FIG. 13.

3D printing in the fabrication of paper-based devices. (A) (a) Substrate fabrication process which involves creating a 3D model of the microfluidic device using 3D modeling software. The 3D model is transmitted to the 3D printing software using an STL file format. Once the substrate is printed, the surface is covered with PDMS until it penetrates into the flaws of the substrate (2min). The excess PDMS is wiped off and the covered substrate is then dried in the oven at 60 °C for 1 h to create a sealed, thin, hydrophobic layer. (b) The second step of the fabrication process is to fill the hollow channels on the substrate with a mixture of cellulose powder and de-ionized water. The substrate is then dried in an oven at 60 °C for 30min. After this step is complete, the fabricated device is ready to be used. (B) (a) and (b) The resolution of hydrophilic and hydrophobic channels under the microscope at 100× magnification.¹³⁹ Reproduced with permission from He et al., Micromachines 7(7), 108 (2016). Copyright 2016 Author(s), licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) License.