Wu Jie, Meredith J Carson
School of Materials Science and Engineering and ‡School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
School of Materials Science and Engineering and School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
ACS Macro Lett. 2014 Feb 18;3(2):185-190. doi: 10.1021/mz400543f. Epub 2014 Jan 28.
The intricate hierarchical architectures in natural creatures are usually derived from assembly of molecular building blocks into nanoscale structures that then organize into micro- and macroscopic sizes. An example is the complex structure in arthropods (crustaceans, insects) constructed primarily of chitin. Because of chitin's inherent insolubility in common solvents, processes for mimicking the fascinating natural chitin-based nanostructures are still at an early stage of development. Here, we present a facile freeze-drying approach to assemble chitin nanofibers (20 nm diameter) into a variety of structures whose size and morphology are tunable by adjusting freezing temperature and heat transfer characteristics. We show that reducing the freezing rate allows controllable formation of structures ranging from oriented sheets to three-dimensional aperiodic nanofiber networks that mimic the size and interconnectivity of the white beetle cuticle. The formation of nanofibrous structures is not predicted by the widely used particle encapsulation model of freeze-drying. We reason that this structure occurs due to a combination of attractive interactions of the nanofibers and a slow freezing rate that encapsulates and preserves the network structure. The method outlined here is likely applicable to creating fine nanofibrous structures with other polymers and materials classes with size ranges useful in diverse applications such as tissue engineering, filtration, and energy storage.
天然生物体内复杂的层次结构通常源于分子构建单元组装成纳米级结构，然后这些结构再组织成微米级和宏观尺寸。一个例子是节肢动物（甲壳类动物、昆虫）中主要由几丁质构成的复杂结构。由于几丁质在常见溶剂中固有的不溶性，模仿基于几丁质的迷人天然纳米结构的工艺仍处于早期发展阶段。在此，我们提出一种简便的冷冻干燥方法，将几丁质纳米纤维（直径20纳米）组装成各种结构，其尺寸和形态可通过调节冷冻温度和热传递特性来调控。我们表明，降低冷冻速率可可控地形成从定向薄片到三维非周期性纳米纤维网络等各种结构，这些结构模仿了白甲虫角质层的尺寸和互连性。冷冻干燥中广泛使用的颗粒包封模型无法预测纳米纤维结构的形成。我们推断，这种结构的出现是由于纳米纤维的吸引相互作用以及缓慢的冷冻速率共同作用，后者包封并保留了网络结构。这里概述的方法可能适用于用其他聚合物和材料类别创建精细的纳米纤维结构，其尺寸范围在组织工程、过滤和能量存储等各种应用中都很有用。
