Biologics for tendon repair

Self-assembling peptide hydrogel scaffold accelerates healing of patellar tendon injury: A histological and biomechanical study

Although KI24RGDS peptide hydrogel that acts as a cell adhesion has been reported to repair tissue in meniscus injury, its effect on tendon injuries remains unknown. The purpose of this study was to clarify the effect of KI24RGDS for tendon repair based on histological and biomechanical evaluation. After introducing defects (length: 10 mm; width: 3 mm) at the centers of rabbits' patellar tendons, and the KI24RGDS group was implanted with KI24RGDS and observed for 8 weeks. KI24RGDS implantation resulted in limited tendon elongation and better histological scores with uniformed collagen fiber orientation and early vascularization. The failure load of the patellar tendon was higher in the KI24RGDS group than that in the defect group (p < 0.05) and no significant difference with the control group (intact patellar tendon) at 8 weeks postoperatively. In conclusion, KI24RGDS administration might have therapeutic potential for tendon injuries by accelerating collagen remodeling.

Efficacy of an Autologous Dermal Fibroblast Injection in Reducing the Retear Rate After Arthroscopic Rotator Cuff Repair: A Prospective Randomized Controlled Trial

BACKGROUND

Interest in biological augmentation for improving bone-tendon interface (BTI) healing after arthroscopic rotator cuff repair (ARCR) is growing. Dermal fibroblasts, known for collagen synthesis similar to tenocytes, have shown effectiveness in BTI healing in chronic rotator cuff tear (RCT) models in rabbits. However, no human clinical trials have been conducted.

PURPOSE

To evaluate the clinical efficacy of autologous dermal fibroblasts (ADFs) for BTI healing after ARCR in patients with full-thickness RCTs >2 cm.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 2.

METHODS

A total of 86 patients were prospectively enrolled and randomized into 2 groups: an additional ADF injection between the bone and tendon during ARCR (ADF group) or ARCR alone (control group). A skin biopsy from the buttock was performed to obtain ADFs, which were cultured for approximately 4 weeks before surgery. ARCR was standardized to the double-row suture bridge technique to reduce the heterogeneity in different repair methods. The primary variable for evaluating ADF efficacy was the retear rate using magnetic resonance imaging at 6 months postoperatively. Secondary variables included range of motion, the American Shoulder and Elbow Surgeons score, the Constant score, and the Simple Shoulder Test score at baseline and at 6 and 12 months postoperatively.

RESULTS

Overall, 13 patients dropped out because of a subscapularis tendon tear, loss to follow-up, or the withdrawal of consent (7 in the ADF group and 6 in the control group). The retear rate was significantly lower in the ADF group (5.6% [2/36]) than in the control group (24.3% [9/37]) (P = .025). The American Shoulder and Elbow Surgeons, Constant, and Simple Shoulder Test scores showed significant improvement after surgery in both groups (all P values <.001). Functional scores and range of motion did not significantly differ between the 2 groups at 6 and 12 months (all P values >.05).

CONCLUSION

ADF application into the BTI during ARCR significantly decreased the retear rate in patients with full-thickness RCTs >2 cm. Therefore, an ADF injection could be a promising biological supplement to enhance BTI healing in these patients. However, clinical outcomes showed no significant difference between the 2 groups at 6 months and 1 year postoperatively.

Honeycomb-Shaped Collagen Aerogels Formed Using a Multichannel Hydrogel as the Template

This study introduces a novel method for fabricating multicavity, honeycomb-shaped collagen aerogels characterized by continuous pores. We have taken a unique approach to lyophilizing collagen hydrogels, which are UV-irradiated collagen solutions gelatinized in a carbonate buffer solution. The focus of this study was to investigate the effect of UV irradiation times on collagen solutions on collagen hydrogels and aerogels. This investigation revealed significant alterations in the morphological attributes, notably in the pore and short axis cross-sectional areas and the mechanical properties, particularly the elastic modulus, of the resultant collagen gels and aerogels. A notable increase in the ratio of the pore to the short-axis cross-sectional area was observed with extended UV exposure. Further, irrespective of the irradiation duration, we observed a consistent pattern of elongation and proliferation in mouse fibroblast cultures. These findings underscore the potential of our developed collagen aerogels as versatile biomaterials, especially in the realm of cell scaffolds.

Fabrication of a micropatterned shape-memory polymer patch with L-DOPA for tendon regeneration

A scaffold design for tendon regeneration has been proposed, which mimics the microstructural features of tendons and provides appropriate mechanical properties. We synthesized a temperature-triggered shape-memory polymer (SMP) using the ring-opening polymerization of polycaprolactone (PCL) with polyethylene glycol (PEG) as a macroinitiator. We fabricated a micropatterned patch using SMP via capillary force lithography, which mimicked a native tendon, for providing physical cues and guiding effects. The SMP patches (the SMP-flat patch is referred to as SMP-F, and the SMP-patterned patch is referred to as SMP-P) were surface-modified with 3,4-dihydroxy-L-phenylalanine (L-DOPA, referred to as D) for improving cell adhesion. We hypothesized that SMP patches could be applied in minimally invasive surgery and the micropatterned structure would improve tendon regeneration by providing geometrical cues. The SMP patches exhibited excellent shape-memory properties, mechanical performance, and biocompatibility in vitro and in vivo. Especially, SMP-DP demonstrated enhanced cell behaviors in vitro, including cell orientation, elongation, migration, and tenogenic differentiation potential. The in vivo data showed notable biomechanical functionality and histological morphometric findings in various analyses of SMP-DP in the ruptured Achilles tendon model.

Decellularization of various tissues and organs through chemical methods

Due to the increase in demand for donor organs and tissues during the past 20 years, new approaches have been created. These methods include, for example, tissue engineering in vitro and the production of regenerative biomaterials for transplantation. Applying the natural extracellular matrix (ECM) as a bioactive biomaterial for clinical applications is a unique approach known as decellularization technology. Decellularization is the process of eliminating cells from an extracellular matrix while preserving its natural components including its structural and functional proteins and glycosaminoglycan. This can be achieved by physical, chemical, or biological processes. A naturally formed three-dimensional structure with a biocompatible and regenerative structure is the result of the decellularization process. Decreasing the biological factors and antigens at the transplant site reduces the risk of adverse effects including inflammatory responses and immunological rejection. Regenerative medicine and tissue engineering applications can benefit from the use of decellularization, a promising approach that provides a biomaterial that preserves its extracellular matrix.

The current status of various preclinical therapeutic approaches for tendon repair

Tendons are fibroblastic structures that link muscle and bone. There are two kinds of tendon injuries, including acute and chronic. Each form of injury or deterioration can result in significant pain and loss of tendon function. The recovery of tendon damage is a complex and time-consuming recovery process. Depending on the anatomical location of the tendon tissue, the clinical outcomes are not the same. The healing of the wound process is divided into three stages that overlap: inflammation, proliferation, and tissue remodeling. Furthermore, the curing tendon has a high re-tear rate. Faced with the challenges, tendon injury management is still a clinical issue that must be resolved as soon as possible. Several newer directions and breakthroughs in tendon recovery have emerged in recent years. This article describes tendon injury and summarizes recent advances in tendon recovery, along with stem cell therapy, gene therapy, Platelet-rich plasma remedy, growth factors, drug treatment, and tissue engineering. Despite the recent fast-growing research in tendon recovery treatment, still, none of them translated to the clinical setting. This review provides a detailed overview of tendon injuries and potential preclinical approaches for treating tendon injuries.

Erroneous Differentiation of Tendon Stem/Progenitor Cells in the Pathogenesis of Tendinopathy: Current Evidence and Future Perspectives

Tendinopathy is a condition characterized by persistent tendon pain, structural damage, and compromised functionality. Presently, the treatment for tendinopathy remains a formidable challenge, partly because of its unclear pathogenesis. Tendon stem/progenitor cells (TSPCs) are essential for tendon homeostasis, regeneration, remodeling, and repair. An innovative theory has been previously proposed, with insufficient evidence, that the erroneous differentiation of TSPCs may constitute one of the fundamental mechanisms underpinning tendinopathy. Over the past few years, there has been accumulating evidence for plausibility of this theory. In this review, we delve into alterations in the differentiation potential of TSPCs and the underlying mechanisms in the context of injury-induced tendinopathy, diabetic tendinopathy, and age-related tendinopathy to provide updated evidence on the erroneous differentiation theory. Despite certain limitations inherent in the existing body of evidence, the erroneous differentiation theory emerges as a promising and highly pertinent avenue for understanding tendinopathy. In the future, advanced methodologies will be harnessed to further deepen comprehension of this theory, paving the way for prospective developments in clinical therapies targeting TSPCs for the management of tendinopathy.

