Outer Meniscus Research Articles

Epigenetic Dynamics in Meniscus Cell Migration and its Zonal Dependency in Response to Inflammatory Conditions: Implications for Regeneration Strategies.

Meniscus injuries pose significant challenges in clinical settings, primarily due to the intrinsic heterogeneity of the tissue and the limited efficacy of current treatments. Endogenous cell migration is crucial for the healing process, yet the regulatory mechanisms of meniscus cell migration and its zonal dependency within the meniscus are not fully understood. Thus, this study investigates the role of epigenetic mechanisms in governing meniscus cell migration under inflammatory conditions, with a focus on their implications for injury healing and regeneration. Here, we discovered that a proinflammatory cytokine, TNF-α treatment significantly impedes the migration speed of inner meniscus cells, while outer meniscus cells are unaffected, underscoring a zonal-dependent response within the meniscus. Our analysis identified distinct histone modification patterns and chromatin dynamics between inner and outer meniscus cells during migration, highlighting the necessity to consider these zonal-dependent properties in devising repair strategies. Specifically, we found that TNF-α differentially influences histone modifications, particularly H3K27me3, between the two cell types. Transcriptome analysis further revealed that TNF-α treatment induces substantial gene expression changes, with inner meniscus cells exhibiting more pronounced alterations than outer cells. Gene cluster analysis pointed to distinct responses in chromatin remodeling, extracellular matrix assembly, and wound healing processes between the zonal cell populations. Moreover, we identified potential therapeutic targets by employing existing epigenetic drugs, GSKJ4 (a histone demethylase inhibitor) and C646 (a histone acetyltransferase inhibitor), to successfully restore the migration speed of inner meniscus cells under inflammatory conditions. This highlights their potential utility in treating meniscus tear injuries. Overall, our findings elucidate the intricate interplay between epigenetic mechanisms and meniscus cell migration, along with its meniscus zonal dependency. This study provides insights into potential targets for enhancing meniscus repair and regeneration, which may lead to improved clinical outcomes for patients with meniscus injuries and osteoarthritis.

Pediatric meniscus morphology varies with age: a cadaveric study.

In adolescent patients, meniscal tear injury can occur either in isolation (e.g., discoid lateral meniscus tears) or in association with other traumatic injuries including tibial eminence fracture or ACL tear. Damage to meniscal integrity has been shown to increase contact pressure in articular cartilage, increasing risk of early onset osteoarthritis. In symptomatic patients failing conservative management, surgical intervention via meniscus repair or meniscus transplant is indicated. The purpose of this study was to evaluate the radial dimensions of pediatric menisci throughout development. The hypothesis was that the average radial meniscus dimensions will increase as specimen age increases, and mean medial and lateral region measurements will increase at a linear rate. Seventy-eight skeletally immature knee cadaver specimens under age 12years were included in this study. The meniscal specimens were photographed in the axial view with ruler in the plane of the tibial plateau and analyzed using computer-aided design (CAD) software (Autodesk Fusion 360). Measurements were taken from inner to outer meniscus rims at five 45 degree intervals using the clockface as a reference (12:00, 1:30, 3:00, 4:30, 6:00), and total area of meniscus and tibial plateau was recorded. Generalized linear models were used to evaluate the associations of radial width measurements with age, tibial coverage, and lateral vs. medial meniscus widths. All radial width measurements increased significantly with specimen age (p ≤ 0.002), and all lateral-medial meniscal widths increased (p < 0.001). The anterior zones of the meniscus were found to increase at the slowest rate compared to other regions. Tibial plateau coverage was found to not significantly vary with age. Meniscus radial width and lateral-medial meniscus width are related to age. The anterior width of the meniscus varied least with age. Improved anatomic understanding may help surgeons more effectively plan for meniscus repair, discoid resection/saucerization/repair, and also support appropriate selection of meniscus allograft for transplantation.

Cellular features of localized microenvironments in human meniscal degeneration: a single-cell transcriptomic study.

