Carbon filament implants promote axonal growth across the transected rat spinal cord

Current Concepts of Biomaterial Scaffolds and Regenerative Therapy for Spinal Cord Injury

Spinal cord injury (SCI) is a catastrophic condition associated with significant neurological deficit and social and financial burdens. It is currently being managed symptomatically, with no real therapeutic strategies available. In recent years, a number of innovative regenerative strategies have emerged and have been continuously investigated in preclinical research and clinical trials. In the near future, several more are expected to come down the translational pipeline. Among ongoing and completed trials are those reporting the use of biomaterial scaffolds. The advancements in biomaterial technology, combined with stem cell therapy or other regenerative therapy, can now accelerate the progress of promising novel therapeutic strategies from bench to bedside. Various types of approaches to regeneration therapy for SCI have been combined with the use of supportive biomaterial scaffolds as a drug and cell delivery system to facilitate favorable cell-material interactions and the supportive effect of neuroprotection. In this review, we summarize some of the most recent insights of preclinical and clinical studies using biomaterial scaffolds in regenerative therapy for SCI and summarized the biomaterial strategies for treatment with simplified results data. One hundred and sixty-eight articles were selected in the present review, in which we focused on biomaterial scaffolds. We conducted our search of articles using PubMed and Medline, a medical database. We used a combination of "Spinal cord injury" and ["Biomaterial", or "Scaffold"] as search terms and searched articles published up until 30 April 2022. Successful future therapies will require these biomaterial scaffolds and other synergistic approaches to address the persistent barriers to regeneration, including glial scarring, the loss of a structural framework, and biocompatibility. This database could serve as a benchmark to progress in future clinical trials for SCI using biomaterial scaffolds.

Locomotor Behavior Analysis in Spinal Cord Injured Macaca radiata after Predegenerated Peripheral Nerve Grafting-A Preliminary Evidence

INTRODUCTION

Primate animal models are being utilized to explore novel therapies for spinal cord injuries. This study aimed to evaluate the efficiency of the transplantation of predegenerated nerve segments in unilateral spinal cord-hemisected bonnet monkeys' (Macaca radiata) locomotor functions using the complex runways.

MATERIALS AND METHODS

The bonnet monkeys were initially trained to walk in a bipedal motion on grid and staircase runways. In one group of trained monkeys, surgical hemisection was made in the spinal cord at the T12-L1 level. In the other group, hemisection was induced in the spinal cord, and the ulnar nerve was also transected at the same time (transplant group). After one week, the hemisected cavity was reopened and implanted with predegenerated ulnar nerve segments obtained from the same animal of the transplant group.

RESULTS

All the operated monkeys showed significant deficits in locomotion on runways at the early postoperative period. The walking ability of operated monkeys was found to be gradually improved, and they recovered nearer to preoperative level at the fourth postoperative month, and there were no marked differences.

CONCLUSION

The results demonstrate that there were no significant improvements in the locomotion of monkeys on runways after the delayed grafting of nerve segments until one year later. The failure of the predegenerated nerve graft as a possible therapeutic strategy to improve the locomotion of monkeys may be due to a number of factors set in motion by trauma, which could possibly prevent the qualities of regeneration. The exact reason for this ineffectiveness of predegenerated nerve segments and their underlying mechanism is not known.

Research progress and prospects of tissue engineering scaffolds for spinal cord injury repair and protection

Spinal cord injury (SCI) is one of the leading causes of global disability. However, there are currently no effective clinical treatments for SCI. Repair of SCI is essential but poses great challenges. As a comprehensive treatment program combining biological scaffolds, seed cells and drugs or biological factors, tissue engineering has gradually replaced the single transplantation approach to become a focus of research that brings new opportunities for the clinical treatment of SCI.

Molecular self-assembly guides the fabrication of peptide nanofiber scaffolds for nerve repair

The particular features render ionic self-complementary peptide-formed and peptide amphiphile-formed nanofiber scaffolds to be compelling biomaterial substrates for nerve repair.

