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

Cell Transplantation and Neuroengineering Approach for Spinal Cord Injury Treatment: A Summary of Current Laboratory Findings and Review of Literature

Spinal cord injury (SCI) can cause severe traumatic injury to the central nervous system (CNS). Current therapeutic effects achieved for SCI in clinical medicine show that there is still a long way to go to reach the desired goal of full or significant functional recovery. In basic medical research, however, cell transplantation, gene therapy, application of cytokines, and biomaterial scaffolds have been widely used and investigated as treatments for SCI. All of these strategies when used separately would help rebuild, to some extent, the neural circuits in the lesion area of the spinal cord. In light of this, it is generally accepted that a combined treatment may be a more effective strategy. This review focuses primarily on our recent series of work on transplantation of Schwann cells and adult stem cells, and transplantation of stem cell-derived neural network scaffolds with functional synapses. Arising from this, an artificial neural network (an exogenous neuronal relay) has been designed and fabricated by us—a biomaterial scaffold implanted with Schwann cells modified by the neurotrophin-3 (NT-3) gene and adult stem cells modified with the TrkC (receptor of NT-3) gene. More importantly, experimental evidence suggests that the novel artificial network can integrate with the host tissue and serve as an exogenous neuronal relay for signal transfer and functional improvement of SCI.

Schwann Cells Migration on Patterned Polydimethylsiloxane Microgrooved Surface

Schwann cells (SCs) aid in nerve repair in the peripheral nervous system, and their ability to migrate into the injury site is critical for nerve regeneration after injury. The majority of studies on SC behavior have focused on SC alignment through contact guidance, rather than migration. The few studies on SC migration primarily investigated the migration of individual cells over several hours with time-lapse microscopy. However, during neural tissue repair, SCs do not migrate as single cells but as a population of cells over physiologically relevant time and length scales. Thus from a practical perspective, there is a need to understand the migration of large populations of SC and the collective guidance cues from the surrounding environment in designing optimal transplantable scaffolds. This study investigates a large population of migrating SCs over a period of 2 weeks on patterned polydimethylsiloxane (PDMS) microgrooved channels of different sizes. Two methods were used to quantify the migration velocity of a large cell population that minimized the confounding effect due to cell proliferation: one based on a leading edge velocity and a second based on a binary velocity. Both approaches showed that the SC population migrated the fastest on the smallest sized microgrooved channels. The insights provided in this study could inform on future designs of transplantable scaffolds for peripheral nerve regeneration.

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.

Cellular transplantation-based evolving treatment options in spinal cord injury

Spinal cord injury (SCI) often represents a condition of permanent neurologic deficit. It has been possible to understand and delineate the mechanisms contributing to loss of function following primary injury. The clinicians might hope to improve the outcome in SCI injury by designing treatment strategies that could target these secondary mechanisms of response to injury. However, the approaches like molecular targeting of the neurons or surgical interventions have yielded very limited success till date. In recent times, a great thrust is put on to the cellular transplantation mode of treatment strategies to combat SCI problems so as to gain maximum functional recovery. In this review, we discuss about the various cellular transplantation strategies that could be employed in the treatment of SCI. The success of such cellular approaches involving Schwann cells, olfactory ensheathing cells, peripheral nerve, embryonic CNS tissue and activated macrophage has been supported by a number of reports and has been detailed here. Many of these cell transplantation strategies have reached the clinical trial stages. Also, the evolving field of stem cell therapy has made it possible to contemplate the role of both embryonic stem cells and induced pluripotent stem cells to stimulate the differentiation of neurons when transplanted in SCI models. Moreover, the roles of tissue engineering techniques and synthetic biomaterials have also been explained with their beneficial and deleterious effects. Many of these cell-based therapeutic approaches have been able to cause only a little change in recovery and a combinatorial approach involving more than one strategy are now being tried out to successfully treat SCI and improve functional recovery.

Development of a 3D matrix for modeling mammalian spinal cord injury in vitro

Spinal cord injury affects millions of people around the world, however, limited therapies are available to improve the quality of life of these patients. Spinal cord injury is usually modeled in rats and mice using contusion or complete transection models and this has led to a deeper understanding of the molecular and cellular complexities of the injury. However, it has not to date led to development of successful novel therapies, this is in part due to the complexity of the injury and the difficulty of deciphering the exact roles and interactions of different cells within this complex environment. Here we developed a collagen matrix that can be molded into the 3D tubular shape with a lumen and can hence support cell interactions in a similar architecture to a spinal cord. We show that astrocytes can be successfully grown on this matrix in vitro and when injured, the cells respond as they do in vivo and undergo reactive gliosis, one of the steps that lead to formation of a glial scar, the main barrier to spinal cord regeneration. In the future, this system can be used to quickly assess the effect of drugs on glial scar protein activity or to perform live imaging of labeled cells after exposure to drugs.

Biochemical Monitoring of Spinal Cord Injury by FT-IR Spectroscopy--Effects of Therapeutic Alginate Implant in Rat Models

Spinal cord injury (SCI) induces complex biochemical changes, which result in inhibition of nervous tissue regeneration abilities. In this study, Fourier-transform infrared (FT-IR) spectroscopy was applied to assess the outcomes of implants made of a novel type of non-functionalized soft calcium alginate hydrogel in a rat model of spinal cord hemisection (n = 28). Using FT-IR spectroscopic imaging, we evaluated the stability of the implants and the effects on morphology and biochemistry of the injured tissue one and six months after injury. A semi-quantitative evaluation of the distribution of lipids and collagen showed that alginate significantly reduced injury-induced demyelination of the contralateral white matter and fibrotic scarring in the chronic state after SCI. The spectral information enabled to detect and localize the alginate hydrogel at the lesion site and proved its long-term persistence in vivo. These findings demonstrate a positive impact of alginate hydrogel on recovery after SCI and prove FT-IR spectroscopic imaging as alternative method to evaluate and optimize future SCI repair strategies.

