Thermoresponsive, cationic, copolymer brushes poly(N-isopropylacrylamide(IPAAm)-co-N,N-dimethylaminopropylacrylamide-co-N-tert-butylacrylamide(tBAAm)) and poly(IPAAm-co-3-acrylamidopropyl trimethylammonium chloride-co-tBAAm) were prepared on glass substrates through surface-initiated atom transfer radical polymerization. Prepared copolymer brushes were investigated as thermally modulated cell separation materials. Densely packed cationic copolymer brushes were formed on the glass substrates, and the positive charge density was modulated by controlling the composition of cationic moieties and species. During observation of cell adhesion and detachment properties on copolymer brushes, human bone marrow mesenchymal stem cells (hbmMSC) exhibited thermally modulated cell adhesion and detachment, while other bone-marrow-derived cells did not adhere. Using these properties, hbmMSC could be purified from mixtures of human bone-marrow-derived cells simply by changing the external temperature. Therefore, the prepared cationic copolymer brush is useful for separation of hbmMSC.

For preparing a thermally modulated biointerface that separates cells without the modification of cell surfaces for regenerative medicine and tissue engineering, poly(N-isopropylacrylamide-co-butyl methacrylate) (P(IPAAm-co-BMA), thermo-responsive hydrophobic copolymer brushes with various BMA composition were formed on glass substrate through a surface-initiated atom transfer radical polymerization (ATRP). Characterization of the prepared surface was performed by X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared spectroscopy (ATR/FT-IR), and gel-permeation chromatography (GPC) measurement. Prepared copolymer brush surfaces were characterized by observing the adhesion (37 °C) and detachment (20 or 10 °C) of four types of human cells: human umbilical vein endothelial cells (HUVECs), normal human dermal fibroblasts (NHDFs), human aortic smooth muscle cells (SMCs), and human skeletal muscle myoblast cells (HSMMs). HUVECs and NHDFs exhibited their effective detachment temperature at 20 and 10 °C, respectively. Using cells' intrinsic temperature sensitivity for detachment from the copolymer brush, a mixture of green fluorescent protein (GFP)-expressing HUVECs (GFP-HUVECs) and NHDFs was separated.

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