Challenges in tendon-bone healing: emphasizing inflammatory modulation mechanisms and treatment

Tendons are fibrous connective tissues that transmit force from muscles to bones. Despite their ability to withstand various loads, tendons are susceptible to significant damage. The healing process of tendons and ligaments connected to bone surfaces after injury presents a clinical challenge due to the intricate structure, composition, cellular populations, and mechanics of the interface. Inflammation plays a pivotal role in tendon healing, creating an inflammatory microenvironment through cytokines and immune cells that aid in debris clearance, tendon cell proliferation, and collagen fiber formation. However, uncontrolled inflammation can lead to tissue damage, and adhesions, and impede proper tendon healing, culminating in scar tissue formation. Therefore, precise regulation of inflammation is crucial. This review offers insights into the impact of inflammation on tendon-bone healing and its underlying mechanisms. Understanding the inflammatory microenvironment, cellular interactions, and extracellular matrix dynamics is essential for promoting optimal healing of tendon-bone injuries. The roles of fibroblasts, inflammatory cytokines, chemokines, and growth factors in promoting healing, inhibiting scar formation, and facilitating tissue regeneration are discussed, highlighting the necessity of balancing the suppression of detrimental inflammatory responses with the promotion of beneficial aspects to enhance tendon healing outcomes. Additionally, the review explores the significant implications and translational potential of targeted inflammatory modulation therapies in refining strategies for tendon-bone healing treatments.

Advancements in Therapeutic Approaches for Degenerative Tendinopathy: Evaluating Efficacy and Challenges

Degenerative tendinopathy results from the accumulation of minor injuries following unsuccessful tendon repair during acute tendon injuries. The process of tendon repair is prolonged and varies between individuals, making it susceptible to reinjury. Moreover, treating chronic tendinopathy often requires expensive and extensive rehabilitation, along with a variety of combined therapies to facilitate recovery. This condition significantly affects the quality of life of affected individuals, underscoring the urgent need for more efficient and cost-effective treatment options. Although traditional treatments have improved significantly and are being used as substitutes for surgical interventions, the findings have been inconsistent and conflicting. This review aims to clarify these issues by exploring the strengths and limitations of current treatments as well as recent innovations in managing various forms of degenerative tendinopathy.

Effects of Conditioned Media From Human Umbilical Cord-Derived Mesenchymal Stem Cells on Tenocytes From Degenerative Rotator Cuff Tears in an Interleukin 1β-Induced Tendinopathic Condition

Background

Evidence suggests that mesenchymal stem cells (MSCs) are safe for treating different tendinopathies. Synovial fluid is a pooled environment of biomarkers from the inflammatory and degenerative joint cavity. Understanding the effects of synovial fluid on MSCs is important, as it is the first microenvironment that administered MSCs encounter. Several studies have reported that exposure to osteoarthritic synovial fluid-activated MSCs increased the release of soluble factors; however, the paracrine effects of shoulder synovial fluid-stimulated umbilical cord-derived MSCs (SF-UC-MSCs) on tendinopathy have yet to be investigated.

Purpose

To assess the effects of the conditioned media from SF-UC-MSCs on tenocytes from degenerative rotator cuff tears in an interleukin-1β (IL-1β)-induced tendinopathic condition.

Study Design

Controlled laboratory study.

Methods

UC-MSCs were isolated and cultured from healthy, full-term deliveries by cesarean section. Tenocytes were isolated and cultured from patients with degenerative rotator cuff tears. Conditioned media were obtained from UC-MSCs stimulated with synovial fluid. To evaluate the gene expression of proinflammatory and anti-inflammatory cytokines, enzymes and their inhibitors, matrix molecules, and growth factors, the tenocytes were cultured with IL-1β and 50% of the conditioned media from the SF-UC-MSCs; quantitative, real-time, reverse transcriptase polymerase chain reaction was also performed. A prostaglandin E2 (PGE2) assay was performed to investigate the PGE2 level secreted by the tenocytes. Western blotting was performed to examine protein synthesis of collagen type I and III. Cell viability, senescence, and apoptosis assays were also performed.

Results

The conditioned media from the SF-UC-MSCs interfered with the inflammatory gene expression on tenocytes induced by IL-1β, but it increased the gene expression of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-3. Meanwhile, the conditioned media decreased the PGE2 level on cells induced by IL-1β. It did increase the type I/III ratio of gene expression and protein synthesis, mainly through the induction of type I collagen. Conditioned media of SF-UC-MSCs reversed senescence and apoptosis induced by IL-1β.

Conclusion

Study findings indicated that the conditioned media from SF-UC-MSCs had anti-inflammatory effects and cytoprotective effects on IL-1β-treated tenocytes from degenerative rotator cuff tears.

Clinical Relevance

UC-MSCs have useful potential for the treatment of tendinopathy in practice.

Various Strategies of Tendon Stem/Progenitor Cell Reprogramming for Tendon Regeneration

Rotator cuff tears (RCT) are the most common cause of shoulder pain among adults. "Rotator cuff" refers to the four muscles that cover the shoulder joint: supraspinatus, infraspinatus, subscapularis, and teres minor. These muscles help maintain the rotational movement and stability of the shoulder joint. RCT is a condition in which one or more of these four muscles become ruptured or damaged, causing pain in the arms and shoulders. RCT results from degenerative changes caused by chronic inflammation of the tendons and consequent tendon tissue defects. This phenomenon occurs because of the exhaustion of endogenous tendon stem cells. Tendon regeneration requires rejuvenation of these endogenous tendon stem/progenitor cells (TSPCs) prior to their growth phase. TSPCs exhibit clonogenicity, multipotency, and self-renewal properties; they express classical stem cell markers and genes associated with the tendon lineage. However, specific markers for TSPC are yet to be identified. In this review, we introduce novel TSPC markers and discuss various strategies for TSPC reprogramming. With further research, TSPC reprogramming technology could be adapted to treat age-related degenerative diseases, providing a new strategy for regenerative medicine.

Classification of distinct tendinopathy subtypes for precision therapeutics

Rotator cuff tendinopathy is the most common tendinopathy type with the worst prognosis. Conventional treatments often elicit heterogeneous drug responses due to the diversity of tendinopathy. Hence, this study attempted a classification of 126 diseased tendons into three distinct subtypes with opposite pathogenic mechanisms based on transcriptomic and clinical features. The hypoxic atrophic subtype with white appearance (Hw) exhibits downregulated neovascularization pathways. The inflammatory proliferative subtype with white appearance (Iw) shows a moderate upregulation of inflammatory characteristics. The inflammatory proliferative subtype with red appearance (Ir) exhibits the highest levels of upregulated neovascularization and inflammatory pathways, along with severe joint dysfunction. We then established research models, including subtype-specific simulations in animal models and clinical data analysis. These revealed that glucocorticoid, a controversial commonly used drug, was only effective in treating the Ir subtype. Hence, the tendinopathy subtypes elucidated in this study have significant implications for developing precision treatment of tendinopathy.

Fibrin Scaffolds Perfused with Transforming Growth Factor-β1 as an In Vitro Model to Study Healthy and Tendinopathic Human Tendon Stem/Progenitor Cells

A limited understanding of tendon cell biology in healthy and pathological conditions has impeded the development of effective treatments, necessitating in vitro biomimetic models for studying tendon events. We established a dynamic culture using fibrin scaffolds, bioengineered with tendon stem/progenitor cells (hTSPCs) from healthy or diseased human biopsies and perfused with 20 ng/mL of human transforming growth factor-β1 for 21 days. Both cell types showed long-term viability and upregulated Scleraxis (SCX-A) and Tenomodulin (TNMD) gene expressions, indicating tenogenic activity. However, diseased hTSPCs underexpressed collagen type I and III (COL1A1 and COL3A1) genes and exhibited lower SCX-A and TNMD protein levels, but increased type I collagen production, with a type I/type III collagen ratio > 1.5 by day 14, matching healthy cells. Diseased hTSPCs also showed constant high levels of pro-inflammatory cytokines, such as IL-8 and IL-6. This biomimetic environment is a valuable tool for studying tenogenic and inflammatory events in healthy and diseased tendon cells and identifying new therapeutic targets.

