Capillary filling refers to the spontaneous movement of liquid through microchannels driven by surface tension and wetting forces, without the need for external pumps. In organ-on-a-chip systems, this phenomenon is used to introduce culture media or biological fluids into microfluidic networks that mimic physiological environments. The capillary action depends on channel geometry, surface properties, and fluid characteristics such as viscosity and contact angle.

By carefully designing microchannel dimensions and surface treatments, capillary filling enables precise control of fluid delivery, reduces mechanical stress on cells, and supports reproducible experiments in tissue modeling and drug testing.

In this simulation we have used two physics of fluid flow and level set or phase field. The geometry of the microchip and the contact angle which is determined by the material properties are very important. In fact we have to design the geometry in such a way that the fluid does not penetrate into the adjacent channels but stays between the pillars (for mass transfer).

Key topics in this simulation:

• Microfluidics
• Laminar Fluid Flow
• Level Set
• Contact Angle
• Organ on a Chip
• Tumor on a Chip
• Metastasis
• Cell Culture