A Combined Treatment of BMP2 and Soluble VEGFR1 for the Enhancement of Tendon-Bone Healing by Regulating Injury-Activated Skeletal Stem Cell Lineage.

BACKGROUND: Bone morphogenetic protein 2 (BMP2) is an appealing osteogenic and chondrogenic growth factor for promoting tendon-bone healing. Recently, it has been reported that soluble vascular endothelial growth factor (VEGF) receptor 1 (sVEGFR1) (a VEGF receptor antagonist) could enhance BMP2-induced bone repair and cartilage regeneration; thus, their combined application may represent a promising treatment to improve tendon-bone healing. Moreover, BMP2 could stimulate skeletal stem cell (SSC) expansion and formation, which is responsible for wounded tendon-bone interface repair. However, whether the codelivery of BMP2 and sVEGFR1 increases tendon enthesis injury-activated SSCs better than does BMP2 alone needs further research. PURPOSE: To study the effect of BMP2 combined with sVEGFR1 on tendon-bone healing and injury-activated SSC lineage. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 128 C57BL/6 mice that underwent unilateral supraspinatus tendon detachment and repair were randomly assigned to 4 groups: (1) untreated control group; (2) hydrogel group, which received a local injection of the blank hydrogel at the injured site; (3) BMP2 group, which received an injection of hydrogel with BMP2; and (4) BMP2 with sVEGFR1 group, which received an injection of hydrogel with BMP2 and sVEGFR1. Histology, micro-computed tomography, and biomechanical tests were conducted to evaluate tendon-bone healing at 4 and 8 weeks after surgery. In addition, flow cytometry was performed to detect the proportion of SSCs and their downstream differentiated subtypes, including bone, cartilage, and stromal progenitors; osteoprogenitors; and pro-chondrogenic progenitors within supraspinatus tendon enthesis at 1 week postoperatively. RESULTS: The repaired interface in BMP2 with sVEGFR1 group showed a significantly improved collagen fiber continuity, increased fibrocartilage, greater newly formed bone, and elevated mechanical properties compared with the other 3 groups. There were more SSCs; bone, cartilage, and stromal progenitors; osteoprogenitors; and pro-chondrogenic progenitors in the BMP2 with sVEGFR1 group than that in the other groups. CONCLUSION: Our study suggests that the combined delivery of BMP2 and sVEGFR1 could promote tendon-bone healing and stimulate the expansion of SSCs and their downstream progeny within the injured tendon-bone interface. CLINICAL RELEVANCE: Combining BMP2 with sVEGFR1 may be a good clinical treatment for wounded tendon enthesis healing.

The effect of Sildenafil, a phosphodiesterase-5 inhibitor, on tendon healing: an experimental study in rat model of achilles tendon injury.

INTRODUCTION: Sildenafil Citrate has various effects on the body, including widening blood vessels, inhibiting platelet aggregation, promoting the growth of blood vessels, stimulating apoptosis and adhesion of fibroblasts, and reducing inflammation. This research aims to explore how Sildenafil Citrate affects surgically treated Achilles tendons, both in terms of tissue structure and mechanical properties. MATERIALS AND METHODS: Forty-eight Wistar-albino rats weighing 350-400 g were randomly divided into groups, 6 in each group, as the study group was given Sildenafil Citrate and the control group given saline, respectively. The Achilles tendon rupture model was created under ketamine and xylazine anesthesia. During the entire experiment, rats were housed in eight separate cages, six of them each. The study group and control group of the first group were sacrificed at the end of 1 week, and Achilles tendon samples were taken. After that, Achilles tendon samples were taken after sacrificing the second group at 14 days, the third group at 21 days, and the fourth group at 28 days, respectively. Neovascularization, inflammation, fibrosis and fibroblastic activities of the harvested Achilles tendons were evaluated histopathologically. Biomechanically, stretching was applied to the Achilles tendons and continued until the tendon ruptured. the maximum force values at the moment of rupture were calculated. RESULTS: The mean maximum strength value of group T21, which was given sildenafil citrate for 21 days, was 31.1 ± 4.36 N, and the mean maximum strength value of group C21, which was the control group, was 20.56 ± 6.92 N. A significant difference was observed between the groups (p: 0.008). Group T28 (45.17 ± 5.54 N) also demonstrated greater strength than group C28 (34.62 ± 3.21 N) in the comparison (p: 0.004). The study also noted significant differences between the groups in neovascularization, in the first week, 1 mild, 3 moderate and 2 prominent neovascularization was observed in group T7, in group T28, moderate neovascularization was observed in 4 specimens and prominent neovascularization was observed in 2 specimens (p: 0.001). Furthermore, the groups showed significant differences in their levels of fibrosis, inflammation and fibroblastic proliferation (p: 0.017, p: 0.036, (p: 0.035) respectively). CONCLUSIONS: Study has demonstrated that sildenafil citrate can enhance the biomechanical and histopathological aspects of tendon healing, resulting in a stronger tendon.

