Prevascularized Scaffolds Bearing Human Dental Pulp Stem Cells for Treating Complete Spinal Cord Injury

Angiogenic Potential of Various Oral Cavity-Derived Mesenchymal Stem Cells and Cell-Derived Secretome: A Systematic Review and Meta-Analysis

Recent evidence suggests the immense potential of human mesenchymal stem cell (hMSC) secretome conditioned medium-mediated augmentation of angiogenesis. However, angiogenesis potential varies from source and origin. The hMSCs derived from the oral cavity share an exceptional quality due to their origin from a hypoxic environment. Our systematic review aimed to compare the mesenchymal stem cells (MSCs) derived from various oral cavity sources and cell-derived secretomes, and evaluate their angiogenic potential. A literature search was conducted using PubMed and Scopus from January 2000 to September 2020. Source-wise outcomes were systematically analyzed using in vitro, in vivo, and in ovo studies, emphasizing endothelial cell migration, tube formation, and blood vessel formation. Ninety-four studies were included in the systematic review, out of which 4 studies were subsequently included in the meta-analysis. Prominent growth factors and other bioactive components implicated in improving angiogenesis were included in the respective studies. The findings suggest that oral tissues are a rich source of hMSCs. The meta-analysis revealed a positive correlation between dental pulp-derived MSCs (DPMSCs) and stem cells derived from apical papilla (SCAP) compared to human umbilical cord-derived endothelial cell lines as a control. It shows a statistically significant positive correlation between the co-culture of human umbilical vein endothelial cells (HUVECs) and DPMSCs with tubule length formation and total branching points. Our meta-analysis revealed that oral-derived MSCs (dental pulp stem cells and SCAP) carry a better angiogenic potential in vitro than endothelial cell lines alone. The reviewed literature illustrates that oral cavity-derived MSCs (OC-MSCs) increased angiogenesis. The present literature reveals a dearth of investigations involving sources other than dental pulp. Even though OC-MSCs have revealed more significant potential than other MSCs, more comprehensive, target-oriented interinstitutional prospective studies are warranted to determine whether oral cavity-derived stem cells are the most excellent sources of significant angiogenic potential.

Primitive macrophages enable long-term vascularization of human heart-on-a-chip platforms

The intricate anatomical structure and high cellular density of the myocardium complicate the bioengineering of perfusable vascular networks within cardiac tissues. In vivo neonatal studies highlight the key role of resident cardiac macrophages in post-injury regeneration and angiogenesis. Here, we integrate human pluripotent stem-cell-derived primitive yolk-sac-like macrophages within vascularized heart-on-chip platforms. Macrophage incorporation profoundly impacted the functionality and perfusability of microvascularized cardiac tissues up to 2 weeks of culture. Macrophages mitigated tissue cytotoxicity and the release of cell-free mitochondrial DNA (mtDNA), while upregulating the secretion of pro-angiogenic, matrix remodeling, and cardioprotective cytokines. Bulk RNA sequencing (RNA-seq) revealed an upregulation of cardiac maturation and angiogenesis genes. Further, single-nuclei RNA sequencing (snRNA-seq) and secretome data suggest that macrophages may prime stromal cells for vascular development by inducing insulin like growth factor binding protein 7 (IGFBP7) and hepatocyte growth factor (HGF) expression. Our results underscore the vital role of primitive macrophages in the long-term vascularization of cardiac tissues, offering insights for therapy and advancing heart-on-a-chip technologies.

Graphene/ chitosan tubes inoculated with dental pulp stem cells promotes repair of facial nerve injury

Introduction: Facial nerve injury significantly impacts both the physical and psychological] wellbeing of patients. Despite advancements, there are still limitations associated with autografts transplantation. Consequently, there is an urgent need for effective artificial grafts to address these limitations and repair injuries. Recent years have witnessed the recognition of the beneficial effects of chitosan (CS) and graphene in the realm of nerve repair. Dental pulp stem cells (DPSCs) hold great promise due to their high proliferative and multi-directional differentiation capabilities. Methods: In this study, Graphene/CS (G/CST) composite tubes were synthesized and their physical, chemical and biological properties were evaluated, then DPSCs were employed as seed cells and G/CST as a scaffold to investigate their combined effect on promoting facial nerve injury repair. Results and Disscussion: The experimental results indicate that G/CST possesses favorable physical and chemical properties, along with good cyto-compatibility. making it suitable for repairing facial nerve transection injuries. Furthermore, the synergistic application of G/CST and DPSCs significantly enhanced the repair process for a 10 mm facial nerve defect in rabbits, highlighting the efficacy of graphene as a reinforcement material and DPSCs as a functional material in facial nerve injury repair. This approach offers an effective treatment strategy and introduces a novel concept for clinically managing facial nerve injuries.

