Zhang Qianyi, Boniface Antoine, Parashar Virendra K, Gijs Martin A M, Moser Christophe
Laboratory of Applied Photonics Devices, School of Engineering, Institute of Electrical and Micro Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
Laboratory of Microsystems LMIS2, School of Engineering, Institute of Electrical and Micro Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
Nanophotonics. 2023 Jan 10;12(8):1527-1536. doi: 10.1515/nanoph-2022-0598. eCollection 2023 Apr.
The recent development of light-based 3D printing technologies has marked a turning point in additive manufacturing. Through photopolymerization, liquid resins can be solidified into complex objects. Usually, the polymerization is triggered by exciting a photoinitiator with ultraviolet (UV) or blue light. In two-photon printing (TPP), the excitation is done through the non-linear absorption of two photons; it enables printing 100-nm voxels but requires expensive femtosecond lasers which strongly limit their broad dissemination. Upconversion nanoparticles (UCNPs) have recently been proposed as an alternative to TPP for photopolymerization but using continuous-wave lasers. UCNPs convert near-infrared (NIR) into visible/UV light to initiate the polymerization locally as in TPP. Here we provide a study of this multi-photon mechanism and demonstrate how the non-linearity impacts the printing process. In particular, we report on the possibility of fine-tuning the size of the printed voxel by adjusting the NIR excitation intensity. Using gelatin-based hydrogel, we are able to vary the transverse voxel size from 1.3 to 2.8 μm and the axial size from 7.7 to 59 μm by adjusting the NIR power without changing the degree of polymerization. This work opens up new opportunities to construct 3D structures with micrometer feature size by direct laser writing with continuous wave inexpensive light sources.
基于光的3D打印技术的最新发展标志着增材制造的一个转折点。通过光聚合作用，液态树脂可以固化成复杂的物体。通常，聚合反应是通过用紫外线（UV）或蓝光激发光引发剂来触发的。在双光子打印（TPP）中，激发是通过两个光子的非线性吸收来完成的；它能够打印100纳米的体素，但需要昂贵的飞秒激光器，这严重限制了它们的广泛传播。最近，上转换纳米粒子（UCNPs）被提议作为TPP的替代方案用于光聚合，但使用的是连续波激光器。UCNPs将近红外（NIR）光转换为可见光/紫外光，以像在TPP中一样在局部引发聚合反应。在这里，我们对这种多光子机制进行了研究，并展示了非线性如何影响打印过程。特别是，我们报告了通过调整近红外激发强度来微调打印体素尺寸的可能性。使用基于明胶的水凝胶，我们能够在不改变聚合度的情况下，通过调整近红外功率将横向体素尺寸从1.3微米变化到2.8微米，轴向尺寸从7.7微米变化到59微米。这项工作为通过使用连续波廉价光源进行直接激光写入来构建具有微米级特征尺寸的3D结构开辟了新的机会。
