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The convergence of materials science, electronics, and biology, namely bioelectronic interfaces, leads novel and precise communication with biological tissue, particularly with the nervous system. However, the translation of lab‐ based innovation toward clinical use calls for further advances in materials, manufacturing and characterization paradigms, and design rules. Herein, a translational framework engineered to accelerate the deployment of microfabricated interfaces for translational research is proposed and applied to the soft neurotechnology called electronic dura mater, e‐dura. Anatomy, implant function, and surgical procedure guide the system design. A high‐yield, silicone‐ on‐silicon wafer process is developed to ensure reproducible characteristics of the electrodes. A biomimetic multimodal platform that replicates surgical insertion in an anatomy‐based model applies physiological movement, emulates therapeutic use of the electrodes, and enables advanced validation and rapid optimization in vitro of the implants. Functionality of scaled e‐dura is confirmed in nonhuman primates, where epidural neuromodulation of the spinal cord activates selective groups of muscles in the upper limbs with unmet precision. Performance stability is controlled over 6 weeks in vivo. The synergistic steps of design, fabrication, and biomimetic in vitro validation and in vivo evaluation in translational animal models are of general applicability and answer needs in multiple bioelectronic designs and medical technologies.Supporting Information

SU-8 photoresist is commonly used in the field of microfabrication as structural material or for molding of microfluidic devices. One major limitation, however, is the difficulty to process partially freestanding SU-8 structures or monolithic closed cavities and channels on-chip. We propose here a simple method for the fabrication of suspended structures, in particular of monolithic SU-8 microchannels. The method is based on the processing of a SU-8 double-layer. Appropriate modification of the optical properties of the upper layer allows for selective crosslinking in the layer sandwich. This process is suitable for versatile layouts comprising open and hollow SU-8 structures on the same chip.

Several recent detector te chnologies developed for particle physics applications are based on microfabricated structures. Dete ctors built with this approach generally exhibit the overall best performance in te rms of spatial and time resolution. Many properties of the SU-8 photoepoxy make it suitable for the manufacturing of microstructured particle detectors. This arti cle aims to review some emerging detector technologies making use of SU-8 microstructu ring, namely micropatte rn gaseous detectors and microfluidic scintillation detectors. Th e general working principle and main process steps for the fabrication of each device are reported, with a focus on the advantages brought to the device functionality by the us e of SU-8. A novel process based on multiple bonding steps for the fabrication of thin multila yer microfluidic scin tillation detectors developed by the authors is presented. Finally, a brief overview of the applications for the discussed devices is given.

A novel type of particle detector based on scintillation, with precise spatial resolution and high radiation hardness, is being studied. It consists of a single microfluidic channel filled with a liquid scintillator and is designed to define an array of scintillating waveguides each independently coupled to a photodetector. Prototype detectors built using an SU-8 epoxy resin have been tested with electrons from a radioactive source. The experimental results show a light yield compatible with the theoretical expectations and confirm the validity of the approach.

SU8-carbon nanotube composites have been produced to enhance the mechanical, electrical, and thermal properties of SU8 photoresists. Homogeneous composites materials have been obtained when multiwalled carbon nanotubes (MWCNTs) functionalized with COOH groups were used. Indeed, COOH groups can react with the epoxy ring of the SU8 molecule yielding an improved interaction between carbon nanotubes (CNTs) and the polymer matrix. Impedance spectroscopy was used to study the conducting percolation path in the composites, that is the quality of the nanotube dispersion in the epoxy matrix. It turns out that propylene glycol methyl ether acetate (PGMEA) as well as gamma-butyrolacton (GBL) are very suitable solvent to prepare SU8-MWCNTs composites of good homogeneity. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper presents the study of a novel scintillation detector based on standard microfabrication techniques. It consists of a fine pitch array of hollow waveguides filled with a liquid scintillator and optically coupled to photodetectors. The detector has been fabricated by patterning the SU-8 photoresist on silicon wafers. Experimental studies have been performed by exciting the liquid scintillator contained in the SU-8 waveguides with electrons. The scintillation light produced was read out by an external photodetector. The results obtained with this set-up demonstrate the concept of microfluidic scintillation detection and are very encouraging for future developments.

A new nanocomposite photoresist based on SU-8 epoxy resin has been developed. It consists in a homogeneous dispersion of nano-silica particles in the negative tone photosensitive SU-8. The nanocomposite photoresist is more sensitive than the SU-8 photoresist and the photopatterned composite structures show low stress and less cracks than pure SU-8 structures. No significant resolution difference has been observed for both materials.