CARBON NANOTUBE RIBBON AND THREAD SUPPORT ATTACHMENT AND DIFFERENTIATION OF NEURAL STEM CELLS

Carbon nanotubes (CNTs) have properties that promise an exciting role in nervous tissue repair. CNTs are strong, extremely light weight, biocompatible and electrically conductive. A relatively novel form of CNT material, multiple strands of CNTs spun into thread, accentuates the linear geometry of CNTs while retaining electrical conductivity. We propose that CNT thread, which is strong, pliable and readily manipulated, has the potential to support longitudinal growth of nerves after injury, in nervous system prostheses. Towards understanding how CNT materials support nervous tissue regeneration, we examined the in vitro interactions between CNT materials and neural stem cell-containing neurospheres, prepared from newborn mouse cortices. Intact neurospheres attached to pieces of as-grown arrays of CNTs, CNT "ribbon" material pulled from the arrays, and CNT thread. Stem cells differentiated into both neurons and glia under these conditions. Processes and cells aligned with the longitudinal axis of the CNT materials, both with and without coatings. For comparisons, dissociated neurosphere cells were plated on CNT thread, polypropylene surgical suture thread and commercial carbon fibers. Initial cell attachment (within seconds) and attachment at 24 h was greater on CNT thread than on the other fiber types. Stem cells on CNT threads differentiated into neurons and astrocytes over several days, on all fibers. The presence of serum greatly aided the health and spreading of both neurons and astrocytes. These findings demonstrate that CNT materials, in particular the thread form, are viable preparations for neural cell attachment, outgrowth and differentiation.

Engineering therapies in the CNS: what works and what can be translated

Engineering is the art of taking what we know and using it to solve problems. As engineers, we build tool chests of approaches; we attempt to learn as much as possible about the problem at hand, and then we design, build, and test our approaches to see how they impact the system. The challenge of applying this approach to the central nervous system (CNS) is that we often do not know the details of what is needed from the biological side. New therapeutic options for treating the CNS range from new biomaterials to make scaffolds, to novel drug-delivery techniques, to functional electrical stimulation. However, the reality is that translating these new therapies and making them widely available to patients requires collaborations between scientists, engineers, clinicians, and patients to have the greatest chance of success. Here we discuss a variety of new treatment strategies and explore the pragmatic challenges involved with engineering therapies in the CNS.

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.

Functional Recovery Following Spinal Cord Hemisection Mediated by a Unique Polymer Scaffold Seeded with Neural Stem Cells

A dual scaffold structure made of biodegradable polymers and seeded with neural stem cells has been developed to address the issues of spinal cord injury including axonal severance and the loss of neurons and glia. The general design of the scaffold is derived the structure of the spinal cord with an outer section which mimics the white matter with long axial pores to provide axonal guidance and an inner section seeded with neural stem cells to address the issues of cell replacement and mimic the general character of the gray matter. The seeded scaffold leads to improved functional recovery as compared with the lesion control or cells alone following spinal cord injury.

Tissue spinal cord response in rats after implants of polypyrrole and polyethylene glycol obtained by plasma

Most of the biomaterials used nowadays for the reconstruction of the spinal cord (SC) tissue after an injury, tested in animals, have obtained modest results. This work presents a study about the compatibility of two novel, non-biodegradable, semi-conductive materials, obtained by plasma polymerization: iodine-doped pyrrole (PPy/I) and pyrrole-polyethylene glycol (PPy/PEG). Both polymers, separately, were implanted in the SC tissue of rats after a transection. Prior to implantation, the elemental composition and the physico-chemical properties of polymers were studied by electron scanning microscopy, IR Spectroscopy and thermogravimetric analysis. We used adult female Long Evans rats, subjected to SC transection. Animals were randomized to be allocated in one of the treatment groups and were killed four weeks after the lesion for histology study. Results showed that both implants were integrated to the SC tissue, as inflammatory and gliotic responses, similar to those observed in the control group, and rejection of the implant, were not evident. Moreover, the immediate effect of PPy/I or PPy/PEG in the injured SC prevented secondary tissue destruction, as compared to non-implanted control animals. In conclusion, implants of semi-conductive polymers were well-tolerated and integrated favorably to SC tissue after transection.

Repair of spinal cord transection and its effects on muscle mass and myosin heavy chain isoform phenotype

