UC Davis

The long-term goal is to use nanotechnology to regulate and control cellular signaling processes and behaviors. This thesis focuses on applications of nanotechnology to cellular biophysics research, i.e., developing new nanotechnology based methodologies and approaches to further our understanding of single cell biophysics. Specifically, the thesis tackles two specific problems: (a) developing a single cell mechanics based approach to regulate and control cellular motility; and (b) investigations of silver nanowire (AgNW) interactions with macrophages. Cell motility plays critical roles in many biophysical and physiological processes ranging from in vitro biomechanics, wound healing to cancer metastasis. This thesis introduces a new means to trigger and regulate motility individually using transient mechanical stimulus applied to designated cells. Using BV2 microglial cells, our investigations indicate that motility can be initiated, reproducibly and reliably, using mechanical compression of the cells. The impact of location and magnitude of the applied force on the movement of the cell is also discussed. A model to describe the process of mechano-induced cell motility was created, which involves high degrees of myosin activation to repair actin cortex breakages induced by the initial mechanical compression, leading to focal adhesion degradation, lamellipodia detachment, and finally cell polarization and movement. This approach is of generic importance to other cell types beyond BV2 cells, and has intrinsic advantages of being transient, non-toxic, and non-destructive, thus exhibits high translational potentials including mechano-based therapy. The interactions of silver nanowires (AgNWs) with cells are important with respect to their effects on the cells and the overall health of human and living entitles. With AgNW being used in a variety of commercial and research application, the potential for exposure is high, with inhalation exposure being a primary concern. Alveolar macrophages in lungs are among the first encounters with AgNWs, upon inhalation. These macrophage cells are responsible for clearing away foreign material. Thus, the interactions between AgNW and alveolar macrophages are of high importance. NR8383 cell line provides a good model for alveolar macrophages, and was used to study AgNW interactions in this thesis. Using laser scanning confocal microscopy (LSCM) combined with single cell compression, and AFM-based technique to probe the mechanical properties of cells, a number of AgNW-cell interactions were captured in live cells. Among them is frustrated phagocytosis. Previously known for microfibers and carbon nanotubes, first direct observations of frustrated phagocytosis of silver nanowires (AgNWs) among living cells in situ are reported by us and summarized in Chapter 4. Confocal imaging of AgNW frustrated phagocytosis revealed actin participation at the entry sites, whose behavior differ from microwire-induced frustrated phagocytosis. Combining confocal imaging with SCC, the impacts of frustrated phagocytosis on the cellular membrane and cytoskeleton were also measured. Using high resolution laser scanning confocal microscopy, the precise locations of AgNWs can be visualized upon their interactions with a macrophage cell line, NR8383 cells. Combined with membrane and actin tags, this investigation allows direct visualization of AgNWs-interactions. In addition to frustrated phagocytosis, direct piercing of AgNWs into cells were captured, where a portion of wires poked into a cell without significant structural perturbation of its local surroundings. Other situations include failed attempts by AgNWs to pierce due to membrane wrapping of the invading portion of the AgNWs to resist their entry. This study provides a comprehensive view of AgNW-cell interactions. The results benefit the understanding of potential adversary effects of AgNWs to health, and guide the development of preventative measures.