One-Year Outcomes of Total Meniscus Reconstruction Using a Novel Fiber-Reinforced Scaffold in an Ovine Model

Reconstruction of medial meniscus posterior portion deficiency in pigs with an autologous patellar tendon graft: an experimental study

OBJECTIVE

This study was performed to investigate the effectiveness of two surgical procedures, autologous patellar tendon graft reconstruction and trans-tibial plateau pull-out repair, using a pig model. The primary focus was to assess the repair capability of medial meniscus posterior portion (MMPP) deficiency, the overall structural integrity of the meniscus, and protection of the femoral and tibial cartilage between the two surgical groups. The overall aim was to provide experimental guidelines for clinical research using these findings.

METHODS

Twelve pigs were selected to establish a model of injury to the MMPP 10 mm from the insertion point of the tibial plateau. They were randomly divided into three groups of four animals each: reconstruction (autologous tendon graft reconstruction of the MMPP), pull-out repair (suture repair of the MMPP via a trans-tibial plateau bone tunnel), and control (use of a normal medial meniscus as the negative control). The animals were euthanized 12 weeks postoperatively for evaluation of the meniscus, assessment of tendon bone healing, and gross observation of knee joint cartilage. The tibial and femoral cartilage injuries were evaluated using the International Society for Cartilage Repair (ICRS) grade and Mankin score. Histological and immunohistochemical staining was conducted on the meniscus-tendon junction area, primary meniscus, and tendons. The Ishida score was used to evaluate the regenerated meniscus in the reconstruction group. Magnetic resonance imaging (MRI) was used to evaluate meniscal healing.

RESULTS

All 12 pigs recovered well after surgery; all incisions healed without infection, and no obvious complications occurred. Gross observation revealed superior results in the reconstruction and pull-out repair groups compared with the control group. In the tibial cartilage, the reconstruction group had ICRS grade I injury whereas the pull-out repair and control groups had ICRS grade II and III injury, respectively. The Mankin score was significantly different between the reconstruction and control groups; histological staining showed that the structure of the regenerated meniscus in the reconstruction group was similar to that of the original meniscus. Immunohistochemical staining showed that the degree of type I and II collagen staining was similar between the regenerated meniscus and the original meniscus in the reconstruction group. The Ishida score was not significantly different between the regenerated meniscus and the normal primary meniscus in the reconstruction group. MRI showed that the MMPP in the reconstruction and pull-out repair groups had fully healed, whereas that in the control group had not healed.

CONCLUSION

Autologous patellar tendon graft reconstruction of the MMPP can generate a fibrocartilage-like regenerative meniscus. Both reconstruction and pull-out repair can preserve the structural integrity of the meniscus, promote healing of the MMPP, delay meniscal degeneration, and protect the knee cartilage.

Optimized Allogenic Decellularized Meniscal Scaffold Modified by Collagen Affinity Stromal Cell-Derived Factor SDF1α for Meniscal Regeneration: A 6- and 12-Week Animal Study in a Rabbit Model

BACKGROUND

Total meniscectomy for treating massive meniscal tears may lead to joint instability, cartilage degeneration, and even progressive osteoarthritis. The meniscal substitution strategies for advancing reconstruction of the meniscus deserve further investigation.

HYPOTHESIS

A decellularized meniscal scaffold (DMS) modified with collagen affinity stromal cell-derived factor (C-SDF1α) may facilitate meniscal regeneration and protect cartilage from abrasion.

STUDY DESIGN

Controlled laboratory study.

METHODS

The authors first modified DMS with C-SDF1α to fabricate a new meniscal graft (DMS-CBD [collagen-binding domain]). Second, they performed in vitro studies to evaluate the release dynamics, biocompatibility, and differentiation inducibility (osteogenic, chondrogenic, and tenogenic differentiation) on human bone marrow mesenchymal stem cells. Using in vivo studies, they subjected rabbits that received medial meniscectomy to a transplantation procedure to implement their meniscal graft. At postoperative weeks 6 and 12, the meniscal regeneration outcomes and chondroprotective efficacy of the new meniscal graft were evaluated by macroscopic observation, histology, micromechanics, and immunohistochemistry tests.

RESULTS

In in vitro studies, the optimized DMS-CBD graft showed notable biocompatibility, releasing efficiency, and chondrogenic inducibility. In in vivo studies, the implanted DMS-CBD graft after total meniscectomy promoted the migration of cells and extracellular matrix deposition in transplantation and further facilitated meniscal regeneration and protected articular cartilage from degeneration.

CONCLUSION

The new meniscal graft (DMS-CBD) accelerated extracellular matrix deposition and meniscal regeneration and protected articular cartilage from degeneration.

CLINICAL RELEVANCE

The results demonstrate that the DMS-CBD graft can serve as a potential meniscal substitution after meniscectomy.

Bioprinting of scaled-up meniscal grafts by spatially patterning phenotypically distinct meniscus progenitor cells within melt electrowritten scaffolds

Meniscus injuries are a common problem in orthopedic medicine and are associated with a significantly increased risk of developing osteoarthritis. While developments have been made in the field of meniscus regeneration, the engineering of cell-laden constructs that mimic the complex structure, composition and biomechanics of the native tissue remains a significant challenge. This can be linked to the use of cells that are not phenotypically representative of the different zones of the meniscus, and an inability to direct the spatial organization of engineered meniscal tissues. In this study we investigated the potential of zone-specific meniscus progenitor cells (MPCs) to generate functional meniscal tissue following their deposition into melt electrowritten (MEW) scaffolds. We first confirmed that fibronectin selected MPCs from the inner and outer regions of the meniscus maintain their differentiation capacity with prolonged monolayer expansion, opening their use within advanced biofabrication strategies. By depositing MPCs within MEW scaffolds with elongated pore shapes, which functioned as physical boundaries to direct cell growth and extracellular matrix production, we were able to bioprint anisotropic fibrocartilaginous tissues with preferentially aligned collagen networks. Furthermore, by using MPCs isolated from the inner (iMPCs) and outer (oMPCs) zone of the meniscus, we were able to bioprint phenotypically distinct constructs mimicking aspects of the native tissue. An iterative MEW process was then implemented to print scaffolds with a similar wedged-shaped profile to that of the native meniscus, into which we deposited iMPCs and oMPCs in a spatially controlled manner. This process allowed us to engineer sulfated glycosaminoglycan and collagen rich constructs mimicking the geometry of the meniscus, with MPCs generating a more fibrocartilage-like tissue compared to the mesenchymal stromal/stem cells. Taken together, these results demonstrate how the convergence of emerging biofabrication platforms with tissue-specific progenitor cells can enable the engineering of complex tissues such as the meniscus.

Suspension bath bioprinting and maturation of anisotropic meniscal constructs

Due to limited intrinsic healing capacity of the meniscus, meniscal injuries pose a significant clinical challenge. The most common method for treatment of damaged meniscal tissues, meniscectomy, leads to improper loading within the knee joint, which can increase the risk of osteoarthritis. Thus, there is a clinical need for the development of constructs for meniscal repair that better replicate meniscal tissue organization to improve load distributions and function over time. Advanced three-dimensional bioprinting technologies such as suspension bath bioprinting provide some key advantages, such as the ability to support the fabrication of complex structures using non-viscous bioinks. In this work, the suspension bath printing process is utilized to print anisotropic constructs with a unique bioink that contains embedded hydrogel fibers that align via shear stresses during printing. Constructs with and without fibers are printed and then cultured for up to 56 din vitroin a custom clamping system. Printed constructs with fibers demonstrate increased cell and collagen alignment, as well as enhanced tensile moduli when compared to constructs printed without fibers. This work advances the use of biofabrication to develop anisotropic constructs that can be utilized for the repair of meniscal tissue.

