Nerve Guidance by a Decellularized Fibroblast Extracellular Matrix

Engineering cell-derived extracellular matrix for peripheral nerve regeneration

Extracellular matrices (ECMs) play a key role in nerve repair and are recognized as the natural source of biomaterials. In parallel to extensively studied tissue-derived ECMs (ts-ECMs), cell-derived ECMs (cd-ECMs) also have the capability to partially recapitulate the complicated regenerative microenvironment of native nerve tissues. Notably, cd-ECMs can avoid the shortcomings of ts-ECMs. Cd-ECMs can be prepared by culturing various cells or even autologous cells in vitro under pathogen-free conditions. And mild decellularization can achieve efficient removal of immunogenic components in cd-ECMs. Moreover, cd-ECMs are more readily customizable to achieve the desired functional properties. These advantages have garnered significant attention for the potential of cd-ECMs in neuroregenerative medicine. As promising biomaterials, cd-ECMs bring new hope for the effective treatment of peripheral nerve injuries. Herein, this review comprehensively examines current knowledge about the functional characteristics of cd-ECMs and their mechanisms of interaction with cells in nerve regeneration, with a particular focus on the preparation, engineering optimization, and scalability of cd-ECMs. The applications of cd-ECMs from distinct cell sources reported in peripheral nerve tissue engineering are highlighted and summarized. Furthermore, current limitations that should be addressed and outlooks related to clinical translation are put forward as well.

Exploring the properties and potential of the neural extracellular matrix for next-generation regenerative therapies

The extracellular matrix (ECM) is a dynamic and complex network of proteins and molecules that surrounds cells and tissues in the nervous system and orchestrates a myriad of biological functions. This review carefully examines the diverse interactions between cells and the ECM, as well as the transformative chemical and physical changes that the ECM undergoes during neural development, aging, and disease. These transformations play a pivotal role in shaping tissue morphogenesis and neural activity, thereby influencing the functionality of the central nervous system (CNS). In our comprehensive review, we describe the diverse behaviors of the CNS ECM in different physiological and pathological scenarios and explore the unique properties that make ECM-based strategies attractive for CNS repair and regeneration. Addressing the challenges of scalability, variability, and integration with host tissues, we review how advanced natural, synthetic, and combinatorial matrix approaches enhance biocompatibility, mechanical properties, and functional recovery. Overall, this review highlights the potential of decellularized ECM as a powerful tool for CNS modeling and regenerative purposes and sets the stage for future research in this exciting field. This article is categorized under: Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Implantable Materials and Surgical Technologies > Nanomaterials and Implants.

Innervation of an Ultrasound-Mediated PVDF-TrFE Scaffold for Skin-Tissue Engineering

In this work, electrospun polyvinylidene-trifluoroethylene (PVDF-TrFE) was utilized for its biocompatibility, mechanics, and piezoelectric properties to promote Schwann cell (SC) elongation and sensory neuron (SN) extension. PVDF-TrFE electrospun scaffolds were characterized over a variety of electrospinning parameters (1, 2, and 3 h aligned and unaligned electrospun fibers) to determine ideal thickness, porosity, and tensile strength for use as an engineered skin tissue. PVDF-TrFE was electrically activated through mechanical deformation using low-intensity pulsed ultrasound (LIPUS) waves as a non-invasive means to trigger piezoelectric properties of the scaffold and deliver electric potential to cells. Using this therapeutic modality, neurite integration in tissue-engineered skin substitutes (TESSs) was quantified including neurite alignment, elongation, and vertical perforation into PVDF-TrFE scaffolds. Results show LIPUS stimulation promoted cell alignment on aligned scaffolds. Further, stimulation significantly increased SC elongation and SN extension separately and in coculture on aligned scaffolds but significantly decreased elongation and extension on unaligned scaffolds. This was also seen in cell perforation depth analysis into scaffolds which indicated LIPUS enhanced perforation of SCs, SNs, and cocultures on scaffolds. Taken together, this work demonstrates the immense potential for non-invasive electric stimulation of an in vitro tissue-engineered-skin model.

High-strength and high-toughness ECM films with the potential for peripheral nerve repair

Extracellular matrix (ECM) scaffolds are widely applied in the field of regeneration as the result of their irreplaceable biological advantages, and the preparation of ECM scaffolds into ECM hydrogels expands the applications to some extent. However, weak mechanical properties of current ECM materials limit the complete exploitation of ECM's biological advantages. To enable ECM materials to be utilized in applications requiring high strength, herein, we created a kind of new ECM material, ECM film, and evaluated its mechanical properties. ECM films exhibited outstanding toughness with no cracks after arbitrarily folding and crumpling, and dramatically high strength levels of 86 ± 17.25 MPa, the maximum of which was 115 MPa. Such spectacular high-strength and high-toughness films, containing only pure ECM without any crosslinking agents and other materials, far exceed current pure natural polymer gel films and even many composite gel films and synthetic polymer gel films. In addition, both PC12 cells and Schwann cells cultured on the surface of ECM films, especially Schwann cells, showed good proliferation, and the neurite outgrowth of the PC12 cells was promoted, indicating the application potential of ECM film in peripheral nerve repair.

Ultrasound-Activated Piezoelectric Polyvinylidene Fluoride-Trifluoroethylene Scaffolds for Tissue Engineering Applications

Severe peripheral nervous system (PNS) injuries have limited options for therapeutic solutions to regain functional recovery. This can be attributed in part to the lack of regeneration pathways promoted by recapitulating chemical, physical, and electrical cues to direct nerve guidance. To address this, we examined ultrasonic stimulation of a piezoelectric polyvinylidene fluoride-triflouroethylene (PVDF-TrFE) scaffold as a potentially clinically relevant therapy for PNS regeneration. Owing to the piezoelectric modality of PVDF-TrFE, we hypothesize that ultrasound stimulation will activate the scaffold to electrically stimulate cells in response to the mechanical deformation mediated by sound waves. Biocompatible PVDF-TrFE scaffolds were fabricated to be used as an ultrasound-activated, piezoelectric biomaterial to enhance cellular activity for PNS applications. NIH-3T3 fibroblasts were cultured on PVDF-TrFE nanofibers and stimulated with low-, medium-, or high-powered ultrasound. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assays were performed on fibroblasts to measure the metabolic activity of the cells following stimulation. MTT assays showed that ultrasound-stimulated fibroblasts on PVDF-TrFE scaffolds had increased metabolic activity as power was increased, whereas on plain polystyrene, an opposite trend was observed where cells had a decreased metabolic activity with ascending levels of ultrasound power. Ultrasound-stimulated PVDF-TrFE nanofibers hold exciting potential as a therapy for PNS injuries by promoting increased metabolic activity and proliferation. The ability to noninvasively stimulate implantable piezoelectric nanofibers to promote mechanical and electrical stimulation for nerve repair offers a promising benefit to severe trauma patients.

Dual-bionic regenerative microenvironment for peripheral nerve repair

Autologous nerve grafting serves is considered the gold standard treatment for peripheral nerve defects; however, limited availability and donor area destruction restrict its widespread clinical application. Although the performance of allogeneic decellularized nerve implants has been explored, challenges such as insufficient human donors have been a major drawback to its clinical use. Tissue-engineered neural regeneration materials have been developed over the years, and researchers have explored strategies to mimic the peripheral neural microenvironment during the design of nerve catheter grafts, namely the extracellular matrix (ECM), which includes mechanical, physical, and biochemical signals that support nerve regeneration. In this study, polycaprolactone/silk fibroin (PCL/SF)-aligned electrospun material was modified with ECM derived from human umbilical cord mesenchymal stem cells (hUMSCs), and a dual-bionic nerve regeneration material was successfully fabricated. The results indicated that the developed biomimetic material had excellent biological properties, providing sufficient anchorage for Schwann cells and subsequent axon regeneration and angiogenesis processes. Moreover, the dual-bionic material exerted a similar effect to that of autologous nerve transplantation in bridging peripheral nerve defects in rats. In conclusion, this study provides a new concept for designing neural regeneration materials, and the prepared dual-bionic repair materials have excellent auxiliary regenerative ability and further preclinical testing is warranted to evaluate its clinical application potential.

