Tendon-bone Interface Healing Research Articles

Magnetic Seeding of SPIO-BMSCs Into a Biphasic Scaffold Can Promote Tendon-Bone Healing After Rotator Cuff Repair

Background: The tendon-bone interface (TBI) in the rotator cuff has a poor intrinsic capacity for healing, which increases the risk of retear after rotator cuff repair (RCR). However, facilitating regeneration of the TBI still remains a great clinical challenge. Herein, the authors established a novel strategy based on magnetic seeding to enhance the TBI regeneration. Hypothesis: Magnetic seeding bone marrow mesenchymal stem cells labeled with superparamagnetic iron oxide (SPIO-BMSCs) into a biphasic scaffold can promote tendon-bone healing after RCR. Study Design: Controlled laboratory study. Methods: BMSCs were labeled with SPIOs. Prussian blue staining, CCK-8 tests, Western blot, and quantitative reverse transcription polymerase chain reaction (PCR) were used to determine the optimal effect concentration of SPIOs on cell bioactivities and abilities. Then SPIO-BMSCs were magnetically seeded into a biphasic scaffold under a magnetic field. The seeding efficacy was assessed by a scanning electron microscope, and the potential mechanism in chondrogenic differentiation after seeding SPIO-BMSCs into the scaffold was evaluated by Western blot and PCR. Furthermore, the effect of SPIO-BMSC/biphasic scaffold on tendon-bone healing after RCR using a rat model was examined using histological analysis, enzyme-linked immunosorbent assay, and biomechanical evaluation. Results: BMSCs labeled with 100 μg/mL SPIO had no effect on cell bioactivities and the ability of chondrogenic differentiation. SPIO-BMSCs were magnetically seeded into a biphasic scaffold, which offered a high seeding efficacy to enhance chondrogenic differentiation of SPIO-BMSCs via the CDR1as/miR-7/FGF2 pathway for TBI formation in vitro. Furthermore, in vivo application of the biphasic scaffold with magnetically seeded SPIO-BMSCs showed their regenerative potential, indicating that they could significantly accelerate and promote TBI healing with superior biomechanical properties after RCR in a rat rotator cuff tear model. Conclusion: Magnetically seeding SPIO-BMSCs into a biphasic scaffold enhanced seeding efficacy to promote cell distribution and condensation. This construct enhanced the chondrogenesis process via the CDR1as/miR-7/FGF2 pathway and further promoted tendon-bone healing after RCR in a rat rotator cuff tear model. Clinical Relevance: This study provides an alternative strategy for improving TBI healing after RCR.

Age-different BMSCs-derived exosomes accelerate tendon-bone interface healing in rotator cuff tears model

BackgroundRotator cuff tears (RCTs) are culprit of shoulder pain and dysfunction. Tendon-bone interface (TBI) mal-healing is an essential contributor to retear after RCTs. Consequently, present project was conducted to investigate the role of bone marrow mesenchymal stem cells (BMSCs)-derived exosomes on TBI healing. MethodYoung BMSCs (Y-BMSCs) and Aged BMSCs (A-BMSCs) were isolated from Young (3-month-old) and old (24-month-old) SD rats, and their-derived exosomes (A-BMSCs-exo and Y-BMSCs-exo) were identified. RCTs model was established, and A-BMSCs-exo and Y-BMSCs-exo were injected at the rotator cuff using hydrogel as a vehicle. Pathological changes of TBI were observed by HE, Sirius Red and Oil Red O staining. Western blotting and RT-qPCR were applied to assess the expression of extracellular matrix (ECM)-, tendon cell (TCs)-, osteogenic-, tendon-derived stem cell (TDSCs)- and angiogenic-associated proteins and mRNAs in TBI. ResultY-BMSCs exhibited increased activity, osteogenic and lipogenic abilities than A-BMSCs. After A-BMSCs-exo and Y-BMSCs-exo treatment, TBI displayed massive sharpey’s fibers growing along the tendon longitudinally, and a collagen fiber-chondrocyte migration zone forming a typical tendon-noncalcified fibrocartilage-calcified fibrocartilage-bone structure. A-BMSCs-exo and Y-BMSCs-exo significantly upregulated the expression of collagen Col I/II/III, Aggrecan, TNMD, SCX, Runx2, OPN, CD45, Sox2, CD31 and VEGFR2 in TBI. In vitro, A-BMSCs-exo and Y-BMSCs-exo significantly enhanced the activity of TCs and TDSCs, TDSCs stemness, and reduced the osteogenic and lipogenic capacity of TDSCs. The effect of Y-BMSCs-exo was significantly stronger than that of A-BMSCs-exo. ConclusionBMSCs-derived exosomes facilitate ECM remodeling, osteogenic differentiation, angiogenesis, and stemness of TDSCs, thereby accelerating TBI healing in RCTs, with better outcomes using young individual-derived BMSCs.

