The induced changes on silver nanostructures are investigated using a special experimental procedure consisting in depositing and subsequently inducing the changes directly on transmission electron microscopy grids. The nanostructures have different morphologies, from isolated spherical-like particles to quasi-percolated films. The UV laser-induced modifications were investigated using transmission electron microscopy and atomic force microscopy obtaining three-dimensional information on the nanostructures. Upon irradiation with a single laser pulse a quasi-percolated film is transformed into an assembly of silver nanoparticles. Upon further irradiation the nanoparticles grow in size. Furthermore the arrangement of these silver nanoparticles assemblies can be controlled by irradiating the nanostructured silver film through a mask. In the present work, we have used a transmission electron microscopy square grid as a diffractive device and have observed that the corresponding near field diffraction pattern is imprinted on the silver nanostructured film.
Quasi-percolated nanostructured silver thin films are used as the starting morphology for inducing simultaneously changes in shape and ordering effects by laser irradiation. The complex fingered nanostructures are transformed into nanospheres which in turn are arranged in micro-circular patterns when irradiated through a pinhole. These transformations are characterized by transmission electron microscopy and atomic force microscopy. The observed effects are explained using Fresnel diffraction theory. Good agreement with the experimental results is obtained. These results suggest that precise patterning engineering can be achieved through control of the spatial parameters such as the pinhole diameter and the distance from the mask to the sample.
It is well known that, in excitable cells, the dynamics of the ion currents (I i) is extremely important to determine both the magnitude and time course of an action potential (A p). To observe these two processes simultaneously, we cultured NG108-15 cells over a multi-walled carbon nanotubes electrode (MWCNTe) surface and arranged a two independent Patch Clamp system configuration (Bi-Patch Clamp). The first system was used in the voltage or current clamp mode, using a glass micropipette as an electrode. The second system was modified to connect the MWCNTe to virtual ground. While the A p was recorded through the micropipette electrode, the MWCNTe was used to measure the underlying whole-cell current. This configuration allowed us to record both the membrane voltage (V m) and the current changes simultaneously. Images acquired by atomic force microscopy (AFM) and scanning electron microscopy (SEM) indicate that cultured cells developed a complex network of neurites, which served to establish the necessary close contact and strong adhesion to the MWCNTe surface. These features were a key factor to obtain the recording of the whole-cell I i with a high signal to noise ratio (SNR). The experimental results were satisfactorily reproduced by a theoretical model developed to simulate the proposed system. Besides the contribution to a better understanding of the fundamental mechanisms involved in cell communication, the developed method could be useful in cell physiology studies, pharmacology and diseases diagnosis.
Promising strategies for neural tissue engineering are based on the use of three-dimensional substrates for cell anchorage and tissue development. In this work, fibrillar scaffolds composed of electrospun randomly- and aligned-oriented fibers coated with plasma synthesized pyrrole polymer, doped and undoped with iodine, were fabricated and characterized. Infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction analysis revealed the functional groups and molecular integration of each scaffold, as well as the effect of plasma polymer synthesis on crystallinity. Scanning microscopy imaging demonstrated the porous fibrillar micrometric structure of the scaffolds, which afforded adhesion, infiltration, and survival for the neural cells. Orientation analysis of electron microscope images confirmed the elongation of neurite-like cell structures elicited by undoped plasma pyrrole polymer-coated aligned scaffolds, without any biochemical stimuli. The MTT colorimetric assay validated the biocompatibility of the fabricated composite materials, and further evidenced plasma pyrrole polymer-coated aligned scaffolds as permissive substrates for the support of neural cells. These results suggest plasma synthesized pyrrole polymer-coated aligned scaffolds are promising materials for tissue engineering applications.
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