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，过去已经进行了大量的研究。一般来说，卵母细胞的质量取决于其形态。然而，这种标准的使用是有争议的，因为形态特征通常被解释为发育障碍的迹象，只能是自然变异性的产物。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，而且选择它们适当的成熟阶段，以实现最高的受精潜力。在细胞生物学的背景下，已知机械性能是细胞在例如疾病或分化方面的生理状态的极好指示器。这正是本研究项目发挥作用的地方。生物力学(申请者BöL)和生殖医学(申请者Töpfer)的能力相结合，实现了一种独特和高度创新的方法，允许对单个卵母细胞进行全面的表征，并获得关于细胞机械行为的重要信息，以评估其质量。因此，本研究项目有两个主要目标。一方面，将开发一个双相本构模型来描述受精前后卵母细胞的力学行为。另一方面，对不同年龄的卵母细胞进行微机械、实验取样的新方法正在被开发、建立和应用。由于模型的发展和新的实验方法的结合，对细胞力学的总体和对卵母细胞质量的理解有望得到显著的改善，这是目前尚不存在的。特别是，新的实验方法将被开发出来，允许在各种变形状态下对卵母细胞进行采样，如轴向/双轴拉伸、压缩、凹陷和充气。这一大量不同的实验使得对卵母细胞各个成分的机械识别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的卵母细胞的新实验，开发了一个模型，其中考虑了透明带的复杂微结构，这代表着知识的显著增长。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(尤其是透明带)中的负荷转移机制。此外，基于开发的模型，将有可能产生在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，在卵子质量方面。

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.