A number of significant advances have been developed for treating spinal cord injury during the past two decades. The combination of peripheral nerve grafts and acidic fibroblast growth factor (hereafter referred to as PNG) has been shown to partially restore hindlimb function. However, very little is known about the effects of such treatments in restoring normal muscle phenotype. The primary goal of the current study was to test the hypothesis that PNG would completely or partially restore 1) muscle mass and muscle fiber cross-sectional area and 2) the slow myosin heavy chain phenotype of the soleus muscle. To test this hypothesis, we assigned female Sprague-Dawley rats to three groups: 1) sham control, 2) spinal cord transection (Tx), and 3) spinal cord transection plus PNG (Tx+PNG). Six months following spinal cord transection, the open-field test was performed to assess locomotor function, and then the soleus muscles were harvested and analyzed. SDS-PAGE for single muscle fiber was used to evaluate the myosin heavy chain (MHC) isoform expression pattern following the injury and treatment. Immunohistochemistry was used to identify serotonin (5-HT) fibers in the spinal cord. Compared with the Tx group, the Tx+PNG group showed 1) significantly improved Basso, Beattie, and Bresnahan scores (hindlimb locomotion test), 2) less muscle atrophy, 3) a higher percentage of slow type I fibers, and 4) 5-HT fibers distal to the lesion site. We conclude that the combined treatment of PNG is partially effective in restoring the muscle mass and slow phenotype of the soleus muscle in a T-8 spinal cord-transected rat model.

Bioengineered Strategies for Spinal Cord Repair

This article reviews bioengineered strategies for spinal cord repair using tissue engineered scaffolds and drug delivery systems. The pathophysiology of spinal cord injury (SCI) is multifactorial and multiphasic, and therefore, it is likely that effective treatments will require combinations of strategies such as neuroprotection to counteract secondary injury, provision of scaffolds to replace lost tissue, and methods to enhance axonal regrowth, synaptic plasticity, and inhibition of astrocytosis. Biomaterials have major advantages for spinal cord repair because of their structural and chemical versatility. To date, various degradable or non-degradable biomaterial polymers have been tested as guidance channels or delivery systems for cellular and non-cellular neuroprotective or neuroregenerative agents in experimental SCI. There is promise that bioengineering technology utilizing cellular treatment strategies, including Schwann cells, olfactory ensheathing glia, or neural stem cells, can promote repair of the injured spinal cord. This review is divided into three parts: (1) degradable and non-degradable biomaterials; (2) device design; and (3) combination strategies with scaffolds. We will show that bioengineering combinations of cellular and non-cellular strategies have enhanced the potential for experimental SCI repair, although further pre-clinical work is required before this technology can be translated to humans.

Effect of filament diameter and extracellular matrix molecule precoating on neurite outgrowth and Schwann cell behavior on multifilament entubulation bridging devicein vitro

At present there is no clinically effective treatment for injuries or pathological processes that disrupt the continuity of axons in the mature central nervous system. However, a number of studies suggest that a tremendous potential exists for developing biomaterial based therapies. In particular, biomaterials in the form of bridging substrates have been shown to support at least some level of axonal regeneration across the lesion site, but display a limited capacity for directing axons toward their targets. To improve the directionality and outgrowth rate of the axonal regeneration process, filaments and tubes appear promising, but the technology is far from optimized. As a step toward optimization, the influence of filament diameter and various extracellular matrix coatings on nerve regeneration was evaluated in this article using a dorsal root ganglion (DRG) explant model. An increasing pattern of alignment and outgrowth of neurites in the direction parallel the long axis of the packed filament bundles with decreasing filament diameters ranging from supracellular and beyond (500 to 100 mum), cellular (30 mum), down to subcellular size (5 mum) was observed. Such effects became most prominent on filament bundles with individual filament diameters in the range of cellular size and below (5 and 30 mum) where highly directional and robust neuronal outgrowth was achieved. In addition, laminin-coated filaments that approached the size of spinal axons support significantly longer regenerative outgrowth than similarly treated filaments of larger diameter, and exceed outgrowth distance on similarly sized filaments treated with fibronectin. These data suggested the feasibility of using a multifilament entubulation bridging device for supporting directional axonal regeneration.

Decreased functions of astrocytes on carbon nanofiber materials

Carbon nanofibers possess excellent conductivity properties, which may be beneficial in the design of more effective neural prostheses; however, limited evidence on their cytocompatibility properties currently exists. The objective of the present in vitro study was to determine cytocompatibility properties of formulations containing carbon nanofibers pertinent to neural implant applications. Substrates were prepared from four different types of carbon fibers, two with nanoscale diameters (nanophase, or less than or equal to 100 nm) and two with conventional diameters (or greater than 100 nm). Within these two categories, both a high and a low surface energy fiber were investigated and tested. Carbon fibers were compacted in a manual hydraulic press via a uniaxial loading cycle. Astrocytes (glial scar tissue-forming cells) were seeded onto the substrates for adhesion, proliferation, and long-term function studies (such as total intracellular protein and alkaline phosphatase activity). Results provided the first evidence that astrocytes preferentially adhered and proliferated on carbon fibers that had the largest diameter and the lowest surface energy. Based on these results, composite substrates were also formed using different weight percentages (0-25 wt%) of the nanophase, high surface energy fibers in a polycarbonate urethane matrix. Results provided the first evidence of decreased adhesion of astrocytes with increasing weight percents of the high surface energy carbon nanofibers in the polymer composite; this further demonstrates that formulations containing carbon fibers in the nanometer regime may limit astrocyte functions leading to decreased glial scar tissue formation. Positive interactions with neurons, and, at the same time, limited astrocyte functions leading to decreased gliotic scar tissue formation are essential for increased neuronal implant efficacy.