Open-Spaced Ridged Hydrogel Scaffolds Containing TiO2-Self-Assembled Monolayer of Phosphonates Promote Regeneration and Recovery Following Spinal Cord Injury

The spinal cord has a poor ability to regenerate after an injury, which may be due to cell loss, cyst formation, inflammation, and scarring. A promising approach to treating a spinal cord injury (SCI) is the use of biomaterials. We have developed a novel hydrogel scaffold fabricated from oligo(poly(ethylene glycol) fumarate) (OPF) as a 0.08 mm thick sheet containing polymer ridges and a cell-attractive surface on the other side. When the cells are cultured on OPF via chemical patterning, the cells attach, align, and deposit ECM along the direction of the pattern. Animals implanted with the rolled scaffold sheets had greater hindlimb recovery compared to that of the multichannel scaffold control, which is likely due to the greater number of axons growing across it. The immune cell number (microglia or hemopoietic cells: 50-120 cells/mm² in all conditions), scarring (5-10% in all conditions), and ECM deposits (Laminin or Fibronectin: approximately 10-20% in all conditions) were equal in all conditions. Overall, the results suggest that the scaffold sheets promote axon outgrowth that can be guided across the scaffold, thereby promoting hindlimb recovery. This study provides a hydrogel scaffold construct that can be used in vitro for cell characterization or in vivo for future neuroprosthetics, devices, or cell and ECM delivery.

Extracellular matrix composition affects outgrowth of dendrites and dendritic spines on cortical neurons

The composition of the extracellular matrix (ECM) in nervous tissue plays an important role in controlling neuronal outgrowth and synapse development. Changes in both protein and glycosaminoglycan components of the ECM occur with tissue injury and may affect neuron growth. To investigate neuron responses to alterations in fibronectin (FN), a major component of the wound ECM, we grew cortical neurons on cell-derived decellularized matrices composed of wild type FN (FN+/+) or of a mutant form of FN (FNΔ/+) from which the III13 heparin-binding site had been deleted by CRISPR-Cas 9 gene editing. The most significant effect of the mutant FN was a reduction in dendrite outgrowth. Not only were dendrites shorter on mutant FNΔ/+-collagen (COL) matrix than on wild type (FN+/+-COL) matrix, but the number of dendrites and dendritic spines per neuron and the spine densities were also dramatically reduced on FNΔ/+-COL matrices. Mass spectrometry and immunostaining identified a reduction in tenascin-C (TN-C) levels in the mutant matrix. TN-C is an ECM protein that binds to the III13 site of FN and modulates cell-matrix interactions and has been linked to dendrite development. We propose that TN-C binding to FN in the wound matrix supports dendrite and spine development during repair of damaged neural tissue. Overall, these results show that changes in ECM composition can dramatically affect elaboration of neurites and support the idea that the ECM microenvironment controls neuron morphology and connectivity.

Injectable hydrogels in central nervous system: Unique and novel platforms for promoting extracellular matrix remodeling and tissue engineering

Repairing central nervous system (CNS) is difficult due to the inability of neurons to recover after damage. A clinically acceptable treatment to promote CNS functional recovery and regeneration is currently unavailable. According to recent studies, injectable hydrogels as biodegradable scaffolds for CNS tissue engineering and regeneration have exceptionally desirable attributes. Hydrogel has a biomimetic structure similar to extracellular matrix, hence has been considered a 3D scaffold for CNS regeneration. An interesting new type of hydrogel, injectable hydrogels, can be injected into target areas with little invasiveness and imitate several aspects of CNS. Injectable hydrogels are being researched as therapeutic agents because they may imitate numerous properties of CNS tissues and hence reduce subsequent injury and regenerate neural tissue. Because of their less adverse effects and cost, easier use and implantation with less pain, and faster regeneration capacity, injectable hydrogels, are more desirable than non-injectable hydrogels. This article discusses the pathophysiology of CNS and the use of several kinds of injectable hydrogels for brain and spinal cord tissue engineering, paying particular emphasis to recent experimental studies.

Transcriptome profiling of a synergistic volumetric muscle loss repair strategy

Volumetric muscle loss overwhelms skeletal muscle's ordinarily capable regenerative machinery, resulting in severe functional deficits that have defied clinical repair strategies. In this manuscript we pair the early in vivo functional response induced by differing volumetric muscle loss tissue engineering repair strategies that are broadly representative of those explored by the field (scaffold alone, cells alone, or scaffold + cells) to the transcriptomic response induced by each intervention. We demonstrate that an implant strategy comprising allogeneic decellularized skeletal muscle scaffolds seeded with autologous minced muscle cellular paste (scaffold + cells) mediates a pattern of increased expression for several genes known to play roles in axon guidance and peripheral neuroregeneration, as well as several other key genes related to inflammation, phagocytosis, and extracellular matrix regulation. The upregulation of several key genes in the presence of both implant components suggests a unique synergy between scaffolding and cells in the early period following intervention that is not seen when either scaffolds or cells are used in isolation; a finding that invites further exploration of the interactions that could have a positive impact on the treatment of volumetric muscle loss.

Peripheral nerve-derived fibroblasts promote neurite outgrowth in adult dorsal root ganglion neurons more effectively than skin-derived fibroblasts

NEW FINDINGS

What is the central question of this study? Although fibroblasts are involved in the regenerative process associated with peripheral nerve injury, detailed information regarding their characteristics is largely lacking. What is the main finding and its importance? Nerve-derived fibroblasts have a greater neurite-promoting effect than skin-derived fibroblasts, and epineurium-derived fibroblasts can promote neurite outgrowth more effectively than parenchyma-derived fibroblasts. The epineurium-derived fibroblasts and parenchyma-derived fibroblasts have distinctly different molecular profiles, including genes of soluble factors to promote axonal growth. Fibroblasts are molecularly and functionally different depending on their localization in nerve tissue, and epineurium-derived fibroblasts might be involved in axon regeneration after peripheral nerve injury more than previously thought.

ABSTRACT

Although fibroblasts (Fb) are components of a peripheral nerve involved in the regenerative process associated with peripheral nerve injury, detailed information regarding their characteristics is largely lacking. The objective of the present study was to investigate the capacity of Fb derived from peripheral nerves to stimulate the outgrowth of neurites from adult dorsal root ganglion neurons and to clarify their molecular characteristics. Fibroblasts were prepared from the epineurium and parenchyma of rat sciatic nerves and skin. The Fb derived from epineurium showed the greatest effect on neurite outgrowth, followed by the Fb derived from parenchyma, indicating that Fb derived from nerves promote neurite outgrowth more effectively than skin-derived Fb. Although both soluble and cell-surface factors contributed evenly to the neurite-promoting effect of nerve-derived Fb, in crush and transection injury models, Fb were not closely associated with regenerating axons, indicating that only soluble factors from Fb are available to regenerating axons. A transcriptome analysis revealed that the molecular profiles of these Fb were distinctly different and that the gene expression profiles of soluble factors that promote axonal growth are unique to each Fb. These findings indicate that Fb are molecularly and functionally different depending on their localization in nerve tissue and that Fb derived from epineurium might be involved more than was previously thought in axon regeneration after peripheral nerve injury.