Anti-Adhesive Resorbable Indomethacin/Bupivacaine-Eluting Nanofibers for Tendon Rupture Repair: In Vitro and In Vivo Studies.

The treatment and surgical repair of torn Achilles tendons seldom return the wounded tendon to its original elasticity and stiffness. This study explored the in vitro and in vivo simultaneous release of indomethacin and bupivacaine from electrospun polylactide-polyglycolide composite membranes for their capacity to repair torn Achilles tendons. These membranes were fabricated by mixing polylactide-polyglycolide/indomethacin, polylactide-polyglycolide/collagen, and polylactide-polyglycolide/bupivacaine with 1,1,1,3,3,3-hexafluoro-2-propanol into sandwich-structured composites. Subsequently, the in vitro pharmaceutic release rates over 30 days were determined, and the in vivo release behavior and effectiveness of the loaded drugs were assessed using an animal surgical model. High concentrations of indomethacin and bupivacaine were released for over four weeks. The released pharmaceutics resulted in complete recovery of rat tendons, and the nanofibrous composite membranes exhibited exceptional mechanical strength. Additionally, the anti-adhesion capacity of the developed membrane was confirmed. Using the electrospinning technique developed in this study, we plan on manufacturing degradable composite membranes for tendon healing, which can deliver sustained pharmaceutical release and provide a collagenous habitat.

The effect of caffeic acid on tendon healing in rats with an Achilles tendon injury model.

OBJECTIVES: This study aims to examine the effect of caffeic acid on tendon healing histopathologically and biomechanically in rats with an Achilles tendon injury model. MATERIALS AND METHODS: Twenty male Wistar-albino rats were used in this study. The rats were divided into two groups as the experimental group and control group. All rats underwent a bilateral achillotomy injury model and then surgical repair. Postoperatively, for four weeks, the experimental group was given intraperitoneal caffeic acid (100 mg/kg/day suspended in saline), while the control group was given only intraperitoneal saline. At the end of four weeks, after sacrificing each rat, right Achilles tendons were subjected to biomechanical analysis and the Achilles tendons were subjected to histopathological analysis. Bonar and Movin scores were used for histopathological analysis. In biomechanical analysis, tensile test was applied to Achilles tendons until rupture. For each tendon, failure load, displacement, cross-sectional area, maximum energy, total energy, length, stiffness, ultimate stress and strain parameters were recorded. RESULTS: According to Bonar and Movin scoring, the experimental group had lower scoring values than the control group (p=0.002 and p=0.002, respectively). Bonar scoring parameters were analyzed separately. Vascularity, collagen, and ground substance scores were lower in the experimental group compared to the control group (p=0.001, p=0.003, and p=0.047, respectively). No significant difference was found for tenocyte (p=0.064). In biomechanical analysis, failure load, displacement, ultimate stress, strain, and stiffness values were found to be higher in the experimental group compared to the control group (p=0.049, p=0.005, p=0.028, p=0.021, and p=0.049, respectively). CONCLUSION: The caffeic acid contributed positively to tendon healing histopathologically and biomechanically in rats with an Achilles tendon injury model.

Can pirfenidone prevent tendon adhesions? An experimental study in rats.