Musculoskeletal tissue degeneration impairs the life quality and function of many people. Meniscus degeneration is a major origin of knee osteoarthritis and a common threat to athletic ability, but its cellular mechanism remains elusive. We built a cell atlas of 12 healthy or degenerated human meniscus samples from the inner and outer meniscal zones of 8 patients using scRNA-seq to investigate meniscal microenvironment homeostasis and its changes in the degeneration process and verified findings with immunofluorescent imaging. We identified and localized cell types in inner and outer meniscus and found new chondrocyte subtypes associated with degeneration. The observations suggested understandings on how cellular compositions, functions, and interactions participated in degeneration, and on the possible loop-like interactions among extracellular matrix disassembly, angiogenesis, and inflammation in driving the degeneration. The study provided a rich resource reflecting variations in the meniscal microenvironment during degeneration and suggested new cell subtypes as potential therapeutic targets. The hypothesized mechanism could also be a general model for other joint degenerations. The National Natural Science Foundation of China (81972123, 82172508, 62050178, 61721003), the National Key Research and Development Program of China (2021YFF1200901), Fundamental Research Funds for the Central Universities (2015SCU04A40); The Innovative Spark Project of Sichuan University (2018SCUH0034); Sichuan Science and Technology Program (2020YFH0075); Chengdu Science and Technology Bureau Project (2019-YF05-00090-SN); 1.3.5 Project for Disciplines of Excellence of West China Hospital Sichuan University (ZYJC21030, ZY2017301); 1.3.5 Project for Disciplines of Excellence - Clinical Research Incubation Project, West China Hospital, Sichuan University (2019HXFH039).

The Evaluation of Meniscus Regenerative Effects of LIPUS-Induced CCN Proteins: Induction by LIPUS of CCN2 and Meniscus-Related Genes in Cultured Meniscus Cells and Meniscus Tissues.

Menisci are a pair of crescent-shaped fibrocartilages and composed primarily of type I collagen. Inner region of the meniscus has similar characteristics to articular cartilage. Low-intensity pulsed ultrasound (LIPUS) has been reported to have chondroprotective effects on chondrocytes by inducing the expression of chondrocyte differentiation markers and CCN2/CTGF production. Here, we describe an experimental approach that investigates the distinct cellular behavior of human inner and outer meniscus cells in response to LIPUS stimulation. Our experimental model can analyze the relationships between LIPUS-induced CCN2 and its repairing role in the meniscus.

Prospective Application of Partially Digested Autologous Chondrocyte for Meniscus Tissue Engineering.

Background: Meniscus tissue engineering has yet to achieve clinical application because it requires chondrogenic induction and in vitro cell expansion. Contrarily, cartilage engineering from autologous chondrocytes has been successfully applied in one-stage surgery. If the natural chondrogenic potential of meniscus cells can be demonstrated, meniscus tissue engineering would have more value in clinical settings. Materials and Methods: In total, 10 menisci and pieces of cartilage were obtained during total knee replacements. The tissues were collected for cell isolation and expansion. Their chondrogenic properties were examined by immunohistofluorescence and gene expression analyses. Results: In native cartilage, immunofluorescence demonstrated the presence of collagen I, aggrecan, and traces of collagen I, whereas comparable staining was seen in the inner and middle meniscus. The presence of collagen I but the absence of collagen II and aggrecan were observed in the outer meniscus. In passage 2, chondrocytes showed the presence of collagen II and aggrecan, and the absence of vimentin. The vimentin and aggrecan staining were comparable in the inner and middle meniscus cells, whereas the outer cells showed only vimentin staining. In the gene expression analyses, the expressions of collagen II and aggrecan in the native chondrocyte and the inner and middle meniscus were higher than those of the cells from the outer meniscus, but they were not different in collagen I. In the passage 2 culture, chondrocytes had a higher expression of collagen II and aggrecan than the meniscus cells. Cells from the inner and middle areas had higher collagen II and aggrecan expression than those from the outer meniscus. Conclusion: Without chondrogenic induction, inner and middle meniscus cells possess a chondrogenic phenotype. Specifically, native meniscus cells exhibited more robust chondrogenic potential compared with those of the passage 2 monolayer culture.

