Microthermoforming and Sealing of COP Films to Form Thin Walled Lab-on-a-chip Cartridges

摘要

This paper describes a process chain to form and seal thermoplastic films to obtain enclosed microfluidic cartridges with thin walls. Especially applications requiring fast thermocycling such as polymerase chain reaction (PCR) highly benefit from this lab-on-a-foil approach, due to an improved heat transfer. The cartridge fabrication is a two-step process comprising microthermoforming by soft lithography followed by a novel gas pressure assisted thermal sealing. As film material a 188 μm thick cyclic olefin polymer (COP) is used, which is microthermoformed over a male Polydimethylsiloxane (PDMS) mold to shape the intended thin walled microstructures. The process parameters have been optimized and feature sizes in the range of a few micrometers to millimeters with aspect ratios up to three are replicated. The forming of the thermoplastic film is caused by heating the film above glass transition temperature (T_g) and applying a gas pressure of 310 kPa. After cooling and demolding the COP structures are thermally sealed with a special coextruded COC film. The coextruded film consists of a temperature stable TOPAS COC 6013 (T_g ～ 135°C) layer and a thin layer of TOPAS COC 8007 (T_g ～ 79°C) acting like hot melt. An additional mold for bond support, which is commonly needed for positive thermoformed structures, has been eliminated by a gas pressure assisted bonding approach. The processes enable fast and flexible prototyping of thin walled microfluidic cartridges within 8 - 10 hours.