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

Pawan Kumar,Ákos Kukovecz,Ágota Tóth,Dániel Sebők,Dezső Horváth

doi:10.1021/acs.langmuir.1c02097

Pawan Kumar, Ákos Kukovecz + Show 3 more

Open Access

https://doi.org/10.1021/acs.langmuir.1c02097

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Abstract

Soft materials such as gels or biological tissues can develop via self-assembly 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.

Highlights

Structures with multi-level complexity are of utmost importance because they can be used as actuators,[1] motors,[2] adhesives,[3] and so forth
It has been successfully applied to yield promising organized formations and structural modifications, where the strong affinity of CS to transition metal ions induces the orientation to layered transition and the weak affinity between alkaline earth metals and CS leads to composite gel structures.[23]
Our goal is to manipulate the patterns evolving at various length scales by changing the composition of metal salts added to the CS solution

Summary

Introduction

Structures with multi-level complexity are of utmost importance because they can be used as actuators,[1] motors,[2] adhesives,[3] and so forth They can be designed by a bottom-up approach starting from initial building blocks and creating the structure on a smaller length scale.[4,5] Building an ordered polysaccharide polymer structure always gains attention as it enhances the functionality and performance of soft materials.[6,7] The natural polysaccharide polymer chitosan (CS) is a potential candidate because of its biomedical applications[8,9] and intrinsic properties such as biocompatibility,[10] biodegradability,[11] and bioactivity.[12] The sol−gel transition leads to a multilayered CS polymer using special molds,[13] stopping the gelation process[14,15] or starting from appropriate salt compound.[16]. Our goal is to manipulate the patterns evolving at various length scales by changing the composition of metal salts added to the CS solution

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Results

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