Analysis of retrieved polymer fiber based replacements for the ACL

Mechanical, Biological and In Vitro Degradation Investigation of Braided Scaffolds for Tendon and Ligament Tissue Engineering Based on Different Polycaprolactone Materials with Chitosan-Graft-PCL Surface Modification

Injuries to tendons and ligaments are highly prevalent in the musculoskeletal system. Current treatments involve autologous transplants with limited availability and donor site morbidity. Tissue engineering offers a new approach through temporary load-bearing scaffolds. These scaffolds have to fulfill numerous requirements, the majority of which can be met using braiding combined with high-strength polycaprolactone (PCL) fibers. Considering regulatory requirements, several medical-grade PCL materials were assessed regarding their mechanical, degradational and cell biological properties. In the course of the investigation, an excellent fiber tensile strength of up to 850 MPa was achieved. The fibers were braided into multilayer scaffolds and scaled to match the human ACL. These were characterized regarding their morphology and their mechanical and degradational properties. Two strategies were followed to provide biological cues: (a) applying a chitosan-graft-PCL surface modification and (b) using non-circular fiber morphologies as topographical stimuli. Cell vitality assays showed generally positive cytocompatibility and no impairments due to the surface modification or material grade. The best cell vitality was achieved with a scaffold consisting of snowflake-shaped monofilaments combined with a 25° braiding angle. The surface modification equips the scaffold with a release platform for function molecules (as recently demonstrated) so that a holistic approach to addressing the numerous requirements is provided.

Application of Nondegradable Synthetic Materials for Tendon and Ligament Injury

Tendon and ligament injuries, prevalent requiring surgical intervention, significantly impact joint stability and function. Owing to excellent mechanical properties and biochemical stability, Nondegradable synthetic materials, including polyethylene terephthalate (PET) and polytetrafluoroethylene (PTFE), have demonstrated significant potential in the treatment of tendon and ligament injuries. These above materials offer substantial mechanical support, joint mobility, and tissue healing promotion of the shoulder, knee, and ankle joint. This review conclude the latest development and application of nondegradable materials such as artificial patches and ligaments in tendon and ligament injuries including rotator cuff tears (RCTs), anterior cruciate ligament (ACL) injuries, and Achilles tendon ruptures.

A wear model to predict damage of reconstructed ACL

Impingement with surrounding tissues is a major cause of failure of anterior cruciate ligament reconstruction. However, the complexity of the knee kinematics and anatomical variations make it difficult to predict the occurrence of contact and the extent of the resulting damage. Here we hypothesise that a description of wear between the reconstructed ligament and adjacent structures captures the in vivo damage produced with physiological loadings. To test this, we performed an in vivo study on a sheep model and investigated the role of different sources of damage: overstretching, excessive twist, excessive compression, and wear. Seven sheep underwent cranial cruciate ligament reconstruction using a tendon autograft. Necropsy observations and pull-out force measurements performed postoperatively at three months showed high variability across specimens of the extent and location of graft damage. Using 3D digital models of each stifle based on X-ray imaging and kinematics measurements, we determined the relative displacements between the graft and the surrounding bones and computed a wear index describing the work of friction forces underwent by the graft during a full flexion-extension movement. While tensile strain, angle of twist and impingement volume showed no correlation with pull-out force (ρ = -0.321, p = 0.498), the wear index showed a strong negative correlation (r = -0.902, p = 0.006). Moreover, contour maps showing the distribution of wear on the graft were consistent with the observations of damage during the necropsy. These results demonstrate that wear is a good proxy of graft damage. The proposed wear index could be used in implant design and surgery planning to minimise the risk of implant failure. Its application to sheep can provide a way to increase preclinical testing efficiency.

3D-Braided Poly-ε-Caprolactone-Based Scaffolds for Ligament Tissue Engineering

The anterior cruciate ligament (ACL) is the most commonly injured intra-articular ligament of the knee. Due to its limited intrinsical healing potential and vascularization, injuries of the ACL do not heal satisfactorily, and surgical intervention is usually required. The limitations of existing reconstructive grafts and autologous transplants have prompted interest in tissue-engineered solutions. A tissue engineering scaffold for ACL reconstruction must be able to mimic the mechanical properties of the native ligament, provide sufficient porosity to promote cell growth of the neoligament tissue, and be biodegradable. This study investigates long-term biodegradable poly-ε-caprolactone (PCL)-based scaffolds for ACL replacement using the 3D hexagonal braiding technique. The scaffolds were characterized mechanically as well as morphologically. All scaffolds, regardless of their braid geometry, achieved the maximum tensile load of the native ACL. The diameter of all scaffolds was lower than that of the native ligament, making the scaffolds implantable with established surgical methods. The 3D hexagonal braiding technique offers a high degree of geometrical freedom and, thus, the possibility to develop novel scaffold architectures. Based on the findings of this study, the 3D-braided PCL-based scaffolds studied were found to be a promising construct for tissue engineering of the anterior cruciate ligament.

Hybrid Nanofibrous Composites with Anisotropic Mechanics and Architecture for Tendon/Ligament Repair and Regeneration

Rupture of tendons and ligaments (T/L) is a major clinical challenge due to T/L possess anisotropic mechanical properties and hierarchical structures. Here, to imitate these characteristics, an approach is presented by fabricating hybrid nanofibrous composites. First, hybrid fiber-reinforced yarns are fabricated via successively electrospinning poly(L-lactide-co-ε-caprolactone) (PLCL) and gelatin (Ge) nanofibers onto polyethylene terephthalate (PET) fibers to improve biodurability and biocompatibility. Then, by comparing different manufacturing methods, the knitted structure succeeds in simulating anisotropic mechanical properties, even being stronger than natural ligaments, and possessing comfort compliance superior to clinically used ligament advanced reinforcement system (LARS) ligament. Moreover, after inoculation with tendon-derived stem cells and transplantation in vivo, hybrid nanofibrous composites are integrated with native tendons to guide surrounding tissue ingrowth due to the highly interconnected and porous structure. The knitted hybrid nanofibrous composites are also ligamentized and remodeled in vivo to promote tendon regeneration. Specifically, after the use of optimized anisotropic hybrid nanofibrous composites to repair tendon, the deposition of tendon-associated extracellular matrix proteins is more significant. Thus, this study indicates a strategy of manufacturing anisotropic hybrid nanofibrous composites with superior mechanical properties and good histocompatibility for clinical reconstruction.

A regeneration process-matching scaffold with appropriate dynamic mechanical properties and spatial adaptability for ligament reconstruction

Ligament regeneration is a complicated process that requires dynamic mechanical properties and allowable space to regulate collagen remodeling. Poor strength and limited space of currently available grafts hinder tissue regeneration, yielding a disappointing success rate in ligament reconstruction. Matching the scaffold retreat rate with the mechanical and spatial properties of the regeneration process remains challenging. Herein, a scaffold matching the regeneration process was designed via regulating the trajectories of fibers with different degradation rates to provide dynamic mechanical properties and spatial adaptability for collagen infiltration. This core-shell structured scaffold exhibited biomimetic fiber orientation, having tri-phasic mechanical behavior and excellent strength. Besides, by the sequential material degradation, the available space of the scaffold increased from day 6 and remained stable on day 24, consistent with the proliferation and deposition phase of the native ligament regeneration process. Furthermore, mature collagen infiltration and increased bone integration in vivo confirmed the promotion of tissue regeneration by the adaptive space, maintaining an excellent failure load of 67.65% of the native ligament at 16 weeks. This study proved the synergistic effects of dynamic strength and adaptive space. The scaffold matching the regeneration process is expected to open new approaches in ligament reconstruction.

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Regeneration process-matching scaffold was made via regulating fiber trajectory.

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The scaffold showed tri-phasic mechanical behavior and fatigue properties.

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Matching repair process with dynamic mechanical property and spatial adaptability.

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A feasible substitute for the T/L reconstruction by spatial adaptability.

