Thermoplastic elastomers for microfluidics: Towards a high-throughput fabrication method of multilayered microfluidic devices

Abstract

Multilayer soft lithography of polydimethylsiloxane (PDMS) is a well-known method for the fabrication of complex fluidic functions. With advantages and drawbacks, this technique allows fabrication of valves, pumps and micro-mixers. However, the process is inadequate for industrial applications. Here, we report a rapid prototyping technique for the fabrication of multilayer microfluidic devices, using a different and promising class of polymers. Using styrenic thermoplastic elastomers (TPE), we demonstrate a rapid technique for the fabrication and assembly of pneumatically driven valves in a multilayer microfluidic device made completely from thermoplastics. This material solution is transparent, biocompatible and as flexible as PDMS, and has high throughput thermoforming processing characteristics. We established a proof of principle for valving and mixing with three different grades of TPE using an SU-8 master mold. Specific viscoelastic properties of each grade allow us to report enhanced bonding capabilities from room temperature bonding to free pressure thermally assisted bonding. In terms of microfabrication, beyond classically embossing means, we demonstrate a high-throughput thermoforming method, where TPE molding experiments have been carried out without applied pressure and vacuum assistance within an overall cycle time of 180 s. The quality of the obtained thermoplastic systems show robust behavior and an opening/closing frequency of 5 Hz.

3D thermoplastic elastomer microfluidic devices for biological probe immobilization

“…We have recently identified commercially available thermoplastic 45 elastomers (TPE) that can adapt to other surfaces through conformal contact in a similar way than PDMS, while providing the appealing ability to be processed using conventional thermoforming methods such as hot embossing lithography (HEL) or injection molding. 29,53,55,56 In this 50 paper, we extend this work by demonstrating the rapid and reliable patterning of open through-holes and channels in thin TPE membranes using a method based on HEL. We then discuss the design of a TPE-based 3D microfluidic patterning device that permits the immobilization of up to 96 different 55 biological probes in a 10 × 10 array format of 50 × 50 m 2 spots.…”

“…29,53,55,56 In this 50 paper, we extend this work by demonstrating the rapid and reliable patterning of open through-holes and channels in thin TPE membranes using a method based on HEL. We then discuss the design of a TPE-based 3D microfluidic patterning device that permits the immobilization of up to 96 different 55 biological probes in a 10 × 10 array format of 50 × 50 m 2 spots. We also present an optimization of the channel geometry using 3D Lattice-Boltzmann numerical simulations to ensure the complete filling of the devices using only capillary forces.…”

“…The cost per kg of most TPEs is also considerably lower than that of PDMS, which would lead to very significant savings in 15 a mass production process. 55 Moreover, thin membranes fabricated from standard PDMS formulations (e.g., Sylgard ® 184) are relatively fragile, which makes their handling nontrivial and limits the scope of possible applications. The copolymer structure of TPE can provide superior mechanical 20 characteristics as reflected by the relatively large elongation at break (e.g., 780% for CL30 vs. ~140% for PDMS 60 ), which minimizes the risk of damage during removal from the mold and thus provides better margins to scale both vertical and lateral dimensions of the features.…”

“…Note that four of the 96 channels are connected to two spotting holes to compensate for the smaller number of inlets. To facilitate the manual filling of the devices, the 96 inlets are kept as large as possible (i.e., 500 m in diameter) and dispersed evenly across the surface 55 of the device, while the 96 outlets (150 m in diameter) are distributed along the periphery of the device. The design has been optimized to drive the liquid through the channels by capillary action only, which represents a far more practical option than interfacing such a highly-integrated device with 60 an external pumping system.…”

“…1,22 Pin spotting employs a set of metallic micropins to deliver minute amounts of liquid upon contact with a surface. However, accurate positioning and registration of the spots between each successive printing cycle are difficult to control 55 and require costly and sophisticated tools. Also, the rapid and uncontrolled drying of liquid can lead to non-uniform spots and denaturation of sensitive material, especially when the dimensions of the spots are decreased below ~80 m.…”