Socket-Anchor Technique for 3-Portal All-Inside Arthroscopic Anterior Talofibular Ligament Reconstruction Using Allograft Tendon

Arthroscopic techniques for anterior talofibular ligament (ATFL) reconstruction have been developed in recent years. Allograft tendons are often used in ATFL reconstruction, and surgical indications include an insufficiently strong ligament remnant, high-demand activities, repeated ankle sprains, and revision cases. We describe a socket-anchor technique for talar tunnel creation: A 10-mm-deep bone tunnel (socket) is created along a previously located guidewire at the ATFL talar footprint; an absorbable suture anchor is inserted into the end of the socket; and the graft is tied to the suture, pulled into the socket, and finally, secured using an arthroscopic knot pusher. This technique provides the advantages of being minimally invasive, ensuring a sufficient tendon-bone interface healing area of the graft, avoiding medial neurovascular bundle injury and the risk of talar neck fracture caused by screw fixation, and having no special restrictions on the direction of the anchor with blind tunnel creation. In addition, the procedure is easy to perform with high fault tolerance and no need for intraoperative fluoroscopy.

Slit Guidance Ligand 3 (SLIT3) Loaded in Hydrogel Microparticles Enhances the Tendon-Bone Healing through Promotion of Type-H Vessel Formation: An Experimental Study in Mice.

Poor tendon-bone interface (TBI) integration is one of the major causes contributing to unsatisfactory healing quality in patients after anterior cruciate ligament (ACL) reconstruction. Type H vessels have been recently found to closely modulate bone formation via regulation of the osteo-angiogenic crosstalk, so the strategies favoring type H vessel formation may be promising therapeutic approaches for improved graft osteointegration. In this study, we reported for the first time the treatment outcome of slit guidance ligand 3 (slit3), a novel proangiogenic factor favoring type H vessel formation, in TBI healing in mice with ACL reconstruction. The mice (n = 87) were divided into three groups for various treatments: hydrogel microparticles (HMP, control group), slit3@HMP, and slit3 neutralizing antibody@HMP (slit3-AB@HMP). Histological analysis, gait performance, radiographic measurement, and biomechanical testing were performed to assess the TBI healing quality. Increased bony ingrowth and reduced fibrous scar tissue was formed at the TBI in the slit3@HMP group when compared to the HMP group. Meanwhile, the slit3-AB@HMP inhibited the osseous ingrowth and increased fibrous scar tissue formation relative to the HMP group. Compared to the HMP group, the slit3@HMP favored type H vessel formation at the TBI while the slit3-AB@HMP impeded it. According to micro-CT assessment, compared to the HMP group, the slit3@HMP significantly increased the peri-tunnel bone mass while the slit3-AB@HMP significantly reduced the peri-tunnel bone mass. The mice in the slit3@HMP group showed the best gait performance in terms of stance time, stride length, paw print area, and stance pressure. Dynamic laxity measurement and tensile testing showed the slit3@HMP group exhibited significantly reduced laxity displacement and improved failure load and stiffness relative to the other two groups. Collectively, the injection of slit3 could be used to enhance tendon-bone integration, which may be ascribed to modulation of angiogenesis-osteogenesis crosstalk coupled by type H vessels.

Assessment of a Synergistic Effect of Platelet-Rich Plasma and Stem Cell-Seeded Hydrogel for Healing of Rat Chronic Rotator Cuff Injuries.