Intrinsic and extrinsic determinants of central nervous system axon outgrowth into alginate-based anisotropic hydrogels

Appropriate target reinnervation and functional recovery after spinal cord injury depend on longitudinally directed regrowth of injured axons. Anisotropic alginate-based capillary hydrogels (ACH) support peripheral nervous system derived axon growth, which is accompanied by glial supporting cell migration into the ACH. The aim of the present study was to analyze central nervous system (CNS) derived (entorhinal cortex, spinal cord slice cultures) axon regrowth into ACH containing linearly aligned capillaries of defined capillary sizes without and with gelatin constituent. Anisotropic ACH were prepared by ionotropic gel formation using Ba(2+), Cu(2+), Sr(2+), or Zn(2+) ions resulting in gels with average capillary diameters of 11, 13, 29, and 89μm, respectively. Postnatal rat entorhinal cortex or spinal cord slice cultures were placed on top of 500μm thick ACH. Seven days later axon growth and astroglial migration into the ACH were determined. Axon density within capillaries correlated positively with increasing capillary diameters, whereas longitudinally oriented axon outgrowth diminished with increasing capillary diameter. Axons growing into the hydrogels were always accompanied by astrocytes strongly suggesting that respective cells are required to mediate CNS axon elongation into ACH. Overall, midsize capillary diameter ACH appeared to be the best compromise between axon density and orientation. Taken together, ACH promote CNS axon ingrowth, which is determined by the capillary diameter and migration of slice culture derived astroglia into the hydrogel.

STATEMENT OF SIGNIFICANCE

Biomaterials are investigated as therapeutic tools to bridge irreversible lesions following traumatic spinal cord injury. The goal is to develop biomaterials, which promote longitudinally oriented regeneration of as many injured axons as possible as prerequisite for substantial functional recovery. Optimal parameters of the biomaterial have yet to be defined. In the present study we show that increasing capillary diameters within such hydrogels enhanced central nervous system axon regeneration at the expense of longitudinal orientation. Axon ingrowth into the hydrogels was only observed in the presence of glial supporting cells, namely astrocytes. This suggests that alginate-based hydrogels need to be colonized with respective cells in order to facilitate axon ingrowth.

Biomaterial Approaches to Enhancing Neurorestoration after Spinal Cord Injury: Strategies for Overcoming Inherent Biological Obstacles

While advances in technology and medicine have improved both longevity and quality of life in patients living with a spinal cord injury, restoration of full motor function is not often achieved. This is due to the failure of repair and regeneration of neuronal connections in the spinal cord after injury. In this review, the complicated nature of spinal cord injury is described, noting the numerous cellular and molecular events that occur in the central nervous system following a traumatic lesion. In short, postinjury tissue changes create a complex and dynamic environment that is highly inhibitory to the process of neural regeneration. Strategies for repair are outlined with a particular focus on the important role of biomaterials in designing a therapeutic treatment that can overcome this inhibitory environment. The importance of considering the inherent biological response of the central nervous system to both injury and subsequent therapeutic interventions is highlighted as a key consideration for all attempts at improving functional recovery.

Drug delivery, cell-based therapies, and tissue engineering approaches for spinal cord injury

Spinal cord injury (SCI) results in devastating neurological and pathological consequences, causing major dysfunction to the motor, sensory, and autonomic systems. The primary traumatic injury to the spinal cord triggers a cascade of acute and chronic degenerative events, leading to further secondary injury. Many therapeutic strategies have been developed to potentially intervene in these progressive neurodegenerative events and minimize secondary damage to the spinal cord. Additionally, significant efforts have been directed toward regenerative therapies that may facilitate neuronal repair and establish connectivity across the injury site. Despite the promise that these approaches have shown in preclinical animal models of SCI, challenges with respect to successful clinical translation still remain. The factors that could have contributed to failure include important biologic and physiologic differences between the preclinical models and the human condition, study designs that do not mirror clinical reality, discrepancies in dosing and the timing of therapeutic interventions, and dose-limiting toxicity. With a better understanding of the pathobiology of events following acute SCI, developing integrated approaches aimed at preventing secondary damage and also facilitating neuroregenerative recovery is possible and hopefully will lead to effective treatments for this devastating injury. The focus of this review is to highlight the progress that has been made in drug therapies and delivery systems, and also cell-based and tissue engineering approaches for SCI.

Effects of brain‑derived neurotrophic factor and neurotrophin‑3 on the neuronal differentiation of rat adipose‑derived stem cells

Tissue engineering is a promising method that may be used to treat spinal cord injury (SCI). The underlying repair mechanism of tissue engineering involves the stable secretion of neurotrophins from seed cells, which eventually differentiate into neurons; therefore, the selection of appropriate seed cells, which stably secrete neurotrophins that easily differentiate into neurons requires investigation. Adipose‑derived stem cells (ADSCs), which are adult SCs, are advantageous due to convenience sampling and easy expansion; therefore, ADSCs are currently the most popular type of seed cell. Brain‑derived neurotrophic factor (BDNF) and neurotrophin‑3 (NT‑3) possess superior properties, when compared with other neurotrophic factors, in the maintenance of neuronal survival and promotion of SC differentiation into neurons. The present study used two lentiviruses, which specifically express BDNF and NT‑3 [Lenti‑BDNF‑green fluorescent protein (GFP), Lenti‑NT‑3‑red fluorescent protein (RFP)], to transfect third‑generation ADSCs. Three types of seed cell were obtained: i) Seed cells overexpressing BDNF (ADSC/Lenti‑BDNF‑GFP); ii) seed cells overexpressing NT‑3 (ADSC/Lenti‑NT‑3‑RFP); and iii) seed cells overexpressing BDNF and NT‑3 (ADSC/Lenti‑BDNF‑GFP and NT‑3‑RFP). The transfected cells were then induced to differentiate into neurons and were divided into a further four groups: i) The BDNF and NT‑3 co‑overexpression group; ii) the BDNF overexpression group; iii) the NT‑3 overexpression group; and iv) the control group, which consisted of untransfected ADSCs. The results of the present study demonstrate that BDNF and NT‑3 expression was higher 10 days after induction, as detected by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blotting. Neuron‑specific enolase is a neuronal marker, the expression of which was highest in the BDNF and NT‑3 co‑overexpression group, followed by the BDNF overexpression group and then by the NT‑3 overexpression group. The lowest expression levels of NSE were detected in the control group, as determined by RT‑qPCR, western blotting and immunofluorescent staining. These results indicate that BDNF and NT‑3 exert a synergistic effect, which may promote the neuronal differentiation of ADSCs. The present study provides a solid theoretical foundation for future experiments regarding the use of tissue engineering technology for the treatment of SCI.

