Although nanotopography has been shown to be a potent modulator of cell behavior, it is unclear how the nanotopographical cue, through focal adhesions, affects the nucleus, eventually influencing cell phenotype and function. Thus, current methods to apply nanotopography to regulate cell behavior are basically empirical. We, herein, engineered nanotopographies of various shapes (gratings and pillars) and dimensions (feature size, spacing and height), and thoroughly investigated cell spreading, focal adhesion organization and nuclear deformation of human primary fibroblasts as the model cell grown on the nanotopographies. We examined the correlation between nuclear deformation and cell functions such as cell proliferation, transfection and extracellular matrix protein type I collagen production. It was found that the nanoscale gratings and pillars could facilitate focal adhesion elongation by providing anchoring sites, and the nanogratings could orient focal adhesions and nuclei along the nanograting direction, depending on not only the feature size but also the spacing of the nanogratings. Compared with continuous nanogratings, discrete nanopillars tended to disrupt the formation and growth of focal adhesions and thus had less profound effects on nuclear deformation. Notably, nuclear volume could be effectively modulated by the height of nanotopography. Further, we demonstrated that cell proliferation, transfection, and type I collagen production were strongly associated with the nuclear volume, indicating that the nucleus serves as a critical mechanosensor for cell regulation. Our study delineated the relationships between focal adhesions, nucleus and cell function and highlighted that the nanotopography could regulate cell phenotype and function by modulating nuclear deformation. This study provides insight into the rational design of nanotopography for new biomaterials and the cell–substrate interfaces of implants and medical devices.
Two-dimensional, nano-scale photonic crystals (PhCs) in silicon and biocompatible polymer materials, such as: Polydimethylsiloxane (PDMS) and epoxy, are potential core structures in ultra-sensitive biosensors enhancing fluorescence emission in the near IR and visible range. A triangular PhC lattice (r/a = 0.33) of silicon pillars suspended in toluene was designed to enhance emission in the near-IR range. We present here a 27-fold enhancement of PbS-Quantum-Dot emission at 1100 nm. Moving to more biocompatible materials, we also present frequency-domain modeling results demonstrating partial photonic bandgaps for triangular PhC lattices in PDMS and epoxy. The existence of these bandgaps suggests that PhCs in polymer materials could potentially enhance visible-range fluorescence emission and become co-integrated with other on-chip components, such as microfluidic channels and optical waveguides, to produce cost-effective biosensors.
Detecting labeled or naturally-fluorescent biomolecules at very low concentrations is of a significant importance for health sciences, agricultural sciences, and security-related applications. Photonic crystals (PhC) are microfabricated nano-structures of periodic dielectric permittivity in one, two, or three dimensions that possess unique light manipulation properties. These include the ability to localize electromagnetic waves at particular PhC lattice locations. Ultra-sensitive detection using thin-film PhC structures fabricated in semiconductor materials has been demonstrated in both "active" and "passive" modalities. In the active modality, the adsorption of target molecules to the PhC surface causes a refractive index change that is translated into reflectance or transmission peak shifts [1][2][3][4][5]. The passive modality demonstrated by our group utilizes the PhC structure to observe enhanced fluorescent emission within resonant defect cavities in a 2D PhC lattice [6][7][8]. Integrating these semiconductor-based PhC structures with biocompatible microfluidic channels is a challenging task that can significantly increase the final cost of the sensor system. We demonstrate here soft lithographic nanomolding techniques for polymer-based PhC structures that are easily integrated with microfluidic channels to provide a portable means of biosensing. A TE bandgap of 2.857% for a 2D PhC fabricated in poly(dimethylsiloxane) (PDMS) will allow these lattices to become core structures in PhC-based biosensors incorporating both active and passive modalities. Modeling and initial optical characterization results of the Si-and PDMS-based PhC biosensor will also be presented.
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