Developing Fibrous Biomaterials to Modulate Epithelial-to-Mesenchymal Transition.

Despite their critical roles in tissue repair and pathological processes such as fibrosis, tumor invasion, and metastasis, the origins of mesenchymal cells remain poorly understood. Among the likely routes, epithelial-to-mesenchymal transitions (EMTs) emerge as important source of these cells. EMTs manifest themselves as a phenotypic transition in terminally differentiated epithelial cells into mesenchymal cells which are closely related to embryogenesis and organ development as well as in chronically inflamed tissues and neoplasia. There exists a potential for successful engineering of biomimetic environments that closely reflects and reciprocates the dynamic changes in the cellular microenvironment during EMT and relies on integrating the mechanical sensing mechanisms found in the native tissues into the synthetic scaffolds to understand cellular plasticity. Extracellular matrix (ECM) has complex structures composed of a collection of extracellular molecules including fibrous proteins and glycoproteins in a hydrated mixture of glycosaminoglycans and proteoglycans. Therefore, fibrous materials have been increasingly applied in tissue engineering applications since biomaterials need to restore ECM structures to provide physical, biochemical, and biomechanical signals to define cellular behaviors and tissue functions. This review summarizes materials used for fibrous scaffolds including natural and synthetic materials, highlights recent development of fabrication techniques, characteristic architectures, and properties and different applications of fibrous scaffolds in tissue engineering. The prospects and challenges about fibrous materials in tissue engineering applications are also discussed. Finally, we summarized relevant bioengineering approaches to modulate each type of EMT as potential avenues to consider toward future biomaterials design.

Plasma-Induced Catalytic Conversion of Nitrogen and Hydrogen to Ammonia over Zeolitic Imidazolate Frameworks ZIF-8 and ZIF-67.

Microporous crystals have emerged as highly appealing catalytic materials for the plasma catalytic synthesis of ammonia. Herein, we demonstrate that zeolitic imidazolate frameworks (ZIFs) can be employed as efficient catalysts for the cold plasma ammonia synthesis using an atmospheric dielectric barrier discharge reactor. We studied two prototypical ZIFs denoted as ZIF-8 and ZIF-67, with a uniform window pore aperture of 3.4 Å. The resultant ZIFs displayed ammonia synthesis rates as high as 42.16 µmol NH3/min gcat. ZIF-8 displayed remarkable stability upon recycling. The dipole-dipole interactions between the polar ammonia molecules and the polar walls of the studied ZIFs led to relatively low ammonia uptakes, low storage capacity, and high observed ammonia synthesis rates. Both ZIFs outperform other microporous crystals including zeolites and conventional oxides in terms of ammonia production. Furthermore, we demonstrate that the addition of argon to the reactor chamber can be an effective strategy to improve the plasma environment. Specifically, the presence of argon helped to improve the plasma uniformity, making the reaction system more energy efficient by operating at a low specific energy input range allowing abundant formation of nitrogen vibrational species.