Placement of sutures for inside-out meniscal repair: both sutures through meniscal tissue reduces displacement on cyclical loading

PurposeThe inside-out meniscal repair is widely performed to preserve the function of meniscus. In this technique, the outer suture is passed through the capsule as well as the outer meniscus, while the inner suture is inserted into the meniscus. The aim of this study was to biomechanically compare the suture stability between meniscus-meniscus and meniscus-capsule suture methods for the longitudinal meniscal tear with inside-out technique.MethodsTwenty-seven porcine knees were dissected to maintain the femur-medial capsule/meniscus-tibia complex, and the inner meniscus was cut off along the meniscus circumferential fiber with 3 mm width of the peripheral meniscus preserved. After one needle with a 2-0 polyester suture was inserted into the inner portion of the meniscus, the other needle was inserted through 1) the peripheral meniscus (Group A), 2) capsule just above the meniscus (Group B), and 3) capsule at 10 mm apart from the meniscus-capsule junction (Group C) in the inside-out manner. Then, the suture was manually tied on the capsule. The suture gap at the repair site during 300 times of cyclic loading and the ultimate failure load in the load-to-failure test were measured. The statistical significance of the data between two groups in each combination was considered by Bonferroni correction, following a one-way analysis of variance.ResultsIn the cyclic loading test, the suture gap was 0.68 ± 0.26 mm in Group A, 1.08 ± 0.36 mm in Group B, and 1.94 ± 0.57 mm in Group C with a significant difference. In the load-to-failure test, the ultimate failure load was 59.1 ± 13.6 N in Group A, 60.0 ± 7.9 N in Group B, and 57.4 ± 4.7 N in Group C, and there was no significant difference.ConclusionThe stitching region in the inside-out technique for longitudinal meniscal tear affected the stability of the tear site, and stitching the mid-substance region of the meniscus provides good stability in response to cyclic tensile loading. In addition, the stitching region did not affect the ultimate failure load.Clinical relevanceIn the inside-out meniscal repair, the outer suture should be inserted into the remaining peripheral meniscus or the capsule near the meniscus.

Arthroscopic meniscus transplantation without bone blocks

Replacement of the lateral or medial meniscus with an allogeneic graft. Complete loss of inner or outer meniscus. Grade 3 to 4 cartilage damage in the corresponding compartment, uncorrected varus or valgus deformities > 5°, symptomatic instabilities. Knee joint arthroscopy via the high anterolateral standard portal and checking the indication. Thaw the allogeneic meniscus graft in NaCl at room temperature and incubate in vancomycin solution. Refreshment of the capsule and resection of remnants of the meniscus. Search for the insertion zones on the tibial plateau, debridement, insert atranstibial targeting device and drill target wires in the middle of the insertion zones. Overdrill the target wires with a4.5 mm drill. Short medial or lateral arthrotomy (approx. 2 cm). Reinforcement of the anterior and posterior horns of the meniscus graft with nonresorbable suture material (e.g. "fiber wire" size5). Insertion of K‑wires with thread loops into the tibial bone tunnel. The reinforcement threads of the meniscus transplant are drawn into the bone tunnel via the thread loops, and the meniscus transplant is drawn into the joint. Reduction of the meniscus base to the capsule and refixation of the meniscus to the capsule with "inside out" or "all inside" sutures. Six weeks partial weight-bearing using ahinged brace, then gradually increased load. Range of motion: 4weeks 0‑0-60°, then 2weeks 0‑0-90°, followed by no restrictions. In our hospital, 15patients (6 × medial, 9 × lateral) were treated using the described surgical technique. After aminimum period of 1year (mean = 14.2months), meniscus extrusion-measured in the MRI-averaged 2.7 mm. The Lysholm score rose from an average of70.2 (±7.4) to 90.1points (±10.6). In one case, due to an early reruption, revision with renewed meniscus refixation had to be performed 10days after the operation. In another case, meniscus resection was performed 6months after the meniscus transplant due to areruption. Thrombosis, infection and arthrofibrosis were not observed.

Artificial Intelligence in Repairing Meniscus Injury in Football Sports with Perovskite Nanobiomaterials.