Fluid shear in viscous fibronectin gels allows aggregation of fibrous materials for CNS tissue engineering

Fibronectin (Fn) materials prepared from human plasma have been used in various forms as substrates for tissue engineering. Such purposes require that the soluble protein aggregates into insoluble fibrous structures which encourage the attachment and migration of cells. The method of aggregation due to mechanical shear was investigated by applying fluid shear forces directly to a viscous solution of Fn. Structural analysis revealed that mechanical shear resulted in the formation of an orientated fibrous protein material that was less soluble than its non-sheared counterpart. The suitability of this shear aggregated Fn material for CNS repair purposes was assessed in vitro where it supported the growth of fibroblasts, S100 immunoreactive Schwann cells and GFAP immunoreactive astrocytes. Implantation of the shear aggregated Fn material into a rat model of spinal cord injury provided a permissive environment for axonal growth. This was extended using an impermeable coating to improve orientation and straightness of axonal growth.

Locomotor performance of the rat after neonatal repairing of spinal cord injuries: quantitative assessment and electromyographic study

In spinal cord injuries, various attempts have been made to reconstruct neural connections once disrupted. To improve current procedures and develop therapeutic methodologies it appears important to compare these reconstructive attempts via a standardized quantification of any ensuing functional recovery with parallel correlations to any potentially repaired neural connections. We have reported previously a quantitative assessment of neural connections across the graft site of rats whose spinal cord segments were neonatally replaced with embryonic spinal cord segments or a peripheral nerve section under comparable conditions. Using this same experimental model the present study assessed locomotor performance quantitatively using an open field locomotor scale at various postoperative intervals from day 0 to 5 weeks postinjury. To examine hind-forelimb coordination in further detail, electromyography was employed to record simultaneously from all four limbs during locomotion. Half of the rats whose spinal cord segments were repaired by replacement with embryonic homologous structures acquired virtually normal locomotor function, with a delay of five days compared with that of sham-operated rats. Detailed analysis revealed an abnormality in ankle joint movement and the stability of trunk during locomotion. Electromyography revealed that the pattern of locomotion in these rats was similar to controls. Grafted segments joined with the host spinal cord without gliosis at the host-graft interface. The remaining rats with an embryonic tissue graft showed various grades of hind-forelimb coordination. Gliosis and cavity were observed at the host-graft interface. The rats whose spinal cord was repaired by periphral nerve graft lacked hind-forelimb coordination despite the achievement of weight-supported steps. It appears likely that the grade of locomotor performance depends on quantity and quality of reestablished neural connections across the graft.

Stimulating regeneration in the damaged spinal cord

Great progress has been made in recent years in experimental strategies for spinal cord repair. In this review we describe two of these strategies, namely the use of neurotrophic factors to promote functional regeneration across the dorsal root entry zone (DREZ), and the use of synthetic fibronectin conduits to support directed axonal growth. The junction between the peripheral nervous system (PNS) and central nervous system (CNS) is marked by a specialized region, the DREZ, where sensory axons enter the spinal cord from the dorsal roots. After injury to dorsal roots, axons will regenerate as far as the DREZ but no further. However, recent studies have shown that this barrier can be overcome and function restored. In animals treated with neurotrophic factors, regenerating axons cross the DREZ and establish functional connections with dorsal horn cells. For example, intrathecal delivery of neurotrophin 3 (NT3) supports ingrowth of A fibres into the dorsal horn. This ingrowth is revealed using a transganglionic anatomical tracer (cholera toxin subunit B) and analysis at light and electron microscopic level. In addition to promoting axonal growth, spinal cord repair is likely to require strategies for supporting long-distance regeneration. Synthetic fibronectin conduits may be useful for this purpose. Experimental studies indicate that fibronectin mats implanted into the spinal cord will integrate with the host tissue and support extensive and directional axonal growth. Growth of both PNS and CNS axons is supported by the fibronectin, and axons become myelinated by Schwann cells. Ongoing studies are aimed at developing composite conduits and promoting axonal growth from the fibronectin back into the spinal cord.

