Rapid assembly of multilayer microfluidic structures via 3D-printed transfer molding and bonding

Abstract

A critical feature of state-of-the-art microfluidic technologies is the ability to fabricate multilayer structures without relying on the expensive equipment and facilities required by soft lithography-defined processes. Here, three-dimensional (3D) printed polymer molds are used to construct multilayer poly(dimethylsiloxane) (PDMS) devices by employing unique molding, bonding, alignment, and rapid assembly processes. Specifically, a novel single-layer, two-sided molding method is developed to realize two channel levels, non-planar membranes/valves, vertical interconnects (vias) between channel levels, and integrated inlet/outlet ports for fast linkages to external fluidic systems. As a demonstration, a single-layer membrane microvalve is constructed and tested by applying various gate pressures under parametric variation of source pressure, illustrating a high degree of flow rate control. In addition, multilayer structures are fabricated through an intralayer bonding procedure that uses custom 3D-printed stamps to selectively apply uncured liquid PDMS adhesive only to bonding interfaces without clogging fluidic channels. Using integrated alignment marks to accurately position both stamps and individual layers, this technique is demonstrated by rapidly assembling a six-layer microfluidic device. By combining the versatility of 3D printing while retaining the favorable mechanical and biological properties of PDMS, this work can potentially open up a new class of manufacturing techniques for multilayer microfluidic systems.

Keywords: 3D printing; PDMS; microfluidics.

Figure 1

Illustration of fabrication process (top) and technical capabilities (bottom) of 3D-printed transfer molding for double-sided microfluidic devices. Fabrication: (a) mold is 3D-printed from a CAD model, treated, fitted using alignment marks, and (b) filled with PDMS and cured. Excess PDMS is cut away and the mold is removed. (c) The resulting PDMS component contains integrated inlets/outlets, membranes, and vias, and is (d) bonded to glass to create a device with enclosed channels of arbitrary cross-section. Technical capabilities: the multilevel microfluidic device shown in cross-section in (e) and photographed in (f) is fabricated using double-sided molding techniques and exhibits numerous design elements, such as two-layer fluid flow, multiple microfluidic vias, integrated fluid inlets/outlets, an elliptical 350-μm domed membrane, and a “Quake”-style membrane value, as well as alignment marks for use in generating multilayer devices. 3D, three-dimensional; PDMS, poly(dimethylsiloxane).

Figure 2

Single-sided fabrication and bonding process flow. (a) 3D-printed mold is printed from CAD file, including integrated inlet/outlet ports and guideposts to assist the removal of PDMS. (b) Mold is filled with ℓPDMS, degassed, and baked, and (c) cured PDMS is demolded. (d) Cured PDMS is bonded to glass using the PDMS–glass ℓPDMS spin-bonding technique to compensate for surface roughness. (e) Final conceptual image with enclosed channel and 20-gauge connector pins attached. (f) Photograph of glass-bonded device with colored fluid. 3D, three-dimensional; PDMS, poly(dimethylsiloxane).

Figure 3

Double-sided molding techniques and results. Conceptual illustration of alignment marks: (a) mold–mold, (b) mold–PDMS, (c) PDMS–PDMS, and (d) PDMS height limiters. (e and f) Microfluidic devices with integrated fluidic vias: (e) simple overpass and (f) repeated crossover with mixing. (g and h) Membranes (350-μm thick) for fluid storage or hydrodynamic capacitance: (g) domed membrane (h) sinusoidal membrane for increased flexibility. (i) Fully circular channels fabricated by bonding two complementary components using integrated PDMS-PDMS alignment marks. PDMS, poly(dimethylsiloxane).

Figure 4

'Quake'-style membrane valves generated by single-step double-sided molding procedure. (a) Conceptual and (b) cross-sectional photograph of the membrane valve. (c) Top-down photograph, (d) microscope image illustrating the active valve region, and (e) microscope images of valve under various P_G. (f) Valve characteristic curves under parametric P_S sweep. Further Q, P_G time series analysis: (g) flow rate compared with varying gate pressures and (h) rates of change of flow rate and gate pressures.

Figure 5

Rapid assembly of multilayer PDMS microfluidic devices achieved with 3D-printed molding. (a) Use of a 3D-printed stamp to selectively apply uncured PDMS to non-channel areas. (b) Conceptual illustration of alignment and assembly of multilayer microfluidic device with illustration of intralayer fluid flow. (c) Intruded stamp topography. (d) Second layer of six-layer device with corresponding stamp, which exhibits extruded stamp topography. (e–h) Rapid assembly of multilayer microfluidic device: (e) CAD model, (f) stacked individual layers, (g) assembled and bonded, and (h) fluid flow spiraling between layers and mixing. 3D, three-dimensional; PDMS, poly(dimethylsiloxane).