Effect of meniscus modelling assumptions in a static tibiofemoral finite element model: importance of geometry over material

Finite element studies of the tibiofemoral joint have increased use in research, with attention often placed on the material models. Few studies assess the effect of meniscus modelling assumptions in image-based models on contact mechanics outcomes. This work aimed to assess the effect of modelling assumptions of the meniscus on knee contact mechanics and meniscus kinematics. A sensitivity analysis was performed using three specimen-specific tibiofemoral models and one generic knee model. The assumptions in representing the meniscus attachment on the tibia (shape of the roots and position of the attachment), the material properties of the meniscus, the shape of the meniscus and the alignment of the joint were evaluated, creating 40 model instances. The values of material parameters for the meniscus and the position of the root attachment had a small influence on the total contact area but not on the meniscus displacement or the force balance between condyles. Using 3D shapes to represent the roots instead of springs had a large influence in meniscus displacement but not in knee contact area. Changes in meniscus shape and in knee alignment had a significantly larger influence on all outcomes of interest, with differences two to six times larger than those due to material properties. The sensitivity study demonstrated the importance of meniscus shape and knee alignment on meniscus kinematics and knee contact mechanics, both being more important than the material properties or the position of the roots. It also showed that differences between knees were large, suggesting that clinical interpretations of modelling studies using single geometries should be avoided.

Removal of GAGs Regulates Mechanical Properties, Collagen Fiber Formation, and Alignment in Tissue Engineered Meniscus

The complex fibrillar architecture of native meniscus is essential for proper function and difficult to recapitulate in vitro. In the native meniscus, proteoglycan content is low during the development of collagen fibers and progressively increases with aging. In vitro, fibrochondrocytes produce glycosaminoglycans (GAGs) early in culture, in contrast to native tissue, where they are deposited after collagen fibers have formed. This difference in the timing of GAG production hinders the formation of a mature fiber network in such in vitro models. In this study, we removed GAGs from collagen gel-based tissue engineered constructs using chondroitinase ABC (cABC) and evaluated the effect on the formation and alignment of collagen fibers and the subsequent effect on tensile and compressive mechanical properties. Removal of GAGs during maturation of in vitro constructs improved collagen fiber alignment in tissue engineered meniscus constructs. Additionally, removal of GAGs during maturation improved fiber alignment without compromising compressive strength, and this removal improved not only fiber alignment and formation but also tensile properties. The increased fiber organization in cABC-treated groups also appeared to influence the size, shape, and location of defects in these constructs, suggesting that treatment may prevent the propagation of large defects under loading. This data gives another method of modulating the ECM for improved collagen fiber formation and mechanical properties in tissue engineered constructs.

Quantifying the differential functional behavior between the medial and lateral meniscus after posterior meniscus root tears

Meniscus tears of the knee are among the most common orthopedic knee injury. Specifically, tears of the posterior root can result in abnormal meniscal extrusion leading to decreased function and progressive osteoarthritis. Despite contemporary surgical treatments of posterior meniscus root tears, there is a low rate of healing and an incidence of residual meniscus extrusion approaching 30%, illustrating an inability to recapitulate native meniscus function. Here, we characterized the differential functional behavior of the medial and lateral meniscus during axial compression load and dynamic knee motion using a cadaveric model. We hypothesized essential differences in extrusion between the medial and lateral meniscus in response to axial compression and knee range of motion. We found no differences in the amount of meniscus extrusion between the medial and lateral meniscus with a competent posterior root (0.338mm vs. 0.235mm; p-value = 0.181). However, posterior root detachment resulted in a consistently increased meniscus extrusion for the medial meniscus compared to the lateral meniscus (2.233mm vs. 0.4705mm; p-value < 0.0001). Moreover, detachment of the posterior root of the medial meniscus resulted in an increase in extrusion at all angles of knee flexion and was most pronounced (4.00mm ± 1.26mm) at 30-degrees of knee flexion. In contrast, the maximum mean extrusion of the lateral meniscus was 1.65mm ± 0.97mm, occurring in full extension. Furthermore, only the medial meniscus extruded during dynamic knee flexion after posterior root detachment. Given the differential functional behaviors between the medial and lateral meniscus, these findings suggest that posterior root repair requires reducing overall meniscus extrusion and recapitulating the native functional responses specific to each meniscus.