Functional acellular matrix for tissue repair

In view of their low immunogenicity, biomimetic internal environment, tissue- and organ-like physicochemical properties, and functionalization potential, decellularized extracellular matrix (dECM) materials attract considerable attention and are widely used in tissue engineering. This review describes the composition of extracellular matrices and their role in stem-cell differentiation, discusses the advantages and disadvantages of existing decellularization techniques, and presents methods for the functionalization and characterization of decellularized scaffolds. In addition, we discuss progress in the use of dECMs for cartilage, skin, nerve, and muscle repair and the transplantation or regeneration of different whole organs (e.g., kidneys, liver, uterus, lungs, and heart), summarize the shortcomings of using dECMs for tissue and organ repair after refunctionalization, and examine the corresponding future prospects. Thus, the present review helps to further systematize the application of functionalized dECMs in tissue/organ transplantation and keep researchers up to date on recent progress in dECM usage.

Role of 3D Printing in the Development of Biodegradable Implants for Central Nervous System Drug Delivery

Increased life expectancy has led to a rise in age-related disorders including neurological diseases such as Alzheimer's disease and Parkinson's disease. Limited progress has been made in the development of clinically translatable therapies for these central nervous system (CNS) diseases. Challenges including the blood-brain barrier, brain complexity, and comorbidities in the elderly population are some of the contributing factors toward lower success rates. Various invasive and noninvasive ways are being employed to deliver small and large molecules across the brain. Biodegradable, implantable drug-delivery systems have gained lot of interest due to advantages such as sustained and targeted delivery, lower side effects, and higher patient compliance. 3D printing is a novel additive manufacturing technique where various materials and printing techniques can be used to fabricate implants with the desired complexity in terms of mechanical properties, shapes, or release profiles. This review discusses an overview of various types of 3D-printing techniques and illustrative examples of the existing literature on 3D-printed systems for CNS drug delivery. Currently, there are various technical and regulatory impediments that need to be addressed for successful translation from the bench to the clinical stage. Overall, 3D printing is a transformative technology with great potential in advancing customizable drug treatment in a high-throughput manner.

Application of biomimetic surfaces and 3D culture technology to study the role of extracellular matrix interactions in neurite outgrowth and inhibition

The microenvironment that cells experience during in vitro culture can often be far removed from the native environment they are exposed to in vivo. To recreate the physiological environment that developing neurites experience in vivo, we combine a well-established model of human neurite development with, functionalisation of both 2D and 3D growth substrates with specific extracellular matrix (ECM) derived motifs displayed on engineered scaffold proteins. Functionalisation of growth substrates provides biochemical signals more reminiscent of the in vivo environment and the combination of this technology with 3D cell culture techniques, further recapitulates the native cellular environment by providing a more physiologically relevant geometry for neurites to develop. This biomaterials approach was used to study interactions between the ECM and developing neurites, along with the identification of specific motifs able to enhance neuritogenesis within this model. Furthermore, this technology was employed to study the process of neurite inhibition that has a detrimental effect on neuronal connectivity following injury to the central nervous system (CNS). Growth substrates were functionalised with inhibitory peptides released from damaged myelin within the injured spinal cord (Nogo & OMgp). This model was then utilised to study the underlying molecular mechanisms that govern neurite inhibition in addition to potential mechanisms of recovery.

The impact of physical, biochemical, and electrical signaling on Schwann cell plasticity

Peripheral nervous system (PNS) injuries are an ongoing health care concern. While autografts and allografts are regarded as the current clinical standard for traumatic injury, there are inherent limitations that suggest alternative remedies should be considered for therapeutic purposes. In recent years, nerve guidance conduits (NGCs) have become increasingly popular as surgical repair devices, with a multitude of various natural and synthetic biomaterials offering potential to enhance the design of conduits or supplant existing technologies entirely. From a cellular perspective, it has become increasingly evident that Schwann cells (SCs), the primary glia of the PNS, are a predominant factor mediating nerve regeneration. Thus, the development of severe nerve trauma therapies requires a deep understanding of how SCs interact with their environment, and how SC microenvironmental cues may be engineered to enhance regeneration. Here we review the most recent advancements in biomaterials development and cell stimulation strategies, with a specific focus on how the microenvironment influences the behavior of SCs and can potentially lead to functional repair. We focus on microenvironmental cues that modulate SC morphology, proliferation, migration, and differentiation to alternative phenotypes. Promotion of regenerative phenotypic responses in SCs and other non-neuronal cells that can augment the regenerative capacity of multiple biomaterials is considered along with innovations and technologies for traumatic injury.

Effect of Decellularized Extracellular Matrix Bioscaffolds Derived from Fibroblasts on Skin Wound Healing and Remodeling

The mammalian tissue extracellular matrix (ECM) has been used as a scaffold to facilitate the repair and reconstruction of numerous tissues. However, the material properties of decellularized ECM (dECM) from in vitro cell cultures and the effect of these properties on wound remodeling remain unclear. To elucidate its biological activity, we extracted dECM from human lung fibroblasts, fabricated it into a patch, and applied it to a full-thickness skin wound. The fibroblast-derived dECM (fdECM) maintained the content of collagen Ⅰ, collagen Ⅳ, and elastin, and the extraction process did not damage its critical growth factors. The fdECM-conjugated collagen patch (COL-fdECM) facilitated wound contraction and angiogenesis in the proliferative phase when applied to the in vivo full-thickness skin wound model. Moreover, the COL-fdECM treated wound showed increased regeneration of the epidermal barrier function, mature collagen, hair follicle, and subepidermal nerve plexus, suggesting qualitative skin remodeling. This therapeutic efficacy was similarly observed when applied to the diabetic ulcer model. fdECM was shown to help remodel the tissue by regulating fibroblast growth factors, matrix metalloproteinases, and tissue inhibitors of metalloproteinases via the p38 and ERK signaling pathways in an in vitro experiment for understanding the underlying mechanism. These results provide a biological basis for cell-derived ECM as a multi-functional biomaterial applicable to various diseases.

Decellularized extracellular matrix scaffolds: Recent trends and emerging strategies in tissue engineering

The application of scaffolding materials is believed to hold enormous potential for tissue regeneration. Despite the widespread application and rapid advance of several tissue-engineered scaffolds such as natural and synthetic polymer-based scaffolds, they have limited repair capacity due to the difficulties in overcoming the immunogenicity, simulating in-vivo microenvironment, and performing mechanical or biochemical properties similar to native organs/tissues. Fortunately, the emergence of decellularized extracellular matrix (dECM) scaffolds provides an attractive way to overcome these hurdles, which mimic an optimal non-immune environment with native three-dimensional structures and various bioactive components. The consequent cell-seeded construct based on dECM scaffolds, especially stem cell-recellularized construct, is considered an ideal choice for regenerating functional organs/tissues. Herein, we review recent developments in dECM scaffolds and put forward perspectives accordingly, with particular focus on the concept and fabrication of decellularized scaffolds, as well as the application of decellularized scaffolds and their combinations with stem cells (recellularized scaffolds) in tissue engineering, including skin, bone, nerve, heart, along with lung, liver and kidney.

