Multifunctional Dielectric Elastomer Actuator for in vitro Cell Mechanostimulation

Ongoing research on the human body provides insights that are important for understanding its mechanisms and the impact of new drugs. To study these complex processes in vivo, animal models, such as rodents, are used because they provide a living system that can be observed over an entire life cycle. However, from an ethical standpoint, this practice is increasingly difficult to justify. Following the 3R initiative, future research tries to reduce animal testing. Cell cultures offer an in vitro alternative for studying cell physiology and pharmacological responses. Unfortunately, mechanically active tissues, like human bladder cells, undergo dedifferentiation when grown in static cultures. Mechanical stimulation can solve this problem by mimicking the cells natural state. Current stimulation devices usually rely on electric motors, pneumatic or magnetic systems. These conventional setups suffer from several drawbacks, including out-of-plane deformation, inhomogeneous strain fields and unwanted heating. They are also difficult to miniaturize and implement for high throughput. Dielectric elastomer actuators (DEAs) present a promising alternative. They stand out because of their simple design, adaptable strain fields and good scalability. Despite these advantages, current DEA applications in biology still face specific limitations. For instance, existing setups are mostly limited to uniaxial strain, whereas an equibiaxial approach is required to properly stimulate bladder cells. Furthermore, standard DEAs use opaque carbon black electrodes, which are incompatible with optical microscopy. Consequently, cells are often only attached to small, passive and non-homogeneous areas. Additionally, the bio-safety of the electrical actuation has not been established. To address the limitations of conventional actuators and the current challenges of DEA integration, this thesis presents a novel DEA-based platform designed for the precise mechanical stimulation of human cells, specifically using the TEU-2 bladder cell line. Developing this system involved modeling and strain optimization. Different models and layouts were introduced and compared with each other and with experimental data. To ensure compatibility with optical microscopy, patterned and transparent electrodes were introduced. The use of laser-ablated carbon black electrodes and carbon nanotube (CNT) electrodes represents an alternative approach for DEAs and enable novel solutions for DEA-based cell stretchers. Their fabrication and characterization is discussed in detail. Furthermore, a self-sensing algorithm based on Fast Fourier transform (FFT) was implemented to analyze cell stiffness, enabling the continuous monitoring of cell growth. Moreover, acoustofluidic stimulation was characterized for the first time in combination with DEAs, demonstrating its ability to precisely position cells on the membrane. Finally, in-depth biological evaluations as cell apoptosis assay confirm that this DEA-based