Thermosensitive PHEMA microcarriers: ATRP synthesis, characterization, and usabilities in cell cultures

In this study, we developed a novel microcarrier to enhance the production of anchorage-dependent mammalian cells in large scale by preserving them from the effects of shear forces and to enhance their removal from the surface without using proteolytic enzymes and chelating agents. This 'thermosensitive microcarrier' was synthesized by the grafting thermoresponsive molecule, N-isopropylacrylamide (NIPAAm), to the crosslinked poly(2-hydroxyethyl methacrylate) (PHEMA) beads by surface-initiated atom transfer radical polymerization. NIPAAm was polymerized on bromine-activated beads' surfaces to prepare PHEMA-g-PNIPAAm microcarriers. Then, they were chemically characterized by attenuated total reflectance Fourier transform infrared and electron spectroscopy for chemical analysis. Surface morphologies were further investigated by scanning electron microscope and atomic force microscopy techniques. The results of characterization studies confirmed that PNIPAAm was successfully grafted onto PHEMA beads by the means of atom transfer radical polymerization reaction. The cellular activities of PHEMA-g-PNIPAAm microcarriers were evaluated at static and dynamic culture conditions by using two types of cell lines with different morphology, i.e. L929 mouse fibroblasts and HS2 epithelial human keratinocytes. The microcarriers exhibited better cell adhesion and proliferation characteristics for both cell lines. Although their thermally induced cell detachment efficiencies are lower than that of trypsinization, thermally harvested cells preserved their surface morphologies and proliferation characteristics.