A novel method to prepare multicellular spheroids from varied cell types

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Abstract
A simple method for preparing multicellular spheroids from varied cell types has been successfully developed by using a stepwise gradient surface in cell attachability or detachability. The surface was composed of poly‐N‐isopropylacrylamide (PNIPAAm), a temperature responsive polymer, as a cell detaching component, and collagen as a cell attaching component. The surface functions as a culture substratum at 37°C; then, when lowering the temperature of culture medium, the cells attached to it detach as a self‐supporting sheet. This is because PNIPAAm dissolves into the culture medium below the lower critical solution temperature (LCST; about 30°C), but it is insoluble above the LCST. The detached cell sheet forms a multicellular spheroid. The stepwise gradient surface which consisted of six different sectors was prepared by exposing a surface of the PNIPAAm‐collagen mixture to ultraviolet (UV) irradiation six times using a photomask, sliding the hole position in the photomask, and changing the energy of UV irradiation. This was because crosslinking of collagen depended on the energy of UV irradiation, then, cell attachability to and detachability from the surface were tightly controlled by changing the energy.The stepwise gradient surface allowed us to easily determine optimal surface conditions to obtain good cell attachment and detachment as a self‐supporting sheet from the surface to prepare multicellular spheroids. According to the evaluation of the attachability and detachability of 23 cell types, the optimal surface condition remarkably depended on each cell type. The detached cells under optimal surface conditions, including fibroblasts, osteoblastic cells, smooth muscle cells, and measangial cells, which were very difficult to form spherioids using conventional methods, were able to form multicellular spheroids. The results clearly demonstrate that the above‐described method for preparing multicellular spheroids can be applied to varied cell types. © 1995 John Wiley & Sons, Inc.

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