## 3 Results and Discussion
In the case of the starch cell-plastics composed of 90% of cells rather than 50%, the structures could be strained because the bond between the unicellular _C. reinhardtii_ cells as ingredients could be decreased due to the reduced amount of starches as fillers to connect the cells. Likewise, the same trend regarding the cell-contents was observed even for tensile strength (Figure 4b). Regardless of the ratios of the raw and oxidized starches, the tensile strength decreased with increase in percentage of cell components. The results also indicated that the influence of fillers as cell connectors could be decreased by increasing the cell components. The starch cell-plastics (0.5:1 of oxidated starch versus raw starch; 0% and 50% of cells) were collapsible rather than others so that the Young's modulus and tensile strengths were not steady as shown error bars, respectively. The results indicated that the steady-use of the cell-plastics could need the blending balance of cells and starches. In this study, the Young's moduli of the starch cell-plastics composed of 50% cells were approximately 330 MPa (the ratios of oxidized and raw starches were 0.5:1, 1:1, and 1.5:1, with a Young's modulus value of 327, 340, and 327 MPa, respectively). Note that, in the previous research, the [PERSON]'s modulus value of PBS cell-plastics composed of 50% cells was 240 MPa [14]. It was revealed that all starch cell-plastics composed of 50% cells have a higher Young's modulus value than that of LDPE, which is 165 MPa [18]. Figure 2: SEM images of surfaces and cross-sections of starch cell-plastics and starches, respectively. The white and black arrows show the thickness of those cross-sections. The white lines are inserted as scale bars. Water repellency is an important property of plastics. The water repellent properties of the starch cell-plastics and starches were evaluated (Figure 5) by placing water droplets on films of cell-plastics and starches. In the case of starch-film composed of oxidized and raw starch in the ratio of 0.5:1, the film could not keep the water droplet and lost its form after water absorbance. On the other hand, starch-films composed of oxidized and raw starch in the ratio of 1:1 and 1.5:1 demonstrated water repellency, indicating that increasing the ratio of oxidized starch could endow the water repellency to starch-film owing to the decrease in hydroxy groups. Instead of increasing the ratio of oxidized starch, adding cells to the starch imparted water repellency. The starch cell-plastics, which were composed of cells (50% and 70%) and starch (oxidized and raw starch in the ratio of 0.5:1), showed the water-repellency, indicating that the water repellency could be derived from bumpy surface occurred by adding cells. As seen in the SEM images in Figure 2, all cell-plastics have bumpy surfaces derived from cells. Interestingly, the water repellency of previous PBS cell-plastics was caused by the bumpy surfaces arising from the cells demonstrating the lotus effect. Thus, starch cell-plastics could efficiently exhibit the lotus effect due to the bumpy on their surfaces. Figure 4: Evaluation of tensile strength test for each starch cell-plastic. (**a**) Comparison of [PERSON]’s modulus; (**b**) comparison of tensile strength. Values are the averages of three replicated experiments, \(\pm\)SD. Figure 3: Analysis of stress–strain curves for each starch cell-plastic. To ascertain their carbon recyclability, starch cell-plastics needed to be subjected to biodegradation by using degradation systems found in nature. As shown in Figure 6, the biodegradability of starch cell-plastics was evaluated using \(\alpha\)-amylase, which universally exists in nature. In Figure 6a, although the starch cell-plastics and starches were crumbled with \(\alpha\)-amylase-treatment, those could maintain the structure without \(\alpha\)-amylase-treatment. Additionally, the treated cell-plastics could not be grasped because of being collapsed; however, the non-treated cell-plastics could be grasped and bent.