Simultaneous enhancement of cell proliferation and thermally induced harvest efficiency based on temperature-responsive cationic copolymer-grafted microcarriers

The development of large-scale suspension cell cultures using microcarriers has long been a focus of attention in the fields of pharmacy and biotechnology. Previously, we developed cell-detachable microcarriers based on temperature-responsive poly(N-isopropylacrylamide) (PIPAAm)-grafted beads, on which adhering cells can be noninvasively harvested by only reducing the temperature without the need for proteolytic enzyme treatment. In this study, to improve the cell harvest efficiency from bead surfaces while maintaining cell adhesion and proliferation properties, we prepared temperature-responsive cationic copolymer-grafted beads bearing a copolymer brush consisting of IPAAm, positively charged quaternary amine monomer (3-acrylamidopropyl trimethylammonium chloride; APTAC), and hydrophobic monomer (N-tert-butylacrylamide; tBAAm). The incorporation of positively charged APTAC into the grafted copolymer brush facilitated bead dispersibility in a cell culture system containing Chinese hamster ovary (CHO-K1) cells and consequently allowed for enhanced cell proliferation in the system compared to that of unmodified CMPS and conventional PIPAAm homopolymer-grafted beads. Additionally, P(IPAAm-co-APTAC-co-tBAAm) terpolymer-grafted beads exhibited the most rapid and efficient cell detachment behavior after the temperature was reduced to 20 °C, presumably because the highly hydrated APTAC promoted the overall hydration of the P(IPAAm-co-APTAC-co-tBAAm) chains. Therefore, P(IPAAm-co-APTAC-co-tBAAm) terpolymer-grafted microcarriers are effective in facilitating both cell proliferation and thermally induced cell detachment in a suspension culture system.