Micropatterning of single crystals for technological applications is a complex, multistep process. Nature provides alternative fabrication strategies, when crystals with exquisite micro-ornamentation directly develop within preorganized frameworks. We report a bio-inspired approach to growing large micropatterned single crystals. Micropatterned templates organically modified to induce the formation of metastable amorphous calcium carbonate were imprinted with calcite nucleation sites. The template-directed deposition and crystallization of the amorphous phase resulted in the fabrication of millimeter-sized single calcite crystals with sub-10-micron patterns and controlled crystallographic orientation. We suggest that in addition to regulating the shape, micropatterned frameworks act as sites for stress and impurity release during the amorphous-to-crystalline transition. The proposed mechanisms may have direct biological relevance and broad implications in materials synthesis.
We report on the fabrication of biologically-inspired "smart" surfaces using hybrid architectures comprising polymer microbristle embedded in a hydrogel layer. The dynamic bending of the microposts—the passive structural element in the design—and their return to the upright orientation are achieved during the volume-phase transition of the hydrogel layer—the active element of the structure—upon hydration/dehydration. We compare the performance of the hybrid architectures bearing soft and stiff microposts and show that the use of soft polymeric materials results in bending actuation of the posts in cases where actuation of identically-sized posts of stiffer materials, such as silicon, would not have been possible. Modeling of the actuation process and the supporting experimental results confirm that the bending orientation of the microposts can be individually controlled by modulating the thickness gradients in the active hydrogel layer achieved by transferring micropatterns to the liquid-phase hydrogel precursor. Such procedures orchestrate coordinated actuation of the microbristle and make it possible to create elaborate reconfigurable micropatterns, such as opening/closing microflorets and microtraps. In combination with diverse hydrogel systems exhibiting response to various stimuli, these "smart" hybrid all-polymer architectures open a new avenue in advanced functional materials that harness the adaptive nature of these structures for various applications.
Abstract Biological strategies for bottom‐up synthesis of inorganic crystalline and amorphous materials within topographic templates have recently become an attractive approach for fabricating complex synthetic structures. Inspired by these strategies, herein the synthesis of multi‐layered, hierarchical inverse colloidal crystal films formed directly on topographically patterned substrates via evaporative deposition, or “co‐assembly”, of polymeric spheres with a silicate sol–gel precursor solution and subsequent removal of the colloidal template, is described. The response of this growing composite colloid–silica system to artificially imposed 3D spatial constraints of various geometries is systematically studied, and compared with that of direct colloidal crystal assembly on the same template. Substrates designed with arrays of rectangular, triangular, and hexagonal prisms and cylinders are shown to control crystallographic domain nucleation and orientation of the direct and inverse opals. With this bottom‐up topographical approach, it is demonstrated that the system can be manipulated to either form large patterned single crystals, or crystals with a fine‐tuned extent of disorder, and to nucleate distinct colloidal domains of a defined size, location, and orientation in a wide range of length‐scales. The resulting ordered, quasi‐ordered, and disordered colloidal crystal films show distinct optical properties. Therefore, this method provides a means of controlling bottom‐up synthesis of complex, hierarchical direct and inverse opal structures designed for altering optical properties and increased functionality.
We introduce a 3D porous photonic crystal whose inner surfaces are chemically functionalized in arbitrary spatial patterns with micro-scale resolution. We use this platform to demonstrate pattern-formation.
The data underlying this published work have been made publicly available in this repository as part of the IMASC Data Management Plan. This work was supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis (IMASC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012573.
Inorganic microstructured materials are ubiquitous in nature. However, their formation in artificial self-assembly systems is challenging as it involves a complex interplay of competing forces during and after assembly. For example, colloidal assembly requires fine-tuning of factors such as the size and surface charge of the particles and electrolyte strength of the solvent to enable successful self-assembly and minimize crack formation. Co-assembly of templating colloidal particles together with a sol-gel matrix precursor material helps to release stresses that accumulate during drying and solidification, as previously shown for the formation of high-quality inverse opal (IO) films out of amorphous silica. Expanding this methodology to crystalline materials would result in microscale architectures with enhanced photonic, electronic, and catalytic properties. This work describes tailoring the crystallinity of metal oxide precursors that enable the formation of highly ordered, large-area (mm2 ) crack-free titania, zirconia, and alumina IO films. The same bioinspired approach can be applied to other crystalline materials as well as structures beyond IOs.