Brachial plexus bridging with specific extracellular matrix modified chitosan/silk scaffold: a new expand of tissue engineered nerve graft

OBJECTIVE

Brachial plexus injuries result in serious dysfunction and are currently treated using autologous nerve graft (autograft) transplantation. With the development of tissue engineering, tissue engineered nerve grafts (TENGs) have emerged as promising alternatives to autografts but have not yet been widely applied to the treatment of brachial plexus injuries. Herein, we developed a TENG modified with extracellular matrix (ECM) generated by skin-derived precursor Schwann cells (SKP-SCs) and expand its application in upper brachial plexus defects in rats.

APPROACH

SKP-SCs were co-cultured with chitosan neural conduits or silk fibres and subjected to decellularization treatment. Ten bundles of silk fibres (five fibres per bundle) were placed into a conduit to obtain the TENG, which was used to bridge an 8 mm gap in the upper brachial plexus. The efficacy of this treatment was examined for TENG-, autograft- and scaffold-treated groups at several times after surgery using immunochemical staining, behavioural tests, electrophysiological measurements, and electron microscopy.

MAIN RESULTS

Histological analysis conducted two weeks after surgery showed that compared to scaffold bridging, TENG treatment enhanced the growth of regenerating axons. Behavioural tests conducted four weeks after surgery showed that TENG-treated rats performed similarly to autograft-treated ones, with a significant improvement observed in both cases compared with the scaffold treatment group. Electrophysiological and retrograde tracing characterisations revealed that the target muscles were reinnervated in both TENG and autograft groups, while transmission electron microscopy and immunohistochemical staining showed the occurrence of the superior myelination of regenerated axons in these groups.

SIGNIFICANCE

Treatment with the developed TENG allows the effective bridging of proximal nerve defects in the upper extremities, and the obtained results provide a theoretical basis for clinical transformation to expand the application scope of TENGs.

Differential Regulation of Neurite Outgrowth and Growth Cone Morphology by 3D Fibronectin and Fibronectin-Collagen Extracellular Matrices

The extracellular matrix (ECM) plays a critical role in development, homeostasis, and regeneration of tissue structures and functions. Cell interactions with the ECM are dynamic and cells respond to ECM remodeling by changes in morphology and motility. During nerve regeneration, the ECM facilitates neurite outgrowth and guides axons with target specificity. Decellularized ECMs retain structural, biochemical, and biomechanical cues of native ECM and have the potential to replace damaged matrix to support cell activities during tissue repair. To determine the ECM components that contribute to nerve regeneration, we analyzed neuron-ECM interactions on two types of decellularized ECM. One matrix was composed primarily of fibronectin (FN) fibrils, and the other FN-rich ECM also contained significant numbers of type I collagen (COL I) fibrils. Using primary neurons dissociated from superior cervical ganglion (SCG) explants, we found that neurites were extended on both matrices without a significant difference in average neurite length after 24 h. The most distinctive features of neurites on the FN matrix were numerous short actin-filled protrusions and longer branches extending from neurite shafts. Very few protrusions and branches were detected on FN-COL matrix. Growth cone morphologies also differed with mostly filopodial growth cones on FN matrix whereas on FN-COL matrix, equivalent numbers of filopodial and slender growth cones were formed. Our work provides new information about how changes in major components of the ECM during tissue repair modulate neuron and growth cone morphologies and helps to define the contributions of neuron-ECM interactions to nerve development and regeneration.

[Inhibition of TGF-β promotes functional recovery of spinal cord injury in mice by reducing fibronectin deposition]

OBJECTIVE

To investigate the effect of transforming growth factor (TGF-β) inhibition on functional recovery of spinal cord injury in mice.

METHODS

Twelve mice were divided into treatment group, control group and sham-operated group (n=4). The mice in the treatment group were subjected to hemisection of the spinal cord and received intraperitoneal injection of TGF-β neutralizing antibody (1D11) 3 times a week (25 μL each time), and those in control group were injected with the vehicle antibody (13C4) following spinal cord hemisection. The sham-operated mice underwent sham operation to expose the spinal cord without hemisection. Four weeks later, the heart of the mice was perfused and 1-2 cm of the spinal cord spanning the injury site was harvested. Immunofluorescence staining of FSP1, fibronectin, and PGP9.5 was performed to assess fibroblast recruitment in the injury area, fibronectin deposition, and neurological recovery. For further verification of the results, we used a mouse model of spinal cord clamp injury to observe the survival of axons and distribution of astrocytes by detecting expressions of 5-HT and GFAP with immunofluorescence assay.

RESULTS

In the hemisection injury model, fibroblasts recruitment and fibronectin deposition in the injured area was significantly reduced and the neurological function was improved in 1D11 treatment group as compared with those in 13C4-treated group (P < 0.05). In the spinal cord clamp injury model, treatment with 1D11, as compared with the 13C4, resulted in significantly increased number of 5-HT-positive axons with extended axonal length and obviously increased the number of GFAP-positive astrocytes in the injured area (P < 0.05).

CONCLUSION

Inhibiting TGF-β after spinal cord injury can reduce the recruitment of fibroblasts and fibronectin deposition to promote recovery of neurological function and repair of the injured spinal cord in mice.

Disease-specific extracellular matrix composition regulates placental trophoblast fusion efficiency

The placental syncytiotrophoblast is a multinucleated layer that regulates transport between the mother and fetus. Fusion of trophoblasts is essential to form this layer, but this process can be disrupted in pregnancy-related disorders such as preeclampsia. Disease progression is also associated with changes in the extracellular matrix (ECM), but whether disease-specific ECM compositions play any causal role in establishing syncytiotrophoblast disease phenotypes remains unknown. Here, we develop a decellularization-based platform to isolate and characterize the role of human placental ECM composition on cell function, while controlling for the confounding effects of matrix structure and mechanics that can arise in conventional tissue decellularization/recellularization experiments. Using this approach, we demonstrate that ECM compositional changes that occur in preeclampsia have a statistically significant effect on adhesion, spreading, and fusion of placental trophoblasts. Proteomic analysis of ECM content then allowed us to identify and recreate selected differences in matrix composition; indicating that replacement of normally present Type IV Collagen by Type I Collagen in preeclampsia significantly affects fusion efficiency. These results indicate that disease-specific matrix compositions can play an important role in trophoblast fusion, suggesting novel matrix-targeting therapeutic strategies for pregnancy-related disorders. More broadly, this work demonstrates the utility of a decellularization-based approach in understanding the functional contributions of matrix composition in driving cellular disease phenotypes.

Cell-derived extracellular matrix materials for tissue engineering

The involvement of cell-derived extracellular matrix (CDM) in assembling tissue engineering scaffolds has yielded significant results. CDM possesses excellent characteristics, such as ideal cellular microenvironment mimicry and good biocompatibility, which make it a popular research direction in the field of bionanomaterials. CDM has significant advantages as an expansion culture substrate for stem cells, including stabilization of phenotype, reversal of senescence, and guidance of specific differentiation. In addition, the applications of CDM-assembled tissue engineering scaffolds for disease simulation and tissue organ repair are comprehensively summarized; the focus is mainly on bone and cartilage repair, skin defect or wound healing, engineered blood vessels, peripheral nerves, and periodontal tissue repair. We consider CDM a highly promising bionic biomaterial for tissue engineering applications and propose a vision for its comprehensive development.

Induction of Neurogenesis and Angiogenesis in a Rat Hemisection Spinal Cord Injury Model With Combined Neural Stem Cell, Endothelial Progenitor Cell, and Biomimetic Hydrogel Matrix Therapy

Acute spinal cord injury is a devastating injury that may lead to loss of independent function. Stem-cell therapies have shown promise; however, a clinically efficacious stem-cell therapy has yet to be developed. Functionally, endothelial progenitor cells induce angiogenesis, and neural stem cells induce neurogenesis. In this study, we explored using a multimodal therapy combining endothelial progenitor cells with neural stem cells encapsulated in a bioactive biomimetic hydrogel matrix to facilitate stem cell-induced neurogenesis and angiogenesis in a rat hemisection spinal cord injury model.

