transplanted into the peripheral nerve defected miniature pigs. At 2 and 4 weeks after cell transplantation, well-preserved transplanted cells and remarkable in vivo nerve regeneration, including histologically complete nerve bundles, were observed in the regenerated nerve tissues. Moreover, S-100 protein and p75 nerve growth factor receptor were more highly detected in regenerated nerve fibres compared to non-cell grafted control fibres. These results suggest that autologous pSMSCs transplanted with fibrin glue scaffold can induce prominent nerve regeneration in porcine peripheral nerve defect sites.

Suspension matrices for improved Schwann-cell survival after implantation into the injured rat spinal cord

Trauma to the spinal cord produces endogenously irreversible tissue and functional loss, requiring the application of therapeutic approaches to achieve meaningful restoration. Cellular strategies, in particular Schwann-cell implantation, have shown promise in overcoming many of the obstacles facing successful repair of the injured spinal cord. Here, we show that the implantation of Schwann cells as cell suspensions with in-situ gelling laminin:collagen matrices after spinal-cord contusion significantly enhances long-term cell survival but not proliferation, as well as improves graft vascularization and the degree of axonal in-growth over the standard implantation vehicle, minimal media. The use of a matrix to suspend cells prior to implantation should be an important consideration for achieving improved survival and effectiveness of cellular therapies for future clinical application.

Topography, cell response, and nerve regeneration

In the body, cells encounter a complex milieu of signals, including topographical cues, in the form of the physical features of their surrounding environment. Imposed topography can affect cells on surfaces by promoting adhesion, spreading, alignment, morphological changes, and changes in gene expression. Neural response to topography is complex, and it depends on the dimensions and shapes of physical features. Looking toward repair of nerve injuries, strategies are being explored to engineer guidance conduits with precise surface topographies. How neurons and other cell types sense and interpret topography remains to be fully elucidated. Studies reviewed here include those of topography on cellular organization and function as well as potential cellular mechanisms of response.

Investigation of the regenerative capacity of an acellular porcine medial meniscus for tissue engineering applications

Previously, we have described the development of an acellular porcine meniscal scaffold. The aims of this study were to determine the immunocompatibility of the scaffold and capacity for cellular attachment and infiltration to gain insight into its potential for meniscal repair and replacement. Porcine menisci were decellularized by exposing the tissue to freeze-thaw cycles, incubation in hypotonic tris buffer, 0.1% (w/v) sodium dodecyl sulfate in hypotonic buffer plus protease inhibitors, nucleases, hypertonic buffer followed by disinfection using 0.1% (v/v) peracetic, and final washing in phosphate-buffered saline. In vivo immunocompatibility was assessed after implantation of the acellular meniscal scaffold subcutaneously into galactosyltransferase knockout mice for 3 months in comparison to fresh and acellular tissue treated with α-galactosidase (negative control). The cellular infiltrates in the explants were assessed by histology and characterized using monoclonal antibodies against: CD3, CD4, CD34, F4/80, and C3c. Static culture was used to assess the potential of acellular porcine meniscal scaffold to support the attachment and infiltration of primary human dermal fibroblasts and primary porcine meniscal cells in vitro. The explants were surrounded by capsules that were more pronounced for the fresh meniscal tissue compared to the acellular tissues. Cellular infiltrates compromised mononuclear phagocytes, CD34-positive cells, and nonlabeled fibroblastic cells. T-lymphocytes were sparse in all explanted tissue types and there was no evidence of C3c deposition. The analysis revealed an absence of a specific immune response to all of the implanted tissues. Acellular porcine meniscus was shown to be capable of supporting the attachment and infiltration of primary human fibroblasts and primary porcine meniscal cells. In conclusion, acellular porcine meniscal tissue exhibits excellent immunocompatibility and potential for cellular regeneration in the longer term.

Varying the diameter of aligned electrospun fibers alters neurite outgrowth and Schwann cell migration

