## 3 Results and Discussion  
In this study, starch cell-plastics were prepared by mixing varying ratios of _C. reinhardtii_ cells and starches as well as by mixing ratios of raw starch and oxidized starch (Figure 1). All starch cell-plastics fabricated using variable ratios of cells versus starches and of raw starch versus oxidized starch could successfully maintain their self-standing structures. In a previous research, PBS cell-plastics composed of 3:1 cells to PBS ratio could not stably maintain the structure because of the loss of powder-like particles on the surface [14]. However, starch cell-plastics sustained their structures even when composed of ingredient cell content nine times more than starch content. The result was majorly attributable to the good mix of cells and fillers because of their hydrophilic properties, unlike PBS, which is hydrophobic. The structures of the surface and cross-section of the starch cell-plastics were visually evaluated via SEM (Figure 2). The starches used as control displayed smooth surfaces and packed cross-sections, even with different component ratios of raw and oxidized starch. The pasted starch formed a structure similar to that of a smooth film (Figure 1) such that the results of SEM observation had sufficient validity. On the other hand, all starch cell-plastics displayed particle structures, presumably composed of cells on their surfaces, and packed cross-sections, although the cross-sectional structures were bumpy, presumably formed by cells. There was no correlation between the ratios of raw and oxidized starch. As shown in Figures 1 and 2, the differences between previous PBS cell-plastics and starch cell-plastics clearly lie in the filler spreading among the ingredient cells. Although the unstable structures of PBS cell-plastics were confirmed under the fabrication condition of 75% or more composition of _C. reinhardtii_ cells, all starch cell-plastics, even under the fabrication condition of 90% of _C. reinhardtii_ cells could maintain their packed structures. For the fabrication of PBS cell-plastics, the hydrophilic cells were forcibly mixed with PBS in hydrophobic dichloromethane; on the other hand, for starch cell-plastics, the cells were mixed with starches in water. In the case of starch cell-plastics, packed structures could be explained by the fact that cells and starches easily combined under hydrophilic conditions. Figure 1: Pictures of starch cell-plastics, starch and cells. (**a**) Components of starch cell-plastics. (**b**) Starch cell-plastics. Tensile tests were conducted to evaluate the mechanical properties of the starch cell-plastics (Figures 3 and 4). As seen in the stress-strain curve (S-S curve) in Figure 3, all starches, irrespective of the ratios between raw and oxidized starch, immediately fractured after reaching their maximum tensile strength. Due to sudden rupture without observable structural glide, the starch cell-plastics also immediately fractured after reaching their maximum tensile strength. These rupturing properties did not depend upon the ratio of raw starch to oxidized starch. The starches showed Young's modulus of 566 \(\pm\) 249 MPa in 0.5 oxidized starch: 1 raw starch, 279 \(\pm\) 30 MPa in 1 oxidized starch: 1 raw starch, and 187 \(\pm\) 37 MPa in 1.5 oxidized starch: 1 raw starch, respectively (Figure 4). The decreasing values of Young's modulus related to the increasing ratio of oxidized starch, indicating a negative correlation between Young's modulus and the ratio of oxidized starch. The hydroxy group of starch was changed to a carboxyl group via oxidation. Therefore, it is possible that the hydrogen bonds between the polymer chains along with the chain length decreased, resulting in a decline in the intermolecular force. Regardless of the ratio of raw starch and oxidized starch, starch cell-plastics composed of 90% of cells tended to show a lower Young's modulus value than those composed of 50% of cells.