The primary objective of this research is to develop an efficient protocol which can be used to 3D print multi-material microfluidic devices with a high resolution. During this research, the fabrication of multi-material microfluidic valves is discussed as a showcase to verify the multi-material protocol, using a single affordable printer and multiple resin vats. In contrast to single material microfluidic fabrication methods, complex geometries can be created by the use of combinations of stiff and flexible materials in a single 3D print. This protocol aims to streamline the fabrication process while ensuring precise feature reproduction and robust mechanical properties in multi-material 3D printed microfluidic parts.

In this study, the effects of UV light exposure on feature accuracy and mechanical performance is systematically investigated. It is observed that for the rigid material, Anycubic High Clear, sample sizes increase and void features shrink when the exposure to UV light increases. For the soft material, Liqcreate Elastomer-X, shrinkage rates after swelling due to IPA absorption are compared under different conditions, revealing that shrinkage occurs more rapidly with a heat source than at ambient temperature.

Mechanical properties are further evaluated through tensile testing of four sets of printed dogbones, showing that extended UV exposure enhances mechanical properties such as the Young's modulus, ultimate tensile strength and strength at break. Elastomeric materials assessed in this study demonstrate an optimal measurement accuracy within a strain range of 10% to 50%. The influence of print orientation is assessed for the hard material. This experiment is executed for layer thicknesses from 10 µm to 200 µm across horizontal, vertical, and diagonal orientations, with vertically printed samples being closest to the intended dimensions.

A comprehensive multi-material 3D printing protocol based on the existing "print-pause-print" technique and utilizing the software UVTools is presented. Finally, a microfluidic Quake valve is designed and optimized for 3D printing, its performance is analyzed through finite element (FEM) simulation and analytical calculations.

The results of this study offer valuable insights into the optimization of multi-material 3D printing for microfluidic applications, highlighting several critical parameters that affect feature resolution and mechanical performance. The proposed protocol and findings serve as a foundation for future advancements in the fabrication of complex microfluidic devices.