Degenerative Meniscus in Knee Osteoarthritis: From Pathology to Treatment

Knee osteoarthritis is a common degenerative joint disease characterized by chronic knee pain and disability in daily living. The lesion can involve the cartilage as well as the synovium, bone, ligaments, and meniscus, indicating a complicated pathology for knee osteoarthritis. The association with the meniscus has recently attracted much attention. Meniscal tears can initiate and progress knee osteoarthritis, with deleterious effects on the important roles of the meniscus in load distribution, shock absorption, and stability of the knee joint. Degenerative meniscus lesions are commonly observed in elderly people, but they have less impact on the prognosis of osteoarthritis. However, they are often accompanied by meniscal extrusion, which substantially decreases the hoop function of the meniscus and increases the risk of knee osteoarthritis. When surgical treatment is necessary, meniscal tears should be repaired to the greatest extent possible to preserve meniscus function. Long-term studies show better clinical outcomes and less degenerative osteoarthritis changes following meniscal repair than following partial meniscectomy. For meniscal extrusion repair, centralization techniques have been proposed that involve suturing the meniscus-capsule complex to the edge of the tibial plateau. Advancements in orthobiologics, such as platelet-rich plasma or stem cell therapy, have the potential to prevent the initiation or progression of osteoarthritis.

Strength of interference screw fixation of meniscus prosthesis matches native meniscus attachments

PURPOSE

Meniscal surgery is one of the most common orthopaedic surgical interventions. Total meniscus replacements have been proposed as a solution for patients with irreparable meniscal injuries. Reliable fixation is crucial for the success and functionality of such implants. The aim of this study was to characterise an interference screw fixation system developed for a novel fibre-matrix-reinforced synthetic total meniscus replacement in an ovine cadaveric model.

METHODS

Textile straps were tested in tension to failure (n = 15) and in cyclic tension (70-220 N) for 1000 cycles (n = 5). The textile strap-interference screw fixation system was tested in 4.5 mm-diameter single anterior and double posterior tunnels in North of England Mule ovine tibias aged > 2 years using titanium alloy (Ti6Al4Va) and polyether-ether-ketone (PEEK) screws (n ≥ 5). Straps were preconditioned, dynamically loaded for 1000 cycles in tension (70-220 N), the fixation slippage under cyclic loading was measured, and then pulled to failure.

RESULTS

Strap stiffness was at least 12 times that recorded for human meniscal roots. Strap creep strain at the maximum load (220 N) was 0.005 following 1000 cycles. For all tunnels, pull-out failure resulted from textile strap slippage or bone fracture rather than strap rupture, which demonstrated that the textile strap was comparatively stronger than the interference screw fixation system. Pull-out load (anterior 544 ± 119 N; posterior 889 ± 157 N) was comparable to human meniscal root strength. Fixation slippage was within the acceptable range for anterior cruciate ligament graft reconstruction (anterior 1.9 ± 0.7 mm; posterior 1.9 ± 0.5 mm).

CONCLUSION

These findings show that the textile attachment-interference screw fixation system provides reliable fixation for a novel ovine meniscus implant, supporting progression to in vivo testing. This research provides a baseline for future development of novel human meniscus replacements, in relation to attachment design and fixation methods. The data suggest that surgical techniques familiar from ligament reconstruction may be used for the fixation of clinical meniscal prostheses.

A New Method to Develop the Primate Model of Knee Osteoarthritis With Focal Cartilage Defect

Objective: Osteoarthritis (OA) is a common degenerative joint disease, and animal models have proven pivotal in investigating this disease. This study aimed to develop a primate model of OA that may be more relevant to research studies on OA in humans.

Method: Twelve female rhesus macaques were randomly divided into three groups. Four animals were untreated (Control group); four were subjected to the modified Hulth method, involving cutting of the anterior and posterior cruciate ligaments, and transecting the meniscus (Hulth group); and four were subjected to the modified Hulth method combined with cartilage defect (MHCD group). Each primate was subjected to motor ability tests, and underwent arthroscopic, radiographic, morphological, and pathological observation of the knee joints at various times for up to 180 days.

Results: Motor ability on Day 180 was significantly lower in the MHCD group than in the Control (p＜0.01) and Hulth (p＜0.05) groups. Radiographic and morphological examination showed that the severity of knee joint deformity and articular cartilage injury were greater in the MHCD group than in the other groups. Pathological examination showed that cartilage thickness was significantly lower in the MHCD group than in the other groups at the same time points. The Mankin score on Day 180 was markedly higher in the MHCD group than in the Hulth (p＜0.05) and Control (p＜0.001) groups.

Conclusion: The MHCD model of OA closely resembles the pathophysiological processes of spontaneous knee OA in humans. The time required to develop knee OA is shorter using the MHCD model than using the Hulth method.

Meniscal repair: The current state and recent advances in augmentation

Meniscal injuries represent one of the most common orthopedic injuries. The most frequent treatment is partial resection of the meniscus, or meniscectomy, which can affect joint mechanics and health. For this reason, the field has shifted gradually towards suture repair, with the intent of preservation of the tissue. "Save the Meniscus" is now a prolific theme in the field; however, meniscal repair can be challenging and ineffective in many scenarios. The objectives of this review are to present the current state of surgical management of meniscal injuries and to explore current approaches being developed to enhance meniscal repair. Through a systematic literature review, we identified meniscal tear classifications and prevalence, approaches being used to improve meniscal repair, and biological- and material-based systems being developed to promote meniscal healing. We found that biologic augmentation typically aims to improve cellular incorporation to the wound site, vascularization in the inner zones, matrix deposition, and inflammatory relief. Furthermore, materials can be used, both with and without contained biologics, to further support matrix deposition and tear integration, and novel tissue adhesives may provide the mechanical integrity that the meniscus requires. Altogether, evaluation of these approaches in relevant in vitro and in vivo models provides new insights into the mechanisms needed to salvage meniscal tissue, and along with regulatory considerations, may justify translation to the clinic. With the need to restore long-term function to injured menisci, biologists, engineers, and clinicians are developing novel approaches to enhance the future of robust and consistent meniscal reparative techniques.