Central femoral tunnel placement can reduce stress and strain around bone tunnels and graft more than anteromedial femoral tunnel in anterior cruciate ligament reconstruction

The present study investigated the effects of anteromedial (AM) and central femoral footprint placement on stress and strain distribution around the femoral and tibial tunnel and graft following anterior cruciate ligament reconstruction (ACLR). A three-dimensional (3D) reconstructed knee model was validated and used for simulating ACLR by finite element analysis. A combined loading during normal human walking was applied to the knee models using different anatomic femoral tunnel placement at 20° knee flexion. The results of von Mises stress and principal strain at the entrances of the femoral and tibial tunnel and ACL graft was determined. The peak von Mises stress and the maximum principal strain in the AM footprint group were 8.78 MPa and 8850.89 μ-strain at the entrance of femoral tunnel, and 5.29 MPa and 5553.27 μ-strain at the entrance of tibial tunnel. The results in the AM footprint group were higher than that in the central footprint group. The peak von Mises stress around the ACL graft following AM footprint ACLR was 28.63 MPa, higher than that following the central footprint ACLR. The AM footprint ACLR generated more significant peak von Mises stress and maximum principal strain around the entrances of femoral and tibial tunnel and the graft than the central footprint. The present results are of clinical relevance as they can provide a better understanding of tunnel enlargement and graft failure.

Melt-Spun, Cross-Section Modified Polycaprolactone Fibers for Use in Tendon and Ligament Tissue Engineering

Tissue Engineering is considered a promising route to address existing deficits of autografts and permanent synthetic prostheses for tendons and ligaments. However, the requirements placed on the scaffold material are manifold and include mechanical, biological and degradation-related aspects. In addition, scalable processes and FDA-approved materials should be applied to ensure the transfer into clinical practice. To accommodate these aspects, this work focuses on the high-scale fabrication of high-strength and highly oriented polycaprolactone (PCL) fibers with adjustable cross-sectional geometry and degradation kinetics applying melt spinning technology. Four different fiber cross-sections were investigated to account for potential functionalization and cell growth guidance. Mechanical properties and crystallinity were studied for a 24-week exposure to phosphate-buffered saline (PBS) at 37 °C. PCL fibers were further processed into scaffolds using multistage circular braiding with three different hierarchical structures. One structure was selected based on its morphology and scaled up in thickness to match the requirements for a human anterior cruciate ligament (ACL) replacement. Applying a broad range of draw ratios (up to DR9.25), high-strength PCL fibers with excellent tensile strength (up to 69 cN/tex) could be readily fabricated. The strength retention after 24 weeks in PBS at 37 °C was 83–93%. The following braiding procedure did not affect the scaffolds’ mechanical properties as long as the number of filaments and the braiding angle remained constant. Up-scaled PCL scaffolds resisted loads of up to 4353.88 ± 37.30 N, whilst matching the stiffness of the human ACL (111–396 N/mm). In conclusion, this work demonstrates the fabrication of highly oriented PCL fibers with excellent mechanical properties. The created fibers represent a promising building block that can be further processed into versatile textile implants for tissue engineering and regenerative medicine.

Long-term outcomes of surgery using the Ligament Advanced Reinforcement System as treatment for anterior cruciate ligament tears

AIMS

The aim of this prospective study was to assess the long-term clinical, radiological, functional, and quality of life (QoL)-related outcome of patients treated with the synthetic Ligament Advanced Reinforcement System (LARS) device for anterior cruciate ligament (ACL) rupture.

METHODS

A total of 41 patients who underwent ACL reconstruction with the LARS device (mean age 39.8 years (SD 12.1 ); 32% females (n = 13)) were prospectively included between August 2001 and March 2005. MRI scans and radiographs were performed at a median follow-up of 2.0 years (interquartile range (IQR) 1.3 to 3.0; n = 40) and 12.8 years (IQR 12.1 to 13.8; n = 22). Functional and QoL-related outcome was assessed in 29 patients at a median follow-up of 12.8 years (IQR 12.0 to 14.0) and clinically reconfirmed at latest median follow-up of 16.5 years (IQR 15.5 to 17.9). International Knee Documentation Committee (IKDC) and Tegner scores were obtained pre- and postoperatively, and Lysholm score postoperatively only. At latest follow-up, range of motion, knee stability tests, 36-Item Short Form Health Survey (SF-36), and IKDC scores were ascertained. Complications and reoperations during follow-up were documented.

RESULTS

Cumulative complication rate was 66% (n = 27), with 11 developing within one year from surgery and 16 after one year (including five patients with both early and late complications). Ten graft failures (24%) and eight cases of reactive synovitis were observed (20%). All 11 patients with early complications and ten with late complications underwent reoperation (including five with another surgical procedure for early complications), amounting to a cumulative reoperation rate of 51% (n = 21). Revision ACL reconstruction was performed in one patient (2.4%). Median IKDC at latest follow-up was 89.7 (IQR 78.2 to 93.1), being significantly worse in the event of previous complications. Lachman test was positive in 56% (n = 15) of reconstructed knees. All norm-based SF-36 items were at or above median at latest follow-up, and did not differ depending on development of complications.

CONCLUSION

Despite good functional and QoL-related results in the long term, the cumulative complication rate of 66%, including graft failures and reactive synovitis, has to be viewed with great concern. Cite this article: Bone Joint J 2022;104-B(2):242-248.

The Femoral Tunnel Drilling Angle at 45° Coronal and 45° Sagittal Provided the Lowest Peak Stress and Strain on the Bone Tunnels and Anterior Cruciate Ligament Graft

Purpose: The aims of this study were to 1) investigate the effects of femoral drilling angle in coronal and sagittal planes on the stress and strain distribution around the femoral and tibial tunnel entrance and the stress distribution on the graft, following anterior cruciate ligament reconstruction (ACLR), 2) identify the optimal femoral drilling angle to reduce the risk of the tunnel enlargement and graft failure.

Methods: A validated three-dimensional (3D) finite element model of a healthy right cadaveric knee was used to simulate an anatomic ACLR with the anteromedial (AM) portal technique. Combined loading of 103.0 N anterior tibial load, 7.5 Nm internal rotation moment, and 6.9 Nm valgus moment during normal human walking at joint flexion of 20° was applied to the ACLR knee models using different tunnel angles (30°/45°/60° and 45°/60° in the coronal and sagittal planes, respectively). The distribution of von Mises stress and strain around the tunnel entrances and the graft was calculated and compared among the different finite element ACLR models with varying femoral drilling angles.

Results: With an increasing coronal obliquity drilling angle (30° to 60°), the peak stress and maximum strain on the femoral and tibial tunnel decreased from 30° to 45° and increased from 45° to 60°, respectively. With an increasing sagittal obliquity drilling angle (45° to 60°), the peak stress and the maximum strain on the bone tunnels increased. The lowest peak stress and maximum strain at the ACL tunnels were observed at 45° coronal/45° sagittal drilling angle (7.5 MPa and 7,568.3 μ-strain at the femoral tunnel entrance, and 4.0 MPa and 4,128.7 μ-strain at the tibial tunnel entrance). The lowest peak stress on the ACL graft occurred at 45° coronal/45° sagittal (27.8 MPa) drilling angle.

Conclusions: The femoral tunnel drilling angle could affect both the stress and strain distribution on the femoral tunnel, tibial tunnel, and graft. A femoral tunnel drilling angle of 45° coronal/ 45° sagittal demonstrated the lowest peak stress, maximum strain on the femoral and tibial tunnel entrance, and the lowest peak stress on the ACL graft.

Hydrogel, Electrospun and Composite Materials for Bone/Cartilage and Neural Tissue Engineering

Injuries of the bone/cartilage and central nervous system are still a serious socio-economic problem. They are an effect of diversified, difficult-to-access tissue structures as well as complex regeneration mechanisms. Currently, commercially available materials partially solve this problem, but they do not fulfill all of the bone/cartilage and neural tissue engineering requirements such as mechanical properties, biochemical cues or adequate biodegradation. There are still many things to do to provide complete restoration of injured tissues. Recent reports in bone/cartilage and neural tissue engineering give high hopes in designing scaffolds for complete tissue regeneration. This review thoroughly discusses the advantages and disadvantages of currently available commercial scaffolds and sheds new light on the designing of novel polymeric scaffolds composed of hydrogels, electrospun nanofibers, or hydrogels loaded with nano-additives.

Differences in artificial ligament graft osseointegration of the anterior cruciate ligament in a sheep model: a comparison between interference screw and cortical suspensory fixation

Background

Interference screws are the most common femoral fixation for anterior cruciate ligament (ACL) reconstruction with polyethylene terephthalate (PET) artificial ligaments. However, interference screws have several disadvantages, such as the risk of one tunnel blowout and damage to the graft. Suspensory fixations have the advantages of high tensile strength and promotion of graft bone contact. The purpose of this study was to compare PET artificial ligament graft osseointegration between interference screw fixation (ISF) and cortical suspensory fixation (CSF) for ACL reconstruction.

