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Dunning, Kylie R. Dholakia, Kishan Wright, Amanda J. (University of Nottingham) Mendonca, Tania (University of Nottingham) Campugan, Carl Adrian Ang School of Biomedicine 2025 https://hdl.handle.net/2440/151870 This thesis is a joint doctoral degree between the University of Adelaide and the University of Nottingham Despite advances in assisted reproductive technologies (ART) such as in vitro fertilisation (IVF), success rates remain low at around 20% per initiated cycle. The quality of oocytes and embryos are key determinants of IVF success. During an IVF cycle, multiple oocytes are harvested, and several embryos generated. Accurate assessment and ranking of these to identify those with the highest developmental potential would assist in patients achieving pregnancy in fewer IVF cycles. However, current assessments are subjective or invasive and importantly, do not improve live birth rate. This highlights the need for objective methods for evaluating oocyte and embryo quality. Light-based technologies, such as optical imaging, show promise in assessing intrinsic indicators of quality including metabolic activity. Beyond this, light can also be innovatively applied to measure the viscous properties of the microenvironment surrounding oocytes and embryos—an area previously unexplored in IVF but known to correlate with health in other cell types. This thesis investigates the use of optical tweezers for passive microrheology to measure viscosity in the oocyte and embryo microenvironment, examining its potential relationship with viability. Furthermore, as light-based technologies increase in prominence, I also investigated how light exposure affects embryos. The first part of this thesis demonstrated the utility of optical tweezers to quantify the viscosity of the cumulus-oocyte extracellular matrix (ECM). I found that the viscosity of the ECM positively correlated with oocyte viability. This approach has the potential to become an objective and reliable method for assessing oocyte quality in the future. This thesis then explored how optical tweezers can measure the viscosity of the microenvironment surrounding 4 cell- and blastocyst-stage embryos. Here, I report that the viscosity of the blastocyst microenvironment was significantly higher than that of the earlier 4 cell-stage embryo. The findings of this study were the first to show a developmental-stage difference in the viscosity of the embryo microenvironment. These findings provide novel insights into extracellular changes that accompany pre- implantation development and dynamic shifts in metabolism. Finally, this thesis investigated the impact of light exposure on embryo development, a crucial but often overlooked aspect of IVF. Using standardised experimental conditions, assessed how exposure to I specific wavelengths of light—common in optical imaging systems—affects embryo development, cell lineage allocation, DNA integrity, lipid abundance, and post-transfer outcomes. The findings show that morphological evaluation alone fails to capture wavelength-specific effects of light exposure on embryos. This underscores the critical importance of controlling light exposure during IVF procedures. Collectively, Chapter 2 and 3 introduce a novel use of light, via optical tweezers, to quantitatively measure the viscosity of the microenvironment surrounding the oocyte and embryo. These studies highlight the potential for microrheology with optical tweezers to non-invasively measure viability- and developmental stage-specific differences in viscosity. While the use of light is essential in ART, Chapter 4 highlights the importance of managing the exposure of embryos to specific wavelengths during handling or imaging. Certain wavelengths may need to be avoided, or their effects mitigated to safeguard embryo viability. Thesis (Ph.D.) -- University of Adelaide, School of Biomedicine, 2025 en Optical tweezers light in vitro fertilisation oocytes pre-implantation embryo microrheology Utilising Light in Assistive Reproductive Technologies Thesis This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legalsopen.access