OBJECTIVES: In this experimental study, we aimed to investigate the effectiveness of oral pirfenidone (PFD) treatment on preventing tendon adhesion and tendon healing in rats. MATERIALS AND METHODS: A total of 21 rats were assigned into three groups including seven rats in each group. In Group 1 (sham group), no surgical procedure was performed. In Group 2 (control group), tendon repair was performed following right achillotomy. In Group 3 (treatment group), the rats also underwent tendon repair after right achillotomy. Additionally, 30 mg/kg of oral PFD was initiated from the postoperative Day 1 and administered via gavage for 28 days. At the end of the study, tendon healing and fibrosis levels in the tendon repair site were compared macroscopically, histopathologically, and immunohistochemically among the groups. RESULTS: Macroscopically, moderate and severe adhesions were observed in four and three rats, respectively in the control group, while no adhesion was found in four rats and filmy adhesions were observed in three rats in the treatment group (p<0.01). Microscopically, there was moderate adhesions in three rats and severe adhesions in four rats in the control group, while three rats had no adhesions and four rats had slight adhesions in the treatment group (p<0.01). Microscopically, tendon healing was good in six rats and fair in one rat in the control group, while five rats showed excellent tendon healing and two rats showed good tendon healing in the treatment group (p<0.01). Immunohistochemically, expressions of collagen I (p<0.01), collagen III (p<0.001), vascular endothelial growth factor (VEGF) (p<0.001), and proliferating cell nuclear antigen (PCNA) (p<0.001) significantly decreased in the treatment group compared to the control group. CONCLUSION: Our study results indicated that PFD decreased collagen synthesis and prevented the formation of peritendinous adhesion in rats; however, it did not impair tendon healing.

Bioactive and Elastic Emulsion Electrospun DegraPol Tubes Delivering IGF-1 for Tendon Rupture Repair.

Tendon injuries can result in two major drawbacks. Adhesions to the surrounding tissue may limit the range of motion, while fibrovascular scar formation can lead to poor biomechanical outcomes. Prosthetic devices may help to mitigate those problems. Emulsion electrospinning was used to develop a novel three-layer tube based on the polymer DegraPol (DP), with incorporated insulin-like growth factor-1 (IGF-1) in the middle layer. Scanning electron microscopy was utilized to assess the fiber diameter in IGF-1 containing pure DP meshes. Further characterization was performed with Fourier Transformed Infrared Spectroscopy, Differential Scanning Calorimetry, and water contact angle, as well as through the assessment of mechanical properties and release kinetics from ELISA, and the bioactivity of IGF-1 by qPCR of collagen I, ki67, and tenomodulin in rabbit Achilles tenocytes. The IGF-1-containing tubes exhibited a sustained release of the growth factor up to 4 days and showed bioactivity by significantly upregulated ki67 and tenomodulin gene expression. Moreover, they proved to be mechanically superior to pure DP tubes (significantly higher fracture strain, failure stress, and elastic modulus). The novel three-layer tubes intended to be applied over conventionally sutured tendons after a rupture may help accelerate the healing process. The release of IGF-1 stimulates proliferation and matrix synthesis of cells at the repair site. In addition, adhesion formation to surrounding tissue can be reduced due to the physical barrier.

Metformin suppressed tendon injury-induced adhesion via hydrogel-nanoparticle sustained-release system.

Tendon adhesion is one of the sequelae of tendon injury and can lead to disability in severe cases. Metformin is a commonly used antidiabetic drug. Some studies had shown that metformin could reduce tendon adhesion as well. Considering the characteristic of low absorption rate and short half-life, we established a sustained-release system, i.e., hydrogel-nanoparticle system to deliver metformin. In vitro, metformin could effectively suppress TGF-ß1-induced cell proliferation and accelerate cell apoptosis, according to cell counting kit-8, flow cytometry, and 5-ethynyl-2'-deoxyuridine (EdU) staining studies. In vivo, hydrogel-nanoparticle/metformin system could significantly lower adhesion scores and improve the gliding function of repaired flexor tendons, as well as decrease the expression of fibrotic proteins Col1a1, Col3a1, and α-smooth muscle actin (α-SMA). Histological staining revealed that the inflammation had subsided and that the gap between the tendon and the surrounding tissue was wider in the hydrogel-nanoparticle/metformin treatment group. Finally, we speculated that effect of metformin on reducing tendon adhesion might be achieved by regulating both Smad and MAPK-TGF-ß1 signaling pathways. In conclusion, metformin delivered through hydrogel-nanoparticle sustained-release system may be a promising strategy for coping with tendon adhesion.

