Hierarchical Self-Assembly of Metal-Ion-Modulated Chitosan Tubules

Abstract

Soft materials such as gels or biological tissues can develop via selfassembly under chemo-mechanical forces. Here, we report the instantaneous formation of soft tubular structures with a two-level hierarchy by injecting a mixture of inorganic salt and chitosan (CS) solution from below into a reactor filled with alkaline solution. Folding and wrinkling instabilities occur on the originally smooth surface controlled by the salt composition and concentration. Liesegang-like precipitation patterns develop on the outer surface on a μm length scale in the presence of calcium chloride, while the precipitate particles are distributed evenly in the bulk as corroborated by X-ray μ-CT. On the other hand, barium hydroxide precipitates out only in the thin outer layer of the CS tubule when barium chloride is introduced into the CS solution. Independent of the concentration of the weakly interacting salt, an electric potential gradient across the CS membrane develops, which vanishes when the pH difference between the two sides of the membrane diminishes.

Flow-driven synthesis of calcium phosphate–calcium alginate hybrid chemical gardens

“…28 Nonetheless, the complexity and the fragility of the structures impede the systematic characterization of electrochemical measurements. A simple approach has been developed to enhance the membrane properties by aggregating the precipitation on a porous dialysis membrane 37 or creating an organic membrane 28 at the interface of aqueous solutions like in a fuel-cell setup.…”

“…24 Nowadays, organic and inorganic composites are of great interest in an effort to control the fabrication of functional materials. Researchers have developed complex architectures, 25,26 hierarchical patterns 27,28 and synthesized inorganic micro-and nanomaterials, in particular calcium carbonate 29 and calcium phosphate. [30][31][32] The organic component provides adhesivity and flexibility, while the inorganic component enhances the mechanical strength of the materials.…”

“…36 In the last few years, there were several reports on the electrochemical activities of various minerals, e.g., iron-sulfide and iron-hydroxide, 37 calcium-carbonate, 38 silica-based chemical gardens, 7,39 or even chitosan membranes. 28 Nonetheless, the complexity and the fragility of the structures impede the systematic characterization of electrochemical measurements. A simple approach has been developed to enhance the membrane properties by aggregating the precipitation on a porous dialysis membrane 37 or creating an organic membrane 28 at the interface of aqueous solutions like in a fuel-cell setup.…”

Downward fingering accompanies upward tube growth in a chemical garden grown in a vertical confined geometry

“…[19][20][21][22][23][24][25][26] Chemical gardens have been shown to produce a wide range of precipitate structures, including lobes, spirals, hairs, filaments, worms, flowers, bulbs, plumes, tubes, and fingers. [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] Precipitate colour depends on both the oxidation state of the metal cation and the coordination of water molecules around the precipitate structures. Taking the system of cobalt chloride and sodium silicate as an example, the precipitate varies in colour from pink to blue/green depending on whether there is octahedral or tetrahedral coordination of local water molecules.…”

Pattern selection of directionally oriented chitosan tubes

“…Metal-ion organic gardens, for example iron(III) oleate, have been produced in polar organic solvent such as isopropanol. 12 Hydrogel tubes 13 along with inorganic composites [14][15][16] are also explored via flow-injection techniques, where the adhesive nature of the gel aids in guiding the soft tubules.…”