Collaborative Research: Microfabrication and Self-Assembly of Shape-Changing Hydrogels with Chromonic Liquid Crystalline Order

形状可改变的液晶水凝胶是一种柔软的橡胶材料，可以像“人造”肌肉一样执行机械工作，而不需要马达、关节或控制系统。它们会在轻微的温度变化时自发移动，并可以设计成以不同的几何形状弯曲。这项合作研究的重点是开发技术来设计这些材料，以生产新的设备，如自清洁表面。就像从人类肺部清除污染物的纤毛一样，表面将覆盖着随着温度波动而移动的微型水凝胶结构。这些新型活性涂层将满足医疗保健应用中对自清洁设备的迫切需求，并可以防止细菌污染，这种污染每年在美国导致频繁的感染和数千人死亡。此外，还将设计社区外展工作，以吸引年轻学生，并将有助于扩大技术劳动力的多样性，研究实习将帮助高中生为科学和工程方面的高级学习做好准备。智能生物医学设备需要能够对环境刺激做出机械反应的智能可编程材料。具有显色液晶有序的水凝胶对此类应用很感兴趣，因为它们可以随着生物良性温度变化而各向异性地变形，并且因为它们的驱动轨迹可以通过对材料的分子排列进行图案化来编程。一个关键的挑战是制造这样复杂的致动器，其长度尺度太小，无法通过3D打印获得，并且形状轮廓不是平板薄膜。该奖项支持设计和微制造形状变形水凝胶的新技术的开发，使用通过结合软光刻和液晶自组装实现的分子取向的分层图案化。这项基础研究将检验这样一种假设，即软性光刻模具的形状可以用于在由显色液晶水凝胶制成的微尺度结构中形成分子排列图案，并且这些排列的水凝胶可以在生物良性温度变化的响应下进行可编程的驱动。这种加工方法将被用来创造人造纤毛状结构。实验工作将在两个层面上与理论/模拟紧密结合。首先，将模拟软光刻模具表面锚定和液晶手性所产生的分子有序(向列相指向矢)。其次，采用非线性有限元弹性动力学模拟方法，模拟了有源水凝胶微器件在给定的指向场作用下的形状演化过程。这个协作项目汇集了一个多学科团队，在响应性材料化学、材料建模和机械设计方面具有互补的专业知识。

Shape-changing liquid crystal hydrogels are soft, rubbery materials that can perform mechanical work as "artificial" muscles, without motors, joints, or control systems. They move spontaneously in response to slight temperature changes, and can be designed to flex in different geometries. This collaborative research effort focuses on developing techniques to engineer these materials to produce novel devices such as self-cleaning surfaces. Like the cilia that sweep contaminants from human lungs, surfaces will be coated with micro-scale hydrogel structures that move as temperature fluctuates. These novel active coatings will address a critical need for self-cleaning devices in healthcare applications, and could prevent bacterial contamination that leads to frequent infections and thousands of deaths annually in the United States. In addition, community outreach efforts will be designed that engage young students and will help to broaden the diversity of the technical workforce, and research internships will help prepare high school students for advanced studies in science and engineering. Smart, programmable materials that respond mechanically to environmental stimuli are needed for smart biomedical devices. Hydrogels with chromonic liquid crystalline order are of interest for such applications because they morph anisotropically in response to biologically-benign temperature changes, and because their actuation trajectory can be programmed by patterning the material's molecular alignment. A key challenge is to fabricate such complex actuators at length scales too small to access via 3D printing and in shape profiles that are not flat films. This award supports development of novel techniques for design and microfabrication of shape-morphing hydrogels, using hierarchical patterning of molecular orientation achieved by combining soft lithography and liquid crystal self-assembly. This fundamental research will test the hypothesis that the shape of soft lithography molds can be used to pattern molecular alignment in micro-scale structures made of chromonic liquid crystal hydrogels, and that these aligned hydrogels can undergo programmable actuation in response to biologically-benign temperature changes. This processing approach will be used to create artificial cilia-like structures. Experimental efforts will be closely coupled to theory/simulation at two levels. First, the molecular order (nematic director) arising from surface anchoring from the soft lithography mold and liquid crystal chirality will be modeled. Second, nonlinear finite element elastodynamics simulations will be used to model shape evolution of active hydrogel micro-devices with a given director field as they transform under stimulus. This collaborative project brings together a multidisciplinary team with complementary expertise in responsive materials chemistry, materials modeling, and mechanical design.