There's an interesting article in the October 22, 2009 issue of PNAS about using paper as a support matrix for growing cells.
The paper is written by Ratmir Derda, a researcher in George Whitesides' lab at Harvard. The title, Paper-supported 3D cell culture for tissue-based bioassays, sums up the topic pretty well but only hints at the significance of this area of research.
For most of my life basic cancer research has been done the same way. You grow some cancer cells on a plastic surface, usually a flask or petri dish, then test those cells in a variety of ways. The problem is that real cancer cells grow in tumors which are three dimensional and a lot more complicated than some cells growing on a flat surface.
Recently there's been a lot of progress at developing matrix systems for growing cells in more natural but still controlled settings. This paper details one such system and what I like about this method is that it uses pieces of paper in a stack, with cells injected into them. The advantage is that once the group of cancer cells is growing in a tumor-like configuration, you can conduct your experiments and then afterwards take the tumor apart slice by slice by just peeling off the layers of paper. Pretty slick!