Sequential intervention of anti-inflammatory and osteogenesis with silk fibroin coated polyethylene terephthalate artificial ligaments for anterior cruciate ligament reconstruction.

Graft-host integration after the anterior cruciate ligament (ACL) reconstruction sequentially follows the prognosis from the inflammation period to the regeneration period. However, due to insufficient bioactivity, polyethylene terephthalate (PET) artificial ligaments often require a long period for graft-host integration. To improve graft-host integration, sequential therapy targeting multifactor is widely advocated. In this study, a multilayer regenerated silk fibroin (RSF) coating loaded with heparin and bone morphogenetic protein binding peptide (BBP) for differentiated release was introduced on the surface of the PET artificial ligament by a stepwise deposition method. The drug release profiles of heparin and BBP on the coated PET artificial ligament indicated the features of differential drug release, i.e., with heparin in the outermost layer releasing a significant amount (more than 60%) during the first 5 days while BBP in the inner layer only releasing a small amount (ca. 30%) within 1 week without burst release. Based on the isometric ACL reconstruction model of rabbits, such drug-loaded RSF coating was verified to be able to modulate the early inflammatory response and promote the maturation of the graft in the articular cavity, meanwhile, it provided a continuous and stable signal of osteogenic induction to improve graft-bone integration. Thus, sequential intervention with heparin and BBP proved to be a reliable combination, and multifunctional RSF-coated PET artificial ligaments hold great potential for improving the clinical efficacy of ACL reconstruction.

A Knitted PET Patch Enhances the Maturation of Regenerated Tendons in Bridging Reconstruction of Massive Rotator Cuff Tears in a Rabbit Model.

BACKGROUND: Although nondegradable synthetic grafts for bridging reconstruction of massive rotator cuff tears (MRCTs) have shown satisfactory clinical outcomes, their function and details on graft-tendon healing and enthesis regeneration have not been fully studied. HYPOTHESIS: The knitted polyethylene terephthalate (PET) patch as a nondegradable synthetic graft could provide sustained mechanical support, facilitating enthesis and tendon regeneration in the treatment of MRCTs. STUDY DESIGN: Controlled laboratory study. METHODS: A knitted PET patch was fabricated for bridging reconstruction (PET group) in a New Zealand White rabbit model of MRCTs (negative control group), and an autologous Achilles tendon was used as a control (autograft group). The animals were sacrificed, and tissue samples were harvested for gross observation as well as histological and biomechanical analyses at 4, 8, and 12 weeks postoperatively. RESULTS: Histological analysis showed no significant difference in the graft-bone interface score between the PET and autograft groups at 4, 8, and 12 weeks postoperatively. Interestingly, in the PET group, Sharpey-like fibers were observed at 8 weeks, while fibrocartilage formation and the ingrowth of chondrocytes were recognized at 12 weeks. Meanwhile, the tendon maturing score was significantly higher in the PET group than in the autograft group (19.7 ± 1.5 vs 15.3 ± 1.2, respectively; P = .008) at 12 weeks, with parallel-oriented collagen fibers around the knitted PET patch. Moreover, the ultimate failure load of the PET group was similar to that of a healthy rabbit tendon at 8 weeks (125.6 ± 13.6 vs 130.8 ± 28.6 N, respectively; P > .05) and no different from that of the autograft group at 4, 8, and 12 weeks. CONCLUSION: The knitted PET patch could not only immediately reconstruct the mechanical support for the torn tendon postoperatively in the rabbit model of MRCTs but also enhanced maturation of the regenerated tendon by fibrocartilage formation and improved the organization of collagen fibers. Herein, the knitted PET patch could be a promising candidate graft adopted in bridging reconstruction of MRCTs. CLINICAL RELEVANCE: A nondegradable knitted PET patch can safely bridge MRCTs with satisfactory mechanical strength and the promotion of tissue regeneration.

Establishment of near and non isometric anterior cruciate ligament reconstruction with artificial ligament in a rabbit model.

