A model of grade transition is presented for a commercialized fluidized bed gas-phase polyethylene production process. The quantity of off-specification product and the time of grade transition can be minimized by the...A model of grade transition is presented for a commercialized fluidized bed gas-phase polyethylene production process. The quantity of off-specification product and the time of grade transition can be minimized by the optimization of operating variables, such as polymerization temperature, the ratio of hydrogen to ethylene, the ratio of co-monomer to ethylene, feed rate of catalyst, and bed level. A new performance index, the ratio of melt flow (MFR), is included in the objective function, for restraining the sharp adjustment of operation variables and narrowing the distribution of molecular weight of the resin. It is recommended that catalyst feed rate and bed level are decreased in order to reduce the grade transition time and the quantity of off-specification product. This optimization problem is solved by an algorithm of sequential quadratic programming (SQP) in MATLAB. There is considerable difference between the forward transition and reverse transition of grade with regard to the operating variables due to the non-linearity of the system. The grade transition model is extended to a high space time yield (STY) process with the so-called condensed model operation. In the end, an optimization strategy for multi-product transition is proposed with two-level optimization of the objective function J(x,u) on the basis of the optimal grade transition model. A sequential transition of six commercial polyethylene grades is illustrated for an optimal multi-product operation.展开更多
To enhance the adhesion of seeding-cells to the biomaterial scaffolds, the PEG-hydrogels were modified. Porcine aortic valves were decellularized with Triton X-100 and trypsin. The cells were encapsulated into the PEG...To enhance the adhesion of seeding-cells to the biomaterial scaffolds, the PEG-hydrogels were modified. Porcine aortic valves were decellularized with Triton X-100 and trypsin. The cells were encapsulated into the PEG-hydrogels to complete the process of the cells attaching to the acellular porcine aortic valves. Herein, the autologous mesenchymal stem cells （MSCs） of goats were selected as the seeding-cells and the tendency of MSCs toward differentiation was observed when the single semilunar TEHV had been implanted into their abdominal aortas. Furthermore, VEGF, TGF-β1, and the cell adhesive peptide motif RGD were incorporated. Light and electron microscopy observations were performed. Analysis of modified PEG-hydrogels TEHV＇s （PEG-TEHV） tensile strength, and the ratio of reendothelial and mural thrombosis revealed much better improvement than the naked acellular porcine aortic valve （NAPAV）. The data illustrated the critical importance of MSC differentiation into endothelial and myofibroblast for remodeling into native tissue. Our results indicate that it is feasible to reconstruct TEHV efficiently by combining modified PEG-hydrogels with acellular biomaterial scaffold andautologous MSCs cells.展开更多
A PVA-GAG-COL composite scaffold is fabricated by polyvinyl alcohol （PVA）, glyeosaminoglycan （GAG） and collagen （COL）. Laser surface modification technology is used to make holes on the surface of the scaffolds....A PVA-GAG-COL composite scaffold is fabricated by polyvinyl alcohol （PVA）, glyeosaminoglycan （GAG） and collagen （COL）. Laser surface modification technology is used to make holes on the surface of the scaffolds. Inside and outside interconnection micro-porous structure is obtained. Bioeompatibility test of the scaffolds shows that PVA-GAG-COL scaffold can promote the adhesion and proliferation of the fibroblast. Also, fibroblast can grow normally on the scaffolds with pore diameter from 115 um to 255 um and pore distance from 500 um to 2000 um. PVA-GAG-COL scaffolds possess excellent cell biocompatibility. The porous structure is suitable for cell culture in tissue engineering.展开更多
文摘A model of grade transition is presented for a commercialized fluidized bed gas-phase polyethylene production process. The quantity of off-specification product and the time of grade transition can be minimized by the optimization of operating variables, such as polymerization temperature, the ratio of hydrogen to ethylene, the ratio of co-monomer to ethylene, feed rate of catalyst, and bed level. A new performance index, the ratio of melt flow (MFR), is included in the objective function, for restraining the sharp adjustment of operation variables and narrowing the distribution of molecular weight of the resin. It is recommended that catalyst feed rate and bed level are decreased in order to reduce the grade transition time and the quantity of off-specification product. This optimization problem is solved by an algorithm of sequential quadratic programming (SQP) in MATLAB. There is considerable difference between the forward transition and reverse transition of grade with regard to the operating variables due to the non-linearity of the system. The grade transition model is extended to a high space time yield (STY) process with the so-called condensed model operation. In the end, an optimization strategy for multi-product transition is proposed with two-level optimization of the objective function J(x,u) on the basis of the optimal grade transition model. A sequential transition of six commercial polyethylene grades is illustrated for an optimal multi-product operation.
文摘To enhance the adhesion of seeding-cells to the biomaterial scaffolds, the PEG-hydrogels were modified. Porcine aortic valves were decellularized with Triton X-100 and trypsin. The cells were encapsulated into the PEG-hydrogels to complete the process of the cells attaching to the acellular porcine aortic valves. Herein, the autologous mesenchymal stem cells （MSCs） of goats were selected as the seeding-cells and the tendency of MSCs toward differentiation was observed when the single semilunar TEHV had been implanted into their abdominal aortas. Furthermore, VEGF, TGF-β1, and the cell adhesive peptide motif RGD were incorporated. Light and electron microscopy observations were performed. Analysis of modified PEG-hydrogels TEHV＇s （PEG-TEHV） tensile strength, and the ratio of reendothelial and mural thrombosis revealed much better improvement than the naked acellular porcine aortic valve （NAPAV）. The data illustrated the critical importance of MSC differentiation into endothelial and myofibroblast for remodeling into native tissue. Our results indicate that it is feasible to reconstruct TEHV efficiently by combining modified PEG-hydrogels with acellular biomaterial scaffold andautologous MSCs cells.
基金863 Program grant number: 2077AA09Z436+1 种基金Guangdong Province '211' Fund for Biomaterials and Tissue Engineering grantnumber: 50621030
文摘A PVA-GAG-COL composite scaffold is fabricated by polyvinyl alcohol （PVA）, glyeosaminoglycan （GAG） and collagen （COL）. Laser surface modification technology is used to make holes on the surface of the scaffolds. Inside and outside interconnection micro-porous structure is obtained. Bioeompatibility test of the scaffolds shows that PVA-GAG-COL scaffold can promote the adhesion and proliferation of the fibroblast. Also, fibroblast can grow normally on the scaffolds with pore diameter from 115 um to 255 um and pore distance from 500 um to 2000 um. PVA-GAG-COL scaffolds possess excellent cell biocompatibility. The porous structure is suitable for cell culture in tissue engineering.
