This study demonstrated the spin-coating of functional diblock copolymers to develop smart culture inserts for thermoresponsive cell adhesion/detachment control. One part of the block components, the poly(n-butyl methacrylate) block, strongly supported the water stable surface-immobilization of the thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) block, regardless of temperature. The chain length of the PNIPAAm blocks was varied to regulate thermal surface functions. Immobilized PNIPAAm concentrations became larger with increasing chain length (1.0-1.6 μg cm-2) and the thicknesses of individual layers were relatively comparable at 10-odd nanometers. A nanothin coating scarcely inhibited the permeability of the original porous membrane. When human fibroblasts were cultured on each surface at 37 °C, the efficiencies of cell adhesion and proliferation decreased with longer PNIPAAm chains. Meanwhile, by reducing the temperature to 20 °C, longer PNIPAAm chains promoted cell detachment owing to the significant thermoresponsive alteration of cell-surface affinity. Consequently, we successfully produced a favorable cell sheet by choosing an appropriate PNIPAAm length for block copolymers.