3D-bioprinted gradient-structured scaffold generates anisotropic cartilage with vascularization by pore-size-dependent activation of HIF1α/FAK signaling axis

Articular cartilage injury is one of the most common diseases in orthopedics, which seriously affects patients' life quality, the development of a biomimetic scaffold that mimics the multi-layered gradient structure of native cartilage is a new cartilage repair strategy. It has been shown that scaffold topography affects cell attachment, proliferation, and differentiation; the underlying molecular mechanism of cell-scaffold interaction is still unclear. In the present study, we construct an anisotropic gradient-structured cartilage scaffold by three-dimensional (3D) bioprinting, in which bone marrow stromal cell (BMSC)-laden anisotropic hydrogels micropatterns were used for heterogeneous chondrogenic differentiation and physically gradient synthetic poly (ε-caprolactone) (PCL) to impart mechanical strength. In vitro and in vivo, we demonstrated that gradient-structured cartilage scaffold displayed better cartilage repair effect. The heterogeneous cartilage tissue maturation and blood vessel ingrowth were mediated by a pore-size-dependent mechanism and HIF1α/FAK axis activation. In summary, our results provided a theoretical basis for employing 3D bioprinting gradient-structured constructs for anisotropic cartilage regeneration and revealed HIF1α/FAK axis as a crucial regulator for cell-material interactions, so as to provide a new perspective for cartilage regeneration and repair.

Combining TGF-β1 and Mechanical Anchoring to Enhance Collagen Fiber Formation and Alignment in Tissue-Engineered Menisci

Recapitulating the collagen fiber structure of native menisci is one of the major challenges in the development of tissue-engineered menisci. Native collagen fibers are developed by the complex interplay of biochemical and biomechanical signals. In this study, we optimized glucose and transforming growth factor-β1 (TGF-β1) concentrations in combination with mechanical anchoring to balance contributions of proteoglycan synthesis and contractile behavior in collagen fiber assembly. Glucose had a profound effect on the final dimensions of collagen-based constructs. TGF-β1 influenced construct contraction rate and glycosaminoglycan (GAG) production with two half-maximal effective concentration (EC₅₀) ranges, which are 0.23 to 0.28 and 0.53 to 1.71 ng/mL, respectively. At concentrations less than the EC₅₀, for the GAG production and contraction rate, TGF-β1 treatment resulted in less organized collagen fibers. At concentrations greater than the EC₅₀, TGF-β1 led to dense, disorganized collagen fibers. Between the two EC₅₀ values, collagen fiber diameter and length increased. The effects of TGF-β1 on fiber development were enhanced by mechanical anchoring, leading to peaks in fiber diameter, length, and alignment index. Fiber diameter and length increased from 7.9 ± 1.4 and 148.7 ± 16.4 to 17.5 ± 2.1 and 262.0 ± 13.0 μm, respectively. The alignment index reached 1.31, comparable to that of native tissue, 1.40. These enhancements in fiber architecture resulted in significant increases in tensile modulus and ultimate tensile stress (UTS) by 1.6- and 1.4-fold. Correlation analysis showed that tensile modulus and UTS strongly correlated with collagen fiber length, diameter, and alignment, while compressive modulus correlated with GAG content. These outcomes highlight the need for optimization of both biochemical and biomechanical cues in the culture environment for enhancing fiber development within tissue-engineered constructs.

Biosynthetic scaffolds for partial meniscal loss: A systematic review from animal models to clinical practice

Acute or degenerative meniscus tears are the most common knee lesions. Meniscectomy provides symptomatic relief and functional recovery only in the short- to mid-term follow-up but significantly increases the risk of osteoarthritis. For this reason, preserving the meniscus is key, although it remains a challenge. Allograft transplants present many disadvantages, so during the last 20 years preclinical and clinical research focused on developing and investigating meniscal scaffolds. The aim of this systematic review was to collect and evaluate all the available evidence on biosynthetic scaffolds for meniscus regeneration both in vivo and in clinical studies. Three databases were searched: 46 in vivo preclinical studies and 30 clinical ones were found. Sixteen natural, 15 synthetic, and 15 hybrid scaffolds were studied in vivo. Among them, only 2 were translated into clinic: the Collagen Meniscus Implant, used in 11 studies, and the polyurethane-based scaffold Actifit®, applied in 19 studies. Although positive outcomes were described in the short- to mid-term, the number of concurrent procedures and the lack of randomized trials are the major limitations of the available clinical literature. Few in vivo studies also combined the use of cells or growth factors, but these augmentation strategies have not been applied in the clinical practice yet. Current solutions offer a significant but incomplete clinical improvement, and the regeneration potential is still unsatisfactory. Building upon the overall positive results of these “old” technologies to address partial meniscal loss, further innovation is urgently needed in this field to provide patients better joint sparing treatment options.

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Animal studies employed natural, synthetic and hybrid natural/synthetic scaffolds.

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Only in a few animal studies scaffold augmentation with cells or GFs was tested.

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Only two meniscal scaffolds have reached clinical application: CMI and Actifit.

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Clinical results are promising, but complete meniscus regeneration has not been achieved.

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There is urgent need for technological innovation in the field of meniscal regeneration.

Functional Characteristics and Mechanical Performance of PCU Composites for Knee Meniscus Replacement

The potential use of fiber-reinforced based polycarbonate-urethanes (PCUs) as candidate meniscal substitutes was investigated in this study. Mechanical test pieces were designed and fabricated using a compression molding technique. Ultra-High Molecular Weight Polyethylene (UHMWPE) fibers were impregnated into PCU matrices, and their mechanical and microstructural properties evaluated. In particular, the tensile moduli of the PCUs were found unsuitable, since they were comparatively lower than that of the meniscus, and may not be able to replicate the inherent role of the meniscus effectively. However, the inclusion of fibers produced a substantial increment in the tensile modulus, to a value within a close range measured for meniscus tissues. Increments of up to 227% were calculated with a PCU fiber reinforcement composite. The embedded fibers in the PCU composites enhanced the fracture mechanisms by preventing the brittle failure and plastic deformation exhibited in fractured PCUs. The behavior of the composites in compression varied with respect to the PCU matrix materials. The mechanical characteristics demonstrated by the developed PCU composites suggest that fiber reinforcements have a considerable potential to duplicate the distinct and multifaceted biomechanical roles of the meniscus.

Meniscectomy-induced osteoarthritis in the sheep model for the investigation of therapeutic strategies: a systematic review

PURPOSE

One of the major risk factors for OA is meniscectomy (Mx) that causes a rapid and progressive OA. Mx has been employed in various animal models, especially in large ones, to study preclinical safety and strategy effectiveness to counteract OA. The aim of the present study is to review in vivo studies, performed in sheep and published in the last ten years.

METHODS

The search strategy was performed in three websites: www.scopus.com, www.pubmed.com, and www.webofknowledge.com, using "Meniscectomy and osteoarthritis in sheep" keywords.

RESULTS

The 25 included studies performed unilateral total medial Mx (MMx), unilateral partial MMx, bilateral MMx, unilateral total lateral Mx (LMx), unilateral partial LMx, and bilateral LMx and MMx combined with anterior cruciate ligament transaction. The most frequently performed is the unilateral total MMx that increases changes in cartilage and subchondral bone more than the other techniques. Gross evaluations, histology, radiography, and biochemical tests are used to assess the degree of OA. The most widely tested treatments are related to scaffolds with or without mesenchymal stem cells.

CONCLUSION

OA therapeutic strategies require the use of large animal models due to similarities with human joint anatomy. A protocol for future in vivo studies on post-traumatic OA is clarified.

