Michael Price in Science:
For women looking to become pregnant through in vitro fertilization (IVF), a diamond petri dish could be a girl’s best friend. That’s one conclusion from a new study, which finds that human sperm cells live longer and move more efficiently on diamond surfaces compared with traditional polystyrene petri dishes. The researchers also discovered that shining a red light on the sperm cells improved their performance. Combining these techniques might significantly increase the chances of IVF success. During IVF procedures, sperm is introduced to an egg in a petri dish. If the egg is successfully fertilized, the resulting zygote is implanted into the woman’s uterus. The critical fertilization stage usually takes place on polystyrene, a plastic from which almost all petri dishes are made. Sperm, like most cells, exude harmful, cell-disrupting molecules known as reactive oxygen species (ROS). Inside the body, these ROS last only fractions of a second and are quickly neutralized as they bind with nearby molecules. But polystyrene naturally forms a thin, gluelike nano-layer of water on its surface, which traps the ROS. “The sperm is stewing in its own ROS,” says Andrei Sommer, a physicist who led the study while working at Ulm University in Germany and who is currently working as an independent scientist. “This longer exposure is highly, highly, highly destructive to the cell.” The upshot is that many sperm cells exposed to polystyrene quickly lose their motility, turning from “guided missiles” into barely moving or immobile cells incapable of fertilizing an egg. Generally, the more highly motile sperm cells a sample contains, the more likely it is that an IVF procedure will result in pregnancy, though a host of other factors like sperm count and egg quality also play a role. (Eggs produce less ROS and therefore are less susceptible to oxidative damage than are sperm cells.)
Building on previous work by his lab, Sommer and colleagues wondered whether keeping sperm cells on a material like diamond, which forms a slick, not sticky, surface layer of water, would protect them from ROS. The researchers coated quartz petri dishes with a superthin layer of diamond less than a micron thick, and put human sperm cells on them. They assigned the cells one of four grades ranging from A (rapidly moving and the most likely to fertilize) to D (completely immobile and incapable of fertilization). Then they did the same thing for sperm cells taken from the same sample but placed on traditional polystyrene petri dishes.