BACKGROUND: Tunnel position deicide the isometry of graft attachment in synthetic anterior cruciate ligament (ACL) reconstruction. Near-isometric tunnel position may have advantage in graft integration and knee function in ACL reconstruction (ACLR) with polyethylene terephthalate (PET) ligament. Few studies focused on tunnel position isometry when conduct ACLR with an animal model. This study aimed to establish a preclinical rabbit model of near and non isometric ACLR with PET ligament and investigate the advantage of near-isometric ACLR compared to non-isometric ACLR. METHODS: Nine hind limbs of rabbit were used in tunnel position study. Two femoral(anatomic, nonanatomic) tunnels and three tibial(anterior, middle, posterior) tunnels were used to measure tunnel position isometry during knee full range of motion. The tunnel position combination with minimal isometry was considered as near-isometric tunnel position. Then, 48 rabbits divided into two groups were conducted near or non isometric ACLR with PET ligament with graft fixation angle of 30° and constant tension of 5N. PET ligament isometry, range of motion(ROM) restriction, knee laxity were recorded after operation and followed up with macroscopic observation, microcomputed tomography (micro-CT) analysis, histology assessment and biomechanical test at 4 and 8 weeks postoperatively. RESULTS: The tunnel combination with minimal isometry was femoral anatomic position and tibial posterior position(5.19 â€‹± â€‹1.78%) and considered as near-isometric tunnel position. ROM restriction were observed in non-isometric group (22.50 â€‹± â€‹14.14°) while none in near-isometric group. However, no ROM restriction observed at 8 weeks in both group. Knee laxity compared to contralateral knee were better in near-isometric group than non-isometric group (stable/slack/total 10/2/12 VS 3/9/12, p â€‹= â€‹0.012) at 8 weeks postoperatively. Supeiror PET ligament integration were also observed in near-isometric group through macroscopic observation, micro-CT analysis, histology assessment at both 4 and 8 weeks. The failure load in the Near-Isometric group at 8 weeks were higher than timezero reconstruction with statistical difference (156.8N â€‹± â€‹25.98N vs.102.6 â€‹± â€‹22.96N, p â€‹= â€‹0.02). CONCLUSION: A rabbit model of ACLR based on tunnel position isometry was successfully established in this study. The near-isometric tunnel position in rabbit model was femoral anatomic position and tibial posterior position. A near-isometric ACLR with PET ligament did not cause ROM restriction and had a better graft integration and follow-up stability than non-isometric ACLR with ROM restriction. THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE: The study demonstrate the establishmentof near-isometric tunnel position and non-isometric tunnel position with significant difference of ROM restriction and graft-bone integration. The described tunnel positions with differential isometry in a rabbit ACLR provides a reproducible and translational small animal model and enables preclinical research between tunnel position isometry and its affection on variable grafts, graft integration and knee function.

An interference screw made using a silk fibroin-based bulk material with high content of hydroxyapatite for anterior cruciate ligament reconstruction in a rabbit model.

Upgradation is still in need for the clinically applied interference screws in anterior cruciate ligament reconstruction for more reliable fixation. Silk fibroin bulk materials offer a promising opportunity for this application except lacking osteoinductivity to some extent. Here we report a novel silk-based bulk material with high content of hydroxyapatite-silk fibroin (HA-SF) hybrid particles, which is prepared via a dual-network hydrogel. This composite bulk material possesses a compression modulus of 3.2 GPa, comparable to that of the natural compact bone, and presents satisfactory cytocompatibility and osteoinductivity in vitro when combined with the HA-SF nanoparticles particularly. This composite bulk material shaped into interference screws exhibits remarkable biomechanical properties and significant new-bone ingrowth in the host bone tunnel in a rabbit anterior cruciate ligament reconstruction (ACLR) model at 4 weeks and 12 weeks post-operatively. Moreover, considering that this "hydrogel method" allows the material to be formed in a mold, avoiding complicated post fabrication, it is a potential candidate for clinical translation.

Arthroscopic Superior Capsular Reconstruction Using "Sandwich" Patch Technique for Irreparable Rotator Cuff Tears.

The technique of superior capsular reconstruction (SCR) using fascia lata autograft, described by Mihata et al. in 2012, has been an acceptable and effective method for treating irreparable massive rotator cuff tears, especially in cases with severe fatty infiltration and tendon retraction. After the SCR procedure of Mihata et al., it was found that some graft failure occurred with thinning and elongation during the follow-up time, which was called graft "creep." To avoid graft creep and reduce graft failure rates after SCR, we created an arthroscopic SCR technique with a "sandwich" patch augmented with polyethylene terephthalate scaffold interspaced between 2 folded layers of fascia lata autograft.

