Michel Marcel Jose Decre

Gravity-driven flows of viscous liquids over two-dimensional topographies

Using phase-stepped interferometry, we have measured full two-dimensional maps of the free-surface shape of a thin liquid film of water flowing over an inclined plate with topography. The measurement technique allows us to image automatically the shape of the free surface in a single field of view of about 2.4 by 1.8 mm, with a lateral resolution of 3.1 μm and a height resolution of 0.3 μm. By imaging neighbouring regions and combining them, complete two-dimensional free-surface profiles of gravity-driven liquid films with a thickness ranging between 80 and 120 μm are measured, over step, trench, rectangular and square topographies with depths of 10 and 20 μm, and lateral dimensions of the order of 1 to several mm. The experimental results for both one- and two-dimensional flows are found to be in good agreement with existing models, including a recent two-dimensional Greens function of the linearized problem by Hayes et al. This extends the applicability of simple models to cases with a high value of topography steepness and low-viscosity liquids as in our experiments. A corollary of the agreement with the linear two-dimensional model is that our experimental results behave linearly, a convenient property that allows the free-surface response to complex topographies to be worked out from knowledge of the response to an elementary topography like a square.

Functional connectivity and dynamics of cortical-thalamic networks co-cultured in a dual compartment device

Co-cultures containing dissociated cortical and thalamic cells may provide a unique model for understanding the pathophysiology in the respective neuronal sub-circuitry. In addition, developing an in vitro dissociated co-culture model offers the possibility of studying the system without influence from other neuronal sub-populations. Here we demonstrate a dual compartment system coupled to microelectrode arrays (MEAs) for co-culturing and recording spontaneous activities from neuronal sub-populations. Propagation of electrical activities between cortical and thalamic regions and their interdependence in connectivity is verified by means of a cross-correlation algorithm. We found that burst events originate in the cortical region and drive the entire cortical-thalamic network bursting behavior while mutually weak thalamic connections play a relevant role in sustaining longer burst events in cortical cells. To support these experimental findings, a neuronal network model was developed and used to investigate the interplay between network dynamics and connectivity in the cortical-thalamic system.

Dual-Compartment Neurofluidic System for Electrophysiological Measurements in Physically Segregated and Functionally Connected Neuronal Cell Culture

We developed a dual-compartment neurofluidic system with inter-connecting microchannels to connect neurons from their respective compartments, placed on a planar microelectrode arrays. The design and development of the compartmented microfluidic device for neuronal cell culture, protocol for sustaining long-term cultures, and neurite growth through microchannels in such a closed compartment device are presented. Using electrophysiological measurements of spontaneous network activity in the compartments and selective pharmacological manipulation of cells in one compartment, the biological origin of network activity and the fluidic isolation between the compartments are demonstrated. The connectivity between neuronal populations via the microchannels and the crossing-over of neurites are verified using transfection experiments and immunofluorescence staining. In addition to the neurite cross-over to the adjacent compartment, functional connectivity between cells in both the compartments is verified using cross-correlation (CC) based techniques. Bidirectional signal propagation between the compartments is demonstrated using functional connectivity maps. CC analysis and connectivity maps demonstrate that the two neuronal populations are not only functionally connected within each compartment but also with each other and a well connected functional network was formed between the compartments despite the physical barrier introduced by the microchannels.

Cover Layer Technology for the High-Numerical-Aperture Digital Video Recording System

It is experimentally demonstrated that two techniques allow the manufacture of a 100-µm-thick cover layer within the requirements of the digital video recording system, that uses a high numerical aperture of 0.85 at 650 nm wavelength. The first technique uses spin-coating of an ultraviolet curable resin and the second is the ultraviolet bonding of a 100-µm-thick polycarbonate sheet. Both techniques guarantee thickness variations within ±3 µm, and display disc radial and tangential tilts within sufficient margins.