Aligned, electrospun fibers have shown great promise in facilitating directed neurite outgrowth within cell and animal models. While electrospun fiber diameter does influence cellular behavior, it is not known how aligned, electrospun fiber scaffolds of differing diameter influence neurite outgrowth and Schwann cell (SC) migration. Thus, the goal of this study was to first create highly aligned, electrospun fiber scaffolds of varying diameter and then assess neurite and SC behavior from dorsal root ganglia (DRG) explants. Three groups of highly aligned, electrospun poly-l-lactic acid (PLLA) fibers were created (1325+383 nm, large diameter fibers; 759+179 nm, intermediate diameter fibers; and 293+65 nm, small diameter fibers). Embryonic stage nine (E9) chick DRG were cultured on fiber substrates for 5 days and then the explants were stained against neurofilament and S100. DAPI stain was used to assess SC migration. Neurite length and SC migration distance were determined. In general, the direction of neurite extension and SC migration were guided along the aligned fibers. On the small diameter fiber substrate, the neurite length was 42% and 36% shorter than those on the intermediate and large fiber substrates, respectively. Interestingly, SC migration did not correlate with that of neurite extension in all situations. SCs migrated equivalently with extending neurites in both the small and large diameter scaffolds, but lagged behind neurites on the intermediate diameter scaffolds. Thus, in some situations, topography alone is sufficient to guide neurites without the leading support of SCs. Scanning electron microscopy images show that neurites cover the fibers and do not reside exclusively between fibers. Further, at the interface between fibers and neurites, filopodial extensions grab and attach to nearby fibers as they extend down the fiber substrate. Overall, the results and observations suggest that fiber diameter is an important parameter to consider when constructing aligned, electrospun fibers for nerve regeneration applications.

Guidance of Olfactory Ensheathing Cell Growth and Migration on Electrospun Silk Fibroin Scaffolds

Transplantation of olfactory ensheathing cells (OECs) is a potential treatment for spinal cord injury (SCI). However, this process lacks extracellular matrix guiding cell growth, tissue morphogenesis, and remodeling. In order to solve this problem, we fabricated silk fibroin scaffolds (SFS) with different fiber diameters by electrospinning. The behaviors of OECs on 300 and 1800 nm SFS were studied by analyzing cell morphological feature, distribution, and proliferation. The results showed the 300 nm SFS with good potential to guide OECs growth. Subsequently, the properties of 300 nm SFS were further investigated along with PLL. With 300 nm SFS, the preservation of cell phenotype was confirmed by the presence of cell-specific markers, including nerve growth factor receptor p75 and glial fibrillary acidic protein. And the migration behaviors of OECs were also observed by Leica AF6000. In addition, migration tracks, turning behavior, migration distances, migration speeds, and forward migration indices were calculated. Furthermore, the expression of neurotrophic factors was assayed at transcription and protein levels using RT-PCR and ELISA. All these results indicated the diameter of the fiber played an important role in guiding cell adhesion, growth, and migration in vitro and the 300 nm SFS could be suitable to construct tissue-engineered scaffolds for SCI repair.

Current tissue engineering and novel therapeutic approaches to axonal regeneration following spinal cord injury using polymer scaffolds

This review highlights current tissue engineering and novel therapeutic approaches to axonal regeneration following spinal cord injury. The concept of developing 3-dimensional polymer scaffolds for placement into a spinal cord transection model has recently been more extensively explored as a solution for restoring neurologic function after injury. Given the patient morbidity associated with respiratory compromise, the discrete tracts in the spinal cord conveying innervation for breathing represent an important and achievable therapeutic target. The aim is to derive new neuronal tissue from the surrounding, healthy cord that will be guided by the polymer implant through the injured area to make functional reconnections. A variety of naturally derived and synthetic biomaterial polymers have been developed for placement in the injured spinal cord. Axonal growth is supported by inherent properties of the selected polymer, the architecture of the scaffold, permissive microstructures such as pores, grooves or polymer fibres, and surface modifications to provide improved adherence and growth directionality. Structural support of axonal regeneration is combined with integrated polymeric and cellular delivery systems for therapeutic drugs and for neurotrophic molecules to regionalize growth of specific nerve populations.

Advances in progenitor cell therapy using scaffolding constructs for central nervous system injury

Traumatic brain injury (TBI) is a major cause of morbidity and mortality in the United States. Current clinical therapy is focused on optimization of the acute/subacute intracerebral milieu, minimizing continued cell death, and subsequent intense rehabilitation to ameliorate the prolonged physical, cognitive, and psychosocial deficits that result from TBI. Adult progenitor (stem) cell therapies have shown promise in pre-clinical studies and remain a focus of intense scientific investigation. One of the fundamental challenges to successful translation of the large body of pre-clinical work is the delivery of progenitor cells to the target location/organ. Classically used vehicles such as intravenous and intra arterial infusion have shown low engraftment rates and risk of distal emboli. Novel delivery methods such as nanofiber scaffold implantation could provide the structural and nutritive support required for progenitor cell proliferation, engraftment, and differentiation. The focus of this review is to explore the current state of the art as it relates to current and novel progenitor cell delivery methods.