Substrate-bound human recombinant L1 selectively promotes neuronal attachment and outgrowth in the presence of astrocytes and fibroblasts

Axonal pathfinding is a complex process that is mediated through cell-matrix and cell-cell interactions. A large number of studies have demonstrated that ECM and ECM-derived proteins and peptides are potent promoters of neurite outgrowth, however much less attention is given to the fact that these same ligands also elicit responses in a wide variety of non-neuronal cell types. We examined the use of a substrate-bound recombinant form of human L1, an integral membrane protein, as a ligand for bridging materials for repairing the CNS by studying its effectiveness in promoting specific responses of neuronal cells in the presence of astrocytes and fibroblasts. L1, a cell adhesion molecule expressed in the developing CNS and PNS, has strong neurite promoting activity, and contributes to axonal guidance and axonal fasciculation during development. In this study, substrates treated with L1-Fc were compared to subtrates treated with fibronectin and poly-lysine (PDL) with respect to their interaction with a variety of cell types, including three types of neurons (DRG neurons, cerebellar granule neurons, and hippocampal neurons), astrocytes, dermal fibroblasts, and meningeal cells. L1-Fc-treated substrates supported significantly higher levels of neurite outgrowth relative to fibronectin and PDL, while inhibiting the attachment of astrocytes, meningeal cells, and fibroblasts. We also show that neuronal cells attach to and extend neurites on 30 microm diameter L1-Fc-treated filaments as an example of a potentially useful bridging substrate. The high level of biological specificity displayed by surface-bound L1, along with the fact that it is a potent promoter of neurite outgrowth, is normally expressed on axons and regulates axonal fasciculation during normal development bodes well for its use on bridging materials for the repair of the CNS, and suggests that cell adhesion molecules, in general, may be useful for biomaterial modification. Moreover, small diameter filaments coated with L1-Fc may function in an analogous way to pioneering axons that guide the growth of axons to distal targets during development.

Poly(D,L-lactide) foams modified by poly(ethylene oxide)-block-poly(D,L-lactide) copolymers and a-FGF: in vitro and in vivo evaluation for spinal cord regeneration

The first goal of this study was to examine the influence that poly(ethylene oxide)-block-poly(D,L-lactide) (PELA) copolymer can have on the wettability, the in vitro controlled delivery capability, and the degradation of poly(D,L-lactide) (PDLLA) foams. These foams were prepared by freeze-drying and contain micropores (10 microm) in addition of macropores (100 microm) organized longitudinally. Weight loss, water absorption, changes in molecular weight, polymolecularity (Mw/Mn) and glass transition temperature (Tg) of PDLLA foams mixed with various amounts of PELA were followed with time. It was found that 10wt% of PELA increased the wettability and the degradation rate of the polymer foams. The release of sulforhodamine (SR) was compared for PDLLA and PDLLA-PELA foams in relation with the foam porosity. An initial burst release was observed only in the case of the 90:10 PDLLA/PELA foam. The ability of the foam of this composition to be integrated and to promote tissue repair and axonal regeneration in the transected rat spinal cord was investigated. After implantation of ca. 20 polymer rods assembled with fibrin-glue, the polymer construct was able to bridge the cord stumps by forming a permissive support for cellular migration, angiogenesis and axonal regrowth.

Bridging areas of injury in the spinal cord

There is a devastating loss of function when substantial numbers of axons are interrupted by injury to the spinal cord. This loss may be eventually reversed by providing bridging prostheses that will enable axons to regrow across the injury site and enter the spinal cord beyond. This review addresses the bridging strategies that are being developed in a number of spinal cord lesion models: complete and partial transection and cavities arising from contusion. Bridges containing peripheral nerve, Schwann cells, olfactory ensheathing glia, fetal tissue, stem cells/neuronal precursor cells, and macrophages are being evaluated as is the administration of neurotrophic factors, administered by infusion or secreted by genetically engineered cells. Biomaterials may be an important factor in developing successful strategies. Due to the complexity of the sequelae following spinal cord injury, no one strategy will be effective. The compelling question today is: What combinations of the strategies discussed, or new ones, along with an initial neuroprotective treatment, will substantially improve outcome after spinal cord injury?