The use of low-stress SU8 nanocomposites as a functional material for micro-parts and coating applications is described in this paper. It was found that the nanoparticles lower the internal stress and decrease the wear rate and frictional coefficient of the SU8 epoxy. The applicability of this technology is demonstrated on gear wheels configuration and coating multilayer capping technology on moving micro-parts.

A conductive composite photoresist has been developed for the direct photopatterning of electrodes. It is based on a dispersion of silver nanoparticles in SU8, a non-conductive, negative-tone photoresist. Manufactured structures have an electrical conductivity at a low silver content of around 6 vol.-%

Microstereolithography is a technique that allows the manufacture of small and complex three-dimensional (3D) components in plastic material. Many of the components produced by this technique are too small and too complex to be replicated by molding and, consequently, the produced components need to have adequate mechanical or chemical characteristics to be useful. Until now, the choice of materials available in the microstereolithography process was limited to plastic, with only a few photosensitive resins available. In this paper we describe new polymer/composite photosensitive resins that can be used in the microstereolithography process for manufacturing complex 3D components. These resins are based on the insertion of a high load (up to 80 wt%) of alumina nanoparticles in a photosensitive polymer matrix. The resulting composite objects can undergo a debinding and sintering step to be transformed into pure ceramic microcomponents. During this process, their shape is unaltered, but the components undergo some shrinkage. If the load of filler material in the composite resin is high enough, no deformations and no cracks can be seen in the final ceramic components. We present different examples of complex 3D structures in composite material and in pure ceramic.

Cell-derived membrane vesicles that are released in biofluids, like blood or saliva, are emerging as potential non-invasive biomarkers for diseases, such as cancer. Techniques capable of measuring the size and concentration of membrane vesicles directly in biofluids are urgently needed. Fluorescence single particle tracking microscopy has the potential of doing exactly that by labelling the membrane vesicles with a fluorescent label and analysing their Brownian motion in the biofluid. However, an unbound dye in the biofluid can cause high background intensity that strongly biases the fluorescence single particle tracking size and concentration measurements. While such background intensity can be avoided with light sheet illumination, current set-ups require specialty sample holders that are not compatible with high-throughput diagnostics. Here, a microfluidic chip with integrated light sheet illumination is reported, and accurate fluorescence single particle tracking size and concentration measurements of membrane vesicles in cell culture medium and in interstitial fluid collected from primary human breast tumours are demonstrated.

A new type of scintillation detector is being developed with standard microfabrication techniques. It consists of a dense array of scintillating waveguides obtained by coupling microfluidic channels filled with a liquid scintillator to photodetectors. Easy manipulation of liquid scintillators inside microfluidic devices allow their flushing, renewal, and exchange making the active medium intrinsically radiation hard. Prototype detectors have been fabricated by photostructuration of a radiation hard epoxy resin (SU-8) deposited on silicon wafers and coupled to a multi-anode photomultiplier tube (MAPMT) to read-out the scintillation light. They have been characterized by exciting the liquid scintillator in the 200 micrometers thick microchannels with electrons from a Sr-90 yielding approximately 1 photoelectron per impinging Minimum Ionizing Particle (MIP). These promising results demonstrate the concept of microfluidic scintillating detection and are very encouraging for future developments.

The following paper describes a sacrificial layer method for the manufacturing of microfluidic devices in polyimide and SU-8. The technique uses heat-depolymerizable polycarbonates embedded in polyimide or SU-8 for the generation of microchannels and sealed cavities. The volatile decomposition products originating from thermolysis of the sacrificial material escape out of the embedding material by diffusion through the cover layer. The fabrication process was studied experimentally and theoretically with a focus on the decomposition of the sacrificial materials and their diffusion through the polyimide or SU-8 cover layer. It is demonstrated that the sacrificial material removal process is independent of the actual channel geometry and advances linearly with time unlike conventional sacrificial layer techniques. The fabrication method provides a versatile and fast technique for the manufacturing of microfluidic devices for applications in the field of microTAS and Lab-on-a-Chip.