Electrospun PCL/Gel-aligned scaffolds enhance the biomechanical strength in tendon repair.

Tendons can transmit mechanical force from muscles to bones for movement. However, the mechanical strength of tendons is compromised after surgery, thus causing a high rate of tendon retear. Hence, the design and preparation of biodegradable materials with excellent mechanical properties have become an urgent demand for sports medicine. In this study, biomimetic polycaprolactone (PCL)/gelatin (Gel)-aligned scaffolds were fabricated for the mechanical restoration of the injured tendon in a rabbit model. The diameter of nanofibers was about 427.82 ± 56.99 nm, which was approximate to that of the native collagen fibrils; the directional consistency of the nanofibers in PCL/Gel-aligned scaffolds reached 77.33 ± 3.22%, which were ultrastructurally biomimetic. Compared to the observations for the control group, the in vitro mechanical results showed that the PCL/Gel-aligned scaffolds (P/G-A) were anisotropic in terms of failure load, tensile strength, and Young's modulus. After verifying their good cytocompatibility, the scaffolds were implanted into the rabbit patellar tendon in situ. The biomechanical properties of the repaired tendon in P/G-A reached 343.97 ± 65.30 N in failure load, 85.99 ± 16.33 MPa in tensile strength, 590.84 ± 201.87 MPa in Young's modulus, and 171.29 ± 61.50 N mm-1 in stiffness in vivo at 8 weeks post operation. In a word, our results demonstrated that P/G-A could support the regenerated tissue of injured patellar tendons to restore the biomechanical strength in a rabbit model. This suggested that the PCL/Gel-aligned scaffolds can pave a promising way to improve the healing of injured tendons in the clinic in the future.

Encapsulation of a nanoporous simvastatin-chitosan composite to enhance osteointegration of hydroxyapatite-coated polyethylene terephthalate ligaments.

PURPOSE: This study was designed to evaluate the in vitro and in vivo biocompatibility and osteointegration of plasma-sprayed hydroxyapatite (HA)-coated polyethylene terephthalate (PET) ligaments encapsulated with a simvastatin (SV)-chitosan (CS) composite. METHODS: This study compared the in vitro and in vivo bone responses to three different PET ligaments: SV/CS/PET-HA, CS/PET-HA and PET-HA. A field emission scanning electron microscope was used to characterize the morphology, and the in vitro SV release profile was analyzed. MC3T3 cells were cocultured with SV/CS/PET-HA, CS/PET-HA and PET-HA to test their biocompatibility using CCK-8 tests. Osteogenic differentiation was investigated by the expression of marker genes using qPCR. Osteointegration was performed by implanting the PET ligaments into the proximal tibia bone tunnels of male Sprague-Dawley rats for 3 weeks and 6 weeks. The bone-implant interface was evaluated by micro-computed tomography (micro-CT) and histological analysis. RESULTS: The characteristic nanoporous structures mainly formed on the surface of the plasma-sprayed HA particles in the SV/CS/PET-HA and CS/PET-HA groups. The SV release test showed that the sustained release of simvastatin lasted for 25 days in the SV/CS/PET-HA group. The in vitro studies demonstrated that the SV/CS/PET-HA ligaments induced osteogenic differentiation in the MC3T3 cells, with higher mRNA expression levels of collagen-1, bone morphogenetic protein-2, osteocalcin and alkaline phosphatase than those in the CS/PET-HA and PET-HA ligament groups. The in vivo tests showed that both micro-CT analysis (bone mineral density and bone volume per total volume) and histological analysis (bone implant contact and interface area) revealed significantly higher peri-implant bone formation and less interface area in the SV/CS/PET-HA group than in the other groups. CONCLUSION: The SV-CS composite nanoporous structure was associated with the improved biocompatibility and osteogenic differentiation in vitro and enhanced osteointegration process in vivo of plasma-sprayed HA-coated PET ligaments.

The Effect of Remnant Preservation on Tibial Tunnel Enlargement in Anterior Cruciate Ligament Reconstruction with Polyethylene Terephthalate Artificial Ligament in a Large Animal Model.

