Alternative culture systems for bovine oocyte in vitro maturation: liquid marbles and differentially shaped 96-well plates

In vivo matured oocytes exhibit higher developmental competence than those matured in vitro, but mimicking the in vivo environment by in vitro conditions has been challenging. Till now, conventional two-dimensional (2D) systems have been used for in vitro maturation of bovine cumulus-oocytes-complexes (COCs). However, using such systems may cause cell flattening and does not allow cumulus expansion in all dimensions, which is less physiological. Therefore, implementing a low-cost and highly effective in vivo-like microenvironment methodology may help to optimize oocyte in vitro maturation. Here, we used two different systems to culture COCs and evaluate their potential influence on embryo development and quality. In the first system, we used treated fumed silica particles to create a 3D microenvironment (liquid marbles; LM) to mature COCs. In the second system, we cultured COCs in 96-well plates with different dimensions (flat, ultra-low attachment round-bottom, and V-shaped 96-well plates). In both systems, the nuclear maturation rate remained similar to the control in 2D, showing that most oocytes reached metaphase II. However, the subsequent blastocyst rate remained lower in the liquid marble system compared to 96-well plates and control 2D systems. Interestingly, a lower total cell number was found in the resulting embryos from both systems (LM and 96-well plates) compared to the control. In conclusion, oocytes matured in liquid marbles or 96-well plates showed no remarkable change in terms of meiotic resumption, embryo development, and quality in both systems. None of the surface geometries influenced embryo development. These findings provide important inferences in many aspects of oocyte and embryo development. Further investigation is needed to determine other aspects like toxicity testing and ultrastructural changes in oocytes.