Characterization of regional meniscal cell and chondrocyte phenotypes and chondrogenic differentiation with histological analysis in osteoarthritic donor-matched tissues

Meniscus degeneration is closely related to the progression of knee osteoarthritis (OA). However, there is currently a lack of quantitative and objective metrics to assess OA meniscal cell phenotypes. In this study we investigated the phenotypic markers and chondrogenic potency of avascular and vascular meniscal cells and chondrocytes from medial OA knee joints (n = 10). Flow cytometry results showed that a significantly greater percentage of meniscal cells were positive for CD49b, CD49c and CD166 compared to donor-matched chondrocytes after 14 days in monolayer culture. The integrins, CD49b and CD29, were expressed at a significantly higher level on avascular meniscal cells derived from tissues with a more degenerated inner border than non-degenerate menisci, suggesting that the integrin family may play an important role in meniscus OA pathology. Collagen fibres arranged in a "tree-like" formation within the meniscus appeared to have less blood vessels associated with them in the vascular region of the most degenerate menisci, which may indicate that such structures are involved in the pathological process. We have demonstrated that meniscal cells derived from the lateral meniscus in medial OA patients have chondrogenic capacity in vitro and hence could represent a potential cell source to consider for meniscus tissue engineering.

Measuring the Internal Stress in Ovine Meniscus During Simulated In Vivo Gait Kinematics: A Novel Method Using Fibre Optic Technology

Changes in stress transferred across articular joints have been described as a substantial factor in the initiation and progression of joint disease such as post-traumatic osteoarthritis and have thus been of interest to biomechanical researchers. However, to date, stress magnitudes within the menisci have not been successfully measured. In this study, a novel method for measuring stress within the menisci is presented. Small Fibre Bragg Grating (FBG) sensors were inserted inside menisci and used to measure mechanical stress during replicated gait cycles. In-vitro stress measurements within the menisci were preformed for healthy gait and gait following surgical damage to the joints. Together with our capability to reproduce in vivo motions accurately, the improvements in fibre optic technology have allowed for the first direct measurement of mechanical stress in menisci.

EMG-Assisted Muscle Force Driven Finite Element Model of the Knee Joint with Fibril-Reinforced Poroelastic Cartilages and Menisci

Abnormal mechanical loading is essential in the onset and progression of knee osteoarthritis. Combined musculoskeletal (MS) and finite element (FE) modeling is a typical method to estimate load distribution and tissue responses in the knee joint. However, earlier combined models mostly utilize static-optimization based MS models and muscle force driven FE models typically use elastic materials for soft tissues or analyze specific time points of gait. Therefore, here we develop an electromyography-assisted muscle force driven FE model with fibril-reinforced poro(visco)elastic cartilages and menisci to analyze knee joint loading during the stance phase of gait. Moreover, since ligament pre-strains are one of the important uncertainties in joint modeling, we conducted a sensitivity analysis on the pre-strains of anterior and posterior cruciate ligaments (ACL and PCL) as well as medial and lateral collateral ligaments (MCL and LCL). The model produced kinematics and kinetics consistent with previous experimental data. Joint contact forces and contact areas were highly sensitive to ACL and PCL pre-strains, while those changed less cartilage stresses, fibril strains, and fluid pressures. The presented workflow could be used in a wide range of applications related to the aetiology of cartilage degeneration, optimization of rehabilitation exercises, and simulation of knee surgeries.

The Meniscus Tear: A Review of Stem Cell Therapies

Meniscal injuries have posed a challenging problem for many years, especially considering that historically the meniscus was considered to be a structure with no important role in the knee joint. This led to earlier treatments aiming at the removal of the entire structure in a procedure known as a meniscectomy. However, with the current understanding of the function and roles of the meniscus, meniscectomy has been identified to accelerate joint degradation significantly and is no longer a preferred treatment option in meniscal tears. Current therapies are now focused to regenerate, repair, or replace the injured meniscus to restore its native function. Repairs have improved in technique and materials over time, with various implant devices being utilized and developed. More recently, strategies have applied stem cells, tissue engineering, and their combination to potentiate healing to achieve superior quality repair tissue and retard the joint degeneration associated with an injured or inadequately functioning meniscus. Accordingly, the purpose of this current review is to summarize the current available pre-clinical and clinical literature using stem cells and tissue engineering for meniscal repair and regeneration.