Evaluation of culture conditions for in vitro meniscus repair model systems using bone marrow-derived mesenchymal stem cells

Purpose: Meniscal injury and loss of meniscus tissue lead to osteoarthritis development. Therefore, novel biologic strategies are needed to enhance meniscus tissue repair. The purpose of this study was to identify a favorable culture medium for both bone marrow-derived mesenchymal stem cells (MSCs) and meniscal tissue, and to establish a novel meniscus tissue defect model that could be utilized for in vitro screening of biologics to promote meniscus repair.Materials and Methods: In parallel, we analyzed the biochemical properties of MSC - seeded meniscus-derived matrix (MDM) scaffolds and meniscus repair model explants cultured in different combinations of serum, dexamethasone (Dex), and TGF-β. Next, we combined meniscus tissue and MSC-seeded MDM scaffolds into a novel meniscus tissue defect model to evaluate the effects of chondrogenic and meniscal media on the tissue biochemical properties and repair strength.Results: Serum-free medium containing TGF-β and Dex was the most promising formulation for experiments with MSC-seeded scaffolds, whereas serum-containing medium was the most effective for meniscus tissue composition and integrative repair. When meniscus tissue and MSC-seeded MDM scaffolds were combined into a defect model, the chondrogenic medium (serum-free with TGF-β and Dex) enhanced the production of proteoglycans and promoted integrative repair of meniscus tissue. As well, cross-linked scaffolds improved repair over the MDM slurry.Conclusions: The meniscal tissue defect model established in this paper can be used to perform in vitro screening to identify and optimize biological treatments to enhance meniscus tissue repair prior to conducting preclinical animal studies.

Regulation of proteoglycan production by varying glucose concentrations controls fiber formation in tissue engineered menisci

Fibrillar collagens are highly prevalent in the extracellular matrix of all connective tissues and therefore commonly used as a biomaterial in tissue engineering applications. In the native environment, collagen fibers are arranged in a complex hierarchical structure that is often difficult to recreate in a tissue engineered construct. Small leucine rich proteoglycans as well as hyaluronan binding proteoglycans, aggrecan and versican, have been implicated in regulating fiber formation. In this study, we modified proteoglycan production in vitro by altering culture medium glucose concentrations (4500, 1000, 500, 250, and 125 mg/L), and evaluated its effect on the formation of collagen fibers inside tissue engineered meniscal constructs. Reduction of extracellular glucose resulted in a dose dependent decrease in total sulfated glycosaminoglycan (GAG) production, but minimal decreases of decorin and biglycan. However, fibromodulin doubled in production between 125 and 4500 mg/L glucose concentration. A peak in fiber formation was observed at 500 mg/L glucose concentration and corresponded with reductions in total GAG production. Fiber formation reduction at 125 and 250 mg/L glucose concentrations are likely due to changes in metabolic activity associated with a limited supply of glucose. These results point to proteoglycan production as a means to manipulate fiber architecture in tissue engineered constructs. STATEMENT OF SIGNIFICANCE: Fibrillar collagens are highly prevalent in the extracellular matrix of all connective tissues; however achieving appropriate assembly and organization of collagen fibers in engineered connective tissues is a persistent challenge. Proteoglycans have been implicated in regulating collagen fiber organization both in vivo and in vitro, however little is known about methods to control proteoglycan production and the subsequent fiber organization in tissue engineered menisci. Here, we show that media glucose content can be optimized to control proteoglycan production and collagen fiber assembly, with optimal collagen fiber assembly occurring at sub-physiologic levels of glucose.

Point-of-Care Procedure for Enhancement of Meniscal Healing in a Goat Model Utilizing Infrapatellar Fat Pad-Derived Stromal Vascular Fraction Cells Seeded in Photocrosslinkable Hydrogel

BACKGROUND

Large radial tears of the meniscus involving the avascular region can compromise meniscal function and result in poor healing and subsequent osteochondral degeneration. Augmentation of surgical repairs with adipose-derived stromal vascular fraction (SVF), which contains mesenchymal stromal cells, may improve meniscal healing and preserve function (ie, chondroprotection).

PURPOSES

(1) To develop a goat model of a radial meniscal tear with resulting osteoarthritis and (2) to explore the efficacy of a 1-step procedure utilizing infrapatellar fat pad-derived SVF cells seeded in a photocrosslinkable hydrogel to enhance meniscal healing and mitigate osteochondral degeneration.

STUDY DESIGN

Controlled laboratory study.

METHODS

A full-thickness radial tear spanning 90% of the medial meniscal width was made at the junction of the anterior and middle bodies of the goat stifle joint. Tears received 1 of 3 interventions (n = 4 per group): untreated, repair, or repair augmented with photocrosslinkable methacrylated gelatin hydrogel containing 2.0 × 10⁶ SVF cells/mL and 2.0 µg/mL of transforming growth factor β3. The contralateral (left) joint served as a healthy control. At 6 months, meniscal healing and joint health were evaluated by magnetic resonance imaging (MRI) and assessed by histological and macroscopic scoring. The Whole-Organ Magnetic Resonance Imaging Score and the presence of a residual tear, as evaluated with T2 MRI sequences, were determined by a single blinded orthopaedic surgeon.

RESULTS

When compared with tears left untreated or repaired with suture alone, augmented repairs demonstrated increased tissue formation in the meniscal tear site, as seen on MRI and macroscopically. Likewise, the neotissue of augmented repairs possessed a histological appearance more similar, although still inferior, to healthy meniscus. Osteochondral degeneration in the medial compartment, as evaluated by the Whole-Organ Magnetic Resonance Imaging Score and Inoue (macroscopic) scale, revealed increased degeneration in the untreated and repair groups, which was mitigated in the augmented repair group. Histological evaluation with a modified Mankin score showed a similar trend. In all measures of osteochondral degeneration, the augmented repair group did not differ significantly from the uninjured control.

CONCLUSION

A radial tear spanning 90% of the medial meniscal width in a goat stifle joint showed poor healing potential and resulted in osteochondral degeneration by 6 months, even if suture repair was performed. Augmentation of the repair with a photocrosslinkable hydrogel containing transforming growth factor β3 and SVF cells, isolated intraoperatively by rapid enzymatic digestion, improved meniscal healing and mitigated osteoarthritic changes.

CLINICAL RELEVANCE

Repair augmentation with an SVF cell-seeded hydrogel may support successful repair of meniscal tears previously considered irreparable.