Instantaneous self-healing and strongly adhesive self-adaptive hyaluronic acid-based hydrogel for controlled drug release to promote tendon wound healing.

The treatment of tendon injuries is an important healthcare challenge. Irregular wounds, hypocellularity, and prolonged inflammation impede the rate of healing for tendon injuries. To address these problems, a high-tenacity shape-adaptive, mussel-like hydrogel (PH/GMs@bFGF&PDA) was designed and constructed with polyvinyl alcohol (PVA) and hyaluronic acid grafted with phenylboronic acid (BA-HA) by encapsulating polydopamine and gelatin microspheres containing basic fibroblast growth factor (GMs@bFGF). The shape-adaptive PH/GMs@bFGF&PDA hydrogel can quickly adapt to irregular tendon wounds, and the strong adhesion (101.46 ± 10.88 kPa) can keep the hydrogel adhered to the wound at all times. In addition, the high tenacity and self-healing properties allow the hydrogel to move with the tendon without fracture. Additionally, even if fractured, it can quickly self-heal and continue to adhere to the tendon wound, while slowly releasing basic fibroblast growth factor during the inflammatory phase of the tendon repair process, promoting cell proliferation, migration and shortening the inflammatory phase. In acute tendon injury and chronic tendon injury models, PH/GMs@bFGF&PDA significantly alleviated inflammation and promoted collagen I secretion, enhancing wound healing through the synergistic effects of its shape-adaptive and high-adhesion properties.

Screening for autophagy/hypoxia/ferroptosis/pyroptosis-related genes of tendon injury and repair in a rat model after celecoxib and lactoferrin treatment.

BACKGROUND: Tendon injuries are among the most common musculoskeletal disorders. Celecoxib possesses an effective anti-inflammatory activity in the tendon injury treatment. Lactoferrin has a great potential for the tendon regeneration. However, the efficacy of celecoxib combined with lactoferrin in the treatment of tendon injury has not been reported. In this study, we aimed to investigate the effect of celecoxib and lactoferrin on tendon injury and repair, and screen for the crucial genes associated with the tendon injury and repair. METHODS: The rat tendon injury models were established and divided into four groups: normal control group (n = 10), tendon injury model group (n = 10), celecoxib treatment group (n = 10), and celecoxib + lactoferrin treatment group (n = 10). Then, RNA sequencing was performed to identify differentially expressed lncRNAs (DElncRNAs), miRNAs (DEmiRNAs) and mRNAs (DEmRNAs) in celecoxib treatment group and celecoxib + lactoferrin treatment group. Next, autophagy/hypoxia/ferroptosis/pyroptosis-related DEmRNAs were further identified. Subsequently, functional enrichment, protein-protein interaction (PPI) network and transcriptional regulatory network construction for these genes were performed. RESULTS: The animal study demonstrated that combinational administration of celecoxib with lactoferrin rescued the harmful effects caused by celecoxib in the treatment of tendon injury. Compared to tendon injury model group, 945 DEmRNAs, 7 DEmiRNAs and 34 DElncRNAs were obtained in celecoxib treatment group, and 493 DEmRNAs, 8 DEmiRNAs and 21 DElncRNAs were obtained in celecoxib + lactoferrin treatment group, respectively. Subsequently, 376 celecoxib + lactoferrin treatment group-specific DEmRNAs were determined. Then, 25 DEmRNAs associated with autophagy/hypoxia/ferroptosis/pyroptosis were identified. CONCLUSIONS: Several genes, such as, Ppp1r15a, Ddit4, Fos, Casp3, Tgfb3, Hspb1 and Hspa8, were identified to be associated with tendon injury and repair.

Biologically-coupled bisphosphonate chaperones effectively deliver molecules to the site of soft tissue-bone healing.