Biomaterial strategies for regulating the neuroinflammatory response

Injury and disease in the central nervous system (CNS) can result in a dysregulated inflammatory environment that inhibits the repair of functional tissue. Biomaterials present a promising approach to tackle this complex inhibitory environment and modulate the mechanisms involved in neuroinflammation to halt the progression of secondary injury and promote the repair of functional tissue. In this review, we will cover recent advances in biomaterial strategies, including nanoparticles, hydrogels, implantable scaffolds, and neural probe coatings, that have been used to modulate the innate immune response to injury and disease within the CNS. The stages of inflammation following CNS injury and the main inflammatory contributors involved in common neurodegenerative diseases will be discussed, as understanding the inflammatory response to injury and disease is critical for identifying therapeutic targets and designing effective biomaterial-based treatment strategies. Biomaterials and novel composites will then be discussed with an emphasis on strategies that deliver immunomodulatory agents or utilize cell-material interactions to modulate inflammation and promote functional tissue repair. We will explore the application of these biomaterial-based strategies in the context of nanoparticle- and hydrogel-mediated delivery of small molecule drugs and therapeutic proteins to inflamed nervous tissue, implantation of hydrogels and scaffolds to modulate immune cell behavior and guide axon elongation, and neural probe coatings to mitigate glial scarring and enhance signaling at the tissue-device interface. Finally, we will present a future outlook on the growing role of biomaterial-based strategies for immunomodulation in regenerative medicine and neuroengineering applications in the CNS.

Molars to Medicine: A Focused Review on the Pre-Clinical Investigation and Treatment of Secondary Degeneration following Spinal Cord Injury Using Dental Stem Cells

Spinal cord injury (SCI) can result in the permanent loss of mobility, sensation, and autonomic function. Secondary degeneration after SCI both initiates and propagates a hostile microenvironment that is resistant to natural repair mechanisms. Consequently, exogenous stem cells have been investigated as a potential therapy for repairing and recovering damaged cells after SCI and other CNS disorders. This focused review highlights the contributions of mesenchymal (MSCs) and dental stem cells (DSCs) in attenuating various secondary injury sequelae through paracrine and cell-to-cell communication mechanisms following SCI and other types of neurotrauma. These mechanistic events include vascular dysfunction, oxidative stress, excitotoxicity, apoptosis and cell loss, neuroinflammation, and structural deficits. The review of studies that directly compare MSC and DSC capabilities also reveals the superior capabilities of DSC in reducing the effects of secondary injury and promoting a favorable microenvironment conducive to repair and regeneration. This review concludes with a discussion of the current limitations and proposes improvements in the future assessment of stem cell therapy through the reporting of the effects of DSC viability and DSC efficacy in attenuating secondary damage after SCI.

The potential therapeutic roles of dental pulp stem cells in spinal cord injury

Spinal cord injury (SCI) can lead to serious functional disorders, which have serious impacts on patients and society. The current traditional treatments of SCI are not effective the injured spinal cord is difficult to repair and regenerate. In recent years, stem cell transplantation for the treatment of SCI has been a hot research topic. Dental pulp stem cells have strong abilities of self-renewal and multi-directional differentiation, and have been applied for tissue engineering and regenerative medicine. And dental pulp stem cells have certain advantages in neuro-regenetation, bringing new hope to biotherapy for SCI. This article reviews the characteristics of dental pulp stem cells and their research progress in the treatment of SCI.

Bioengineering Cell Therapy for Treatment of Peripheral Artery Disease

Peripheral artery disease is an atherosclerotic disease associated with limb ischemia that necessitates limb amputation in severe cases. Cell therapies comprised of adult mononuclear or stromal cells have been clinically tested and show moderate benefits. Bioengineering strategies can be applied to modify cell behavior and function in a controllable fashion. Using mechanically tunable or spatially controllable biomaterials, we highlight examples in which biomaterials can increase the survival and function of the transplanted cells to improve their revascularization efficacy in preclinical models. Biomaterials can be used in conjunction with soluble factors or genetic approaches to further modulate the behavior of transplanted cells and the locally implanted tissue environment in vivo. We critically assess the advances in bioengineering strategies such as 3-dimensional bioprinting and immunomodulatory biomaterials that can be applied to the treatment of peripheral artery disease and then discuss the current challenges and future directions in the implementation of bioengineering strategies.

Analogies and Differences Between Dental Stem Cells: Focus on Secretome in Combination with Scaffolds in Neurological Disorders

Mesenchymal stem cells (MSCs) are well known for their beneficial effects, differentiation capacity and regenerative potential. Dental-derived MSCs (DSCs) are more easily accessible and have a non-invasive isolation method rather than MSCs isolated from other sources (umbilical cord, bone marrow, and adipose tissue). In addition, DSCs appear to have a relevant neuro-regenerative potential due to their neural crest origin. However, it is now known that the beneficial effects of MSCs depend, at least in part, on their secretome, referring to all the bioactive molecules (neurotrophic factors) released in the conditioned medium (CM) or in the extracellular vesicles (EVs) in particular exosomes (Exos). In this review, we described the similarities and differences between various DSCs. Our focus was on the secretome of DSCs and their applications in cell therapy for neurological disorders. For neuro-regenerative purposes, the secretome of different DSCs has been tested. Among these, the secretome of dental pulp stem cells and stem cells from human exfoliated deciduous teeth have been the most widely studied. Both CM and Exos obtained from DSCs have been shown to promote neurite outgrowth and neuroprotective effects as well as their combination with scaffold materials (to improve their functional integration in the tissue). For these reasons, the secretome obtained from DSCs in combination with scaffold materials may represent a promising tissue engineering approach for neuroprotective and neuro-regenerative treatments.