Methods

Forty sheep underwent ACL reconstruction of the right knee with PET artificial ligament. The graft was fixed with ISF or CSF for femoral fixation. Animals were randomly assigned to the ISF (n=20) or the CSF (n=20) groups. The sheep were sacrificed at 3 or 12 months postoperatively for biomechanical tests, micro computed tomography (micro-CT) scans, and histological assessments.

Results

The mean load-to-failure between the CSF group (836±355 N) appeared higher than that of the ISF group (604±277 N) at 3 months, but no significant difference was detected between the groups (P=0.24). At 12 months, there was also no significant difference in load-to-failure between the CSF and ISF groups (1,194±350 vs. 1,097±764 N; P=0.78). According to the micro-CT scan results, the femoral bone tunnel diameter of the ISF group appeared larger than that of the CSF group at 3 months (12±1 vs. 10±1 mm; P=0.02) and similar to that of the CSF group at 12 months (12±1 vs. 11±2 mm; P=0.38). Furthermore, histological results showed that at the graft-tunnel interface of the femoral tunnel aperture, disoriented fibers formed in the ISF group while oriented and dense fibers formed in the CSF group.

Conclusions

ACLR with synthetic ligament by cortical suspension devices with adjustable loops demonstrated a better graft-bone healing capacity at the femoral tunnel aperture compared with that from titanium interference screws over 12 months postoperatively. No significant difference was found in biomechanical strength between the two fixation methods during the early healing stage.

Acceleration of ligamentization and osseointegration processes after anterior cruciate ligament reconstruction with autologous tissue-engineered polyethylene terephthalate graft

Background

Despite the advantages of excellent mechanical properties for rapid return to sports and early rehabilitation after anterior cruciate ligament (ACL) reconstruction with polyethylene terephthalate (PET) artificial ligament, the graft failure rate during long-term follow-up is relatively high due to poor graft-host incorporation. The purpose of the present study was to investigate the effect of autologous tissue-engineered PET (ATE-PET) grafts on osseointegration and ligamentization after ACL reconstruction.

Methods

Forty-eight New Zealand white rabbits were randomly divided into PET group (n=24) and ATE-PET group (n=24). In the ATE-PET group, the rabbits initially underwent subcutaneous implantation of the PET ligament. Two weeks later, unilateral ipsilateral ACL reconstruction was performed using an ATE-PET graft. In the PET group, the rabbits underwent ACL reconstruction using PET grafts as controls. Macroscopic observation, micro-computed tomography, histological and immunofluorescent staining, and biomechanical tests were conducted to evaluate the effects at 4 and 12 weeks postoperatively.

Results

The ATE-PET graft was highly pre-vascularized with myofibroblast aggregation after two weeks of subcutaneous implantation. With regard to the intraosseous part of the graft, the ATE-PET group had significantly higher bone mineral density and bone volume/total volume ratio at 12 weeks. Histologically, the width of the interface between the graft and bone was smaller. Regarding the intra-articular part, thicker tissue coverage with a glossy appearance was observed in the ATE-PET group at 12 weeks on macroscopic observation. Histological staining also showed more collagen fibers grew in the grafts with fewer inflammatory reactions of the ATE-PET group at both 4 and 12 weeks. Immunofluorescently, both α-SMA-positive vessels and α-SMA-positive myofibroblasts were found to be significantly greater around the graft in the ATE-PET group at 4 weeks and markedly declined at 12 weeks. Moreover, the ATE-PET group presented significantly greater failure load and stiffness than the PET group at 12 weeks (53.7±5.4 vs. 42.5±4.5 N, P<0.01; 12.9±3.0 vs. 9.8±1.3 N/mm, P=0.04).

Conclusions

The ATE-PET artificial ligament with pre-vascularization and myofibroblast aggregation could effectively accelerate intra-articular graft ligamentization and intraosseous graft osseointegration, thus enhancing the biomechanical properties after ACL reconstruction in a rabbit model.

A Cell-free Biodegradable Synthetic Artificial Ligament for the Reconstruction of Anterior Cruciate Ligament in a Rat Model

Traditional Anterior Cruciate Ligament (ACL) reconstruction is commonly performed using an allograft or autograft and possesses limitations such as donor site morbidity, decreased range of motion, and potential infection. However, a biodegradable synthetic graft could greatly assist in the prevention of such restrictions after ACL reconstruction. In this study, artificial grafts were generated using "wet" and "dry" electrospinning processes with a biodegradable elastomer, poly (ester urethane) urea (PEUU), and were evaluated in vitro and in vivo in a rat model. Four groups were established: (1) Wet PEUU artificial ligament, (2) Dry PEUU artificial ligament, (3) Dry polycaprolactone artificial ligament (PCL), and (4) autologous flexor digitorum longus tendon graft. Eight weeks after surgery, the in vivo tensile strength of wet PEUU ligaments had significantly increased compared to the other synthetic ligaments. These results aligned with increased infiltration of host cells and decreased inflammation within the wet PEUU grafts. In contrast, very little cellular infiltration was observed in PCL and dry PEUU grafts. Micro-computed tomography analysis performed at 4 and 8 weeks postoperatively revealed significantly smaller bone tunnels in the tendon autograft and wet PEUU groups. The Wet PEUU grafts served as an adequate functioning material and allowed for the creation of tissues that closely resembled the ACL.

Controllable four axis extrusion-based additive manufacturing system for the fabrication of tubular scaffolds with tailorable mechanical properties

Many tubular tissues such as blood vessels and trachea can suffer long-segmental defects through trauma and disease. With current limitations in the use of autologous grafts, the need for a synthetic substitute is of continuous interest as possible alternatives. Fabrication of these tubular organs is commonly done with techniques such as electrospinning and melt electrowriting using a rotational collector. Current additive manufacturing (AM) systems do not commonly implement the use of a rotational axis, which limits their application for the fabrication of tubular scaffolds. In this study, a four axis extrusion-based AM system similar to fused deposition modeling (FDM) has been developed to create tubular hollow scaffolds. A rectangular and a diamond pore design were further investigated for mechanical characterization, as a standard and a biomimicry pore geometry respectively. We demonstrated that in the radial compression mode the diamond pore design had a higher Young's modulus (19,8 ± 0,7 MPa compared to 2,8 ± 0,5 MPa), while in the longitudinal tensile mode the rectangular pore design had a higher Young's modulus (5,8 ± 0,2 MPa compared to 0,1 ± 0,01 MPa). Three-point bending analyses revealed that the diamond pore design is more resistant to luminal collapse compared to the rectangular design. This data showed that by changing the scaffold pore design, a wide range of mechanical properties could be obtained. Furthermore, a full control over scaffold design and geometry can be achieved with the developed 4-axis extrusion-based system, which has not been reported with other techniques. This flexibility allow the manufacturing of scaffolds for diverse tubular tissue regeneration applications by designing suitable deposition patterns to match their mechanical pre-requisites.

Natural Biomineralization-Inspired Magnesium Silicate Composite Coating Upregulates Osteogenesis, Enabling Strong Anterior Cruciate Ligament Graft-Bone Healing In Vivo

Artificial ligaments prepared from polyethylene terephthalate (PET) are widely accepted for clinical anterior cruciate ligament (ACL) reconstruction to recover the native function of knee joints. However, due to the chemical inertness and hydrophobicity of PET, improving its bioactivity and promoting graft-bone integration are still great challenges. Inspired by the natural biomineralization process on the surface of a historical stone, in this study, a bioactive organic/inorganic composite coating that is composed of poly(allylamine hydrochloride) and chondroitin sulfate with magnesium silicate (MgSiO₃) doping is developed for surface modification of PET (MSPC-PET). This composite coating promotes adhesion and proliferation of bone marrow mesenchymal stem cells (BMSCs) and its bioactive inorganic components (MgSiO₃) could induce osteogenic differentiation of BMSCs. Furthermore, an in vivo experiment indicated that this composite coating might afford superior graft-bone integration between MSPC-PET and the host bone tunnel, and fibrous scar tissue formation was also inhibited. More importantly, a biomechanical analysis proved that there was a strong integration between the MSPC-PET graft and the bone tunnel, which will improve biomechanical properties for the restoration of ACL function. This study shows that this bioactive composite coating-modified PET graft for the ACL reconstruction can effectively achieve good integration of ACL artificial grafts and bone tunnels and prevent surgical failure.

