Thermally responsive microcarriers with optimal poly(N-isopropylacrylamide) grafted density for facilitating cell adhesion/detachment in suspension culture

Large-scale cell culture of anchorage-dependent cells based on microcarriers is a crucial method for industrial-scale cell culture and large-scale expansion of therapeutic cells. Previously, the authors developed temperature-responsive microcarriers bearing poly(N-isopropylacrylamide) (PIPAAm)-grafted chains on their outer surface for the non-invasive detachment of cultured cells through temperature reduction without proteolytic enzyme treatment. In this study, to further facilitate cell adhesion and thermally induced detachment efficiency, PIPAAm-grafted beads with various grafted amounts and various grafted PIPAAm chain densities were prepared. Contact angle measurements at different temperatures revealed that the magnitude of the contact angle change from 37 to 20 °C decreased with increasing brush density. Additionally, the amount of fibronectin adsorbed on the bead surface decreased with increasing brush density. Chinese hamster ovary (CHO-K1) cells adhered to the surface of PIPAAm-grafted beads at 37 °C, and a negligible difference in the cell adhesive property was observed by varying the brush density of the PIPAAm-grafted beads. When the temperature was reduced to 20 °C, the adhering cells were found to detach themselves from the PIPAAm-grafted bead surfaces. Of particular interest, PIPAAm-grafted beads with intermediate brush density exhibited the highest efficiency of thermally induced cell detachment. Thus, the brush density of PIPAAm-grafted beads strongly affected the efficiency of thermally induced cell detachment.