Yuta Nakashima

Microplastics (MPs) can adsorb heavy metals and metalloids and may cause a potential health hazard. Precise measurements of their size, shape, composition, and concentration at a single-MP level are important to evaluate their potential toxicity and identify their original source. However, current single-MP analytical methods such as micro-Raman spectroscopy and scanning electron microscopy have low throughput. Therefore, in this study, we applied the ion current sensing method, which has been used for single cell analysis, to single-MP analysis and examined whether size measurement and composition analysis of MPs at the single particle level are possible. In single-MP measurements, plastic particles must be mono-dispersed in solution at least within the measurement time. The agglomeration behavior was carefully observed after adding sodium dodecyl sulfate to tris-borate-EDTA buffer at 2–16 mM. Under these conditions, the size of polystyrene beads could be measured using the ion current sensing under the mono-dispersed condition. Next, ion current sensing was performed on four pseudo MPs fabricated from different materials (polyethylene, polyethylene terephthalate, polypropylene, and polyvinyl chloride) that were mechanically grazed and UV-irradiated to imitate real marine MPs. Although significant differences in the ion current signals from different material MPs were not observed, fast (100 MPs within 2 s) and precise measurements in the MPs’ sizes at a single-MP level were successfully achieved.

Tissue formation from heterogeneous cell types, similar to those in vivo, is an important technique for development of new drugs and formation of artificial organs. In vivo tissues are complex arrangements of heterogeneous cells that interact with each other. To create such tissues in vitro, it is essential to develop a technique that arranges heterogeneous cells in an arbitrary configuration. Currently, we are developing a new gel patterning technique to create effective cell micropatterns by using photolithography and alginate gel, which inhibits cellular adhesion. In this study, we considered that a more flexible gel patterning technique was required for creating order-made formations of complex tissues. We created gel patterns by removing the alginate gel using laser processing, and cells were cultured on the formed patterns. Complex heterogeneous cell patterns were achieved by adjusting various technical parameters such as the laser power, spot diameter, and alginate gel film thickness. Based on our results, we anticipate that our technique will prove useful for the development of regenerative medicine and tissue engineering.