Structure, ingredient, and function-based biomimetic scaffolds for accelerated healing of tendon-bone interface

Background

Tendon-bone interface (TBI) repair is slow and challenging owing to its hierarchical structure, gradient composition, and complex function. In this work, enlightened by the natural characteristics of TBI microstructure and the demands of TBI regeneration, a structure, composition, and function-based scaffold was fabricated. Methods: The biomimetic scaffold was designed based on the "tissue-inducing biomaterials" theory: (1) a porous scaffold was created with poly-lactic-co-glycolic-acid, nano-hydroxyapatite and loaded with BMP2-gelatinmp to simulate the bone (BP); (2) a hydrogel was produced from sodium alginate, type I collagen, and loaded with TGF-β3 to simulate the cartilage (CP); (3) the L-poly-lactic-acid fibers were oriented to simulate the tendon (TP). The morphology of tri-layered constructs, gelation kinetics, degradation rate, release kinetics and mechanical strength of the scaffold were characterized. Then, bone marrow mesenchymal stem cells (MSCs) and tenocytes (TT-D6) were cultured on the scaffold to evaluate its gradient differentiation inductivity. A rat Achilles tendon defect model was established, and BMSCs seeded on scaffolds were implanted into the lesionsite. The tendon-bone lesionsite of calcaneus at 4w and 8w post-operation were obtained for gross observation, radiological evaluation, biomechanical and histological assessment.

Results

The hierarchical microstructures not only endowed the scaffold with gradual composition and mechanical properties for matching the regional biophysical characteristics of TBI but also exhibited gradient differentiation inductivity through providing regional microenvironment for cells. Moreover, the scaffold seeded with cells could effectively accelerate healing in rat Achilles tendon defects, attributable to its enhanced differentiation performance.

Conclusion

The hierarchical scaffolds simulating the structural, compositional, and cellular heterogeneity of natural TBI tissue performed therapeutic effects on promoting regeneration of TBI and enhancing the healing quality of Achilles tendon.

The translational potential of this article

The novel scaffold showed the great efficacy on tendon to bone healing by offering a structural and compositional microenvironment. The results meant that the hierarchical scaffold with BMSCs may have a great potential for clinical application.

Rehabilitation Approaches for Proximal Peroneal Tendinopathy With Concurrent Anterior Cruciate Ligament (ACL) Sprain: A Case Report

Proximal peroneal tendinopathy is a relatively rare condition and can cause severe pain, discomfort, and often disability, especially if it coexists with other pathologies of the lower limbs. This case report discusses a 32-year-old male surgeon with the condition of chronic lateral ankle pain due to proximal peroneal tendinopathy, complicated by an anterior cruciate ligament sprain, a posterior cruciate ligament ganglion cyst, and early medial meniscus degeneration. His ability to perform surgeries has been compromised due to the need to stand for prolonged periods. A multi-factorial rehabilitation approach was designed to address the tendon pathology and the knee dysfunctions associated with it. The treatment program included patient education, therapeutic exercise, and pain management. There were considerable improvements in terms of pain, range of motion, muscle strength, and function from the previous stage of six weeks. This case indicates the clinical necessity of kinetic-chain-oriented, very individualized approaches to rehabilitation for complex musculoskeletal conditions such as this, especially in active professionals. The success of the rehabilitation lies in the potential for recovery even with some tough conditions if the treatment modality is appropriately designed to address the interactive aspects of the patient's condition. This case highlights the importance of an integrated approach in managing complex peroneal tendonitis, especially when associated with upstream joint pathology. The positive outcome underscores the value of early recognition and individualized management to restore function and avoid permanent complications. Additionally, the report serves as a guide for future research into the potential long-term benefits of holistic, patient-specific approaches for similar cases.

Hydrogel-exosome system in tissue engineering: A promising therapeutic strategy

Characterized by their pivotal roles in cell-to-cell communication, cell proliferation, and immune regulation during tissue repair, exosomes have emerged as a promising avenue for "cell-free therapy" in clinical applications. Hydrogels, possessing commendable biocompatibility, degradability, adjustability, and physical properties akin to biological tissues, have also found extensive utility in tissue engineering and regenerative repair. The synergistic combination of exosomes and hydrogels holds the potential not only to enhance the efficiency of exosomes but also to collaboratively advance the tissue repair process. This review has summarized the advancements made over the past decade in the research of hydrogel-exosome systems for regenerating various tissues including skin, bone, cartilage, nerves and tendons, with a focus on the methods for encapsulating and releasing exosomes within the hydrogels. It has also critically examined the gaps and limitations in current research, whilst proposed future directions and potential applications of this innovative approach.

Paratenon preserving repair of the midsubstance acute Achilles tendon rupture: a systematic review and meta-analysis with best- and worst-case analyses for rerupture rates

INTRODUCTION

Paratenon preserving techniques to facilitate acute Achilles tendon rupture repair (AATR) functions by maintaining vascularity and biology for optimal healing response. Therefore, the purpose is to evaluate the outcomes following paratenon preserving repair of the midsubstance AATR. The hypothesis was that paratenon-preserving techniques demonstrate high return to play rates and low complication rates for the repair of the midsubstance AATR.

MATERIALS AND METHODS

A systematic review of the PubMed, Embase, and the Cochrane Library databases was performed by two authors using specific search terms and eligibility criteria. The assessment of the evidence was two-fold: level and quality of evidence. A meta-analysis of proportions for the various complication rates was performed using the restricted maximum likelihood method following the Freeman-Tukey double-arcsine transformation. Fixed effects models were employed if I2 < 25% (low heterogeneity), and random effects models were employed if I2 ≥ 25% (moderate to high heterogeneity).

RESULTS

The pooled return to play rate was 90.3%. The pooled rerupture rate as reported was 0.9% (best-case scenario 0.8% and worst-case scenario 6.8%). No meaningful subgroup analysis for rerupture rates could be performed based on the meta-regression. The pooled complication rate other than reruptures was 4.8%. The pooled infection rates were 0.3%, DVT rates were 1.6%, and sural nerve injury rates were 0.3%.

CONCLUSIONS

Paratenon preserving techniques that are minimally invasive in nature demonstrated safe and favorable outcomes with high return to play rates and low complication rates for the repair of the midsubstance AATR.

The Efficacy of Intratissue Percutaneous Electrolysis (EPI®) and Nutritional Factors for the Treatment of Induced Tendinopathy in Wistar Rats: Hepatic Intermediary Metabolism Effects

Achilles tendinopathy (TP) is characterized as the third most common disease of the musculoskeletal system, and occurs in three phases. There is currently no evidence of effective treatment for this medical condition. In this study, the modulatory effects of the minimally invasive technique intratissue percutaneous electrolysis (EPI) and combinations of EPI with four nutritional factors included in the diet, hydroxytyrosol (HT), maslinic acid (MA), glycine, and aspartate (AA), on hepatic intermediary metabolism was examined in Wistar rats with induced tendinopathy at various stages of TP. Results obtained showed that induced tendinopathy produced alterations in the liver intermediary metabolisms of the rats. Regarding carbohydrate metabolism, a reduction in the activity of pro-inflammatory enzymes in the later stages of TP was observed following treatment with EPI alone. Among the combined treatments using nutritional factors with EPI, HT+EPI and AA+EPI had the greatest effect on reducing inflammation in the late stages of TP. In terms of lipid metabolism, the HT+EPI and AA+EPI groups showed a decrease in lipogenesis. In protein metabolism, the HT+EPI group more effectively reduced the inflammatory effects of induced TP. Treatment with EPI combined with nutritional factors might help regulate intermediary metabolism in TP disease and reduce the inflammation process.

Hyaluronic acid/PEO electrospun tube reduces tendon adhesion to levels comparable to native tendons - An in vitro and in vivo study

A major problem after tendon injury is adhesion formation to the surrounding tissue leading to a limited range of motion. A viable strategy to reduce adhesion extent is the use of physical barriers that limit the contact between the tendon and the adjacent tissue. The purpose of this study was to fabricate an electrospun bilayered tube of hyaluronic acid/polyethylene oxide (HA/PEO) and biodegradable DegraPol® (DP) to improve the anti-adhesive effect of the implant in a rabbit Achilles tendon full laceration model compared to a pure DP tube. Additionally, the attachment of rabbit tenocytes on pure DP and HA/PEO containing scaffolds was tested and Scanning Electron Microscopy, Fourier-transform Infrared Spectroscopy, Differential Scanning Calorimetry, Water Contact Angle measurements, and testing of mechanical properties were used to characterize the scaffolds. In vivo assessment after three weeks showed that the implant containing a second HA/PEO layer significantly reduced adhesion extent reaching levels comparable to native tendons, compared with a pure DP implant that reduced adhesion formation only by 20 %. Tenocytes were able to attach to and migrate into every scaffold, but cell number was reduced over two weeks. Implants containing HA/PEO showed better mechanical properties than pure DP tubes and with the ability to entirely reduce adhesion extent makes this implant a promising candidate for clinical application in tendon repair.

