Light-Regulated Microstructure Growth of Dynamic Hydrogels for Flexible Manufacturing of Microlens Arrays

Microlenses are the basis of diverse modern instruments, which demand for more flexible fabrication. Thermal reflowing after photolithography of non-cross-linked polymers is the most widely applied strategy for manufacturing final products or primary molds of microlenses with desired microcurvatures. However, this approach can commonly form only one specific curvature for the same precursor system, lacking manufacturing flexibility. Here we report the direct growth of microstructures with flexible control of the curvature after one-step photolithography. This method relies on spatial UV irradiation, which induces network rearrangements in a dynamically cross-linked hydrogel. Upon subsequent water swelling, the irradiated locations develop microstructures with tunable curvature controlled by the irradiation time. Following by a secondary ionic cross-linking, the hydrogels are mechanically strengthened for practical microlens replication. Consequently, microlens arrays with a roughness around 20 nm are rapidly molded from the hydrogel templates. Multiple focuses are uniformly projected on a targeted plane, indicating the fine imaging capability of the microlenses. Moreover, the focal lengths are facilely adjustable not only in a wide range but also in a spatially selective manner. Our growth strategy paves a versatile and efficient method for the flexible fabrication of functional optical devices.