Single Cell Transcriptomics-Informed Induced Pluripotent Stem Cells Differentiation to Tenogenic Lineage

During vertebrate embryogenesis, axial tendons develop from the paraxial mesoderm and differentiate through specific developmental stages to reach the syndetome stage. While the main roles of signaling pathways in the earlier stages of the differentiation have been well established, pathway nuances in syndetome specification from the sclerotome stage have yet to be explored. Here, we show stepwise differentiation of human iPSCs to the syndetome stage using chemically defined media and small molecules that were modified based on single cell RNA-sequencing and pathway analysis. We identified a significant population of branching off-target cells differentiating towards a neural phenotype overexpressing Wnt. Further transcriptomics post-addition of a WNT inhibitor at the somite stage and onwards revealed not only total removal of the neural off-target cells, but also increased syndetome induction efficiency. Fine-tuning tendon differentiation in vitro is essential to address the current challenges in developing a successful cell-based tendon therapy.

Degradable biomedical elastomers: paving the future of tissue repair and regenerative medicine

Degradable biomedical elastomers (DBE), characterized by controlled biodegradability, excellent biocompatibility, tailored elasticity, and favorable network design and processability, have become indispensable in tissue repair. This review critically examines the recent advances of biodegradable elastomers for tissue repair, focusing mainly on degradation mechanisms and evaluation, synthesis and crosslinking methods, microstructure design, processing techniques, and tissue repair applications. The review explores the material composition and cross-linking methods of elastomers used in tissue repair, addressing chemistry-related challenges and structural design considerations. In addition, this review focuses on the processing methods of two- and three-dimensional structures of elastomers, and systematically discusses the contribution of processing methods such as solvent casting, electrostatic spinning, and three-/four-dimensional printing of DBE. Furthermore, we describe recent advances in tissue repair using DBE, and include advances achieved in regenerating different tissues, including nerves, tendons, muscle, cardiac, and bone, highlighting their efficacy and versatility. The review concludes by discussing the current challenges in material selection, biodegradation, bioactivation, and manufacturing in tissue repair, and suggests future research directions. This concise yet comprehensive analysis aims to provide valuable insights and technical guidance for advances in DBE for tissue engineering.

The alteration of the structure and macroscopic mechanical response of porcine patellar tendon by elastase digestion

Background: The treatment of patellar tendon injury has always been an unsolved problem, and mechanical characterization is very important for its repair and reconstruction. Elastin is a contributor to mechanics, but it is not clear how it affects the elasticity, viscoelastic properties, and structure of patellar tendon. Methods: The patellar tendons from six fresh adult experimental pigs were used in this study and they were made into 77 samples. The patellar tendon was specifically degraded by elastase, and the regional mechanical response and structural changes were investigated by: (1) Based on the previous study of elastase treatment conditions, the biochemical quantification of collagen, glycosaminoglycan and total protein was carried out; (2) The patellar tendon was divided into the proximal, central, and distal regions, and then the axial tensile test and stress relaxation test were performed before and after phosphate-buffered saline (PBS) or elastase treatment; (3) The dynamic constitutive model was established by the obtained mechanical data; (4) The structural relationship between elastin and collagen fibers was analyzed by two-photon microscopy and histology. Results: There was no statistical difference in mechanics between patellar tendon regions. Compared with those before elastase treatment, the low tensile modulus decreased by 75%-80%, the high tensile modulus decreased by 38%-47%, and the transition strain was prolonged after treatment. For viscoelastic behavior, the stress relaxation increased, the initial slope increased by 55%, the saturation slope increased by 44%, and the transition time increased by 25% after enzyme treatment. Elastin degradation made the collagen fibers of patellar tendon become disordered and looser, and the fiber wavelength increased significantly. Conclusion: The results of this study show that elastin plays an important role in the mechanical properties and fiber structure stability of patellar tendon, which supplements the structure-function relationship information of patellar tendon. The established constitutive model is of great significance to the prediction, repair and replacement of patellar tendon injury. In addition, human patellar tendon has a higher elastin content, so the results of this study can provide supporting information on the natural properties of tendon elastin degradation and guide the development of artificial patellar tendon biomaterials.

