| Abstract |
Biomimetics offer the possibility of biological systems simulation on artificial surfaces, with desired properties. There are many attempts to fabricate artificially these surfaces.
The present thesis comprises two parts. The first one is the fabrication of micropatterned silicon substrates via ultra-short pulsed laser irradiation under different experimental parameters, including laser fluence and irradiation environment. The second part is the fabrication of hierarchical micro-nano-patterned substrates. These comprise micro-patterned silicon substrates which have been nano-decorated with spherical gold nanoparticles of various functionalities and sizes. Gold nanoparticles have been attached via silane chemistry. Both types of substrates have been characterized with respect to their morphological, wetting and optical properties.
Regarding the micropatterned substrates, the morphological characterization showed that as the laser fluence increased the roughness of the surface increased as well. Micropatterned substrates comprised microcones of varying height and density. Specifically, the density and the height of the micro-features (i.e. microcones) decreased and increased respectively, with increasing laser fluence. The study of the contact angle showed that as the surface roughness increased, the substrates became more hydrophobic. Optical characterization showed that as the surface roughness increases, the reflectivity decreased, across the range of wavelength (250-2500nm). The layer of silicon oxide on flat silicon substrates lead to reduction of the reflectance, in contrast with the case of micro-structured substrates, where silicon oxide layer increased the reflectivity, in near infrared spectrum.
Regarding the hierarchical micro-nano substrates, SEM analysis confirmed the successful deposition of the gold nanoparticles on the micropattenred silicon substrates. Deposition gave a homogenous distribution of single nanoparticles and some regions of small clusters. All types of the gold nanoparticles (NPs) being tested, which carried diverse functionalities (e.g. oligopeptides, including the CALNN and CALNN-RGD and organic moieties, including the stabilizer citrate and DMAP) have been successfully attached on the surfaces of the micropatterned silicon substrates. Remarkably, the NPs covered the whole 3D surface of the micropatterned substrates giving a distribution that was comparable to that on the flat silicon substrates. The study of the contact angle showed that the initially hydrophobic micropatterned silicon substrates became more hydrophilic with the addition of gold nanoparticles . Optical characterization showed that gold nanoparticles caused a reduction of the reflectivity of the oxidized micro-patterned silicon substrates.
Finally, both the micropatterned and the hierarchical micro-nano substrates have been characterized for their use as cell culture platfroms for the growth of neural stem cells. In the case of the micro-patterned substrates it was shown that the greater majority of the cells attached preferentially on the medium roughness surfaces. Remarkably, cells aligned along the major axis of the microcones. This cellular response was more pronounced in the respective hierarchical substrates which had been decorated with the RGD cell binding motif.
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Fabrication and characterization of micro-structured silicon substrates and hierarchical micro-nano-structured silicon substrates with gold nanoparticles
