Microstructure Analysis and Reconstruction of a Meniscus

Revealing the complexity of meniscus microvasculature through 3D visualization and analysis

Three-dimensional information is essential for a proper understanding of the healing potential of the menisci and their overall role in the knee joint. However, to date, the study of meniscal vascularity has relied primarily on two-dimensional imaging techniques. Here we present a method to elucidate the intricate 3D meniscal vascular network, revealing its spatial arrangement, connectivity and density. A polymerizing contrast agent was injected into the femoral artery of human cadaver legs, and the meniscal microvasculature was examined using micro-computed tomography at different levels of detail and resolution. The 3D vascular network was quantitatively assessed in a zone-base analysis using parameters such as diameter, length, tortuosity, and branching patterns. The results of this study revealed distinct vascular patterns within the meniscus, with the highest vascular volume found in the outer perimeniscal zone. Variations in vascular parameters were found between the different circumferential and radial meniscal zones. Moreover, through state-of-the-art 3D visualization using micro-CT, this study highlighted the importance of spatial resolution in accurately characterizing the vascular network. These findings, both from this study and from future research using this technique, improve our understanding of microvascular distribution, which may lead to improved therapeutic strategies.

On the fractional transversely isotropic functionally graded nature of soft biological tissues: Application to the meniscal tissue

This paper focuses on the origin of the poroelastic anisotropic behaviour of the meniscal tissue and its spatially varying properties. We present confined compression creep test results on samples extracted from three parts of the tissue (Central body, Anterior horn and Posterior horn) in three orientations (Circumferential, Radial and Vertical). We show that a poroelastic model in which the fluid flow evolution is ruled by non-integer order operators (fractional Darcy's law) provides accurate agreement with the experimental creep data. The model is validated against two additional sets of experimental data: stress relaxation and fluid loss during the consolidation process measured as weight reduction. Results show that the meniscus can be considered as a transversely isotropic poroelastic material. This behaviour is due to the fluid flow rate being about three times higher in the circumferential direction than in the radial and vertical directions in the body region of the meniscus. The 3D fractional poroelastic model is implemented in the finite element software to estimate the weight loss during the confined compression tests.

Region- and layer-specific investigations of the human menisci using SHG imaging and biaxial testing

In this paper, we examine the region- and layer-specific collagen fiber morphology via second harmonic generation (SHG) in combination with planar biaxial tension testing to suggest a structure-based constitutive model for the human meniscal tissue. Five lateral and four medial menisci were utilized, with samples excised across the thickness from the anterior, mid-body, and posterior regions of each meniscus. An optical clearing protocol enhanced the scan depth. SHG imaging revealed that the top samples consisted of randomly oriented fibers with a mean fiber orientation of 43.3 ^o . The bottom samples were dominated by circumferentially organized fibers, with a mean orientation of 9.5 ^o . Biaxial testing revealed a clear anisotropic response, with the circumferential direction being stiffer than the radial direction. The bottom samples from the anterior region of the medial menisci exhibited higher circumferential elastic modulus with a mean value of 21 MPa. The data from the two testing protocols were combined to characterize the tissue with an anisotropic hyperelastic material model based on the generalized structure tensor approach. The model showed good agreement in representing the material anisotropy with a mean r ² = 0.92.

Meniscus regeneration by 3D printing technologies: Current advances and future perspectives

Meniscal tears are a frequent orthopedic injury commonly managed by conservative strategies to avoid osteoarthritis development descending from altered biomechanics. Among cutting-edge approaches in tissue engineering, 3D printing technologies are extremely promising guaranteeing for complex biomimetic architectures mimicking native tissues. Considering the anisotropic characteristics of the menisci, and the ability of printing over structural control, it descends the intriguing potential of such vanguard techniques to meet individual joints’ requirements within personalized medicine. This literature review provides a state-of-the-art on 3D printing for meniscus reconstruction. Experiences in printing materials/technologies, scaffold types, augmentation strategies, cellular conditioning have been compared/discussed; outcomes of pre-clinical studies allowed for further considerations. To date, translation to clinic of 3D printed meniscal devices is still a challenge: meniscus reconstruction is once again clear expression of how the integration of different expertise (e.g., anatomy, engineering, biomaterials science, cell biology, and medicine) is required to successfully address native tissues complexities.