Characterization of interconnects used in PDMS microfluidic systems

This paper reports the characterization of a microfluidic packaging technique involving the use of press-fit interconnects to microfluidic channels molded in PDMS. This packaging technique is implemented by, first, coring a small hole in the PDMS to access molded or buried microchannels using a modified 20 gauge needle; and second, inserting an unmodified needle into the hole to create a direct connection to the microchannel that requires no bonding or molding. The needles can then easily be removed and reinserted multiple times since the seal is created purely by the compression of the PDMS around the needle. The luer fitting on the needles can easily be connected to standard fluid fittings. The quality of the interconnects is correlated with observations of the PDMS after coring. Methods of coring examined include pushing straight through and twisting the coring tool by hand or by machine. These comparisons demonstrated that all methods can produce viable interconnects; however, machine coring was the most consistent. The interconnects were characterized mechanically primarily by measuring their leak resistance under pressure. Leak tests were performed on interconnects (1) fabricated using different methods, (2) experiencing rotation or bending and (3) fabricated at various linear densities. Static pressure testing revealed that interconnect pressure limits varied from 100 kPa to over 700 kPa depending on the fabrication method. Suggestions are presented on how the technique could be modified to reach much higher pressures. Interconnect flexibility testing demonstrated a minimum of 30 of bending and a maximum of 60 before failure depending on the direction rotated. Density testing showed that PDMS was strong enough to allow at least six interconnects on a 1 cm linear channel.