Browsing by Author "Wang, Yung-Li"

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Effects of the Grain Size on Dynamic Capillary Pressure and the Modified Green-Ampt Model for Infiltration
(2018-01-01)
Tsai, Yi-Zhih
;
Liu, Yu-Tung
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Wang, Yung-Li
;
Chang, Liang-Cheng
;
Hsu, Shao-Yiu
Darcy-scale capillary pressure is traditionally assumed to be constant. By contrast, a considerable gap exists between the measured and equilibrium capillary pressures when the same moisture saturation is considered with a high flow rate, and this gap is called the dynamic effect on the capillary pressure. In this study, downward infiltration experiments of sand columns are performed to measure cumulative infiltration and to calculate the wetting front depth and wetting front velocity in sands with different grain sizes. We estimate the equilibrium capillary pressure head or suction head at the wetting front using both the classical Green-Ampt (GAM) and modified Green-Ampt (MGAM) models. The results show that the performance of MGAM in simulating downward infiltration is superior to that of GAM. Moreover, because GAM neglects the dynamic effect, it systematically underestimates the equilibrium suction head in our experiments. We also find that the model parameters (alpha) over cap and beta of MGAM are affected by the grain size of sands and porosity, and the dynamic effect of the capillary pressure increases with decreasing grain size and increasing porosity.
Self-Assembled Peptide-Based Hydrogels as Scaffolds for Proliferation and Multi-Differentiation of Mesenchymal Stem Cells
(2017-04-01)
Wang, Yung-Li
;
Lin, Shih-Pei
;
Nelli, Srinivasa Rao
;
Zhan, Fu-Kai
;
Cheng, Hsun
Fluorenyl-9-methoxycarbonyl (Fmoc)-diphenylalanine (Fmoc-FF) and Fmoc-arginine-glycine-aspartate (Fmoc-RGD) peptides self-assemble to form a 3D network of supramolecular hydrogel (Fmoc-FF/Fmoc-RGD), which provides a nanofibrous network that uniquely presents bioactive ligands at the fiber surface for cell attachment. In the present study, mesenchymal stem cells (MSCs) in Fmoc-FF/Fmoc-RGD hydrogel increase in proliferation and survival compared to those in Fmoc-FF/Fmoc-RGE hydrogel. Moreover, MSCs encapsulated in Fmoc-FF/Fmoc-RGD hydrogel and induced in each defined induction medium undergo in vitro osteogenic, adipogenic, and chondrogenic differentiation. For in vivo differentiation, MSCs encapsulated in hydrogel are induced in each defined medium for one week, followed by injection into gelatin sponges and transplantation into immunodeficient mice for four weeks. MSCs in Fmoc-FF/Fmoc-RGD hydrogel increase in differentiation into osteogenic, adipogenic, and chondrogenic differentiation, compared to those in FmocFF/Fmoc-RGE hydrogel. This study concludes that nanofibers formed by the self-assembly of Fmoc-FF and Fmoc-RGD are suitable for the attachment, proliferation, and multi-differentiation of MSCs, and can be applied in musculoskeletal tissue engineering.