Cells are grown in suspension by using low melting point agar. Basically, the agar is heated just enough to melt it, then living cells (we can culture bacteria this way, as well) are added, and the agar is allowed to solidify. If the experimenter has done it correctly, the cells won't be killed by the heat, the agar won't solidify before pouring, and the cells will be suspended, and colonies of bacteria, or cancerous tissue can grow in 3 dimensions, just like they would within a living thing.