PCL-MECM-Based Hydrogel Hybrid Scaffolds and Meniscal Fibrochondrocytes Promote Whole Meniscus Regeneration in a Rabbit Meniscectomy Model

Regeneration of an injured meniscus continues to be a scientific challenge due to its poor self-healing potential. Tissue engineering provides an avenue for regenerating a severely damaged meniscus. In this study, we first investigated the superiority of five concentrations (0%, 0.5%, 1%, 2%, and 4%) of meniscus extracellular matrix (MECM)-based hydrogel in promoting cell proliferation and the matrix-forming phenotype of meniscal fibrochondrocytes (MFCs). We found that the 2% group strongly enhanced chondrogenic marker mRNA expression and cell proliferation compared to the other groups. Moreover, the 2% group showed the highest glycosaminoglycan (GAG) and collagen production by day 14. We then constructed a hybrid scaffold by 3D printing a wedge-shaped poly(ε-caprolactone) (PCL) scaffold as a backbone, followed by injection with the optimized MECM-based hydrogel (2%), which served as a cell delivery system. The hybrid scaffold (PCL-hydrogel) clearly yielded favorable biomechanical properties close to those of the native meniscus. Finally, PCL scaffold, PCL-hydrogel, and MFCs-loaded hybrid scaffold (PCL-hydrogel-MFCs) were implanted into the knee joints of New Zealand rabbits that underwent total medial meniscectomy. Six months postimplantation we found that the PCL-hydrogel-MFCs group exhibited markedly better gross appearance and cartilage protection than the PCL scaffold and PCL-hydrogel groups. Moreover, the regenerated menisci in the PCL-hydrogel-MFCs group had similar histological structures, biochemical contents, and biomechanical properties as the native menisci in the sham operation group. In conclusion, PCL-MECM-based hydrogel hybrid scaffold seeded with MFCs can successfully promote whole meniscus regeneration, and cell-loaded PCL-MECM-based hydrogel hybrid scaffold may be a promising strategy for meniscus regeneration in the future.

Ectopic chondrogenesis of nude mouse induced by nano gene delivery enhanced tissue engineering technology

Background: Many techniques and methods have been used clinically to relieve pain from cartilage repair, but the long-term effect is still unsatisfactory. Purpose: The objective of this study was to form an artificial chondroid tissue gene enhanced tissue engineering system to repair cartilage defects via nanosized liposomes. Methods: Cationic nanosized liposomes were prepared and characterized using transmission electron microscope (TEM) and dynamic laser light scattering (DLS). The rat mesenchymal stem cells (rMSCs) were isolated, cultivated, and induced by SRY (Sex-Determining Region Y)-Box 9 (Sox9) via cationic nanosized liposomes. The induced rMSCs were mixed with a thermo-sensitive chitosan hydrogel and subcutaneously injected into the nude mice. Finally, the newly-formed chondroid tissue obtained in the injection parts, and the transparent parts were detected by HE, collagen II, and safranin O. Results: It was found that the presently prepared cationic nanosized liposomes had the diameter of 85.76±3.48 nm and the zeta potential of 15.76±2.1 mV. The isolated rMSCs proliferation was fibroblast-like, with a cultivated confluence of 90% confluence in 5-8 days, and stained positive for CD29 and CD44 while negative for CD34 and CD45. After transfection with cationic nanosized liposomes, we observed changes of cellular morphology and a higher expression of SOX9 compared with control groups, which indicated that rMSCs could differentiate into chondrocyte in vitro. By mixing transfected rMSCs with the thermo-sensitive hydrogel of chitosan in nude mice, chondroid tissue was successfully obtained, demonstrating that rMSCs can differentiate into chondrogenic cells in vivo. Conclusion: This study explored new ways to improve the quality of tissue engineered cartilage, thus accelerating clinical transformation and reducing patient pain.

Orchestrated biomechanical, structural, and biochemical stimuli for engineering anisotropic meniscus

Reconstruction of the anisotropic structure and proper function of the knee meniscus remains an important challenge to overcome, because the complexity of the zonal tissue organization in the meniscus has important roles in load bearing and shock absorption. Current tissue engineering solutions for meniscus reconstruction have failed to achieve and maintain the proper function in vivo because they have generated homogeneous tissues, leading to long-term joint degeneration. To address this challenge, we applied biomechanical and biochemical stimuli to mesenchymal stem cells seeded into a biomimetic scaffold to induce spatial regulation of fibrochondrocyte differentiation, resulting in physiological anisotropy in the engineered meniscus. Using a customized dynamic tension-compression loading system in conjunction with two growth factors, we induced zonal, layer-specific expression of type I and type II collagens with similar structure and function to those present in the native meniscus tissue. Engineered meniscus demonstrated long-term chondroprotection of the knee joint in a rabbit model. This study simultaneously applied biomechanical, biochemical, and structural cues to achieve anisotropic reconstruction of the meniscus, demonstrating the utility of anisotropic engineered meniscus for long-term knee chondroprotection in vivo.

Partial Meniscus Replacement with a Collagen-Hyaluronan Infused Three-Dimensional Printed Polymeric Scaffold

IMPACT STATEMENT

The only FDA-approved partial meniscus scaffold, the Collagen Meniscus Implant (CMI), is not approved for reimbursement by government and only reimbursable by certain private insurers. Scaffolds with improved mechanical properties and greater efficacy are needed. A previous study (Ghodbane, et al. DOI: 10.1002/jbm.b.34331) demonstrated the ability of our novel acellular, off-the shelf scaffold to restore knee biomechanics following partial meniscectomy, which could potentially decrease the risk of osteoarthritis following partial meniscectomy, providing the motivation for this study. This article presents a first-in-animal feasibility study.

Biomechanical characterization of a novel collagen-hyaluronan infused 3D-printed polymeric device for partial meniscus replacement

The menisci transmit load by increasing the contact area and decreasing peak contact stresses on the articular surfaces. Meniscal lesions are among the most common orthopedic injuries, and resulting meniscectomies are associated with adverse polycaprolactone contact mechanics changes and, ultimately, an increased likelihood of osteoarthritis. Meniscus scaffolds were fabricated by 3D-printing a network of circumferential and radial filaments of resorbable polymer (poly(desaminotyrosyl-tyrosine dodecyl ester dodecanoate)) and infused with collagen-hyaluronan. The scaffold demonstrated an instantaneous compressive modulus (1.66 ± 0.44 MPa) comparable to native meniscus (1.52 ± 0.59 MPa). The scaffold aggregate modulus (1.33 ± 0.51 MPa) was within 2% of the native value (1.31 ± 0.36 MPa). In tension, the scaffold displayed a comparable stiffness to native tissue (127.6-97.1 N/mm) and an ultimate load of 33% of the native value. Suture pull-out load of scaffolds (83.1 ± 10.0 N) was within 10% of native values (91.5 ± 15.4 N). Contact stress analysis demonstrated the scaffold reduced peak contact stress by 60-67% and increased contact area by 38%, relative to partial meniscectomy. This is the first meniscal scaffold to match both the axial compressive properties and the circumferential tensile stiffness of the native meniscus. The improvement of joint contact mechanics, relative to partial meniscectomy alone, motivates further investigation using a large animal model. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2457-2465, 2019.

The challenge of implant integration in partial meniscal replacement: an experimental study on a silk fibroin scaffold in sheep

PURPOSE

To restore meniscal function after excessive tissue damage, a silk fibroin implant for partial meniscal replacement was developed and investigated in an earlier sheep model. After 6 months implantation, it showed promising results in terms of chondroprotection and biocompatibility. To improve surgical fixation, the material was subjected to optimisation and a fibre mesh was integrated into the porous matrix. The aim of the study was the evaluation of this second generation of silk fibroin implants in a sheep model.

METHODS

Nine adult merino sheep received subtotal meniscal replacement using the silk fibroin scaffold. In nine additional animals, the defect was left untreated. Sham surgery was performed in another group of nine animals. After 6 months of implantation macroscopic, biomechanical and histological evaluations of the scaffold, meniscus, and articular cartilage were conducted.

