Teaching sperms how to swim

The sperm cell is the male reproductive cell. For successful fertilisation, it needs to traverse the oviduct and reach the egg. The inability to do so due to faulty swimming is one of the major causes of reduced fertility.

And this is what Ashwin Nandagiri, a research scholar at the IITB-Monash Research Academy, is attempting to rectify. Understanding the reasons for sub-fertility has a wide range of potential applications, which include male infertility treatments, animal breeding, and wildlife conservation.

Figure 1: A sperm cell swimming towards the egg (Source)

The IITB-Monash Research Academy is a collaboration between India and Australia that endeavours to strengthen scientific relationships between the two countries. Graduate research scholars here study for a dually-badged PhD from both IIT Bombay and Monash University, spending time at both institutions to enrich their research experience.

Ashwin believes that it is sometimes necessary to swim against the tide. “The sperm cell,” he explains, “consists of a head containing genetic material required for fertilisation and a long whip-like flagellum that propels the cell. Sperm cells have the ability to sense and follow chemical, thermal, and flow gradients. This directed motion is achieved by manipulating the flagellum. However, this manipulation leads to complex flows in the surrounding fluid, which in turn influences the motion. Our aim is to understand how sperm manipulate their flagella to achieve directed motion in a fluid.”

The hydrodynamics of flagellar propulsion has been studied using mathematical modelling for over half a century. In classical studies, the beating shape of the flagellum is specified and the net motion of the swimmer is calculated. However recent work suggests that flagellar motion may be more complex. The shape of the flagellar beat and the trajectories are the result of a complex interaction between the flexible body and the surrounding fluid.

Ashwin likens this interaction to the periodic waving of a flag in the wind. “The periodicity in this case is not externally imposed, but emerges out of an interaction with the surrounding flow. We are using mathematical modelling and computer simulations to understand whether a similar fluid interaction plays a role in the manipulation of flagella to achieve motion.”

Figure 2 (Left): Flow field around a swimming cell from computer simulations. Figure 3 (right) : Shape of the flagellar beat from computer simulations

Says Prof Murali Sastry, CEO of the Academy, “Today’s research challenges require a strongly multi-disciplinary approach. And the way in which the IITB-Monash Research Academy has been set up makes it very possible for such multi-disciplinary investigations to be carried out. This gives me immense hope that the Academy will create significant science, societal and industry impact in the future. Ashwin’s work could provide insight into possible mechanical reasons for defective sperm swimming, and therefore infertility. This might help design better infertility testing techniques and suggest improvements to existing ART (Assisted Reproductive Technology) treatments for infertility.”

The subject researchers like Ashwin are tackling is at the crossroads of biology and engineering. “Sperm cells are tiny machines that propel themselves through a fluid by consuming chemical energy. As a mechanical engineer, studying these machines and their mechanisms excites me,” he says.

As Woodrow Wilson famously said, “The man who is swimming against the stream knows the strength of it.”

Research scholar: Ashwin Nandagiri, IITB-Monash Research Academy

Project title: Computational Fluid Dynamics of swimming and propulsion at micro/nano scales

Supervisors: Dr Sameer Jadhav, Dr Prabhakar Ranganathan

Contact details: ashwin.nandagiri@monash.edu

This story was written by Mr Krishna Warrier based on inputs from the research student, his supervisors and IITB-Monash Research Academy. Copyright IITB-Monash Research Academy.