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

可变形的液晶水凝胶是一种柔软的橡胶材料，可以像“人造”肌肉一样进行机械工作，而不需要马达、关节或控制系统。它们可以自发地响应轻微的温度变化，并可以设计成不同的几何形状。这项合作研究的重点是开发技术来设计这些材料，以生产新型设备，如自清洁表面。就像清除人体肺部污染物的纤毛一样，表面将覆盖一层微尺度的水凝胶结构，这种结构会随着温度的波动而移动。这些新型的活性涂层将解决医疗保健应用中对自清洁设备的关键需求，并且可以防止导致频繁感染和美国每年数千人死亡的细菌污染。此外，将设计社区外展工作，吸引年轻学生，这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对环境刺激做出机械反应的智能、可编程材料。具有慢性液晶顺序的水凝胶对此类应用很有兴趣，因为它们在响应生物良性温度变化时具有各向异性的形态，并且因为它们的驱动轨迹可以通过材料的分子排列模式来编程。一个关键的挑战是制造这种复杂的执行器，其长度太小，无法通过3D打印访问，并且形状轮廓不是平面薄膜。该奖项支持设计和微制造可变形水凝胶的新技术的发展，使用通过结合软光刻和液晶自组装实现的分子取向分层模式。这项基础研究将验证软光刻模具的形状可以用于在由慢性液晶水凝胶制成的微尺度结构中绘制分子排列的假设，并且这些排列的水凝胶可以响应生物良性的温度变化进行可编程驱动。这种处理方法将用于制造人工纤毛状结构。实验工作将在两个层面上与理论/模拟紧密结合。首先，对软光刻模具表面锚定产生的分子序（向列方向）和液晶手性进行建模。其次，采用非线性有限元弹性动力学模拟方法，模拟具有给定方向场的有源水凝胶微器件在刺激下的变形过程。这个合作项目汇集了一个多学科团队，在响应材料化学、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.