Multiwalled carbon nanotubes (MWCNTs)/SU8 composites have been produced to enhance the mechanical properties of SU8 photoresist. We have studied the influence of SU8 solvent on the structural homogeneity of composites through nano-indentation testing. It is found that acetone and propylene glycol methyl ether acetate (PGMEA) are very suitable solvents to prepare MWCNTs/SU8 composites with significant increase of the Young's modulus (E-Y). The highest increase of E-Y in respect to the parent material of 104% was obtained with acetone as solvent. It was noticed that the remaining solvent in the composite influences strongly E-Y, as well. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A new electrically conductive photosensitive composite resist has been formulated and used to build micro-components. This composite material is based on the SU-8 photopolymer, an insulating negative-tone photoresist, in which silver nano-particles have been dispersed to enhance the electrical properties of the polymer. The properties of this new photosensitive composite have been characterized by optical and electrical measurements. The patterned composite structures can be obtained for a wide range of values of the electrical conductivity, by varying the powder volume fraction of the composite. The lateral resolution of the produced structures were evaluated, and depending on the patterning conditions, can be better than 5 /spl mu/m.

The increasing interests in micro-electro-mechanical systems (MEMS) has raised the requirement for photoresist materials with improved friction and wear properties for mechanically loaded 3D shaped microstructures. In this work, SU8 photoresist layers reinforced with different amounts of silica nanoparticles were produced and thermally treated. Dry sliding tests indicate that SU8 composite epoxies produced in the form of thin films exhibit similar or even better tribological properties than bulk epoxies. The SU8 nanocomposites exhibit reduced wear rates and frictional coefficient compared to the un-reinforced material. Further, nanoparticle content, heat treatment and nature of the sliding counter piece were found to affect wear and friction. The tribological behaviour was discussed in terms of mechanical properties and contact pressures.

Microstereolithography is a technology at the interface of the microengineering and rapid prototyping domains. It has evolved from the stereolithography technique, and is also based on a light-induced layer-stacking manufacturing. As the resolution of the microstereolithography technique is far better than the one of rapid prototyping technologies, this technique is of particular interest in the microengineering domain where its 3D capability allows the production of components no other microfabrication technique can create.The first developments of the microstereolithography technique have started in 1993 and different research teams have developed machines since, using different approaches. This paper reviews the major microstereolithography processes developed until now.Microstereolithography is starting to be a commercially available manufacturing process. As the market for miniaturized products grows rapidly, there is an increasing need for highresolution small size prototype parts. If the production of small mechanical components is the first commercial application of microstereolithography, this technology can also produce useful components for the microrobotic, microfluidic, microsystems and biomedical fields. Current research in the microstereolithography field is focused on using ceramic composites as material to manufacture complex three-dimensional parts that can be sintered to produce pure alumina microcomponents.

We report a process for the realization of polyimide films with custom-designed microporosity based on the heat-induced depolymerization of polyimide-embedded polypropylene carbonate microstructures. The foam-like microstructures are up to 40 µm thick and incorporate air cavities with a width ranging from 20 to 200 µm, a length up to 5 mm and a height of 20 µm. We model the mechanical stress–strain properties of the microcavities using both analytical and numerical methods. The simulation data are in good agreement with the results of nanoindentation and microcompression experiments, which show the reduction of the effective Young's modulus from 5.77 ± 0.06 GPa for bulk polyimide to 2.51 ± 0.03 GPa for a foam-like layer.

We describe a novel surface micromachining process for the fabrication of ceramic-type MEMS devices, such as free-standing cantilevers, that is based on the use of high-aspect ratio micromolds of SU8 and aluminum as sacrificial layer. 250μm-high and 100-1000μm-wide molds were used to confine a liquid precursor of SiC/Si3N4 based ceramics on the sacrificial layer that enables the detachment of the green body before the pyrolysis step at 1000°C. The final ceramic cantilever has dimensions ranging from 100-500μm x 1-2mm x 50μm and a smooth surface. Details of the processing, structural and material characterization such as Dynamic Rheological and Thermogravimetric Analysis under UV will be presented and compared to those found in the literature.

Keywords: percolation ; conductivity ; photoresist ; polymer ; mems Reference LMIS4-ARTICLE-2004-011doi:10.1002/adem.200400068View record in Web of Science Record created on 2005-09-13, modified on 2017-05-10

This paper describes new polymer/ceramic photosensitive resins that can be used in the microstereolithography process for manufacturing complex 3D components in composite material. These new resins contain high loads (up to 80 wt.%) of alumina nanoparticles, used as fillers in a photosensitive acrylate-based resin of low viscosity. With the nanopowder-filled resin we developed, various small polymer/alumina composite components having a real geometric complexity were produced with small manufacturing times. When using a reactive medium containing a high enough percentage of ceramic nanoparticles, no deformation or cracks are observed after debinding and sintering, even if some shrinkage occurs during these steps. This process makes it possible to manufacture a new set of micro-components in ceramic material that could be of interest for high-temperature micro-reaction technologies, or for the production of new components in the biomedical domain.