Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University , Singapore 637371.
Institute of Materials Research and Engineering , Agency for Science, Technology and Research (A*STAR), 3 Research Link, Singapore 117602.
ACS Nano. 2015 Oct 27;9(10):9708-17. doi: 10.1021/acsnano.5b04300. Epub 2015 Sep 22.
Two-dimensional (2D) geometrical shape-shifting is prevalent in nature, but remains challenging in man-made "smart" materials, which are typically limited to single-direction responses. Here, we fabricate geometrical shape-shifting bovine serum albumin (BSA) microstructures to achieve circle-to-polygon and polygon-to-circle geometrical transformations. In addition, transformative two-dimensional microstructure arrays are demonstrated by the ensemble of these responsive microstructures to confer structure-to-function properties. The design strategy of our geometrical shape-shifting microstructures focuses on embedding precisely positioned rigid skeletal frames within responsive BSA matrices to direct their anisotropic swelling under pH stimulus. This is achieved using layer-by-layer two photon lithography, which is a direct laser writing technique capable of rendering spatial resolution in the sub-micrometer length scale. By controlling the shape, orientation and number of the embedded skeletal frames, we have demonstrated well-defined arc-to-corner and corner-to-arc transformations, which are essential for dynamic circle-to-polygon and polygon-to-circle shape-shifting, respectively. We further fabricate our shape-shifting microstructures in periodic arrays to experimentally demonstrate the first transformative 2D patterned arrays. Such versatile array configuration transformations give rise to structure-to-physical properties, including array porosity and pore shape, which are crucial for the development of on-demand multifunctional "smart" materials, especially in the field of photonics and microfluidics.
二维（2D）几何形状转变在自然界中很普遍，但在人造“智能”材料中仍然具有挑战性，因为人造“智能”材料通常仅限于单方向响应。在这里，我们制造了几何形状转变的牛血清白蛋白（BSA）微结构，以实现圆形到多边形和多边形到圆形的几何转变。此外，通过这些响应性微结构的集合来展示可变形的二维微结构阵列，以赋予结构到功能的特性。我们几何形状转变微结构的设计策略侧重于在响应性 BSA 基质中嵌入精确定位的刚性骨架框架，以在 pH 刺激下引导其各向异性膨胀。这是通过使用逐层双光子光刻来实现的，这是一种直接激光写入技术，能够在亚微米长度尺度上实现空间分辨率。通过控制嵌入骨架框架的形状、方向和数量，我们已经展示了定义明确的弧形到拐角和拐角到弧形的转变，这对于动态圆形到多边形和多边形到圆形的形状转变分别是至关重要的。我们进一步在周期性阵列中制造我们的形状转变微结构，以实验证明第一个可变形的二维图案化阵列。这种多功能的阵列配置转换产生了结构到物理性质的转变，包括阵列孔隙率和孔形状，这对于按需多功能“智能”材料的发展至关重要，特别是在光子学和微流控学领域。