Knee meniscus injuries are more likely to occur in young adults in clinical practice, and their lower age of onset and greater impact on joint function after injury also put forward higher requirements for the treatment and rehabilitation of meniscus injuries. With the rapid development of artificial intelligence technology and arthroscopic minimally invasive technology, arthroscopic meniscus plasty and perovskite nanobiomaterial repair have gradually replaced the previous open meniscus surgery of the knee joint and has become the main method of meniscus injury treatment, and the perovskite nanobiomaterial repair technique that incorporates artificial intelligence technology is also gradually being applied. Therefore, this article studies the role of perovskite nanobiomaterials in the repair of meniscus injuries in football sports and analyzes the biological characteristics of the inner and outer meniscus to provide help to improve the healing rate of meniscus injuries. The study selected six male meniscus-injured patients (meniscus injuries caused by football sports) and obtained six injured menisci. The same cross section of the same part of the meniscus was analyzed inside and outside the meniscus. At the same time, a meniscal injury step was performed on the patient. The biological characteristics of perovskite nano-biomaterials in the repair of meniscus injuries in football sports were compared and analyzed, and the patient's gait before and after surgery was also compared. Experiments have shown that the percentage of the postoperative support phase of the affected limb is significantly higher than that before surgery (P < 0.05), the percentage of the postoperative support phase and flatfoot phase decreased compared with that before surgery, and the gait cycle parameters of both lower extremities improved after surgery, obviously (P < 0.05). It explains that the arthroscopic repair of perovskite nanobiomaterials combined with the artificial intelligence technology to repair the meniscus anterior angle injury is simple and does not require special equipment, has fewer complications, is safe and reliable, and has a high clinical healing rate and a high patient satisfaction rate after surgery. The curative effect is significant; artificial intelligence technology and the application of perovskite nanobiomaterials provide more possibilities for meniscus repair.

Bubble optics: Leonardo's cross revisited-Part 3, nonparaxial analytical methods.

In about 1508, Leonardo da Vinci first noted and sketched a cross-shaped caustic produced by a plane wave diagonally incident on the circularly symmetric meniscus surrounding a bubble on the surface of a water-filled container. This caustic was analyzed in two companion papers using a numerical ray theory spot diagram approach, and paraxial analytical methods. In this study we employ nonparaxial analytical methods, which are necessary when the outer bubble meniscus rises high above the ambient water surface. We also use a simple exactly soluble approximation to the outer meniscus shape, and obtain a distorted astroid caustic. We show that one of the refraction astroid cusp points is blocked by an aperture effect for steeply diagonally incident light, and the missing cusp is approximately replaced by a new cusp due to light transmitted through the bubble into the water, and reflecting from the underside of the outer meniscus.

Bubble optics: Leonardo's cross revisited-Part 1, numerical methods.

Around 1508, Leonardo DaVinci observed a curious image of the sun formed by a floating bubble. Now, some 500 years later, we give a full picture of the surprisingly rich phenomenology of the light pattern formed below surface bubbles. Under shallow illumination, and for shallow depths of water, the caustic deviates from the symmetrical astroid shape obtained for larger depths and/or near-vertical illumination. Whereas the astroid caustic involves refraction through the outer meniscus only, more complex ray paths explain the asymmetric, multicomponent (composite) light pattern.

