Florian Larramendy

CMOS-based neural probe with enhanced electronic depth control

This paper reports on the design, fabrication, and testing of complementary-metal-oxide-semiconductor (CMOS)-based high-density neural probes. An enhanced electronic depth control (EDC) scheme is implemented using a switch matrix integrated in the slender probe shaft, allowing simultaneous reconfiguration and recording on unaffected channels. The number of simultaneously available analog output channels is increased to 16 compared to the initial EDC probes of our group. Probe shaft length up to 10 mm with a shaft width and thickness of 100 μm and 40 μm, respectively, have been realized. A maximum number of 334 electrodes is achieved on the longest probe variant with an inter-electrode spacing of 30 μm along the probe shafts. The addressing and switching scheme is realized using the commercial 0.18 μm six-metal, double-poly CMOS process from XFAB combined with an in-house post processing of the electrode metallization and probe patterning. The probe functionality is verified using bench tests and the electrode impedance characterization revealing 1.4±0.2 MΩ at 1 kHz for platinum electrodes with a diameter of 30 μm.

Microchannel-connected SU-8 honeycombs by single-step projection photolithography for positioning cells on silicon oxide nanopillar arrays

We report on the fabrication, functionalization and testing of SU-8 microstructures for cell culture and positioning over large areas. The microstructure consists of a honeycomb arrangement of cell containers interconnected by microchannels and centered on nanopillar arrays designed for promoting cell positioning. The containers have been dimensioned to trap single cells and, with a height of 50 µm, prevent cells from escaping. The structures are fabricated using a single ultraviolet photolithography exposure with focus depth in the lower part of the SU-8 resist. With optimized process parameters, microchannels of various aspect ratios are thus produced. The cell containers and microchannels serve for the organization of axonal growth between neurons. The roughly 2 µm-high and 500 nm-wide nanopillars are made of silicon oxide structured by deep reactive ion etching. In future work, beyond their cell positioning purpose, the nanopillars could be functionalized as sensors. The proof of concept of the novel microstructure for organized cell culture is given by the successful growth of interconnected PC12 cells. Promoted by the honeycomb geometry, a dense network of interconnections between the cells has formed and the intended intimate contact of cells with the nanopillar arrays was observed by scanning electron microscopy. This proves the potential of these new devices as tools for the controlled cell growth in an interconnected container system with well-defined 3D geometry.

High-topography surface functionalization based on parylene-C peel-off for patterned cell growth

This paper introduces a new technique for patterning functionalization layers on substrates with high-topography. The method is based on a parylene-C template shaped by a structured, sacrificial photoresist layer and attached to the substrate where functionalization is not intended. After photoresist removal and surface functionalization, the parylene layer is peeled off, leaving all areas initially covered by the sacrificial polymer functionalized. The technique has several advantages: (i) In contrast to microcontact printing, it allows surfaces with complex topographies to be functionalized; (ii) complex functionalization patterns are possible; (iii) the parylene structure can be reutilized. We successfully demonstrate the technique with the guided growth of neuron-like PC12 cells on honeycomb-shaped protein patterns on micropillars and microwells. The range and limits of the technique are analyzed and discussed in detail.

Stackable octahedron-based photoresist scaffold by direct laser writing for controlled three-dimensional cell networks

This paper reports a new technique for creating controlled, three-dimensional (3D) cellular networks. The method is based on stackable photoresist structural layers realized by direct laser writing. Cells can be positioned and cultured on the layers, which are then stacked, forming 30-μm-wide cages containing the cultured cells. Cells are able to communicate from cage to cage through openings, e.g., by developing neurites in networks of neuron-like cell. We demonstrate the successful stacking of three layers and the positioning and interconnection of neuron-like PC-12 cells in the intended locations.

Simulation study of SU-8 structures realized by single-step projection photolithography

This paper introduces the efficient three-dimensional (3D) simulation of thick SU-8 structures realized by single-step projection lithography. Profiles of 3D structures obtained by this lithography method depends on two process parameters: (i) The exposure dose and (ii) the focus depth. For fabricating complex 3D structures used in microfluidics or bio-engineering tools, the resulting geometries depending of these two process parameters should be predicted before processing. Although several lithography simulation methods have been developed for SU-8 processing, the existing models are unsuited for single-step projection lithography technique. This paper described how the simulation process have been developed and successfully tested on a specific design of honeycomb structures. Through the various experiments, simulation results revealed similar dependence on two process parameters, and the validity of simulation algorithm was therefore confirmed.

Surface modification for patterned cell growth on substrates with pronounced topographies using sacrificial photoresist and parylene-C peel-off

A range of methods including soft lithography are available for patterning protein layers for cell adhesion on quasi-planar substrates. Suitably structured, these layers favor the geometrically constrained, controlled growth of cells and the development of cellular extensions on them. For this purpose, the ability to control the shape and dimension of cell-adhesive areas with high precision is crucial. For more advanced studies of cell interactions, the surface modification or functionalization of substrates with complex topographies is desirable. This paper describes a simple technique allowing to produce surface modification patterns using delicate molecules such as laminin on substrates exhibiting pronounced topographies with recessed and protruding microstructures. The technique is based on the combination of sacrificial photoresist structures with a connected parylene-C layer. This layer locally adheres to the substrate wherever the substrate needs to be protected against the surface modification. After surface modification, the parylene-C layer is peeled off. Patterns comprising arbitrary networks of modified and unmodified substrate areas can thus be realized. We demonstrate the technique with the guided growth of neuron-like PC12 cells on networks of laminin lines on substrates structured with micropillars and microwells.

Origami microfluidics integrated with gold micropatterns

In this report, we show a concept of 3D microfluidic device by folding parylene layers with gold pattern in a microfluidic channel. Recently, we have proposed origami-3D microfluidic device. In this device, multi-layer fluidic channels were fabricated only by folding 2D-pattern. This simple process enables us to integrate several fluidic channel into a small chip. This report shows that gold layer was patterned in the origami-microfluidic devices. We believe that our fabrication method will contribute to the development of biomolecule analysis, because gold layer can potentially immobilize biomolecules, such as protein and DNA.