Lab-on-a-chip devices with nanophase surface topography for neural electrophysiological applications

In this study, a novel class of neural electrophysiological devices featuring vertically aligned three-dimensional conducting nanostructures was designed and fabricated. This class of device features enhanced (i) cell-biomaterial interaction (resulting from the coating of the device nanostructured electrodes with poly-D-lysine and laminin, and from the structured topography of these electrodes), in combination with enhanced (ii) signal selectivity (originating from a spatial resolution ranging between 1.20*10-3 channels/mum 2 and 1.68 channels/mum2, and a temporal resolution of 2 mus/sample) and (iii) signal discrimination (emerging from the signal-to-noise ratio for a cell generating an action potential, relative to its noise background level at rest, measured equal to 12.64 dB).; The deflection of the three-dimensional electrode tips generated by neurons adhering on the hierarchically-structured substrates over multiple weeks was used to transduce the elastoplastic force, energy and power generated by a neuron to adhere on a substrate. These dimensions were found to be a strong function of scale and were therefore measured at three different spatial resolutions -- (i) at the focal adhesive level (invariant focal adhesive force of 16.5 muN, strain energy between 10 pJ and 15 pJ and strain power ranging from 175 aW after the first day of culture, to approximately 10 aW measured 20 days after cell seeding), (ii) at the dendritic levels (focal adhesive force varying between a minimum of 20 muN to almost 45 muN, strain energy varying between 40 pJ and less than 10 pJ, while the strain power varies between a maximum of 425 aW after the first day of culture, to less than 25 aW, measured 20 days after cell seeding occurred) and (iii) at the aggregate cellular level (adhesive force varying between a minimum of about 50 muN to 750 muN, adhesive strain energy between 35 pJ and 750 pJ measured at day 20, maximal strain power one day after neuron seeding, equal to 2.8 fW1, and subsequently decreased to a minimum of approximately 100 aW measured at day 12 after seeding).; These results suggest a relative invariance of force and energy at the focal adhesive level, while at the dendritic and cellular levels both force and energy are found to vary greatly during the weeks of the experiment; at the cellular level, force and energy reach a maximum during the last day of the experiment, indicating a likely increase for these two dimensions for longer time intervals, therefore leading to conclude that at this level adhesive force and energy are a strong function of cell diversification---specifically cellular increase in area and production of dendritic extroflections or arborizations. Conversely, the strain power was maximal for all the levels of analysis, at day one after seeding. This factor seems to suggest that the high power expenditure of the cell during the initial stages of development is necessary both to anchor the spherically-shaped and intrinsically unstable cell on the substrate, as well as to differentiate the spherical geometry---typically a very stable, low energy configuration---into a diversified, polar morphology, with considerably higher surface and associated energy.; The voltage for an action potential relative to the resting potential measured for the same cell was then used to measure the electrical signal emanating from the cell at subsecond timescale, and was then analyzed in form of information theory, using the Kullback-Leibler definition of divergence of the distribution from a reference measure---aptly derived with few modifications from Shannon's definition of entropy---to calculate the information entropy of an action potential.; Finally, the experimental results gathered in this thesis are analyzed in combination with the literature to determine the thermodynamic energy balance for a neuron generating an action potential at sub-second timescale. Under the assumption of a constant capacitance, the electrical ener...