The physics of sperm: the movie

By James Dacey

Luke Skywalker et al. re-entered the public imagination recently with the release of the trailer for Star Wars: the Last Jedi. But where that movie takes you on a galactic adventure, a new short web film by the Wyss Institute in the US takes you on a swashbuckling tour of the microscopic – tracking animated sperm on a mission to fertilize an egg.

The Beginning is based on collaborative work between a pair of researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard University. Founding director Don Ingber teamed up with the biophysicist/professional animator Charles Reilly to seek an atomic-level understanding of sperm movement. Combining molecular dynamics simulations with film animation software, they have visualized how a sperm tail moves based on scientific data.

“Applying an artistic process to science frees you from the typically reductionist approach of analysing one particular hypothesis and teaches you a different way of observing things,” says Reilly. Now a staff scientist at the Wyss, Reilly previously worked at Hollywood film director Peter Jackson’s Park Road post-production facility in New Zealand. The goal for this latest project was to create a film that captures the public imagination but also depicts valid scientific models.

In the classic Star Wars trope, tilted text drifting off into space informs viewers: “Countless agents have been deployed, and are on their way, each willing to sacrifice its life to complete the mission.” The agents in this adventure are individual sperm cells, propelling themselves through the darkness with their whip-like tails towards an egg. Tension-filled classical music heightens the drama, as the film realistically depicts the mechanics of how sperm move, [spoiler alert] culminating with one Jedi sperm penetrating the egg membrane to trigger the creation of new life.

At one point, the film zooms in on the tail – known as the “axoneme” – revealing it at a range of scales. We see a tube comprising pairs of microtubules arranged in a column around a central pair. Zooming in further, we see rows of motor proteins called “dyneins” attached to the microtubules, which exert the required force for the system to bend and thrust forwards. According to the researchers, the unique features of their simulation is its consistency across the range of scales. They say it even sheds new light on the specific biomolecular process that ultimately enables sperm to travel in the required direction. By their own omission, it was tricky to find a journal willing to publish the work (probably due to its novel approach), but the findings have now been published in ACS Nano.

“Science is the pursuit of the unknown,” says Ingber. “We have a responsibility to reach out to the public and convey that excitement of exploration and discovery, and fortunately, the film industry is already great at doing that.

Ingber is no stranger to interdisciplinary research, in fact the entire Wyss philosophy is based on teaming people with varied backgrounds, as he explained in this interview for the recent Physics World special report on the US. Ingber also features in this recent Physics World film (below) about a Wyss project to recreate human organs on chips. The goal of that project to develop an alternative to drug-testing on animals and pave the way to personalized treatments.