Controlled self-assembly of three-dimensional shapes holds great potential for fabrication of functional materials. Their practical realization requires a theoretical framework to quantify and guide the dynamic sculpting of the curved structures that often arise in accretive mineralization. Motivated by a variety of bioinspired coprecipitation patterns of carbonate and silica, we develop a geometrical theory for the kinetics of the growth front that leaves behind thin-walled complex structures. Our theory explains the range of previously observed experimental patterns and, in addition, predicts unexplored assembly pathways. This allows us to design a number of functional base shapes of optical microstructures, which we synthesize to demonstrate their light-guiding capabilities. Overall, our framework provides a way to understand and control the growth and form of functional precipitating microsculptures.
The diversity, hierarchy, and complexity of mineralized architectures formed by living organisms seem virtually unlimited.
Microscopic acantharea up to reef building corals are able to precisely control the development of intricate mineral skeletons. Our aim is not so much to reproduce any particular shapes seen in nature, but to get to the root of what kind of physical and chemical principles might allow for such amazing control, and trying to adapt these ideas to design our own complex shapes.
Mineralization processes in living organisms continuously respond to environmental changes such as the temperature, CO2 concentration and acidity. Building on this principle, we dynamically modulate the environmental conditions in a beaker to actively steer mineralizing compounds into deterministic patterns. We have developed a comprehensive model for predicting the evolution of patterns a priori, and have used it to derive sequences of simple, subtle modulations of CO2, pH, and temperature that serve as building strategies for intricate higher-order nano/microarchitectures.
Using continuous and/or stepwise adjustments, we showed that the precipitating reactants can be steered into complex flowers, corals, vases, and messages, with precise control over placement of stems, leaves, etc. via sequential combinatorial assembly of the developing shapes.
Currently, we are further developing a detailed mathematical theory that predicts the emergence of the different shapes along with new experimental strategies that allow an even more precise manipulation of the growth conditions. This more and more refined control over the construction of micro architectures moves towards the control that is required for many practical applications, such as in optical materials, and catalysts.
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