Modified ECM-Based Bioink for 3D Printing of Multi-Scale Vascular Networks

The survival and function of tissues depend on appropriate vascularization. Blood vessels of the tissues supply oxygen, and nutrients and remove waste and byproducts. Incorporating blood vessels into engineered tissues is essential for overcoming diffusion limitations, improving tissue function, and thus facilitating the fabrication of thick tissues. Here, we present a modified ECM bioink, with enhanced mechanical properties and endothelial cell-specific adhesion motifs, to serve as a building material for 3D printing of a multiscale blood vessel network. The bioink is composed of natural ECM and alginate conjugated with a laminin adhesion molecule motif (YIGSR). The hybrid hydrogel was characterized for its mechanical properties, biochemical content, and ability to interact with endothelial cells. The pristine and modified hydrogels were mixed with induced pluripotent stem cells derived endothelial cells (iPSCs-ECs) and used to print large blood vessels with capillary beds in between.

Skin precursor‐derived Schwann cells accelerate in vivo prevascularization of tissue‐engineered nerves to promote peripheral nerve regeneration

Prevascularization strategies have become a hot spot in tissue engineering. As one of the potential candidates for seed cells, skin precursor-derived Schwann cells (SKP-SCs) were endowed with a new role to more efficiently construct prevascularized tissue-engineered peripheral nerves. The silk fibroin scaffolds seeded with SKP-SCs were prevascularized through subcutaneously implantation, which was further assembled with the SKP-SC-containing chitosan conduit. SKP-SCs expressed pro-angiogenic factors in vitro and in vivo. SKP-SCs significantly accelerated the satisfied prevascularization in vivo of silk fibroin scaffolds compared with VEGF. Moreover, the NGF expression revealed that pregenerated blood vessels adapted to the nerve regeneration microenvironment through reeducation. The short-term nerve regeneration of SKP-SCs-prevascularization was obviously superior to that of non-prevascularization. At 12 weeks postinjury, both SKP-SCs-prevascularization and VEGF-prevascularization significantly improved nerve regeneration with a comparable degree. Our figures provide a new enlightenment for the optimization of prevascularization strategies and how to further utilize tissue engineering for better repair.

The Application of Biomaterials in Spinal Cord Injury

The spinal cord and the brain form the central nervous system (CNS), which is the most important part of the body. However, spinal cord injury (SCI) caused by external forces is one of the most difficult types of neurological injury to treat, resulting in reduced or even absent motor, sensory and autonomic functions. It leads to the reduction or even disappearance of motor, sensory and self-organizing nerve functions. Currently, its incidence is increasing each year worldwide. Therefore, the development of treatments for SCI is urgently needed in the clinic. To date, surgery, drug therapy, stem cell transplantation, regenerative medicine, and rehabilitation therapy have been developed for the treatment of SCI. Among them, regenerative biomaterials that use tissue engineering and bioscaffolds to transport cells or drugs to the injured site are considered the most promising option. In this review, we briefly introduce SCI and its molecular mechanism and summarize the application of biomaterials in the repair and regeneration of tissue in various models of SCI. However, there is still limited evidence about the treatment of SCI with biomaterials in the clinic. Finally, this review will provide inspiration and direction for the future study and application of biomaterials in the treatment of SCI.

3D printing of cell-delivery scaffolds for tissue regeneration

Tissue engineering strategy that combine biomaterials with living cells has shown special advantages in tissue regeneration and promoted the development of regenerative medicine. In particular, the rising of 3D printing technology further enriched the structural design and composition of tissue engineering scaffolds, which also provided convenience for cell loading and cell delivery of living cells. In this review, two types of cell-delivery scaffolds for tissue regeneration, including 3D printed scaffolds with subsequent cell-seeding and 3D cells bioprinted scaffolds, are mainly reviewed. We devote a major part to present and discuss the recent advances of two 3D printed cell-delivery scaffolds in regeneration of various tissues, involving bone, cartilage, skin tissues etc. Although two types of 3D printed cell-delivery scaffolds have some shortcomings, they do have generally facilitated the exploration of tissue engineering scaffolds in multiple tissue regeneration. It is expected that 3D printed cell-delivery scaffolds will be further explored in function mechanism of seeding cells in vivo, precise mimicking of complex tissues and even organ reconstruction under the cooperation of multiple fields in future.

