Introducing FELIX™

3rd June 2026

5:30 to 7:00pm

FELIX™ sperm selection: a new approach to sperm preparation for ICSI

When undergoing ICSI, selecting sperm for treatment is an important part of the laboratory process. At Harley Street Fertility Clinic, we currently offer the FELIX™ System as an additional sperm preparation option for suitable ICSI patients.

FELIX™ is a rapid, automated sperm separation system designed to help select mature sperm with favourable characteristics, including good motility, normal morphology and lower levels of DNA fragmentation. It does this using an electrophoretic process, which separates sperm according to their electrical charge and size.

For some patients, particularly where sperm quality is a concern, FELIX™ may offer an alternative to conventional sperm preparation. The system can technically be used for both IVF and ICSI, but because the process reduces the overall number of sperm recovered, Harley Street Fertility Clinic is currently introducing FELIX™ for ICSI cycles only.

How does the FELIX™ System work?

The FELIX™ System has two main components: a reusable console and a single-use cartridge. The console supplies the electrical power and standardises the preparation process, while the cartridge contains the electrodes and membranes used to separate the sperm cells.

The technology makes use of a change that takes place as sperm mature. Late in the maturation process, a layer containing negatively charged sialic acid develops on the outer membrane of the sperm cell. The quality of sperm DNA is strongly linked with the magnitude of this negative surface charge.

When an electrical field is applied within the FELIX™ cartridge, mature sperm carrying a stronger negative charge are drawn through a membrane towards the positive electrode. The cartridge also uses size-exclusion membranes to help separate sperm from larger cells found in semen, including leukocytes.

A microporous membrane with a pore size of five microns is large enough to allow sperm to pass through while helping prevent larger, unwanted cells from entering the collection area. Finer restriction membranes also keep the sperm separated from the electrodes while allowing ions to flow and conduct the electrical current.

The selected sperm are collected from the cartridge's harvest chamber after approximately six minutes.

What are the potential benefits of FELIX™ sperm selection?

The aim of FELIX™ is to select a population of sperm with favourable characteristics for use in assisted reproductive treatment. The system is used to select sperm with higher motility, normal morphology and lower DNA fragmentation.

Unlike some conventional preparation approaches, FELIX™ is not completely dependent on sperm motility or concentration. This means it may be considered in some cases where a semen sample has high viscosity, a lower sperm concentration, reduced motility or higher levels of DNA damage.

The process is also automated, which helps standardise preparation. The entire separation takes place within one cartridge, reducing the need to transfer the sample between multiple containers during preparation. Together with its ability to select according to sperm charge and size rather than depending mainly on motility and concentration, this is what distinguishes FELIX™ from more conventional preparation approaches.

Fresh or frozen sperm can be prepared using the FELIX™ System.

Why can sperm DNA quality matter?

Sperm quality involves more than simply the number of sperm present in a semen sample. Motility, morphology and the quality of the DNA carried within the sperm are also relevant considerations in fertility treatment.

DNA fragmentation refers to damage or breaks within the genetic material carried by sperm. FELIX™ has been designed to help isolate more mature sperm with relatively lower levels of DNA damage by using the relationship between sperm maturation and the negative charge on the cell surface.

Studies comparing electrophoretic sperm separation with conventional preparation techniques have reported encouraging findings, including the selection of sperm with lower DNA damage. Some research has also suggested that clinical pregnancy may be more likely when this type of sperm selection is used.

What happens on the day of ICSI?

On the day of your ICSI procedure, the semen sample is assessed by the embryology team. To use the FELIX™ System, approximately 1 mL of sample is needed for the cartridge.

If the sample volume is below this, the embryologist may be able to add laboratory media to increase the volume, while taking the original sperm concentration and resulting dilution into account.

The sample is then gently loaded into the sample chamber of the single-use FELIX™ cartridge. During the six-minute separation process, sperm with the appropriate size and negative charge move through the membranes and into the harvest chamber.

The selected sperm are then collected and the ICSI procedure continues in the standard way.

Who can use FELIX™?

FELIX™ can be used to prepare both fresh and frozen ejaculated sperm. Although the system can technically be used for IVF or ICSI, Harley Street Fertility Clinic is currently introducing it for ICSI cycles because the process reduces the overall number of sperm recovered. Because FELIX™ is not completely reliant on motility or concentration, it may also be an option for some samples that are more challenging to prepare using standard techniques.

Is FELIX™ right for me?

Whether FELIX™ is appropriate will depend on your individual circumstances, your semen analysis and the type of fertility treatment you are having.

The technology offers a different way of selecting sperm for ICSI, with the aim of isolating mature sperm with good motility and morphology and lower DNA fragmentation. Its rapid, automated process can also be useful for some semen samples with characteristics such as low motility, low concentration, high viscosity or higher DNA damage.

At Harley Street Fertility Clinic, our embryology and clinical teams can discuss the available sperm selection options with you and explain whether FELIX™ may be suitable as part of your ICSI treatment. Our aim is to help you understand the choices available, the potential benefits and the limitations, so you can make an informed decision about your care.