DESIGN

Laboratory experimentation.

SETTING

University laboratory.

SUBJECTS

Female Fischer 344 rats.

INTERVENTIONS

Three groups of rats: 1) control, 2) biomimetic hydrogel therapy, and 3) combined neural stem cell, endothelial progenitor cell, biomimetic hydrogel therapy underwent right-sided spinal cord hemisection at T9-T10. The blinded Basso, Beattie, and Bresnahan motor score was obtained weekly; after 4 weeks, observational histologic analysis of the injured spinal cords was completed.

MEASUREMENTS AND MAIN RESULTS

Blinded Basso, Beattie, and Bresnahan motor score of the hind limb revealed significantly improved motor function in rats treated with combined neural stem cell, endothelial progenitor cell, and biomimetic hydrogel therapy (p < 0.05) compared with the control group. The acellular biomimetic hydrogel group did not demonstrate a significant improvement in motor function compared with the control group. Immunohistochemistry evaluation of the injured spinal cords demonstrated de novo neurogenesis and angiogenesis in the combined neural stem cell, endothelial progenitor cell, and biomimetic hydrogel therapy group, whereas, in the control group, a gap or scar was found in the injured spinal cord.

CONCLUSIONS

This study demonstrates proof of concept that multimodal therapy with endothelial progenitor cells and neural stem cells combined with a bioactive biomimetic hydrogel can be used to induce de novo CNS tissue in an injured rat spinal cord.

Cell Shape and Matrix Stiffness Impact Schwann Cell Plasticity via YAP/TAZ and Rho GTPases

Schwann cells (SCs) are a highly plastic cell type capable of undergoing phenotypic changes following injury or disease. SCs are able to upregulate genes associated with nerve regeneration and ultimately achieve functional recovery. During the regeneration process, the extracellular matrix (ECM) and cell morphology play a cooperative, critical role in regulating SCs, and therefore highly impact nerve regeneration outcomes. However, the roles of the ECM and mechanotransduction relating to SC phenotype are largely unknown. Here, we describe the role that matrix stiffness and cell morphology play in SC phenotype specification via known mechanotransducers YAP/TAZ and RhoA. Using engineered microenvironments to precisely control ECM stiffness, cell shape, and cell spreading, we show that ECM stiffness and SC spreading downregulated SC regenerative associated proteins by the activation of RhoA and YAP/TAZ. Additionally, cell elongation promoted a distinct SC regenerative capacity by the upregulation of Rac1/MKK7/JNK, both necessary for the ECM and morphology changes found during nerve regeneration. These results confirm the role of ECM signaling in peripheral nerve regeneration as well as provide insight to the design of future biomaterials and cellular therapies for peripheral nerve regeneration.

Promoting Neuronal Outgrowth Using Ridged Scaffolds Coated with Extracellular Matrix Proteins

Spinal cord injury (SCI) results in cell death, demyelination, and axonal loss. The spinal cord has a limited ability to regenerate, and current clinical therapies for SCI are not effective in helping promote neurologic recovery. We have developed a novel scaffold biomaterial that is fabricated from the biodegradable hydrogel oligo(poly(ethylene glycol)fumarate) (OPF). We have previously shown that positively charged OPF scaffolds (OPF+) in an open spaced, multichannel design can be loaded with Schwann cells to support axonal generation and functional recovery following SCI. We have now developed a hybrid OPF+ biomaterial that increases the surface area available for cell attachment and that contains an aligned microarchitecture and extracellular matrix (ECM) proteins to better support axonal regeneration. OPF+ was fabricated as 0.08 mm thick sheets containing 100 μm high polymer ridges that self-assemble into a spiral shape when hydrated. Laminin, fibronectin, or collagen I coating promoted neuron attachment and axonal outgrowth on the scaffold surface. In addition, the ridges aligned axons in a longitudinal bipolar orientation. Decreasing the space between the ridges increased the number of cells and neurites aligned in the direction of the ridge. Schwann cells seeded on laminin coated OPF+ sheets aligned along the ridges over a 6-day period and could myelinate dorsal root ganglion neurons over 4 weeks. This novel scaffold design, with closer spaced ridges and Schwann cells, is a novel biomaterial construct to promote regeneration after SCI.

Peripheral nerves preferentially regenerate in intramuscular endoneurial tubes to reinnervate denervated skeletal muscles

Schwann cells are essential for peripheral nerve regeneration but, over short distances in acellular nerve grafts, extracellular matrix (ECM) molecules can support growth. The ECM molecules are present also on denervated muscle surfaces where they can support nerve growth. In this study, we addressed the efficacy of the ECM molecules of denervated muscle to support nerve fiber regeneration and muscle reinnervation. In the hindlimb of Sprague-Dawley rats, the proximal stump of the transected posterior tibial nerve, was cross-sutured to the distal nerve stump (NN) of each of three denervated muscles, tibialis anterior, extensor digitorum longus, and soleus, or implanted onto the denervated muscles' surfaces (N-M), proximal or distal to the endplate zone. Recordings of muscle and motor unit (MU) isometric forces and silver/cholinesterase histochemical staining of longitudinal muscle cryosections were used to determine the numbers of reinnervated MUs and the spatial course of regenerating nerve fibers, respectively. MU numbers declined significantly after N-M (>50%) as compared to those after NN. Muscle forces were reduced despite each nerve reinnervating up to three times the normal MU muscle fiber number. Regenerating nerves 'streamed' from the N-M site either proximal or distal to endplate zones toward the denervated intramuscular endoneurial tubes, with reduced numbers reinnervating endplates. We conclude that there is preferential reinnervation through the endoneurial tube and that it is important to drive implanted nerve fibers to enter endoneurial tubes for optimal muscle reinnervation. Schwann cells play the essential role in guiding regenerating nerve fibers to reinnervate denervated muscle fibers.

Human Platelet Lysate Acts Synergistically With Laminin to Improve the Neurotrophic Effect of Human Adipose-Derived Stem Cells on Primary Neurons in vitro

Background

Despite the advancements in microsurgical techniques and noteworthy research in the last decade, peripheral nerve lesions have still weak functional outcomes in current clinical practice. However, cell transplantation of human adipose-derived stem cells (hADSC) in a bioengineered conduit has shown promising results in animal studies. Human platelet lysate (hPL) has been adopted to avoid fetal bovine serum (FBS) in consideration of the biosafety concerns inherent with the use of animal-derived products in tissue processing and cell culture steps for translational purposes. In this work, we investigate how the interplay between hPL-expanded hADSC (hADSC^hPL) and extracellular matrix (ECM) proteins influences key elements of nerve regeneration.

Methods

hADSC were seeded on different ECM coatings (laminin, LN; fibronectin, FN) in hPL (or FBS)-supplemented medium and co-cultured with primary dorsal root ganglion (DRG) to establish the intrinsic effects of cell–ECM contact on neural outgrowth. Co-cultures were performed “direct,” where neural cells were seeded in contact with hADSC expanded on ECM-coated substrates (contact effect), or “indirect,” where DRG was treated with their conditioned medium (secretome effect). Brain-derived nerve factor (BDNF) levels were quantified. Tissue culture plastic (TCPS) was used as the control substrate in all the experiments.