Multiphasic bone-ligament-bone integrated scaffold enhances ligamentization and graft-bone integration after anterior cruciate ligament reconstruction

The escalating prevalence of anterior cruciate ligament (ACL) injuries in sports necessitates innovative strategies for ACL reconstruction. In this study, we propose a multiphasic bone-ligament-bone (BLB) integrated scaffold as a potential solution. The BLB scaffold comprised two polylactic acid (PLA)/deferoxamine (DFO)@mesoporous hydroxyapatite (MHA) thermally induced phase separation (TIPS) scaffolds bridged by silk fibroin (SF)/connective tissue growth factor (CTGF)@Poly(l-lactide-co-ε-caprolactone) (PLCL) nanofiber yarn braided scaffold. This combination mimics the native architecture of the ACL tissue. The mechanical properties of the BLB scaffolds were determined to be compatible with the human ACL. In vitro experiments demonstrated that CTGF induced the expression of ligament-related genes, while TIPS scaffolds loaded with MHA and DFO enhanced the osteogenic-related gene expression of bone marrow stem cells (BMSCs) and promoted the migration and tubular formation of human umbilical vein endothelial cells (HUVECs). In rabbit models, the BLB scaffold efficiently facilitated ligamentization and graft-bone integration processes by providing bioactive substances. The double delivery of DFO and calcium ions by the BLB scaffold synergistically promoted bone regeneration, while CTGF improved collagen formation and ligament healing. Collectively, the findings indicate that the BLB scaffold exhibits substantial promise for ACL reconstruction. Additional investigation and advancement of this scaffold may yield enhanced results in the management of ACL injuries.

Advancements in scaffold for treating ligament injuries; in vitro evaluation

Tendon/ligament (T/L) injuries are a worldwide health problem that affects millions of people annually. Due to the characteristics of tendons, the natural rehabilitation of their injuries is a very complex and lengthy process. Surgical treatment of a T/L injury frequently necessitates using autologous or allogeneic grafts or synthetic materials. Nonetheless, these alternatives have limitations in terms of mechanical properties and histocompatibility, and they do not permit the restoration of the original biological function of the tissue, which can negatively impact the patient's quality of life. It is crucial to find biological materials that possess the necessary properties for the successful surgical treatment of tissues and organs. In recent years, the in vitro regeneration of tissues and organs from stem cells has emerged as a promising approach for preparing autologous tissue and organs, and cell culture scaffolds play a critical role in this process. However, the biological traits and serviceability of different materials used for cell culture scaffolds vary significantly, which can impact the properties of the cultured tissues. Therefore, this review aims to analyze the differences in the biological properties and suitability of various materials based on scaffold characteristics such as cell compatibility, degradability, textile technologies, fiber arrangement, pore size, and porosity. This comprehensive analysis provides valuable insights to aid in the selection of appropriate scaffolds for in vitro tissue and organ culture.

iPSC-derived tenocytes seeded on microgrooved 3D printed scaffolds for Achilles tendon regeneration

Tendons and ligaments have a poor innate healing capacity, yet account for 50% of musculoskeletal injuries in the United States. Full structure and function restoration postinjury remains an unmet clinical need. This study aimed to assess the application of novel three dimensional (3D) printed scaffolds and induced pluripotent stem cell-derived mesenchymal stem cells (iMSCs) overexpressing the transcription factor Scleraxis (SCX, iMSCSCX+ ) as a new strategy for tendon defect repair. The polycaprolactone (PCL) scaffolds were fabricated by extrusion through a patterned nozzle or conventional round nozzle. Scaffolds were seeded with iMSCSCX+ and outcomes were assessed in vitro via gene expression analysis and immunofluorescence. In vivo, rat Achilles tendon defects were repaired with iMSCSCX+ -seeded microgrooved scaffolds, microgrooved scaffolds only, or suture only and assessed via gait, gene expression, biomechanical testing, histology, and immunofluorescence. iMSCSCX+ -seeded on microgrooved scaffolds showed upregulation of tendon markers and increased organization and linearity of cells compared to non-patterned scaffolds in vitro. In vivo gait analysis showed improvement in the Scaffold + iMSCSCX+ -treated group compared to the controls. Tensile testing of the tendons demonstrated improved biomechanical properties of the Scaffold + iMSCSCX+ group compared with the controls. Histology and immunofluorescence demonstrated more regular tissue formation in the Scaffold + iMSCSCX+ group. This study demonstrates the potential of 3D-printed scaffolds with cell-instructive surface topography seeded with iMSCSCX+ as an approach to tendon defect repair. Further studies of cell-scaffold constructs can potentially revolutionize tendon reconstruction by advancing the application of 3D printing-based technologies toward patient-specific therapies that improve healing and functional outcomes at both the cellular and tissue level.