Outcomes after repair of chronic rotator cuff injuries remain suboptimal. Type-1 collagen-rich tendon hydrogel was previously reported to improve healing in a rat chronic rotator cuff injury model. Stem cell seeding of the tendon hydrogel improved bone quality in the same model. This study aimed to examine whether there was a synergistic and dose-dependent effect of platelet-rich plasma (PRP) on tendon-bone interface healing by combining PRP with stem cell-seeded tendon hydrogel. Human cadaveric tendons were processed into a hydrogel. PRP was prepared at two different platelet concentrations: an initial concentration (initial PRP group) and a higher concentration (concentrated PRP group). Tendon hydrogel was mixed with adipose-derived stem cells and one of the platelet concentrations. Methylcellulose, as opposed to saline, was used as a negative control due to comparable viscosity. The supraspinatus tendon was detached bilaterally in 33 Sprague-Dawley rats (66 shoulders). Eight weeks later, each detached tendon was repaired, and a hydrogel mixture or control was injected at the repair site. Eight weeks after repair, shoulder samples were harvested and assigned for biomechanical testing (n = 42 shoulders) or a combination of bone morphological and histological assessment (n = 24 shoulders). Biomechanical testing showed significantly higher failure load and stiffness in the concentrated PRP group than in control. Yield load in the initial and concentrated PRP groups were significantly higher than that in the control. There were no statistically significant differences between the initial and concentrated PRP groups. The addition of the highly concentrated PRP to stem cells-seeded tendon hydrogel improved healing biomechanically after chronic rotator cuff injury in rats compared to control. However, synergistic and dose-dependent effects were not seen.

Simvastatin promotes rat Achilles tendon-bone interface healing by promoting osteogenesis and chondrogenic differentiation of stem cells

To investigate the effect and mechanism of simvastatin on cell components of tendon-bone healing interface. The tendon-bone healing model was established by inserting the end of the Achilles tendon into the tibial tunnel on 24 rats, and simvastatin was used locally at the tendon-bone interface. Healing was evaluated at 8weeks by mechanical testing, micro-CT, and qualitative histology including H&E, Toluidine blue, and immunohistochemical staining. In vitro, bone marrow stromal cells (BMSCs) and tendon-derived mesenchymal stem cells (TDSCs) underwent osteogenic and chondrogenic differentiation respectively by plate co-culture. An analysis was performed on days 7 and 14 of cell differentiation. Biomechanical testing demonstrated a significant increase in maximum stiffness in the simvastatin-treated group. Micro-CT analysis showed that the bone tunnels in the simvastatin group were smaller in diameter and had higher bone density. H&E and Toluidine blue staining demonstrated that tendon-bone healing was significantly greater with better tissue arrangement and more extracellular matrix in the simvastatin-treated group than that in the control group, and immunohistochemical staining showed the expression of VEGF in simvastatin group was significantly higher. Histological staining and RT-PCR confirmed that simvastatin could promote the differentiation of co-cultured BMSCs and TDSCs into osteoblasts and chondroblasts, respectively. The effect of promoting osteogenic differentiation was more tremendous at 14days, while its effect on promoting chondroblast differentiation was more evident on the 7th day of differentiation. In conclusion, local administration of simvastatin can promote the tendon-bone healing by enhancing neovascularization, chondrogenesis, and osteogenesis in different stages of the tendon-bone healing process.

Comparison of Healing Effect Between Fibrin Gel Complex Bone Morphological Protein and Reconstituted Bone Xenograft After Reconstruction of Sports Ligament Injury

To study the effect of fibrin gel complex bone morphological protein (FG-BMP) and RBX on the healing of tendon-bone interface. 51 live rabbits were selected, and 51 rabbits were randomly divided into 3 groups: FG-BMP, RBX and control groups. Bilateral ACL reconstruction was performed in 51 rabbits, with different biomaterials injected at the tendon-bone interface, and none applied in the FG-BMP, RBX, and control groups. Material extraction, imaging examination, histological analysis, and biomechanical tests were conducted at 2 weeks after surgery, 6 weeks later, and 12 weeks after surgery, respectively. The tendon-interbone growth rate of rabbits using FG-BMP biomaterials and RBX biomaterials was significantly improved in the FG-BMP and RBX groups compared with the control group (P < 0.05). Histological results showed that all rabbits in the RBX group were surrounded by newborn bone tissue around the tendon-bone transplantation tendon and had a significantly greater number of newborn bone tissue than in the FG-BMP group (P < 0.05). The biomechanical test results showed that the two groups of FG-BMP biomaterials improved the maximum tension compared with the control group (P < 0.05), where the RBX tension, the difference was significant (P < 0.05), and the FG-BMP group although higher than the control group (P > 0.05). Conclusion: In the comparison of promoting tendon-bone interface healing, FG-BMP biomaterials and RBX biomaterials have significant results, especially RBX materials have obvious advantages in accelerating tendon-bone interface healing.

