Switchable, bistable microactuator systems based on stimuli-responsive polymers

由于其3D可打印性、可调特性以及与细胞无害相互作用的能力，刺激响应水凝胶是在微流体装置中产生微致动器系统的引人注目的材料。然而，目前基于水凝胶的微致动器往往非常简单，而复杂的特性，如双稳定性，在很大程度上仍未得到开发；因此，该领域尚不成熟，许多潜在的应用尚未实现。在第一个资助期的工作基础上，我们已经彻底表征并改进了基于pnipam的热响应微致动器的驱动，我们在此提出了一种基于热响应/pH响应水凝胶和形状记忆聚合物组合的新策略来实现双稳态微致动器系统。材料将使用双光子直接激光写入成形成微致动器系统，这允许制造高度复杂的3D几何形状，并且它们在响应刺激中的驱动将被深入和优化。我们将通过分析单个微致动器之间的串扰来探讨使用热响应水凝胶构建微致动器阵列/系统的优点和缺点。我们假设形状记忆材料与热响应和/或ph响应材料的组合可以用来利用单个微致动器之间的串扰，以增加整个微致动器系统的功能。这个项目的最后演示将包括一个不同形状和配置的微致动器系统，包括用于动态微流体系统的主动微通道壁和刺激响应微阀。虽然商业上最先进的微流控装置在制造过程中具有预先定义的特性，但我们的微致动器系统将基于主动特性，通过单个微致动器的合作，为微流控装置增加动态灵活性。类似的原理将用于设计自主操作的细胞和类器官培养系统，其中ph响应微阀将调节细胞介质的流动。该项目的成功将导致微流体系统前所未有的适应性和自主性，从而提高各种工具和程序的可及性和吞吐量。

Stimuli-responsive hydrogels are compelling materials for generating microactuator systems within microfluidic devices due to their 3D printability, tunable features, and ability to interact harmlessly with cells. Current hydrogel-based microactuators, however, tend to be very simple, and complex features, e.g. bistability, remain largely unexploited; therefore, the field remains immature and many potential applications have not yet been realized. To build on work from the first funding period, where we have thoroughly characterized and improved the actuation of PNIPAM-based thermoresponsive microactuators, we herein propose a novel strategy to achieve bistable microactuator systems based on combinations of thermoresponsive/pH responsive hydrogels and shape-memory polymers. The materials will be shaped into microactuator systems using two-photon direct laser writing, which allows for the fabrication of highly complex 3D geometries, and their actuation in response stimuli will be characterized in-depth and optimized. We will explore the advantages and disadvantages of using thermally responsive hydrogels to construct microactuator arrays/systems by analyzing the cross-talk that occurs between individual microactuators. We hypothesize that the combination of a shape-memory material with a thermoresponsive and/or pH-responsive material can be used to take even advantage of cross-talk between individual microactuators to increase the functionality of the whole microactuator system. The final demonstration of this proposed project will consist of a system of microactuators in different shapes and configurations, including active microchannel walls and stimuli responsive microvalves for applications in dynamic microfluidic systems. While commercially available state-of-the-art microfluidic devices suffer from having their properties pre-defined during fabrication, our microactuator system will instead be based on active features that will add dynamic flexibility into microfluidic devices through the cooperation of individual microactuators. Similar principles will be used to design autonomously operating cell and organoid culturing systems, where pH-responsive microvalves will regulate cell medium flow. The success of this project will result in unprecedented adaptability and autonomy in microfluidic systems, leading to improved accessibility and throughput of a wide variety of tools and procedures.