Therapeutic Approaches Targeting Vascular Repair After Experimental Spinal Cord Injury: A Systematic Review of the Literature

Traumatic spinal cord injury (SCI) disrupts the spinal cord vasculature resulting in ischemia, amplification of the secondary injury cascade and exacerbation of neural tissue loss. Restoring functional integrity of the microvasculature to prevent neural loss and to promote neural repair is an important challenge and opportunity in SCI research. Herein, we summarize the course of vascular injury and repair following SCI and give a comprehensive overview of current experimental therapeutic approaches targeting spinal cord microvasculature to diminish ischemia and thereby facilitate neural repair and regeneration. A systematic review of the published literature on therapeutic approaches to promote vascular repair after experimental SCI was performed using PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) standards. The MEDLINE databases PubMed, Embase, and OVID MEDLINE were searched using the keywords "spinal cord injury," "angiogenesis," "angiogenesis inducing agents," "tissue engineering," and "rodent subjects." A total of 111 studies were identified through the search. Five main therapeutic approaches to diminish hypoxia-ischemia and promote vascular repair were identified as (1) the application of angiogenic factors, (2) genetic engineering, (3) physical stimulation, (4) cell transplantation, and (5) biomaterials carrying various factor delivery. There are different therapeutic approaches with the potential to diminish hypoxia-ischemia and promote vascular repair after experimental SCI. Of note, combinatorial approaches using implanted biomaterials and angiogenic factor delivery appear promising for clinical translation.

Cellular orientational fluctuations, rotational diffusion and nematic order under periodic driving

The ability of living cells to sense the physical properties of their microenvironment and to respond to dynamic forces acting on them plays a central role in regulating their structure, function and fate. Of particular importance is the cellular sensitivity and response to periodic driving forces in noisy environments, encountered in vital physiological conditions such as heart beating, blood vessel pulsation and breathing. Here, we first test and validate two predictions of a mean-field theory of cellular reorientation under periodic driving, which combines the minimization of cellular anisotropic elastic energy with active remodeling forces. We then extend the mean-field theory to include uncorrelated, additive nonequilibrium fluctuations, and show that the theory quantitatively agrees with the experimentally observed stationary probability distributions of the cell body orientation, under a range of biaxial periodic driving forces. The fluctuations theory allows the extraction of the dimensionless active noise amplitude of various cell types, and consequently their rotational diffusion coefficient. We then focus on intra-cellular nematic order, i.e. on orientational fluctuations of actin stress fibers around the cell body orientation, and show experimentally that intra-cellular nematic order increases with both the magnitude of the driving forces and the biaxiality strain ratio. These results are semi-quantitatively explained by applying the same cell body fluctuations theory to orientationally correlated actin stress fiber domains. Finally, an estimate of the energy scale of cellular orientational fluctuations for one cell type is shown to be about six order of magnitude larger than the thermal energy at room temperature. The implications of our findings, which make the quantitative analysis of cell mechanosensitivity more accessible, are discussed.

Development and Application of Three-Dimensional Bioprinting Scaffold in the Repair of Spinal Cord Injury

Spinal cord injury (SCI) is a disabling and destructive central nervous system injury that has not yet been successfully treated at this stage. Three-dimensional (3D) bioprinting has become a promising method to produce more biologically complex microstructures, which fabricate living neural constructs with anatomically accurate complex geometries and spatial distributions of neural stem cells, and this is critical in the treatment of SCI. With the development of 3D printing technology and the deepening of research, neural tissue engineering research using different printing methods, bio-inks, and cells to repair SCI has achieved certain results. Although satisfactory results have not yet been achieved, they have provided novel ideas for the clinical treatment of SCI. Considering the potential impact of 3D bioprinting technology on neural studies, this review focuses on 3D bioprinting methods widely used in SCI neural tissue engineering, and the latest technological applications of bioprinting of nerve tissues for the repair of SCI are discussed. In addition to introducing the recent progress, this work also describes the existing limitations and highlights emerging possibilities and future prospects in this field.

A concise review of the orofacial mesenchymal stromal cells as a novel therapy for neurological diseases and injuries

Orofacial mesenchymal stromal cells (OFMSCs) are mesenchymal stromal cells isolated from the oral and facial regions, which possess typical mesenchymal stromal cell features such as self-renewing, multilineage differentiation, and immunoregulatory properties. Recently, increasing studies have been carried out on the neurotrophic and neuroregenerative properties of OFMSCs as well as their potential to treat neurological diseases. In this review, we summarize the current evidence and discuss the prospects regarding the therapeutic potential of OFMSCs as a new approach to treat different neurological diseases and injuries.