Local Administration of Metformin Improves Bone Microarchitecture and Biomechanical Properties During Ruptured Canine Achilles Tendon–Calcaneus Interface Healing

Background: Tendon-bone interface (TBI) healing is a clinical dilemma that is closely relevant to new bone formation and remodeling at the repair site. Previous studies showed that metformin is an osteogenic inducer for stem cells in vitro and capable of stimulating bone regeneration in vivo. Hypothesis: Metformin would be effective for promoting TBI healing by enhancing new bone formation and remodeling. Study Design: Controlled laboratory study. Methods: Canine bone marrow stem cells (BMSCs) were cultured with various concentrations of metformin (0, 10, 50, 100, 200 μM). The effect of metformin on the osteogenic differentiation of canine BMSCs was evaluated via alizarin red staining and osteogenic gene expression. Eighteen mature beagles were included in a bilateral Achilles tendon–calcaneus (ATC) interface injury model. The right interface was reattached via surgical repair only, while the left was surgically reattached after implanting a fibrin glue containing metformin. At postoperative week 4 or 8, the healing quality of the wounded ATC interfaces was evaluated. Results: In vitro experiments determined that metformin was an osteogenic inducer for canine BMSCs. In vivo experiments showed that the metformin-treated ATC interfaces were repaired with significantly greater failure load and stiffness than was the no-metformin control site (P < .05 for all). Micro–computed tomography analysis showed that the metformin-treated specimens presented significantly higher bone volume/total volume and trabecular thickness than did the no-metformin control specimens (P < .05 for all), as confirmed via hematoxylin and eosin staining. Immunohistochemical staining showed that significantly more osteocalcin-positive cells were located at the newly formed bones treated with metformin than at the no-metformin control site at week 4 (P < .05). Masson trichrome staining showed that significantly more oriented collagen fibers anchored into the newly formed bone of the metformin-treated site than the no-metformin control site (P < .05). Conclusion: Metformin induced the osteogenesis of canine BMSCs in vitro, and local administration of metformin provided an improvement of bone microarchitecture at the calcaneus as well as an increase in the tensile properties of the repaired ATC interfaces in canines. Clinical Relevance: Findings of the study indicate that local administration of metformin may be an effective strategy for TBI healing in clinic.

Canine ACL reconstruction with an injectable hydroxyapatite/collagen paste for accelerated healing of tendon-bone interface.

Healing of an anterior cruciate ligament (ACL) autologous graft in a bone tunnel occurs through the formation of fibrovascular scar tissue, which is structurally and compositionally inferior to normal fibrocartilaginous insertion and thus may increase the reconstruction failure and the rate of failure recurrence. In this study, an injectable hydroxyapatite/type I collagen (HAp/Col Ⅰ) paste was developed to construct a suitable local microenvironment to accelerate the healing of bone-tendon interface. Physicochemical characterization demonstrated that the HAp/Col Ⅰ paste was injectable, uniform and stable. The in vitro cell culture illustrated that the paste could promote MC3T3-E1 cells proliferation and osteogenic expression. The results of a canine ACL reconstruction study showed that the reconstructive ACL had similar texture and color as the native ACL. The average width of the tunnel, total bone volume, bone volume/tissue volume and trabecular number acquired from micro-CT analysis suggested that the healing of tendon-bone interface in experimental group was better than that in control group. The biomechanical test showed the maximal loads in experimental group achieved approximately half of native ACL's maximal load at 24 weeks. According to histological examination, Sharpey fibers could be observed as early as 12 weeks postoperatively while a typical four-layer transitional structure of insertion site was regenerated at 48 weeks in the experimental group. The injectable HAp/Col Ⅰ paste provided a biomimetic scaffold and microenvironment for early cell attachment and proliferation, further osteogenic expression and extracellular matrix deposition, and in vivo structural and functional regeneration of the tendon-bone interface.

3D cell-printing of gradient multi-tissue interfaces for rotator cuff regeneration.

Owing to the prevalence of rotator cuff (RC) injuries and suboptimal healing outcome, rapid and functional regeneration of the tendon–bone interface (TBI) after RC repair continues to be a major clinical challenge. Given the essential role of the RC in shoulder movement, the engineering of biomimetic multi-tissue constructs presents an opportunity for complex TBI reconstruction after RC repair. Here, we propose a gradient cell-laden multi-tissue construct combined with compositional gradient TBI-specific bioinks via 3D cell-printing technology. In vitro studies demonstrated the capability of a gradient scaffold system in zone-specific inducibility and multi-tissue formation mimicking TBI. The regenerative performance of the gradient scaffold on RC regeneration was determined using a rat RC repair model. In particular, we adopted nondestructive, consecutive, and tissue-targeted near-infrared fluorescence imaging to visualize the direct anatomical change and the intricate RC regeneration progression in real time in vivo. Furthermore, the 3D cell-printed implant promotes effective restoration of shoulder locomotion function and accelerates TBI healing in vivo. In summary, this study identifies the therapeutic contribution of cell-printed constructs towards functional RC regeneration, demonstrating the translational potential of biomimetic gradient constructs for the clinical repair of multi-tissue interfaces.

