Electrohydrodynamic jet printed templates for hot embossing of microfluidic devices

Hot embossing is a scalable method of fabricating microfluidic devices involving precise replication of micrometer-sized features from a master mold onto a thermoplastic substrate. Typically, high-resolution master molds for hot embossing are fabricated using expensive, resource-intensive processes such as photolithography and electron-beam lithography. Here, we present a maskless, cost-effective, and rapid microfabrication process based on electrohydrodynamic jet printing (EJP) for fabricating high-resolution reusable master templates for hot embossing of thermoplastic microfluidic devices. Our method is based on EJP to fabricate intricate polymeric templates, with feature sizes of order 100 µm, followed by a double casting process to obtain stiff PDMS master molds. Using these PDMS molds, we demonstrate the hot embossing of microfluidic devices with excellent reproducibility across multiple embossing cycles. In particular, we demonstrate the fabrication of microfluidic devices with simple geometries of cross-shape and Y-shape to complex geometries of flow-focusing droplet generator and tree-shaped gradient generator. Subsequently, we demonstrate the use of hot-embossed microfluidic devices for hydrodynamic focusing, droplet generation, and stable concentration gradient generation. Our method offers a low-cost and rapid alternative to traditional lithographic processes for fabricating master molds for hot embossing with comparable feature resolution.