GROWTH OF THE PEDIATRIC KNEE MENISCUS: A CADAVERIC STUDY

Background:The menisci of the knee play a critical role in maintaining structural integrity, as well as in load bearing and shock absorption. In adolescent patients, meniscal tear is a very common sports injury, and is frequently associated with concomitant traumatic injuries including tibial eminence fracture or ACL tear. The incidence of pediatric meniscal tears is increasing, and anatomic studies to guide repair, saucerization and transplantation do not exist.Hypothesis/Purpose:This study’s purpose was to evaluate meniscus dimensions in the developing meniscus and provide anatomic parameters for repair, saucerization, resection, transplantation.Methods:From images of 29 dissected cadaveric knee specimens between 1 month and 132 months of age obtained on a copy stand (14 left knee, 15 right knee), we made direct length measurements from the inner to outer meniscus rim at 45 degree intervals (12, 1:30/10:30, 3:00/9:00, 4:30/7:30 o’clock, 6 o’clock) using Autodesk Fusion 360 software (Figure 1.1). We also measured width between the outer medial and lateral meniscus rims, as well as CT measurements of coronal and sagittal width of the tibial plateau using OsiriX DICOM software. Generalized linear models were used to evaluate the associations of meniscal length measurements with age, tibial width, and meniscal width measurements. All statistical analyses were completed with a two-sided level of significance of 0.05.Results:All radial length measurements were predicted to increase significantly with age (p < 0.01), as coronal tibial width increases (p < 0.05), and as lateral-medial meniscal width increases (p < 0.001) (Figure 1.2). Other than the lateral 3 o’clock measurement (p = 0.119), all radial measurements were predicted to increase significantly as sagittal tibial width increases (p < 0.05). The posterior zones of the medial meniscus (6:00, 4:30/7:30) were found to increase in radial length at a faster rate than the anterior zones. The anterior zones of the medial meniscus (12:00, 1:30/10:30) had the slowest rate of growth.Discussion/Conclusion:Meniscus radial length is related to age, tibial plateau width, and lateral-medial meniscus width. Radial dimensions from normal lateral menisci may allow the surgeon to obtain ideal size of resection, saucerization of discoid menisci. The growth of medial meniscus posterior zones is greater than the anterior zones. This may be attributed to increased posterior region load bearing which increases with ambulation in the developing child. Improved anatomic understanding may help surgeons plan for discoid resection/saucerization/repair, and also support appropriate selection of meniscus allograft for transplantation.Figure 1.1.Figure 1.2.

Growth of The Pediatric Knee Meniscus: A Cadaveric Study

Objectives:The menisci of the knee (Figure 1) play a critical role in maintaining structural integrity, as well as in load bearing and shock absorption. In adolescent patients, meniscal tear is a very common sports injury, and is frequently associated with concomitant traumatic injuries including tibial eminence fracture or ACL tear. Depending on the severity of meniscal tear, surgical treatment options include arthroscopic partial or total meniscectomy, with a reported 78-88% success rate. Given the high incidence of pediatric meniscal injuries and reliance on landmarks to guide arthroscopic meniscus repair, surprisingly few human pediatric cadaveric studies are reported in the current literature. The primary purpose of our research was to evaluate the rates at which different zones of the meniscus rim lengthen with age during early adolescence. Our null hypothesis was that meniscus rim length is unrelated to patient age, tibial plateau width, or to lateral-medial meniscus width.Methods:From images of 29 dissected cadaveric knee specimens between 1 month and 132 months of age obtained on a copy stand (14 left knee, 15 right knee), we made direct length measurements from the inner to outer meniscus rim at 45 degree intervals (12, 1:30/10:30, 3:00/9:00, 4:30/7:30 o’clock, 6 o’clock) using Autodesk Fusion 360 software (Figure 2). We also measured width between the outer medial and lateral meniscus rims, as well as CT measurements of coronal and sagittal width of the tibial plateau using OsiriX DICOM software. Generalized linear models were used to evaluate the associations of meniscal length measurements with age, tibial width, and meniscal width measurements. All statistical analyses were completed with a two-sided level of significance of 0.05.Results:All meniscal length measurements were predicted to increase significantly as age increases (p < 0.01 for all), as coronal tibial width increases (p < 0.05 for all), and as lateral-medial meniscal width increases (p < 0.001 for all). Other than the lateral 3 o’clock measurement (p = 0.119), all meniscal length measurements were predicted to increase significantly as sagittal tibial width increases (p < 0.05 for the rest). Interestingly, the posterior zones of the medial meniscus (6 o’clock and 4:30/7:30 o’clock) were found to increase in length at a faster rate than the anterior zones (Figure 3), which supports our hypothesis that increased weight bearing is correlated with meniscus growth. The same length correlation was not identified in the lateral meniscus. Furthermore, the anterior zones of the medial meniscus (12 o’clock and 1:30/10:30 o’clock) were found to have the slowest rate of growth, presumably due to reduced weight bearing function anteriorly.Conclusions:We reject our null hypothesis that meniscus rim length is unrelated to age, tibial plateau width, or to lateral-medial meniscus width. Surprisingly, the posterior zones of the medial meniscus were found to grow at a faster rate with age compared to the anterior zones, which we attribute to the effect of increased weight bearing experienced by the posterior zones during knee bending exercise. Additionally, the anterior, lesser-weight bearing regions of the medial meniscus were found to develop at the slowest rate out of all zones measured. Further studies are underway to generalize these observations to all adolescent patients. This information will be useful for meniscus repair and transplantation surgical planning.