A micro-channel array in a tissue engineered vessel graft guides vascular morphogenesis for anastomosis with self-assembled vascular networks

Vascularization of 3D engineered tissues poses a great challenge in the field of tissue engineering. One promising approach for vascularizing engineered tissue is cocultivation with endothelial cells (ECs), which spontaneously self-assemble into a natural capillary network in the presence of supportive cells. However, the ECs do not self-assemble according to physiological hierarchy which is required to support blood supply. This work describes the design and fabrication of an AngioTube, a biodegradable engineered macro-vessel surrounded by cylindrical micro-channel array, which is designed to support physiological flow distribution and enable the integration with living capillaries. The well-defined geometry of the engineered micro-channels guides endothelial cells to form patent micro-vessels which sprouted in accordance with the channel orientation. Three different in-vitro models were used to demonstrate anastomosis of these engineered micro-vessels with self-assembled vascular networks. Finally, in-vivo functionality was demonstrated by direct anastomosis with the femoral artery in a rat hindlimb model. This unique approach proposes a new micro-fabrication strategy which introduces uncompromised micro-fluidic device geometrical accuracy at the tissue-scale level. STATEMENT OF SIGNIFICANCE: This study proposes a micro-fabrication strategy suitable for processing real-scale cylindrical implants with very high accuracy, which will enable translation of the high-resolution geometry of micro-fluidic devices to clinically relevant implants containing functional multi-scale vascular networks. Moreover, this approach promises to advance the field of tissue engineering by opening new opportunities to explore the impact of well controlled and uncompromised 3D micro-geometry on cellular behavior.

Advances in vascularization and innervation of constructs for neural tissue engineering

A growing number of technologies are being developed to promote vascularization and innervation in engineered tissues. Organ-on-a-chip, organoid and 3D printing technologies, as well as pre-vascularized and oriented scaffolds, have been employed for vascularization and innervation of engineered tissues both in vivo and in vitro. Both vascularization and innervation are critical for neural tissue engineering, as these complex tissues require provision of both blood and nerves. As such, this review will have particular focus on neural tissue engineering. We examine state-of-the-art approaches for tissue vascularization and innervation and identify promising methods for developing vascularized and innervated engineered neural constructs.

The Role of Biomaterials in Peripheral Nerve and Spinal Cord Injury: A Review

Peripheral nerve and spinal cord injuries are potentially devastating traumatic conditions with major consequences for patients’ lives. Severe cases of these conditions are currently incurable. In both the peripheral nerves and the spinal cord, disruption and degeneration of axons is the main cause of neurological deficits. Biomaterials offer experimental solutions to improve these conditions. They can be engineered as scaffolds that mimic the nerve tissue extracellular matrix and, upon implantation, encourage axonal regeneration. Furthermore, biomaterial scaffolds can be designed to deliver therapeutic agents to the lesion site. This article presents the principles and recent advances in the use of biomaterials for axonal regeneration and nervous system repair.

Microcomputed Tomography-Based Analysis of Neovascularization within Bioengineered Vascularized Tissues

In the field of tissue engineering, evaluating newly formed vascular networks is considered a fundamental step in deciphering the processes underlying tissue development. Several common modalities exist to study vessel network formation and function. However, a proper methodology that allows through three-dimensional visualization of neovessels in a reproducible manner is required. Here, we describe in-depth exploration, visualization, and analysis of vessels within newly formed tissues by utilizing a contrast agent perfusion protocol and high-resolution microcomputed tomography. Bioengineered constructs consisting of porous, biocompatible, and biodegradable scaffolds are loaded with cocultures of adipose-derived microvascular endothelial cells (HAMECs) and dental pulp stem cells (DPSCs) and implanted in a rat femoral bundle model. After 14 days of in vivo maturation, we performed the optimized perfusion protocol to allow host penetrating vascular visualization and assessment within neotissues. Following high-resolution microCT scanning of DPSC:HAMEC explants, we performed the volumetric and spatial analysis of neovasculature. Eventually, the process was repeated with a previously published coculture system for prevascularization based on adipose-derived mesenchymal stromal cells (MSCs) and HAMECs. Overall, our approach allows a comprehensive understanding of vessel organization during engraftment and development of neotissues.

Dental stem cell-derived extracellular vesicles as promising therapeutic agents in the treatment of diseases

Dental stem cells (DSCs), an important source of mesenchymal stem cells (MSCs), can be easily obtained by minimally invasive procedures and have been used for the treatment of various diseases. Classic paradigm attributed the mechanism of their therapeutic action to direct cell differentiation after targeted migration, while contemporary insights into indirect paracrine effect opened new avenues for the mystery of their actual low engraftment and differentiation ability in vivo. As critical paracrine effectors, DSC-derived extracellular vesicles (DSC-EVs) are being increasingly linked to the positive effects of DSCs by an evolving body of in vivo studies. Carrying bioactive contents and presenting therapeutic potential in certain diseases, DSC-EVs have been introduced as promising treatments. Here, we systematically review the latest in vivo evidence that supports the therapeutic effects of DSC-EVs with mechanistic studies. In addition, current challenges and future directions for the clinical translation of DSC-EVs are also highlighted to call for more attentions to the (I) distinguishing features of DSC-EVs compared with other types of MSC-EVs, (II) heterogeneity among different subtypes of DSC-derived EVs, (III) action modes of DSC-EVs, (IV) standardization for eligible DSC-EVs and (V) safety guarantee for the clinical application of DSC-EVs. The present review would provide valuable insights into the emerging opportunities of DSC-EVs in future clinical applications.