Assembly of Interfacial Polyelectrolyte Complexation Fibers with Mineralization Gradient for Physiologically-Inspired Ligament Regeneration

Current synthetic grafts for ligament rupture repair often fail to integrate well with the surrounding biological tissue, leading to complications such as graft wear, fatigue, and subsequent re-rupture. To address this medical challenge, this study aims at advancing the development of a biological ligament through the integration of physiologically-inspired principles and tissue engineering strategies. In this study, interfacial polyelectrolyte complexation (IPC) spinning technique, along with a custom-designed collection system, to fabricate a hierarchical scaffold mimicking native ligament structure, is utilized. To emulate the bone-ligament interface and alleviate stress concentration, a hydroxyapatite (HAp) mineral gradient is strategically introduced near both ends of the scaffold to enhance interface integration and diminish the risk of avulsion rupture. Biomimetic viscoelasticity is successfully displayed to provide similar mechanical support to native ligamentous tissue under physiological conditions. By introducing the connective tissue growth factor (CTGF) and conducting mesenchymal stem cells transplantation, the regenerative potential of the synthetic ligament is significantly amplified. This pioneering study offers a multifaceted solution combining biomimetic materials, regenerative therapies, and advanced techniques to potentially transform ligament rupture treatment.

Tissue-engineered mesenchymal stem cell constructs alleviate tendinopathy by suppressing vascularization

Tendinopathy leads to low-grade tissue inflammation and chronic damage, which progresses due to pathological imbalance in angiogenesis. Reducing early pathological vascularization may be a new approach in helping to regenerate tendon tissue. Conventional stem cell therapy and tissue engineering scaffolds have not been highly effective at treating tendinopathy. In this study, tissue engineered stem cells (TSCs) generated using human umbilical cord mesenchymal stem cells (hUC-MSCs) were combined with microcarrier scaffolds to limit excessive vascularization in tendinopathy. By preventing VEGF receptor activation through their paracrine function, TSCs reduced in vitro angiogenesis and the proliferation of vascular endothelial cells. TSCs also decreased the inflammatory expression of tenocytes while promoting their anabolic and tenogenic characteristics. Furthermore, local injection of TSCs into rats with collagenase-induced tendinopathy substantially reduced early inflammation and vascularization. Mechanistically, transcriptome sequencing revealed that TSCs could reduce the progression of pathological angiogenesis in tendon tissue, attributed to Rap1-mediated vascular inhibition. TSCs may serve as a novel and practical approach for suppressing tendon vascularization, and provide a promising therapeutic agent for early-stage clinical tendinopathy.

Stem Cell‐Based Therapies and Tissue Engineering Innovations for Tendinopathy: A Comprehensive Review of Current Strategies and Future Directions

Tendon diseases commonly lead to physical disability, exerting a profound impact on the routine of affected patients. These conditions respond poorly to existing treatments, presenting a substantial challenge for orthopedic scientists. Research into clinical translational therapy has yet to yield highly versatile interventions capable of effectively addressing tendon diseases, including tendinopathy. Stem cell‐based therapies have emerged as a promising avenue for modifying the biological milieu through the secretion of regenerative and immunomodulatory factors. The current review provides an overview of the intricate tendon microenvironment, encompassing various tendon stem progenitor cells within distinct tendon sublocations, gene regulation, and pathways pertinent to tendon development, and the pathology of tendon diseases. Subsequently, the advantages of stem cell‐based therapies are discussed that utilize distinct types of autologous and allogeneic stem cells for tendon regeneration at the translational level. Moreover, this review outlines the challenges, gaps, and future innovations to propose a consolidated stem cell‐based therapy to treat tendinopathy. Finally, regenerative soluble therapies, insoluble bio‐active therapies, along with insoluble bio‐active therapies, and implantable 3D scaffolds for tendon tissue engineering are discussed, thereby presenting a pathway toward enhanced tissue regeneration and engineering.

Fabrication of atelocollagen-coated bioabsorbable suture and the evaluation of its regenerative efficacy in Achilles tendon healing using a rat experimental model

Recently, the incidence of Achilles tendon ruptures (ATRs) has become more common, and repair surgery using a bioabsorbable suture is generally preferred, particularly in the case of healthy patients. Sutures composed of poly(lactic-co-glycolic acid) (PLGA) are commonly used in ATR surgeries. Nevertheless, owing to the inherent limitations of PLGA, novel bioabsorbable sutures that can accelerate Achilles tendon healing are sought. Recently, several studies have demonstrated the beneficial effects of atelocollagen on tendon healing. In this study, poly(3,4-dihydroxy-L-phenylalanine) (pDOPA), a hydrophilic biomimetic material, was used to modify the hydrophobic surface of a PLGA suture (Vicryl, VC) for the stable coating of atelocollagen on its surface. The main objective was to fabricate an atelocollagen-coated VC suture and evaluate its performance in the healing of Achilles tendon using a rat model of open repair for ATR. Structural analyses of the surface-modified suture indicated that the collagen was successfully coated on the VC/pDOPA suture. Postoperative in vivo biomechanical analysis, histological evaluation, ultrastructural/morphological analyses, and western blotting confirmed that the tendons in the VC/pDOPA/Col group exhibit superior healing than those in the VC and VC/pDOPA groups after 1 and 6 weeks following the surgery. The this study suggests that atelocollagen-coated PLGA/pDOPA sutures are preferable for future medical applications, especially in the repair of ATR.

Integrated transcriptomics and metabolomics study of embryonic breast muscle of Jiaji ducks

Because number of matured muscle fibers in poultry does not increase after birth, the meat yield is mainly determined during embryogenesis. We previously indicated breast muscle grew rapidly from 18th day after hatching (E18) to E27, and almost stopped from E27 to E34 of Jiaji ducks, while the mechanism is unclear. This study utilized RNA-seq to explore the related genes of muscle development and their relationship with small molecule metabolites at E18, E27 and E34 of Jiaji ducks. Several thousand differentially expressed genes (DEGs) were detected among E18, E27 and E34. DEGs expression profiles included 8 trend maps, among which trend 1 was opposite to and trend 6 was consistent with breast muscle development trend of Jiaji ducks. Through joint analysis between trend 1 of DEGs and trend 1 of differential metabolites (DEMs), protein digestion and absorption pathway stood out. The decrease of COL8A2 gene expression will lead to the decrease of arginine content, which will inhibit the development of breast muscle in embryonic Jiaji duck. Similarly, joint analysis between trend 6 of DEGs and trend 6 of DEMs indicated the increase of GAMT gene expression will cause the increase of proline content, and then promote the development of breast muscle of Jiaji duck in embryonic period. These results will be helpful for further understanding the mechanism of muscle yields of Jiaji ducks.

Engineering an extracellular matrix-functionalized, load-bearing tendon substitute for effective repair of large-to-massive tendon defects

A significant clinical challenge in large-to-massive rotator cuff tendon injuries is the need for sustaining high mechanical demands despite limited tissue regeneration, which often results in clinical repair failure with high retear rates and long-term functional deficiencies. To address this, an innovative tendon substitute named "BioTenoForce" is engineered, which uses (i) tendon extracellular matrix (tECM)'s rich biocomplexity for tendon-specific regeneration and (ii) a mechanically robust, slow degradation polyurethane elastomer to mimic native tendon's physical attributes for sustaining long-term shoulder movement. Comprehensive assessments revealed outstanding performance of BioTenoForce, characterized by robust core-shell interfacial bonding, human rotator cuff tendon-like mechanical properties, excellent suture retention, biocompatibility, and tendon differentiation of human adipose-derived stem cells. Importantly, BioTenoForce, when used as an interpositional tendon substitute, demonstrated successful integration with regenerative tissue, exhibiting remarkable efficacy in repairing large-to-massive tendon injuries in two animal models. Noteworthy outcomes include durable repair and sustained functionality with no observed breakage/rupture, accelerated recovery of rat gait performance, and >1 cm rabbit tendon regeneration with native tendon-like biomechanical attributes. The regenerated tissues showed tendon-like, wavy, aligned matrix structure, which starkly contrasts with the typical disorganized scar tissue observed after tendon injury, and was strongly correlated with tissue stiffness. Our simple yet versatile approach offers a dual-pronged, broadly applicable strategy that overcomes the limitations of poor regeneration and stringent biomechanical requirements, particularly essential for substantial defects in tendon and other load-bearing tissues.

