Spontaneous re-arrangement of evaporating suspension into mesh-patterns towards concentration gradient generation on a chip

Microscale mesh patterns on surfaces are useful in several domains of application including surface texturing, microfluidics, biomimicking, and so on. Currently available techniques for fabrication of smooth microscale mesh patterns, based on MEMS technology or two photon 3D printing are complex, time-consuming, expensive, and lack scalability. Scalable manufacturing of array and fractal-like geometry via innovative concept of ‘shaping the fluid and retaining the shapes’ has been proposed recently. In this paper, we extend this concept by introducing evaporating polymer suspension in place of non-evaporating ceramic particle suspension, used previously. Fabrication process involves squeezing (with sealed holes) of the polymer solution (in a volatile solvent) between two cell plates, having an array of drilled holes, followed by parallel lifting (with the unsealed holes) of cell plates. Lifting induces a pressure drop within the stretched fluid film, dragging in the surrounding air from each hole, reorganizing the fluid into square or hexagonal mesh patterns based on the location of the holes. The volatile nature of the suspension allows self-curing of the structure that eliminates the post-curing step. This mesh fabrication process is demonstrated to be scalable in terms of the mesh dimensions (controlled by source holes pitch) and mesh density (controlled by the number of source holes on the cell plates). The fabricated mesh pattern is further used in the soft lithography step to obtain a vascular microchannel mesh replica in PDMS for developing the proposed Concentration Gradient Generator (CGG) on chip. The source and sink are punched over the PDMS to prepare the proposed diffusion-based static CGG devices. Finally, we experimentally demonstrated the stability of the concentration gradient in the proposed square mesh CGG device. The results of experiments were compared to those obtained using finite element analysis-based simulation software COMSOL Multiphysics. We further tweaked the device design parameters in simulated parametric analysis to demonstrate the flexibility of CGG for various bio-engineering applications. In summary, this work establishes a novel, scalable, low-cost, time-efficient, and lithography-less fabrication pathway for fabrication of mesh like geometries along with demonstration of their use for CGG applications.