Biodegradable PEG-Based Amphiphilic Block Copolymers for Tissue Engineering Applications

Biodegradable tissue engineering scaffolds have great potential for delivering cells/therapeutics and supporting tissue formation. Polyesters, the most extensively investigated biodegradable synthetic polymers, are not ideally suited for diverse tissue engineering applications due to limitations associated with their hydrophobicity. This review discusses the design and applications of amphiphilic block copolymer scaffolds integrating hydrophilic poly(ethylene glycol) (PEG) blocks with hydrophobic polyesters. Specifically, we highlight how the addition of PEG results in striking changes to the physical properties (swelling, degradation, mechanical, handling) and biological performance (protein & cell adhesion) of the degradable synthetic scaffolds in vitro. We then perform a critical review of how these in vitro characteristics translate to the performance of biodegradable amphiphilic block copolymer-based scaffolds in the repair of a variety of tissues in vivo including bone, cartilage, skin, and spinal cord/nerve. We conclude the review with recommendations for future optimizations in amphiphilic block copolymer design and the need for better-controlled in vivo studies to reveal the true benefits of the amphiphilic synthetic tissue scaffolds.

Extracellular matrices, artificial neural scaffolds and the promise of neural regeneration

Over last 20 years, extracellular matrices have been shown to be useful in promoting tissue regeneration. Recently, they have been used and have had success in achieving neurogenesis. Recent developments in extracellular matrix design have allowed their successful in vivo incorporation to engender an environment favorable for neural regeneration in animal models. Promising treatments under investigation include manipulation of the intrinsic extracellular matrix and incorporation of engineered naometer-sized scaffolds through which inhibition of molecules serving as barriers to neuroregeneration and delivery of neurotrophic factors and/or cells for successful tissue regeneration can be achieved. Further understanding of the changes incurred within the extracellular matrix following central nervous system injury will undoubtedly help design a clinically efficacious extracellular matrix scaffold that can mitigate or reverse neural degeneration in the clinical setting.

Novel nanometer scaffolds regulate the biological behaviors of neural stem cells

Ideal tissue-engineered scaffold materials regulate proliferation, apoptosis and differentiation of cells seeded on them by regulating gene expression. In this study, aligned and randomly oriented collagen nanofiber scaffolds were prepared using electronic spinning technology. Their diameters and appearance reached the standards of tissue-engineered nanometer scaffolds. The nanofiber scaffolds were characterized by a high swelling ratio, high porosity and good mechanical properties. The proliferation of spinal cord-derived neural stem cells on novel nanofiber scaffolds was obviously enhanced. The proportions of cells in the S and G2/M phases noticeably increased. Moreover, the proliferation rate of neural stem cells on the aligned collagen nanofiber scaffolds was high. The expression levels of cyclin D1 and cyclin-dependent kinase 2 were increased. Bcl-2 expression was significantly increased, but Bax and caspase-3 gene expressions were obviously decreased. There was no significant difference in the differentiation of neural stem cells into neurons on aligned and randomly oriented collagen nanofiber scaffolds. These results indicate that novel nanofiber scaffolds could promote the proliferation of spinal cord-derived neural stem cells and inhibit apoptosis without inducing differentiation. Nanofiber scaffolds regulate apoptosis and proliferation in neural stem cells by altering gene expression.

Electrospinning growth factor releasing microspheres into fibrous scaffolds

This procedure describes a method to fabricate a multifaceted substrate to direct nerve cell growth. This system incorporates mechanical, topographical, adhesive and chemical signals. Mechanical properties are controlled by the type of material used to fabricate the electrospun fibers. In this protocol we use 30% methacrylated Hyaluronic Acid (HA), which has a tensile modulus of ~500 Pa, to produce a soft fibrous scaffold. Electrospinning on to a rotating mandrel produces aligned fibers to create a topographical cue. Adhesion is achieved by coating the scaffold with fibronectin. The primary challenge addressed herein is providing a chemical signal throughout the depth of the scaffold for extended periods. This procedure describes fabricating poly(lactic-co-glycolic acid) (PLGA) microspheres that contain Nerve Growth Factor (NGF) and directly impregnating the scaffold with these microspheres during the electrospinning process. Due to the harsh production environment, including high sheer forces and electrical charges, protein viability is measured after production. The system provides protein release for over 60 days and has been shown to promote primary nerve cell growth.

