Optical tweezers for microrheology of the cumulus matrix in a microlitre volume

In the field of in vitro fertilisation (IVF), there is a need to understand how cell properties of the cumulus oocyte complex may be used to predict successful pregnancy and live birth rates post-IVF. Here we used optical tweezers for the first time to measure the viscosity of the cumulus cell matrix surrounding the oocyte (egg). This study aimed to determine whether the viscosity of the cumulus cell matrix – prior to fertilisation – is reflective of subsequent embryo developmental potential and indicative of pregnancy success. Measurements were performed using a 1µm diameter silica probe particle trapped by a focused 1064nm laser. We benchmarked the accuracy of the system by measuring the viscosity of glycerol with varying mass fractions. Viscosity measurements of the cumulus cell matrix were performed in isolation from both the cumulus cells and the oocyte. This showed that the viscosity of cumulus matrix was significantly higher when sampled from oocytes with a higher developmental potential (in vivo matured) compared to those of lower quality (in vitro matured).