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.

Understanding the Stiff-to-Compliant Transition of the Meniscal Attachments by Spatial Correlation of Composition, Structure, and Mechanics

Recently, the scientific community has shown considerable interest in engineering tissues with organized compositional and structural gradients to mimic hard-to-soft tissue interfaces. This effort is hindered by an incomplete understanding of the construction of native tissue interfaces. In this work, we combined Raman microscopy and confocal elastography to map compositional, structural, and mechanical features across the stiff-to-compliant interface of the attachments of the meniscus in the knee. This study provides new insight into the methods by which biology mediates multiple orders of magnitude changes in stiffness over tens of microns. We identified how the nano- to mesoscale architecture mediates complex microscale transitional regions across the interface: two regions defined by chemical composition, five distinguished by structural features, and three mechanically distinct regions. We identified three major components that lead to a robust interface between a soft tissue and bone: mobile collagen fiber units, a continuous interfacial region, and a local stiffness gradient. This tissue architecture allows for large displacements of collagen fibers in the attachments, enabling meniscal movement without localizing strains to the soft tissue-to-bone interface. The interplay of these regions reveals a method relying on hierarchical structuring across multiple length scales to minimize stress concentrators between highly dissimilar materials. These insights inspire new design strategies for synthetic soft tissue-to-bone attachments and biomimetic material interfaces.

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.

Cellular and Chemical Gradients to Engineer the Meniscus-to-Bone Insertion

Tissue-engineered menisci hold promise as an alternative to allograft procedures but require a means of robust fixation to the native bone. The insertion of the meniscus into bone is critical for meniscal function and inclusion of a soft tissue-to-bone interface in a tissue engineered implant can aid in the fixation process. The native insertion is characterized by gradients in composition, tissue architecture, and cellular phenotype, which are all difficult to replicate. In this study, a soft tissue-to-bone interface is tissue engineered with a cellular gradient of fibrochondrocytes and mesenchymal stem cells and subjected to a biochemical gradient through a custom media diffusion bioreactor. These constructs, consisting of interpenetrating collagen and boney regions, display improved mechanical performance and collagen organization compared to controls without a cellular or chemical gradient. Media gradient exposure produces morphological features in the constructs that appear similar to the native tissue. Collectively, these data show that cellular and biochemical gradients improve integration between collagen and bone in a tissue engineered soft tissue-to-bone construct.

Decorin age-related variations in the distribution of pig extracellular matrix meniscus

Menisci act like shock absorbers and transmit load across the tibiofemoral joint by increasing congruency during movements or body weight load. This leads to decreasing the resultant stress on the articular cartilages. The meniscus has a dense extracellular matrix (ECM) composed of water, different types of collagens, and proteoglycans, such as decorin, aggrecan and biglycan. Decorin (DCN) regulates collagen fibrillogenesis acting on collagen fibrils diameter and fibrils orientation to achieve the proper assembly of its network. This work investigates the spatial disposition of this fundamental protein in pig meniscus' matrix by immunohistochemistry and western blot analysis. DCN shows an increasing trend, moving from neonatal to adult pig menisci. Adult meniscus, in porcine species, is the only one that could be considered fully mature and functional, and, even if an increasing trend is seen, no precise phenotypical switch points are seen in the age stages considered in this study.

