Engineering meniscus structure and function via multi-layered mesenchymal stem cell-seeded nanofibrous scaffolds

Abstract

Despite advances in tissue engineering for the knee meniscus, it remains a challenge to match the complex macroscopic and microscopic structural features of native tissue, including the circumferentially and radially aligned collagen bundles essential for mechanical function. To mimic this structural hierarchy, this study developed multi-lamellar mesenchymal stem cell (MSC)-seeded nanofibrous constructs. Bovine MSCs were seeded onto nanofibrous scaffolds comprised of poly(ε-caprolactone) with fibers aligned in a single direction (0° or 90° to the scaffold long axis) or circumferentially aligned (C). Multi-layer groups (0°/0°/0°, 90°/90°/90°, 0°/90°/0°, 90°/0°/90°, and C/C/C) were created and cultured for a total of 6 weeks under conditions favoring fibrocartilaginous tissue formation. Tensile testing showed that 0° and C single layer constructs had stiffness values several fold higher than 90° constructs. For multi-layer groups, the stiffness of 0°/0°/0° constructs was higher than all other groups, while 90°/90°/90° constructs had the lowest values. Data for collagen content showed a general positive interactive effect for multi-layers relative to single layer constructs, while a positive interaction for stiffness was found only for the C/C/C group. Collagen content and cell infiltration occurred independent of scaffold alignment, and newly formed collagenous matrix followed the scaffold fiber direction. Structural hierarchies within multi-lamellar constructs dictated biomechanical properties, and only the C/C/C constructs with non-orthogonal alignment within layers featured positive mechanical reinforcement as a consequence of the layered construction. These multi-layer constructs may serve as functional substitutes for the meniscus as well as test beds to understand the complex mechanical principles that enable meniscus function.

Micromechanical anisotropy and heterogeneity of the meniscus extracellular matrix

“…Unfortunately, similar to articular cartilage, the meniscus has limited self-healing capabilities, especially in the avascular, proteoglycan-rich inner zone [16]. To repair damaged meniscus and recover normal joint function, it is necessary not only to replicate the whole tissue morphology of the native meniscus [17], but also to restore its matrix structural heterogeneity at the nano-to-microscale [18], which is critical for the tissue to perform its specialized tissue-level properties [1]. To this end, it is imperative to understand the structure-mechanical function principles of the native meniscus ECM at multiple length scales [19].…”

Meniscus mechanics and mechanobiology

“…A complete understanding of tissue level mechanics is also important as it sets design criteria for the next generation of replacement devices. Abdelgaied et al (2015) describe the impact of decellularization on the biomechanical properties of a potential xenogeneic replacement tissue, while Fisher et al (2015) and Puetzer et al (2015) focus on the mechanical behavior of newly developed tissue engineered constructs. Fisher et al assess the impact of mimicking the structural complexities of the meniscus within multi-lamellar mesenchymal stem cell-seeded nanofibrous constructs while Puetzer et al highlight the important of mechanical anchoring on the development of anisotropic behavior in collagen gels seeded with meniscal fibrochondrocytes.…”

Multilayered polycaprolactone/gelatin fiber-hydrogel composite for tendon tissue engineering

“…To achieve this goal, the rapid, robust integration between scaffold layers and sufficient incorporation of therapeutic cells must be carefully balanced [46, 50, 51]. In the scaffold described here, the gelatin component was found evenly distributed throughout the depth of PCL mesh, and therefore enabled integration of multiple sheets along the z axis upon photocrosslinking.…”