Could an Anterior Cruciate Ligament Be Tissue-Engineered from Silk?

Silk has a long history as an exclusive textile, but also as a suture thread in medicine; nowadays, diverse cell carriers are manufactured from silk. Its advantages are manifold, including high biocompatibility, biomechanical strength and processability (approved for nearly all manufacturing techniques). Silk's limitations, such as scarcity and batch to batch variations, are overcome by gene technology, which allows for the upscaled production of recombinant "designed" silk proteins. For processing thin fibroin filaments, the sericin component is generally removed (degumming). In contrast to many synthetic biomaterials, fibroin allows for superior cell adherence and growth. In addition, silk grafts demonstrate superior mechanical performance and long-term stability, making them attractive for anterior cruciate ligament (ACL) tissue engineering. Looking at these promising properties, this review focusses on the responses of cell types to silk variants, as well as their biomechanical properties, which are relevant for ACL tissue engineering. Meanwhile, sericin has also attracted increasing interest and has been proposed as a bioactive biomaterial with antimicrobial properties. But so far, fibroin was exclusively used for experimental ACL tissue engineering approaches, and fibroin from spider silk also seems not to have been applied. To improve the bone integration of ACL grafts, silk scaffolds with osteogenic functionalization, silk-based tunnel fillers and interference screws have been developed. Nevertheless, signaling pathways stimulated by silk components remain barely elucidated, but need to be considered during the development of optimized silk cell carriers for ACL tissue engineering.

Cell Guiding Multicomponent Nanoyarn Tendon Scaffolds with Tunable Morphology and Flexibility

Nanofibrous scaffolds are widely investigated for tendon tissue engineering due to their porous structure, high flexibility, and the ability to guide cells in a preferred direction. Previous research has shown that providing a microenvironment similar to in vivo settings improves tissue regeneration. Therefore, in this work, ingenious multicomponent nanoyarn scaffolds that mimic the fibrillar and tubular structures of tendons are developed for the first time through electrospinning and bundling nanoyarns followed by electrospinning of a nanofibrous shell around the bundle. Multicomponent nanoyarn scaffolds out of poly(ε-caprolactone) with varying porosity, density, and diameter were successfully produced by coelectrospinning with water-soluble poly(2-ethyl-2-oxazoline) as a sacrificial component. The diameter and fiber orientation of the nanoyarns were successfully tuned based on parameter-morphology models obtained by the design of experiments. Cyclic bending tests were performed, indicating that the flexibility of the multicomponent nanoyarn scaffolds depends on the morphology and can be tuned through controlling the number of nanoyarns in the bundle and the porosity. Indirect and direct cell culture tests using mouse and equine tendon cells revealed excellent cytocompatibility of the nanofibrous products and demonstrated the potential of the nanoyarns to guide the growing cells along the nanofiber direction, which is crucial for tendon tissue engineering.

Research progress of biomaterials and innovative technologies in urinary tissue engineering

Substantial interests have been attracted to multiple bioactive and biomimetic biomaterials in recent decades because of their ability in presenting a structural and functional reconstruction of urinary tissues. Some innovative technologies have also been surging in urinary tissue engineering and urological regeneration by providing insights into the physiological behavior of the urinary system. As such, the hierarchical structure and tissue function of the bladder, urethra, and ureter can be reproduced similarly to the native urinary tissues. This review aims to summarize recent advances in functional biomaterials and biomimetic technologies toward urological reconstruction. Various nanofirous biomaterials derived from decellularized natural tissues, synthetic biopolymers, and hybrid scaffolds were developed with desired microstructure, surface chemistry, and mechanical properties. Some growth factors, drugs, as well as inorganic nanomaterials were also utilized to enhance the biological activity and functionality of scaffolds. Notably, it is emphasized that advanced approaches, such as 3D (bio) printing and organoids, have also been developed to facilitate structural and functional regeneration of the urological system. So in this review, we discussed the fabrication strategies, physiochemical properties, and biofunctional modification of regenerative biomaterials and their potential clinical application of fast-evolving technologies. In addition, future prospective and commercial products are further proposed and discussed.