Surface characterization of poly(methyl methacrylate) microgrooved for contact guidance of mammalian cells

High-resolution patterns of grooves have been made in poly(methyl methacrylate) films, PMMA, by an electron-beam microlithographic process. The surface of films processed over a large width was characterized in terms of chemical composition (X-ray photoelectron spectroscopy (XPS). time of flight secondary ion mass spectroscopy), wettability (sessile drop) and topography (atomic force microscopy). Collagen adsorption was also studied (radiocounting, XPS) as such or in competition with Pluronic F68. The chemical alteration of the surface induced by the electron-beam irradiation disappeared after the dissolution involved in the development process. W138 human fibroblasts cultivated on microgrooved substrata (grooves 1 microm deep and 0.5-10 microm wide) showed a strong orientation parallel to the grooves. The contact guidance is induced by the topography of the surface and not by the alternation of zones with different physico-chemical properties. It may be explained in terms of probability of successful substratum contact by cell protrusions.

Surfactant-immobilized fibronectin enhances bioactivity and regulates sensory neurite outgrowth

A PEO-containing surface coating was investigated as a means to control neurite outgrowth in the presence of serum. Various ratios of end-group-activated tri-block copolymer Pluronic F108 were used to immobilize the extracellular matrix protein fibronectin (FN). Primary cultures of dorsal root ganglion neurons were cultured on F108-immobilized FN or, as a control, on FN adsorbed from solution directly to polystyrene. Although FN surface concentration could be controlled in a dose-dependent manner by either technique, dose-dependent control of neuronal behaviors was best achieved on F108-immobilized FN. This effect was similar regardless of the presence of serum in the culture medium. F108-immobilized FN supported twofold greater maximal neurite outgrowth than did directly adsorbed FN. Furthermore, at similar surface concentrations, F108-FN was significantly more active in promoting neurite outgrowth. Polypropylene filament bundles treated with F108-immobilized FN supported robust outgrowth from explants of dorsal root ganglia, demonstrating the utility of the surface coating on clinically relevant materials with more complex shapes. The ability to control neuronal behaviors in a serum-resistant manner, coupled with enhanced biologic activity, demonstrates the potential for surfactant-based immobilization as a method for generating biointeractive materials for tissue engineering.

Transplantation of nasal olfactory tissue promotes partial recovery in paraplegic adult rats

Recent reports have highlighted the potential therapeutic role of olfactory ensheathing cells for repair of spinal cord injuries. Previously ensheathing cells collected from the olfactory bulbs within the skull were used. In humans a source of these cells for autologous therapy lies in the nasal mucosa where they accompany the axons of the olfactory neurons. The aim of the present study was to test the therapeutic potential of nasal olfactory ensheathing cells for spinal cord repair. Olfactory ensheathing cells cultured from the olfactory lamina propria or pieces of lamina propria from the olfactory mucosa were transplanted into the transected spinal cord. Three to ten weeks later these animals partially recovered movement of their hind limbs and joints which was abolished by a second spinal cord transection. Control rats, receiving collagen matrix, respiratory lamina propria or culture medium, did not recover hind limb movement. Recovery of movement was associated with recovery of spinal reflex circuitry, assessed using the rate-sensitive depression of the H-reflex from an interosseous muscle. Histological analysis of spinal cords grafted with olfactory tissue demonstrated nerve fibres passing through the transection site, serotonin-positive fibres in the spinal cord distal to the transection site, and retrograde labelling of brainstem raphe and gigantocellularis neurons from injections into the distal cord, indicating regeneration of descending pathways. Thus, olfactory lamina propria transplantation promoted partial restoration of function after relatively short recovery periods. This study is particularly significance because it suggests an accessible source of tissue for autologous grafting in human paraplegia.

Carbon filaments direct the growth of postlesional plastic axons after spinal cord injury

