The printhead interface consists of a linear array of nozzles with diameters on the order of tens of microns, allowing for the printing of high-density liquid droplet arrays known as microarrays. A linear array of specially-manufactured gaskets allows several different fluids to be transferred to the printhead in a single operation, providing user flexibility.
When gaskets are compressed, they push back. A seal is maintained if the fluid flowing inside a seal pocket exerts a pressure lower than that the gasket pushes back with. In a microfluidic system with very small, closely spaced gasket pockets, the fluid pressure may push back and deform the rubber, resulting in an unexpected deformation of a neighbouring seal pocket. In highly coupled fluidic manifolds, such behaviour can result in unpredictable fluid transfer and printing behaviour.
Xi worked with Arrayjet to study contact sealing forces of gaskets at a range of compressions and analysed the effect of applied internal seal wall pressure on material deformation. These mechanical studies helped provide guidelines on rubber (a.k.a. hyperelastic) material properties, and necessary compression in practical systems.
Computational Fluid Dynamics (CFD) studies provided the essential complement to the solid hypereleastic gasket compression studies. Flow rates during both sample fluid collection and cleaning were applied to study flow patterns and pressure distributions along the entire fluidic path, including not just the seal pocket but also the printhead manifold and the tubing to the well plates. Understanding pressure drops over all segments of the flow path was necessary to understand the applied pressure in the seal pocket itself. A range of flow rates was considered, with variation in the seal pocket shape as well as nozzle offset and partial blockage. Analysis of the flow patterns under these different possible mounting configurations, which may, for example, represent errant gasket installation, provides insight into whether fluid is evenly distributed to the nozzles, whether undesired recirculation zones form, or if asymmetries in pressure distributions are present.