Cells attach to each other in a variety of ways (see Chapter 5), but the “glue” is essentially a group of speci‹c molecules (cell adhesion molecules, or CAMs) located on the cell surface. Certain enzymes can break down these CAMs, leading to disaggregation. These disaggregated cells can be grown in specialized nutrient £uids (“media”), and the ability to do this is the basis of emerging tissue engineering technologies. Cells can attach to surfaces particularly if these surfaces are negatively charged and “wettable.” New instruments such as atomic force microscopes and laser tweezers (see Chapter 27) can be used to measure adhesion forces. The cell membrane is remarkably tough (see Figure 1.2), with typical values of elastic (Young’s) modulus of 103 Pa.