Thixotropic materials, which become less viscous under stress and return to their original state when stress is removed(1), have been used to deliver gel-cell constructs(2) and therapeutic agents(3). Here we show that a polymer-silica nanocomposite thixotropic gel can be used as a three-dimensional cell culture material. The gel liquefies when vortexed-allowing cells and biological components to be added-and resolidifies to trap the components when the shear force from spinning is removed. Good permeability of nutrients and gases through the gel allows various cell types to proliferate and be viable for up to three weeks. Human mesenchymal stem cells cultured in stiffer gels developed bone-like behaviour, showing that the rheological properties of the gel can control cell differentiation. No enzymatic(4), chemical(5,6), or photo-crosslinking(7-9), changes in ionic strength(10-14) or temperature(15,16) are required to form or liquefy the gel, offering a way to sub-culture cells without using trypsin-a protease commonly used in traditional cell culture techniques.