Tendon injuries are common and often treated surgically, however, current tendon repair healing results in poorly organized fibrotic tissue. While certain growth factors have been reported to improve both the strength and organization of the repaired enthesis, their clinical applicability is severely limited due to a lack of appropriate delivery strategies. In this study, we evaluated a recently developed fluorescent probe, Osteoadsorptive Fluorogenic Sentinel-3 that is composed of a bone-targeting bisphosphonate (BP) moiety linked to fluorochrome and quencher molecules joined via a cathepsin K-sensitive peptide sequence. Using a murine Achilles tendon-to-bone repair model, BP-based and/or Ctsk-coupled imaging probes were applied either locally or systemically. Fluorescence imaging was used to quantify the resultant signal in vivo. After tendon-bone repair, animals that received either local or systemic administration of imaging probes demonstrated significantly higher fluorescence signal at the repair site compared to the sham surgery group at all time points (p < 0.001), with signal peaking at 7-10 days after surgery. Our findings demonstrate the feasibility of using a novel BP-based targeting and Ctsk-activated delivery of molecules to the site of tendon-to-bone repair and creates a foundation for further development of this platform as an effective strategy to deliver bioactive molecules to sites of musculoskeletal injury.

Drug Delivery Approaches to Improve Tendon Healing.

Tendon injuries disrupt the transmission of forces from muscle to bone, leading to chronic pain, disability, and a large socioeconomic burden. Tendon injuries are prevalent; there are over 300,000 tendon repair procedures a year in the United States to address acute trauma or chronic tendinopathy. Successful restoration of function after tendon injury remains challenging clinically. Despite improvements in surgical and physical therapy techniques, the high complication rate of tendon repair procedures motivates the use of therapeutic interventions to augment healing. While many biological and tissue engineering approaches have attempted to promote scarless tendon healing, there is currently no standard clinical treatment to improve tendon healing. Moreover, the limited efficacy of systemic delivery of several promising therapeutic candidates highlights the need for tendon-specific drug delivery approaches to facilitate translation. This review article will synthesize the current state-of-the-art methods that have been used for tendon-targeted delivery through both systemic and local treatments, highlight emerging technologies used for tissue-specific drug delivery in other tissue systems, and outline future challenges and opportunities to enhance tendon healing through targeted drug delivery.

Insulin-like growth factor binding protein 4 loaded electrospun membrane ameliorating tendon injury by promoting retention of IGF-1.

Tendon injury is one of the most common musculoskeletal disorders that impair joint mobility and lower quality of life. The limited regenerative capacity of tendon remains a clinical challenge. Local delivery of bioactive protein is a viable therapeutic approach for tendon healing. Insulin-like growth factor binding protein 4 (IGFBP-4) is a secreted protein capable of binding and stabilizing insulin-like growth factor 1 (IGF-1). Here, we applied an aqueous-aqueous freezing-induced phase separation technology to obtain the IGFBP4-encapsulated dextran particles. Then, we added the particles into poly (L-lactic acid) (PLLA) solution to fabricate IGFBP4-PLLA electrospun membrane for efficient IGFBP-4 delivery. The scaffold showed excellent cytocompatibility and a sustained release of IGFBP-4 for nearly 30 days. In cellular experiments, IGFBP-4 promoted tendon-related and proliferative markers expression. In a rat Achilles tendon injury model, immunohistochemistry and quantitative real-time polymerase chain reaction confirmed better outcomes by using the IGFBP4-PLLA electrospun membrane at the molecular level. Furthermore, the scaffold effectively promoted tendon healing in functional performance, ultrastructure and biomechanical properties. We found addition of IGFBP-4 promoted IGF-1 retention in tendon postoperatively and then facilitated protein synthesis via IGF-1/AKT signaling pathway. Overall, our IGFBP4-PLLA electrospun membrane provides a promising therapeutic strategy for tendon injury.

In Vitro and In Vivo Effects of IGF-1 Delivery Strategies on Tendon Healing: A Review.