An enlarged bone tunnel may affect the graft-bone integration and pose a problem for revision anterior cruciate ligament (ACL) surgery. The purpose of this study was to evaluate the effect of remnant preservation on tibial tunnel enlargement in ACL reconstruction with polyethylene terephthalate (PET) artificial ligament. Twenty-four skeletally mature male beagles underwent ACL reconstruction with PET artificial ligament for both knees. One knee was reconstructed with remnant preservation using sleeve technique (remnant group), while the contralateral was reconstructed without remnant preservation (control group). The animals were sacrificed at 1 day, 6 weeks, and 12 weeks after surgery for further evaluation including macroscopic observation, microcomputed tomography (micro-CT), histological assessment, and biomechanical testing. The remnant group had better synovial coverage than the control group at 6 and 12 weeks after surgery. The micro-CT analysis showed the tibial tunnel area (TTA) of the remnant group was significantly smaller and the bone volume/total volume fraction (BV/TV) value was higher than those of the control group at 6 and 12 weeks. Moreover, TTA and BV/TV at each time point were divided into three groups according to the different grade of synovial coverage. Significant association was observed between the synovial coverage degree and the TTA and BV/TV values. The histological assessment revealed that the interface width between the graft and host bone in the remnant group was smaller than that in the control group in the tibial tunnels at 6 and 12 weeks. Moreover, the remnant group had better failure load and stiffness than the control group at 12 weeks. The remnant preservation using sleeve technique could effectively promote the synovial coverage of the graft, decrease the risk of tibial tunnel enlargement by sealing the bone tunnel entrance, and enhance the biological environment for graft-bone healing after ACL reconstruction using PET artificial ligament. This technique provides a potential solution for bone tunnel enlargement following artificial ligament surgery for the acute ACL rupture in the clinical practice.

Bone Marrow Stem Cells-Seeded Polyethylene Terephthalate Scaffold in Repair and Regeneration of Rabbit Achilles Tendon.

The objective of this study was to evaluate the effect of bone marrow stem cells (BMSCs)-seeded polyethylene terephthalate (PET) scaffold for Achilles tendon repair in a rabbit model. The allogeneic BMSCs were seeded onto the PET scaffold and cultured in vitro for 14 days. Sixteen mature New Zealand rabbits underwent surgery to establish a 2-cm Achilles tendon defect model. The BMSCs-seeded PET scaffold was implanted into the defect of one limb (BMSCs-PET group), while the PET scaffold without BMSCs was implanted into the defect of contralateral limb as the control (PET group). All rabbits were sacrificed at 6 and 12 weeks after surgery. At 12 weeks after surgery, macroscopic and histological results showed formation of tendon-like tissues, and the structure was more mature in the BMSCs-PET group. Immunohistochemical analysis and real-time polymerase chain reaction (RT-PCR) demonstrated that the collagen I and collagen III were significantly higher in the BMSCs-PET group compared with those in the PET group. Mechanically, both the failure load and the average stiffness were significantly higher in the BMSCs-PET group than those in the PET group. In conclusion, BMSCs-seeded PET scaffold could effectively facilitate the healing process after being implanted in a rabbit Achilles tendon defect model.

Dual-layer aligned-random nanofibrous scaffolds for improving gradient microstructure of tendon-to-bone healing in a rabbit extra-articular model.

BACKGROUND: Tendon/ligament injuries are common sports injuries. Clinically, the repair of a ruptured tendon or ligament to its bony insertion is needed, but the enthesis structure is not well reestablished following surgical repair. Herein, we fabricated dual-layer aligned-random scaffold (ARS) by electrospinning and aimed to investigate the effect of the scaffold on tendon-to-bone healing in vivo. MATERIALS AND METHODS: The random and dual-layer aligned-random silk fbroin poly(L-lactic acid-co-e-caprolactone) (P(LLA-CL)) nanofibrous scaffolds were successfully fabricated by electrospinning methods. Ninety New Zealand white rabbits were randomly divided into three groups (random scaffold [RS], ARS, and control groups), and they were subjected to surgery to establish an extra-articular tendon-to-bone healing model with autologous Achilles tendon. RESULTS: Histological assessment showed that the ARS significantly increased the area of metachromasia, decreased the interface width, and improved collagen maturation and organization at the tendon-bone interface compared with the RS and control groups. Microcomputed tomography analysis showed that the bone tunnel area of RS and ARS groups was significantly smaller than those of the control group. Real-time polymerase chain reaction showed that BMP-2 and osteopontin expression levels of the tissue at the interface between the bone and graft in the RS and ARS groups were higher than those of the control group at 6 weeks. Collagen I expression level of the ARS group was significantly higher than those of the RS and control groups at 6 and 12 weeks. Moreover, the ARS groups had a better ultimate load-to-failure and stiffness than the RS and control groups. CONCLUSION: ARS could effectively augment the tendon-to-bone integration and improve gradient microstructure in a rabbit extra-articular model by inducing the new bone formation, increasing the area of fibrocartilage, and improving collagen organization and maturation. The dual-layer aligned-random silk fibroin/P(LLA-CL) nanofibrous scaffold is proved to be a promising biomaterial for tendon-to-bone healing.

