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.
After an hour, the diamond-coated petri dishes contained 300% more Grade A sperm cells than did the polystyrene dishes, the team reports in the Annals of Translational Medicine. That’s likely because ROS can’t stick to the diamond surface in the same way that they do to polystyrene, Sommer says. “The ROS, when landing on diamond, have no chance to harm the cells.”
In a separate set of experiments, the team tested how light affects sperm cells. Previous studies have shown that exposing cells to a particular wavelength of light, 670 nanometers, toward the red end of the visible spectrum, causes their energy-producing mitochondria to boost production of adenosine triphosphate, which powers the cells. When the researchers exposed sperm cells to this wavelength, they found about twice as many Grade A cells after 30 minutes than were in control groups.
Used in conjunction, diamond-coated petri dishes and near-infrared light might make sperm cells intended for IVF procedures more energetic and longer lasting, increasing the chance of a successful fertilization, Sommer says, although more testing is needed before any of these techniques could be used in the clinic.
Of course, diamond dishes are a lot more expensive than plastic ones. It costs about $100 to make a diamond-coated petri dish like the one used in the study—compared with polystyrene dishes that cost mere pennies—but Sommer says the expense isn’t unreasonable given that IVF procedures routinely cost $10,000 or more.
The study’s findings are intriguing and significant for the field of reproductive biology, says Ashok Agarwal, a biologist who directs research at the American Center for Reproductive Medicine at the Cleveland Clinic in Ohio. “The use of diamond associated with an increase in motility by 300% is surprising,” he wrote in an email to Science. Some researchers have found that nanodiamond is toxic to sperm cells and fertilized eggs, though, “so proper investigation is needed to confirm its impact on germ cell and the health of the embryo,” he says.
Sommer contends those studies involve diamond nanoparticles that have entered the cell, which wouldn’t happen with sperm cells sitting on a chemically inert diamond surface, but he agrees more research is needed to ensure the technique is safe.