Tendon injuries suffer from a slow healing, often ending up in fibrovascular scar formation, leading to inferior mechanical properties and even re-rupture upon resumption of daily work or sports. Strategies including the application of growth factors have been under view for decades. Insulin-like growth factor-1 (IGF-1) is one of the used growth factors and has been applied to tenocyte in vitro cultures as well as in animal preclinical models and to human patients due to its anabolic and matrix stimulating effects. In this narrative review, we cover the current literature on IGF-1, its mechanism of action, in vitro cell cultures (tenocytes and mesenchymal stem cells), as well as in vivo experiments. We conclude from this overview that IGF-1 is a potent stimulus for improving tendon healing due to its inherent support of cell proliferation, DNA and matrix synthesis, particularly collagen I, which is the main component of tendon tissue. Nevertheless, more in vivo studies have to be performed in order to pave the way for an IGF-1 application in orthopedic clinics.

Outpatient fluoroquinolone use in relation to European Medicines Agency's recommendation: An Estonian nationwide drug utilization study.

PURPOSE: To determine possible changes in prescribing of fluoroquinolones in relation to the European Medicines Agency's (EMA) recommendation in October 2018. METHODS: We conducted a nationwide time-series study on outpatient use of fluoroquinolones during January 2016-June 2021 in Estonia. Joinpoint regression was used to identify change points over time. Several subgroup analyses by prescriber specialty, indication group, risk factors for tendon injury, aortic aneurysm/dissection or heart valve regurgitation/incompetence and the prescribing of other antibiotics were performed. RESULTS: During the study period 236 989 prescriptions of fluoroquinolones were dispensed to 142 659 persons. The number of episodes per month declined from 3780 (2.9/1000 inhabitants) to 2570 (1.9/1000 inhabitants). We identified three change points with four different trend segments: from January 2016 to November 2018 monthly percent change (MPC) -0.4%, from November 2018 to June 2019 MPC -2.5%, from June 2019 to July 2020 MPC 1.7% and from July 2020 to June 2021 MPC -3.3%. Prescribing for indications which were removed or restricted by EMA's recommendation comprised a small proportion of all fluoroquinolone episodes -2.8% and 6.3%, respectively. The risk factors for tendon injury and for cardiac disorders (aortic aneurysm/dissection or heart valve regurgitation/incompetence) were present in 46.4% and 57.8% episodes of fluoroquinolone users, respectively. No changes in the trend of prescribing to users with risk factors was detected. CONCLUSIONS: The EMA's recommendation may have contributed to the greater decline in the use of fluoroquinolones. However, there is still a high proportion of users with predisposing factors for tendon injury and serious cardiac disorders.

N-Acetyl-L-cysteine facilitates tendon repair and promotes the tenogenic differentiation of tendon stem/progenitor cells by enhancing the integrin α5/ß1/PI3K/AKT signaling.

BACKGROUND: Tendon injury is associated with oxidative stress, leading to reactive oxygen species (ROS) production and inflammation. N-acetyl-L-cysteine (NAC) is a potent antioxidant. However, how NAC affects the biological functions of tendon stem/progenitor cells (TSPCs) and tendon repair has not been clarified.  METHOD: The impacts of NAC on the viability, ROS production, and differentiation of TSPCs were determined with the cell counting kit-8, fluorescence staining, Western blotting, and immunofluorescence. The effect of NAC on gene transcription in TSPCs was analyzed by transcriptomes and bioinformatics and validated by Western blotting. The potential therapeutic effect of NAC on tendon repair was tested in a rat model of Achilles tendon injury. RESULTS: Compared with the untreated control, treatment with 500 µM NAC greatly promoted the proliferation of TSPCs and significantly mitigated hydrogen peroxide-induced ROS production and cytotoxicity in vitro. NAC treatment significantly increased the relative protein expression of collagen type 1 alpha 1 (COL1A1), tenascin C (TNC), scleraxis (SCX), and tenomodulin (TNMD) in TPSCs. Bioinformatics analyses revealed that NAC modulated transcriptomes, particularly in the integrin-related phosphoinositide 3-kinase (PI3K)/AKT signaling, and Western blotting revealed that NAC enhanced integrin α5ß1 expression and PI3K/AKT activation in TSPCs. Finally, NAC treatment mitigated the tendon injury, but enhanced the protein expression of SCX, TNC, TNMD, and COLIA1 in the injured tissue regions of the rats. CONCLUSION: NAC treatment promoted the survival and differentiation of TSPCs to facilitate tendon repair after tendon injury in rats. Thus, NAC may be valuable for the treatment of tendon injury.

