Cell viability of the cells grown on the collagen microspheres. (A-C) Fabricated collagen microspheres. The diameter of collagen microspheres increased when the stirring speed for the mixture of collagen solution, paraffin oil and surfactant was increased. The stirring speeds for the fabrication of collagen microspheres are 600 rpm (A), 800 rpm (B) and 1,000 rpm (C). Scale bar: 200 μm. (D-F) 3T3 cells that grew on collagen microspheres were labeled with Calcein (D) and Ethidium (E) in the LIVE/DEAD® cell viability assay. (G) Quantification of microsphere diameter fabricated at different stirring speed. (H) Quantification of live cells of PC12 cells and 3T3 cells grown in cell culture plate or on collagen microspheres. Scale bar: 200 μm (I) alamarBlue cell viability assay of B104 cells, PC12 cells and oligodendrocyte progenitor cells (OPCs) growing in cell culture plate or on collagen microspheres.