Integration of movable structures in PDMS microfluidic channels

In this paper, we analyzed the behavior of moving structures in a check valve micropumping system and proposed a method to improve the freedom of motion of such structures. A model ball valve in a microchannel system was designed for this study. The behavior of the glass sphere, which acted as an independent flow check valve in the PDMS microfluidic channel, was analyzed. We found that the motion of the ball valve in the microchannel was sensitive to the properties of the interface between the ball, channel, and liquid. The glass ball valve moved freely when methanol or ethanol was introduced into the PDMS channel. However, the ball valve adhered to the PDMS channel when deionized (DI) water or cell culture media was introduced. Such behavior inhibits the applicability of this micropump to biological systems. The adhesion properties were modeled using the theory of interfacial actions between heterogeneous materials. The theoretical model successfully predicted the interaction properties that governed ball valve motion in the PDMS microchannels. To ameliorate the excessive adhesion in DI water or cell culture media, a hybrid inorganic/organic polymer (HR4) was used to coat the PDMS channel. In the HR4-coated ball valve micropump, the glass ball moved freely in DI water and cell culture media. Finally, the biocompatibility of the HR4 coating was evaluated by pumping human mesenchymal stem cells (hMSCs) suspended in media, and the pumped cells were cultured and evaluated for viability. A good viability demonstrated that the HR4 pump was biocompatible.