Recently, cell separation methods have become important for preparing cells for transplantation therapy. In this study, a thermoresponsive cationic block copolymer brush is developed as an effective cell separation tool. This brush is prepared on glass surfaces using two steps of activator regenerated by electron transfer–atom transfer radical polymerization (ARGET‐ATRP). The cationic segment is prepared in the first step of the ARGET‐ATRP of N,N‐dimethylaminopropylacrylamide (DMAPAAm). In the second step, the thermoresponsive segment is prepared, attached to the bottom cationic segment, through ARGET‐ATRP with N‐isopropylacrylamide (NIPAAm). The cell adhesion behavior of the prepared thermoresponsive cationic copolymer, PDMAPAAm‐b‐PNIPAAm, brush is observed using umbilical cord‐derived mesenchymal stem cells (UCMSC), fibroblasts, and macrophages. At 37 °C, all three types of cells adhere to the thermoresponsive cationic copolymer brush. Then, by reducing the temperature to 20 °C, the adhered UCMSC are detached from the copolymer brush, whereas the fibroblasts and macrophages remain adhered to the copolymer brush. Using this copolymer brush, UCMSC can be purified from the cell mixture simply by changing the temperature. Therefore, the prepared thermoresponsive cationic copolymer brush is useful as a cell separation tool for the purification of mesenchymal stem cells.

Front Cover: In article number 2000308 by Kenichi Nagase and co‐workers, functional thermoresponsive‐cationic block copolymer brushes are fabricated by two steps of surface‐initiated ATRP of N,N‐dimethylaminopropyl acrylamide and N‐isopropylacrylamide. All three types of tested cells adhere to the copolymer brush at 37 °C and selective detachment of mesenchymal stem cells from the copolymer brush occurs at 20 °C. Thus, the copolymer brush can be useful as an effective tool to separate stem cells from contaminant cells.