PDMS stamp

Abstract: This paper describes a fabrication technique for building three-dimensional (3-D) micro-channels in polydimethylsiloxane (PDMS) elastomer. The process allows for the stacking of many thin (less than 100-/spl mu/m thick) patterned PDMS layers to realize complex 3-D channel paths. The master for each layer is formed on a silicon wafer using an epoxy-based photoresist (SU 8). PDMS is cast against the master producing molded layers containing channels and openings. To realize thin layers with openings, a sandwich molding configuration was developed that allows precise control of the PDMS thickness. The master wafer is clamped within a sandwich that includes flat aluminum plates, a flexible polyester film layer, a rigid Pyrex wafer, and a rubber sheet. A parametric study is performed on PDMS surface activation in a reactive-ion-etching system and the subsequent methanol treatment for bonding and aligning very thin individual components to a substrate. Low RF power and short treatment times are better than high RF power and long treatment times, respectively, for instant bonding. Layer-to-layer alignment of less then 15 /spl mu/m is achieved with manual alignment techniques that utilize surface tension driven self-alignment methods. A coring procedure is used to realize off-chip fluidic connections via the bottom PDMS layer, allowing the top layer to remain smooth and flat for complete optical access.

Abstract: This paper describes a procedure for making topologically complex three-dimensional microfluidic channel systems in poly(dimethylsiloxane) (PDMS). This procedure is called the “membrane sandwich” method to suggest the structure of the final system: a thin membrane having channel structures molded on each face (and with connections between the faces) sandwiched between two thicker, flat slabs that provide structural support. Two “masters” are fabricated by rapid prototyping using two-level photolithography and replica molding. They are aligned face to face, under pressure, with PDMS prepolymer between them. The PDMS is cured thermally. The masters have complementary alignment tracks, so registration is straightforward. The resulting, thin PDMS membrane can be transferred and sealed to another membrane or slab of PDMS by a sequence of steps in which the two masters are removed one at a time; these steps take place without distortion of the features. This method can fabricate a membrane containing a channel...

Abstract: We report the first fabrication of a solvent-compatible microfluidic device based on photocurable “Liquid Teflon” materials The materials are highly fluorinated functionalized perfluoropolyethers (PFPEs) that have liquidlike viscosities that can be cured into tough, highly durable elastomers that exhibit the remarkable chemical resistance of fluoropolymers such as Teflon Poly(dimethylsiloxane) (PDMS) elastomers have rapidly become the material of choice for many recent microfluidic device applications Despite the advantages of PDMS in relation to microfluidics technology, the material suffers from a serious drawback in that it swells in most organic solvents The swelling of PDMS-based devices in organic solvents greatly disrupts the micrometer-sized features and makes it impossible for fluids to flow inside the channels Our approach to this problem has been to replace PDMS with photocurable perfluoropolyethers Device fabrication and valve actuation were accomplished using established procedures for

Abstract: In recent years, there has been considerable progress on fabricating microfluidic devices with multiple functionalities, with the goal of attaining lab-on-a-chip [1–3] integration. These efforts have benefited from the development of microfabrication technologies such as soft lithography. [4] In this context the material polydimethylsiloxane (PDMS) has played an important role, not only serving as the stamp for pattern transfer, but also as an unique material in chip fabrication owing to its properties such as transparency, biocompatibility, and good flexibility. [5] Because such microfluidic devices may be constructed using simple manufacturing techniques such as micromolding, they are generally inexpensive to produce. By employing PDMS, micropumps, valves, mixer/reactors, and other components have been integrated into all-in-one chips with complex functionalities, used in chemical reactions, bio-analysis, drug discovery, etc. [2] However, PDMS is a non-conducting polymer, on which patterning metallic structures during the fabrication of microdevices is challenging due to the weak adhesion between the metal and PDMS. Hence, the integration of conducting structures into bulk PDMS has been a critical issue, especially for those applications such as electrokinetic micropumps, microsensors, microheaters, electro-rheological (ER) actuators, etc., [6–8] which require electrodes for control and signal detection. Patterning metallic structures is popular in microelectronics, but the metals cannot adhere to PDMS strongly due to the low surface energy of PDMS. Lee et al. reported the transfer and subsequent embedding of thin films of gold patterns into PDMS via chemical adhesion mediated by a silane coupling agent. [9] Lim et al. [10] developed a method of transferring and stacking metal layers onto a PDMS substrate by using serial and selective etching techniques. However, the incompatibility between PDMS and the metal usually caused failures in the fabrication process, especially in the bonding of thin layers. To minimize the difference in material properties, other conductive materials were considered. Gawron et al. reported the embedding of thin carbon fibers into PDMS-based microchips for capillary electrophoresis detection. [11] Carbon