Constructing high-strength nano-micro fibrous woven scaffolds with native-like anisotropic structure and immunoregulatory function for tendon repair and regeneration

Tendon injuries are common debilitating musculoskeletal diseases with high treatment expenditure in sports medicine. The development of tendon-biomimetic scaffolds may be promising for improving the unsatisfactory clinical outcomes of traditional therapies. In this study, we combined an advanced electrospun nanofiber yarn-generating technique with a traditional textile manufacturing strategy to fabricate innovative nano-micro fibrous woven scaffolds with tendon-like anisotropic structure and high-strength mechanical properties for the treatment of large-size tendon injury. Electrospun nanofiber yarns made from pure poly L-lactic acid (PLLA) or silk fibroin (SF)/PLLA blend were fabricated, and their mechanical properties matched and even exceeded those of commercial PLLA microfiber yarns. The PLLA or SF/PLLA nanofiber yarns were then employed as weft yarns interlaced with commercial PLLA microfiber yarns as warp yarns to generate two new types of nanofibrous scaffolds (nmPLLA and nmSF/PLLA) with a plain-weaving structure. Woven scaffolds made from pure PLLA microfiber yarns (both weft and warp directions) (mmPLLA) were used as controls.In vitroexperiments showed that the nmSF/PLLA woven scaffold with aligned fibrous topography significantly promoted cell adhesion, elongation, proliferation, and phenotypic maintenance of tenocytes compared with mmPLLA and nmPLLA woven scaffolds. Moreover, the nmSF/PLLA woven scaffold exhibited the strongest immunoregulatory functions and effectively modulated macrophages towards the M2 phenotype.In vivoexperiments revealed that the nmSF/PLLA woven scaffold notably facilitated Achilles tendon regeneration with improved structure by macroscopic, histological, and ultrastructural observations six months after surgery, compared with the other two groups. More importantly, the regenerated tissue in the nmSF/PLLA group had excellent biomechanical properties comparable to those of the native tendon. Overall, our study provides an innovative biological-free strategy with ready-to-use features, which presents great potential for clinical translation for damaged tendon repair.

Vascularized dental pulp regeneration using cell-laden microfiber aggregates

Regeneration of dental pulp via the transplantation of dental pulp stem cells (DPSCs) has emerged as a novel therapy for dental pulp necrosis after inflammation and injury. However, providing sufficient oxygen and nutrients to support stem cell survival, self-renewal, and differentiation in the narrow root canal remains a great challenge. In this study, we explored a novel strategy based on cell-laden microfibers for dental pulp regeneration. Firstly, we fabricated suitable GelMA hydrogels that facilitate the survival and proliferation of DPSCs and human umbilical vein endothelial cells (HUVECs) and possess satisfactory biomechanical properties to generate microfibers. Two kinds of GelMA microfibers were fabricated with DPSCs and HUVECs via a silicone-tube-based coagulant bath-free method. Live/dead and Ki-67 immunofluorescence staining assays identified that these two cell lines maintained high survival rate and proliferation ability in GelMA microfibers. Immunofluorescence staining confirmed that DPSCs fully spread in the microfibers and highly expressed CD90 and laminin. HUVECs positively express CD31 and VE-cad in microfibers and could migrate well in the GelMA hydrogel. In vitro permeation experiments confirmed the superiority of microfiber aggregates (MAs) in liquid permeation compared to GelMA hydrogel blocks. We further adopted an ectopic pulp regeneration assay in nude mice to validate the regeneration of the aggregates of mixed DPSC-microfibers and HUVEC-microfibers in vivo. Compared to a conventional mixture of DPSCs and HUVECs in GelMA hydrogel blocks, the aggregates of cell-laden microfibers generated more pulp-like tissue, blood vessels, and odontoblast-like cells that positively express DMP-1 and DSPP. To our knowledge, this is the first attempt to apply cell-laden MAs for pulp regeneration. Our study proposes a new solution to the challenge of pulp regeneration, which might promote the clinical translation and application of stem cell-based therapy.

Development of tropoelastin-functionalized anisotropic PCL scaffolds for musculoskeletal tissue engineering

