CAREER: High-Aspect-Ratio Multi-Material Three-Dimensional Microstructures via Microfluidic Direct Laser Writing

这项教师早期职业发展（Career）资助将专注于理解和推进一种新的增材制造策略，以实现全新的多材料范式，进而实现亚微米尺度的多功能三维（3D）结构，用于新兴的科学应用。制造几何复杂但功能优越的由多种完全集成的材料组成的微系统的能力-对应于所需的光学，生物，化学，电学和/或机械性能-提供了革命性的众多领域的潜力，包括生物医学，光学和光子学，超材料和微型机器人。最近发明的一种增材制造技术，“微流体直接激光书写”，是唯一适合实现这种能力的技术。通过使用紧密聚焦的激光脉冲在指定位置固化不同的、顺序加载的光反应性液体，这种方法允许在100纳米长度尺度上构建具有无与伦比的几何多功能性的多材料3D微结构。目前这种规模的增材制造方法似乎仅限于建造具有小高宽比的3D结构。该研究项目旨在理解、解释并最终控制迄今为止阻碍使用直接激光书写打印具有大宽高比的多材料3D微结构的基本过程机制。与此同时，该职业计划将建立直接与研究计划相结合或受其启发的教育和推广活动，包括：(i)针对高中女生的非竞争性增材制造活动，（ii）针对高中生的为期一年的综合研究项目，（iii）针对本科生的为期四年的荣誉论文项目，以及（iv）针对增材制造课程的新多材料项目。通过利用增材制造（或通俗地说，“3D打印”）的独特可及性，这些活动有望增加科学和工程的曝光率，并激发高中、本科生和研究生对先进制造研究的持久兴趣和信心，重点是女性和有色人种学生的参与。该研究的总体目标是揭示和进入微流体直接激光书写加工设计空间的区域，以实现全新类别的多材料3D纳米结构部件的精确和可重复制造，这些部件不受低纵横比的限制。目前，潜在的微流体直接激光写入过程因素的作用-即源于双光子聚合现象和微尺度力学-流体相互作用的因素-仍然知之甚少。为了弥合这些知识差距，本研究项目将结合理论和实验研究，系统地研究和揭示以下基本关系：(i)扫描激光逐点逐层写入路径，（ii）微流体注入条件，（iii）基于机械和收缩的微观结构变形动力学，以及（iv）中间微流体直接激光写入阶段的材料错位误差传播。预计研究活动的成果将促进光学、生物医学和微电子技术在学术、商业和政府部门的应用。该项目将使PI在多材料增材微/纳米制造方面的知识水平显著提高，扩大直接激光书写的使用，并牢固地确立PI在先进制造领域的长期职业生涯。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This Faculty Early Career Development (CAREER) grant will focus on understanding and advancing a novel additive manufacturing strategy to enable entirely new paradigms of multi-material, and in turn multi-functional, three-dimensional (3D) structures at sub-micron scales for emerging scientific applications. The ability to manufacture geometrically complex yet functionally advantageous microsystems comprised of multiple fully-integrated materials—corresponding to desired optical, biological, chemical, electrical, and/or mechanical properties—offers the potential to revolutionize a multitude of fields, including biomedicine, optics and photonics, metamaterials, and microrobotics. A recently created additive manufacturing technique, "microfluidic direct laser writing," is uniquely suited to realize such capabilities. By using tightly-focused laser pulses to solidify distinct, sequentially loaded photoreactive liquids in designated locations, this approach allows for multi-material 3D microstructures to be built with unparalleled geometric versatility at 100-nanometer length scales. Current methods of additive manufacturing at this scale appear to be limited to building 3D constructs with small height-to-width aspect ratios. This research project seeks to understand, explain, and ultimately control the fundamental process mechanisms that have heretofore hindered the use of direct laser writing for printing multi-material 3D microstructures with large aspect ratios. In concert, this CAREER program will establish education and outreach activities that are either directly integrated with or inspired by the research plans, including: (i) non-competitive additive manufacturing activities for high school women, (ii) year-long integrated research projects for high school students, (iii) a four-year-long Honors Thesis project for undergraduate students, and (iv) new multi-material projects for the additive manufacturing curriculum. By leveraging the unique accessibility of additive manufacturing (or colloquially, "3D printing"), these activities are expected to increase science and engineering exposure and inspire a lasting interest and confidence in advanced manufacturing research for high school, undergraduate, and graduate students, with an emphasis on inclusion for women and students of color.The overarching goal of the research is to uncover and access regions of the microfluidic direct laser writing processing design space to achieve accurate and repeatable manufacturing of entirely new classes of multi-material 3D nanostructured components that are not restricted to low aspect ratios. At present, the roles of underlying microfluidic direct laser writing process factors—namely, those stemming from two-photon polymerization phenomena and microscale mechano-fluidic interactions—remain poorly understood. To bridge these knowledge gaps, this research project will combine theoretical and experimental studies to systematically investigate and reveal the fundamental relationships connecting: (i) the point-by-point, layer-by-layer writing path of the scanning laser, (ii) microfluidic infusion conditions, (iii) mechanical and shrinkage-based microstructure deformation dynamics, and (iv) material misalignment error propagation during intermediate microfluidic direct laser writing stages. It is envisioned that the results of the research activities will catalyze new technologies for optical, biomedical, and microelectronics applications in academic, commercial, and governmental sectors. This project will allow the PI to significantly advance the state of knowledge in multi-material additive micro/nanomanufacturing, expand the use of direct laser writing, and firmly establish the PI's long-term career in advanced manufacturing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.