Spreading Shape and Area Regulate the Osteogenesis of Mesenchymal Stem Cells

BACKGROUND: Mesenchymal stem cells (MSCs) have strong self-renewal ability and multiple differentiation potential. Some studies confirmed that spreading shape and area of single MSCs influence cell differentiation, but few studies focused on the effect of the circularity of cell shape on the osteogenic differentiation of MSCs with a confined area during osteogenic process.METHODS: In the present study, MSCs were seeded on a micropatterned island with a spreading area lower than that of a freely spreading area. The patterns had circularities of 1.0 or 0.4, respectively, and areas of 314, 628, or 1256 µm² . After the cells were grown on a micropatterned surface for 1 or 3 days, cell apoptosis and F-actin were stained and analyzed. In addition, the expression of β-catenin and three osteogenic differentiation markers were immunofluorescently stained and analyzed, respectively.RESULTS: Of these MSCs, the ones with star-like shapes and large areas promoted the expression of osteogenic differentiation markers and the survival of cells. The expression of F-actin and its cytosolic distribution or orientation also correlated with the spreading shape and area. When actin polymerization was inhibited by cytochalasin D, the shape-regulated differentiation and apoptosis of MSCs with the confined spreading area were abolished.CONCLUSION: This study demonstrated that a spreading shape of low circularity and a larger spreading area are beneficial to the survival and osteogenic differentiation of individual MSCs, which may be regulated through the cytosolic expression and distribution of F-actin.

EFFECTOF SOLDERING CONDITION ON THE TENSILE STRENGTH TITANIUM SOLDER JOINT WITH 14K GOLD SOLDER / 대한치과보철학회지

This study was performed to evaluate the tensile strength of solder joint in titanium and the wettability of 14K gold solder on titanium. Two pieces of titanium rod 30 mm in length and 3mm in diameter were butt-soldered with a 14K gold solder using the electric resistance heating under flux-argon atmosphere, the infrared heating under argon atmosphere, and the infrared heating under vacuum-argon atmosphere. A tensile test was performed at a crosshead speed of 0.5mm/min, and fractere surfaces were examined by SEM. To evaluate the wettability of 14K gold solder on titanium, titanium plates of a 17x17x1mm were polished with #80-#2000 emery papers, and the spreading areas of solder 10mg were measures by heating at 840 * for 60 seconds. The solder-matrix interface regions were etched by the solution of 10% KCN-10%(NH4)2S2O8, and analyzed by EPMA. The results obtained were summarized as follows: 1. The maximun tensile strength was obtained when the titanium surface was polished with #2000 emery paper and soldered using the electric resistance heating under fluxargon atmosphere. Soldering strengths showed the significant difference between the electric resistance heating and the infrared heating(p<0.05). 2. The fracture surfaces showed the aspect of brittle fracture, and the failure developed along the interfaces of solder-matrix reaction zone. 3. The EPMA data for the solder-matrix interface region revealed that the diffusion of Au and Cu occurred to the titanium matrix, and the reaction zone showed the higher contents of Au, Cu and Ti than others.