In vivo study on the repair of rat Achilles tendon injury treated with non-thermal atmospheric-pressure helium microplasma jet

Non-thermal atmospheric-pressure plasma (NTAPP) has been widely studied for clinical applications, e.g., disinfection, wound healing, cancer therapy, hemostasis, and bone regeneration. It is being revealed that the physical and chemical actions of plasma have enabled these clinical applications. Based on our previous report regarding plasma-stimulated bone regeneration, this study focused on Achilles tendon repair by NTAPP. This is the first study to reveal that exposure to NTAPP can accelerate Achilles tendon repair using a well-established Achilles tendon injury rat model. Histological evaluation using the Stoll's and histological scores showed a significant improvement at 2 and 4 weeks, with type I collagen content being substantial at the early time point of 2 weeks post-surgery. Notably, the replacement of type III collagen with type I collagen occurred more frequently in the plasma-treated groups at the early stage of repair. Tensile strength test results showed that the maximum breaking strength in the plasma-treated group at two weeks was significantly higher than that in the untreated group. Overall, our results indicate that a single event of NTAPP treatment during the surgery can contribute to an early recovery of an injured tendon.

Novel In Vitro Platform for Studying the Cell Response to Healthy and Diseased Tendon Matrices

Current in vitro models poorly represent the healthy or diseased tendon microenvironment, limiting the translation of the findings to clinics. The present work aims to establish a physiologically relevant in vitro tendon platform that mimics biophysical aspects of a healthy and tendinopathic tendon matrix using a decellularized bovine tendon and to characterize tendon cells cultured using this platform. Bovine tendons were subjected to various decellularization techniques, with the efficacy of decellularization determined histologically. The biomechanical and architectural properties of the decellularized tendons were characterized using an atomic force microscope. Tendinopathy-mimicking matrices were prepared by treating the decellularized tendons with collagenase for 3 h or collagenase-chondroitinase (CC) for 1 h. The tendon tissue collected from healthy and tendinopathic patients was characterized using an atomic force microscope and compared to that of decellularized matrices. Healthy human tendon-derived cells (hTDCs) from the hamstring tendon were cultured on the decellularized matrices for 24 or 48 h, with cell morphology characterized using f-actin staining and gene expression characterized using real-time PCR. Tendon matrices prepared by freeze-thawing and 48 h nuclease treatment were fully decellularized, and the aligned structure and tendon stiffness (1.46 MPa) were maintained. Collagenase treatment prepared matrices with a disorganized architecture and reduced stiffness (0.75 MPa), mimicking chronic tendinopathy. Treatment with CC prepared matrices with a disorganized architecture without altering stiffness, mimicking early tendinopathy (1.52 MPa). hTDCs on a healthy tendon matrix were elongated, and the scleraxis (SCX) expression was maintained. On tendinopathic matrices, hTDCs had altered morphological characteristics and lower SCX expression. The expression of genes related to actin polymerization, matrix degradation and remodeling, and immune cell invasion were higher in hTDCs on tendinopathic matrices. Overall, the present study developed a physiological in vitro system to mimic healthy tendons and early and late tendinopathy, and it can be used to better understand tendon cell characteristics in healthy and diseased states.

Exogenous interleukin-1 beta stimulation regulates equine tenocyte function and gene expression in three-dimensional culture which can be rescued by pharmacological inhibition of interleukin 1 receptor, but not nuclear factor kappa B, signaling

We investigated how Interleukin 1 beta (IL-1β) impacts equine tenocyte function and global gene expression in vitro and determined if these effects could be rescued by pharmacologically inhibiting nuclear factor-κB (NF-KB) or interleukin 1 signalling. Equine superficial digital flexor tenocytes were cultured in three-dimensional (3D) collagen gels and stimulated with IL-1β for two-weeks, with gel contraction and interleukin 6 (IL6) measured throughout and transcriptomic analysis performed at day 14. The impact of three NF-KB inhibitors on gel contraction and IL6 secretion were measured in 3D culture, with NF-KB-P65 nuclear translocation by immunofluorescence and gene expression by qPCR measured in two-dimensional (2D) monolayer culture. In addition, daily 3D gel contraction and transcriptomic analysis was performed on interleukin 1 receptor antagonist-treated 3D gels at day 14. IL-1β increased NF-KB-P65 nuclear translocation in 2D culture and IL6 secretion in 3D culture, but reduced daily tenocyte 3D gel contraction and impacted > 2500 genes at day 14, with enrichment for NF-KB signaling. Administering direct pharmacological inhibitors of NF-KB did reduce NF-KB-P65 nuclear translocation, but had no effect on 3D gel contraction or IL6 secretion in the presence of IL-1β. However, IL1Ra restored 3D gel contraction and partially rescued global gene expression. Tenocyte 3D gel contraction and gene expression is adversely impacted by IL-1β which can only be rescued by blockade of interleukin 1 receptor, but not NF-KB, signalling.

Comparison of three techniques for decellularization of porcine bone-tendon-bone grafts

Anterior cruciate ligament injuries are frequent afflictions related to sports or physical trauma. Autograft reconstruction strategies cause secondary injury to the patient. One alternative, supported by clinical evidence, is porcine xenografts. For clinical use, xenografts must be conditioned to avoid immune rejection. The most widely accepted procedure is tissue decellularization. We analyzed three decellularization strategies: the application of the anionic detergent sodium dodecyl sulfate (SDS), sonication, and freezing and thawing cycles. The treated tissues were evaluated histologically using H&E, Masson's trichrome, Verhoeff-van Gieson staining, and DAPI for fluorescent staining of nuclei. Finally, collagen fiber preservation was evaluated by quantifying this protein by colorimetry. The most efficient decellularization techniques were sonication and SDS. Collagen fibers were preserved in all experimental conditions.

Equine Musculoskeletal Pathologies: Clinical Approaches and Therapeutical Perspectives-A Review

Musculoskeletal injuries such as equine osteoarthritis, osteoarticular defects, tendonitis/desmitis, and muscular disorders are prevalent among sport horses, with a fair prognosis for returning to exercise or previous performance levels. The field of equine medicine has witnessed rapid and fruitful development, resulting in a diverse range of therapeutic options for musculoskeletal problems. Staying abreast of these advancements can be challenging, prompting the need for a comprehensive review of commonly used and recent treatments. The aim is to compile current therapeutic options for managing these injuries, spanning from simple to complex physiotherapy techniques, conservative treatments including steroidal and non-steroidal anti-inflammatory drugs, hyaluronic acid, polysulfated glycosaminoglycans, pentosan polysulfate, and polyacrylamides, to promising regenerative therapies such as hemoderivatives and stem cell-based therapies. Each therapeutic modality is scrutinized for its benefits, limitations, and potential synergistic actions to facilitate their most effective application for the intended healing/regeneration of the injured tissue/organ and subsequent patient recovery. While stem cell-based therapies have emerged as particularly promising for equine musculoskeletal injuries, a multidisciplinary approach is underscored throughout the discussion, emphasizing the importance of considering various therapeutic modalities in tandem.

Recent Advances in the Use of Stem Cells in Tissue Engineering and Adjunct Therapies for Tendon Reconstruction and Future Perspectives

Due to their function, tendons are exposed to acute injuries. This type of damage to the musculoskeletal system represents a challenge for clinicians when natural regeneration and treatment methods do not produce the expected results. Currently, treatment is long and associated with long-term complications. In this review, we discuss the use of stem cells in the treatment of tendons, including how to induce appropriate cell differentiation based on gene therapy, growth factors, tissue engineering, proteins involved in regenerative process, drugs and three-dimensional (3D) structures. A multidirectional approach as well as the incorporation of novel components of the therapy will improve the techniques used and benefit patients with tendon injuries in the future.

Janus Membranes Patch Achieves High-Quality Tendon Repair: Inhibiting Exogenous Healing and Promoting Endogenous Healing

The imbalance between endogenous and exogenous healing is the fundamental reason for the poor tendon healing. In this study, a Janus patch was developed to promote endogenous healing and inhibit exogenous healing, leading to improved tendon repair. The upper layer of the patch is a poly(dl-lactide-co-glycolide)/polycaprolactone (PLGA/PCL) nanomembrane (PMCP-NM) modified with poly(2-methylacryloxyethyl phosphocholine) (PMPC), which created a lubricated and antifouling surface, preventing cell invasion and mechanical activation. The lower layer is a PLGA/PCL fiber membrane loaded with fibrin (Fb) (Fb-NM), serving as a temporary chemotactic scaffold to regulate the regenerative microenvironment. In vitro, the Janus patch effectively reduced 92.41% cell adhesion and 79.89% motion friction. In vivo, the patch inhibited tendon adhesion through the TGF-β/Smad signaling pathway and promoted tendon maturation. This Janus patch is expected to provide a practical basis and theoretical guidance for high-quality soft tissue repair.

