RESUMEN
Support of somatic growth is a fundamental requirement of tissue-engineered valves. However, efforts thus far have been unable to maintain this support long term. A key event that will determine the valve's long-term success is the extent to which healthy host tissue remodeling can occur on the valve soon after implantation. The construct's phenotypic-status plays a critical role in accelerating tissue remodeling and engineered valve integration with the host via chemotaxis. In the current study, human bone-marrow-derived mesenchymal stem cells were utilized to seed synthetic, biodegradable scaffolds for a period of 8 days in rotisserie culture. Subsequently, cell-seeded scaffolds were exposed to physiologically relevant oscillatory shear stresses (overall mean, time-averaged shear stress, ~7.9 dynes/cm2; overall mean, oscillatory shear index, ~0.18) for an additional 2 weeks. The constructs were found to exhibit relatively augmented endothelial cell expression (CD31; compared to static controls) but concomitantly served to restrict the level of the activated smooth muscle phenotype (α-SMA) and also produced very low stem cell secretion levels of fibronectin (p < 0.05 compared to static and rotisserie controls). These findings suggest that fluid-induced oscillatory shear stresses alone are important in regulating a healthy valve phenotype of the engineered tissue matrix. Moreover, as solid stresses could lead to increased α-SMA levels, they should be excluded from conditioning during the culture process owing to their associated potential risks with pathological tissue remodeling. In conclusion, engineered valve tissues derived from mesenchymal stem cells revealed both a relatively robust valvular phenotype after exposure to physiologically relevant scales of oscillatory shear stress and may thereby serve to accelerate healthy valve tissue remodeling in the host post-implantation.
RESUMEN
The growing demand for a sustainable leather industry with a low environmental impact has prompted the development of alternative vegetable-based materials. In this study, a biodegradable mushroom-based leather derived from the fruiting body of Phellinus ellipsoideus is investigated. The biodegradable leather proves to be thermally stable up to 250 °C. The mechanically robust macrostructure combines a tensile strength of 1.2 MPa and ductility (101% strain at break) attributed to the natural balance of chitin (0.3) and proteins (0.7) constituting the mycelium fibers. The chitin-protein system results in an intrinsic scratch-resistant structure with exciting damping properties in a low frequency range. Enhanced damping capabilities within 5-20 Hz (tan δ: 0.1-0.20) are attributed to the macrostuctural alignment of the mycelium under cyclic tension. Whereas, increasing frequencies >20 Hz induce micromolecular interactions between chitin and proteins within the fibers. Exposure of the bioleather to acidic (pH 4, 5) and basic (pH 8, 9) media demonstrated the selective dissolution of proteins (basic) and chitin (acid) components within the mycelium, opening an opportunity for tunable mechanical response. Reducing the protein content induced an increase in stiffness and strength (pH 8 and 9), while reducing its chitin component showed variable ductility (pH 4 and 5). Owing to the entirely natural composition of the mushroom leather, intrinsic antifungal and antibacterial properties found in the mycelium resist fungal invasion and bacterial growth. Thus, this study displays the unique morphology-property relationship of a biodegradable mushroom leather, proving its potential as a fully sustainable and environmentally friendly alternative.