Three-dimensional (3D) printing is an intriguing and facile material processing method that enables quick turnaround of complicated structures from concept to prototype. Different mechanism-based 3D printers have high demands for suitable material categories. In another aspect, microfluidic platforms offer the most important contributions to biological and chemical analysis due to the low sample consumption, small size, and high integration. The miniaturized size of microfluidic devices is particularly convenient in single-cell studies, which unveils cell heterogeneity related to a top human killer, cancer. Microfluidics benefit greatly from 3D printing for the rapid fabrication of molds, but the limitation of printable material categories impedes the creation of 3D microfluidic structu...[ Read more ]

Three-dimensional (3D) printing is an intriguing and facile material processing method that enables quick turnaround of complicated structures from concept to prototype. Different mechanism-based 3D printers have high demands for suitable material categories. In another aspect, microfluidic platforms offer the most important contributions to biological and chemical analysis due to the low sample consumption, small size, and high integration. The miniaturized size of microfluidic devices is particularly convenient in single-cell studies, which unveils cell heterogeneity related to a top human killer, cancer. Microfluidics benefit greatly from 3D printing for the rapid fabrication of molds, but the limitation of printable material categories impedes the creation of 3D microfluidic structures in desired materials. It would also be interesting to incorporate 3D structures in a single-cell study platform. There are three projects in my work, which are divided into two parts. One is to explore novel methods to fabricate complicated 3D structures in desired materials. Another is to build up an integrated and individually-addressable microfluidic single-cell array.

In the first part, we demonstrated replicating 3D printed structures into functional materials by constructing a non-porous, heat-resistance nickel mold. Complicated structures with overhanging structures were reconstructed in polydimethylsiloxane (PDMS), paraffin, and polyacrylamide replicas. The method displays high fidelity and high resolution (< 1 μm). Moreover, we reduced the feature size of the 3D replica by electroless plating the interior of the nickel mold. The cost-effective electroless plating was further employed to deposit thick metal films in both PDMS microchannels and patterned PDMS sheets. The as-plated hollow nickel mold can be sacrificed to create Teflon chips; the freestanding microcomponents, such as microgears, can also be used in microelectromechanical systems (MEMS). We believe our 3D-replication methods can inspire other researchers to fabricate 3D structures in desired materials, whether unextrudable Teflon or rigid nickel, without direct 3D printing.

In the second part, we constructed a microfluidic single-cell array chip that can realize addressable cell release at low cost. With rational geometric designs, we realized high cell capture efficiency (~90%) and release of a single cell in a 10 x 10 array. Asymmetric microelectrode pairs were devised to produce addressable electrolytic bubbles in the 10 x 10 microelectrode array (MEA). This platform combines passive and active manipulation techniques to control the motion of a single cell. We believe this device is promising to be coupled with a downstream single-cell module and form a cost-economical single-cell analysis platform.