Assessing the functional potential of conditioned media derived from amniotic epithelial stem cells engineered on 3D biomimetic scaffolds: An in vitro model for tendon regeneration

Tendon diseases pose a significant challenge in regenerative medicine due to the limited healing capacity of this tissue. Successful tendon regeneration requires a combination of angiogenesis, immune response, and tenogenesis processes. An effective tendon engineering (TE) strategy must finely tune this systems' interplay toward homeostasis. This study explores in vitro the paracrine influence of amniotic epithelial stem cells (AECs) engineered on a validated 3D electrospun PLGA scaffolds on HUVECs (angiogenesis), PBMCs/Jurkat (immune response), and AECs (tenogenic stem cell activation). The results revealed the role of scaffold's topology and topography in significantly modulating the paracrine profile of the cells. In detail, AECs basal release of bioactive molecules was boosted in the cells engineered on 3D scaffolds, in particular VEGF-D, b-FGF, RANTES, and PDGF-BB (p < 0.0001 vs. CMCTR). Moreover, biological tests demonstrated 3D scaffolds' proactive role in potentiating AECs' paracrine inhibition on PBMCs proliferation (CM3Dvs. CTR, p < 0.001) and LPS-mediated Jurkat activation with respect to controls (CM3D and CM2Dvs. CTR, p < 0.01 and p < 0.05, respectively), without exerting any in vitro pro-angiogenic role in promoting HUVECs proliferation and tubule formation. Teno-inductive paracrine ability of AECs engineered on 3D scaffolds was assessed on co-cultured ones, which formed tendon-like structures. These latter demonstrated an upregulation of tendon-related genes (SCX, THBS4, COL1, and TNMD) and the expression TNMD and COL1 proteins. Overall, this research underscores the pivotal role of the 3D topology and topography of PLGA tendon mimetic scaffolds in orchestrating effective tendon regeneration through modulating cell behavior and crosstalk between engineered stem cells and different subpopulations in the damaged tendon.

Effects of evidence-based nursing care interventions on wound pain and wound complications following surgery for finger tendon injury

We conducted this study aimed to examine the impact of evidence-based nursing interventions on postoperative wound pain and complications after surgery for finger tendon injury. A total of 86 patients treated for finger tendon injuries at our hospital from January 2021 to October 2023 were selected and randomly divided into an experimental group and a control group. The control group received conventional nursing care, while the experimental group received evidence-based nursing interventions. The study compared the postoperative wound pain intensity, incidence of complications and patient satisfaction with nursing care between the two groups. The analysis revealed that compared with conventional care, evidence-based nursing interventions significantly reduced the level of wound pain (p = 0.034) and the incidence of complications (4.65% vs. 18.60%, p = 0.043). It also increased patient satisfaction with the nursing care (97.67% vs. 83.72%, p = 0.026). The study indicates that the application of evidence-based nursing interventions for patients with finger tendon injuries can reduce postoperative wound pain, decrease the incidence of complications and enhance patient satisfaction with nursing care.

The role of macrophage polarization in tendon healing and therapeutic strategies: Insights from animal models

Tendon injuries, a common musculoskeletal issue, usually result in adhesions to the surrounding tissue, that will impact functional recovery. Macrophages, particularly through their M1 and M2 polarizations, play a pivotal role in the inflammatory and healing phases of tendon repair. In this review, we explore the role of macrophage polarization in tendon healing, focusing on insights from animal models. The review delves into the complex interplay of macrophages in tendon pathology, detailing how various macrophage phenotypes contribute to both healing and adhesion formation. It also explores the potential of modulating macrophage activity to enhance tendon repair and minimize adhesions. With advancements in understanding macrophage behavior and the development of innovative biomaterials, this review highlights promising therapeutic strategies for tendon injuries.

The Transplantation of 3-Dimensional Spheroids of Adipose-Derived Stem Cells Promotes Achilles Tendon Healing in Rabbits by Enhancing the Proliferation of Tenocytes and Suppressing M1 Macrophages

BACKGROUND

Tendons have limited regenerative potential, so healing of ruptured tendon tissue requires a prolonged period, and the prognosis is suboptimal. Although stem cell transplantation-based approaches show promise for accelerating tendon repair, the resultant therapeutic efficacy remains unsatisfactory.

HYPOTHESIS

The transplantation of stem cells preassembled as 3-dimensional spheroids achieves a superior therapeutic outcome compared with the transplantation of single-cell suspensions.

STUDY DESIGN

Controlled laboratory study.

METHODS

Adipose-derived stem cells (ADSCs) were assembled as spheroids using a methylcellulose hydrogel system. The secretome of ADSC suspensions or spheroids was collected and utilized to treat tenocytes and macrophages to evaluate their therapeutic potential and investigate the mechanisms underlying their effects. RNA sequencing was performed to investigate the global difference in gene expression between ADSC suspensions and spheroids in an in vitro inflammatory microenvironment. For the in vivo experiment, rabbits that underwent Achilles tendon transection, followed by stump suturing, were randomly assigned to 1 of 3 groups: intratendinous injection of saline, rabbit ADSCs as conventional single-cell suspensions, or preassembled ADSC spheroids. The tendons were harvested for biomechanical testing and histological analysis at 4 weeks postoperatively.

RESULTS

Our in vitro results demonstrated that the secretome of ADSCs assembled as spheroids exhibited enhanced modulatory activity in (1) tenocyte proliferation (P = .015) and migration (P = .001) by activating extracellular signal-regulated kinase (ERK) signaling and (2) the suppression of the secretion of interleukin-6 (P = .005) and interleukin-1α (P = .042) by M1 macrophages via the COX-2/PGE2/EP4 signaling axis. Gene expression profiling of cells exposed to an inflammatory milieu revealed significantly enriched terms that were associated with the immune response, cytokines, and tissue remodeling in preassembled ADSC spheroids. Ex vivo fluorescence imaging revealed that the engraftment efficiency of ADSCs in the form of spheroids was higher than that of ADSCs in single-cell suspensions (P = .003). Furthermore, the transplantation of ADSC spheroids showed superior therapeutic effects in promoting the healing of sutured stumps, as evidenced by improvements in the tensile strength (P = .019) and fiber alignment (P < .001) of the repaired tendons.

CONCLUSION

The assembly of ADSCs as spheroids significantly advanced their potential to harness tenocytes and macrophages. As a proof of concept, this study clearly demonstrates the effectiveness of using ADSC spheroids to promote tendon regeneration.

CLINICAL RELEVANCE

The present study lays a foundation for future clinical applications of stem cell spheroid-based therapy for the management of tendon injuries.

Biocompatibility of hydrogel derived from equine tendon extracellular matrix in horses subcutaneous tissue

Tendinopathies account for a substantial proportion of musculoskeletal injuries. To improve treatment outcomes for partial and total tendon ruptures, new therapies are under investigation. These include the application of mesenchymal stem cells (MSCs) and biocompatible scaffolds derived from the Extracellular Matrix (ECM). Synthetic polymer hydrogels have not demonstrated results as promising as those achieved with ECM hydrogels sourced from the original tissue. This study aimed to evaluate the biocompatibility of a hydrogel formulated from equine tendon ECM. Six horses were administered three subcutaneous doses of the hydrogel, with a saline solution serving as a control. Biopsies were conducted on days 7, 14, and 56 post-application to gauge the hydrogel's impact. Throughout the experiment, the horse's physical condition remained stable. Thermographic analyses revealed a temperature increase in the treated groups compared to the control group within the initial 12 h. The von Frey test, used to measure the mechanical nociceptive threshold, also showed significant differences between the treated group and the control group at 6 h, 21 days, and 28 days. Histopathological analyses identified an inflammatory response on day 7, which was absent on days 14 and 56. Transmission electron microscopy indicated a decrease in inflammatory cellularity, while immunohistochemistry staining suggested an increased presence of inflammatory factors on day 14. In summary, the hydrogel is easily injectable, triggers a temporary local inflammatory response, and integrates into the adjacent tissue from day 14 onwards.

Inhibition of PI3K/AKT signaling pathway prevents blood-induced heterotopic ossification of the injured tendon

Objective

It is a common clinical phenomenon that blood infiltrates into the injured tendon caused by sports injuries, accidental injuries, and surgery. However, the role of blood infiltration into the injured tendon has not been investigated.