Possible reparative effect of low-intensity pulsed ultrasound (LIPUS) on injured meniscus.

Menisci are a pair of crescent-shaped fibrocartilages, particularly of which their inner region of meniscus is an avascular tissue. It has characteristics similar to those of articular cartilage, and hence is inferior in healing. We previously reported that low-intensity pulsed ultrasound (LIPUS) treatment stimulates the production of CCN2/CTGF, a protein involved in repairing articular cartilage, and the gene expression of major cartilage matrices such as type II collagen and aggrecan in cultured chondrocytes. Therefore, in this present study, we investigated whether LIPUS has also favorable effect on meniscus cells and tissues. LIPUS applied with a 60mW/cm2 intensity for 20min stimulated the gene expression and protein production of CCN2 via ERK and p38 signaling pathways, as well as gene expression of SOX9, aggrecan, and collagen type II in human inner meniscus cells in culture, and slightly stimulated the gene expression of CCN2 and promoted the migration in human outer meniscus cells in culture. LIPUS also induced the expression of Ccn2, Sox9, Col2a1, and Vegf in rat intact meniscus. Furthermore, histological evaluations showed that LIPUS treatment for 1 to 4weeks promoted healing of rat injured lateral meniscus, as evidenced by better and earlier angiogenesis and extracellular matrix synthesis. The data presented indicate that LIPUS treatment might prevent meniscus from degenerative change and exert a reparative effect on injured meniscus via up-regulation of repairing factors such as CCN2 and that it might thus be useful for treatment of an injured meniscus as a non-invasive therapy.

Hyaluronic acid promotes proliferation and migration of human meniscus cells via a CD44-dependent mechanism

ABSTRACTPurpose: Treatment of meniscal injury is important for osteoarthritis (OA) prevention. Meniscus cells are divided between inner and outer cells, which have different characteristics and vascularity. We evaluated the effects of hyaluronic acid (HA) on the proliferation and migration of human inner and outer meniscus cells, and investigated the underlying healing mechanisms.Materials and Methods: Lateral menisci from 18 patients who underwent total knee arthroplasty were used. Meniscus cells were harvested from the outer and inner menisci and evaluated using migration and proliferation assays after treatment with HA or chondroitin sulfate (CS). The effects of HA on prostaglandin E2 (PGE2)-induced apoptosis and gene expression were evaluated.Results: Cell migration and proliferation were increased by HA in a concentration-dependent manner, in both inner and outer meniscus cells. PGE2-induced apoptosis and caspase-3/7 activity were suppressed by HA in both inner and outer meniscus cells, and these effects were blocked by an anti-CD44 antibody. COL2A1 and ACAN mRNA levels were upregulated following HA treatment of inner meniscus cells. MMP13 mRNA was downregulated following CS stimulation of both inner and outer meniscus cells. These results suggest that CS treatment suppresses the inflammatory reaction rather than providing meniscal restoration. The phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways were activated by HA in both types of meniscus cells; these effects were blocked by treatment with an anti-CD44 antibody.Conclusions: HA promoted human meniscus regeneration by inhibiting apoptosis, promoting cell migration, and accelerating cell proliferation, potentially through the PI3K/MAPK pathway via the CD44 receptor.

Meniscus ECM-functionalised hydrogels containing infrapatellar fat pad-derived stem cells for bioprinting of regionally defined meniscal tissue.