Integrating engineered macro vessels with self-assembled capillaries in 3D implantable tissue for promoting vascular integration in-vivo

A functional multi-scale vascular network can promote 3D engineered tissue growth and improve transplantation outcome. In this work, by using a combination of living cells, biological hydrogel, and biodegradable synthetic polymer we fabricated a biocompatible, multi-scale vascular network (MSVT) within thick, implantable engineered tissues. Using a templating technique, macro-vessels were patterned in a 3D biodegradable polymeric scaffold seeded with endothelial and support cells within a collagen gel. The lumen of the macro-vessel was lined with endothelial cells, which further sprouted and anastomosed with the surrounding self-assembled capillaries. Anastomoses between the two-scaled vascular systems displayed tightly bonded cell junctions, as indicated by vascular endothelial cadherin expression. Moreover, MSVT functionality and patency were demonstrated by dextran passage through the interconnected multi-scale vasculature. Additionally, physiological flow conditions were applied with home-designed flow bioreactors, to achieve a MSVT with a natural endothelium structure. Finally, implantation of a multi-scale-vascularized graft in a mouse model resulted in extensive host vessel penetration into the graft and a significant increase in blood perfusion via the engineered vessels compared to control micro-scale-vascularized graft. Designing and fabricating such multi-scale vascular architectures within 3D engineered tissues may benefit both in vitro models and therapeutic translation research.

Application of dental stem cells in three-dimensional tissue regeneration

Dental stem cells can differentiate into different types of cells. Dental pulp stem cells, stem cells from human exfoliated deciduous teeth, periodontal ligament stem cells, stem cells from apical papilla, and dental follicle progenitor cells are five different types of dental stem cells that have been identified during different stages of tooth development. The availability of dental stem cells from discarded or removed teeth makes them promising candidates for tissue engineering. In recent years, three-dimensional (3D) tissue scaffolds have been used to reconstruct and restore different anatomical defects. With rapid advances in 3D tissue engineering, dental stem cells have been used in the regeneration of 3D engineered tissue. This review presents an overview of different types of dental stem cells used in 3D tissue regeneration, which are currently the most common type of stem cells used to treat human tissue conditions.

Anisotropic scaffolds for peripheral nerve and spinal cord regeneration

The treatment of long-gap (>10 mm) peripheral nerve injury (PNI) and spinal cord injury (SCI) remains a continuous challenge due to limited native tissue regeneration capabilities. The current clinical strategy of using autografts for PNI suffers from a source shortage, while the pharmacological treatment for SCI presents dissatisfactory results. Tissue engineering, as an alternative, is a promising approach for regenerating peripheral nerves and spinal cords. Through providing a beneficial environment, a scaffold is the primary element in tissue engineering. In particular, scaffolds with anisotropic structures resembling the native extracellular matrix (ECM) can effectively guide neural outgrowth and reconnection. In this review, the anatomy of peripheral nerves and spinal cords, as well as current clinical treatments for PNI and SCI, is first summarized. An overview of the critical components in peripheral nerve and spinal cord tissue engineering and the current status of regeneration approaches are also discussed. Recent advances in the fabrication of anisotropic surface patterns, aligned fibrous substrates, and 3D hydrogel scaffolds, as well as their in vitro and in vivo effects are highlighted. Finally, we summarize potential mechanisms underlying the anisotropic architectures in orienting axonal and glial cell growth, along with their challenges and prospects.

3D Bioprinting of Engineered Tissue Flaps with Hierarchical Vessel Networks (VesselNet) for Direct Host-To-Implant Perfusion

Engineering hierarchical vasculatures is critical for creating implantable functional thick tissues. Current approaches focus on fabricating mesoscale vessels for implantation or hierarchical microvascular in vitro models, but a combined approach is yet to be achieved to create engineered tissue flaps. Here, millimetric vessel-like scaffolds and 3D bioprinted vascularized tissues interconnect, creating fully engineered hierarchical vascular constructs for implantation. Endothelial and support cells spontaneously form microvascular networks in bioprinted tissues using a human collagen bioink. Sacrificial molds are used to create polymeric vessel-like scaffolds and endothelial cells seeded in their lumen form native-like endothelia. Assembling endothelialized scaffolds within vascularizing hydrogels incites the bioprinted vasculature and endothelium to cooperatively create vessels, enabling tissue perfusion through the scaffold lumen. Using a cuffing microsurgery approach, the engineered tissue is directly anastomosed with a rat femoral artery, promoting a rich host vasculature within the implanted tissue. After two weeks in vivo, contrast microcomputer tomography imaging and lectin perfusion of explanted engineered tissues verify the host ingrowth vasculature's functionality. Furthermore, the hierarchical vessel network (VesselNet) supports in vitro functionality of cardiomyocytes. Finally, the proposed approach is expanded to mimic complex structures with native-like millimetric vessels. This work presents a novel strategy aiming to create fully-engineered patient-specific thick tissue flaps.

Generation of a novel model of bioengineered human oral mucosa with increased vascularization potential

Objective

The aim of this study was to generate novel models of bioartificial human oral mucosa with increased vascularization potential for future use as an advanced therapies medicinal product, by using different vascular and mesenchymal stem cell sources.