RESULTS

Macroscopic evaluation revealed no signs of inflammation of the operated knee joint and most implants were located in the defect. However, there was no solid connection to the remaining peripheral meniscal rim and three devices showed a radial rupture at the middle zone. The equilibrium modulus of the scaffold increased after 6 months implantation time as identified by biomechanical testing (before implantation 0.6 ± 0.3 MPa; after implantation: 0.8 ± 0.3 MPa). Macroscopically and histologically visible softening and fibrillation of the articular cartilage in the meniscectomy- and implant group were confirmed biomechanically by indentation testing of the tibial cartilage.

CONCLUSIONS

In the current study, biocompatibility of the silk fibroin scaffold was reconfirmed. The initial mechanical properties of the silk fibroin implant resembled native meniscal tissue. However, stiffness of the scaffold increased considerably after implantation. This might have prevented integration of the device and chondroprotection of the underlying cartilage. Furthermore, the increased stiffness of the material is likely responsible for the partial destruction of some implants. Clinically, we learn that an inappropriate replacement device might lead to similar cartilage damage as seen after meniscectomy. Given the poor acceptance of the clinically available partial meniscal replacement devices, it can be speculated that development of a total meniscal replacement device might be the less challenging option.

Cell-Free Strategies for Repair and Regeneration of Meniscus Injuries through the Recruitment of Endogenous Stem/Progenitor Cells

The meniscus plays a vital role in protecting the articular cartilage of the knee joint. The inner two-thirds of the meniscus are avascular, and injuries to this region often fail to heal without intervention. The use of tissue engineering and regenerative medicine techniques may offer novel and effective approaches to repairing meniscal injuries. Meniscal tissue engineering and regenerative medicine typically use one of two techniques, cell-based or cell-free. While numerous cell-based strategies have been applied to repair and regenerate meniscal defects, these techniques possess certain limitations including cellular contamination and an increased risk of disease transmission. Cell-free strategies attempt to repair and regenerate the injured tissues by recruiting endogenous stem/progenitor cells. Cell-free strategies avoid several of the disadvantages of cell-based techniques and, therefore, may have a wider clinical application. This review first compares cell-based to cell-free techniques. Next, it summarizes potential sources for endogenous stem/progenitor cells. Finally, it discusses important recruitment factors for meniscal repair and regeneration. In conclusion, cell-free techniques, which focus on the recruitment of endogenous stem and progenitor cells, are growing in efficacy and may play a critical role in the future of meniscal repair and regeneration.

Tissue-Engineered Total Meniscus Replacement With a Fiber-Reinforced Scaffold in a 2-Year Ovine Model

BACKGROUND

Meniscus injuries and associated meniscectomies cause patients long-term pain and discomfort and can lead to joint deterioration.

PURPOSE

To evaluate a collagen-hyaluronan sponge reinforced with synthetic resorbable polymer fiber for total meniscus reconstruction in a long-term ovine model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eleven skeletally mature sheep were implanted with the total meniscus scaffold. At 2 years, explants were evaluated biologically (radial/circumferential histology, immunofluorescence) and mechanically (compression, tension), and articular surfaces were examined for damage.

RESULTS

The fiber-reinforced scaffold induced formation of functional neomeniscus tissue that was intact in 8 of 11 animals. The implant was remodeled into organized circumferentially aligned collagen bundles to resist meniscus hoop stresses. Moreover, type II collagen and proteoglycan deposition near the inner margin suggested a direct response to compressive stresses and confirmed fibrocartilage formation. Cartilage damage was observed, but end-stage (severe) joint deterioration associated with meniscectomy was avoided, even with limitations regarding the ovine surgical procedure and postoperative care.

CONCLUSION

A fiber-reinforced total meniscus replacement device induces formation of functional neomeniscus tissue that has the potential to prevent catastrophic joint deterioration associated with meniscectomy.

CLINICAL RELEVANCE

An off-the-shelf meniscus device that can be remodeled into functional tissue and thus prevent or delay the onset of osteoarthritis could address a widespread clinical need after meniscus injury.

Interference Screw Versus Suture Endobutton Fixation of a Fiber-Reinforced Meniscus Replacement Device in a Human Cadaveric Knee Model

BACKGROUND

Meniscal lesions represent one of the most common intra-articular knee injuries. Meniscus replacement devices are needed to restore load distribution and knee stability after meniscectomy. Fixation of these devices is crucial to the generation of hoop stresses and the distribution of loads in the joint.

PURPOSE

To evaluate 2 different fixation techniques (suture endobutton and interference screw) for implantation of a novel meniscus device.

STUDY DESIGN

Controlled laboratory study.

METHODS

In 7 human cadaveric knees (aged 17-61 years), 1 anterior and 2 potential posterior tunnel locations were investigated, and both fixation techniques were tested in each tunnel. The native meniscus roots, devices fixed with a suture endobutton, and devices fixed with an interference screw were gripped with cryoclamps, and tibias were drilled and loaded into a custom jig. Samples were preloaded, preconditioned, loaded for 500 cycles (50-150 N), and tested in tension until failure.

RESULTS

For all 3 tunnels, suture fixation resulted in greater elongation (54.1%-150.7% greater; P < .05) during cyclic loading than interference screw fixation, which approximated the native roots. Both fixation techniques displayed ultimate tensile loads in the same range as native roots. However, stiffness of the suture fixation groups (36.5-41.6 N/mm) was only 28% to 37% of that of the interference screw fixation groups (98.7-131.6 N/mm), which had values approaching those of the native roots (anterior: 175.4 ± 24.2 N/mm; posterior: 157.6 ± 22.9 N/mm).

CONCLUSION

Interference screw fixation was found to be superior to suture fixation with regard to elongation and stiffness, a finding that should be considered in the design and implantation of novel meniscus replacement devices.

CLINICAL RELEVANCE

With the emergence of various devices for total meniscus replacement, the establishment of fixation strategies is crucial for the generation of tensile hoop stresses and the efficacy of these approaches.

An electrospun fiber reinforced scaffold promotes total meniscus regeneration in rabbit meniscectomy model

Low vascularization in meniscus limits its regeneration ability after injury, and tissue engineering is the most promising method to achieve meniscus regeneration. In this study, we fabricated a kind of composite scaffold by decellularized meniscus extracellular matrix/polycaprolactone (DMECM/PCL) electrospinning fibers and porous DMECM, in which DMECM/PCL fibers were used as reinforcing component. The tensile modulus of the composite scaffold in longitudinal and crosswise directions were 8.5 ± 1.9 and 2.3 ± 0.3 MPa, respectively. Besides that, the DMECM/PCL electrospinning fibers enhanced suture resistance of the composite scaffold more than 5 times than DMECM scaffold effectively. In vitro cytocompatibility showed that the porous structure provided by DMECM component facilitated meniscus cells' proliferation. DMECM was also the main component to regulate cell behaviors, which promoted meniscus cells expressing extracellular matrix related genes such as COL I, COL II, SOX9 and AGG. Rabbits with total meniscectomy were used as animal model to evaluated the composited scaffolds performance in vivo at 3 and 6 months. Results showed that rabbits with scaffold implanting could regenerate neo-menisci in both time points. The neo-menisci had similar histology structure and biochemical content with native menisci. Although neo-menisci had inferior tensile modulus than native ones, its modulus was improved with implanting time prolonging. MRI imaging showed the signal of neo-meniscus in the body is clear, and X-ray imaging of knee joints demonstrated the implantation of scaffolds could relief joint space narrowing. Moreover, rabbits with neo-menisci had better cartilage condition in femoral condyle and tibial plateau compared than meniscectomy group.

