Anisotropy and inhomogeneity of permeability and fibrous network response in the pars intermedia of the human lateral meniscus

Advances in meniscus tissue engineering: Towards bridging the gaps from bench to bedside

Meniscus is vital for maintaining the anatomical and functional integrity of knee. Injuries to meniscus, commonly caused by trauma or degenerative processes, can result in knee joint dysfunction and secondary osteoarthritis, while current conservative and surgical interventions for meniscus injuries bear suboptimal outcomes. In the past decade, there has been a significant focus on advancing meniscus tissue engineering, encompassing isolated scaffold strategies, biological augmentation, physical stimulus, and meniscus organoids, to improve the prognosis of meniscus injuries. Despite noteworthy promising preclinical results, translational gaps and inconsistencies in the therapeutic efficiency between preclinical and clinical studies exist. This review comprehensively outlines the developments in meniscus tissue engineering over the past decade (Scheme 1). Reasons for the discordant results between preclinical and clinical trials, as well as potential strategies to expedite the translation of bench-to-bedside approaches are analyzed and discussed.

Understanding the Structure-Function Relationship through 3D Imaging and Biomechanical Analysis: A Novel Methodological Approach Applied to Anterior Cruciate Ligaments

Understanding the microstructure of fibrous tissues, like ligaments, is crucial due to their nonlinear stress-strain behavior from unique fiber arrangements. This study introduces a new method to analyze the relationship between the microstructure and function of anterior cruciate ligaments (ACL). We tested the procedure on two ACL samples, one from a healthy individual and one from an osteoarthritis patient, using a custom tensioning device within a micro-CT scanner. The samples were stretched and scanned at various strain levels (namely 0%, 1%, 2%, 3%, 4%, 6%, 8%) to observe the effects of mechanical stress on the microstructure. The micro-CT images were processed to identify and map fibers, assessing their orientations and volume fractions. A probabilistic mathematical model was then proposed to relate the geometric and structural characteristics of the ACL to its mechanical properties, considering fiber orientation and thickness. Our feasibility test indicated differences in mechanical behavior, fiber orientation, and volume distribution between ligaments of different origins. These indicative results align with existing literature, validating the proposed methodology. However, further research is needed to confirm these preliminary observations. Overall, our comprehensive methodology shows promise for improving ACL diagnosis and treatment and for guiding the creation of tissue-engineered grafts that mimic the natural properties and microstructure of healthy tissue, thereby enhancing integration and performance in biomedical applications.

Model Properties and Clinical Application in the Finite Element Analysis of Knee Joint: A Review

The knee is the most complex joint in the human body, including bony structures like the femur, tibia, fibula, and patella, and soft tissues like menisci, ligaments, muscles, and tendons. Complex anatomical structures of the knee joint make it difficult to conduct precise biomechanical research and explore the mechanism of movement and injury. The finite element model (FEM), as an important engineering analysis technique, has been widely used in many fields of bioengineering research. The FEM has advantages in the biomechanical analysis of objects with complex structures. Researchers can use this technology to construct a human knee joint model and perform biomechanical analysis on it. At the same time, finite element analysis can effectively evaluate variables such as stress, strain, displacement, and rotation, helping to predict injury mechanisms and optimize surgical techniques, which make up for the shortcomings of traditional biomechanics experimental research. However, few papers introduce what material properties should be selected for each anatomic structure of knee FEM to meet different research purposes. Based on previous finite element studies of the knee joint, this paper summarizes various modeling strategies and applications, serving as a reference for constructing knee joint models and research design.

The biomechanical properties of human menisci: A systematic review

Biomechanical characterization of meniscal tissue ex vivo remains a critical need, particularly for the development of suitable meniscus replacements or therapeutic strategies that target the native mechanical properties of the meniscus. To date, a huge variety of test configurations and protocols have been reported, making it extremely difficult to compare the respective outcome parameters, thereby leading to misinterpretation. Therefore, the purpose of this systematic review was to identify test-specific parameters that contribute to uncertainties in the determination of mechanical properties of the human meniscus and its attachments, which derived from common quasi-static and dynamic tests in tension, compression, and shear. Strong evidence was found that the determined biomechanical properties vary significantly depending on the specific test parameters, as indicated by up to tenfold differences in both tensile and compressive properties. Test mode (stress relaxation, creep, cyclic) and configuration (unconfined, confined, in-situ), specimen shape and dimensions, preconditioning regimes, loading rates, post-processing of experimental data, and specimen age and degeneration were identified as the most critical parameters influencing the outcome measures. In conclusion, this work highlights an unmet need for standardization and reporting guidelines to facilitate comparability and may prove beneficial for evaluating the mechanical properties of novel meniscus constructs. STATEMENT OF SIGNIFICANCE: The biomechanical properties of the human meniscus have been studied extensively over the past decades. However, it remains unclear to what extent both test protocol and specimen-related differences are responsible for the enormous variability in material properties. Therefore, this systematic review analyzes the biomechanical properties of the human meniscus in the context of the underlying testing protocol. The most sensitive parameters affecting the determination of mechanical properties were identified and critically discussed. Currently, it is of utmost importance for scientists evaluating potential meniscal scaffolds and biomaterials to have a control group rather than a direct comparison to the literature. Standardization of both test procedures and reporting requirements is needed to improve and accelerate the development of meniscal replacement constructs.