Background

Oral mucosa substitutes could contribute to the clinical treatment of complex diseases affecting the oral cavity. Although several models of artificial oral mucosa have been described, biointegration is a major issue that could be favored by the generation of novel substitutes with increased vascularization potential once grafted in vivo.

Methods

Three types of mesenchymal stem cells (MSCs) were obtained from adipose tissue, bone marrow, and dental pulp, and their in vitro potential was evaluated by inducing differentiation to the endothelial lineage using conditioning media. Then, 3D models of human artificial oral mucosa were generated using biocompatible fibrin‐agarose biomaterials combined with human oral mucosa fibroblasts and each type of MSC before and after induction to the endothelial lineage, using human umbilical vein endothelial cells (HUVEC) as controls. The vascularization potential of each oral mucosa substitute was assessed in vitro and in vivo in nude mice.

Results

In vitro induction of MSCs kept in culture was able to increase the expression of VEGF, CD31, and vWF endothelial markers, especially in bone marrow and dental pulp‐MSCs, and numerous proteins with a role in vasculogenesis become overexpressed. Then, in vivo grafting resulted in a significant increase in blood vessels formation at the interface area between the graft and the host tissues, with significantly positive expression of VEGF, CD31, vWF, and CD34 as compared to negative controls, especially when pre‐differentiated MSCs derived from bone marrow and dental pulp were used. In addition, a significantly higher number of cells committed to the endothelial lineage expressing the same endothelial markers were found within the bioartificial tissue.

Conclusion

Our results suggest that the use of pre‐differentiated MSCs could contribute to a rapid generation of a vascular network that may favor in vivo biointegration of bioengineered human oral mucosa substitutes.

Investigating lymphangiogenesis in vitro and in vivo using engineered human lymphatic vessel networks

Lymphatic vessel networks are important for various biological processes; thus, incorporating them into engineered constructs can have both research and clinical implications. Engineered lymphatic vessels can improve biomimicry and functionality of in vitro tissue assays and serve as a treatment for various diseases associated with impaired lymphatic function. In this work, we created functional engineered lymphatic vessels that anastomosed to the host lymphatic system postimplantation. We investigated the effect of supporting cells, cell-secreted extracellular matrix, and mechanical forces on lymphatic vessel formation within engineered constructs. Interestingly, lymphatic vasculature responded differently to cyclic stretch compared to blood vasculature. This phenomenon opens up an avenue for investigating the variability of cellular responses to mechanical stimulation.

The lymphatic system is involved in various biological processes, including fluid transport from the interstitium into the venous circulation, lipid absorption, and immune cell trafficking. Despite its critical role in homeostasis, lymphangiogenesis (lymphatic vessel formation) is less widely studied than its counterpart, angiogenesis (blood vessel formation). Although the incorporation of lymphatic vasculature in engineered tissues or organoids would enable more precise mimicry of native tissue, few studies have focused on creating engineered tissues containing lymphatic vessels. Here, we populated thick collagen sheets with human lymphatic endothelial cells, combined with supporting cells and blood endothelial cells, and examined lymphangiogenesis within the resulting constructs. Our model required just a few days to develop a functional lymphatic vessel network, in contrast to other reported models requiring several weeks. Coculture of lymphatic endothelial cells with the appropriate supporting cells and intact PDGFR-β signaling proved essential for the lymphangiogenesis process. Additionally, subjecting the constructs to cyclic stretch enabled the creation of complex muscle tissue aligned with the lymphatic and blood vessel networks, more precisely biomimicking native tissue. Interestingly, the response of developing lymphatic vessels to tensile forces was different from that of blood vessels; while blood vessels oriented perpendicularly to the stretch direction, lymphatic vessels mostly oriented in parallel to the stretch direction. Implantation of the engineered lymphatic constructs into a mouse abdominal wall muscle resulted in anastomosis between host and implant lymphatic vasculatures, demonstrating the engineered construct's potential functionality in vivo. Overall, this model provides a potential platform for investigating lymphangiogenesis and lymphatic disease mechanisms.

Spinal Cord Repair: From Cells and Tissue Engineering to Extracellular Vesicles

Spinal cord injury (SCI) is a debilitating condition, often leading to severe motor, sensory, or autonomic nervous dysfunction. As the holy grail of regenerative medicine, promoting spinal cord tissue regeneration and functional recovery are the fundamental goals. Yet, effective regeneration of injured spinal cord tissues and promotion of functional recovery remain unmet clinical challenges, largely due to the complex pathophysiology of the condition. The transplantation of various cells, either alone or in combination with three-dimensional matrices, has been intensively investigated in preclinical SCI models and clinical trials, holding translational promise. More recently, a new paradigm shift has emerged from cell therapy towards extracellular vesicles as an exciting "cell-free" therapeutic modality. The current review recapitulates recent advances, challenges, and future perspectives of cell-based spinal cord tissue engineering and regeneration strategies.