STATEMENT OF SIGNIFICANCE

We fabricated the meniscus scaffold by combining porous decellularized meniscus extracellular matrix (DMECM) and DMECM/PCL electrospinning fibers together, which used the porous structure of DMECM, and the good tensile property of electrospinning fibers. We believe single material cannot satisfy increasing needs of scaffold. Therefore, we combined not only materials but also fabrication methods together to develop scaffold to make good use of each part. DMECM in electrospinning fibers also made these two components possible to be integrated through crosslinking. Compared to existing meniscus scaffold, the composite scaffold had (1) soft structure and extrusion would not happen after implantation, (2) ability to be trimmed to suitable shape during surgery, and (3) good resistance to suture.

Carbodiimide cross-linking counteracts the detrimental effects of gamma irradiation on the physical properties of collagen-hyaluronan sponges

Collagen-based scaffolds are extensively used in biomaterials and tissue engineering applications. These scaffolds have shown great biocompatibility and versatility, but their relatively low mechanical properties may limit use in orthopaedic load-bearing applications. Moreover, terminal sterilization with gamma irradiation, as is commonly performed with commercial devices, presents concerns over structural integrity and enzymatic stability. Therefore, the goal of this study was to test the hypothesis that EDC/NHS cross-linking (10 mM/5 mM) can protect collagen-hyaluronan sponges from the damaging effects of gamma irradiation. Specifically, we evaluated compressive and tensile mechanical properties, enzymatic stability, porosity and pore size, and swelling ratio. Ultimate tensile strength and elastic modulus exhibited increases (168.5 and 245.8%, respectively) following irradiation, and exhibited over tenfold increases (1049.2 and 1270.6%, respectively) following cross-linking. Irradiation affected pore size (38.4% decrease), but cross-linking prior to irradiation resulted in only a 17.8% decrease. Cross-linking also showed an offsetting effect on the equilibrium modulus, enzymatic stability, and swelling ratio of sponges. These results suggest that carbodiimide cross-linking of collagen-hyaluronan sponges can mitigate the structural damage typically experienced during gamma irradiation, warranting their use in tissue engineering applications.

A Macaca Fascicularis Knee Osteoarthritis Model Developed by Modified Hulth Combined with Joint Scratches

BACKGROUND Osteoarthritis is a common degenerative disease of joints, and animal models have important significance in the investigation of this disease. The aim of this study was to develop a better method for developing osteoarthritis models in primates by comparing the modified Hulth score combined with joint scratches modeling method with others. MATERIAL AND METHODS We randomly divided 15 young male Macaca fascicularis and 3 old male Macaca fascicularis into 6 groups (n=3). Knee osteoarthritis (KOA) models were developed with different methods: modified Hulth combined with joint scratches (Group A), modified Hulth (Group B), Hulth (Group C), spontaneous models (Group D); sham-operated (Group E), and blank control (Group F). Morphology and pathology of knee joints were observed at the 8th week after surgery. The levels of WBC, IL-1b, and TGF-b1 in synovial fluid were detected by ELISA. The levels of COL-II, ACAN, and MMP-13 in articular cartilage were examined by RT-qPCR and Western blot. RESULTS In Brittberg and modified Mankin score, Group A was higher than B (P<0.05) and lower than C (P<0.05), and there was no statistically significant difference between Group A and D (P>0.05). Except for Group E and F, the differences were statistically significant among others in WBC, IL-1β, and TGF-β1 (P<0.05). COL-II and ACAN decreased and MMP-13 increased, and there was no significant difference between Groups A and D (P>0.05) or between Groups E and F (P>0.05). There were statistically significant differences among other groups (P<0.05). CONCLUSIONS The models developed by modified Hulth combined with joint scratches were the closet to spontaneous models at the 8th week after surgery.

The Utility of Biologics, Osteotomy, and Cartilage Restoration in the Knee

The management of complex cartilage and meniscal pathology in young, athletic patients is extremely challenging. Joint preservation surgery is most difficult in patients with concomitant knee pathologies, including cartilage defects, meniscal deficiency, malalignment, and/or ligamentous insufficiency. Clinical decision making for these patients is further complicated by articular cartilage lesions, which often are incidental findings; therefore, treatment decisions must be based on the confirmed contribution of articular cartilage lesions to symptomatology. Surgical management of any of the aforementioned knee pathologies that is performed in isolation typically results in acceptable patient outcomes; however, concomitant procedures for the management of concomitant knee pathologies often are essential to the success of any single procedure. The use of biologic therapy as an alternative to or to augment more conventional surgical management has increased in popularity in the past decade, and indications for biologic therapy continue to evolve. Orthopaedic surgeons should understand knee joint preservation techniques, including biologic and reconstructive approaches in young, high-demand patients.

Meniscal repair and regeneration: Current strategies and future perspectives

The management of meniscal injuries remains difficult and challenging. Although several clinical options exist for the treatment of such injuries, complete regeneration of the damaged meniscus has proved difficult due to the limited healing capacity of the tissue. With the advancements in tissue engineering and cell-based technologies, new therapeutic options for patients with currently incurable meniscal lesions now potentially exist. This review will discuss basic anatomy, current repair techniques and treatment options for loss of meniscal integrity. Specifically, we focus on the possibility and feasibility of the latest tissue engineering approaches, including 3D printing technologies. Therefore, this discussion will facilitate a better understanding of the latest trends in meniscal repair and regeneration, and contribute to the future application of such clinical therapies for patients with meniscal injuries.

* The Ovine Model for Meniscus Tissue Engineering: Considerations of Anatomy, Function, Implantation, and Evaluation

Meniscus injuries represent one of the most-common intra-articular knee injuries. The current treatment options include meniscectomy and allograft transplantation, both with poor long-term outcomes. Therefore, there is a need for regenerative techniques to restore meniscal function. To preclinically test scaffolds for meniscus replacement, large animal models need to be established and standardized. This review establishes the anatomical and compositional similarities between human and sheep menisci and provides guidance for implantation and evaluation of such devices. The ovine meniscus represents a scaled-down version of the human meniscus, with only slight structural differences that can be addressed during device fabrication. Implantation protocols in sheep remain a challenge, as the meniscus cannot be visualized with the arthroscopic-assisted procedures commonly performed in human patients. Thus, we recommend the appropriate implantation protocols for meniscus visualization, ligamentous restoration, and surgical fixation of both total and partial meniscus replacement devices. Last, due to the lack of standardization in evaluation techniques, we recommend a comprehensive battery of tests to evaluate the efficacy of meniscus replacement implants. We recommend other investigators utilize these surgical and testing techniques to establish the ovine model as the gold standard for preclinical evaluation of meniscus replacement devices.