Results

hPL as supplement alone did not promote higher neurite elongation than FBS when combined with DRG on ECM substrates. However, in the presence of hADSC, hPL could dramatically enhance the stem cell effect with increased DRG neurite outgrowth when compared with FBS conditions, regardless of the ECM coating (in both indirect and direct co-cultures). The role of ECM substrates in influencing neurite outgrowth was less evident in the FBS conditions, while it was significantly amplified in the presence of hPL, showing better neural elongation in LN conditions when compared with FN and TCPS. Concerning hADSC growth factor secretion, ELISA showed significantly higher concentrations of BDNF when cells were expanded in hPL compared with FBS-added medium, without significant differences between cells cultured on the different ECM substrates.

Conclusion

The data suggest how hADSC grown on LN and supplemented with hPL could be active and prone to support neuron–matrix interactions. hPL enhanced hADSC effects by increasing both proliferation and neurotrophic properties, including BDNF release.

Cell-free scaffolds functionalized with bionic cartilage acellular matrix microspheres to enhance the microfracture treatment of articular cartilage defects

Microfracture surgery remains the most popular treatment for articular cartilage lesions in the clinic, but often leads to the formation of inferior fibrocartilage tissue and damage to subchondral bone. To overcome these problems, extracellular matrix (ECM) scaffolds derived from decellularized natural cartilaginous tissues were introduced and showed excellent biological properties to direct the differentiation of bone marrow stem cells. However, besides the limited allogenic/allogenic supply and the risk of disease transfer from xenogeneic tissues, the effectiveness of ECM scaffolds always varied with a high variability of natural tissue quality. In this study, we developed composite scaffolds functionalized with a cell-derived ECM source, namely, bionic cartilage acellular matrix microspheres (BCAMMs), that support the chondrogenic differentiation of bone marrow cells released from microfracture. The scaffolds with BCAMMs at different developmental stages were investigated in articular cartilage regeneration and subchondral bone repair. Compared to microfracture, the addition of cell-free BCAMM scaffolds has demonstrated a great improvement of regenerated cartilage tissue quality in a rabbit model as characterized by a semi-quantitative analysis of cells, histology and biochemical assays as well as micro-CT images. Moreover, the variation in ECM properties was found to significantly affect the cartilage regeneration, highlighting the challenges of homogenous scaffolds in working with microfracture. Together, our results demonstrate that the biofunctionalized BCAMM scaffold with cell-derived ECM shows great potential to combine with microfracture for clinical translation to repair cartilage defects.

Boosting osteogenic potential and bone regeneration by co-cultured cell derived extracellular matrix incorporated porous electrospun scaffold

Implants for bone regeneration to remedy segmental bone defects, osteomyelitis, necrotic bone tissue and non-union fractures have worldwide appeal. Although biomaterials offer most of the advantages by improving tissue growth but developments are more commonly achieved via biologically derived molecules. To aid site specific bone tissue regeneration by synthetic scaffold, cell derived extracellular matrix (ECM) can be a crucial component. In this study, co-cultured bone marrow mesenchymal stem cell and osteoblastic cells derived ECM incorporated electrospun polycaprolactone (PCL) membranes were assessed for bone tissue engineering application. The preliminary experimental details indicated that, co-culture of cells supported enhanced in vitro ECM synthesis followed by successful deposition of osteoblastic ECM into electrospun membranes. The acellular samples revealed retention of ECM related biomacromolecules (collagen, glycosaminoglycan) and partial recovery of pores after decellularization. In vitro biocompatibility tests ensured improvement of proliferation and osteoblastic differentiation of MC3T3-E1 cells in decellularized ECM containing membrane (PCL-ECM) compared to bare membrane (PCL-B) which was further confirmed by osteogenic marker proteins expression analysis. The decellularized PCL-ECM membrane allowed great improvement of bone regeneration over the bare membrane (PCL-B) in 8 mm size critical sized rat skull defects at 2 months of post implantation. In short, the outcome of this study could be impactful in development and application of cell derived ECM based synthetic electrospun templates for bone tissue engineering application.[Formula: see text].

Interaction between Schwann cells and other cells during repair of peripheral nerve injury

Peripheral nerve injury (PNI) is common and, unlike damage to the central nervous system injured nerves can effectively regenerate depending on the location and severity of injury. Peripheral myelinating glia, Schwann cells (SCs), interact with various cells in and around the injury site and are important for debris elimination, repair, and nerve regeneration. Following PNI, Wallerian degeneration of the distal stump is rapidly initiated by degeneration of damaged axons followed by morphologic changes in SCs and the recruitment of circulating macrophages. Interaction with fibroblasts from the injured nerve microenvironment also plays a role in nerve repair. The replication and migration of injury-induced dedifferentiated SCs are also important in repairing the nerve. In particular, SC migration stimulates axonal regeneration and subsequent myelination of regenerated nerve fibers. This mobility increases SC interactions with other cells in the nerve and the exogenous environment, which influence SC behavior post-injury. Following PNI, SCs directly and indirectly interact with other SCs, fibroblasts, and macrophages. In addition, the inter- and intracellular mechanisms that underlie morphological and functional changes in SCs following PNI still require further research to explain known phenomena and less understood cell-specific roles in the repair of the injured peripheral nerve. This review provides a basic assessment of SC function post-PNI, as well as a more comprehensive evaluation of the literature concerning the SC interactions with macrophages and fibroblasts that can influence SC behavior and, ultimately, repair of the injured nerve.

Cell derived extracellular matrix-rich biomimetic substrate supports podocyte proliferation, differentiation and maintenance of native phenotype

Current technologies and available scaffold materials do not support long-term cell viability, differentiation and maintenance of podocytes, the ultra-specialized kidney resident cells that are responsible for the filtration of the blood. We developed a new platform which imitates the native kidney microenvironment by decellularizing fibroblasts grown on surfaces with macromolecular crowding. Human immortalized podocytes cultured on this platform displayed superior viability and metabolic activity up to 28 days compared to podocytes cultured on tissue culture plastic surfaces. The new platform displayed a softer surface and an abundance of growth factors and associated molecules. More importantly it enabled podocytes to display molecules responsible for their structure and function and a superior development of intercellular connections/interdigitations, consistent with maturation. The new platform can be used to study podocyte biology, test drug toxicity and determine whether sera from patients with podocytopathies are involved in the expression of glomerular pathology.

Micropatterning Decellularized ECM as a Bioactive Surface to Guide Cell Alignment, Proliferation, and Migration

Bioactive surfaces and materials have displayed great potential in a variety of tissue engineering applications but often struggle to completely emulate complex bodily systems. The extracellular matrix (ECM) is a crucial, bioactive component in all tissues and has recently been identified as a potential solution to be utilized in combination with biomaterials. In tissue engineering, the ECM can be utilized in a variety of applications by employing the biochemical and biomechanical cues that are crucial to regenerative processes. However, viable solutions for maintaining the dimensionality, spatial orientation, and protein composition of a naturally cell-secreted ECM remain challenging in tissue engineering. Therefore, this work used soft lithography to create micropatterned polydimethylsiloxane (PDMS) substrates of a three-dimensional nature to control cell adhesion and alignment. Cells aligned on the micropatterned PDMS, secreted and assembled an ECM, and were decellularized to produce an aligned matrix biomaterial. The cells seeded onto the decellularized, patterned ECM showed a high degree of alignment and migration along the patterns compared to controls. This work begins to lay the groundwork for elucidating the immense potential of a natural, cell-secreted ECM for directing cell function and offers further guidance for the incorporation of natural, bioactive components for emerging tissue engineering technologies.