Biomechanical analysis of the meniscus and cartilage of the knee during a typical Tai Chi movement-brush-knee and twist-step

This study aimed to analyze the biomechanical response of the knee cartilage and meniscus to a typical Tai Chi (TC) movement, brush-knee and twist-step (BKTS). Kinematic and kinetic data was recorded while an experienced TC practitioner performed normal walking, jogging and BKTS. The kinetic data were then imported into a validated finite element model of the knee joint to examine the biomechanical response of the articular cartilage and meniscus. Compared with walking and jogging, the BKTS movement showed a greater increase in the range of motion (ROM) of the knee. The ROM in the sagittal plane was 56° (walking), 38° (jogging) and 93° (BKTS). In coronal plane, the knee ROM was 8° (walking), 11° (jogging) and 28° (BKTS). And in horizontal plane the ROM was 17° (walking), 15° (jogging) and 29° (BKTS). The finite element simulation demonstrated that the pressure contact stress is much more concentrated during walking and jogging than BKTS, which is consistent with the lower peak contact stresses recorded on the cartilage and meniscus. In conclusion, the TC movement produced a gentler stress state on the meniscus and cartilage, while also requiring a greater knee ROM. Practicing TC may have a lower risk of knee joint injury compared to walking and jogging.

The ionic contribution of proteoglycans to mechanical stiffness of the meniscus

Load transmission is an important function of the meniscus. In articular cartilage, proteoglycans help maintain hydration via negatively charged moieties. We aimed to investigate the influence of electrostatic effects on stiffness of meniscal tissue. Circular discs from bovine menisci of 8 mm diameter and 5 mm thickness were placed within a confined compression chamber. The apparatus was bathed in distilled water, 0.14 M PBS or 3 M PBS before being subjected to 5% ramp compressive strain and held for 300s. FEBio software was used to fit resultant relaxation curves to a non-linear poroviscoelastic model with strain dependent Holmes-Mow permeability. Analysis was conducted using one-way ANOVA with Tukey post-hoc analysis. 10 samples were tested in each solution. Significant differences (p < 0.05) were observed between the values for Young's modulus, zero strain dependent permeability and the viscoelastic coefficient for samples tested in 3 M PBS as compared to deionised water/0.14 M PBS. No significant differences were observed in the strain dependent/stiffening coefficients or the relaxation time. Approximately 79% of the stiffness of the meniscus appears attributable to ionic effects. Ionic effects play a significant role in the mechanical stiffness of the meniscus. It is important to include the influence of ionic effects when developing mathematical models of this tissue.

Surgical Feasibility of a One-Stage Cell-Based Arthroscopic Procedure for Meniscus Regeneration: A Cadaveric Study

IMPACT STATEMENT

Meniscus injury remains the most common indication for orthopedic surgery, but loss of functioning meniscus tissue is strongly correlated with development of early osteoarthritis. However, current clinical options for tissue engineering of the meniscus are limited. This study demonstrates the feasibility of combining human meniscus cells with mesenchymal stromal cells to enhance a meniscus scaffold for meniscus regeneration in a one-stage solution for partial meniscal deficiency.

Current Concepts in Meniscus Tissue Engineering and Repair

The meniscus is the most commonly injured structure in the human knee. Meniscus deficiency has been shown to lead to advanced osteoarthritis (OA) due to abnormal mechanical forces, and replacement strategies for this structure have lagged behind other tissue engineering endeavors. The challenges include the complex 3D structure with individualized size parameters, the significant compressive, tensile and shear loads encountered, and the poor blood supply. In this progress report, a review of the current clinical treatments for different types of meniscal injury is provided. The state-of-the-art research in cellular therapies and novel cell sources for these therapies is discussed. The clinically available cell-free biomaterial implants and the current progress on cell-free biomaterial implants are reviewed. Cell-based tissue engineering strategies for the repair and replacement of meniscus are presented, and the current challenges are identified. Tissue-engineered meniscal biocomposite implants may provide an alternative solution for the treatment of meniscal injury to prevent OA in the long run, because of the limitations of the existing therapies.