Dual-Cues Laden Scaffold Facilitates Neurovascular Regeneration and Motor Functional Recovery After Complete Spinal Cord Injury

Complete transection spinal cord injury (SCI) severely disrupts the integrity of both neural circuits and the microvasculature system. Hence, fabricating a functional bio-scaffold that could coordinate axonal regeneration and vascular reconstruction in the lesion area may emerge as a new paradigm for complete SCI repair. In this study, a photosensitive hydrogel scaffold loaded with collagen-binding stromal cell-derived factor-1a and Taxol liposomes is capable of inducing migration of endothelial cells and promoting neurite outgrowth of neurons in vitro. In addition, when implanted into a rat T8 complete transection SCI model, the above dual-cues laden scaffold exhibits a synergistic effect on facilitating axon and vessel regeneration in the lesion area within 10 days after injury. Moreover, long-term therapeutic effects are also observed after dual-cues laden scaffold implantation, including revascularization, descending and propriospinal axonal regeneration, fibrotic scar reduction, electrophysiological recovery, and motor function improvement. In summary, the dual-cues laden scaffold has good clinical application potential for patients with severe SCI.

Stimulating Extracellular Vesicles Production from Engineered Tissues by Mechanical Forces

Extracellular vesicles (EVs) have emerged as a promising strategy to promote tissue regeneration. However, overcoming the low EV production yield remains a big challenge in translating EV-based therapies to the clinical practice. Current EV production relies heavily on 2D cell culture, which is not only less physiologically relevant to cells but also requires substantial medium and space. In this study, we engineered tissues seeded with stem cells from dental pulp or adipose tissues, or skeletal muscle cells, and significantly enhanced the EV production yield by applying mechanical stimuli, including flow and stretching, in bioreactors. Further mechanistic investigation revealed that this process was mediated by yes-associated protein (YAP) mechanosensitivity. EVs from mechanically stimulated dental pulp stem cells on 3D scaffolds displayed superior capability in inducing axonal sprouting than the 2D counterparts. Our results demonstrate the promise of this strategy to boost EV production and optimize their functional performance toward clinical translation.

Vascularized organoids on a chip: strategies for engineering organoids with functional vasculature

Human organoids, self-organized and differentiated from homogenous pluripotent stem cells (PSC), replicate the key structural and functional characteristics of their in vivo counterparts. Despite the rapid advancement of organoid technology and its diverse applications, major limitations in achieving truly in vivo like functionality have been the lack of matured structural organization and constraints on tissue size, both of which are direct consequences of lacking a functional vasculature. In the absence of perfusable vessels, a core region within organoids quickly becomes necrotic during development due to increased metabolic demands that cannot be met by diffusion alone. Thus, incorporating functional vasculature in organoid models is indispensable for their growth in excess of several hundred microns and maturaturation beyond the embryonic and fetal phase. Here, we review recent advancements in vascularizing organoids and engineering in vitro capillary beds, and further explore strategies to integrate them on a microfluidic based platform, aiming for establishing perfused vasculature throughout organoids in vitro.

Hypoxia response element-directed expression of bFGF in dental pulp stem cells improve the hypoxic environment by targeting pericytes in SCI rats

Cell-based transplantation strategies possess great potential for spinal cord injury (SCI) repair. Basic fibroblast growth factor (bFGF) has been reported to have multiple neuro-promoting effects on developing and adult nervous system of mammals and considered a promising therapy for nerve injury following SCI. Human dental pulp stem cells (DPSCs) are abundant stem cells with low immune rejection, which can be considered for cell replacement therapy. The purpose of this study was to investigate the roles of DPSCs which express bFGF under the regulation of five hypoxia-responsive elements (5HRE) using an adeno-associated virus (AAV-5HRE-bFGF-DPSCs) in SCI repairing model. In this study, DPSCs were revealed to differentiate into CD13⁺ pericytes and up-regulate N-cadherin expression to promote the re-attachment of CD13⁺ pericytes to vascular endothelial cells. The re-attachment of CD13⁺ pericytes to vascular endothelial cells subsequently increased the flow rate of blood in microvessels via the contraction of protuberance. As a result, increased numbers of red blood cells carried more oxygen to the damaged area and the local hypoxia microenvironment in SCI was improved. Thus, this study represents a step forward towards the potential use of AAV-5HRE-bFGF-DPSCs in SCI treatment in clinic.

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) 5HRE-bFGF-DPSCs secrete bFGF in a hypoxia dependent manner, making the administration more precise.

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CD13+ pericyte regulate vascular diameter and promote the recovery of hypoxia microenvironment via DDC-5HT-5HT-1B in SCI.

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5HRE-bFGF-DPSCs can differentiate into CD13+ pericyte to compensate for the mass death of CD13+ pericyte after SCI.

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5HRE-bFGF-DPSCs promote CD13+ pericyte adhesion to vascular endothelial cell by secreting bFGF through N-cadherin.

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5HRE-bFGF-DPSCs promote the recovery of SCI by restoring hypoxic microenvironment and inhibit autophagy pathway.