Comparison of cellular architecture, axonal growth, and blood vessel formation through cell-loaded polymer scaffolds in the transected rat spinal cord

The use of multichannel polymer scaffolds in a complete spinal cord transection injury serves as a deconstructed model that allows for control of individual variables and direct observation of their effects on regeneration. In this study, scaffolds fabricated from positively charged oligo[poly(ethylene glycol)fumarate] (OPF(+)) hydrogel were implanted into rat spinal cords following T9 complete transection. OPF(+) scaffold channels were loaded with either syngeneic Schwann cells or mesenchymal stem cells derived from enhanced green fluorescent protein transgenic rats (eGFP-MSCs). Control scaffolds contained extracellular matrix only. The capacity of each scaffold type to influence the architecture of regenerated tissue after 4 weeks was examined by detailed immunohistochemistry and stereology. Astrocytosis was observed in a circumferential peripheral channel compartment. A structurally separate channel core contained scattered astrocytes, eGFP-MSCs, blood vessels, and regenerating axons. Cells double-staining with glial fibrillary acid protein (GFAP) and S-100 antibodies populated each scaffold type, demonstrating migration of an immature cell phenotype into the scaffold from the animal. eGFP-MSCs were distributed in close association with blood vessels. Axon regeneration was augmented by Schwann cell implantation, while eGFP-MSCs did not support axon growth. Methods of unbiased stereology provided physiologic estimates of blood vessel volume, length and surface area, mean vessel diameter, and cross-sectional area in each scaffold type. Schwann cell scaffolds had high numbers of small, densely packed vessels within the channels. eGFP-MSC scaffolds contained fewer, larger vessels. There was a positive linear correlation between axon counts and vessel length density, surface density, and volume fraction. Increased axon number also correlated with decreasing vessel diameter, implicating the importance of blood flow rate. Radial diffusion distances in vessels significantly correlated to axon number as a hyperbolic function, showing a need to engineer high numbers of small vessels in parallel to improving axonal densities. In conclusion, Schwann cells and eGFP-MSCs influenced the regenerating microenvironment with lasting effect on axonal and blood vessel growth. OPF(+) scaffolds in a complete transection model allowed for a detailed comparative, histologic analysis of the cellular architecture in response to each cell type and provided insight into physiologic characteristics that may support axon regeneration.

Directed axonal outgrowth using a propagating gradient of IGF-1

The temporospatial regulation of axon outgrowth is useful for guiding de novo connectivity or re-connectivity of neurons in neurological injury or disease. Here we report the successful construction of a biocompatible guidance device, in which a linear propagation of IGF-1 gradient sequentially directs axon outgrowth. We observe the extensive in vitro axonal extension over 5 mm with a desired growth rate of ∼ 1 mm/day.

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.

Poly(trimethylene carbonate-co-ε-caprolactone) promotes axonal growth

Mammalian central nervous system (CNS) neurons do not regenerate after injury due to the inhibitory environment formed by the glial scar, largely constituted by myelin debris. The use of biomaterials to bridge the lesion area and the creation of an environment favoring axonal regeneration is an appealing approach, currently under investigation. This work aimed at assessing the suitability of three candidate polymers – poly(ε-caprolactone), poly(trimethylene carbonate-co-ε-caprolactone) (P(TMC-CL)) (11∶89 mol%) and poly(trimethylene carbonate) - with the final goal of using these materials in the development of conduits to promote spinal cord regeneration. Poly(L-lysine) (PLL) coated polymeric films were tested for neuronal cell adhesion and neurite outgrowth. At similar PLL film area coverage conditions, neuronal polarization and axonal elongation was significantly higher on P(TMC-CL) films. Furthermore, cortical neurons cultured on P(TMC-CL) were able to extend neurites even when seeded onto myelin. This effect was found to be mediated by the glycogen synthase kinase 3β (GSK3β) signaling pathway with impact on the collapsin response mediator protein 4 (CRMP4), suggesting that besides surface topography, nanomechanical properties were implicated in this process. The obtained results indicate P(TMC-CL) as a promising material for CNS regenerative applications as it promotes axonal growth, overcoming myelin inhibition.

The preparation and comparison of decellularized nerve scaffold of tissue engineering

To integrate tissue engineering concepts into strategies to repair spinal cord injury (SCI) has been a hotspot in recent years, and the choice of scaffolding material is crucial to tissue engineering. Recently, decellularized nerve scaffold becomes a central concern due to its peculiar superiority. In this study, the decellularized nerve scaffold was prepared with three different methods and a comparison was made to acquire an ideal scaffold materials. All sciatic nerves from Sprague-Dawley (SD) rats were randomly divided into four groups: A: normal control group, B: TritonX-100 with sodium deoxycholate group, C: TritonX-100 with enzyme group and D: freezing-thawing with enzyme group. Histology and transmission electron microscope were exploited to evaluate the effect of removing cells and immunological histological chemistry was exploited to evaluate immunogenicity. Meanwhile the mechanical properties were evaluated by mechanics index. Hematoxylin and eosin (HE) staining and electron microscopic examinations reveal that the cell components and myelin sheaths are the least in the freezing-thawing with enzyme group. Immunohistochemistry shows that the immunogenicity is lower in group B, C, and D than the control group, and the group D has the lowest immunogenicity. Mechanical testing shows that there is no significant difference after acellular processing. Sciatic nerve, cell-extracted by freezing-thawing with enzyme, could obtain the ideal scaffold materials which has no cells and myelin sheaths. In addition, the decellularized nerve scaffold has no immunogenicity and the mechanical property of normal sciatic nerve is preserved.