Combined Verapamil-Polydopamine Nanoformulation Inhibits Adhesion Formation in Achilles Tendon Injury Using Rat Model.

Introduction: Topical verapamil has been demonstrated to reduce the fibroproliferative scar. Therefore, it was hypothesized that topical verapamil could reduce adhesion formation after tendon repair. The current study aimed to examine the effects of verapamil-loaded polydopamine nanoparticles (VP-PDA NPs) on the adhesion formation of Achilles tendon laceration and repair in a rat model. Methods: We randomly assigned 72 male Sprague-Dawley rats to the control, the PDA NPs, and the VP-PDA NPs groups (n = 24 per group). The quality of tendon healing was evaluated by the maximal tensile strength four and six weeks after surgery. The degree of tendon adhesion was scored on days 4, 15, 29, and 43 after surgery. The expressions of transforming growth factor-beta 1 (TGF-ß1), vimentin, α-smooth muscle actin (α-SMA), and collagens type I and III were detected through Western blotting or immunohistochemistry at four weeks after surgery. Results: In vitro release tests revealed that 61.3% of verapamil was released from VP-PDA NPs in four weeks. There was a significant increase in average failure to load in the VP-PDA NPs group (89.27 ± 5.09 N) compared with the PDA NPs group (65.52 ± 2.04 N) (p = 0.003) and the control group (74.52 ± 4.24 N) (p = 0.029). Adhesion scores were significantly reduced in the VP-PDA NPs group at six weeks (3.175 ± 0.08) and four weeks (3.35 ± 0.25) compared with the other groups. Moreover, VP-PDA NPs significantly reduced the expression of vimentin, α-SMA, TGF-ß1, and collagens type I and III. Conclusion: These data suggest that VP-PDA NPs reduced adhesion formation and enhanced tendon healing during rat tendon injury. Since topical verapamil has been used in clinics without side effects, VP-PDA NPs would have direct translation implications. However, its anti-adhesive effects on intrasynovial tendon injury must be examined.

Platelet-derived growth factor AA-modified electrospun fibers promote tendon healing.

Platelet-derived growth factor AA (PDGF-AA) is an important promoter of tissue injury repair and might be a candidate for improving the mechanical properties of repaired tendons. Here, we designed a PDGF-AA-modified poly(lactide-co-glycolide) acid (PLGA) electrospun fibers to promote tendon rehabilitation after injury. In the present study, we grafted PDGF-AA on the surface of PLGA. In structural experiments, we found that the hydrophilicity of PLGA containing PDGF-AA (PLGA-PDGF-AA) increased, but the strength of the material did not change significantly. Moreover, no significant changes in tendon cell proliferation and viability were observed in the PLGA-PDGF-AA treatment compared with the control group. The mouse tendon injury model (n = 9) experiment illustrated that PLGA-PDGF-AA effectively promoted tendon healing, and we confirmed that PLGA-PDGF-AA promoted collagen synthesis and deposition by immunohistochemistry and RT-PCR. Moreover, the mechanical strength of PLGA-PDGF-AA-treated mouse (n = 9) tendon tissue was also higher than that of the PLGA-treated group alone. In conclusion, PLGA-PDGF-AA promoted regeneration after tendon injury and serves as a potential adjuvant material for surgical tendon injury repair.

Tamoxifen Prevents Peritendinous Adhesions: A Preliminary Report.

