Elastomer-based Cellular Micromechanical Stimulators for Mechanobiological Study

Cells in vivo are constantly exposed to mechanical stimuli originated from their extracellular environment, such as the contraction from cardiac muscle and the laminar shear from blood flow. These mechanical stimuli are essential for maintaining cellular functions and regulating cellular behaviors in many physiological processes. Hence, it is important to understand how mechanical stimuli induce cellular responses. This requires specific tools that can deliver controllable mechanical signals in magnitude, duration, frequency, and direction. To this end, many engineered cell loading tools have been developed for applying different types of mechanical loads to in vitro cultured cells to trigger different types of cellular responses. By using these tools, it has been demonstrated that cyclic mechanical loads can regulate cell alignment, migration, proliferation, apoptosis, and can affect stem cell differentiation. Nonetheless, current cell loading tools still have many limitations. For example, tools with conventional-scale loading sites are often with low throughput, since few loading site can be arranged onto the limited space of a tool. Moreover, the large loading site inevitably leads to unnecessary consumption of precious cells and reagents, especially when the study requires parallel and multiplexed loading parameters. Tools with miniaturized loading sites can largely increase the loading throughput. However, device fabrication and assembly are increasingly challenging when the dimension of the loading site decreases. Moreover, the magnitudes of the simultaneously applied mechanical loads at different loading sites are not well controllable, especially at the dynamic loading conditions. Besides, most of the tools are designed for loading 2D cultured cells, while specific tools for loading 3D cells are still in need.To address these limitations, this thesis describes the development of elastomeric-membrane-based cellular micromechanical stimulators for mechanobiological study. A cellular micromechanical stimulator with hydraulic-pressure-driven PDMS micro-membranes is first developed at a much lower fabrication complexity, and demonstrates its effectiveness in delivering controllable mechanical strain to 2D cultured cells. The loading membranes are then tailored with a contoured thickness profile for optimizing the homogeneity of the applied strain field towards delivering homogeneous equi-biaxial, which is validated by loading 2D cultured cells under dynamic loading conditions. Application of controlled mechanical loading on 3D cell aggregates is implemented by integrating polymeric micro-grippers onto the loading membranes. The effectiveness of the device in 3D cell loading is demonstrated by inducing stem cell differentiation. For increasing the loading throughput, microfluidic actuation systems that can simultaneously deliver a desired pattern of loading pressure at multiple loading membranes by a single pumping unit are devised. Such design allows further miniaturization of the cell mechanical stimulators for multiplexing and parallel cell stimulation assay at both static and dynamic loading conditions. By the simplicity of fabrication, ease of operation, capability for further miniaturization and high throughput actuation, availability for both 2D and 3D loading, and excellent controllability of loading strain at both static and dynamic loading conditions, the cell micromechanical stimulators reported in the thesis thus provide promising solutions for systematically investigating of the complex cascades of cellular mechanobiological events under a conventional biological laboratory environment.