Methods

A blood-induced rat model was established and the impact of blood infiltration on inflammation and HO of the injured tendon was assessed. Cell adhesion, viability, apoptosis, and gene expression were measured to evaluate the effect of blood treatment on tendon stem/progenitor cells (TSPCs). Then RNA-seq was used to assess transcriptomic changes in tendons in a blood infiltration environment. At last, the small molecule drug PI3K inhibitor LY294002 was used for in vivo and in vitro HO treatment.

Results

Blood caused acute inflammation in the short term and more severe HO in the long term. Then we found that blood treatment increased cell apoptosis and decreased cell adhesion and tenonic gene expression of TSPCs. Furthermore, blood treatment promoted osteochondrogenic differentiation of TSPCs. Next, we used RNA-seq to find that the PI3K/AKT signaling pathway was activated in blood-treated tendon tissues. By inhibiting PI3K with a small molecule drug LY294002, the expression of osteochondrogenic genes was markedly downregulated while the expression of tenonic genes was significantly upregulated. At last, we also found that LY294002 treatment significantly reduced the tendon HO in the rat blood-induced model.

Conclusion

Our findings indicate that the upregulated PI3K/AKT signaling pathway is implicated in the aggravation of tendon HO. Therefore, inhibitors targeting the PI3K/AKT pathway would be a promising approach to treat blood-induced tendon HO.

The Use of Shear-Wave Ultrasound Elastography in the Diagnosis and Monitoring of Musculoskeletal Injuries

Ultrasound elastography is a valuable method employed to evaluate tissue stiffness, with shear-wave elastography (SWE) recently gaining significance in various settings. This literature review aims to explore the potential of SWE as a diagnostic and monitoring tool for musculoskeletal injuries. In total, 15 studies were found and included in the review. The outcomes of these studies demonstrate the effectiveness of SWE in detecting stiffness changes in individuals diagnosed with Achilles tendinopathy, Achilles tendon rupture, rotator cuff rupture, tendinosis of the long head of the biceps tendon, injury of the supraspinatus muscle, medial tibial stress syndrome, and patellar tendinopathy. Moreover, SWE proves its efficacy in distinguishing variations in tissue stiffness before the commencement and after the completion of rehabilitation in cases of Achilles tendon rupture and patellar tendinopathy. In summary, the findings from this review suggest that SWE holds promise as a viable tool for diagnosing and monitoring specific musculoskeletal injuries. However, while the field of ultrasound elastography for assessing musculoskeletal injuries has made considerable progress, further research is imperative to corroborate these findings in the future.

Exploring polysaccharide and protein-enriched decellularized matrix scaffolds for tendon and ligament repair: A review

Tissue engineering (TE) has become a primary research topic for the treatment of diseased or damaged tendon/ligament (T/L) tissue. T/L injuries pose a severe clinical burden worldwide, necessitating the development of effective strategies for T/L repair and tissue regeneration. TE has emerged as a promising strategy for restoring T/L function using decellularized extracellular matrix (dECM)-based scaffolds. dECM scaffolds have gained significant prominence because of their native structure, relatively high bioactivity, low immunogenicity, and ability to function as scaffolds for cell attachment, proliferation, and differentiation, which are difficult to imitate using synthetic materials. Here, we review the recent advances and possible future prospects for the advancement of dECM scaffolds for T/L tissue regeneration. We focus on crucial scaffold properties and functions, as well as various engineering strategies employed for biomaterial design in T/L regeneration. dECM provides both the physical and mechanical microenvironments required by cells to survive and proliferate. Various decellularization methods and sources of allogeneic and xenogeneic dECM in T/L repair and regeneration are critically discussed. Additionally, dECM hydrogels, bio-inks in 3D bioprinting, and nanofibers are briefly explored. Understanding the opportunities and challenges associated with dECM-based scaffold development is crucial for advancing T/L repairs in tissue engineering and regenerative medicine.

Micro-nano hierarchical scaffold providing temporal-matched biological constraints for tendon reconstruction

Due to the limitations of tendon biology, high-quality tendon repair remains a clinical and scientific challenge. Here, a micro-nano hierarchical scaffold is developed to promote orderly tendon regeneration by providing temporal-matched biological constraints. In short, fibrin (Fb), which provides biological constraints, is loaded into poly (DL-lactide-co-glycolide) nanoyarns with suitable degradation cycles (Fb-loaded nanofiber yarns (Fb-NY)). Then further combined with braiding technology, temporary chemotactic Fb scaffolds with tendon extracellular matrix-like structures are obtained to initiate the regeneration process. At the early stage of healing (2 w), the regeneration microenvironment is regulated (inducing M2 macrophages and restoring the early blood supply necessary for healing) by Fb, and the alignment of cells and collagen is induced by nanoyarn. At the late healing stage (8 w), with the degradation of Fb-NY, non-functional vascular regression occurs, and the newborn tissues gradually undergo load-bearing remodeling, restoring the anvascularous and ordered structure of the tendon. In summary, the proposed repair strategy provides temporal-matched biological constraints, offering a potential pathway to reconstruct the ordered structure and function of tendons.

Concentrations of Selected Adipocytokines in the Blood Plasma in Proximal Suspensory Desmopathy of Horses, with a Focus on Their Physical Activity-A Pilot Study

Chronic tendon and ligament diseases are commonly encountered in both athletic humans and animals, especially horses. Distal limb diseases, including suspensory ligament (SL) pathology due to anatomical, histological, and biomechanical properties, can be considered a model for tendon and ligament pathologies in humans. The appropriate selection of therapy is often crucial in optimising the healing process. One decisive factor influencing the possibility of returning to pre-disease training levels appears to be the utilisation of physical activity, including controlled movement, during the rehabilitation process. In the pathogenesis of musculoskeletal diseases and rehabilitation, adipocytokines play diverse roles. However, it is unclear what significance they hold in horses and in specific disease entities as well as the consequences of their mutual interactions. Recent studies indicate that in the pathogenesis of diseases with varied aetiologies in humans, their value varies at different stages, resulting in a diverse response to treatment. The results of this study demonstrate lower resistin concentrations in the venous blood plasma of horses with proximal suspensory desmopathy (PSD), while higher levels were observed in regularly trained and paddocked animals. The horses investigated in this study showed higher concentrations of resistin and IL-8, particularly in paddocked horses as well as in the working group of horses. The results suggest that these concentrations, including resistin in blood plasma, may be clinically significant. This attempt to explore the aetiopathogenesis of the processes occurring in the area of the proximal attachment of the suspensory ligament may optimise the procedures for the treatment and rehabilitation of horses.

Recent advances of exosomes in soft tissue injuries in sports medicine: A critical review on biological and biomaterial applications

Sports medicine is generally associated with soft tissue injuries including muscle injuries, meniscus and ligament injuries, tendon ruptures, tendinopathy, rotator cuff tears, and tendon-bone healing during injuries. Tendon and ligament injuries are the most common sport injuries accounting for 30-40% of all injuries. Therapies for tendon injuries can be divided into surgical and non-surgical methods. Surgical methods mainly depend on the operative procedures, the surgeons and postoperative interventions. In non-surgical methods, cell therapy with stem cells and cell-free therapy with secretome of stem cell origin are current directions. Exosomes are the main paracrine factors of mesenchymal stem cells (MSCs) containing biological components such as proteins, nucleic acids and lipids. Compared with MSCs, MSC-exosomes (MSC-exos) possess the capacity to escape phagocytosis and achieve long-term circulation. In addition, the functions of exosomes from various cell sources in soft tissue injuries in sports medicine have been gradually revealed in recent years. Along with the biological and biomaterial advances in exosomes, exosomes can be designed as drug carriers with biomaterials and exosome research is providing promising contributions in cell biology. Exosomes with biomaterial have the potential of becoming one of the novel therapeutic modalities in regenerative researches. This review summarizes the derives of exosomes in soft tissue regeneration and focuses on the biological and biomaterial mechanism and advances in exosomal therapy in soft tissue injuries.

High-Performance Artificial Ligament Made from Helical Polyester Fibers Wrapped with Aligned Carbon Nanotube Sheets

Repairing high-load connective tissues, such as ligaments, by surgically implanting artificial grafts after injury is challenging because they lack biointegration with host bones for stable interfaces. Herein, a high-performance helical composite fiber (HCF) ligament by wrapping aligned carbon nanotube (CNT) sheets around polyester fibers is proposed. Anterior cruciate ligament (ACL) reconstruction surgery shows that HCF grafts could induce effective bone regeneration, thus allowing the narrowing of bone tunnel defects. Such repair of the bone tunnel is in strong contrast to the tunnel enlargement of more than 50% for commercial artificial ligaments made from bare polyester fibers. Rats reconstructed with this HCF ligament show normal jumping, walking, and running without limping. This work allows bone regeneration in vivo through a one-step surgery without seeding cells or transforming growth factors, thereby opening an avenue for high-performance artificial tissues.

