The current system of disposal of plastic materials fabricated from petroleum‐based resources causes serious environmental pollution. To solve the problem, a bioplastic called “cell‐plastic” is developed, in which unicellular green algal cells serve as a fundamental resource. This approach converts CO₂ in the atmosphere directly into plastic products by exploiting the photosynthetic‐driven proliferation of algal cells. Herein, cell‐plastic films are fabricated using biodegradable and water‐soluble polyvinyl alcohol (PVA) as a matrix, in which the effects of a cell‐to‐matrix mixing ratio and the chemical structure of the matrix on the mechanical and thermal properties are investigated. As a method of the chemical structural change, a cross‐linking structure is introduced to the matrix by connecting hydroxy groups of PVA using aldehyde. The tensile tests reveal that the PVA‐cell‐plastic film maintains the mechanical properties of PVA film. Moreover, a cross‐linked cell‐plastic film exhibits high water absorption, making it suitable as a functional cell‐plastic material.

In the current system, the disposal of plastic materials causes serious environmental pollution such as the generation of carbon dioxide and destruction of the ecosystem by micro-plastics. To solve this problem, bioplastics, biomass and biodegradable plastics have been developed. As part of our research, we have developed novel bioplastics called “cell-plastics”, in which a unicellular green algal cell serves as a fundamental resource. The production of the cell-plastics would be expected to reduce environmental impact due to the usage of a natural product. Herein, to overcome the mechanical strength of cell-plastics, we used thermosetting epoxy and urethane resins containing Chlorella sp. as the green algae. We successfully fabricated thermosetting resins with a Chlorella sp. content of approximately 70 wt% or more. IR measurements revealed that the chemical structure of an epoxide or isocyanate monomer mixed with Chlorella sp. was modified, which suggests that the resins were hardened by the chemical reaction. In addition, we investigated the effect of thermosetting conditions such as temperature and compression for curing both resins. It was revealed that the Young’s moduli and tensile strengths were controlled by thermosetting temperature and compression, whereas the elongation ratios of the resins were constant at low values regardless of the conditions.

Recently, cell-plastics, which are composed of unicellular green algal cells and biodegradable compounds as ingredients and fillers, have been suggested as carbon-recyclable materials instead of petroleum-based plastics. In this study, cell-plastics, fabricated with Chlamydomonas reinhardtii as an ingredient and a mixture of two types of starches (raw and oxidized starches) as a filler, were successfully stabilized as independent structures despite the quantity of algal cells being nine times more than that of starch. All starch cell-plastics were water repellent, possibly due to their bumpy surface structures. The starch cell-plastic, composed of 50% cells and 50% starch (1.5:1 of oxidized starch versus raw starch), showed 327 ± 52 MPa as Young’s modulus and 6.45 ± 1.20 MPa as tensile strength, indicating the possibility to be a suitable replacement for petroleum-based plastics. Additionally, all starch cell-plastics showed water-repellency and maintained those structures dipped in phosphate-buffered saline buffer as a water environment for 24 h, meaning that all starch cell-plastics had evaluable water resistance. On the other hand, by adding α-amylase, all starch cell-plastics were collapsed and lost the weight efficiently, indicated their biodegradability. This is the first paper to describe starch cell-plastics from their fabrication to biodegradation.

Cell plastics which are composed of unicellular green algal cells have been proposed in previous studies. While unicellular green algae can be freely arranged using fabrication processes, a matrix is required to attach the cells together. To date, although the cell contents collected from Chlamydomonas reinhardtii show the possibility of attaching cells, but it is unclear which components can be considered attachment factors. Therefore, in this study, C. reinhardtii cells were disrupted with sonication, and the components were separated and purified with hexane. The cell plastics with only 0.5 wt% of intermediate showed similar mechanical properties to those with 17 wt% and 25 wt% of cell components that were untreated with hexane, meaning that the purified intermediates could function as matrices. The purified intermediate was composed of approximately 60 wt% of protein as the main component, and proteomic analysis was performed to survey the main proteins that remained after hexane treatment. The protein compositions of the cell content and purified intermediate were compared via proteomic analysis, revealing that the existing ratios of 532 proteins were increased in the purified intermediate rather than in the cell content. In particular, the outer structure of each of the 49 proteins—the intensity of which was increased by over 10 times—had characteristically random coil conformations, containing ratios of proline and alanine. The information could suggest a matrix of cell plastics, inspiring the possibility to endow the cell plastics with more properties and functions.

An approach to synthesize a two‐dimensional polymer (2DP) using a preorganized host‐guest network at the liquid/solid interface is presented. As a host network, we used a self‐assembled monolayer of a dehydrobenzo[12]annulene derivative having aminophenyl groups at three alkoxy chain ends and, as a guest, a hexakis(phenylethynyl)benzene derivative having six formyl groups, aiming to connect the host to the guest embedded in the host matrix by imine bond formation. STM observations of host‐guest mixtures with trifluoroacetic acid at the 1‐phenyloctane/highly oriented pyrolytic graphite interface revealed that the guest was observed as a spoke‐like feature in the nanowells. Based on the STM image analysis, short distances between the diagonal phenyl groups in the nanowells are detected, indicating that the imine bonds are formed. However, the small abundance and random distribution of the short phenyl‐phenyl distance indicate that the periodically ordered 2DP structure is not formed, probably because the network cannot tolerate the structural change due to partial bond formation.

The surface modification of zinc oxide nanoparticles (ZnONPs) with organic compounds has been shown to improve their dispersibility. In this study, to develop a highly functional material, ZnONP modified with 6-amino-1-hexanol bearing both amino and hydroxyl functional groups was synthesized. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS) analyses confirmed that functionalized ZnONP was successfully obtained by a hydrothermal synthetic method. The mechanical properties of composite films of polylactic acid (PLA) reinforced with the functionalized ZnONP were then evaluated. The composite containing functionalized ZnONP exhibited a higher maximum stress than that containing unmodified ZnONP. These ZnONP/polymer composites therefore show promise as novel high-performance materials.