VAT photopolymerization 3D printing optimization of high aspect ratio structures for additive manufacturing of chips towards biomedical applications

Organ-on-chip and Lab-on-chip are microfluidic devices widely applied in the biomedical field. They are traditionally produced by soft lithography: starting from a mold fabricated by optical photolithography, a Polydimethylsiloxane (PDMS) device is obtained by casting and baking. While this technique offers the possibility to produce features with high resolution, it is not flexible enough to respond to the necessity of customization and prototyping. In this study, we propose as alternative the production of devices by digital light processing (DLP), a vat photopolymerization technology, in combination with a commercially available, biocompatible resin. Studying the process factors by a statistical methodology called Design of Experiment (DoE), we were able to achieve small features with high aspect ratio (60). DoE method allowed us to have a deep understanding of the process without the need of any physical inspection of the involved phenomena, and to generate empirical models, correlating the process factors to the dimensions of the final printed object. We proved that this optimization was beneficial also in terms of transparency (evaluated by UV-Vis spectrophotometry), and mechanical strength (evaluated by a compression test) of the printed resin. Finally, a proof-of-concept microfluidic device was fabricated, sealed to a PDMS membrane through an oxygen plasma treatment, and tested against leakage on a microfluidic circuit for one week. As result, we proved that DLP printing is not only a suitable method to develop microfluidic devices, but if correctly optimized it can also reproduce small features in the order of tens of micrometers rapidly.