Frame Coating of Single-Walled Carbon Nanotubes in Collagen on PET Fibers for Artificial Joint Ligaments

The coating formation technique for artificial knee ligaments was proposed, which provided tight fixation of ligaments of polyethylene terephthalate (PET) fibers as a result of the healing of the bone channel in the short-term period after implantation. The coating is a frame structure of single-walled carbon nanotubes (SWCNT) in a collagen matrix, which is formed by layer-by-layer solidification of an aqueous dispersion of SWCNT with collagen during spin coating and controlled irradiation with IR radiation. Quantum mechanical method SCC DFTB, with a self-consistent charge, was used. It is based on the density functional theory and the tight-binding approximation. The method established the optimal temperature and time for the formation of the equilibrium configurations of the SWCNT/collagen type II complexes to ensure maximum binding energies between the nanotube and the collagen. The highest binding energies were observed in complexes with SWCNT nanometer diameter in comparison with subnanometer SWCNT. The coating had a porous structure-pore size was 0.5-6 μm. The process of reducing the mass and volume of the coating with the initial biodegradation of collagen after contact with blood plasma was demonstrated. This is proved by exceeding the intensity of the SWCNT peaks G and D after contact with the blood serum in the Raman spectrum and by decreasing the intensity of the main collagen bands in the SWCNT/collagen complex frame coating. The number of pores and their size increased to 20 μm. The modification of the PET tape with the SWCNT/collagen coating allowed to increase its hydrophilicity by 1.7 times compared to the original PET fibers and by 1.3 times compared to the collagen coating. A reduced hemolysis level of the PET tape coated with SWCNT/collagen was achieved. The SWCNT/collagen coating provided 2.2 times less hemolysis than an uncoated PET implant. MicroCT showed the effective formation of new bone and dense connective tissue around the implant. A decrease in channel diameter from 2.5 to 1.7 mm was detected at three and, especially, six months after implantation of a PET tape with SWCNT/collagen coating. MicroCT allowed us to identify areas for histological sections, which demonstrated the favorable interaction of the PET tape with the surrounding tissues. In the case of using the PET tape coated with SWCNT/collagen, more active growth of connective tissue with mature collagen fibers in the area of implantation was observed than in the case of only collagen coating. The stimulating effect of SWCNT/collagen on the formation of bone trabeculae around and inside the PET tape was evident in three and six months after implantation. Thus, a PET tape with SWCNT/collagen coating has osteoconductivity as well as a high level of hydrophilicity and hemocompatibility.

Stiffness and shape of the ACL graft affects tunnel enlargement and graft wear

PURPOSE

Tunnel enlargement and graft rupture are common complications associated with ACL reconstruction (ACLR). This study aims to explore how variations in graft stiffness and shape affect the strain energy density (SED) around bone tunnel entrances and stress on the graft and subsequently influencing the level of tunnel enlargement and graft wear.

METHODS

Finite element ACLR models were developed using different graft stiffnesses (323 N/mm, 545 N/mm and 776 N/mm) and shapes (circular and elliptical). The models were subjected to a combined loading of 103 N anterior tibial load, 7.5 Nm internal tibial moment, and 6.9 Nm valgus tibial moment at joint flexion of 30°. SED at tunnel entrances and stresses on the graft was recorded and compared among the different models.

RESULTS

Increasing the graft stiffness resulted in greater stress on the graft (17.2, 24.4 and 31.7 MPa for graft stiffnesses of 323 N/mm, 545 N/mm and 776 N/mm), but had little effect on the SED reduction around the tunnel entrances. Changing the cross section of the graft from circular to elliptical caused an additional reduction in SED (56.8 vs 2.8 kJ/m³) at the posterior zone of the femoral tunnel entrance and increased the stress on the graft (31.7 MPa vs 38.9 MPa).

CONCLUSIONS

This study recommends using ACL grafts with lower stiffness and a circular cross section to reduce tunnel enlargement and graft wear following ACLR.

Histological analysis of ACL reconstruction failures due to synthetic-ACL (LARS) ruptures

INTRODUCTION

Anterior Cruciate Ligament (ACL) reconstruction is an established surgical procedure. Synthetic ligaments represent an option for ACL reconstruction. Their popularity declined for the raising concerns due to re-ruptures, knee synovitis and early arthritis related to I and II generation artificial ligaments. The introduction of a III generation synthetic ligament (Ligament Advanced Reinforcement System-LARS) permitted renewed interest in the adoption of this kind of graft. Main purpose of our study was to describe the histological findings on samples obtained from a consecutive series of ACL revision surgeries due to LARS ACL reconstruction failures. Secondary aim was to determine the reason for LARS rupture.

METHODS

In a period between 2016 and 2018 eleven patients underwent ACL revision surgery due to LARS ACL reconstruction failure. At the time of the arthroscopic procedure, samples of synovial membrane and remnants of the torn LARS were sent to the Pathological-Anatomy Institute of our Hospital for a histological analysis.

RESULTS

Histological analysis of the synovial tissues confirmed the arthroscopic evidence of synovitis mainly characterized by chronic inflammation with predominance of multinucleated giant cells. The adoption of polarized light microscopy revealed the presence of brightly bi-refractive material (LARS wear particles) in the synovial tissue; at higher magnification wear debris were detected inside the cytoplasma of multi nucleated cells. The histological analysis of the removed LARS revealed a surrounding typical foreign body reaction with poor signs of fibrovascular ingrowth of the synthetic ligament.

CONCLUSIONS

Our findings could not clearly advocate a unique mechanism of LARS-ACL reconstruction failure: biologic issues (poor tissue ingrowth) and mechanical issues (fibers properties and tunnel position) probably concur in a multi factorial manner. ACL reconstruction using artificial ligaments can not be considered a simple surgery. Artificial augments require some expertise and could therefore achieve better results if used by skilled sport surgeons other than trainees or low volume surgeons. The Authors believe that ACL reconstruction with synthetic devices still have restricted indications for selected patients (e.g. elderly patients who require a fast recovery, professional athlete, autologous tendons not available and/or refusing donor tendons). Our study arises additional suspicion on the unresponsiveness of synthetic fibers and claim some concern in the implantation of synthetic devices.

Role of Biomaterials and Controlled Architecture on Tendon/Ligament Repair and Regeneration

Engineering synthetic scaffolds to repair and regenerate ruptured native tendon and ligament (T/L) tissues is a significant engineering challenge due to the need to satisfy both the unique biological and biomechanical properties of these tissues. Long-term clinical outcomes of synthetic scaffolds relying solely on high uniaxial tensile strength are poor with high rates of implant rupture and synovitis. Ideal biomaterials for T/L repair and regeneration need to possess the appropriate biological and biomechanical properties necessary for the successful repair and regeneration of ruptured tendon and ligament tissues.

High-Strength Fiber-Reinforced Composite Hydrogel Scaffolds as Biosynthetic Tendon Graft Material

The development of suitable synthetic scaffolds for use as human tendon grafts to repair tendon ruptures remains a significant engineering challenge. Previous synthetic tendon grafts have demonstrated suboptimal tissue ingrowth and synovitis due to wear particles from fiber-to-fiber abrasion. In this study, we present a novel fiber-reinforced hydrogel (FRH) that mimics the hierarchical structure of the native human tendon for synthetic tendon graft material. Ultrahigh molecular weight polyethylene (UHMWPE) fibers were impregnated with either biosynthetic polyvinyl alcohol/gelatin hydrogel (FRH-PG) or with polyvinyl alcohol/gelatin + strontium-hardystonite (Sr-Ca₂ZnSi₂O₇, Sr-HT) composite hydrogel (FRH-PGS). The scaffolds were fabricated and assessed to evaluate their suitability for tendon graft applications. The microstructure of both FRH-PG and FRH-PGS showed successful impregnation of the hydrogel component, and the tendon scaffolds exhibited equilibrium water content of ∼70 wt %, similar to the values reported for native human tendon, compared to ∼50 wt % water content retained in unmodified UHMWPE fibers. The tensile strength of FRH-PG and FRH-PGS (77.0-81.8 MPa) matched the range of human Achilles' tendon tensile strengths reported in the literature. In vitro culture of rat tendon stem cells showed cell and tissue infiltration into both FRH-PG and FRH-PGS after 2 weeks, and the presence of Sr-HT ceramic particles influenced the expression of tenogenic markers. On the other hand, FRH-PG supported the proliferation of murine C2C12 myoblasts, whereas FRH-PGS seemingly did not support it under static culture conditions. In vivo implantation of FRH-PG and FRH-PGS scaffolds into full-thickness rat patellar tendon defects showed good collagenous tissue ingrowth into these scaffolds after 6 weeks. This study demonstrates the potential viability for our FRH-PG and FRH-PGS scaffolds to be used for off-the-shelf biosynthetic tendon graft material.