The highly organized extracellular matrix (ECM) of musculoskeletal tissues, encompassing tendons, ligaments and muscles, is structurally anisotropic, hierarchical and multi-compartmental. These features collectively contribute to their unique function. Previous studies have investigated the effect of tissue-engineered scaffold anisotropy on cell morphology and organization for musculoskeletal tissue repair and regeneration, but the hierarchical arrangement of ECM and compartmentalization are not typically replicated. Here, we present a method for multi-compartmental scaffold design that allows for physical mimicry of the spatial architecture of musculoskeletal tissue in regenerative medicine. This design is based on an ECM-inspired macromolecule scaffold. Polycaprolactone (PCL) scaffolds were fabricated with aligned fibers by electrospinning and mechanical stretching, and then surface-functionalized with the cell-supporting ECM protein molecule, tropoelastin (TE). TE was attached using two alternative methods that allowed for either physisorption or covalent attachment, where the latter was achieved by plasma ion immersion implantation (PIII). Aligned fibers stimulated cell elongation and improved cell alignment, in contrast to randomly oriented fibers. TE coatings bound by physisorption or covalently following 200 s PIII treatment promoted fibroblast proliferation. This represents the first cytocompatibility assessment of novel PIII-treated TE-coated PCL scaffolds. To demonstrate their versatility, these 2D anisotropic PCL scaffolds were assembled into 3D hierarchical constructs with an internally compartmentalized structure to mimic the structure of musculoskeletal tissue.

Recent Advances in Designing Fibrous Biomaterials for the Domain of Biomedical, Clinical, and Environmental Applications

Unique properties and potential applications of nanofibers have emerged as innovative approaches and opportunities in the biomedical, healthcare, environmental, and biosensor fields. Electrospinning and centrifugal spinning strategies have gained considerable attention among all kinds of strategies to produce nanofibers. These techniques produce nanofibers with high porosity and surface area, adequate pore architecture, and diverse chemical compositions. The extraordinary characteristics of nanofibers have unveiled new gates in nanomedicine to establish innovative fiber-based formulations for biomedical use, healthcare, and a wide range of other applications. The present review aims to provide a comprehensive overview of nanofibers and their broad range of applications, including drug delivery, biomedical scaffolds, tissue/bone-tissue engineering, dental applications, and environmental remediation in a single place. The review begins with a brief introduction followed by potential applications of nanofibers. Finally, the future perspectives and current challenges of nanofibers are demonstrated. This review will help researchers to engineer more efficient multifunctional nanofibers with improved characteristics for their effective use in broad areas. We strongly believe this review is a reader's delight and will help in dealing with the fundamental principles and applications of nanofiber-based scaffolds. This review will assist students and a broad range of scientific communities to understand the significance of nanofibers in several domains of nanotechnology, nanomedicine, biotechnology, and environmental remediation, which will set a benchmark for further research.

Use of Bombyx mori silk fibroin in tissue engineering: From cocoons to medical devices, challenges, and future perspectives

Silk fibroin has become a prominent material in tissue engineering (TE) over the last 20 years with almost 10,000 published works spanning in all the TE applications, from skeleton to neuronal regeneration. Fibroin is an extremely versatile biopolymer that, due to its ease of processing, has enabled the development of an entire plethora of materials whose properties and architectures can be tailored to suit target applications. Although the research and development of fibroin TE materials and devices is mature, apart from sutures, only a few medical products made of fibroin are used in the clinical routines. <40 clinical trials of Bombyx mori silk-related products have been reported by the FDA and few of them resulted in a commercialized device. In this review, after explaining the structure and properties of silk fibroin, we provide an overview of both fibroin constructs existing in the literature and fibroin devices used in clinic. Through the comparison of these two categories, we identified the burning issues faced by fibroin products during their translation to the market. Two main aspects will be considered. The first is the standardization of production processes, which leads both to the standardization of the characteristics of the issued device and the correct assessment of its failure. The second is the FDA regulations, which allow new devices to be marketed through the 510(k) clearance by demonstrating their equivalence to a commercialized medical product. The history of some fibroin medical devices will be taken as a case study. Finally, we will outline a roadmap outlining what actions we believe are needed to bring fibroin products to the market.

Advanced Nanofiber-Based Scaffolds for Achilles Tendon Regenerative Engineering

The Achilles tendon (AT) is responsible for running, jumping, and standing. The AT injuries are very common in the population. In the adult population (21–60 years), the incidence of AT injuries is approximately 2.35 per 1,000 people. It negatively impacts people’s quality of life and increases the medical burden. Due to its low cellularity and vascular deficiency, AT has a poor healing ability. Therefore, AT injury healing has attracted a lot of attention from researchers. Current AT injury treatment options cannot effectively restore the mechanical structure and function of AT, which promotes the development of AT regenerative tissue engineering. Various nanofiber-based scaffolds are currently being explored due to their structural similarity to natural tendon and their ability to promote tissue regeneration. This review discusses current methods of AT regeneration, recent advances in the fabrication and enhancement of nanofiber-based scaffolds, and the development and use of multiscale nanofiber-based scaffolds for AT regeneration.