Nanoparticulate strategies for the five R’s of traumatic spinal cord injury intervention: restriction, repair, regeneration, restoration and reorganization

Nanomedicinal approaches for spinal cord injury (SCI) intervention encompasses the use of nanoscale materials and devices that prevent primary to secondary injury transition and improvement in the anatomical, physiological and functional outcomes of SCI. This review provides an incursion into the advances in nanoparticle-based neurotherapeutics for SCI and focuses on neuroactive-loaded nanoparticles for localized delivery of therapeutic factors to the severed spinal cord, targeted or nontargeted systemic drug delivery and nanoenclatherated neuroscaffolds. Special emphasis has been placed on the use of metal nanoparticles and functionalized structures as ‘drug-free’ interventions in SCI. Despite the immense advancements in nanoscience, nanointerventions still pose key challenges that need to be resolved in SCI. Several combinatorial strategies are proposed for the reconstruction of spinal architecture via restriction of the secondary injury cascade, reparation of the tethered neural architecture, regeneration of axons, restoration of biochemical functions and reorganization of the topographical and cortical networks of the spinal cord.

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.

Enhanced GLT-1 mediated glutamate uptake and migration of primary astrocytes directed by fibronectin-coated electrospun poly-L-lactic acid fibers

Bioengineered fiber substrates are increasingly studied as a means to promote regeneration and remodeling in the injured central nervous system (CNS). Previous reports largely focused on the ability of oriented scaffolds to bridge injured regions and direct outgrowth of axonal projections. In the present work, we explored the effects of electrospun microfibers on the migration and physiological properties of brain astroglial cells. Primary rat astrocytes were cultured on either fibronectin-coated poly-L-lactic acid (PLLA) films, fibronectin-coated randomly oriented PLLA electrospun fibers, or fibronectin-coated aligned PLLA electrospun fibers. Aligned PLLA fibers strongly altered astrocytic morphology, orienting cell processes, actin microfilaments, and microtubules along the length of the fibers. On aligned fibers, astrocytes also significantly increased their migration rates in the direction of fiber orientation. We further investigated if fiber topography modifies astrocytic neuroprotective properties, namely glutamate and glutamine transport and metabolism. This was done by quantifying changes in mRNA expression (qRT-PCR) and protein levels (Western blotting) for a battery of relevant biomolecules. Interestingly, we found that cells grown on random and/or aligned fibers increased the expression levels of two glutamate transporters, GLAST and GLT-1, and an important metabolic enzyme, glutamine synthetase, as compared to the fibronectin-coated films. Functional assays revealed increases in glutamate transport rates due to GLT-1 mediated uptake, which was largely determined by the dihydrokainate-sensitive GLT-1. Overall, this study suggests that aligned PLLA fibers can promote directed astrocytic migration, and, of most importance, our in vitro results indicate for the first time that electrospun PLLA fibers can positively modify neuroprotective properties of glial cells by increasing rates of glutamate uptake.

Nanomedicine for treating spinal cord injury

Spinal cord injury results in significant mortality and morbidity, lifestyle changes, and difficult rehabilitation. Treatment of spinal cord injury is challenging because the spinal cord is both complex to treat acutely and difficult to regenerate. Nanomaterials can be used to provide effective treatments; their unique properties can facilitate drug delivery to the injury site, enact as neuroprotective agents, or provide platforms to stimulate regrowth of damaged tissues. We review recent uses of nanomaterials including nanowires, micelles, nanoparticles, liposomes, and carbon-based nanomaterials for neuroprotection in the acute phase. We also review the design and neural regenerative application of electrospun scaffolds, conduits, and self-assembling peptide scaffolds.

A mechanical microconnector system for restoration of tissue continuity and long-term drug application into the injured spinal cord

Complete transection of the spinal cord leaves a gap of several mm which fills with fibrous scar tissue. Several approaches in rodent models have used tubes, foams, matrices or tissue implants to bridge this gap. Here, we describe a mechanical microconnector system (mMS) to re-adjust the retracted spinal cord stumps. The mMS is a multi-channel system of polymethylmethacrylate (PMMA), designed to fit into the spinal cord tissue gap after transection, with an outlet tubing system to apply negative pressure to the mMS thus sucking the spinal cord stumps into the honeycomb-structured holes. The stumps adhere to the microstructure of the mMS walls and remain in the mMS after removal of the vacuum. We show that the mMS preserves tissue integrity and allows axonal regrowth at 2, 5 and 19 weeks post lesion with no adverse tissue effects like in-bleeding or cyst formation. Preliminary assessment of locomotor function in the open field suggested beneficial effects of the mMS. Additional inner micro-channels enable local substance delivery into the lesion center via an attached osmotic minipump. We suggest that the mMS is a suitable device to adapt and stabilize the injured spinal cord after surgical resection of scar tissue (e.g., for chronic patients) or traumatic injuries with large tissue and bone damages.

Biocompatibility study of a silk fibroin-chitosan scaffold with adipose tissue-derived stem cells in vitro

The use of tissue engineering technology in the repair of spinal cord injury (SCI) is a topic of current interest. The success of the repair of the SCI is directly affected by the selection of suitable seed cells and scaffold materials with an acceptable biocompatibility. In this study, adipose tissue-derived stem cells (ADSCs) were incorporated into a silk fibroin-chitosan scaffold (SFCS), which was constructed using a freeze-drying method, in order to assess the biocompatibility of the ADSCs and the SFCS and to provide a foundation for the use of tissue engineering technology in the repair of SCI. Following the seeding of the cells onto the scaffold, the adhesion characteristics of the ADSCs and the SFCS were assessed. A significant difference was observed between the experimental group (a composite of the ADSCs with the SFCS) and the control group (ADSCs without the scaffold) following a culture period of 6 h (P<0.05). The differences in the results at the following time-points were statistically insignificant (P>0.05). The use of an MTT assay to assess the proliferation of the cells on the scaffold revealed that there were significant differences between the experimental and control groups following culture periods of 2 and 4 days (P<0.05). However, the results at the subsequent time-points were not statistically significantly different (P>0.05). Scanning electron microscopy (SEM), using hematoxylin and eosin (H&E) staining, was used to observe the cellular morphology following seeding, and this revealed that the cells displayed the desired morphology. The results indicate that ADSCs have a good biocompatibility with a SFCS and thus provide a foundation for further studies using tissue engineering methods for the repair of SCI.