Segmentally Demineralized Cortical Bone With Stem Cell-Derived Matrix Promotes Proliferation, Migration and Differentiation of Stem Cells in vitro.

A recent study has shown that demineralized cortical bone (DCB) did not improve the healing of tendon-bone interface. Considering that there is a gradient of mineral content in the tendon-bone interface, we designed a segmentally demineralized cortical bone (sDCB) scaffold with two different regions: undemineralized cortical bone section within the scaffold (sDCB-B) and complete demineralized cortical bone section within the scaffold (sDCB-D), to mimic the natural structure of the tendon-bone interface. Furthermore, the extracellular matrix (ECM) from tendon-derived stem cells (TDSCs) was used to modify the sDCB-D region of sDCB to construct a novel scaffold (sDCB-ECM) for enhancing the bioactivity of the sDCB-D. The surface topography, elemental distribution, histological structure, and surface elastic modulus of the scaffold were observed using scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, histological staining and atomic force microscopy. Cell proliferation of bone marrow mesenchymal stem cells (BMSCs) and TDSCs cultured on scaffolds was evaluated using the Cell Counting kit-8, and cell viability was assessed by Live/Dead cell staining. Cell morphology was detected by fluorescent staining. The ability of the scaffolds to recruit stem cells was tested using transwell migration assay. The expression levels of bone-, cartilage- and tendon-related genes and proteins in stem cells were assessed by the polymerase chain reaction and western blotting. Our results demonstrated that there was a gradient of Ca and P elements in sDCB, and TDSC-derived ECM existed on the surface of the sDCB-D region of sDCB. The sDCB-ECM could promote stem cell proliferation and migration. Moreover, the sDCB-B region of sDCB-ECM could stimulate osteogenic and chondrogenic differentiation of BMSCs, and the sDCB-D-ECM region of sDCB-ECM could stimulate chondrogenic and tenogenic differentiation of TDSCs when compared to DCB. Our study indicated that sDCB-ECM might be a potential bioscaffold to enhance the tendon-bone interface regeneration.

Adipose-Derived Stem Cell Sheets Improve Early Biomechanical Graft Strength in Rabbits After Anterior Cruciate Ligament Reconstruction

Background: Although various reconstruction techniques are available for anterior cruciate ligament (ACL) injuries, a long recovery time is required before patients return to sports activities, as the reconstructed ACL requires time to regain strength. To date, several studies have reported use of mesenchymal stem cells in orthopaedic surgery; however, no studies have used adipose-derived stem cell (ADSC) sheets in ACL reconstruction (ACLR). Hypothesis: ADSC sheet transplantation can improve biomechanical strength of the autograft used in ACLR. Study Design: Controlled laboratory study. Methods: A total of 68 healthy Japanese white rabbits underwent unilateral ACLR with a semitendinosus tendon autograft after random enrollment into a control group (no sheet; n = 34) and a sheet group (ADSC sheet; n = 34). At 2, 4, 8, 16, and 24 weeks after surgery, rabbits in each group were sacrificed to evaluate tendon-bone healing using histological staining, micro–computed tomography, and biomechanical testing. At 24 weeks, scanning transmission electron microscopy of the graft midsubstance was performed. Results: The ultimate failure load for the control and sheet groups, respectively, was as follows: 17.2 ± 5.5 versus 37.3 ± 10.3 (P = .01) at 2 weeks, 28.6 ± 1.9 versus 47.4 ± 10.4 (P = .003) at 4 weeks, 53.0 ± 14.3 versus 48.1 ± 9.3 (P = .59) at 8 weeks, 66.2 ± 9.3 versus 95.2 ± 43.1 (P = .24) at 16 weeks, and 66.7 ± 27.3 versus 85.3 ± 29.5 (P = .39) at 24 weeks. The histological score was also significantly higher in the sheet group compared with the control group at early stages up to 8 weeks. On micro–computed tomography, relative to the control group, the bone tunnel area was significantly narrower in the sheet group at 4 weeks, and the bone volume/tissue volume of the tendon-bone interface was significantly greater at 24 weeks. Scanning transmission electron microscopy at 24 weeks indicated that the mean collagen fiber diameter in the midsubstance was significantly greater, as was the occupation ratio of collagen fibers per field of view, in the sheet group. Conclusion: ADSC sheets improved biomechanical strength, prevented bone tunnel enlargement, and promoted tendon-bone interface healing and graft midsubstance healing in an in vivo rabbit model. Clinical Relevance: ADSC sheets may be useful for early tendon-bone healing and graft maturation in ACLR.

