On-ratio PDMS bonding for multilayer microfluidic device fabrication

Integrated elastomeric valves, also referred to as Quake valves, enable precise control and manipulation of fluid within microfluidic devices. Fabrication of such valves requires bonding of multiple layers of the silicone polymer polydimethylsiloxane (PDMS). The conventional method for PDMS-PDMS bonding is to use varied base to crosslinking agent ratios between layers, typically 20:1 and 5:1. This bonding technique, known as “off-ratio bonding,” provides strong, effective PDMS-PDMS bonding for multi-layer soft-lithography, but it can yield adverse PDMS material properties and can be wasteful of PDMS. Here we demonstrate the effectiveness of on-ratio PDMS bonding for multilayer soft lithography. We show the efficacy of this technique among common variants of PDMS: Sylgard 184, RTV 615, and Sylgard 182.

Analysis and Experiment on the Response Characteristics of a Pneumatic Micro Actuator Based on TBC Model

Using basic physical arguments, we present a design and method for the fabrication of a pneumatic micro PDMS actuator using multilayer soft lithography based on dry-film photoresist. Its novel structure consists of a three-way electromagnetic microvalve for gas flow control which is connected with gas inlet microchannel for the actuator. Then the whole system is considered as a throttle blind capacitor (TBC) model and it is used to predict the response time of the pneumatic actuator by correlating its characteristics such as gas pressurizing, air resistance and membrane deformation. For this micro actuator, upward deformation motions of actuated area are observed of actuated area under 100KPa (N2) pressure and the fast open response (~ 15 ms) was achieved at 50KPa pressure. Our method provides a simple, cheap and save-time pneumatic micro actuator which can be used in active functions, such as valves, pumps and mixers integrated on pneumatic microfluidic chips for downsizing the driving pressure and improving the whole efficiency of microchips.

Centrifugal Casting of Microfluidic Components With PDMS

This work describes the centrifugal casting and fast curing of double-sided, polydimethylsiloxane (PDMS)-based components with microfeatures. Centrifugal casting permits simultaneous patterning of multiple sides of a component and allows control of the thickness of the part in an enclosed mold without entrapment of bubbles. Spinning molds filled with PDMS at thousands of revolutions per minute for several minutes causes entrapped bubbles within the PDMS to migrate toward the axis of rotation or dissolve into solution. To cure the parts quickly (<10 min), active elements heat and cool cavities filled with PDMS after the completion of spinning. Microfluidic channels produced from the process have a low coefficient of variation (<2% for the height and width of channels measured in 20 parts). This process is also capable of molding functional channels in opposite sides of a part as demonstrated through a device with a system of valves typical to multilayer soft lithography.