The effect of implantation of carbon filaments and fetal tissues on the axonal regeneration following contusion injury in a rat model was investigated by in situ immunofluorescence. Female Sprague-Dawley rats were subjected to severe contusion injury to the spinal cord at T9-T10. All animals were divided into 5 groups (N = 5/group): normal controls. surgical controls, with carbon filament implants, with fetal tissue implants and with implants consisting of fetal tissue cocultured with carbon filaments. After a 10-week survival period, the astroglial response was assessed by immunoreactive glial fibrillary acidic protein and the neuro-axonal profile by immunoreactive phosphorylated and nonphosphorylated neurofilament proteins. The contusion injury resulted in: (a) dramatically increased immunoreactivity of glial fibrillary acidic protein indicating injury-associated reactive astrogliosis, (b) increase in immunoreactive phosphorylated neurofilament protein indicating upregulated phosphorylation of neurofilament protein, (c) with no change in the highly differentiated nonphosphorylated neurofilament protein which normally occur in the nonregenerating mature neurons. Implantation of fetal tissues alone following contusion injury did not show any appreciable change with regard to the immunoreactivities for the glial and neuronal markers studied, compared to the injury controls. However, the implantation of carbon filaments alone or together with fetal tissues directed the growth of glial fibrillary acidic protein-positive astroglia and phosphoneurofilament-positive neurites along the carbon fibers, with no effect on nonphosphoneurofilament protein. In conclusion, implantation of carbon filaments appears to be critical for facilitating the attachment of astroglia forming a substrate and scaffolding that can further support and direct the growth of postlesional plastic axons across the lesion. In addition, carbon filament prostheses in combination with fetal tissue implants provides an improved combinational approach to promote regrowth of injured neurons following injury.

Regrowth of axons into the distal spinal cord through a Schwann-cell-seeded mini-channel implanted into hemisected adult rat spinal cord

Schwann cells (SCs) have been shown to be a key element in promoting axonal regeneration after being grafted into the central nervous system (CNS). In the present study, SC-supported axonal regrowth was tested in an adult rat spinal cord implantation model. This model is characterized by a right spinal cord hemisection at the eighth thoracic segment, implantation of a SC-containing mini-channel and restoration of cerebrospinal fluid circulation by suturing the dura. We demonstrate that a tissue cable containing grafted SCs formed an effective bridge between the two stumps of the hemicord 1 month after transplantation. Approximately 10 000 myelinated and unmyelinated axons (1 : 9) per cable were found at its midpoint. In addition to propriospinal axons and axons of peripheral nervous system (PNS) origin, axons from as many as 19 brainstem regions also grew into the graft without additional treatments. Most significantly, some regenerating axons in the SC grafts were able to penetrate through the distal graft-host interface to re-enter the host environment, as demonstrated by anterograde axonal labelling. These axons coursed toward, and then entered the grey matter where terminal bouton-like structures were observed. In channels containing no SCs, limited axonal growth was seen within the graft and no axons penetrated the distal interface. These findings further support the notion that SCs are strong promotors of axonal regeneration and that the mini-channel model may be appropriate for further investigation of axonal re-entry, synaptic reconnection and functional recovery following spinal cord injury.

Orientation of cell adhesion and growth on patterned heterogeneous polystyrene surface

Studies of neurite outgrowth or cell migration, two important processes in neuronal networks formation, are facilitated by cell culture models capable of orientating cellular growth and of designing a well-defined cellular pattern. Heterogeneous polystyrene surfaces composed of oxygen plasma-treated stripes (PSox) with a low hydrophobicity separated by non-treated areas (PS) have these properties. In this study, to guide cell growth, we developed a cell culture model using these supports and we identified the molecular factors involved in cellular orientation. When the heterogeneous supports were not coated, proteins from a serum culture medium were required for cells to line up on PSox. On the other hand, cell orientation on coated surfaces was clearly influenced by competitive adsorption of adhesive proteins such as fibronectin or collagen and anti-adhesive molecules as pluronic F68 or albumin. Attachment factors were adsorbed on PSox stripes while adsorption of anti-adhesive molecules on the most hydrophobic PS areas prevented cell adhesion or growth. Thus, we describe the preparation of a cell culture substrate that succeeded in orientating cell growth and that led to a line of cells on adhesive PSox stripes ranging from 2 to 100 microns width.

Preparation of brain-derived neurotrophic factor- and neurotrophin-3-secreting Schwann cells by infection with a retroviral vector

One reason that the central nervous system of adult mammals does not regenerate after injury is that neurotrophic factors are present only in low concentrations in these tissues. Recent studies have shown that the application of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) acts to encourage the regrowth of motor and sensory fibers after spinal cord injury. Other studies have reported that the regrowth of axons after injury was enhanced by the implantation of Schwann cells, which normally secrete BDNF and NT-3. The purpose of the present study was to genetically modify Schwann cells to secrete increased amounts of BDNF or NT-3 by infection with a retroviral vector. Retroviral vectors were constructed by the ligation of BDNF or NT-3 cDNA to the LXSN vector. Viruses were generated from the plasmid forms of the vectors by transient transfection of PA317 amphotrophic retroviral packaging cells. Viruses were harvested and used to infect the human Schwann cell line designated NF-1T. Northern blot analysis of poly (A+) RNA prepared from Schwann cells that were infected with BDNF- or NT-3-containing virus showed the presence of BDNF or NT-3 mRNA. An enzyme-linked immunosorbent assay (ELISA) for BDNF and NT-3 was performed on media the cells were grown in, and on cellular extracts prepared from the BDNF- and NT-3-infected Schwann cells. The ELISA results demonstrated that the Schwann cells were secreting increased levels of immunologically active BDNF or NT-3. Immunocytochemical staining of these cells revealed the presence of these two neurotrophic factors located in perinuclear granules. These neurotrophic factor-secreting Schwann cells are currently being evaluated for their efficacy in the treatment of spinal cord injury.