Early treadmill running delays rotator cuff healing via Neuropeptide Y mediated inactivation of the Wnt/β-catenin signaling.

BackgroundDefining the optimal rehabilitation programs for rotator cuff healing remains a challenge. Early treadmill running may have negative effects on tendon-bone interface (TBI) healing with increased expression of Neuropeptide Y (NPY). However, the underlying mechanism is still unknown.MethodsThe mice were randomly assigned to four groups: control group, treadmill group, treadmill ​+ ​BIBO3304 group and BIBO3304 group alone. Specifically, the control group was allowed free cage activity without any treatment after surgery. The treadmill group received early treadmill running initiated from postoperative day 2. The treadmill ​+ ​BIBO3304 group received treadmill running combined with intra-articular injection of BIBO3304 postoperatively. The BIBO3304 group only received type 1 NPY receptor (Y1 receptor, Y1R) antagonist BIBO3304 postoperatively. Healing outcomes of the rotator cuff were evaluated by histological analysis, synchrotron radiation micro-computed tomography (SR-μCT) scanning, and biomechanical testing at 4 and 8 weeks after surgery. The expression of NPY and its Y1 receptor during the treadmill running were tested by immunofluorescence. In addition, the related signaling pathway of Neuropeptide Y among all groups was detected by immunohistochemistry and western-blot.ResultsImmunofluorescence results show that early treadmill training could lead to a significant increase in the expression of NPY at the healing site, and Y1R was widely expressed in both normal or injured rotator cuff without statistical difference. At the same time, early treadmill running delayed the healing of rotator cuff, as indicated with unsatisfactory outcomes, including a significantly lower histological score, decreased bone formation and inferior biomechanical properties at postoperative week 4 and 8. Moreover, the use of BIBO3304 could partly alleviate the negative effects of early treadmill running on the healing of rotator cuff and promote the natural healing process of rotator cuff, as evidenced by significant differences observed between the treadmill and treadmill ​+ ​BIBO3304 groups, as well as observed between the control and BIBO3304 groups. On the other hand, the expressions of Wnt3a and β-catenin in the treadmill group were significantly lower compared with the other groups, while the expression in the BIBO3304 group was the highest, as evaluated by immunohistochemistry and western-blot.ConclusionsEarly treadmill running increased the expression of NPY at the RC healing site, which might burden the expression of Wnt3a/β-catenin and delay the healing process, inhibition of Y1 receptor with BIBO3304 could promote bone-tendon healing through the Wnt/β-catenin signaling.The translational potential of this article: This is the first study to evaluate the specific role of the NPY-Y1R axis and its underlying mechanism by which early treadmill running delays bone-tendon healing. Further, our study may provide references of precise and individualized exercise-based rehabilitation strategies for TBI healing in clinic.The translational potential of this articleThis is the first study to evaluate the specific role of the NPY-Y1R axis and its underlying mechanism by which early treadmill running delays bone-tendon healing. Further, our study may provide references of precise and individualized exercise-based rehabilitation strategies for TBI healing in clinic.

Combination of graphene oxide and platelet-rich plasma improves tendon-bone healing in a rabbit model of supraspinatus tendon reconstruction.