"Swiss roll"-like bioactive hybrid scaffolds for promoting bone tissue ingrowth and tendon-bone healing after anterior cruciate ligament reconstruction

The choice of grafts for anterior cruciate ligament (ACL) reconstruction is a critical issue in sports medicine. Previous studies have revealed that scaffolds prepared from a single material could not achieve complete integration between the graft and autogenous bone tunnel. To solve this problem, we hypothesize that combining degradable scaffolds with nondegradable scaffolds can produce a novel hybrid ligament with the advantages of both types of scaffolds. In this study, a bone morphogenetic protein 7 (BMP-7)-loaded polycaprolactone (PCL) nanofibrous membrane was first manufactured as the degradable part of the hybrid ligament by using layer-by-layer (LbL) self-assembly. Then, we fabricated a multifunctional novel hybrid ligament by rolling up this nanofibrous membrane and polyethylene terephthalate (PET) mesh fabric (nondegradable part) into a "swiss roll" structure. The in vitro experimental results showed that this hybrid ligament could significantly improve the biocompatibility of pure PET ligament and further promote cell mineralization. The in vivo experimental results showed that this unique structure significantly promoted the integration of hybrid ligaments and bone tunnels, thereby achieving real "ligamentization" after ACL reconstruction surgery. These results suggest that this novel hybrid biomimetic artificial ligament scaffold provides a new direction for graft selection for ACL reconstruction.

Implantation Time Has No Effect on the Morphology and Extent of Previously Reported "Degradation" of Prolene Pelvic Mesh

OBJECTIVES

Prolene polypropylene ("Prolene") meshes demonstrate no in vivo degradation, yet some claim degradation continues until no more Prolene polypropylene can be oxidized. We studied whether implantation time affects the morphology/extent of previously reported as cracking/degradation of completely cleaned Prolene explants.

METHODS

Urogynecological explants (248 patients) were collected. After excluding non-Prolene/unknown meshes and those without known implantation times, completely cleaned explants (n = 205; 0.2-14.4 years implantation) were analyzed with light microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy. Based on implant times and storage (fixative or dry), representative specimens were randomly selected for comparison. Controls were unused ("exemplar") TVT specimens with and without intentional oxidation via ultraviolet light exposure.

RESULTS

Prolene explants included 31 dry (18 TVT; 7 Prolift; 4 Gynemesh; 2 others) and 174 wet (87 TVT; 47 Prolift; 10 Gynemesh; 30 others) specimens. Specimens had similar morphologies before cleaning. Progressive cleaning removed tissue and cracked tissue-related material exposing smooth, unoxidized, and nondegraded fibers, with no visible gradient-type/ductile damage. Fourier transform infrared spectroscopy of the explants confirmed progressive loss of proteins. Cleaning intentionally oxidized exemplars did not remove oxidized carbonyl frequencies and showed deep cracks and gross fiber rupture/embrittlement, unlike the explants and nonoxidized exemplars.

CONCLUSIONS

If in vivo Prolene degradation exists, there should be wide-ranging crack morphology and nonuniform crack penetration, as well as more cracking, degradation, and physical breakage for implants of longer implantation times, but this was not the case. There is no morphologic or spectral/chemical evidence of Prolene mesh degradation after up to 14.4 years in vivo.

Evaluation of a bioengineered ACL matrix's osteointegration with BMP-2 supplementation

A poly (l-lactic) acid bioengineered anterior cruciate ligament (ACL) matrix has previously demonstrated the ability to support tissue regeneration in a rabbit ACL reconstruction model. The matrix was designed for optimal bone and ligament regeneration by developing a matrix with differential pore sizes in its bone and ligament compartments. Building upon past success, we designed a new bioengineered ACL matrix that is easier to install and can be used with endobutton fixation during ACL reconstruction. To achieve this, a new braiding procedure was developed to allow the matrix to be folded in half, making two-limbs, while maintaining its bone and ligament compartments. The osteointegration of the matrix with and without bone morphogenetic protein 2 (BMP-2) supplementation was evaluated in a rabbit ACL reconstruction model. Two doses of BMP-2 were evaluated, 1 and 10 μg, and delivered by saline injection into the bone tunnel at the end of surgery. A fibrous matrix-to-bone interface with occasional Sharpey’s fibers was the primary mode of osteointegration observed. The matrix was also found to support a fibrocartilage matrix-to-bone interface. In some cases, the presence of chondrocyte-like cells was observed at the aperture of the bone tunnel and the center of the matrix within the bone tunnel. Treatment with BMP-2 was associated with a trend towards smaller bone tunnel cross-sectional areas, and 1 μg of BMP-2 was found to significantly enhance osteoid seam width in comparison with no BMP-2 or 10 μg of BMP-2 treatment. Regenerated tissue was well organized within the bioengineered ACL matrix and aligned with the poly (l-lactic) acid fibers. Disorganized tissue was found between the two-limbs of the bioengineered ACL matrix and hypothesized to be due to a lack of structural scaffolding. This study suggests that the bioengineered ACL matrix can undergo similar modes of osteointegration as current autografts and allografts, and that BMP-2 treatment may enhance osteoblastic activity within the bone tunnels.

Primary ACL reconstruction using the LARS device is associated with a high failure rate at minimum of 6-year follow-up

PURPOSE

The Ligament Augmentation and Reconstruction System (LARS^®) is a synthetic ligament consisting of fibres made of polyethylene terephthalate. Despite the LARS being used as an anterior cruciate ligament (ACL) device for nearly 30 years and the well-documented complications from earlier synthetic ligament designs, there is a paucity of published medium- to long-term results. The aim of this study is to report the clinical and functional outcomes after ACL reconstruction using the LARS at a minimum follow-up of 6 years.

METHODS

Results of a single surgeon's entire cohort of 55 patients who underwent primary LARS ACL surgery were reviewed at a median of 7.8 years (6.0-9.4). Patient-reported outcome measures including the International Knee Documentation Committee (IKDC) score and 36-Item Short Form Health Survey (SF-36) were collected and clinical assessment consisted of range of motion (ROM) and the KT-1000 arthrometer to assess the side-side difference in the operative and non-operative knee. Mechanical failures of the graft were confirmed at revision surgery and a survivorship analysis was performed using the Kaplan-Meier method.

RESULTS

The overall mechanical failure rate was 17/51 (33.3%) with ruptures occurring at a median 3.9 years (0.6-8.8 years) following primary LARS ACL surgery. Secondary operative procedures were performed in 39.2% of patients. For intact grafts, there was no statistically significant difference is side-to-side ROM or anterior knee laxity and subjective scores revealed a median IKDC subjective score of 85.1 (26.4-100) and SF-36 physical component score of 94.1.

CONCLUSION

The rates of LARS ACL construct failure (33.3%) in this cohort are high and based on these results the LARS should not be considered as a graft option for primary ACL reconstruction.

LEVEL OF EVIDENCE

III, cohort study.

Scaffolds in the management of massive rotator cuff tears: current concepts and literature review

Injuries to the rotator cuff (RC) are common and could alter shoulder kinematics leading to arthritis. Synthetic and biological scaffolds are increasingly being used to bridge gaps, augment RC repair and enhance healing potential. Our review evaluates the clinical applications, safety and outcome following the use of scaffolds in massive RC repair.

A search was performed using EBSCO-Hosted Medline, CINAHL, Cochrane and PubMed using various combinations of the keywords ‘rotator cuff’, ‘scaffold’, ‘biological scaffold’, ‘massive rotator cuff tear’ ‘superior capsular reconstruction’ and ‘synthetic scaffold’ between 1966 and April 2018. The studies that were most relevant to the research question were selected. All articles relevant to the subject were retrieved, and their bibliographies hand searched.

Synthetic, biosynthetic and biological scaffolds are increasingly being used for the repair/reconstruction of the rotator cuff. Allografts and synthetic grafts have revealed more promising biomechanical and early clinical results than xenografts. The retear rates and local inflammatory reactions were alarmingly high in earlier xenografts. However, this trend has reduced considerably with newer versions. Synthetic patches have shown lower retear rates and better functional outcome than xenografts and control groups.

The use of scaffolds in the treatment of rotator cuff tear continues to progress. Analysis of the current literature supports the use of allografts and synthetic grafts in the repair of massive cuff tears in reducing the retear rate and to provide good functional outcome. Though earlier xenografts have been fraught with complications, results from newer ones are promising. Prospective randomized controlled trials from independent centres are needed before widespread use can be recommended.

