Arnaud Bertsch

Wireless contact lens sensor for intraocular pressure monitoring: assessment on enucleated pig eyes

Purpose:  Assessment on enucleated pig eyes of a novel and minimally invasive method for the continuous monitoring of intraocular pressure (IOP), based on a novel wireless contact lens sensor (CLS).

Rapid prototyping of small size objects

The commercialization of new products integrating many functions in a small volume requires more and more often the rapid prototyping of small high‐resolution objects, having intricate details, small openings and smooth surfaces. To give an answer to this demand, the stereolithography process has started to evolve towards a better resolution: the “small spot” stereolithography technology allows to reach a sufficient resolution for the manufacturing of a large range of small and precise prototype parts. Microstereolithography, a technique with resolution about an order of magnitude better than conventional stereolithography, is studied by different academic research groups. The integral microstereolithography machine developed at the Swiss Federal Institute of Technology in Lausanne is described in this paper, and potential applications are presented. The resolutions of conventional, small spot and microstereolithography technologies are compared and the potential of the microstereolithography technique is shown for the manufacturing of small and complex objects.

3D microfabrication by combining microstereolithography and thick resist UV lithography

A new approach for the realization of true 3D polymer structures is presented in this paper. It consists in adding, in a post-processing microstereolithography step, 3D polymer microstructures on top of a micropart patterned by means of planar processes such as thin films, bulk silicon etching or high aspect ratio structuration (LIGA, RIE, thick resist). In this way, some shape limitations of the planar technologies can be overcome for new functional applications. Moreover, the direct processing of microstereolithography on predefined structures eliminates manipulations which are associated with micro-assembly of separated parts. To demonstrate this combination of microstructuration processes, an example showing a conical axle added by microstereolithography on a SU-8 piece of gearing is presented.

Microfabrication of ceramic components by microstereolithography

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.

A soft contact lens with a MEMS strain gage embedded for intraocular pressure monitoring

We propose a novel approach to intraocular pressure (IOP) measurement allowing minimal invasive continuous monitoring over prolonged periods, regardless of patient position and activities. The key element of this innovative measurement method is a soft contact lens with a microfabricated strain gage embedded allowing the measurement of the cornea curvature deformation due to IOP changes. Tests on a eye-simulating device have shown that the sensor is capable of monitoring continuously a deformation of cornea radius inferior to 0.0055 mm, which corresponds to a sensitivity of better than 2 mmHg IOP, according to an in vitro and an in vivo studies about the correlation between IOP and corneal curvature in human beings.

Polyimide and SU-8 microfluidic devices manufactured by heat-depolymerizable sacrificial material technique

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.

In Vivo Electrical Impedance Spectroscopy of Tissue Reaction to Microelectrode Arrays

The goal of this experiment was to determine the electrical properties of the tissue reaction to implanted microelectrode arrays. We describe a new method of analyzing electrical impedance spectroscopy data to determine the complex impedance of the tissue reaction as a function of postimplantation time. A model is used to extract electrical model parameters of the electrode-tissue interface, and is used to isolate the impedance of the tissue immediately surrounding the microelectrode. The microelectrode arrays consist of microfabricated polyimide probes, incorporating four 50-mum-diameter platinum microelectrodes. The devices were implanted in the primary motor cortex of adult rats, and measurements were performed for 12 weeks. Histology was performed on implants at three time points in one month. Results demonstrate that the tissue reaction causes a rapid increase in bioimpedance over the first 20 days, and then stabilizes. This result is supported by histological data.

Polyimide microfluidic devices with integrated nanoporous filtration areas manufactured by micromachining and ion track technology

This paper reports on polyimide microfluidic devices fabricated by photolithography and a layer transfer lamination technology. The microchannels are sealed by laminating an uncured polyimide film on a partially cured layer and subsequent imidization. Selected areas of the microchannels were irradiated with heavy ions of several hundred MeV and the generated ion tracks are chemically etched to submicron pores of high aspect ratio. The ion beam parameters and the track etching conditions define density, length, diameter and shape of the pores. Membrane permeability and separation performance is demonstrated in cross-flow filtration experiments. The devices can be used for selective delivery or probing of fluids to biological tissue, e.g. drug delivery or microdialysis. For chip-based devices the filters can be used as a sample pre-treatment unit for filtration or concentration of particles or molecules.

Combining microstereolithography and thick resist UV lithography for 3D microfabrication

A new approach for the realization of true 3D polymer structures is presented in this paper. It consists in adding, in a post-processing microstereolithography step, 3D polymer microstructures on top of a micropart patterned by means of planar processes such as thin films, bulk silicon etching or high aspect ratio structuration (LIGA, RIE, thick resist). This way, some shape limitations of the planar technologies can be the new functional applications. Direct processing of microstereolithography on predefined structures prevents manipulations which are associated with microassembly of separated parts. To demonstrate this combination of microstructuration processes, an example showing a conical axle added by microstereolithography on a SU-8 piece of gearing is presented.

Partial release and detachment of microfabricated metal and polymer structures by anodic metal dissolution

The large majority of microelectromechanical systems (MEMS) are fabricated on silicon, glass or Pyrex substrates by manufacturing techniques, which originated from the semiconductors industry. However, their final application often requires removal of the fabrication substrate or at least a partial release of some section of the device. This paper describes a technique based on anodic dissolution of sacrificial metal layers for the complete or partial detachment of microstructures. As an example, a thin-film of sacrificial aluminum is selectively removed in a neutral sodium chloride solution by applying a small positive potential to the aluminum. The method is evaluated theoretically and experimentally in a defined geometry and compared to diffusion-limited, chemical etching. It is shown experimentally that the process is significantly faster than conventional wet chemical etching and the method has been used to release planar and nonplanar thin-film devices made from polymers and metals. The method is applicable for a wide range of metals as sacrificial materials and is very versatile with respect to electrolyte composition and applied voltages. Ease of sacrificial material deposition (sputtering or evaporation) and structuring and the possibility of high process temperature and the nondestructive chemical environment (also environmentally friendly) during detachment make the process technology an interesting alternative to conventional chemical etching.