Silk fibroin and hydroxyapatite segmented coating enhances graft ligamentization and osseointegration processes of the polyethylene terephthalate artificial ligament in vitro and in vivo.

The inferior biocompatibility of the polyethylene terephthalate (PET) artificial ligament may lead to poor healing in both the intra-articular part (IAP) and the intraosseous part (IOP) after anterior cruciate ligament (ACL) reconstruction. This study aimed to systematically investigate the effect of silk fibroin (SF) and hydroxyapatite (HA) segmented coating on graft ligamentization and osseointegration processes of the PET ligament. Several techniques including scanning electron microscopy (SEM) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray diffraction (XRD) and water contact angle (WCA) measurements were carried out to validate the introduction of SF and HA. The segmented coating ligament was assessed both in vitro and in vivo. The results of SEM and cell counting kit-8 (CCK-8) assay revealed that the L929 fibroblasts and MC3T3-E1 osteoblasts exhibited better adhesion and proliferation performance on the PET-SF and PET-HA fibers, respectively, compared to those on the uncoated PET fibers. HA promoted osteogenic differentiation of MC3T3-E1 in terms of the levels of alkaline phosphatase (ALP) activity and calcium deposition. Furthermore, the in vivo study in a beagle ACL reconstruction model demonstrated that the segmented coating could enhance the graft ligamentization and osseointegration processes as indicated by the better tissue infiltration in the IAP and more bone ingrowth in the IOP of the ligament than the control group according to the results of micro-computed tomography (micro-CT), histology, real-time polymerase chain reactions (RT-PCRs) and biomechanical tests. Therefore, the SF and HA segmented coating ligaments may display a great potential application for the clinical augmentation of graft healing in ACL reconstruction surgery.

[Anatomical study on anterolateral ligament in a Chinese population].

Objective: To make further exploration of the structure characteristics of anterolateral ligament (ALL) and provide clinical reference for diagnosis and treatment of ALL injury, especially for ALL reconstruction through anatomical study of ALL in a Chinese population. Methods: Sixteen cadaveric knees, including 8 left knees and 8 right knees with sex ratio of 1∶1 and a mean age of 73.5 years (range, 57-84 years), were dissected to reveal the ALL through a standard approach. A qualitative and a quantitative characterizations of the ALL were performed. Results: ALL was seen in 75.0% of the specimens, originating on the lateral femoral epicondyle, proximal and posterior to the lateral collateral ligament (LCL). It coursed on LCL or was parallel to LCL, anterodistally to its anterolateral tibial attachment approximately midway between the center of the Gerdy's tubercle and the lateral margin of the fibular head. A strong connection was observed between the middle part of the ALL and the periphery of the meniscal body of the lateral meniscus. The distance between the center of the insertion and Gerdy's tubercle was (23.9±3.3) mm; and the distance between the center of the insertion and the lateral margin of the fibular head was (23.8±4.0) mm. The ALL length at 0° and 60° flexion and neutral knee rotation were (44.8±5.1) mm and (47.8±5.5) mm respectively ( t=14.071, P=0.000), and the ligament had its great extend at 60° of knee flexion and internal rotation. Furthermore, the ALL length at 0° and 60° flexion of males were both significantly higher than those of females ( t=2.920, P=0.015; t=2.806, P=0.019), while other measurements differences were significant between males and females ( P>0.05). Conclusion: ALL is an independent and a non-isometric ligament located in the anterolateral area to the knee, of which the length is different between males and females. ALL plays a role in rotational stability of the knee, and should be put much emphasis in clinical practice.