Static and dynamic fatigue properties of carbon ligament prosthesis

The aim of the present paper was to characterize the static and dynamic mechanical properties of carbon braids used in medicine as prostheses of ligaments and tendons. A computing system (PC software) was used to register and analyze the data of mechanical tests. Tensile static tests (creep testing) were utilized to determine the failure-free value of static force. Fatigue dynamic properties of carbon braids in tensile-tensile cyclic tests including the effect of simulated body conditions were analyzed. The braids were immersed in isotonic solution at 37 degrees C. Fatigue life was markedly lowered in air in comparison with simulated body conditions. For a given value of maximum cyclic force, decreasing the minimum/maximum force ratio decreased the number of cycles to failure. The mechanical approach of fatigue behavior based on approximately maximum fatigue force and number of cycles to failure by analytical expression was given. Energy dissipation due to the hysteresis loop was considered.

Electrophysiological improvement after co-implantation of carbon filaments and fetal tissue in the contused rat spinal cord

The electrophysiological integrity of the adult rat spinal cord was assessed at the lumbar, lower cervical and cortical levels after the animals sustained a severe contusion injury at the mid-thoracic level (T8) and received either carbon filament cultured with fetal spinal cord tissue implants, fetal tissue implants, or carbon filament implants alone. Somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) were recorded from all animal groups at the end of the 8-week survival period. The results of this study demonstrate that the spinal cord injured animals that received carbon filament cultured with fetal spinal cord tissue implants had the highest degree of electrophysiological recovery, indicating that this combination plays an important role in promoting recovery after injury.

Sprouting and regeneration of lesioned corticospinal tract fibres in the adult rat spinal cord

We have studied the effects of tissue transplants and antibodies (IN-1) against the myelin-associated neurite growth inhibitory proteins on sprouting and regeneration of the rat corticospinal tract (CST). Transplantation of embryonic spinal cord tissue into bilateral transection lesions of the lower thoracic spinal cord in young adult rats resulted in a marked increase of the sprouting of the lesioned CST. This sprouting effect was probably elicited by soluble factors released from the transplants, and was enhanced by the IN-1 antibodies. The retraction of lesioned CST fibres normally observed with prolonged survival times was also reduced by the presence of transplants. In spite of these growth-promoting effects of the transplants, the regenerative elongation of CST sprouts into the caudal spinal cord was dependent upon the neutralization of the myelin-associated inhibitory proteins. In the controls (no antibodies or control antibodies) only 27% of the animals showed elongation of CST fibres exceeding the sprouting distance of 0.7 mm. These fibres grew to a maximal length of 1.8 mm (mean +/- SEM, 1.2 +/- 0.1). In contrast, 60% of the IN-1-treated, transplant-containing rats showed elongations of > 0.7 mm, and these fibres grew up to 10.1 mm (4.6 +/- 0.5). Regenerating fibres crossed the lesion site through remaining tissue bridges. Neither embryonic spinal cord transplants nor a variety of implanted bridge materials could serve as a substrate for the regenerating CST axons.

Tissue engineering in the USA

Tissue engineering is the application of the principles and methods of engineering and the life sciences towards the development of biological substitutes to restore, maintain or improve functions. It is an area which is emerging in importance worldwide. In the USA it has been actively fostered by the National Science Foundation, both through research grants and the sponsorship of a series of workshops starting in 1988. This brief review of activities in the USA focuses on cell culture technology as a foundation for tissue engineering and then discusses examples of applications. These include artificial skin and the use of encapsulated cells in the development of bioartificial organs. Also discussed is the reconstitution of a blood vessel in culture, both for use in basic research and for implantation as an artificial blood vessel in bypass surgery. In conclusion, other potential applications are mentioned as well as generic areas of technology for future development.