Structure-Function relationships of equine menisci

Meniscal pathologies are among the most common injuries of the femorotibial joint in both human and equine patients. Pathological forces and ensuing injuries of the cranial horn of the equine medial meniscus are considered analogous to those observed in the human posterior medial horn. Biomechanical properties of human menisci are site- and depth- specific. However, the influence of equine meniscus topography and composition on its biomechanical properties is yet unknown. A better understanding of equine meniscus composition and biomechanics could advance not only veterinary therapies for meniscus degeneration or injuries, but also further substantiate the horse as suitable translational animal model for (human) meniscus tissue engineering. Therefore, the aim of this study was to investigate the composition and structure of the equine knee meniscus in a site- and age-specific manner and their relationship with potential site-specific biomechanical properties. The meniscus architecture was investigated histologically. Biomechanical testing included evaluation of the shore hardness (SH), stiffness and energy loss of the menisci. The SH was found to be subjected to both age and site-specific changes, with an overall higher SH of the tibial meniscus surface and increase in SH with age. Stiffness and energy loss showed neither site nor age related significant differences. The macroscopic and histologic similarities between equine and human menisci described in this study, support continued research in this field.

Lateral atlantoaxial joint meniscoid volume in individuals with whiplash associated disorder: A case-control study

BACKGROUND

Lateral atlantoaxial (LAA) joints are established sources of nociceptive input in chronic whiplash associated disorder (WAD). These joints contain intra-articular meniscoids that may be damaged in whiplash trauma. LAA joint meniscoid morphology has not been investigated comprehensively in a chronic WAD population, and it is unclear whether morphological differences exist compared to a pain-free population.

OBJECTIVES

This study examined LAA joint meniscoid volume in individuals with chronic WAD who report pain in a distribution consistent with LAA joint pain.

DESIGN

Case-control study.

METHOD

Fourteen individuals with chronic WAD with pain in an LAA joint distribution (mean [SD] age 38.1 [10.8] years; six female) and 14 age- and sex-matched pain-free controls (38.0 [10.5] years) underwent cervical spine magnetic resonance imaging. LAA joint images were inspected for meniscoids; meniscoid volume was calculated in mm³ and as a percentage of articular cavity volume. Symptom duration, location and intensity were recorded. Data were analysed using paired t-tests, Wilcoxon signed-rank testing, Spearman's rank testing, linear and logistic regression (α < 0.05).

RESULTS

Ventral and dorsal meniscoids (n = 112) were found in each LAA joint. Greater dorsal meniscoid volume as a percentage of articular cavity volume was associated with higher pain intensity (odds ratio 1.48, p = 0.03; likelihood ratio test chi-square₂ = 6.64, p = 0.04), however no significant differences existed between meniscoid volumes of WAD and control participants.

CONCLUSIONS

Findings indicate a potential link between dorsal LAA joint meniscoid volume and pain, suggesting larger meniscoid size may have pathoanatomical significance in WAD.

The fibular meniscus of the kangaroo as an adaptation against external tibial rotation during saltatorial locomotion

The kangaroo knee is, as in other species, a complex diarthrodial joint dependent on interacting osseous, cartilaginous and ligamentous components for its stability. While principal load bearing occurs through the femorotibial articulation, additional lateral articulations involving the fibula and lateral fabella also contribute to the functional arrangement. Several fibrocartilage and ligamentous structures in this joint remain unexplained or have been misunderstood in previous studies. In this study, we review the existing literature on the structure of the kangaroo 'knee' before providing a new description of the gross anatomical and histological structures. In particular, we present strong evidence that the previously described 'femorofibular disc' is best described as a fibular meniscus on the basis of its gross and histological anatomy. Further, we found it to be joined by a distinct tendinous tract connecting one belly of the m. gastrocnemius with the lateral meniscus, via a hyaline cartilage cornu of the enlarged lateral fabella. The complex of ligaments connecting the fibular meniscus to the surrounding connective tissues and muscles appears to provide a strong resistance to external rotation of the tibia, via the restriction of independent movement of the proximal fibula. We suggest this may be an adaptation to resist the rotational torque applied across the joint during bipedal saltatory locomotion in kangaroos.