Biomaterial-based interventions for neuronal regeneration and functional recovery in rodent model of spinal cord injury: a systematic review

CONTEXT

There is considerable interest in translating laboratory advances in neuronal regeneration following spinal cord injury (SCI). A multimodality approach has been advocated for successful functional neuronal regeneration. With this goal in mind several biomaterials have been employed as neuronal bridges either to support cellular transplants, to release neurotrophic factors, or to do both. A systematic review of this literature is lacking. Such a review may provide insight to strategies with a high potential for further investigation and potential clinical application.

OBJECTIVE

To systematically review the design strategies and outcomes after biomaterial-based multimodal interventions for neuronal regeneration in rodent SCI model. To analyse functional outcomes after implantation of biomaterial-based multimodal interventions and to identify predictors of functional outcomes.

METHODS

A broad PubMed, CINHAL, and a manual search of relevant literature databases yielded data from 24 publications; 14 of these articles included functional outcome information. Studies reporting behavioral data in rat model of SCI and employing biodegradable polymer-based multimodal intervention were included. For behavioral recovery, studies using severe injury models (transection or severe clip compression (>16.9 g) or contusion (50 g/cm)) were categorized separately from those investigating partial injury models (hemisection or moderate-to-severe clip compression or contusion).

RESULTS

The cumulative mean improvements in Basso, Beattie, and Bresnahan scores after biomaterial-based interventions are 5.93 (95% CI = 2.41 - 9.45) and 4.44 (95% CI = 2.65 - 6.24) for transection and hemisection models, respectively. Factors associated with improved outcomes include the type of polymer used and a follow-up period greater than 6 weeks.

CONCLUSION

The functional improvement after implantation of biopolymer-based multimodal implants is modest. The relationship with neuronal regeneration and functional outcome, the effects of inflammation at the site of injury, the prolonged survival of supporting cells, the differentiation of stem cells, the effective delivery of neurotrophic factors, and longer follow-up periods are all topics for future elucidation. Future investigations should strive to further define specific factors associated with improved functional outcomes in clinically relevant models.

Preparation and characterization of genipin-crosslinked rat acellular spinal cord scaffolds

The feasibility of rat acellular spinal cord scaffolds for tissue engineering applications was investigated. Fresh rat spinal cords were decellularized and crosslinked with genipin (GP) to improve their structural stability and mechanical properties. The GP-crosslinked spinal cord scaffolds possessed a porous structure with an average pore diameter of 31.1 μm and a porosity of 81.5%. The resultant scaffolds exhibited a water uptake ratio of 229%, and moderate in vitro degradation rates of less than 5% in phosphate-buffered saline (PBS) and slightly more than 20% in trypsin-containing buffer, within 14 days. The ultimate tensile strength and elastic modulus of GP-crosslinked spinal cord scaffolds were determined to be 0.193±0.064 MPa and 1.541±0.082 MPa, respectively. Compared with glutaraldehyde (GA)-crosslinked acellular spinal cord scaffolds, GP-crosslinked scaffolds demonstrated similar microstructure and mechanical properties but superior biocompatibility as indicated by cytotoxicity evaluation and rat mesenchymal stem cell (MSC) adhesion behavior. Cells were able to penetrate throughout the crosslinked scaffold due to the presence of an interconnected porous structure. The low cytotoxicity of GP facilitated cell proliferation and extracellular matrix (ECM) secretion in vitro on the crosslinked scaffolds over 7 days. Thus, these GP-crosslinked spinal cord scaffolds show great promise for tissue engineering applications.

An ice-templated, linearly aligned chitosan-alginate scaffold for neural tissue engineering

Several strategies have been investigated to enhance axonal regeneration after spinal cord injury, however, the resulting growth can be random and disorganized. Bioengineered scaffolds provide a physical substrate for guidance of regenerating axons towards their targets, and can be produced by freeze casting. This technique involves the controlled directional solidification of an aqueous solution or suspension, resulting in a linearly aligned porous structure caused by ice templating. In this study, freeze casting was used to fabricate porous chitosan-alginate (C/A) scaffolds with longitudinally oriented channels. Chick dorsal root ganglia explants adhered to and extended neurites through the scaffold in parallel alignment with the channel direction. Surface adsorption of a polycation and laminin promoted significantly longer neurite growth than the uncoated scaffold (poly-L-ornithine + Laminin = 793.2 ± 187.2 μm; poly-L-lysine + Laminin = 768.7 ± 241.2 μm; uncoated scaffold = 22.52 ± 50.14 μm) (P < 0.001). The elastic modulus of the hydrated scaffold was determined to be 5.08 ± 0.61 kPa, comparable to reported spinal cord values. The present data suggested that this C/A scaffold is a promising candidate for use as a nerve guidance scaffold, because of its ability to support neuronal attachment and the linearly aligned growth of DRG neurites.

Using extracellular matrix for regenerative medicine in the spinal cord

Regeneration within the mammalian central nervous system (CNS) is limited, and traumatic injury often leads to permanent functional motor and sensory loss. The lack of regeneration following spinal cord injury (SCI) is mainly caused by the presence of glial scarring, cystic cavitation and a hostile environment to axonal growth at the lesion site. The more prominent experimental treatment strategies focus mainly on drug and cell therapies, however recent interest in biomaterial-based strategies are increasing in number and breadth. Outside the spinal cord, approaches that utilize the extracellular matrix (ECM) to promote tissue repair show tremendous potential for various application including vascular, skin, bone, cartilage, liver, lung, heart and peripheral nerve tissue engineering (TE). Experimentally, it is unknown if these approaches can be successfully translated to the CNS, either alone or in combination with synthetic biomaterial scaffolds. In this review we outline the first attempts to apply the potential of ECM-based biomaterials and combining cell-derived ECM with synthetic scaffolds.