Selective pharmacological manipulation of cortical-thalamic co-cultures in a dual-compartment device

In this study, we demonstrate capabilities to selectively manipulate dissociated co-cultures of neurons plated in dual-compartment devices. Synaptic receptor antagonists and tetrodotoxin solutions were used to selectively control and study the network-wide burst propagation and cell firing in cortical-cortical and cortical-thalamic co-culture systems. The results show that in cortical-thalamic dissociated co-cultures, burst events initiate in the cortical region and propagate to the thalamic region and the burst events in thalamic region can be controlled by blocking the synaptic receptors in the cortical region. Whereas, in cortical-cortical co-culture system, one of the region acts as a site of burst initiation and facilitate propagation of bursts in the entire network. Tetrodotoxin, a sodium channel blocker, when applied to either of the regions blocks the firing of neurons in that particular region with significant influence on the firing of neurons in the other region. The results demonstrate selective pharmacological manipulation capabilities of co-cultures in a dual compartment device and helps understand the effects of neuroactive compounds on networks derived from specific CNS tissues and the dynamic interaction between them.

Steering deep brain stimulation fields using a high resolution electrode array

Deep brain stimulation (DBS) therapy relies on electrical stimulation of neuronal elements in small brain targets. However, the lack of fine spatial control over field distributions in current systems implies that stimulation easily spreads into adjacent structures that may induce adverse side-effects. This study investigates DBS field steering using a novel DBS lead design carrying a high-resolution electrode array. We apply computational models to simulate voltage distributions and DBS activation volumes in order to theoretically assess the potential of field steering in DBS. Our computational analysis demonstrates that the DBS-array is capable of accurately displacing activation volumes with sub-millimeter precision. Our findings demonstrate that future systems for DBS therapy may provide for more accurate target coverage than currently available systems achieve.

An experimental approach towards the development of an in vitro cortical-thalamic co-culture model

In this paper, we propose an experimental approach to develop an in vitro dissociated cortical-thalamic co-culture model using a dual compartment neurofluidic device. The device has two compartments separated by 10 μm wide and 3 μm high microchannels. The microchannels provide a physical isolation of neurons allowing only neurites to grow between the compartments. Long-term viable co-culture was maintained in the compartmented device, neurite growth through the microchannels was verified using immunofluorescence staining, and electrophysiological recordings from the co-culture system was investigated. Preliminary analysis of spontaneous activities from the co-culture shows a distinctively different firing pattern associated with cultures of individual cell types and further analysis is proposed for a deeper understanding of the dynamics involved in the network connectivity in such a co-culture system.

Dual compartment neurofluidic system for electrophysiological measurements in physically isolated neuronal cell cultures

This work investigates an approach to record electrophysiological measurements of neuronal cell cultures in a dual compartment neurofluidic system. The two compartments are separated by 10-μm-wide and 3-μm-high microchannels and this provides a physical isolation of neurons allowing only neurites to grow between the compartments. We present long-term cell viability in closed compartment devices, neurite growth across the microchannels and a recording setup for the long-term recording of the network activity over 21 Days-in-Vitro (DIV). Structural and fluidic isolation between the compartments are demonstrated using transfection experiments and neurotoxin exposure, respectively.

Multigrid Methods for Thin Liquid Film Spreading Flows

A range of industrial processes involve the spreading of thin layers of liquid or molten polymeric materials that subsequently solidify. Their function may be: to form a protective barrier; to give added value to a particular product (magnetic/optical storage media, etc.); the production of laminates, tapes, sheets ([5], [7], [8], [12]). Their quality depends ultimately on the homogeneity of the resultant polymer film or surface covering.

Towards circuit integration on fully flexible parylene substrates

We present a substrate transfer technology which allows devices to be fully processed using conventional silicon-based fabrication techniques prior to their integration with parylene. A parylene-based metal microelectrode array with high-temperature silicon oxide passivation layers was demonstrated. Combining high quality devices from well-established processes with thin, flexible and biocompatible substrates, this technology could provide exciting opportunities, especially in biomedical applications such as implantable neural interfaces.