Ulrike Schimpf, researcher and Head of technical operations at the Department of Chemistry,

Ulrike Schimpf, researcher and Head of Technical Operations at the Department of Chemistry, is delving into the complex structure of this vital gel to better understand infertility and improve women’s health, with the support of world-class research facilities at the Arrhenius laboratory

– Cervical mucus plays a gatekeeping role in human reproduction – yet we still know surprisingly little about its structure and function, says Ulrike Schimpf, standing in front of a scanning electron microscope at the Arrhenius Laboratory’s state-of-the-art Electron Microscopy Centre (EMC).

Schimpf’s research investigates the molecular architecture of cervical mucus – a viscoelastic gel secreted in the cervix that acts as a barrier between the vagina and the uterus. Throughout most of the menstrual cycle, this barrier is impermeable to sperm. But during ovulation, a remarkable transformation takes place: the gel’s molecular structure and chemical composition shift to allow sperm to pass through.

From contraceptives to fertility

Originally from Germany, Schimpf’s fascination with cervical mucus began after moving to Sweden, where she joined a multidisciplinary research team exploring new forms of contraception.

– We were testing chitosan – a natural polymer – to see how it interacts with mucins, the glycoproteins that form a mesh in cervical mucus, she explains. Our lab experiments showed that chitosan strengthened the mucus, making it impenetrable to sperm even at ovulation. This suggested that a chitosan-based gel could serve as a non-hormonal, on-demand contraceptive.

But as often happens in science, one question led to another – and Schimpf soon found herself drawn to the inverse problem – why, in some cases, sperm cannot get through at all.

 – One of the causes of infertility is when the mucin network becomes overly dense, forming a barrier too thick for sperm to traverse, even during ovulation,” she notes. If we can learn how to replicate the looser, ovulatory structure of the mucus, we may be able to help more people conceive naturally.

A complex substance, hard to grasp

Despite its biological importance, cervical mucus is notoriously difficult to study. It is made up of several types of mucin polymers, proteins, salts, cells, and up to 98 percent water. During ovulation, the gel becomes extremely elastic and difficult to section or preserve for analysis.

– The mucus dries out quickly, changes its structure under handling, and is very heterogeneous. Traditional preparation techniques just don’t do it justice, Schimpf says.

Air-dried and gold coated human ovulatory cervical mucus under scanning electron microscope. Fern patterns are cervical mucus visible through crystallization of sodium chloride on mucins. Free crystals consist of potassium chloride.

That is where the Electron Microscopy Centre at the Arrhenius Laboratory comes in. Here, Schimpf is harnessing scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) to examine both the physical and chemical makeup of cervical mucus at an unprecedented level of detail.

– SEM has been an excellent starting point. It allows me to study the ultrastructure in high resolution, while EDS gives insights into the elemental composition. Together, they offer a clearer picture of what makes the mucus function as it does – or fail to, she explains.

Seeking alternatives to IVF

While assisted reproductive technologies such as in vitro fertilisation (IVF) has helped millions, Schimpf believes that a deeper understanding of cervical mucus could pave the way for less invasive and more accessible alternatives.

– If we understand how to restore or mimic the natural structure of cervical mucus, we might develop new treatments for mucus-related infertility. Right now, the options are limited – and IVF is both expensive and physically demanding. We need to broaden the toolkit.

Her current work involves developing new sample preparation methods that better preserve the natural characteristics of mucus, allowing for more accurate scientific analysis.

– There’s still so much we don’t know – not only about cervical mucus, but about women’s reproductive health more broadly. It’s an area that’s been historically under-researched. I hope this work helps to change that, Schimpf concludes.