Protein corona coated onto the hydrophilic cellulose fiber turns into hydrophobic upon UV irradiation without hindering the porosity of the paper while simultaneously reducing nonspecific adsorption. Taking advantage of the biofouling-resistant, hydrophobic, and fluid transport through property, we demonstrated hanging drop three-dimensional (3D) spheroid culture and in-site analysis, including drug testing, time-dependent detection of secreted protein, and fluorescence staining without disturbing the spheroids. This single hanging drop system can also be extended to a networked hanging drop chip to mimic in vivo microphysiology by combining with wax-patterned microfluidic channels, where well-to-well interaction can be accurately controlled in a passive manner. As a proof of concept, the effects of a concentration gradient of nutrient and variable dosage of anticancer drugs were studied in the 3D spheroids cultured on paper. The experimental results suggested that a complex network device could be fabricated on a large scale on demand at a minimal cost for 3D spheroid culture. Our method demonstrates a future possibility for paper as a low cost, high-throughput 3D spheroid-based "body-on-a-chip" platform material.
Keywords: cellulose; chemotactic gradient; drug testing; paper microfluidics; protein coating.