Investigation of the effects of laminin present in the basal lamina of the peripheral nervous system on axon regeneration and remyelination using the nerve acellular scaffold

This study aimed to investigate the effects of laminin (LN) located in the basal lamina, which are important components of the peripheral nervous system-extracellular matrix, on axon regeneration and remyelination. Nerve acellular scaffolds (NASs) (S-untreated) were prepared using the acellular technique. The active component LN in the NASs was blocked (S-LN^- ) or upregulated (S-LN⁺ ); S-LN+ contained seven times more LN than did the S-untreated group. The adhesion capacity of Schwann cells (SCs) to the three types of NAS (S-untreated, S-LN^- , and S-LN⁺ ) was assessed in vitro. Our results showed that the adhesion of SCs to the NASs was significantly reduced in the S-LN^- group, whereas no difference was observed between the S-LN⁺ and S-untreated groups. The pretreated NASs were used to repair nerves in a nerve injury mouse model with the animals divided into four groups (S-LN^- group, S-untreated group, S-LN⁺ group, and autograft group). Two weeks after surgery, although there was no difference in the S-LN^- group, S-untreated group and S-LN⁺ group, the newly formed basal lamina in the S-LN^- group were significantly lower than those in the other two groups. Four weeks after surgery, the S-LN⁺ group had higher numbers of newly generated axons and their calibers, more myelinated fibers, thicker myelin sheaths, increased myelin basic protein expression, and improved recovery of neural function compared to those of the S-LN^- and S-untreated groups, but all of these parameters were significantly worse than those of the autograft group. Downregulation of the LN level in the NAS leads to a reduction in all of the above parameters.

Development of a Piezoelectric PVDF-TrFE Fibrous Scaffold to Guide Cell Adhesion, Proliferation, and Alignment

Severe peripheral nervous system injuries currently hold limited therapeutic solutions. Existing clinical techniques such as autografts, allografts, and newer nerve guidance conduits have shown variable outcomes in functional recovery, adverse immune responses, and in some cases low or minimal availability. This can be attributed in part to the lack of chemical, physical, and electrical cues directing both nerve guidance and regeneration. To address this pressing clinical issue, electrospun nanofibers and microfibers composed of piezoelectric polyvinylidene flouride-triflouroethylene (PVDF-TrFE) have been introduced as an alternative template for tissue engineered biomaterials, specifically as it pertains to their relevance in soft tissue and nerve repair. Here, biocompatible scaffolds of PVDF-TrFE are fabricated and their ability to generate an electrical response to mechanical deformations and produce a suitable regenerative microenvironment is examined. It is determined that 20% (w/v) PVDF-TrFE in (6:4) dimethyl formamide (DMF):acetone solvent maintains a desirable piezoelectric coefficient and the proper physical and electrical characteristics for tissue regeneration. Further, it is concluded that scaffolds of varying thickness promoted the adhesion and alignment of Schwann cells and fibroblasts. This work offers a prelude to further advancements in nanofibrous technology and a promising outlook for alternative, autologous remedies to peripheral nerve damage.

Collagen fiber structure guides 3D motility of cytotoxic T lymphocytes

Lymphocyte motility is governed by a complex array of mechanisms, and highly dependent on external microenvironmental cues. Tertiary lymphoid sites in particular have unique physical structure such as collagen fiber alignment, due to matrix deposition and remodeling. Three dimensional studies of human lymphocytes in such environments are lacking. We hypothesized that aligned collagenous environment modulates CD8+ T cells motility. We encapsulated activated CD8+ T cells in collagen hydrogels of distinct fiber alignment, a characteristic of tumor microenvironments. We found that human CD8+ T cells move faster and more persistently in aligned collagen fibers compared with nonaligned collagen fibers. Moreover, CD8+ T cells move along the axis of collagen alignment. We showed that myosin light chain kinase (MLCK) inhibition could nullify the effect of aligned collagen on CD8+ T cell motility patterns by decreasing T cell turning in unaligned collagen fiber gels. Finally, as an example of a tertiary lymphoid site, we found that xenograft prostate tumors exhibit highly aligned collagen fibers. We observed CD8+ T cells alongside aligned collagen fibers, and found that they are mostly concentrated in the periphery of tumors. Overall, using an in vitro controlled hydrogel system, we show that collagen fiber organization modulates CD8+ T cells movement via MLCK activation thus providing basis for future studies into relevant therapeutics.

Extracellular matrix cues modulate Schwann cell morphology, proliferation, and protein expression

Peripheral nerve injuries require a complex set of signals from cells, macrophages, and the extracellular matrix (ECM) to induce regeneration across injury sites and achieve functional recovery. Schwann cells (SCs), the major glial cell in the peripheral nervous system (PNS), are critical to nerve regeneration due to their inherent capacity for altering phenotype postinjury to facilitate wound healing. The ECM plays a vital role in wound healing as well as regulating cell phenotype during tissue repair. To examine the underlying mechanisms between the ECM and SCs, this work sought to determine how specific ECM cues regulate the phenotype of SCs. To address this, SCs were cultured on polydimethylsiloxane substrates of a variable Young's modulus coated with ECM proteins. Cells were analyzed for spreading area, proliferation, cell and nuclear shape, and c-Jun expression. It was found that substrates with a stiffness of 8.67 kPa coated with laminin promoted the highest expression of c-Jun, a marker signifying a "regenerative" SC. Microcontact printed, cell adhesive areas were then utilized to precisely control the geometry and spreading of SCs and by controlling spreading area and cellular elongation; expression of c-Jun was either promoted or downregulated. These results begin to address the significant interplay between ECM cues and phenotype of SCs, while offering a potential means to enhance PNS regeneration through cellular therapies.

Nanomaterial-Based Approaches for Neural Regeneration

Mechanical, thermal, chemical, or ischemic injury of the central or peripheral nervous system results in neuron loss, neurite damage, and/or neuronal dysfunction, almost always accompanied by sensorimotor impairment which alters the patient's life quality. The regenerative strategies for the injured nervous system are currently limited and mainly allow partial functional recovery, so it is necessary to develop new and effective approaches for nervous tissue regenerative therapy. Nanomaterials based on inorganic or organic and composite or hybrid compounds with tunable physicochemical properties and functionality proved beneficial for the transport and delivery/release of various neuroregenerative-relevant biomolecules or cells. Within the following paragraphs, we will emphasize that nanomaterial-based strategies (including nanosized and nanostructured biomaterials) represent a promising alternative towards repairing and regenerating the injured nervous system.

Controlling the Surface Chemistry of a Hydrogel for Spatially Defined Cell Adhesion

A two-step synthesis is described for activating the surface of a fully hydrated hydrogel that is of interest as a possible scaffold for neural regeneration devices. The first step exploits the water content of the hydrogel and the hydrophobicity of the reaction solvent to create a thin oxide layer on the hydrogel surface using a common titanium or zirconium alkoxide. This layer serves as a reactive interface that enables rapid transformation of the hydrophilic, cell-nonadhesive hydrogel into either a highly hydrophobic surface by reaction with an alkylphosphonic acid, or into a cell-adhesive one using a (α,ω-diphosphono)alkane. Physically imprinting a mask ("debossing") into the hydrogel, followed by a two-step surface modification with a phosphonate, allows for patterning its surface to create spatially defined, cell-adhesive regions.