Large Animal Models of Meniscus Repair and Regeneration: A Systematic Review of the State of the Field

Injury to the meniscus is common, but few viable strategies exist for its repair or regeneration. To address this, animal models have been developed to translate new treatment strategies toward the clinic. However, there is not yet a regulatory document guiding such studies. The purpose of this study was to carry out a systematic review of the literature on meniscus treatment methods and outcomes to define the state of the field. Public databases were queried by using search terms related to animal models and meniscus injury and/or repair over the years 1980-2015. Identified peer-reviewed manuscripts were screened by using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. One of nine reviewers read each manuscript and scored them based on whether the publication described a series of predefined study descriptors and outcome measures. Additional data were extracted to identify common assays used. A total of 128 full-length peer-reviewed manuscripts were identified. The number of publications increased over the time frame analyzed, with 48% focused on augmented repair. Rabbit was, by far, the most prevalent species utilized (46%), with dog (21%) and sheep (20%) being the next most common. Analysis of study descriptors revealed that most studies appropriately documented details of the animal used, the surgical approach, and defect and implant characteristics (e.g., 63% of studies identified clearly the defect size). In terms of outcome parameters, most studies carried out macroscopic (85%), histologic (90%), and healing/integration (83%) analyses of the meniscus. However, many studies did not provide further analysis beyond these fundamental measures, and less than 40% reported on the adjacent cartilage and synovium, as well as joint function. There is intense interest in the field of meniscus repair. However, given the current lack of guidance documentation in this area, preclinical animal models are not performed in a standardized fashion. The development of a "Best Practices" document would increase reproducibility and external validity of experiments, while accelerating advancements in translational research. Advancement is of paramount importance given the high prevalence of meniscal injuries and the paucity of effective repair or regenerative strategies.

The potential of using semitendinosus tendon as autograft in rabbit meniscus reconstruction

Since transplantation of meniscal allograft or artificial menisci is limited by graft sources and a series of adverse events, substitution for meniscus reconstruction still needs to be explored. Natural biomaterials, which can provide a unique 3-D microenvironment, remain a promising alternative for tissue engineering. Among them, autograft is a preferred option for its safety and excellent biocompatibility. In this study, we utilized semitendinosus tendon autograft in meniscus reconstruction to investigate its fibrochondrogenic metaplasticity potential and chondroprotective effect. Tendon-derived stem cells (TDSCs) and synovial-derived mesenchymal stem cells (SMSCs), two most important stem cell sources in our strategy, exhibited excellent viability, distribution, proliferation and fibrochondrogenic differentiation ability in decellularized semitendinosus tendon (DST) scaffolds in vitro. Histologic evaluation of the tendon grafts in vivo suggested endogenous stem cells differentiated into fibrochondrocytes, synthesized proteoglycan, type II collagen and radial type I collagen at 12 weeks and 24 weeks post-surgery. As for elastic modulus and hardness of the grafts, there were no significant differences between native meniscus and regenerated meniscus at 24 weeks. The protection of condylar cartilage from degeneration was significantly better in the reconstruction group comparing to control group. Overall, semitendinosus tendon autograft seems to be a promising substitution in meniscus reconstruction.

3D-Printed Poly(ε-caprolactone) Scaffold Augmented With Mesenchymal Stem Cells for Total Meniscal Substitution: A 12- and 24-Week Animal Study in a Rabbit Model

BACKGROUND

Total meniscectomy leads to knee osteoarthritis in the long term. The poly(ε-caprolactone) (PCL) scaffold is a promising material for meniscal tissue regeneration, but cell-free scaffolds result in relatively poor tissue regeneration and lead to joint degeneration.

HYPOTHESIS

A novel, 3-dimensional (3D)-printed PCL scaffold augmented with mesenchymal stem cells (MSCs) would offer benefits in meniscal regeneration and cartilage protection.

STUDY DESIGN

Controlled laboratory study.

METHODS

PCL meniscal scaffolds were 3D printed and seeded with bone marrow-derived MSCs. Seventy-two New Zealand White rabbits were included and were divided into 4 groups: cell-seeded scaffold, cell-free scaffold, sham operation, and total meniscectomy alone. The regeneration of the implanted tissue and the degeneration of articular cartilage were assessed by gross and microscopic (histological and scanning electron microscope) analysis at 12 and 24 weeks postoperatively. The mechanical properties of implants were also evaluated (tensile and compressive testing).

RESULTS

Compared with the cell-free group, the cell-seeded scaffold showed notably better gross appearance, with a shiny white color and a smooth surface. Fibrochondrocytes with extracellular collagen type I, II, and III and proteoglycans were found in both seeded and cell-free scaffold implants at 12 and 24 weeks, while the results were significantly better for the cell-seeded group at week 24. Furthermore, the cell-seeded group presented notably lower cartilage degeneration in both femur and tibia compared with the cell-free or meniscectomy group. Both the tensile and compressive properties of the implants in the cell-seeded group were significantly increased compared with those of the cell-free group.

CONCLUSION

Seeding MSCs in the PCL scaffold increased its fibrocartilaginous tissue regeneration and mechanical strength, providing a functional replacement to protect articular cartilage from damage after total meniscectomy.

CLINICAL RELEVANCE

The study suggests the potential of the novel 3D PCL scaffold augmented with MSCs as an alternative meniscal substitution, although this approach requires further improvement before being used in clinical practice.

AMECM/DCB scaffold prompts successful total meniscus reconstruction in a rabbit total meniscectomy model

Tissue-engineered meniscus regeneration is a very promising treatment strategy for meniscus lesions. However, generating the scaffold presents a huge challenge for meniscus engineering as this has to meet particular biomechanical and biocompatibility requirements. In this study, we utilized acellular meniscus extracellular matrix (AMECM) and demineralized cancellous bone (DCB) to construct three different types of three-dimensional porous meniscus scaffold: AMECM, DCB, and AMECM/DCB, respectively. We tested the scaffolds' physicochemical characteristics and observed their interactions with meniscus fibrochondrocytes to evaluate their cytocompatibility. We implanted the three different types of scaffold into the medial knee menisci of New Zealand rabbits that had undergone total meniscectomy; negative control rabbits received no implants. The reconstructed menisci and corresponding femoral condyle and tibial plateau cartilage were all evaluated at 3 and 6 months (n = 8). The in vitro study demonstrated that the AMECM/DCB scaffold had the most suitable biomechanical properties, as this produced the greatest compressive and tensile strength scores. The AMECM/DCB and AMECM scaffolds facilitated fibrochondrocyte proliferation and the secretion of collagen and glycosaminoglycans (GAGs) more effectively than did the DCB scaffold. The in vivo experiments demonstrated that both the AMECM/DCB and DCB groups had generated neomeniscus at both 3 and 6 months post-implantation, but there was no obvious meniscus regeneration in the AMECM or control groups, so the neomeniscus analysis could not perform on AMECM and control group. At both 3 and 6 months, histological scores were better for regenerated menisci in the AMECM/DCB than in the DCB group, and significantly better for articular cartilage in the AMECM/DCB group compared with the other three groups. Knee MRI scores (Whole-Organ Magnetic Resonance Imaging Scores (WORMS)) were better in the AMECM/DCB group than in the other three groups at both 3 and 6 months. At both 3 and 6 months, RT-PCR demonstrated that aggrecan, Sox9, and collagen II content was significantly higher, and mechanical testing demonstrated greater tensile strength, in the AMECM/DCB group neomenisci compared with the DCB group.