Free-standing supramolecular hydrogel objects by reaction-diffusion

Abstract

Self-assembly provides access to a variety of molecular materials, yet spatial control over structure formation remains difficult to achieve. Here we show how reaction–diffusion (RD) can be coupled to a molecular self-assembly process to generate macroscopic free-standing objects with control over shape, size, and functionality. In RD, two or more reactants diffuse from different positions to give rise to spatially defined structures on reaction. We demonstrate that RD can be used to locally control formation and self-assembly of hydrazone molecular gelators from their non-assembling precursors, leading to soft, free-standing hydrogel objects with sizes ranging from several hundred micrometres up to centimeters. Different chemical functionalities and gradients can easily be integrated in the hydrogel objects by using different reactants. Our methodology, together with the vast range of organic reactions and self-assembling building blocks, provides a general approach towards the programmed fabrication of soft microscale objects with controlled functionality and shape.

Supramolecular Gluing of Polymeric Hydrogels

“…Applying mechanical force most likely leads to the breakage of hydrogen bonds and other non‐covalent interactions between molecules of HA 3 in fibers stretching across the interface. Additionally, we confirmed our hypothesis of cross‐interface fiber formation using a reaction diffusion model for this system . The model showed that, indeed, if two compartments with H and A are in direct contact, the gelator HA 3 will form supramolecular fibrils across and on both sides of the interface (Figure b).…”

“…Instead, a white, non‐transparent band was created around the contact point. This band was an indication of HA 3 formation . Previous analysis of this opaque supramolecular gel has shown that this material is made up of bundled fibers that consist largely (>95%) of HA 3 molecules .…”

“…Recently, we have reported a supramolecular gelator that is formed by an acid catalyzed chemical reaction between hydrazide ( H ) and aldehyde ( A ) leading to the formation of trishydrazone HA 3 (Figure a) ,. This two‐component reaction proved highly versatile to a range of different conditions, and setups including reaction‐diffusion . Therefore, we envisioned that this reaction could be used for gluing different types of hydrogels.…”

Pros and Cons: Supramolecular or Macromolecular: What Is Best for Functional Hydrogels with Advanced Properties?

“…An entirely different method for spatial differentiation is by reaction diffusion, and this is an example where the worlds of MHGs and SHGs meet. Controlled reaction and diffusion of SHG gelator precursors can lead to SHG object and pattern formation,26d,28 as well as the stabilization of emulsions, typically on timescales of hours to days depending on diffusion lengths. Diffusion is often carried out inside an MHG, leading to the formation of MHG–SHG interpenetrated network hybrid gel materials.…”

Controlled Fabrication of Micropatterned Supramolecular Gels by Directed Self‐Assembly of Small Molecular Gelators

“…For instance, the employment of self‐assembly systems that are sensitive to external stimuli such as light, enzymatic action, pH, and nucleation seeds, has led to DMSA by controlling the spatial distribution of these stimuli. Another example of DMSA is achieved by reaction‐diffusion, i.e., molecular reactants are separately distributed in space and allowed to react after meeting by diffusion, leading to local self‐assembly at a certain preprogrammed location. Despite the recent progress, a major challenge for further advance lies in control of the spatial parameters of the self‐assembled structures …”