Controlled self-assembly of chemical gardens enables fabrication of heterogeneous chemobrionic materials

Erik A B Hughes,Liam M Grover,Richard J A Moakes,Miruna Chipara,Thomas E Robinson

doi:10.1038/s42004-021-00579-y

Abstract

Chemical gardens are an example of a chemobrionic system that typically result in abiotic macro-, micro- and nano- material architectures, with formation driven by complex out-of-equilibrium reaction mechanisms. From a technological perspective, controlling chemobrionic processes may hold great promise for the creation of novel, compositionally diverse and ultimately, useful materials and devices. In this work, we engineer an innovative custom-built liquid exchange unit that enables us to control the formation of tubular chemical garden structures grown from the interface between calcium loaded hydrogel and phosphate solution. We show that systematic displacement of phosphate solution with water (H2O) can halt self-assembly, precisely control tube height and purify structures in situ. Furthermore, we demonstrate the fabrication of a heterogeneous chemobrionic composite material composed of aligned, high-aspect ratio calcium phosphate channels running through an otherwise dense matrix of poly(2-hydroxyethyl methacrylate) (pHEMA). Given that the principles we derive can be broadly applied to potentially control various chemobrionic systems, this work paves the way for fabricating multifunctional materials that may hold great potential in a variety of application areas, such as regenerative medicine, catalysis and microfluidics.

Highlights

Chemical gardens are an example of a chemobrionic system that typically result in abiotic macro, micro- and nano- material architectures, with formation driven by complex out-ofequilibrium reaction mechanisms
To explore the systematic exchange of phosphate solution with H2O as a means to influence calcium phosphate chemical garden growth, we engineered a custom-built liquid exchange unit by modifying a 0.14 L capacity Really Useful Box® with inlet and outlet channels to enable the exchange of liquids as driven by external pumps
The principles described demonstrate a significant leap toward controlling the formation chemical gardens that may further facilitate the fabrication of technologically relevant materials consisting entirely of, or incorporating, chemobrionic components

Summary

Introduction

Chemical gardens are an example of a chemobrionic system that typically result in abiotic macro-, micro- and nano- material architectures, with formation driven by complex out-ofequilibrium reaction mechanisms. From a technological perspective, controlling chemobrionic processes may hold great promise for the creation of novel, compositionally diverse and useful materials and devices. Chemical gardens are a classical example of a chemobrionic system first reported several centuries ago in 16461 These formations are commonly characterised by the spontaneous formation of colourful hollow tubular precipitates following the introduction of metal salt seeds, which provide a broad spectrum of cations (e.g. calcium (Ca2+), copper (Cu2+), iron (Fe2+/3+), etc.), to reservoirs of anionic solution (e.g. carbonate (CO32−), phosphate (PO43−), silicate (SiO44−), etc.)[2]. The growth and acquisition of chemobrionic structures in such a manner that allows for ease of further processing toward technologically relevant materials remains highly challenging

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