Meniscus, articular cartilage and nucleus pulposus: a comparative review of cartilage-like tissues in anatomy, development and function

The degradation of cartilage in the human body is impacted by aging, disease, genetic predisposition and continued insults resulting from daily activity. The burden of cartilage defects (osteoarthritis, rheumatoid arthritis, intervertebral disc damage, knee replacement surgeries, etc.) is daunting in light of substantial economic and social stresses. This review strives to broaden the scope of regenerative medicine and tissue engineering approaches used for cartilage repair by comparing and contrasting the anatomical and functional nature of the meniscus, articular cartilage (AC) and nucleus pulposus (NP). Many review papers have provided detailed evaluations of these cartilages and cartilage-like tissues individually but none have comprehensively examined the parallels and inconsistencies in signaling, genetic expression and extracellular matrix composition between tissues. For the first time, this review outlines the importance of understanding these three tissues as unique entities, providing a comparative analysis of anatomy, ultrastructure, biochemistry and function for each tissue. This novel approach highlights the similarities and differences between tissues, progressing research toward an understanding of what defines each tissue as distinctive. The goal of this paper is to provide researchers with the fundamental knowledge to correctly engineer the meniscus, AC and NP without inadvertently developing the wrong tissue function or biochemistry.

Current advances in the development of natural meniscus scaffolds: innovative approaches to decellularization and recellularization

The increasing rate of injuries to the meniscus indicates the urgent need to develop effective repair strategies. Irreparably damaged menisci can be replaced and meniscus allografts represent the treatment of choice; however, they have several limitations, including availability and compatibility. Another approach is the use of artificial implants but their chondroprotective activities are still not proved clinically. In this situation, tissue engineering offers alternative natural decellularized extracellular matrix (ECM) scaffolds, which have shown biomechanical properties comparable to those of native menisci and are characterized by low immunogenicity and promising regenerative potential. In this article, we present an overview of meniscus decellularization methods and discuss their relative merits. In addition, we comparatively evaluate cell types used to repopulate decellularized scaffolds and analyze the biocompatibility of the existing experimental models. At present, acellular ECM hydrogels, as well as slices and powders, have been explored, which seems to be promising for partial meniscus regeneration. However, their inferior biomechanical properties (compressive and tensile stiffness) compared to natural menisci should be improved. Although an optimal decellularized meniscus scaffold still needs to be developed and thoroughly validated for its regenerative potential in vivo, we believe that decellularized ECM scaffolds are the future biomaterials for successful structural and functional replacement of menisci.

Role of scaffold mean pore size in meniscus regeneration

Recently, meniscus tissue engineering offers a promising management for meniscus regeneration. Although rarely reported, the microarchitectures of scaffolds can deeply influence the behaviors of endogenous or exogenous stem/progenitor cells and subsequent tissue formation in meniscus tissue engineering. Herein, a series of three-dimensional (3D) poly(ε-caprolactone) (PCL) scaffolds with three distinct mean pore sizes (i.e., 215, 320, and 515μm) were fabricated via fused deposition modeling. The scaffold with the mean pore size of 215μm significantly improved both the proliferation and extracellular matrix (ECM) production/deposition of mesenchymal stem cells compared to all other groups in vitro. Moreover, scaffolds with mean pore size of 215μm exhibited the greatest tensile and compressive moduli in all the acellular and cellular studies. In addition, the relatively better results of fibrocartilaginous tissue formation and chondroprotection were observed in the 215μm scaffold group after substituting the rabbit medial meniscectomy for 12weeks. Overall, the mean pore size of 3D-printed PCL scaffold could affect cell behavior, ECM production, biomechanics, and repair effect significantly. The PCL scaffold with mean pore size of 215μm presented superior results both in vitro and in vivo, which could be an alternative for meniscus tissue engineering.

STATEMENT OF SIGNIFICANCE

Meniscus tissue engineering provides a promising strategy for meniscus regeneration. In this regard, the microarchitectures (e.g., mean pore size) of scaffolds remarkably impact the behaviors of cells and subsequent tissue formation, which has been rarely reported. Herein, three three-dimensional poly(ε-caprolactone) scaffolds with different mean pore sizes (i.e., 215, 320, and 515μm) were fabricated via fused deposition modeling. The results suggested that the mean pore size significantly affected the behaviors of endogenous or exogenous stem/progenitor cells and subsequent tissue formation. This study furthers our understanding of the cell-scaffold interaction in meniscus tissue engineering, which provides unique insight into the design of meniscus scaffolds for future clinical application.