Self-assembled monolayers of phosphonates promote primary chondrocyte adhesion to silicon dioxide and polyvinyl alcohol materials

The optimal solution for articular cartilage repair has not yet been identified, in part because of the challenges in achieving integration with the host. Coatings have the potential to transform the adhesive features of surfaces, but their application to cartilage repair has been limited. Self-assembled monolayer of phosphonates (SAMPs) have been demonstrated to increase the adhesion of various immortalized cell types to metal and polymer surfaces, but their effect on primary chondrocyte adhesion has not been studied. The objective of this study was to investigate the response of primary chondrocytes to SAMP coatings. We hypothesized a SAMP terminated with an α,ω-bisphosphonic acid, in particular butane-1,4-diphosphonic acid, would increase the number of adherent primary chondrocytes to polyvinyl alcohol (PVA). To test our hypothesis, we first established our ability to successfully modify silicon dioxide (SiO2) surfaces to enable chondrocytes to attach to the surface, without substantial changes in gene expression. Secondly, we applied identical chemistry to PVA, and quantified chondrocyte adhesion. SAMP modification to SiO2 increased chondrocyte adhesion by ×3 after 4 hr and ×4.5 after 24 hr. PVA modification with SAMPs increased chondrocyte adhesion by at least ×31 after 4 and 24 hours. Changes in cell morphology indicated that SAMP modification led to improved chondrocyte adhesion and spreading, without changes in gene expression. In summary, we modified SiO2 and PVA with SAMPs and observed an increase in the number of adherent primary bovine chondrocytes at 4 and 24 hr post-seeding. Mechanisms of chondrocyte interaction with SAMP-modified surfaces require further investigation.

Tissue Models for Neurogenesis and Repair in 3D

Development and maturation of vascular and neuronal tissues occurs simultaneously in utero, and are regulated by significant crosstalk. We report on the development of a 3D tissue system to model neurogenesis and recapitulate developmental signaling conditions. Human umbilical vein endothelial cells (HUVECs) were seeded inside channels within collagen gels to represent nascent vascular networks. Axons extending from chicken dorsal root ganglia (DRGs) grew significantly longer and preferentially towards the HUVEC seeded channels with respect to unloaded channels. To replicate these findings without the vascular component, channels were loaded with brain-derived neurotrophic factor (BDNF), the principle signaling molecule in HUVEC-stimulated axonal growth, and axons likewise were significantly longer and grew preferentially towards the BDNF-loaded channels with respect to controls. This 3D tissue system was then used as an in vitro replicate for peripheral nerve injury, with neural repair observed within 2 weeks. These results demonstrate that our 3D tissue system can model neural network formation, repair after laceration injuries, and can be utilized to further study how these networks form and interact with other tissues, such as skin or skeletal muscle.

Vitronectin from brain pericytes promotes adult forebrain neurogenesis by stimulating CNTF

Vitronectin (VTN) is a glycoprotein in the blood and affects hemostasis. VTN is also present in the extracellular matrix of various organs but little is known about its function in healthy adult tissues. We show, in adult mice, that VTN is uniquely expressed by approximately half of the pericytes of subventricular zone (SVZ) where neurogenesis continues throughout life. Intracerebral VTN antibody injection or VTN knockout reduced neurogenesis as well as expression of pro-neurogenic CNTF, and anti-neurogenic LIF and IL-6. Conversely, injections of VTN, or plasma from VTN+/+, but not VTN-/- mice, increased these cytokines. VTN promoted SVZ neurogenesis when LIF and IL-6 were suppressed by co-administration of a gp130 inhibitor. Unexpectedly, VTN inhibited FAK signaling and VTN-/- mice had increased FAK signaling in the SVZ. Further, an FAK inhibitor or VTN increased CNTF expression, but not in conditional astrocytic FAK knockout mice, suggesting that VTN increases CNTF through FAK inhibition in astrocytes. These results identify a novel role of pericyte-derived VTN in the brain, where it regulates SVZ neurogenesis through co-expression of CNTF, LIF and IL-6. VTN-integrin-FAK and gp130 signaling may provide novel targets to induce neurogenesis for cell replacement therapies.

The Physicochemical Properties of Decellularized Extracellular Matrix-Coated 3D Printed Poly(ε-caprolactone) Nerve Conduits for Promoting Schwann Cells Proliferation and Differentiation

Although autologous nerve grafting remains the gold standard treatment for peripheral nerve injuries, alternative methods such as development of nerve guidance conduits have since emerged and evolved to counter the many disadvantages of nerve grafting. However, the efficacy and viability of current nerve conduits remain unclear in clinical trials. Here, we focused on a novel decellularized extracellular matrix (dECM) and polydopamine (PDA)-coated 3D-printed poly(ε-caprolactone) (PCL)-based conduits, whereby the PDA surface modification acts as an attachment platform for further dECM attachment. We demonstrated that dECM/PDA-coated PCL conduits possessed higher mechanical properties when compared to human or animal nerves. Such modifications were proved to affect cell behaviors. Cellular behaviors and neuronal differentiation of Schwann cells were assessed to determine for the efficacies of the conduits. There were some cell-specific neuronal markers, such as Nestin, neuron-specific class III beta-tubulin (TUJ-1), and microtubule-associated protein 2 (MAP2) analyzed by enzyme-linked immunosorbent assay, and Nestin expressions were found to be 0.65-fold up-regulated, while TUJ1 expressions were 2.3-fold up-regulated and MAP2 expressions were 2.5-fold up-regulated when compared to Ctl. The methodology of PDA coating employed in this study can be used as a simple model to immobilize dECM onto PCL conduits, and the results showed that dECM/PDA-coated PCL conduits can as a practical and clinically viable tool for promoting regenerative outcomes in larger peripheral nerve defects.

Spinal Cord Injury Scarring and Inflammation: Therapies Targeting Glial and Inflammatory Responses

Deficits in neuronal function are a hallmark of spinal cord injury (SCI) and therapeutic efforts are often focused on central nervous system (CNS) axon regeneration. However, secondary injury responses by astrocytes, microglia, pericytes, endothelial cells, Schwann cells, fibroblasts, meningeal cells, and other glia not only potentiate SCI damage but also facilitate endogenous repair. Due to their profound impact on the progression of SCI, glial cells and modification of the glial scar are focuses of SCI therapeutic research. Within and around the glial scar, cells deposit extracellular matrix (ECM) proteins that affect axon growth such as chondroitin sulfate proteoglycans (CSPGs), laminin, collagen, and fibronectin. This dense deposition of material, i.e., the fibrotic scar, is another barrier to endogenous repair and is a target of SCI therapies. Infiltrating neutrophils and monocytes are recruited to the injury site through glial chemokine and cytokine release and subsequent upregulation of chemotactic cellular adhesion molecules and selectins on endothelial cells. These peripheral immune cells, along with endogenous microglia, drive a robust inflammatory response to injury with heterogeneous reparative and pathological properties and are targeted for therapeutic modification. Here, we review the role of glial and inflammatory cells after SCI and the therapeutic strategies that aim to replace, dampen, or alter their activity to modulate SCI scarring and inflammation and improve injury outcomes.

Cell-derived decellularized extracellular matrices

The ability to create cell-derived decellularized matrices in a dish gives researchers the opportunity to possess a bioactive, biocompatible material made up of fibrillar proteins and other factors that recapitulates key features of the native structure and composition of in vivo microenvironments. By using cells in a culture system to provide a natural ECM, decellularization allows for a high degree of customization through the introduction of selected proteins and soluble factors. The culture system, culture medium, cell types, and physical environments can be varied to provide specialized ECMs for wide-ranging applications to study cell-ECM signaling, cell migration, cell differentiation, and tissue engineering purposes. This chapter describes a procedure for performing a detergent and high pH-based extraction that leaves the native, cell-assembled ECM intact while removing cellular materials. We address common evaluation methods for assessing the ECM and its composition as well as potential uses for a decellularized ECM.