Cite this article: EFORT Open Rev 2019;4:557-566. DOI: 10.1302/2058-5241.4.180040

Mechanical and Cytocompatibility Evaluation of UHMWPE/PCL/Bioglass® Fibrous Composite for Acetabular Labrum Implant

In this study, a fibrous composite was developed as synthetic graft for labral reconstruction treatment, comprised of ultra-high molecular weight polyethylene (UHMWPE) fabric, ultrafine fibre of polycaprolactone (PCL), and 45S5 Bioglass®. This experiment aimed to examine the mechanical performance and cytocompatibility of the composite. Electrospinning and a slurry dipping technique were applied for composite fabrication. To assess the mechanical performance of UHMWPE, tensile cyclic loading test was carried out. Meanwhile, cytocompatibility of the composite on fibroblastic cells was examined through a viability assay, as well as SEM images to observe cell attachment and proliferation. The mechanical test showed that the UHMWPE fabric had a mean displacement of 1.038 mm after 600 cycles, approximately 4.5 times greater resistance compared to that of natural labrum, based on data obtained from literature. A viability assay demonstrated the predominant occupation of live cells on the material surface, suggesting that the composite was able to provide a viable environment for cell growth. Meanwhile, SEM images exhibited cell adhesion and the formation of cell colonies on the material surface. These results indicated that the UHMWPE/PCL/Bioglass® composite could be a promising material for labrum implants.

Foreign Body Reaction Associated With Artificial LARS Ligaments: A Retrieval Study

Background:

Artificial ligaments have been developed and used in the treatment of ligamentous injuries since the 1970s. The early generation of artificial ligaments showed promising short-term results but resulted in high rates of rupture and inflammatory reaction in the surrounding tissues.

Purpose:

To determine whether the use of Ligament Augmentation and Reconstruction System (LARS) ligaments is associated with the development of intra-articular foreign body reaction.

Study Design:

Case series; Level of evidence, 4.

Methods:

LARS ligaments were explanted from 15 patients under 6 consultant orthopaedic surgeons at 8 surgical centers. Of these, 14 explanted samples were sent for macroscopic and histological analysis, with the 1 remaining sample sent for scanning electron microscopy, to assess for inflammatory change as well as the degree of fibrous tissue ingrowth.

Results:

We observed a foreign body reaction in 10 of 14 explanted LARS ligaments. Seven samples demonstrated fibrous tissue ingrowth, with 5 producing only focal or incomplete ingrowth. The 2 samples with extensive fibrous coverage were completely free of any foreign body reaction, while all 5 remaining samples with only focal or partial fibrous ingrowth were associated with at least some degree of harmful immune response.

Conclusion:

The LARS ligament is still associated with a clinically significant degree of foreign body reaction despite the LARS Company’s efforts to reduce complications through improved design. The development and completion of fibrous tissue ingrowth may work to reduce the occurrence of a foreign body reaction.

Impact of chemical and physical treatments on the mechanical properties of poly(ε-caprolactone) fibers bundles for the anterior cruciate ligament reconstruction

The anterior cruciate ligament rupture is one of the most common sport injuries. Due to ligaments’ poor healing capacity, surgical intervention is often required. Nowadays, these injuries are managed using replacement autografts or to a lesser extent using artificial ligaments. With the expansion of tissue engineering, more recent researches focus on the development of biodegradable structures that could allow graft functioning while enhancing host integration. The main challenge is to develop a structure that gradually loses its mechanical properties when at the same time the neo-ligament gains in solidity. Mechanical behavior and reconstruction of natural tissue are the two key points for such a successful device. This article evaluates the mechanical consistency of poly(ε-caprolactone) fibers bundles grafted with sodium polystyrene sulfonate, as a candidate for ligament prosthesis. In order to be medically used, PCL fibers need to cope with multiple steps before implantation including extensive washings, knitting, grafting and sterilization processes. The evolution of mechanical properties at each step of the elaboration process has been investigated. The results show that PCL bundles have the same visco-elastic behavior than the native ACL. Nevertheless, when undergoing physical treatments such as ionizing radiations, like UV or β-rays, the material endures a hardening, increasing its stiffness but also its fragility. At this opposite, the thermal radical grafting acts like an annealing step, increasing significantly the elasticity of the PCL fibers. With this chemical treatment, the stiffness is decreasing, leading to higher energy dissipation. Added to the observation of the structure of the material, this demonstrates the possibility of the PCL to modulate it microstructure. In case of orthopedic prosthesis, the need of such a construct is strongly required to avoid distension of the future prosthesis and to restore good knee stabilization, showing the promising future of PCL ligament prosthesis.

Surface modification of vascular endothelial growth factor-loaded silk fibroin to improve biological performance of ultra-high-molecular-weight polyethylene via promoting angiogenesis

Ultra-high-molecular-weight polyethylene (UHMWPE) has been applied in orthopedics, as the materials of joint prosthesis, artificial ligaments, and sutures due to its advantages such as high tensile strength, good wear resistance, and chemical stability. However, postoperative osteolysis induced by UHMWPE wear particles and poor bone–implant healing interface due to scarcity of osseointegration is a significant problem and should be solved imperatively. In order to enhance its affinity to bone tissue, vascular endothelial growth factor (VEGF) was loaded on the surface of materials, the loading was performed by silk fibroin (SF) coating to achieve a controlled-release delivery. Several techniques including field emission scanning electron microscopy (FESEM) and attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) and water contact angle measurement were used to validate the effectiveness of introduction of SF/VEGF. The result of ELISA demonstrated that the release of VEGF was well maintained up to 4 weeks. The modified UHMWPE was evaluated by both in vitro and in vivo experiments. According to the results of FESEM and cell counting kit-8 (CCK-8) assay, bone marrow mesenchymal stem cells cultured on the UHMWPE coated with SF/VEGF and SF exhibited a better proliferation performance than that of the pristine UHMWPE. The model rabbit of anterior cruciate ligament reconstruction was used to observe the graft–bone healing process in vivo. The results of histological evaluation, microcomputed tomography (micro-CT) analysis, and biomechanical tests performed at 6 and 12 weeks after surgery demonstrated that graft–bone healing could be significantly improved due to the effect of VEGF on angiogenesis, which was loaded on the surface by SF coating. This study showed that the method loading VEGF on UHMWPE by SF coating played an effective role on the biological performance of UHMWPE and displayed a great potential application for anterior cruciate ligament reconstruction.

[Biodegradable synthetic polymers for the design of implantable medical devices: the ligamentoplasty case]

The sector of implantable medical devices is a growing sector of health products especially dynamic in the field of research. To improve the management of patients and to meet clinical requirements, researchers are developing new types of medical devices. They use different families of biomaterials presenting various chemical and physical characteristics in order for providing clinicians with health products optimized for biomedical applications. In this article, we aim to show how, starting from a family of biomaterials (degradable polymers), it is possible to design an implantable medical device for the therapeutic management of the failure of anterior cruciate ligament. The main steps leading to the design of a total ligament reinforcement are detailed. They range from the synthesis and characterization of degradable polymer to the shaping of the knitted implant, through the assessment of the study of the impact of sterilization on mechanical properties and checking cytocompatibility.

Evaluation of an intra-articular synthetic ligament for treatment of cranial cruciate ligament disease in dogs: a six-month prospective clinical trial

OBJECTIVE

Evaluate the short-term outcomes of a novel synthetic ligament for treatment of naturally occurring canine cranial cruciate ligament disease.

STUDY DESIGN

Prospective clinical study.

ANIMALS

Dogs with unilateral cranial cruciate ligament disease (n = 50).

METHODS

Patient parameters evaluated included a five-point lameness score, evaluation of craniocaudal stifle instability, and radiographic findings over 24 weeks. Any postoperative complications were recorded.

RESULTS

Thirty-four out of 42 dogs experienced significant improvements in lameness between the preoperative and 24 week time points. Lameness scores in those dogs improved significantly at all measured time intervals after postoperative week 2. Recurrence of stifle instability increased significantly over the study period from immediate postoperative measurements. Cranial drawer recurred in seven out of 42 of dogs by week 4 and 18/42 by week 24. Implant changes were not noted between the immediate and six-month postoperative radiographs except where complications occurred. Overall, 25 dogs experienced a total of 32 complications (22 major and 10 minor). Sixteen dogs had major complications, and nine had minor complications.

