Sacrificial template replication: fabrication of arbitrary embedded microfluidic channels in transparent fused silica glass

Fused silica glass is an important material for microfluidics. Until recently, microstructuring of glass has been challenging, requiring hazardous etching processes based on hydrofluoric acid or laser-based ablation methods. Classical etching processes can only achieve 2.5-dimensional microfluidic channels, which need to be sealed by bonding in a subsequent step. We have previously demonstrated a concept for fabricating and structuring fused silica glass using silica nanocomposites. These nanocomposites can be structured like a polymer, e.g. via UV-casting or stereolithography printing. After the structuring process, the components are converted into transparent fused silica glass via thermal debinding and sintering. However, the production of three-dimensional microchannels of sizes between 1-100 μm in fused silica remains a challenge. We have therefore developed a novel process, which we call sacrificial template replication (STR), which allows the fabrication of truly arbitrary embedded microchannels in transparent fused silica glass. To achieve microchannel formation, a polymeric template is embedded in the nanocomposite, which is subsequently removed during the thermal debinding process and leaves the inverse cavity after the sintering process. Since the templates are removed in the gas phase, there is no risk for material redeposition or channel blocking. Due to the thermal removal of the template many different templates can be used such as simple nylon threads, a 2.5- dimensional lithographically structured photoresists or highly complex microstructures fabricated via direct laser writing. Using this technology complex microfluidic channels can be fabricated with micron resolution. In this work we demonstrate the usage of these structures in "chemistry-on-chip" applications.