Micromechanical characterisation and three-dimensional modelling of oocytes

在人类生殖医学中，辅助生殖技术的成功往往与卵母细胞的质量有关。为了提高植入成功率，过去已经做了大量的研究。一般来说，卵母细胞的质量是由其形态决定的。然而，这种标准的使用是有争议的，因为形态学特征通常被解释为发育功能障碍的迹象，只能是自然变异的人工产物。因此，未来的目标必须是确定替代的和更客观的措施，不仅选择最好的卵母细胞，而且选择合适的成熟阶段，以实现最高的受精潜力。在细胞生物学的背景下，机械特性被认为是细胞生理状态的一个很好的指标，例如疾病或分化。这正是本研究项目发挥作用的地方。生物力学（申请人Böl）和生殖医学（申请人Töpfer）能力的结合实现了一种独特且高度创新的方法，该方法允许对单个卵母细胞进行全面表征，并获得有关细胞力学行为的重要信息，以评估其质量。因此，目前的研究项目有两个主要目标。一方面，将开发双相本构模型来描述受精前后卵母细胞的机械行为。另一方面，卵母细胞微力学、实验取样的新方法正在开发、建立，并应用于不同年龄的卵母细胞。由于这种模型开发和新的实验方法的结合，对细胞力学的一般理解以及对卵母细胞质量的理解都有了显著的提高，这一点目前还没有实现。特别是，新的实验方法将被开发，允许在各种变形状态下取样卵母细胞，如轴向/双轴拉伸、压缩、压痕和膨胀。大量不同的实验使卵母细胞的单个成分的机械鉴定以及建模方法的验证成为可能。在力学方面，基于对未受精和受精卵母细胞的新实验，考虑到透明带复杂的微观结构的模型的发展，在其他方面代表了知识的重大收获。随着有意义的模型的发展，将有可能更好、更深入地了解发生在卵母细胞（特别是在透明带）中的负载传递机制。此外，基于开发的模型，可以生成实验上无法实现的虚拟场景。这将有助于建立力学和细胞生理学之间的关系，例如，在卵母细胞质量方面。

In human reproductive medicine, the success of assisted reproductive technologies is frequently associated with the quality of oocytes. In order to increase implantation success, much research has been done in the past. In general, the quality of an oocyte is determined by its morphology. However, the use of such criteria is controversial, as morphological features, which are often interpreted as signs of developmental dysfunction, can only be artefacts of natural variability. Therefore, future objectives must be the identification of alternative and much more objective measures to select not only the best oocytes but also their appropriate stages of maturation to achieve the highest fertilisation potential. In the context of cell biology, mechanical properties are known to be an excellent indicator of the physiological state of a cell in terms of e.g. disease or differentiation. This is exactly where the present research project takes effect. The combination of competencies in biomechanics (applicant Böl) and reproductive medicine (applicant Töpfer) implements an unique and highly innovative approach, which allows the comprehensive characterisation of individual oocytes and the derivation of important information on cell mechanical behaviour in order to assess their quality.Therefore, the present research project has two main objectives. On the one hand, a biphasic constitutive model will be developed to describe the mechanical behaviour of oocytes before and after fertilisation. On the other hand, new approaches to the micromechanical, experimental sampling of oocytes are being developed, established, and applied to oocytes of different ages. Due to this combination of model development and new experimental methods, a significantly improved understanding of cell mechanics in general but also in sense of oocyte quality is to be expected, which is not yet available.In particular, new experimental methods are to be developed that allow the sampling of oocytes under various deformations states, as axial/biaxial tension, compression, indentation, and inflation. This large number of different experiments enables the mechanical identification of the individual components of oocytes as well as the validation of the modelling approach. On the side of mechanics, the development of a model, which, based on the new experiments on unfertilised and fertilised oocytes, takes into account, among other things, the complex microstructure of the zona pellucida represents a significant gain in knowledge. With the development of a meaningful model, it will be possible to gain a better, more in-depth understanding of load transfer mechanisms that take place in the oocyte (and here in particular in the zona pellucida). Further, based on the developed model it will be possible to generate virtual scenarios that are experimentally unrealisable. This will help to establish relations between mechanics and cell physiology, e.g., in terms of oocyte quality.