CONCLUSION

The procedure was generally effective at improving lameness scores, but did not consistently maintain postoperative stifle stability and had an unacceptably high complication rate. This synthetic ligament procedure cannot be recommended for use in its current form.

The influence of specimen thickness and alignment on the material and failure properties of electrospun polycaprolactone nanofiber mats

Electrospinning is a versatile fabrication technique that has been recently expanded to create nanofibrous structures that mimic ECM topography. Like many materials, electrospun constructs are typically characterized on a smaller scale, and scaled up for various applications. This established practice is based on the assumption that material properties, such as toughness, failure stress and strain, are intrinsic to the material, and thus will not be influenced by specimen geometry. However, we hypothesized that the material and failure properties of electrospun nanofiber mats vary with specimen thickness. To test this, we mechanically characterized polycaprolactone (PCL) nanofiber mats of three different thicknesses in response to constant rate elongation to failure. To identify if any observed thickness-dependence could be attributed to fiber alignment, such as the effects of fiber reorientation during elongation, these tests were performed in mats with either random or aligned nanofiber orientation. Contrary to our hypothesis, the failure strain was conserved across the different thicknesses, indicating similar maximal elongation for specimens of different thickness. However, in both the aligned and randomly oriented groups, the ultimate tensile stress, short-range modulus, yield modulus, and toughness all decreased with increasing mat thickness, thereby indicating that these are not intrinsic material properties. These findings have important implications in engineered scaffolds for fibrous and soft tissue applications (e.g., tendon, ligament, muscle, and skin), where such oversights could result in unwanted laxity or reduced resistance to failure. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2794-2800, 2016.

Preparation and in vitro evaluation of a biomimetic nanoscale calcium phosphate coating on a polyethylene terephthalate artificial ligament

In the present study, a polyethylene terephthalate (PET) artificial ligament was coated with an organic layer-by-layer (LBL) self-assembled template of chitosan and hyaluronic acid, and then incubated in a calcium phosphate (CaP) solution to prepare a biomimetic CaP coating. The surface characterization of the ligament was examined using scanning electron microscopy, atomic force microscopy and energy-dispersive X-ray spectroscopy. The effects of CaP coatings on the osteogenic activity of MC3T3 E1 mouse osteoblastic cells were investigated by evaluating their attachment, proliferation and the relative expression levels of alkaline phosphatase. The results revealed that the organic LBL template on the PET artificial ligament was effective for CaP apatite formation. Following incubation for 72 h, numerous nanoscale CaP apatites were deposited on the PET ligament fibers. In addition, the results of the in vitro culture of MC3T3-E1 mouse osteoblastic cells demonstrated that the CaP coating had a good biocompatibility for cell proliferation and adhesion, and the CaP-coated group had a significantly higher alkaline phosphatase activity compared with the uncoated control group after seven days of cell culture. Collectively, these results demonstrated that the biomimetic nanoscale CaP-coated PET artificial ligaments have potential in bone-tissue engineering.

LARS Artificial Ligament Versus ABC Purely Polyester Ligament for Anterior Cruciate Ligament Reconstruction

Background:

Graft choice for anterior cruciate ligament (ACL) reconstruction is of critical importance. Various grafts have been used so far, with autografts long considered the optimal solution for the treatment of ACL-deficient knees. Limited data are available on the long-term survivorship of synthetic grafts.

Purpose:

To compare the functional outcome and survivorship of ACL reconstructions performed using the LARS (ligament augmentation and reconstruction system) ligament and the ABC (active biosynthetic composite) purely polyester ligament.

Study Design:

Case series; Level of evidence, 4.

Methods:

The results of 72 patients who underwent primary arthroscopic ACL reconstruction with the LARS ligament and 31 cases with an ABC purely polyester ligament were reviewed. The mean follow-up periods for the LARS and ABC groups were 9.5 and 5.1 years, respectively. A survivorship analysis of the 2 synthetic grafts was performed using the Kaplan-Meier method with a log-rank test (Mantel-Cox, 95% CI). Lysholm, Tegner activity, Knee injury and Osteoarthritis Outcome Score (KOOS), and International Knee Documentation Committee (IKDC) scores as well as laxity measurements obtained using a KT-1000 arthrometer were recorded for all intact grafts, and a Mann-Whitney U test was used for comparison reasons.

Results:

The rupture rates for LARS and ABC grafts were 31% (95% CI, 20%-42%) and 42% (95% CI, 25%-59%), respectively. For intact grafts, the mean Lysholm score was good for both groups (90 for the LARS group and 89 for the ABC group), with the majority of patients returning to their preinjury level of activities, and the mean IKDC score was 90 for the LARS group and 86 for the ABC group.

Conclusion:

The rupture rates of both LARS and ABC grafts were both high. However, the LARS ligament provided significantly better survivorship compared with the ABC ligament at short- to midterm follow-up (95% CI).

Co-effect of silk and amniotic membrane for tendon repair

The objective of the present study was to determine the feasibility and biocompatibility of a silk scaffold and a composite silk scaffold in terms of new tendon generation using a rabbit Achilles tendon model. The silk scaffold was constructed using a weaving machine, then soaked in a 1% collagen-hyaluronan (HA) solution and air-dried, whereas the composite silk scaffold was composed of a silk scaffold containing a lyophilized collagen-HA substrate. Tenocytes were cultured in vitro to compare cell populations in the two groups. The cellular densities on composite silk scaffolds were 40% higher on average than those on silk scaffolds in 30-day tenocyte cultures. The tendon scaffolds had implanted into Achilles tendon defects in 16 white New Zealand rabbits. Rabbits were randomly divided into the following three groups: group I, silk scaffold alone; group II, composite silk scaffold; and group III, composite silk scaffold wrapped by an amniotic membrane. Implants were harvested 2, 8, and 12 weeks post-implantation. Histological examinations were conducted using hematoxylin-eosin (H&E), Masson's trichrome, and by performing immunohistochemical staining for CD34. After 12 weeks, the three groups were distinguishable based on gross examination. The histological examination revealed more organized collagen fibrils in groups III, which showed a dense, parallel, linear organization of collagen bundles. CD34 staining revealed neoangiogenesis in groups III. The results of this research showed that collagen-HA substrates with amniotic membrane accelerate cellular migration and angiogenesis in neotendons.

Enhancement of osseointegration of artificial ligament by nano-hydroxyapatite and bone morphogenic protein-2 into the rabbit femur

The MTT assay showed that the cell proliferation on hydroxyapatite (HAp) and HAp/bone morphogenic protein (BMP) coated group was better than the control and BMP coated groups at 5 days. And after 7 days of culture, the mRNA expression levels of type I collagen, osteonectin, osteopontin, bonesialoprotein, BMP-2, alkaline phosphatase (ALP) and Runx-2 in the HAp/BMP coated group were significantly higher than the other groups. Also, in this group showed the most significant induction of osteogenic gene expression compared to mesenchymal stem cells (MSCs) grown on the other groups. In addition, the cells in the HAp/BMP coated group delivered higher levels of ALP than the other three groups. Also, silk scaffolds were implanted as artificial ligaments in knees of rabbits, and they were harvested 1 and 3 months after implantation. On gross examination, HE staining showed that new bone tissue formation was more observed in the HAp/BMP coated group 3 weeks postoperatively. And masson staining showed that in the HAp/BMP coated group, the silk fibers were encircled by osteoblast, chondrocyte, and collagen. Furthermore, the analysis showed that the width of the graft-bone interface in the HAp and HAp/BMP coated group was narrower than that in the other two groups 3 weeks postoperatively. So, it is concluded that BMP incorporated HAp coated silk scaffold can be enhanced osseointegration and osteogenesis in bone tunnel. As a result, these experimental designs have been demonstrated to be effective in the acceleration of graft-to-bone healing by increasing new bone or fibrocartilage formation at the interface between graft and bone.

