Role of scaffold topography and stimulation via ultrasound on the biosynthetic activity of chondrocytes seeded in three-dimensional matrices

When an organ or part of the organ is damaged a repair process is triggered, however in some instances either an organ has a limited capacity for regeneration or is unable to direct spontaneous regeneration. New advances in material science, such as the incorporation of nanofabrication techniques into the arsenal of material production techniques, opened the opportunity of obtaining materials that more closely resemble natural extracellular matrix. The emergence of new visualization techniques such as confocal microscopy made it possible to improve the characterization of the cell-material interaction and the tracking of cell signaling process by allowing the visualization of activated effectors under specific pathways. However, the interrelationship between cells and materials is far from being completely understood primarily because the connections between different pathways are still unclear. In this dissertation two factors effecting cartilage cell regeneration were studied. Firstly, the effect of scaffold geometry, namely, fiber diameter on the cellular response was addressed. The rationale underlying our research was that electrospun scaffolds closely mimic the extracellular matrix of native cartilage, and that nanofibers would provide increased surface area for cellular interaction. Our results showed that fiber diameter affected chondrocyte differentiation, as smaller diameters promoted an increased synthesis in chondrocytic markers (collagen type II and aggrecan). Also the signaling pathway RhoA/ROCK/mDia1 was observed to be involved in the process of cell response to different fiber diameters. Ultrasound stimulation was the second factor studied. The underlying premise was that chondrocytes are mechano-sensitive cells and mechanical stimulation has been proven to affect cell proliferation and differentiation. Low intensity ultrasound is widely used in therapeutic applications mainly in the area of physical therapy, but the underlying mechanisms of ultrasou