Formulating an Ideal Protein Photoresist for Fabricating Dynamic Microstructures with High Aspect Ratios and Uniform Responsiveness

The physical properties of aqueous-based stimuli-responsive photoresists are crucial in fabricating microstructures with high structural integrity and uniform responsiveness during two-photon lithography. Here, we quantitatively investigate how various components within bovine serum albumin (BSA) photoresists affect our ability to achieve BSA microstructures with consistent stimuli-responsive properties over areas exceeding 10⁴ μm². We unveil a relationship between BSA concentration and dynamic viscosity, establishing a threshold viscosity to achieve robust BSA microstructures. We also demonstrate the addition of an inert polymer to the photoresist as viscosity enhancer. A set of systematically optimized processing parameters is derived for the construction of dynamic BSA microstructures. The optimized BSA photoresists and processing parameters enable us to extend the two-dimensional (2D) microstructures to three-dimensional (3D) ones, culminating in arrays of micropillars with aspect ratio > 10. Our findings foster the development of liquid stimuli-responsive photoresists to build multifunctional complex 3D geometries for applications such as bioimplantable devices or adaptive photonic systems. (Graph Presented).