Injuries to the meniscus of the knee commonly lead to osteoarthritis. Current therapies for meniscus regeneration, including meniscectomies and scaffold implantation, fail to achieve complete functional regeneration of the tissue. This has led to increased interest in cell and gene therapies and tissue engineering approaches to meniscus regeneration. The implantation of a biomimetic implant, incorporating cells, growth factors, and extracellular matrix (ECM)-derived proteins, represents a promising approach to functional meniscus regeneration. The objective of this study was to develop a range of ECM-functionalised bioinks suitable for 3D bioprinting of meniscal tissue. To this end, alginate hydrogels were functionalised with ECM derived from the inner and outer regions of the meniscus and loaded with infrapatellar fat pad-derived stem cells. In the absence of exogenously supplied growth factors, inner meniscus ECM promoted chondrogenesis of fat pad-derived stem cells, whereas outer meniscus ECM promoted a more elongated cell morphology and the development of a more fibroblastic phenotype. With exogenous growth factors supplementation, a more fibrogenic phenotype was observed in outer ECM-functionalised hydrogels supplemented with connective tissue growth factor, whereas inner ECM-functionalised hydrogels supplemented with TGFβ3 supported the highest levels of Sox-9 and type II collagen gene expression and sulfated glycosaminoglycans (sGAG) deposition. The final phase of the study demonstrated the printability of these ECM-functionalised hydrogels, demonstrating that their codeposition with polycaprolactone microfibres dramatically improved the mechanical properties of the 3D bioprinted constructs with no noticeable loss in cell viability. These bioprinted constructs represent an exciting new approach to tissue engineering of functional meniscal grafts.

The decellularized extracellular matrix in regenerative medicine.

The decellularized extracellular matrix in regenerative medicine.

Folded monocentric imager with deformable mirror focus.

We describe a catadioptric monocentric imager using an elastic central element focused by deformation of a fold mirror. We show the design of 6 mm and 12 mm focal length F/2.8 achromats and compare design performance when focusing by translating the sensor, translating the fold mirror, and by spherically deforming the fold mirror. We tested the 12 mm focal length design using a diamond turned polystyrene element as the outer meniscus lens (and mechanical mount), filled with an optical gel in contact with the central aperture and fold mirror, and demonstrate focusing by mechanical deformation of the fold mirror. The resolution at the spherical image surface was inspected by optical relay imaging, yielding a best focus MTF50 of 52.6 lp/mm.

The distribution of vascular endothelial growth factor in human meniscus and a meniscal injury model.

The meniscus plays an important role in controlling the complex biomechanics of the knee. Meniscus injury is common in the knee joint. The perimeniscal capillary plexus supplies the outer meniscus, whereas the inner meniscus is composed of avascular tissue. Angiogenesis factors, such as vascular endothelial growth factor (VEGF), have important roles in promoting vascularization of various tissues. VEGF-mediated neovascularization is beneficial to the healing of injured tissues. However, the distribution and angiogenic role of VEGF remains unclear in the meniscus and injured meniscus. We hypothesized that VEGF could affect meniscus cells and modulate the meniscus healing process. Menisci were obtained from total knee arthroplasty patients. Meniscal injury was created exvivo by a microsurgical blade. VEGF mRNA and protein expression were detected by the polymerase chain reaction and immunohistochemical analyses, respectively. In native meniscal tissue, the expression of VEGF and HIF-1α mRNAs could not be detected. However, VEGF and HIF-1α mRNAs were found in cultured meniscal cells (VEGF: outer>inner; HIF-1α: outer=inner). Injury increased mRNA levels of both VEGF and HIF-1α, with the increase being greatest in the outer area. Immunohistochemical analyses revealed that VEGF protein was detected mainly in the outer region and around injured areas of the meniscus. However, VEGF concentrations were similar between inner and outer menisci-derived media. This study demonstrated that both the inner and outer regions of the meniscus contained VEGF. HIF-1α expression and VEGF deposition were high in injured meniscal tissue. Our results suggest that injury stimulates the expression of HIF-1α and VEGF that may be preserved in the extracellular matrix as the healing stimulator of damaged meniscus, especially in the outer meniscus.