The treatment of rotator cuff tear is one of the major challenges for orthopedic surgeons. The key to treatment is the reconstruction of the tendon–bone interface (TBI). Autologous platelet-rich plasma (PRP) is used as a therapeutic agent to accelerate the healing of tendons, as it contains a variety of growth factors and is easy to prepare. Graphene oxide (GO) is known to improve the physical properties of biomaterials and promote tissue repair. In this study, PRP gels containing various concentrations of GO were prepared to promote TBI healing and supraspinatus tendon reconstruction in a rabbit model. The incorporation of GO improved the ultrastructure and mechanical properties of the PRP gels. The gels containing 0.5 mg/ml GO (0.5 GO/PRP) continuously released transforming growth factor-β1 (TGF-β1) and platelet-derived growth factor (PDGF)-AB, and the released TGF-β1 and PDGF-AB were still at high concentrations, ∼1063.451 pg/ml and ∼814.217 pg/ml, respectively, on the 14th day. In vitro assays showed that the 0.5 GO/PRP gels had good biocompatibility and promoted bone marrow mesenchymal stem cells proliferation and osteogenic and chondrogenic differentiation. After 12 weeks of implantation, the magnetic resonance imaging, micro-computed tomography and histological results indicated that the newly regenerated tendons in the 0.5 GO/PRP group had a similar structure to natural tendons. Moreover, the biomechanical results showed that the newly formed tendons in the 0.5 GO/PRP group had better biomechanical properties compared to those in the other groups, and had more stable TBI tissue. Therefore, the combination of PRP and GO has the potential to be a powerful advancement in the treatment of rotator cuff injuries.

3D cell-printing of tendon-bone interface using tissue-derived extracellular matrix bioinks for chronic rotator cuff repair

The tendon-bone interface (TBI) in rotator cuffs exhibits a structural and compositional gradient integrated through the fibrocartilaginous transition. Owing to restricted healing capacity, functional regeneration of the TBI is considered a great clinical challenge. Here, we establish a novel therapeutic platform based on 3D cell-printing and tissue-specific bioinks to achieve spatially-graded physiology for functional TBI regeneration. The 3D cell-printed TBI patch constructs are created via a spatial arrangement of cell-laden tendon and bone-specific bioinks in a graded manner, approximating a multi-tissue fibrocartilaginous interface. This TBI patch offers a cell favorable microenvironment, including high cell viability, proliferative capacity, and zonal-specific differentiation of encapsulated stem cells for TBI formation in vitro. Furthermore, in vivo application of spatially-graded TBI patches with stem cells demonstrates their regenerative potential, indicating that repair with 3D cell-printed TBI patch significantly accelerates and promotes TBI healing in a rat chronic tear model. Therefore, our findings propose a new therapeutic strategy for functional TBI regeneration using 3D cell-printing and tissue-specific decellularized extracellular matrix bioink-based approach.

Application and research of nano-biomaterials in knee cruciate ligament rehabilitation after sports injury

Anterior cruciate ligament injury of the knee joint is a more common occurrence in sports injuries. In recent years, in the field of sports medicine and rehabilitation medicine, the evaluation of the treatment of anterior cruciate ligament after reconstruction by biomechanical methods has become a research hotspot. The study found that reconstruction of the knee anterior cruciate ligament by surgery can restore knee function to a certain extent, but the biomechanical parameters of the lower limbs may still be abnormal. Therefore, the use of biomechanics to develop a targeted rehabilitation treatment plan for the knee joint after surgery can effectively avoid the recurrence of injuries. This aims to restore patients from their pre-injury state as much as possible through rehabilitation treatment without affecting their future normality life. By analysing the structural and mechanical characteristics of the knee joint, the mechanism of cruciate ligament injury is clarified. The types and characteristics of cruciate ligament repair materials are reviewed to provide a reference for preventing knee cruciate ligament injury and post-injury repair. Comparative evaluation is made of two different biomaterials, fibrin glue composite bone morphogenetic protein (FG-BMP) and recombined xenogeneic bone (RBX) on tendon-bone interface healing.

Magnesium-pretreated periosteum for promoting bone-tendon healing after anterior cruciate ligament reconstruction

Periosteum can improve tendon-bone healing when applied to wrap the tendon graft in both animal studies and clinical trials. As magnesium (Mg) ions can significantly elevate the levels of relevant cytokines involving in the osteogenic differentiation of periosteum-derived stem cells, the Mg-pretreated periosteum may be an innovative approach for enveloping the tendon graft. To test this hypothesis, we compared the effects of Mg-pretreated periosteum (M − P) and the stainless steel (SS)-pretreated periosteum (SS–P) in ACL reconstruction. We firstly found that the released Mg ions from the Mg implants were partially accumulated in periosteum, resulting in higher Mg/Ca ratio in the M − P compared to the SS-P. Additionally, the M − P showed significantly higher expression levels of calcitonin gene-related peptide (CGRP) and periostin than the SS-P due to the decrease in Cathepsin K (CTSK). Elevation of CGRP and periostin was beneficial for the osteogenic differentiation of periosteum-derived stem cells. More importantly, we demonstrated that the M − P remarkably increased the formation of fibrocartilage at the interface between the periosteum and tendon. Collectively, M − P group demonstrated significantly prevented peri-tunnel bone loss, more osseous ingrowth into the tendon graft and higher maximum load to failure as compared to the SS-P group. In summary, our study warrants further investigations for translating the current proof-of-concept findings to optimize the delivery of CGRP, periostin, and cells as novel practical therapeutic strategy for enhancing tendon-bone interface healing in patients undergoing ACL reconstruction.