State-of-the-art review of advanced electrospun nanofiber yarn-based textiles for biomedical applications

The pandemic of the coronavirus disease 2019 (COVID-19) has made biotextiles, including face masks and protective clothing, quite familiar in our daily lives. Biotextiles are one broad category of textile products that are beyond our imagination. Currently, biotextiles have been routinely utilized in various biomedical fields, like daily protection, wound healing, tissue regeneration, drug delivery, and sensing, to improve the health and medical conditions of individuals. However, these biotextiles are commonly manufactured with fibers with diameters on the micrometer scale (> 10 μm). Recently, nanofibrous materials have aroused extensive attention in the fields of fiber science and textile engineering because the fibers with nanoscale diameters exhibited obviously superior performances, such as size and surface/interface effects as well as optical, electrical, mechanical, and biological properties, compared to microfibers. A combination of innovative electrospinning techniques and traditional textile-forming strategies opens a new window for the generation of nanofibrous biotextiles to renew and update traditional microfibrous biotextiles. In the last two decades, the conventional electrospinning device has been widely modified to generate nanofiber yarns (NYs) with the fiber diameters less than 1000 nm. The electrospun NYs can be further employed as the primary processing unit for manufacturing a new generation of nano-textiles using various textile-forming strategies. In this review, starting from the basic information of conventional electrospinning techniques, we summarize the innovative electrospinning strategies for NY fabrication and critically discuss their advantages and limitations. This review further covers the progress in the construction of electrospun NY-based nanotextiles and their recent applications in biomedical fields, mainly including surgical sutures, various scaffolds and implants for tissue engineering, smart wearable bioelectronics, and their current and potential applications in the COVID-19 pandemic. At the end, this review highlights and identifies the future needs and opportunities of electrospun NYs and NY-based nanotextiles for clinical use.

Vascular Endothelial Growth Factor-Capturing Aligned Electrospun Polycaprolactone/Gelatin Nanofibers Promote Patellar Ligament Regeneration

Ligament injuries are common in sports and other rigorous activities. It is a great challenge to achieve ligament regeneration after an injury due the avascular structure and low self-renewal capability. Herein, we developed vascular endothelial growth factor (VEGF)-binding aligned electrospun poly(caprolactone)/gelatin (PCL/Gel) scaffolds by incorporating prominin-1-binding peptide (BP) sequence and exploited them for patellar ligament regeneration. The adsorption of BP onto scaffolds was discerned by various techniques, such as Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and confocal laser scanning microscope. The accumulation of VEGF onto scaffolds correlated with the concentration of the peptide in vitro. BP-anchored PCL/Gel scaffolds (BP@PCL/Gel) promoted the tubular formation of human umbilical vein endothelial cells (HUVECs) and wound healing in vitro. Besides, BP containing scaffolds exhibited higher content of CD31⁺ cells than that of the control scaffolds at 1 week after implantation in vivo. Moreover, BP containing scaffolds improved biomechanical properties and facilitated the regeneration of matured collagen in patellar ligament 4 weeks after implantation in mice. Overall, this strategy of peptide-mediated orchestration of VEGF provides an enticing platform for the ligament regeneration, which may also have broad implications for tissue repair applications. STATEMENT OF SIGNIFICANCE: Ligament injuries are central to sports and other rigorous activities. Given to the avascular nature and poor self-healing capability of injured ligament tissues, it is a burgeoning challenge to fabricate tissue-engineered scaffolds for ligament reconstruction. Vascular endothelial growth factor (VEGF) is pivotal to the neo-vessel formation. However, the high molecular weight of VEGF as well as its short half-life in vitro and in vivo limits its therapeutic potential. To circumvent these limitations, herein, we functionalized aligned electrospun polycaprolactone/gelatin (PCL/Gel)-based scaffolds with VEGF-binding peptide (BP) and assessed their biocompatibility and performance in vitro and in vivo. BP-modified scaffolds accumulated VEGF, improved tube formation of HUVECs, and induced wound healing in vitro, which may have broad implications for regenerative medicine and tissue engineering.