Hyaluronan stimulates chondrogenic gene expression in human meniscus cells

ABSTRACTPurpose/Aim of the Study: Inner meniscus cells have a chondrocytic phenotype, whereas outer meniscus cells have a fibroblastic phenotype. In this study, we examined the effect of hyaluronan on chondrocytic gene expression in human meniscus cells. Materials and Methods: Human meniscus cells were prepared from macroscopically intact lateral meniscus. Inner and outer meniscus cells were obtained from the inner and outer halves of the meniscus. The cells were stimulated with hyaluronan diluted in Dulbecco’s modified Eagle’s medium without serum to the desired concentration (0, 10, 100, and 1000 μg/mL) for 2–7 days. Cellular proliferation, migration, and polymerase chain reaction analyses were performed for the inner and outer cells separately. Meniscal samples perforated by a 2 mm diameter punch were maintained for 3 weeks in hyaluronan-supplemented medium and evaluated by histological analyses. Results: Hyaluronan increased the proliferation and migration of both meniscus cell types. Moreover, cellular counts at the surface of both meniscal tissue perforations were increased by hyaluronan treatments. In addition, hyaluronan stimulated α1(II) collagen expression in inner meniscus cells. Accumulation of type II collagen at the perforated surface of both meniscal samples was induced by hyaluronan treatment. Hyaluronan did not induce type I collagen accumulation around the injured site of the meniscus. Conclusion: Hyaluronan stimulated the proliferation and migration of meniscus cells. Our results suggest that hyaluronan may promote the healing potential of meniscus cells in damaged meniscal tissues.

Region-Specific Effect of the Decellularized Meniscus Extracellular Matrix on Mesenchymal Stem Cell–Based Meniscus Tissue Engineering

Background: The meniscus is the most commonly injured knee structure, and surgical repair is often ineffective. Tissue engineering–based repair or regeneration may provide a needed solution. Decellularized, tissue-derived extracellular matrices (ECMs) have received attention for their potential use as tissue-engineered scaffolds. In considering meniscus-derived ECMs (mECMs) for meniscus tissue engineering, it is noteworthy that the inner and outer regions of the meniscus have different structural and biochemical features, potentially directing the differentiation of cells toward region-specific phenotypes. Purpose: To investigate the applicability of mECMs for meniscus tissue engineering by specifically comparing region-dependent effects of mECMs on 3-dimensional constructs seeded with human bone marrow mesenchymal stem cells (hBMSCs). Study Design: Controlled laboratory study. Methods: Bovine menisci were divided into inner and outer halves and were minced, treated with Triton X-100 and DNase, and extracted with urea. Then, hBMSCs (1 × 106 cells/mL) were encapsulated in a photo–cross-linked 10% polyethylene glycol diacrylate scaffold containing mECMs (60 μg/mL) derived from either the inner or outer meniscus, with an ECM-free scaffold as a control. The cell-seeded constructs were cultured with chondrogenic medium containing recombinant human transforming growth factor β3 (TGF-β3) and were analyzed for expression of meniscus-associated genes as well as for the collagen (hydroxyproline) and glycosaminoglycan content as a function of time. Results: Decellularization was verified by the absence of 4′,6-diamidino-2-phenylindole (DAPI)–stained cell nuclei and a reduction in the DNA content. Quantitative real-time polymerase chain reaction showed that collagen type I expression was significantly higher in the outer mECM group than in the other groups, while collagen type II and aggrecan expression was highest in the inner mECM group. The collagen (hydroxyproline) content was highest in the outer mECM group, while the glycosaminoglycan content was higher in both the inner and outer mECM groups compared with the control group. Conclusion: These results showed that the inner mECM enhances the fibrocartilaginous differentiation of hBMSCs, while the outer mECM promotes a more fibroblastic phenotype. Our findings support the feasibility of fabricating bioactive scaffolds using region-specific mECM preparations for meniscus tissue engineering. Clinical Relevance: This is the first report to demonstrate the feasibility of applying region-specific mECMs for the engineering of meniscus implants capable of reproducing the biphasic, anatomic, and biochemical characteristics of the meniscus, features that should contribute to the feasibility of their clinical application.