Juhee Hong

Micro checkerboard patterned polymeric surface with discrete rigidity for studying cell migration

The control of cell migration has an important role in processes ranging from developmental morphogenesis to the pathogenesis. In this study, we describe a novel approach to develop a micro-checkerboard patterned polymeric flat surface with discrete surface stiffness. This platform as a culture substrate allows us to explore the mechanism of durotaxis, referred to as the directed cell movement via the gradient of surface stiffness. The flat surface with different rigidity was achieved in two stages of fabrication. First, polydimethylsiloxane (PDMS) was pressed and cured on a glass substrate with trenches of varying depths in a checkerboard arrangement, and then, a thin PDMS layer was spin coated on the previous pattern to make the flat surface. The stiff region is defined by a thin layer (2.5 µm) of PDMS and the soft region is defined by a thick one (7.5 µm). To investigate the migratory cell behavior, the NIH 3T3 cell was cultured. The result demonstrates that a single cell showed clearly a migratory cell behavior toward the stiffer regions driven by the difference of effective surface stiffness. At high cell density, the effect of cell migration on effective surface stiffness decreased with increasing cell–cell interactions. However, cell migration was still dominated by difference of effective surface stiffness while fluctuating at the boundary between the stiff and soft regions. This approach enables us to control the mechanical and topological properties of surface. The developed platform will also offer a useful tool to study cell–substrate interaction mediated by surface stiffness (e.g. mechanotransduction).

Development of vacuum assisted microfluidic cell trapping device for repositioning of oocyte intracellular chromosomes

We report the design and micro-fabrication of vacuum-assisted microfluidic trapping device for the rapid capture of single cell such as an oocyte. We also suggest an application of such device for monitoring an intracellular chromosome inside cell that has an interaction with external environments. Real time monitoring is enabled through the fabrication on a silicon-on-glass substrate, offering excellent optical imaging window. We demonstrate the single cell capture event and monitoring of chromosome activity. This result will provide a powerful tool for investigating the physiological and pathological cellular functions.

Surface force sensed by cells used for autonomous migration

In this study, we develop a platform for investigating the mechanical perceptual ability of a cell and monitor its migration guided by a pure surface gradient rigidity. The cells are cultured on a flexible substrate with variable mechanical stiffness with other conditions kept unvarying. The thickness polydimethylsiloxane (PDMS) layer on glass trench surface with thickness variation was used to create a rigidity gradient between stiff (2.5 µm) and soft (7.5 µm) regions. The changes of surface rigidity were 48.8% in normal direction (stiff: 2.9 N/m, soft: 1.4 N/m) and 25.5% in lateral direction (stiff: 1 N/m, soft: 0.8 N/m), respectively. A fabrication process of rigidity gradient composite layered micro-device was developed to minimize the topographical effect that may alter the patterns of cell attachment and migration. We cultured NIH 3T3 cells on the proposed flexible substrate coated with an extracellular matrix (ECM), and demonstrated that the cells were strongly affected by the mechanical rigidity of surface. The designed device can be used to facilitate our understanding of mechanotransduction in cells under a given environment.