Small extracellular vesicles derived from tendon stem cells promote the healing of injured Achilles tendons by regulating miR-145-3p

The therapeutic role of tendon stem cells (TSCs) in tendon-related injuries has been well documented. Small extracellular vesicles (sEVs) are being increasingly used as new biotherapeutic agents for various diseases. Therefore, the potential function of TSC-sEVs in tendon injury repair warrants further investigation. In this study, we explored the effects of TSC-sEVs on TSC proliferation, migration, and differentiation in vitro in an autocrine manner. We further used a novel exosomal topical treatment with TSC-sEVs loaded with gelatin methacryloyl (GelMA) hydrogel in vivo; we mixed sufficient amounts of TSC-sEVs with GelMA hydrogel to cover the damaged molded Achilles tendon tissue and then exposed them to UV irradiation for coagulation. GelMA loading ensured that TSC-sEVs were slowly released at the injury site over a long period, thereby achieving their full local therapeutic effects. Treatment with TSC-sEVs loaded with GelMA significantly improved the histological score of the regenerated tendon by increasing the tendon expression while inhibiting the formation of excessive ossification and improving the mechanical properties of the tissue. Moreover, miRNA sequencing in TSC-sEVs, TSCs, and TSCs receiving sEVs revealed that TSC-sEVs altered the miRNA expression profile of TSCs, with increased expression of miR-145-3p. In conclusion, our study demonstrates that TSC-sEVs can play a key role in treating tendon injuries and that loading them with GelMA can enhance their effect in vivo. Moreover, miR-145-3p has a major functional role in the effect of TSC-sEVs. This study offers new therapeutic ideas for the local treatment of Achilles tendon injuries using sEVs. STATEMENT OF SIGNIFICANCE: In this study, we demonstrated that TSC-sEVs play a key role in treating tendon injuries and that loading them with GelMA hydrogel can act as a fixation and slow release in vivo. Moreover, it identifies the major functional role of miR-145-3p in the effect of TSCs that were identified and validated by miRNA sequencing. Our study provides a basis for further research on GelMA slow-release assays that have potential clinical applications. It offers new therapeutic ideas for the local treatment of Achilles tendon injuries using TSC-sEVs.

Fibroblast Activation Protein-Targeted PET/CT With Al18F-NODA-FAPI-04 for In Vivo Imaging of Tendon Healing in Rat Achilles Tendon Injury Models

BACKGROUND

Fibroblast activation protein (FAP) has shown high expression in inflammatory responses and fibrosis.

HYPOTHESIS

We speculated that FAP could serve as a diagnostic and monitoring target in the tendon healing process.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 72 Sprague-Dawley rats were randomly divided into a tendon crush group and a half-partial tendon laceration group. Four rats in each group were injected with radiotracers weekly for 4 weeks after surgery, with aluminum fluoride-labeled 1,4,7-triazacyclononane-N,N',N″-triacetic acid-conjugated FAP inhibitor (Al18F-NODA-FAPI-04) administered on the first day of each week and 18F-fludeoxyglucose (18F-FDG) on the next day. Small animal positron emission tomography (PET) imaging was performed, and tendon tissue was collected for pathology and quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis each week after surgery.

RESULTS

One week after surgery, both radiotracers showed signal concentration at the lesion site, which was the highest radioactive uptake observed during 4 weeks postoperatively, consistent with the severity of the lesion. Consistent trends were observed for inflammatory cytokines during qRT-PCR analysis. Additionally, Al18F-NODA-FAPI-04 PET exhibited a more precise lesion pattern, attributed to its high specificity for naive fibroblasts when referring to histological findings. Over time, the uptake of both radiotracers at the injury site gradually decreased, with 18F-FDG experiencing a more rapid decrease than Al18F-NODA-FAPI-04. In the fourth week after surgery, the maximum standardized uptake values of Al18F-NODA-FAPI-04 in the injured lesion almost reverted to the baseline levels, indicating a substantial decrease in naive fibroblasts and inflammatory cells and a reduction in inflammation and fibrosis, especially compared with the first week. Corresponding trends were also revealed in pathological and qRT-PCR results.

CONCLUSION

Our findings suggest that inflammation is a prominent feature during the early stage of tendon injury. Al18F-NODA-FAPI-04 PET allows accurate localization and provides detailed morphological imaging, enabling continuous monitoring of the healing progress and assessment of injury severity.

Biocomposite-based strategies for dental bone regeneration

OBJECTIVE

Because of the anatomical complexity of the oral and maxillofacial sites, repairing bone defects in these regions is very difficult. This review article aims to consider the application of biocomposites-based strategies for dental bone regeneration.

STUDY DESIGN

Research papers related to the topic, published over the last 20 years, were selected using the Web of Science, Pubmed, Scopus, and Google Scholar databases.

RESULTS

The strategies of monophasic, biphasic/multiphasic scaffolds, and biopolymer-based nanocomposite scaffolds containing nanomaterials compared with traditional methods used for bone regeneration, such as autografts, allografts, xenografts, and alloplasts are found to be superior because of their ability to overcome the issues (e.g., limited bone sources, pain, immune responses, high cost) related to the applications of the traditional methods.

CONCLUSIONS

In addition, additive manufacturing technologies were found to be highly advantageous for improving the efficacy of biocomposite scaffolds for treating dental bone defects.

Current progress in growth factors and extracellular vesicles in tendon healing

Tendon injury healing is a complex process that involves the participation of a significant number of molecules and cells, including growth factors molecules in a key role. Numerous studies have demonstrated the function of growth factors in tendon healing, and the recent emergence of EV has also provided a new visual field for promoting tendon healing. This review examines the tendon structure, growth, and development, as well as the physiological process of its healing after injury. The review assesses the role of six substances in tendon healing: insulin-like growth factor-I (IGF-I), transforming growth factor β (TGFβ), vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF), and EV. Different growth factors are active at various stages of healing and exhibit separate physiological activities. IGF-1 is expressed immediately after injury and stimulates the mitosis of various cells while suppressing the response to inflammation. VEGF, which is also active immediately after injury, accelerates local metabolism by promoting vascular network formation and positively impacts the activities of other growth factors. However, VEGF's protracted action could be harmful to tendon healing. PDGF, the earliest discovered cytokine to influence tendon healing, has a powerful cell chemotaxis and promotes cell proliferation, but it can equally accelerate the response to inflammation and relieve local adhesions. Also useful for relieving tendon adhesion is TGF- β, which is active almost during the entire phase of tendon healing. As a powerful active substance, in addition to its participation in the field of cardiovascular and cerebrovascular vessels, tumour and chronic wounds, TGF- β reportedly plays a role in promoting cell proliferation, activating growth factors, and inhibiting inflammatory response during tendon healing.

Effect of Aging on Tendon Biology, Biomechanics and Implications for Treatment Approaches

Tendon aging is associated with an increasing prevalence of tendon injuries and/or chronic tendon diseases, such as tendinopathy, which affects approximately 25% of the adult population. Aged tendons are often characterized by a reduction in the number and functionality of tendon stem/progenitor cells (TSPCs), fragmented or disorganized collagen bundles, and an increased deposition of glycosaminoglycans (GAGs), leading to pain, inflammation, and impaired mobility. Although the exact pathology is unknown, overuse and microtrauma from aging are thought to be major causative factors. Due to the hypovascular and hypocellular nature of the tendon microenvironment, healing of aged tendons and related injuries is difficult using current pain/inflammation and surgical management techniques. Therefore, there is a need for novel therapies, specifically cellular therapy such as cell rejuvenation, due to the decreased regenerative capacity during aging. To augment the therapeutic strategies for treating tendon-aging-associated diseases and injuries, a comprehensive understanding of tendon aging pathology is needed. This review summarizes age-related tendon changes, including cell behaviors, extracellular matrix (ECM) composition, biomechanical properties and healing capacity. Additionally, the impact of conventional treatments (diet, exercise, and surgery) is discussed, and recent advanced strategies (cell rejuvenation) are highlighted to address aged tendon healing. This review underscores the molecular and cellular linkages between aged tendon biomechanical properties and the healing response, and provides an overview of current and novel strategies for treating aged tendons. Understanding the underlying rationale for future basic and translational studies of tendon aging is crucial to the development of advanced therapeutics for tendon regeneration.