In vivo evaluation of hybrid patches composed of PLA based copolymers and collagen/chondroitin sulfate for ligament tissue regeneration

Biomaterials for soft tissues regeneration should exhibit sufficient mechanical strength, demonstrating a mechanical behavior similar to natural tissues and should also promote tissues ingrowth. This study was aimed at developing new hybrid patches for ligament tissue regeneration by synergistic incorporation of a knitted structure of degradable polymer fibers to provide mechanical strength and of a biomimetic matrix to help injured tissues regeneration. PLA- Pluronic^® (PLA-P) and PLA-Tetronic^® (PLA-T) new copolymers were shaped as knitted patches and were associated with collagen I (Coll) and collagen I/chondroitine-sulfate (Coll CS) 3-dimensional matrices. In vitro study using ligamentocytes showed the beneficial effects of CS on ligamentocytes proliferation. Hybrid patches were then subcutaneously implanted in rats for 4 and 12 weeks. Despite degradation, patches retained strength to answer the mechanical physiological needs. Tissue integration capacity was assessed with histological studies. We showed that copolymers, associated with collagen and chondroitin sulfate sponge, exhibited very good tissue integration and allowed neotissue synthesis after 12 weeks in vivo. To conclude, PLA-P/CollCS and PLA-T/CollCS hybrid patches in terms of structure and composition give good hopes for tendon and ligament regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1778-1788, 2017.

Enhanced Fibroblast Cellular Ligamentization Process to Polyethylene Terepthalate Artificial Ligament by Silk Fibroin Coating

Artificial ligaments utilized in reconstruction of anterior cruciate ligament (ACL) are usually made of polyethylene terepthalate (PET) because of its good mechanical properties in vivo. However, it was found that the deficiencies in hydrophilicity and biocompatibility of PET hindered the process of ligamentization. Therefore, surface modification of the PET is deemed as a solution in resolving such problem. Silk fibroin (SF), which is characterized by good biocompatibility and low immunogenicity in clinical applications, was utilized to prepare a coating on the PET ligament (PET+SF) in this work. At first, decrease of hydrophobicity and appearance of amino groups were found on the surface of artificial PET ligament after coating with SF. Second, mouse fibroblasts were cultured on the two different kinds of ligament in order to clarify the possible effect of SF coating. It was proved that mouse fibroblasts display better adhesion and proliferation on PET+SF than PET ligament according to the results of several technical methods including SEM observation, cell adhesive force and spread area test, and mRNA analysis. Meanwhile, methylthiazolyldiphenyl-tetrazolium bromide and DNA content tests showed that biocompatibility of PET+SF is better than PET ligament. In addition, collagen deposition tests also indicated that the quantity of collagen in PET+SF is higher than PET ligament. Based on these results, it can be concluded that SF coating is suggested to be an effective approach to modify the surface of PET ligament and enhance the "ligamentization" process in vivo accordingly.

Topologically controlled tensile behaviour of braided prostheses for anterior cruciate ligaments

Anterior cruciate ligament (ACL) is one of the most susceptible ligaments of the knee that can suffer injury. These ruptured ligaments can be treated through surgical intervention using a braided structure that either acts as a substitute graft in isolation or an augmentation device alongside the biological tissue. Therefore, the main objective of the research work is to present an analytical model for predicting the complete set of tensile properties of braided prosthesis consisting of multifilament strands based upon predefined braid geometry and constituent material properties. The model has also accounted for the kinematical changes under defined loading conditions. The research findings have been confirmed by making a comparison between the theoretical and experimental results. The tensile properties of braided prostheses predicted via analytical route matched reasonably well with the experimental results.

Local delivery of controlled-release simvastatin to improve the biocompatibility of polyethylene terephthalate artificial ligaments for reconstruction of the anterior cruciate ligament

The Ligament Advanced Reinforcement System has recently been widely used as the primary graft of choice in anterior cruciate ligament (ACL) reconstruction. But the biological graft-bone healing still remains a problem. Previous studies have shown that simvastatin (SIM) stimulates bone formation. The objective of this study was to investigate whether surface coating with collagen containing low-dose SIM microsphere could enhance the surface biocompatibility of polyethylene terephthalate (PET) artificial ligaments to accelerate graft-to-bone healing. The in vitro studies demonstrated that bone marrow stromal cells on the collagen-coated PET scaffolds (COL/PET) and simvastatin/collagen-coated PET scaffolds (SIM/COL/PET) proliferated vigorously. Compared with the PET group and the COL/PET group, SIM could induce bone marrow stromal cells' osteoblastic differentiation, high alkaline phosphatase activity, more mineralization deposition, and more expression of osteoblast-related genes, such as osteocalcin, runt-related transcription factor 2, bone morphogenetic protein-2, and vascular endothelial growth factor, in the SIM/COL/PET group. In vivo, rabbits received ACL reconstruction with different scaffolds. Histological analysis demonstrated that graft-bone healing was significantly greater with angiogenesis and osteogenesis in the SIM/COL/PET group than the other groups. In addition, biomechanical testing at the eighth week demonstrated a significant increase in the ultimate failure load and stiffness in the SIM/COL/PET group. The low dose of SIM-sustained release from SIM/COL/PET promoted the graft-bone healing via its effect on both angiogenesis and osteogenesis. This study suggested that collagen containing low-dose SIM microsphere coating on the surface of PET artificial ligaments could be potentially applied for ACL reconstruction.

Rolled knitted scaffolds based on PLA-pluronic copolymers for anterior cruciate ligament reinforcement: A step by step conception

The aim of this study was to prepare a new knitted scaffold from PLA-Pluronic block copolymers for anterior cruciate ligament reconstruction. The impact of sterilization methods (beta-ray and gamma-ray sterilization) on copolymers was first evaluated in order to take into account the possible damages due to the sterilization process. Beta-ray radiation did not significantly change mechanical properties in contrast to gamma-ray sterilization. It was shown that ACL cells proliferate onto these copolymers, demonstrating their cytocompatibility. Thirdly, in order to study the influence of shaping on mechanical properties, several shapes were created with copolymers yarns: braids, ropes and linear or rolled knitted scaffolds. The rolled knitted scaffold presented interesting mechanical characteristics, similar to native anterior cruciate ligament (ACL) with a 67 MPa Young's Modulus and a stress at failure of 22.5 MPa. These findings suggest that this three dimensional rolled knitted scaffold meet the mechanical properties of ligament tissues and could be suitable as a scaffold for ligament reconstruction. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 735-743, 2017.

Tensile behaviour of structurally gradient braided prostheses for anterior cruciate ligaments

Anterior cruciate ligament (ACL) is a key fibrous connective tissue that maintains the stability of a knee joint and it is the most commonly injured ligament of the knee. A synthetic prosthesis in the form of a braided structure can be an attractive alternative to biological grafts provided that the mechanical properties can be tailored to mimic the natural ACL. In the present work, the polypropylene based structurally gradient braided prostheses have been designed and developed by understanding their tensile properties. Circular braiding process was employed to fabricate structurally gradient braided prostheses by systematically placing different types of braids in defined set of layers. An analytical model for predicting the tensile properties of structurally gradient braided prostheses has been presented by modifying and combining the existing models available in the literature. Specifically, the full set of stress-strain behaviour of structurally gradient braided prostheses has been computed based upon braid structural characteristics, constituent strand properties and braid kinematics. A triaxial braid in the outer layer of braided prostheses was found to withstand higher tensile stresses in comparison to a biaxial braid having same structural characteristics. A comparison has been made between the theoretical and experimental results of tensile properties of structurally gradient braided prostheses. The tensile properties of structurally gradient braided prostheses predicted through analytical route matched reasonably well with the experimental results.

Poly(vinyl alcohol) hydrogel coatings with tunable surface exposure of hydroxyapatite

Insufficient bone anchoring is a major limitation of artificial substitutes for connective osteoarticular tissues. The use of coatings containing osseoconductive ceramic particles is one of the actively explored strategies to improve osseointegration and strengthen the bone-implant interface for general tissue engineering. Our hypothesis is that hydroxyapatite (HA) particles can be coated robustly on specific assemblies of PVA hydrogel fibers for the potential anchoring of ligament replacements. A simple dip-coating method is described to produce composite coatings made of microscopic hydroxyapatite (HA) particles dispersed in a poly(vinyl alcohol) (PVA) matrix. The materials are compatible with the requirements for implant Good Manufacturing Practices. They are applied to coat bundles of PVA hydrogel fibers used for the development of ligament implants. By means of optical and electronic microscopy, we show that the coating thickness and surface state can be adjusted by varying the composition of the dipping solution. Quantitative analysis based on backscattered electron microscopy show that the exposure of HA at the coating surface can be tuned from 0 to over 55% by decreasing the weight ratio of PVA over HA from 0.4 to 0.1. Abrasion experiments simulating bone-implant contact illustrate how the coating cohesion and wear resistance increase by increasing the content of PVA relative to HA. Using pullout experiments, we find that these coatings adhere well to the fiber bundles and detach by propagation of a crack inside the coating. These results provide a guide to select coated implants for anchoring artificial ligaments.