Viscoelastic microbead stress sensors and validation based on organoid mechanobiology

细胞施加和经历的机械应力在组织形态发生和器官形成中起着重要作用。虽然已经建立了量化机械应力的技术，但它们在活组织和生物体中的研究仍然具有挑战性。最近推出的基于水凝胶的微珠代表了一种新型的应力传感器。这些可变形的、球形的、细胞大小的探针被注入细胞聚集体或组织的细胞间隙，并允许与邻近细胞直接相互作用。在这些微珠产生变形的基础上，应力可以在细胞水平上量化。然而，电流传感器表现出弹性材料特性，在引入粘弹性组织环境后，会影响细胞行为，从而导致测量伪影。此外，细胞的速率依赖性相互作用不能被捕获。除此之外，在现有的传感器中几乎不可能实现额外的功能化，例如，关于荧光位置和方向标记的结合。因此，我们计划在本项目中开发基于粘弹性水凝胶材料的新型微珠应力传感器，这种材料在细胞响应功能化方面具有高度的灵活性。这些微珠将由微流控装置生产，并在微观和宏观尺度上精确表征其机械性能。此外，它们将被纳入多能干细胞衍生的肾类器官，以探索它们在类器官生长的不同发育阶段量化细胞应激的潜力。一种已经建立的称为“细胞尺度应力传感计算分析”（COMPAX）的方法将扩展到粘弹性应力传感器的应用，将用于微珠的后续分析。在这种情况下，将开发并验证一种新的应力计算模拟设置。有了这种新型的应力传感器，我们期望扩大机械生物学工具的范围，以及对类器官形成过程中发育过程的新的时空见解，从而更好地理解细胞过程。

Mechanical stress exerted and experienced by cells plays an important role for tissue morphogenesis and organ formation. While techniques to quantify mechanical stresses are established, their study in living tissues and organisms remains challenging. Recently introduced hydrogel-based microbeads represent a new type of stress sensors. These deformable, spherical, cell-sized probes are injected into the intercellular space of cell aggregates or tissues and allow the direct interaction with neighboring cells. On the basis of the resulting deformations of these microbeads, stresses can be quantified at the cellular level. However, current sensors exhibit elastic material properties which, after introduction into a viscoelastic tissue environment, can influence the cellular behavior and thus lead to measurement artifacts. Furthermore, the rate-dependent interaction of the cells can not be captured. In addition to that, additional functionalization, e.g., regarding incorporation of fluorescent position and orientation markers, is hardly possible in available sensors. Therefore, we plan to develop novel microbead stress sensors in this project based on a viscoelastic hydrogel material which is highly flexible with regard to cell responsive functionalization. These microbeads will be produced by a microfluidic device and precisely characterized in terms of their mechanical properties at the micro- and macroscale. Furthermore, they will be incorporated into pluripotent stem cell-derived kidney organoids to explore their potential to quantify cellular stresses at different developmental stages of organoid growth. An already established method called “Computational Analysis of Cell Scale Stress Sensing” (COMPAX), which will be extended to the application of the viscoelastic stress sensors, will be used for the subsequent analysis of the microbeads. In this context, a new simulation setup for the stress calculations will be developed and validated. With this novel type of stress sensors, we expect an expansion of the range of mechanobiological tools as well as new spatiotemporal insights into the developmental processes during organoid formation enabling a better understanding of cellular processes.