Fabrication of microneedles using two photon-polymerization with low numerical aperture

Three-dimensional (3D) micro-nano fabrication through two-photon polymerization (TPP) is a prominent approach for fabricating complex 3D structures. However, the existing techniques face limitations, such as small fabrication area, dependence on high numerical aperture (e.g., oil immersion) objective lenses, which are more expensive. We developed a 780 nm fs laser system integrated with a 2D galvanometer system and Z axis to create a 3D micro-nano printing system. A method to print arbitrarily complex 3D structures while maintaining an extremely high lateral spatial resolution of sub-100nm is proposed by using a cheap low numerical aperture objective lens with the laser power and exposure time precisely controlled. The impact of the laser power and exposure time on the resolution of 3D micro-nano processing is investigated, and we identify the optimal processing environment for achieving the best resolution. The printed linewidth of 62 nm was achieved without the use of an oil immersed objective lens, and only one laser beam was used instead of stimulated emission depletion. Microneedle arrays for animal injection were fabricated using this strategy, which can improve the performance of animal organoid repair. Our results suggest that TPP micro-nano fabrication is an effective method for processing microneedle arrays for biomedical engineering, with the ability to improve the processing resolution with a cheap low numerical aperture objectives lens (e.g., NA = 0.4) through meticulous control of laser power and exposure time. This approach opens up possibilities for affordable and scalable fabrication in sub-100nm structures.