Comparison of constitutive models for meniscus and their effect on the knee joint biomechanics during gait

Mechanical behavior of meniscus can be modeled using constitutive material models of varying complexity, such as isotropic elastic or fibril reinforced poroelastic (FRPE). However, the FRPE material is complex to implement, computationally demanding in 3D geometries, and simulation is time-consuming. Hence, we aimed to quantify the most suitable and efficient constitutive model of meniscus for simulation of cartilage responses in the knee joint during walking. We showed that simpler constitutive material models can reproduce similar cartilage responses to a knee model with the FRPE meniscus, but only knee models that consider orthotropic elastic meniscus can also reproduce meniscus responses adequately.

Tensile energy dissipation and mechanical properties of the knee meniscus: relationship with fiber orientation, tissue layer, and water content

Introduction: The knee meniscus distributes and dampens mechanical loads. It is composed of water (∼70%) and a porous fibrous matrix (∼30%) with a central core that is reinforced by circumferential collagen fibers enclosed by mesh-like superficial tibial and femoral layers. Daily loading activities produce mechanical tensile loads which are transferred through and dissipated by the meniscus. Therefore, the objective of this study was to measure how tensile mechanical properties and extent of energy dissipation vary by tension direction, meniscal layer, and water content. Methods: The central regions of porcine meniscal pairs (n = 8) were cut into tensile samples (4.7 mm length, 2.1 mm width, and 0.356 mm thickness) from core, femoral and tibial components. Core samples were prepared parallel (circumferential) and perpendicular (radial) to the fibers. Tensile testing consisted of frequency sweeps (0.01-1Hz) followed by quasi-static loading to failure. Dynamic testing yielded energy dissipation (ED), complex modulus (E*), and phase shift (δ) while quasi-static tests yielded Young's Modulus (E), ultimate tensile strength (UTS), and strain at UTS (ε_UTS). To investigate how ED is influenced by the specific mechanical parameters, linear regressions were performed. Correlations between sample water content (φ_w) and mechanical properties were investigated. A total of 64 samples were evaluated. Results: Dynamic tests showed that increasing loading frequency significantly reduced ED (p < 0.05). Circumferential samples had higher ED, E*, E, and UTS than radial ones (p < 0.001). Stiffness was highly correlated with ED (R² > 0.75, p < 0.01). No differences were found between superficial and circumferential core layers. ED, E*, E, and UTS trended negatively with φ_w (p < 0.05). Discussion: Energy dissipation, stiffness, and strength are highly dependent on loading direction. A significant amount of energy dissipation may be associated with time-dependent reorganization of matrix fibers. This is the first study to analyze the tensile dynamic properties and energy dissipation of the meniscus surface layers. Results provide new insights on the mechanics and function of meniscal tissue.

Natural biopolymer scaffold for meniscus tissue engineering

Meniscal injuries caused by trauma, degeneration, osteoarthritis, or other diseases always result in severe joint pain and motor dysfunction. Due to the unique anatomy of the human meniscus, the damaged meniscus lacks the ability to repair itself. Moreover, current clinical treatments for meniscal injuries, including meniscal suturing or resection, have significant limitations and drawbacks. With developments in tissue engineering, biopolymer scaffolds have shown promise in meniscal injury repair. They act as templates for tissue repair and regeneration, interacting with surrounding cells and providing structural support for newly formed meniscal tissue. Biomaterials offer tremendous advantages in terms of biocompatibility, bioactivity, and modifiable mechanical and degradation kinetics. In this study, the preparation and composition of meniscal biopolymer scaffolds, as well as their properties, are summarized. The current status of research and future research prospects for meniscal biopolymer scaffolds are reviewed in terms of collagen, silk, hyaluronic acid, chitosan, and extracellular matrix (ECM) materials. Overall, such a comprehensive summary provides constructive suggestions for the development of meniscal biopolymer scaffolds in tissue engineering.