Mechano-bioengineering of the knee meniscus

The meniscus is a fibrocartilaginous structure of the knee joint that serves a crucial role in joint health and biomechanics. Degeneration or removal of the meniscus is known to lead to a chronic and debilitating disease known as knee osteoarthritis, whose prevalence is expected to increase in the next few decades. Meniscus bioengineering has been developed as a potential alternative to current treatment methods, wherein meniscus-like tissues are engineered using cells, materials, and biomechanical stimuli. The application of mechanical stimulation in meniscus bioengineering has presented varied results but, for the most part, it has been shown to enhance meniscus-like tissue formation. In this review, we summarized literature over the last 10 years of various mechanical stimuli applied in bioengineering meniscus tissues. The role of individual loading types is examined, and the effects on engineered meniscus are evaluated on both molecular and tissue levels. In addition, simulated microgravity is highlighted as the new area of interest in meniscus engineering, and its potential use as a disease-driving platform is discussed. Taken together, with the increased understanding of the effects of mechanical stimulation on the engineered meniscus, the most suitable loading regime could be developed for meniscus tissue engineering and osteoarthritis modelling.

TEMPO-Oxidized Cellulose Nanofiber-Alginate Hydrogel as a Bioink for Human Meniscus Tissue Engineering

Objective: The avascular inner regions of the knee menisci cannot self-heal. As a prospective treatment, functional replacements can be generated by cell-based 3D bioprinting with an appropriate cell source and biomaterial. To that end, human meniscus fibrochondrocytes (hMFC) from surgical castoffs of partial meniscectomies as well as cellulose nanofiber-alginate based hydrogels have emerged as a promising cell source and biomaterial combination. The objectives of the study were to first find the optimal formulations of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)-oxidized cellulose nanofiber/alginate (TCNF/ALG) precursors for bioprinting, and then to use them to investigate redifferentiation and synthesis of functional inner meniscus-like extracellular matrix (ECM) components by expanded hMFCs. Methods: The rheological properties including shear viscosity, thixotropic behavior recovery, and loss tangent of selected TCNF/ALG precursors were measured to find the optimum formulations for 3D bioprinting. hMFCs were mixed with TCNF/ALG precursors with suitable formulations and 3D bioprinted into cylindrical disc constructs and crosslinked with CaCl2 after printing. The bioprinted constructs then underwent 6 weeks of in vitro chondrogenesis in hypoxia prior to analysis with biomechanical, biochemical, molecular, and histological assays. hMFCs mixed with a collagen I gel were used as a control. Results: The TCNF/ALG and collagen-based constructs had similar compression moduli. The expression of COL2A1 was significantly higher in TCNF/ALG. The TCNF/ALG constructs showed more of an inner meniscus-like phenotype while the collagen I-based construct was consistent with a more outer meniscus-like phenotype. The expression of COL10A1 and MMP13 were lower in the TCNF/ALG constructs. In addition, the immunofluorescence of human type I and II collagens were evident in the TCNF/ALG, while the bovine type I collagen constructs lacked type II collagen deposition but did contain newly synthesized human type I collagen.

Mechanotransduction in meniscus fibrochondrocytes: What about caveolae?

Meniscus fibrochondrocytes (MFCs) are an important cell population responsible for regulating the biomechanical properties of the knee meniscus. Despite their significance, not much is known about them, including how they sense and respond to mechanical stimuli. Due to the mechanical nature of the knee joint, it is therefore paramount to our understanding of the meniscus that its mechanotransductive mechanism be elucidated. In this review, we will summarize the current knowledge on mechanotransduction in MFCs and highlight the relevance of caveolae in lieu of a recent discovery. Additionally, we will discuss the importance of future studies in this area to help advance the field of meniscus research.