Background: Scarless healing comprises the ultimate goal after an injury. Since tendon healing results in a fibrotic scar, an injured tendon can never regain the mechanical potential and strength of its uninjured form. A wide variety of studies focus on the tendon healing with an absent or minimal peritendinous adhesions. However, no simple method has managed it at all. Possible complex actions and peritendinous environmental events take place during the tendon healing process. Tamoxifen (TAM), besides its breast cancer-related usage, is a potent antifibrotic drug. Here, we aimed to reduce the peritendinous adhesion with TAM administration. Methods: Achilles tendons of 44 Wistar albino rats were randomly distributed in 4 groups. In group 1, bilateral lower extremities were used as control and sham. Groups 2 and 3 were comprised of low-dose (1 mg/kg) and high-dose (40 mg/kg) systemic administration of TAM, respectively. Group 4 included local administration (1 mg/kg) of TAM. Biomechanical, macroscopical, and histopathological analyses were done and compared statistically. Biomechanically, the maximum force that led to tendon rupture was determined, and tensile force data were recorded via tensile testing device. Macroscopical and histopathological analysis were composed of the quantity, quality, and grade of peritendinous adhesions. Results: Macroscopic and histopathologic findings revealed that groups 2 and 3 had a variety of values ranging between slight to severe adhesions. In group 2, almost half of the animals had moderate adhesions, whereas in group 3, the majority of the animals had moderate adhesions. There were no animals with moderate or severe adhesions in group 4. Statistically significant values were calculated between sham and control groups. Biomechanically, group 2 showed the most significant result. The tendons in group 2 had the highest stiffness when maximal force was applied to rupture the tendons. Henceforth, all these consequences were proven statistically. Conclusion: We achieved less peritendinous adhesion with the local administration of TAM when compared to systemic administration of TAM. A better understanding of the peritendinous environmental process will reveal to develop new therapies in the prevention of peritendinous adhesions.

Enhanced tendon healing by a tough hydrogel with an adhesive side and high drug-loading capacity.

Hydrogels that provide mechanical support and sustainably release therapeutics have been used to treat tendon injuries. However, most hydrogels are insufficiently tough, release drugs in bursts, and require cell infiltration or suturing to integrate with surrounding tissue. Here we report that a hydrogel serving as a high-capacity drug depot and combining a dissipative tough matrix on one side and a chitosan adhesive surface on the other side supports tendon gliding and strong adhesion (larger than 1,000 J m-2) to tendon on opposite surfaces of the hydrogel, as we show with porcine and human tendon preparations during cyclic-friction loadings. The hydrogel is biocompatible, strongly adheres to patellar, supraspinatus and Achilles tendons of live rats, boosted healing and reduced scar formation in a rat model of Achilles-tendon rupture, and sustainably released the corticosteroid triamcinolone acetonide in a rat model of patellar tendon injury, reducing inflammation, modulating chemokine secretion, recruiting tendon stem and progenitor cells, and promoting macrophage polarization to the M2 phenotype. Hydrogels with 'Janus' surfaces and sustained-drug-release functionality could be designed for a range of biomedical applications.

Macrophage-activating lipoprotein (MALP)-2 impairs the healing of partial tendon injuries in mice.

Tendon injuries are accounted for up to 50% of musculoskeletal injuries and often result in poor outcomes. Inflammation is a major hallmark of tendon regeneration. Therefore, we analyzed in this study whether the topical application of the pro-inflammatory mediator macrophage-activating lipoprotein (MALP)-2 improves the healing of partial tendon injuries. C57BL/6 mice underwent a partial tenotomy of the flexor digitorum longus tendon of the left hind limb, which was treated with a solution containing either 0.5 µg MALP-2 or vehicle (control). Repetitive gait analyses were performed prior to the surgical intervention as well as postoperatively on days 1, 3, 7, 14 and 36. The structural stability of the tendons was biomechanically tested on day 7 and 36. In addition, Western blot analyses were performed on isolated tendons that were treated in vitro with MALP-2 or vehicle. In both groups, partial tenotomy resulted in a pathological gait pattern during the initial postoperative phase. On day 7, the gait pattern normalized in vehicle-treated animals, but not in MALP-2-treated mice. Moreover, the tendons of MALP-2-treated mice exhibited a significantly reduced biomechanical stiffness after 7 and 36 days when compared to controls. Western blot analyses revealed a significantly higher expression of heme oxygenase (HO)-1 and lower expression of cyclin D in MALP-2-treated tendons. These findings indicate that MALP-2 delays the healing of injured tendons most likely due to increased intracellular stress and suppressed cell proliferation in this naturally bradytrophic tissue. Hence, the application of MALP-2 cannot be recommended for the treatment of tendon injuries.