Methacrylate-endcapped caprolactone and FM19G11 provide a proper niche for spinal cord-derived neural cells

Spinal cord injury (SCI) is a cause of paralysis. Although some strategies have been proposed to palliate the severity of this condition, so far no effective therapies have been found to reverse it. Recently, we have shown that acute transplantation of ependymal stem/progenitor cells (epSPCs), which are spinal cord-derived neural precursors, rescue lost neurological function after SCI in rodents. However, in a chronic scenario with axon repulsive reactive scar, cell transplantation alone is not sufficient to bridge a spinal cord lesion, therefore a combinatorial approach is necessary to fill cavities in the damaged tissue with biomaterial that supports stem cells and ensures that better neural integration and survival occur. Caprolactone 2-(methacryloyloxy) ethyl ester (CLMA) is a monomer [obtained as a result of ε-caprolactone and 2-hydroxyethyl methacrylate (HEMA) ring opening/esterification reaction], which can be processed to obtain a porous non-toxic 3D scaffold that shows good biocompatibility with epSPC cultures. epSPCs adhere to the scaffolds and maintain the ability to expand the culture through the biomaterial. However, a significant reduction of cell viability of epSPCs after 6 days in vitro was detected. FM19G11, which has been shown to enhance self-renewal properties, rescues cell viability at 6 days. Moreover, addition of FM19G11 enhances the survival rates of mature neurons from the dorsal root ganglia when cultured with epSPCs on 3D CLMA scaffolds. Overall, CLMA porous scaffolds constitute a good niche to support neural cells for cell transplantation approaches that, in combination with FM19G11, offer a new framework for further trials in spinal cord regeneration.

Controlled activity of mouse astrocytes on electrospun PCL nanofiber containing polysaccharides from brown seaweed

The central nervous system (CNS), once injured, rarely recovers original function mainly due to its limited regeneration ability. Astrocytes are cells that play critical roles in neural regeneration. Several biomaterials have been studied to replace and regenerate lost tissues within injured CNS. Seaweeds have extracellular polymeric substances (EPS) with bioactive properties such as antiviral and antioxidant properties. In this study, astrocyte activity was assessed, after being cultured on an electrospun polycaprolactone (PCL) nanofibrous mat containing a brown seaweed EPS. Laminarin and fucoidan, two main components of EPS extract from the brown seaweed, were concluded to increase or decrease astrocyte activity with respect to their concentration. When the concentration was under 10 μg/ml, the astrocytes tended to increase their viability. In contrast, over 10 μg/ml EPS in media suppressed the viability of astrocytes. In addition, when contained in PCL nanofiber, the EPS extract was also proven to influence astrocyte activity in the same way as the case when astrocytes were exposed to EPS in solution. This implies that the brown seaweed EPS-PCL nanofiber mat can be used for temporal control of astrocyte activity by EPS concentration. Through this research, we propose that the electrospun EPS-PCL nanofiber could be used as a nanomedicine or scaffold to treat CNS injuries.

Biomaterials combined with cell therapy for treatment of spinal cord injury

Spinal cord injury (SCI) is a devastating traumatic injury resulting in paralysis or sensory deficits due to tissue damage and the poor ability of axons to regenerate across the lesion. Despite extensive research, there is still no effective treatment that would restore lost function after SCI. A possible therapeutic approach would be to bridge the area of injury with a bioengineered scaffold that would create a stimulatory environment as well as provide guidance cues for the re-establishment of damaged axonal connections. Advanced scaffold design aims at the fabrication of complex materials providing the concomitant delivery of cells, neurotrophic factors or other bioactive substances to achieve a synergistic effect for treatment. This review summarizes the current utilization of scaffolding materials for SCI treatment in terms of their physicochemical properties and emphasizes their use in combination with various cell types, as well as with other combinatorial approaches promoting spinal cord repair.

Photocured biodegradable polymer substrates of varying stiffness and microgroove dimensions for promoting nerve cell guidance and differentiation

Photocross-linkable and biodegradable polymers have great promise in fabricating nerve conduits for guiding axonal growth in peripheral nerve regeneration. Here, we photocross-linked two poly(ε-caprolactone) triacrylates (PCLTAs) with number-average molecular weights of ~7000 and ~10,000 g mol(-1) into substrates with parallel microgrooves. Cross-linked PCLTA7k was amorphous and soft, while cross-linked PCLTA10k was semicrystalline with a stiffer surface. We employed different dimensions of interests for the parallel microgrooves, that is, groove widths of 5, 15, 45, and 90 μm and groove depths of 0.4, 1, 5, and 12 μm. The behaviors of rat Schwann cell precursor line (SpL201) cells with the glial nature and pheochromocytoma (PC12) cells with the neuronal nature were studied on these microgrooved substrates, showing distinct preference to the substrates with different mechanical properties. We found different threshold sensitivities of the two nerve cell types to topographical features when their cytoskeleton and nuclei were altered by varying the groove depth and width. Almost all of the cells were aligned in the narrowest and deepest microgrooves or around the edge of microgrooves. Oriented SpL201 cell movement had a higher motility as compared to unaligned ones. After forskolin treatment, SpL201 cells demonstrated significantly upregulated S-100 and O4 on stiffer substrates or narrower microgrooves, suggesting more differentiation toward early Schwann cells (SCs). PC12 neurites were oriented with enhanced extension in narrower microgrooves. The present results not only improve our fundamental understanding on nerve cell-substrate interactions, but also offer useful conduit materials and appropriate feature dimensions to foster guidance for axonal growth in peripheral nerve regeneration.

