Nanostructured Biomaterials as Guidance Cues for Cell Migration

納米結構生物材料作為細胞遷移的引導線索

Student thesis: Doctoral Thesis

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Award date25 Oct 2023

Abstract

Osteoblasts, such as MC3T3-E1 cells, play a crucial role in bone remodeling by migrating around to form calcified bone matrix. However, severe bone defects are often related to the lack of an osteogenic environment and active cells to regenerate new bone in distal region. Therefore, it is important for implanted scaffolds to induce cell migration from the proximal to the distal region in an organized manner to facilitate bone growth. Although previous research has shown that biomaterials’ topography and surface chemistry can influence cell migration, the impact of nanostructures, surface energy, and ultrathin patterned metal layer on MC3T3-E1 cell migration remains understudied. In this thesis, polydimethylsiloxane (PDMS) based platforms with patterned nanostructures, including nanopillars and nanoholes of varying sizes, were fabricated to investigate the dynamics of MC3T3-E1 cell interaction with nanotopography. Moreover, cell migration behaviors were studied systematically on surfaces with various topographies, including flat PDMS, nanopillars, nanoholes, silicon oxide (SiOx, x=1.7), and titanium oxide (TiOx, x=1.4). The relationships between surface conditions of platforms, migration behavior, and cell traction force were studied. Furthermore, patterned TiOx arrowheads with varying arm lengths were developed to control unidirectional cell migration.

To achieve highly directional guidance for cell migration, both micro- and nano-scale topographies were explored to better understand and mimic the complex extracellular matrix (ECM) environment. PDMS platforms with micro- and nano-topographies revealed that nanotopographies, such as nanoholes and nanopillars, promoted the generation of filopodia and extension of long protrusions, resulting in increased migration speed of MC3T3-E1 cells compared to microtopographies of flat surfaces or gratings. Although cells on grating structures exhibited lower migration speed, they induced more directional cell migration due to their anisotropic topography compared to the isotropic nanohole or nanopillar arrays. To further enhance cell migration directionality, the nanotopographies were patterned in grating arrangements, resulting in more directional cell migration than gratings alone. The effects of physical dimensions of the nanotopographies on cell migration were investigated, and the results showed that increasing the depth of nanoholes in grating arrangements led to less cell elongation and less directional migration. In contrast, increasing the height of nanopillars in grating arrangements resulted in more elongated cells, more directional migration, and higher migration speed. Platforms with nanopillars in grating arrangements and larger heights could be used to control cell migration speed and directionality, potentially enabling cell sorting and screening.

The ECM plays a critical role in providing structural support to cells and offering biophysical and biochemical cues that influence cell migration. Factors such as topography, material, and surface energy have been shown to regulate cell migration behavior. In this study, the responses of MC3T3-E1 cells, including migration speed, morphology, and spreading on various platform surfaces, were investigated. Specifically, PDMS micropost sensing platforms with nanopillars, SiOx, and TiOx coatings on top of the microposts were fabricated, and the dynamic cell traction force during migration was monitored. The aim was to understand the relationships between different platform surfaces, migration behaviors, and cell traction forces. Compared with the flat PDMS surface, cells cultured on SiOx and TiOx surfaces displayed reduced mobility and less elongation. In contrast, cells on the nanopillar surface showed increased elongation and higher migration speed compared to cells on SiOx and TiOx surfaces. Furthermore, MC3T3-E1 cells on microposts with nanopillars exerted a larger traction force than those on flat PDMS microposts and displayed large number of filopodia and long protrusions. These findings provide insights into the interplay between platform surface conditions, migration behavior, and cell traction force, which could have implications for designing biomaterials that promote tissue repair and regeneration by controlling cell migration.

In the context of wound healing and tissue regeneration, precise control of cell migration direction is crucial. To achieve this, PDMS platforms with a patterned thin layer of TiOx in an arrowhead shape were fabricated. Remarkably, MC3T3-E1 cells seeded on these platforms were constrained to migrate along the tips of the arrowheads without physical barriers, as the cells were guided by the asymmetrical arrowhead tips, which provided large contact areas. The 10 nm thick layer of patterned TiOx effectively directed cell migration on the PDMS surface. To the best of our knowledge, this is the first study demonstrating the use of thin TiOx arrowhead pattern in combination with a cell-repellent hydrophobic PDMS surface to provide guided cell migration unidirectionally without a physical barrier. These findings have important implications for designing biointerfaces with ultrathin patterns for precise control of cell migration. Additionally, Au/Cr microelectrodes were integrated with the patterned TiOx arrowheads to enable dynamic monitoring of cell migration using impedance measurement.