Tissue vascularization in vitro is necessary for cell transplantation and is a major challenge in tissue engineering. To construct large and regularly vascularized tissue, we focused on the integration of endothelial cell-covered spheroids. Primary rat hepatocytes were cultured on a rotary shaker, and 100-150 mum spheroids were obtained by filtration. The hepatocyte spheroids were coated with collagen by conjugation with a type 1 collagen solution. Collagen-coated hepatocyte spheroids were cocultured with human umbilical vein endothelial cells (HUVECs), and monolayered HUVEC-covered hepatocyte spheroids were constructed. Without a collagen coat, many HUVECs invaded hepatocyte spheroids but did not cover the spheroid surface. To construct regularly vascularized tissue, we packed HUVEC-covered hepatocyte spheroids in hollow fibers used for plasma separation. Packed spheroids attached to each other forming a large cellular tissue with regular distribution of HUVECs. At day 9 after packing, HUVECs invaded the hepatocyte spheroids and a dense vascular network was constructed. Collagen coating of spheroids is useful for the formation of endothelial cell-covered spheroids and subsequent regular vascularized tissue construction.

Numerical simulations of the film casting process were performed using a finite element method for Newtonian and viscoelasttc fluids. We simplified the governing equations by the assumption that the stress and velocity gradients in the thickness direction were negligible, and obtained the film thickness and mean value of stress and velocity components in the thickness direction as variables. Viscoelasticity was described by the Larson model with multiple relaxation times. Non‐isothermal conditions were considered by applying the time‐temperature superposition law. The simulation results for the several kinds of commercial low‐density polyethylenes wore compared to the experimental data for a laboratory‐scale process at l90°C and a commercial‐scale process at 310°C. The film width and film thickness distribution at chill roll, and the change of film width were in good agreement for the laboratory‐scale process, but the agreement for the commercial‐scale process was; not as good. In the simulation of the commercial‐scale process at high temperature, the value predicted by the use of the Viscoelasticity for the original pellet showed poor agreement owing to the change of Viscoelasticity in the process. The agreement was improved by the use of the Viscoelasticity for the processed resin, which was changed from the original one. Next, viscoelastic effects on neck‐in and edge bead phenomena were investigated. The neck‐in and edge bead phenomena were considered to be affected by both the uniaxial elongational viscosity and planar elongational viscosity.

Melt-mixing in twin-screw extruders is a key process in the development of polymer composites. Quantifying the mixing performance of kneading elements based on their internal physical processes is a challenging problem. We discuss melt-mixing by novel kneading elements called "pitched-tip kneading disk (ptKD)". The disk-stagger angle and tip angle are the main geometric parameters of the ptKDs. We investigated four typical arrangements of the ptKDs, which are forward and backward disk-staggers combined with forward and backward tips. Numerical simulations under a certain feed rate and screw revolution speed were performed, and the mixing process was investigated using Lagrangian statistics. It was found that the four types had different mixing characteristics, and their mixing processes were explained by the coupling effect of drag flow with the disk staggering and pitched-tip and pressure flows, which are controlled by operational conditions. The use of a pitched-tip effectively to controls the balance of the pressurization and mixing ability.

Three‐dimensional flow simulation of a film‐casting process was performed using a finite element method assuming an isothermal and steady Newtonian flow. The simulation was carried out under industrial operation conditions. The neck‐in and the edge bead phenomena could be simulated. The effects of draw ratio, air gap length, and die width on these phenomena are discussed. The neck‐in and the edge bead phenomena were affected by the draw ratio and air gap length and not by the die width. The neck‐in value, which was defined as the difference between the die width and film width at the chill roll, increased with the draw ratio and air gap length.

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