Platelet-rich plasma favors proliferation of canine adipose-derived mesenchymal stem cells in methacrylate-endcapped caprolactone porous scaffold niches

Osteoarticular pathologies very often require an implementation therapy to favor regeneration processes of bone, cartilage and/or tendons. Clinical approaches performed on osteoarticular complications in dogs constitute an ideal model for human clinical translational applications. The adipose-derived mesenchymal stem cells (ASCs) have already been used to accelerate and facilitate the regenerative process. ASCs can be maintained in vitro and they can be differentiated to osteocytes or chondrocytes offering a good tool for cell replacement therapies in human and veterinary medicine. Although ACSs can be easily obtained from adipose tissue, the amplification process is usually performed by a time consuming process of successive passages. In this work, we use canine ASCs obtained by using a Bioreactor device under GMP cell culture conditions that produces a minimum of 30 million cells within 2 weeks. This method provides a rapid and aseptic method for production of sufficient stem cells with potential further use in clinical applications. We show that plasma rich in growth factors (PRGF) treatment positively contributes to viability and proliferation of canine ASCs into caprolactone 2-(methacryloyloxy) ethyl ester (CLMA) scaffolds. This biomaterial does not need additional modifications for cASCs attachment and proliferation. Here we propose a framework based on a combination of approaches that may contribute to increase the therapeutical capability of stem cells by the use of PRGF and compatible biomaterials for bone and connective tissue regeneration.

Biophysics of substrate interaction: influence on neural motility, differentiation, and repair

The identity and behavior of a cell is shaped by the molecular and mechanical composition of its surroundings. Molecular cues have firmly established roles in guiding both neuronal fate decisions and the migration of cells and axons. However, there is growing evidence that topographical and rigidity cues in the extracellular environment act synergistically with these molecular cues. Like chemical cues, physical factors do not elicit a fixed response, but rather one that depends on the sensory makeup of the cell. Moreover, from developmental studies and the plasticity of neural tissue, it is evident that there is dynamic feedback between physical and chemical factors to produce the final morphology. Here, we focus on our current understanding of how these physical cues shape cellular differentiation and migration, and discuss their relevance to repairing the injured nervous system.

Directionality and bipolarity of olfactory ensheathing cells on electrospun nanofibers

Aim: As a preliminary to the construction of olfactory ensheathing cells (OECs) bearing scaffold for bridging larger lesions in the spinal cord, we have investigated the response of purified cultured OECs to nanoscale fibers of varying diameter using US FDA-approved, biodegradable poly(lactic-co-glycolic-acid). Materials & methods: Conventional electrospinning produced fibers of approximately 700 nm diameter (nano-700) while nanocomposite electrospinning with quantum dots produced significantly more uniform fibers of a reduced diameter to approximately 237 nm (nano-250). OECs from adult rat were FACS purified, cultured at low density on either a flat surface or a meshwork of randomly orientated nano-700 and nano-250 fibers, and assessed using cytomorphometric analysis of immunofluorescent confocal images and by scanning electron microscopy. Results & conclusion: Compared with a flat surface, culture on a nano-700 mesh increases cell attachment. Cells change from rounded to stellate forms in random orientation. Further size reduction to the nano-250 favors bipolarity in cells with unidirectional orientation as observed in the case when transplanted OECs were used to bridge areas of damage in rat spinal cords.

Original submitted 26 August 2011; Revised submitted 28 October 2011; Published online 25 May 2012

Silk fibroin in tissue engineering

Tissue engineering (TE) is a multidisciplinary field that aims at the in vitro engineering of tissues and organs by integrating science and technology of cells, materials and biochemical factors. Mimicking the natural extracellular matrix is one of the critical and challenging technological barriers, for which scaffold engineering has become a prime focus of research within the field of TE. Amongst the variety of materials tested, silk fibroin (SF) is increasingly being recognized as a promising material for scaffold fabrication. Ease of processing, excellent biocompatibility, remarkable mechanical properties and tailorable degradability of SF has been explored for fabrication of various articles such as films, porous matrices, hydrogels, nonwoven mats, etc., and has been investigated for use in various TE applications, including bone, tendon, ligament, cartilage, skin, liver, trachea, nerve, cornea, eardrum, dental, bladder, etc. The current review extensively covers the progress made in the SF-based in vitro engineering and regeneration of various human tissues and identifies opportunities for further development of this field.

Rolling the human amnion to engineer laminated vascular tissues

The prevalence of cardiovascular disease and the limited availability of suitable autologous transplant vessels for coronary and peripheral bypass surgeries is a significant clinical problem. A great deal of progress has been made over recent years to develop biodegradable materials with the potential to remodel and regenerate vascular tissues. However, the creation of functional biological scaffolds capable of withstanding vascular stress within a clinically relevant time frame has proved to be a challenging proposition. As an alternative approach, we report the use of a multilaminate rolling approach using the human amnion to generate a tubular construct for blood vessel regeneration. The human amniotic membrane was decellularized by agitation in 0.03% (w/v) sodium dodecyl sulfate to generate an immune compliant material. The adhesion of human umbilical vein endothelial cells (EC) and human vascular smooth muscle cells (SMC) was assessed to determine initial binding and biocompatibility (monocultures). Extended cultures were either assessed as flat membranes, or rolled to form concentric multilayered conduits. Results showed positive EC adhesion and a progressive repopulation by SMC. Functional changes in SMC gene expression and the constructs' bulk mechanical properties were concomitant with vessel remodeling as assessed over a 40-day culture period. A significant advantage with this approach is the ability to rapidly produce a cell-dense construct with an extracellular matrix similar in architecture and composition to natural vessels. The capacity to control physical parameters such as vessel diameter, wall thickness, shape, and length are critical to match vessel compliance and tailor vessel specifications to distinct anatomical locations. As such, this approach opens new avenues in a range of tissue regenerative applications that may have a much wider clinical impact.