Homing of Adipose-Derived Stem Cells to a Tendon-Derived Hydrogel: A Potential Mechanism for Improved Tendon-Bone Interface and Tendon Healing

Tendons are difficult to heal owing to their hypocellularity and hypovascularity. Our laboratory has developed a tendon-derived hydrogel (tHG) that significantly improves tendon healing in an animal model. We hypothesized that a potential mechanism for improved healing with tHG is through the attraction of systemic stem cells. Homing of systemic adipose-derived stem cells (ADSCs) to tendon injuries was assessed with acute and chronic injury models. Injury sites were treated with saline or tHG, and animals given a tail vein injection (TVI) of labeled ADSCs 1 week after treatment. One week following TVI, rats were harvested for histology. To further evaluate a potential difference in homing to tHG, a subcutaneous injection (SQI) model was used. Rats were treated with an SQI of saline, silicone, ADSCs in media, tHG, tHG+ fibroblasts (FBs), or tHG+ ADSCs on day 0. One week after SQI, rats underwent TVI with labeled ADSCs. Samples were harvested 2 or 3 weeks after SQI for analysis. Flow cytometry confirmed homing in the SQI model. Systemically delivered ADSCs homed to both acute tendon and chronic tendon-bone interface (TBI) injury sites. Despite their presence at the injury site, there was no difference in the number of macrophages, amount of cell proliferation, or angiogenesis 1 week after stem cell delivery.In an SQI model, ADSCs homed to tHG. There was no difference in the number of ADSCs homing to tHG alone versus tHG+ ADSCs. However, there was an increase in the number of living cells, general immune cells, and T-cells present at tHG+ ADSC versus tHG alone. The ADSCs home to tendon injury sites and tHG. We believe the attraction of additional systemic ADSCs is one mechanism for improved tendon and TBI healing with tHG. Treatment of tendon and TBI injuries with tHG can augment healing via homing of systemic stem cells.

Enhancement of tendon-bone interface healing and graft maturation with cylindrical titanium-web (TW) in a miniature swine anterior cruciate ligament reconstruction model: histological and collagen-based analysis

BackgroundTendon-bone interface healing and ligamentization of the graft in anterior cruciate ligament (ACL) reconstruction with autografts are important factors affecting treatment outcome. This study aimed to investigate the effectiveness of a cylindrical titanium-web (TW) in tendon-bone interface healing and graft maturation in ACL reconstruction.MethodsFourteen mature female CLAWN miniature swine underwent bilateral ACL reconstructions with patellar tendon (PT) autografts. In one limb, the TW/tendon complex was placed into the proximal side of the tibial tunnel. Only the graft was transplanted into the tunnel in the control limb. The proximal side of the graft was sutured into the stump of the native ACL and the distal end was stapled to the tibia. The animals were euthanized at 4 and 15 weeks postoperatively, for histological and biochemical analyses.ResultsMicroscopic images in TW limbs showed that ingrowth of tendon-like tissue and mineralized bone tissue into the TW connected the bone and the tendon directly. In contrast, fibrous tissue intervened between the bone and tendon in the control limbs. The total amount of collagen cross-links (which defines the strength of collagen fibers) and the maturation of collagen cross-links in TW tendons were significantly higher (p < 0.05) than those of control limbs. There was no significant difference in the ratio of dihydroxy-lysinonorleucine to hydroxy-lysinonorleucine (an indicator of tissue specific collagen maturation) between TW tendons and that of the native PT.ConclusionsTW promoted the maturation and formation of collagen cross-links in the grafted tendon while maintaining the cross-links pattern of native tendon collagen, and enabled direct binding of tendon to bone.

Research progress of structured repair of tendon-bone interface

In sports system, the tendon-bone interface has the effect of tensile and bearing load, so the effect of healing plays a crucial role in restoring joint function. The process of repair is the formation of scar tissue, so it is difficult to achieve the ideal effect for morphology and biomechanical strength. The tissue engineering method can promote the tendon-bone interface healing from the seed cells, growth factors, and scaffolds, and is a new direction in the field of development of the tendon-bone interface healing.