Structuring polymeric materials is important for almost all applications in microsystems engineering, microfluidics and microoptics. Especially rapid prototyping using direct optical printing methods has gained great importance, also for facilitating product development for microfluidic applications. However, the choice of materials is still limited. Polystyrene (PS) is the material of choice for medical, biological and biochemical applications due to its biocompatibility, optical transparency, surface properties and low costs. However, PS is usually structured using industrial polymer replication techniques like injection molding or hot embossing. So far, only little work has been done on rapid prototyping and direct printing of microfluidic chips in PS. In this work, we present a novel liquid polystyrene prepolymer, which can be photocured and structured on the microscale using direct lithography printing. Using this method microchannels with a minimum channel width of 500 µm have been fabricated. The cured PS shows material properties comparable to those of commercially available polystyrene.
Poly(dimethylsiloxane) (PDMS) is one of the widely-used materials to fabricate microfluidic devices because of its facile handling, optical transparency and elastic mechanical properties. However, this polymer has its limitations if chemical, thermal and mechanical stability are needed for novel devices such as flow through “chemistry-on-chip” synthesis. Fused silica glass or borosilicate glass are indubitably the materials of choice for chemical synthesis due to its extraordinary chemical and thermal stability as well as its optical transparency. Microfluidic glass devices are however notoriously difficult to fabricate and usually require wet chemistry or dry etching using hazardous chemicals like hydrofluoric acid (HF). To overcome these fabrication issues, we have developed the Glassomer process that renders the structuration of fused silica glass like a polymer possible including technologies like softlithographic replication or stereolithography printing. In order to take the concept of “chemistry-on-chip” to the next level, electronics need to be integrated into the Glassomer process for the detection and localization of droplets inside microfluidic devices, for electrochemical analysis and electrochemical synthesis. In this work, we show that platinum electrodes can be integrated into the process using wires and sputtering of platinum in the polymeric state. The samples are subsequently converted into transparent fused silica glass via thermal debinding and sintering. We demonstrate that with our process the fabrication of glass microfluidic devices containing electronic conductors is feasible and facile to obtain and that they can be used to detect changes of conductivity
Precise and fast structuring polymeric materials is important for almost all applications in microsystems engineering, microfluidics and microoptics. In addition to 3D printing and soft lithography, grayscale lithography is a promising technique for structuring of complex geometries. It allows for the direct fabrication of relief structures, such as microoptical lenses and microfluidic channel structures, by illuminating a photo-curable material with a light pattern of gradually changing light intensity. However, standard grayscale resists are limited in terms of penetration depth and contrast: a low contrast, i.e. a flat slope of the polymerization rate vs. exposure dose curve is desired for generating accurate grayscale patterns of high resolution. The achievable polymerization depth of these patterns is limited. Hence we have developed a new photoresist for grayscale lithography that makes various polymerization depths independently accessible. The acrylate-based photoresist contains a combination of different initiators and absorbers, which can be polymerized at different wavelengths from ultraviolet to visible light, producing individual polymerization depths, each with a low contrast. Due to the wavelength-dependent absorptions of the initiators and absorbers, the different polymerization depths are addressed independently. The intensity gradients were generated using a custom-built maskless microlithography system based on a digital mirror device (DMD). In this work we will demonstrate that 3D structures with a high complexity can be fabricated fast and easily via grayscale lithography using the multi-level photoresist
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