In Vitro Cellular Strain Models of Tendon Biology and Tenogenic Differentiation

Research has shown that the surrounding biomechanical environment plays a significant role in the development, differentiation, repair, and degradation of tendon, but the interactions between tendon cells and the forces they experience are complex. In vitro mechanical stimulation models attempt to understand the effects of mechanical load on tendon and connective tissue progenitor cells. This article reviews multiple mechanical stimulation models used to study tendon mechanobiology and provides an overview of the current progress in modelling the complex native biomechanical environment of tendon. Though great strides have been made in advancing the understanding of the role of mechanical stimulation in tendon development, damage, and repair, there exists no ideal in vitro model. Further comparative studies and careful consideration of loading parameters, cell populations, and biochemical additives may further offer new insight into an ideal model for the support of tendon regeneration studies.

Osteon-mimetic 3D nanofibrous scaffold enhances stem cell proliferation and osteogenic differentiation for bone regeneration

The scaffold microstructure is important for bone tissue engineering. Failure to synergistically imitate the hierarchical microstructure of the components of bone, such as an osteon with concentric multilayers assembled by nanofibers, hinders the performance for guiding bone regeneration. Here, a 2D bilayer nanofibrous membrane (BLM) containing poly(lactide-co-glycolide) (PLGA)/polycaprolactone (PCL) composite membranes in similar compositions (PCL15 and PCL20), but possessing different degrees of shrinkage, was fabricated via sequential electrospinning. Upon incubation in phosphate buffered saline (PBS) (37 °C), the 2D BLM spontaneously deformed into a 3D shape induced by PCL crystallization within the PLGA matrix, and the PCL15 and PCL20 layer formed a concave and convex surface, respectively. The 3D structure contained curved multilayers with an average diameter of 776 ± 169 μm, and on the concave and convex surface the nanofiber diameters were 792 ± 225 and 881 ± 259 nm, respectively. The initial 2D structure facilitated the even distribution of seeded cells. Adipose-derived stem cells from rats (rADSCs) proliferated faster on a concave surface than on a convex surface. For the 3D BLM, the osteogenic differentiation of rADSCs was significantly higher than that on 2D surfaces, even without osteogenic supplements, which resulted from the stretched cell morphology on the curved sublayer leading to increased expression of lamin-A. After being implanted into cranial defects in Sprague Dawley (SD) rats, 3D BLM significantly accelerated bone formation. In summary, 3D BLM with an osteon-like structure provides a potential strategy to repair bone defects.

Controlled vitamin D delivery with injectable hyaluronic acid-based hydrogel for restoration of tendinopathy

Tendinopathy is a term used to describe tendon disorders that are marked by pain and a loss of function. Recent studies demonstrated that inflammation plays an important role throughout the broad spectrum of tendinopathy. Conventional treatments such as steroid injections, analgesics, and physical modalities simply give pain relief and do not alter the disease progression without the tendon regeneration effect. Tenocytes are responsible for maintaining the tendon matrix and understanding how they function is essential to studying new treatments for tendinopathy. Our previous study showed the protective effects of vitamin D (Vit D) on damaged tenocytes. Besides its well-known effects on bone metabolism, the non-classical action of Vit D is the pleiotropic effects on modulating immune function. In the present study, we developed a Vit D delivery system with hyaluronic acid (HA), which is one of the major components of the extracellular matrix that has anti-inflammation and wound-healing properties. A novel Vit D delivery system with cross-linked HA hydrogel (Gel) and Tween 80 (T80), Vit D@Gel/T80, could be a new regeneration technique for the treatment of tendinopathy. Vit D@Gel/T80 reduced TNF-α induced damage to human tenocytes in vitro. In an animal study, the Vit D@Gel/T80 injected group demonstrated tendon restoration features. As a result, this Vit D@Gel/T80 system might be a local injection material in the treatment for tendinopathy.

A biomimetic hyaluronic acid‐silk fibroin nanofiber scaffold promoting regeneration of transected urothelium

This study was designed to investigate the regulatory effect of hyaluronic acid (HA)—coating silk fibroin (SF) nanofibers during epithelialization of urinary tract for urethral regeneration. The obtained electrospun biomimetic tubular HA‐SF nanofiber scaffold is composed of a dense inner layer and a porous outer layer in order to mimic adhesion and cavernous layers of the native tissue, respectively. A thin layer of HA‐gel coating was fixed in the inner wall to provide SF nanofibers with a dense and smooth surface nano‐topography and higher hydrophilicity. Compared with pure SF nanofibers, HA‐SF nanofibers significantly promoted the adhesion, growth, and proliferation of primary urothelial cells, and up‐regulate the expression of uroplakin‐3 (terminal differentiation keratin protein in urothelium). Using the New Zealand male rabbit urethral injury model, the scaffold composed of tubular HA‐SF nanofibers could recruit lumen and myoepithelial cells from the adjacent area of the host, rapidly reconstructing the urothelial barrier in the wound area in order to keep the urinary tract unobstructed, thereby promoting luminal epithelialization, smooth muscle bundle structural remodeling, and capillary formation. Overall, the synergistic effects of nano‐topography and biophysical cues in a biomimetic scaffold design for effective endogenous regeneration.

