Biomechanical and cellular segmental characterization of human meniscus: building the basis for Tissue Engineering therapies

Regeneration of meniscus tissue using adipose mesenchymal stem cells-chondrocytes co-culture on a hybrid scaffold: In vivo study

The meniscus has poor intrinsic regenerative capacity and its damage inevitably leads to articular cartilage degeneration. We focused on evaluating the effects of Polyvinyl alcohol/Chitosan (PVA/Ch) scaffold seeded by adipose-derived mesenchymal stem cell (ASC) and articular chondrocytes (AC) in meniscus regeneration. The PVA/Ch scaffolds with different molar contents of Ch (Ch1, Ch2, Ch4 and Ch8) were cross-linked by pre-polyurethane chains. By increasing amount of Ch tensile modulus was increased from 83.51 MPa for Ch1 to 110 MPa for Ch8 while toughness showed decrease from 0.33 mJ/mm³ in Ch1 to 0.11 mJ/mm³ in Ch8 constructs. Moreover, swelling ratio and degradation rate increased with an increase in Ch amount. Scanning electron microscopy imaging was performed for pore size measurement and cell attachment. At day 21, Ch4 construct seeded by AC showed the highest expression with 24.3 and 22.64 folds increase in collagen II and aggrecan (p ≤ 0.05), respectively. Since, the mechanical properties, water uptake and degradation rate of Ch4 and Ch8 compositions had no statistically significant differences, Ch4 was selected for in vivo study. New Zealand rabbits were underwent unilateral total medial meniscectomy and AC/scaffold, ASC/scaffold, AC-ASC (co-culture)/scaffold and cell-free scaffold were engrafted. At 7 months post-implantation, macroscopic, histologic, and immunofluorescent studies for regenerated meniscus revealed better results in AC/scaffold group followed by AC-ASC/scaffold and ASC/scaffold groups. In the cell-free scaffold group, there was no obvious meniscus regeneration. Articular cartilages were best preserved in AC/scaffold group. The best histological score was observed in AC/scaffold group. Our results support that Ch4 scaffold seeded by AC alone can successfully regenerate meniscus in tearing injury and ASC has no significant contribution in the healing process.

Viscoelastic properties of rabbit osteoarthritic menisci: A correlation with matrix alterations

The aim of this study was to evaluate the effect of early osteoarthritis (OA) on the viscoelastic properties of rabbit menisci and to correlate the mechanical alterations with the microstructural changes. Anterior Cruciate Ligament Transection (ACLT) was performed in six male New-Zealand White rabbits on the right knee joint. Six healthy rabbits served as controls. Menisci were removed six weeks after ACLT and were graded macroscopically. Indentation-relaxation tests were performed in the anterior and posterior regions of the medial menisci. The collagen fibre organization and glycosaminoglycan (GAG) content were assessed by biphotonic confocal microscopy and histology, respectively. OA menisci displayed severe macroscopic lesions compared with healthy menisci (p=0.009). Moreover, the instantaneous and equilibrium moduli, which were 2.9±1.0MPa and 0.60±0.18MPa in the anterior region of healthy menisci, respectively, decreased significantly (p=0.03 and p=0.004, respectively) in OA menisci by 55% and 57%, respectively, indicating a global decrease in meniscal stiffness in this region. The equilibrium modulus alone decreased significantly (p=0.04) in the posterior region, going from 0.60±0.18MPa to 0.26±012MPa. This induced a loss of tissue elasticity. These mechanical changes were associated in the posterior region with a structural disruption of the superficial layers, from which the tie fibres emanate, and with a decrease in the GAG content in the anterior region. Consequently, the circumferential collagen fibres of the deep zone were dissociated and the collagen bundles were less compact. Our results demonstrate the strong meniscal modifications induced by ACLT at an early stage of OA and highlight the relationship between structural and chemical matrix alterations and mechanical properties.

Very early osteoarthritis changes sensitively fluid flow properties of articular cartilage

In this study, fibril-reinforced poroelastic (FRPE) modeling was used for rabbit knee after anterior cruciate ligament transection (ACLT) to assess how the mechanical properties of collagen, proteoglycans, and fluid in articular cartilage change in early osteoarthritis, and how site-specific these changes are. Unilateral ACLT was performed in eight skeletally mature, female New Zealand white rabbits. A separate control (CTRL) group consisted of knee joints of five non-operated rabbits. Animals were sacrificed at four weeks after ACLT and cartilage-on-bone samples from femoral groove, medial and lateral femoral condyles, and tibial plateaus were harvested. A stress-relaxation protocol in indentation geometry was applied and the FRPE model was fitted to the experimental force-time curve by minimizing the mean absolute error between experiment and simulation. The optimized parameters were: fibril network modulus (Ef), representing the collagen network; non-fibrillar matrix modulus (Enf), representing the PG matrix; and permeability (k), representing fluid flow. Permeability was increased significantly in the ACLT group compared to the CTRL group knees at all sites except for the medial tibial plateau. ACLT also caused a decrease in the Ef at all sites except for the medial and lateral tibial plateaus. The Enf of the ACLT group knees was altered only for the lateral femoral condyle. The results of this study suggest that early osteoarthritis primarily affects cartilage permeability and impairs the collagen network stiffness in a site-specific manner. These findings from early osteoarthritis indicate that fluid flow velocity in articular cartilage may change prior to quantifiable structural alterations in the tissue.