In most microfluidic systems, formation and accumulation of air and other gas bubbles can be detrimental to their operation. Air bubbles in a microfluidic channel induce a pressure profile fluctuation and therefore disturb the stability of the system. Once an air bubble is generated, it is also extremely difficult to remove such bubbles from the microfluidic systems. In tissue and cell culture microfluidic systems, a single air bubble can completely shear off cells that are being cultured. Air bubbles can be especially problematic in microfluidic systems that have to operate for long periods of time, since completely eliminating the generation of air bubbles for prolonged periods of time, where a single air bubble can ruin an entire multi-day/multi-week experiment, is extremely challenging. Several in-line and off-chip bubble traps have been developed so far, but cannot completely eliminate air bubbles from the system or are relatively difficult to integrate into microfluidic systems. Recent advancements in two-photon polymerization (2PP)-based microfabrication method eliminates the restriction in Z-axis control in conventional two-dimensional microfabrication methods, and thus enables complex 3D structures to be fabricated at sub-micrometer resolution. In this work, by utilizing this 2PP technique, we developed a sloped microfluidic structure that is capable of both trapping and real-time removal of air bubbles from the system in a consistent and reliable manner. The novel structures and designs developed in this work present a unique opportunity to overcome many limitations of current methods, bring state-of-the-art solutions in air bubble removal, and enable a multifunctional microfluidic device to operate seamlessly free from air bubble disruption. The microfabricated system was tested in both droplet microfluidics and continuous-flow microfluidics applications, and demonstrated to be effective in preventing air bubble aggregation over time. This simple sloped microstructure can be easily integrated into broad ranges of microfluidic devices to minimize bubble introduction, which will contribute to creating a stable and bubble-free microfluidic platform amenable for long-term operation.

在大多数微流体系统中，空气和其他气泡的形成和积累可能对其运行有害。微流体通道中的气泡会引起压力分布波动，从而扰乱系统的稳定性。一旦产生气泡，从微流体系统中去除此类气泡也极其困难。在组织和细胞培养微流体系统中，单个气泡可以完全剪掉正在培养的细胞。气泡在必须长时间运行的微流体系统中尤其成问题，因为完全消除了长时间内气泡的产生，其中单个气泡可能会毁掉整个多天/多周的实验，极具挑战性。迄今为止，已经开发了几种在线和片外气泡捕获器，但不能完全消除系统中的气泡，或者相对难以集成到微流体系统中。基于双光子聚合（2PP）的微加工方法的最新进展消除了传统二维微加工方法中Z轴控制的限制，从而能够以亚微米分辨率制造复杂的3D结构。在这项工作中，通过利用这种 2PP 技术，我们开发了一种倾斜的微流体结构，能够以一致、可靠的方式捕获和实时去除系统中的气泡。这项工作中开发的新颖结构和设计提供了一个独特的机会来克服当前方法的许多限制，带来最先进的气泡去除解决方案，并使多功能微流体装置能够无缝运行而不受气泡破坏。 该微加工系统在液滴微流体和连续流微流体应用中进行了测试，并被证明可以有效防止气泡随着时间的推移聚集。这种简单的倾斜微结构可以轻松集成到各种微流体装置中，以最大限度地减少气泡的引入，这将有助于创建适合长期运行的稳定且无气泡的微流体平台。