Tendon-bioinspired wavy nanofibrous scaffolds provide tunable anisotropy and promote tenogenesis for tendon tissue engineering

The development of tendon-biomimetic nanofibrous scaffolds with mesenchymal stem cells may represent a promising strategy to improve the unsatisfactory outcomes of traditional treatments in tendon repair. In the present study, the nanofibrous scaffolds comprised of poly(p-dioxanone) (PPDO) and silk fibroin (SF) composites were fabricated by using electrospinning technique and subsequent thermal ethanol treatment. The PPDO/SF composite scaffolds presented parallel fiber arrangement with crimped features and nonlinear mechanical properties, which mimic the structure-function relationship of native tendon tissue mechanics. We demonstrated that the fiber crimp degree and mechanical properties of as-prepared PPDO/SF wavy nanofibrous scaffolds (WNSs) could be tunable by adjusting the mass ratio of PPDO/SF. The biological tests revealed that the addition of SF obviously promoted the cell adhesion, proliferation, and phenotypic maintenance of human tenocytes on the WNSs. A preliminary study on the subcutaneous implantation showed that the PPDO/SF WNSs notably decreased the inflammatory response compared with pure PPDO WNSs. More importantly, a combination of growth factor induction and mechanical stimulation was found to notably enhance the tenogenic differentiation of human adipose derived mesenchymal stem cells on the PPDO/SF WNSs by upregulating the expressions of tendon-associated protein and gene markers. Overall, this study demonstrated that our PPDO/SF WNSs could provide a beneficial microenvironment for various cell activities, making them an attractive candidate for tendon tissue engineering research.

Gas foaming of electrospun poly(L-lactide-co-caprolactone)/silk fibroin nanofiber scaffolds to promote cellular infiltration and tissue regeneration

Electrospun nanofibers emulate extracellular matrix (ECM) morphology and architecture; however, small pore size and tightly-packed fibers impede their translation in tissue engineering. Here we exploited in situ gas foaming to afford three-dimensional (3D) poly(L-lactide-co-ε-caprolactone)/silk fibroin (PLCL/SF) scaffolds, which exhibited nanotopographic cues and a multilayered structure. The addition of SF improved the hydrophilicity and biocompatibility of 3D PLCL scaffolds. Three-dimensional scaffolds exhibited larger pore size (38.75 ± 9.78 μm²) and high porosity (87.1% ± 1.5%) than that of their 2D counterparts. 3D scaffolds also improved the deposition of ECM components and neo-vessel regeneration as well as exhibited more numbers of CD163⁺/CCR7⁺ cells after 2 weeks implantation in a subcutaneous model. Collectively, 3D PLCL/SF scaffolds have broad implications for regenerative medicine and tissue engineering applications.

Fibrous Systems as Potential Solutions for Tendon and Ligament Repair, Healing, and Regeneration

Tendon and ligament injuries caused by trauma and degenerative diseases are frequent and affect diverse groups of the population. Such injuries reduce musculoskeletal performance, limit joint mobility, and lower people's comfort. Currently, various treatment strategies and surgical procedures are used to heal, repair, and restore the native tissue function. However, these strategies are inadequate and, in some cases, fail to re-establish the lost functionality. Tissue engineering and regenerative medicine approaches aim to overcome these disadvantages by stimulating the regeneration and formation of neotissues. Design and fabrication of artificial scaffolds with tailored mechanical properties are crucial for restoring the mechanical function of tendons. In this review, the tendon and ligament structure, their physiology, and performance are presented. On the other hand, the requirements are focused for the development of an effective reconstruction device. The most common fiber-based scaffolding systems are also described for tendon and ligament tissue regeneration like strand fibers, woven, knitted, braided, and braid-twisted fibrous structures, as well as electrospun and wet-spun constructs, discussing critically the advantages and limitations of their utilization. Finally, the potential of multilayered systems as the most effective candidates for tendon and ligaments tissue engineering is pointed out.